Category Archives: Fact Sheet

Disease - Vegetable, Fact Sheet

Pink Eye of Potato

What is pink eye?  Pink eye is a disorder of potato tubers that can cause costly storage losses for potato growers and can reduce tuber quality to the point where tubers will be rejected by potato processors.  Pink eye not only directly affects tubers, but also makes tubers more susceptible to diseases such as Pythium leak, bacterial soft rot (see University of Wisconsin Garden Facts XHT1224), pink rot, and Fusarium dry rot.  These diseases cause additional storage losses and reduction in quality.

Pink eye is characterized by a pink discoloration of the skin of potato tubers.
Pink eye is characterized by a pink discoloration of the skin of potato tubers.

What does pink eye look like?  Pink eye is characterized by a short-lived external pink color that is often, but not always, found around the potato eyes of freshly harvested tubers.  Eyes at the bud ends of tubers (i.e., those farthest from where tubers are attached to stems) more commonly show pink eye symptoms.  Pink eye can eventually develop into corky patch/bull hide, which involves a thickening of areas of tuber skin extending approximately 1/10 of an inch into the tuber flesh.  Corky patch/bull hide can make tubers unmarketable for either fresh market or processing use.

External pink eye symptoms are often accompanied by brown patches in the tuber flesh immediately underneath the skin.  Browning due to pink eye can resemble browning due to other disorders such as internal brown spot or heat necrosis, but these latter disorders tend to occur deeper in the tuber (i.e., inside the vascular ring), rather than just underneath the skin.

Pink eye can also be confused with late blight.  If there is any question whether the problem might be late blight rather than pink eye, contact your county Extension agent for information on submitting a sample to a diagnostic lab for proper testing.

Where does pink eye come from?  Pink eye is a physiological disorder (i.e., an abnormality in plant growth), rather than a true disease that involves a disease-causing microorganism.  Pink eye arises during periods of excessive soil moisture and warm temperatures, especially during the later stages of tuber development.  Pink eye symptoms typically appear within 7 to 10 days after excessive rain.  Excessive soil moisture coupled with high soil temperature causes a lack of oxygen around potato tubers, leading to damage of cells in the tuber skin.  This cell damage

contributes to pink eye development.  Environmental conditions that lead to pink eye also promote tuber infections by the pathogens that cause Pythium leak, bacterial soft rot, pink rot, and Fusarium dry rot (all diseases associated with pink eye in storage).

How do I salvage potato tubers affected by pink eye?  Once pink eye symptoms develop, they are permanent.  If symptoms are minor, tubers may still be usable.  However, when pink eye symptoms are severe, symptomatic tubers will be rejected and discarded.

How do I avoid problems with pink eye in the future?  Growers have no control over the extreme precipitation and high temperatures that promote pink eye development.  However, growers can practice management strategies that minimize water-saturated soils and reduce warm soil temperatures, thus reducing the severity of pink eye.

To minimize water-saturated soils, deep till areas where pink eye has been a problem, areas where water tends to collect for extended periods, and areas where soils may be compacted (e.g., field entrances or head lands).  Deep tillage will break up subsoils in these areas that impede proper drainage during wet weather.  Proper drainage will limit periods when tubers will be oxygen deprived and thus more prone to pink eye development.  Also, avoid any activities that will cause soil compaction such as operation of heavy and large farm tractors and field equipment when soils are wet.  Minimizing water-saturated soils will not only reduce the likelihood of pink eye development but will also help limit development of other tuber diseases.

To promote cooler soil temperatures, be sure to manage diseases (e.g., potato early dying) that reduce canopy coverage.  Loss of canopy allows soils to warm faster on sunny days, thus leading to higher temperatures that are more favorable for pink eye development.

Finally, be sure to scout for pink eye symptoms prior to and during harvest.  Knowing the severity of pink eye in a field can help growers make informed decisions about the appropriate duration for tuber storage and the best end use for symptomatic tubers.

For more information on pink eye:  Contact your county Extension agent.

Fact Sheet, General Horticulture/Weeds

Improving Cranberry Pollination

Successful cranberry production relies on cranberry flowers being adequately pollinated.  This fact sheet discusses several strategies that can be used to optimize pollination.

Proper pollination is important for successful cranberry production. (Photo courtesy of Johnston's Cranberry Marsh & Muskoka Lakes Winery, Ontario, Canada).
Proper pollination is important for successful cranberry production. (Photo courtesy of Johnston’s Cranberry Marsh & Muskoka Lakes Winery, Ontario, Canada).

Increase and diversify plants attractive to pollinators.  Having both native pollinators and honeybees on your marsh serves as an “insurance policy” to promote good fruit set.  Providing diverse sources of nectar and pollen (e.g., through the use of a pollinator garden), will encourage native pollinators to establish themselves long-term near your marsh and improve the health of honeybee colonies.  When planning a pollinator garden, select a site that is sunny and 1/3 to one mile away from your marsh.  Some common native plants to consider for a pollinator garden are listed in the figure below, with their approximate bloom times.

Promote nesting habitats for wild bees.  Wild bees need places to build their nests.  Approximately 70% of native bees nest underground and need areas of bare, sandy or loamy soil to build their nests.  The remaining 30% build nests by tunneling into stumps or twigs, or by constructing nests in cavities (e.g., in mounds of tall grasses, in debris piles, or in deserted rodent nests).  Native pollinators typically travel from 1/8 to one mile from their nests to feed, so suitable nesting areas need to be within this distance of a marsh for the bees to contribute to cranberry pollination.

Several programs can assist with the costs of creating pollinator habitats.  These include the USDA Environmental Quality Incentives Program, the USDA Farm Service Agency, the Wisconsin DNR Land Owner Incentive Program and the Bayer Crop Science Feed a Bee Initiative.

 

LEFT: Approximate bloom times for plants that are recommended to be grown near cranberry marshes as a supplemental nectar and pollen source for cranberry pollinators. RIGHT: Approximate flight periods for major groups of bees (including native species) found in cranberry marshes. The pink columns in both graphs represent the approximate time of cranberry bloom.
LEFT: Approximate bloom times for plants that are recommended to be grown near cranberry marshes as a supplemental nectar and pollen source for cranberry pollinators. RIGHT: Approximate flight periods for major groups of bees (including native species) found in cranberry marshes. The pink columns in both graphs represent the approximate time of cranberry bloom.

Reduce pesticide exposure:  You can optimize bee health by creating a pollinator protection plan that promotes:

  • Practicing integrated pest management (IPM). IPM, which involves monitoring for pests and using a variety of appropriate management strategies, is used by most Wisconsin cranberry growers.
  • Spraying when bees are least active. Most bees forage from early morning until shortly before sunset. Therefore, the best time to apply a pesticide, especially during bloom (if allowed by the pesticide label), is in the late evening or at night.
  • Limiting pesticide drift. Whether plants are blooming or not, using a boom sprayer allows for direct application of pesticides onto cranberry plants.  Other methods that can reduce pesticide drift include calibrating your boom to optimize spray pressure and volume, selecting drift-reducing nozzles, avoiding pesticides with small particles that easily drift, and spraying when winds are under 10 mph and when relative humidity is above 50%.
  • Using insecticides and fungicides that have a reduced risk for bees. See the table below for insecticides and fungicides that are least toxic for bees.
Class
(IRAC or FRAC code)		 Example
Active Ingredient(s)		 Example
Trade Names
Insecticides

(IRAC code)*

 diamide (28) chlorantraniliprole Altacor
diacylhydrazine (18) methoxyfenozide

tebufenozide

 Intrepid

Confirm
biological Bacillus thuringiensis Biobit, Dipel
Fungicides

(FRAC code)*

 strobilurin (11) azoxystrobin Abound, Evito
chitin synthase inhibitor (19) polyoxin D zinc salt Oso
biological Reynoutria sachalinensis Regalia

*  Note that rotating Insecticide Resistance Action Committee (IRAC) classes and Fungicide Resistance Action Committee (FRAC) codes (modes of action) will help delay development of pesticide resistance.

Strengthen your working relationship with beekeepers.  Optimal cranberry pollination requires cooperation between grower and beekeeper.  In some cases, outlining expectations in a signed, written contract can be the best way to prevent misunderstandings.  Topics to consider and discuss with your beekeeper can include, but are not limited to:

  • Hive inspections. Inspecting a random sample of 10% of hives when they are brought onto a march can help ensure that hives are of high quality and contain healthy bees.  Ideally, a third party should conduct the inspections in the presence of both beekeeper and grower.
  • When bees are introduced onto a cranberry marsh and the duration of their stay are important factors in optimizing cranberry pollination, as well as for maintaining honeybee health.  Bees should be brought onto a marsh at around 15% bloom.
  • Hive placement. Within the limits of your bed layout and equipment needs, it is best to place hives in the center of a marsh or near marsh edges with wild habitat, but away from water reservoirs, as bees from hive near water seem to be less likely to visit cranberry plants.
  • Exposures to sprays. Be explicit about when, how and what may be sprayed during bloom.

For more information on improving cranberry pollination:  Watch for UW Extension bulletin A4155, “Practices to improve pollination and protect pollinators in Wisconsin cranberry” (available soon at https://learningstore.uwex.edu/), or University of Wisconsin Garden Facts XHT1213 “Pollinators” (available at https://pddc.wisc.edu/), or contact your county Extension agent.

Fact Sheet, Insect, Pest Alerts

Blueberry Maggot

Blueberry maggot was first detected in Wisconsin in the summer of 2016 in Adams and Sauk Counties.  This pest feeds inside blueberry fruit and caused damage in commercial blueberry production in the eastern and southern United States, as well as in eastern Canada.  This insect is expected to eventually have a significant impact on blueberry production in Wisconsin.

Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)
Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)

Appearance:  The adult blueberry maggot is a fly that is approximately 3/16 inch long and resembles a small housefly, but with dark bands on its wings.  Larvae (or maggots) are legless and can grow up to 5/16 inch in length.  Each larva has a single hook-like tooth at its mouth end.  Blueberry maggots are very similar in appearance to the closely related apple maggot, with adults of both being virtually identical in size and appearance (including wing patterns).  However, apple maggot does not feed on blueberries.

Host Range:  Blueberry (Vaccinium corymbosum) is the only commercially-grown fruit crop affected by blueberry maggot.  Wild hosts include plant species in the genera Vaccinium and Gaylussacia including wild blueberries, lingonberry, dangleberry, deerberry and huckleberry.

Symptoms and Effects:  A single larva feeds inside each fruit causing the berry to become soft as it develops.  Damage may go unnoticed until after harvest, when maggots crawl out of fruit and become visible among fresh fruit or in processed blueberry products (e.g., jams, preserves, pie fillings).

Life Cycle:  Adult blueberry maggots begin to fly in June or July, and continue to fly through August.  Females feed and mate for at least one week before they move to blueberry plants to begin laying eggs.  Females lay a single egg under the skin of a nearly ripe blueberry fruit and can lay up to 100 eggs during their approximately one month-long life span.  Eggs hatch within one week and damage from larvae generally first appears in mid-July, continuing until blueberries have been harvested.  Each maggot feeds in a single blueberry during its two- to three-week development.  After completing their development, larvae drop to the ground and overwinter as pupae in the upper few inches of soil.  A distinctive characteristic of the blueberry maggot is that, although most pupae develop to form adults by the following spring (completing one generation of the insect in a year), some pupae remain underground and do not mature for two or three years.

Monitoring:  Monitor for blueberry maggot adults several weeks before blueberries begin to ripen (usually in early June) using yellow sticky cards impregnated with a feeding attractant (ammonium acetate or ammonium carbonate).  You can buy cards that are pretreated with the attractant, or buy the cards and attractant separately and apply the attractant yourself.  Fold the sticky cards in a V-shape with the yellow side facing down and put up two traps for every five acres.  Because blueberry maggot is currently not widespread in Wisconsin, you can check cards weekly until you find the first adult.  After this initial find, check cards every few days.  Once you find an average of greater than one adult per trap for several days in a row, begin chemical treatments (see below).  Note that the feeding attractant is not specific for blueberry maggot, so you may find other types of flies on the cards – use a hand-lens or magnifying glass to positively identify any blueberry maggot adults.  Remember that blueberry maggot and apple maggot look very similar, but that apple maggot does not feed on blueberries, so flies trapped in blueberry fields/patches are most likely to be blueberry maggot.

Once you have detected adults, you can also test fruit for the presence of larvae.  Collect 100 berries from throughout your planting.  Then break the skins of the berries and mix the berries with a salt-water solution (1 part salt to 4 parts water).  Larvae will float to the surface.  The number of larvae you find represents the percentage of fruit infested.

Control:  Cultural control methods can be useful in preventing blueberry maggot infestations.  Remove weeds to eliminate habitat for blueberry maggot.  Remove wild blueberry and huckleberry plants as these can serve as alternate hosts for the insect.  Harvest fruits thoroughly and heat (to at least 120°F) or freeze any damaged or unusable fruits to kill blueberry maggot larvae.  This is particularly important if you compost fruit, because blueberry maggot pupae can readily survive in compost and serve as a source of an infestation in future years.  Clean soil thoroughly from equipment or beehives that might be moved between blueberry patches.  Blueberry maggot pupae can easily be moved in soil.

A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)
A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)

As noted above, start chemical control once you find an average of greater than one adult blueberry maggot per trap for several days in a row.  Alternatively, if you have had a serious problem in the past, you may want to start sprays one week after you trap your first blueberry maggot fly.  Continue sprays every seven to 10 days through harvest.  Some reduced risk active ingredients, such as novaluron, spinetoram, and spinosad are most effective when used as soon as flies are found in traps.  In addition, consider choosing a product that also provides control of spotted wing drosophila, another serious blueberry pest (see University of Wisconsin Garden Facts XHT1237 for details).  Spinosyn, spinetoram, diamide, carbamate, pyrethroid, and organophosphate-containing insecticides are effective against both insects.  Be sure to rotate use of at least two active ingredients with different modes of action to help delay development of insecticide resistance (see http://www.irac-online.org/modes-of-action/ for details), and be sure consider the effects of sprays on non-target (e.g., beneficial insects).  Finally, because you will be spraying ripe berries, pay particular attention to the pre-harvest interval when choosing insecticides.  Check the most recent Midwest Fruit Pest Management Guide (see https://learningstore.uwex.edu/Midwest-Fruit-Pest-Management-Guide-2017-P1785.aspx) for complete product recommendations.

For more information on or help diagnosing blueberry maggot:  Contact your county Extension agent.

Disease - Fruit Crop, Fact Sheet

San José Scale

San José scale (Diaspidiotus perniciosus) is a fruit tree pest that can be found in most fruit growing regions of the United States.  Native to China, this insect was introduced into the United States in the late 1800s.  In well-managed orchards, populations of San José scale are generally too low to cause economic damage.  In poorly managed orchards however, populations can become high enough in one to two growing seasons to cause tree and fruit injury.  Once established, San José scale can be difficult and expensive to control.  San José scale is of historical interest because, in the early 1900’s, it was the first insect observed to develop resistance to an insecticide.

San José scale damage on apple fruit (left). San José scale black cap stage (center), female (upper right) and male (lower right). [Photos courtesy of Greg Krawczyk (Penn State University), E. Beers (Washington State University) and S. Schoof (North Carolina State University).]
San José scale damage on apple fruit (left). San José scale black cap stage (center), female (upper right) and male (lower right). [Photos courtesy of Greg Krawczyk (Penn State University), E. Beers (Washington State University) and S. Schoof (North Carolina State University).]
Appearance:  San José scale females are yellow, wingless and legless, have a soft, globular shape and are approximately 1/12 inch long.  Male scales are 1/25 inch long, are yellowish-tan with a dark band across the back and have wings and long antennae.  Immature San José scales (called nymphs) go through three stages (crawler, white cap, and black cap).  Crawlers are roughly the diameter of the tip of a pin, are yellow, and have six legs and antennae.  Crawlers develop into the white cap stage as they become immobile and secrete hard, white, waxy coverings.  The black cap stage follows as the waxy coverings turn gray-black.

Host Range:  San José scale feeds on a variety of fruit hosts including apple, pear, plum, cherry, peach, apricot and berries (e.g., raspberry, blackberry), as well as on nut-bearing trees (e.g., walnut) and many ornamental trees and shrubs (e.g., elm, maple, mountain-ash, serviceberry, juniper, white cedar, yew).

Symptoms and Effects:  San José scale sucks sap from branches, leaves and fruit causing overall decline in plant vigor, growth, and yield.  If left uncontrolled, San José scale can ultimately kill plants.  On fruits, San José scale feeding causes slight depressions with red to purple haloes.  If San José scale populations are low, fruit damage is usually concentrated on the bottom of the fruit.  When infestations occur early in the season, fruit may become small, deformed, and poorly colored.  Damage by San José scale (even cosmetic spotting) decreases fruit quality and in commercial settings makes the fruit more difficult to sell.

Life Cycle:  San José scale can complete its life cycle in approximately 37 days.  There are typically two generations of the insect each year, and generations overlap so that all stages of the insect occur at the same time during the summer.  San José scale overwinters in the black cap stage.  Development of the insect resumes in spring when temperatures exceed 51°F.  Around petal fall, mature females and short-lived males emerge.  Males can fly from tree to tree, but females move very little.  After mating, females produce approximately 400 live crawlers over a period of six-weeks.  The first generation of crawlers appears between early and mid-June, with white and black cap stages developing over approximately the next month.  A second generation of adults appears between July and early September.  If warmer temperatures continue into the fall, a third generation of San José scale can occur between late October and early November.

Monitoring:  The first indication of a San José scale problem may be when infested fruit is found at harvest or (in commercial settings) at packing.  However, sometimes the insect can be found earlier on branches.  If a San José scale infestation is detected, careful examination of trees/orchards during dormancy can help determine the level of infestation and the extent of spread.  Watch for trees that retain leaves during winter (a good indication of a San José scale infestation) and check both branches and trunks for the insect.  Mark (e.g., with flagging tape) infested areas on trees to identify where sprays should be applied the following growing season.

In the spring and summer, use pheromone traps to detect the presence of males.  Begin using traps at the pink stage of apple flower bud development, in areas where infestations have been detected.  Place traps on the northern or eastern side of trees at a height of six to seven feet.  Check traps at least weekly.  Traps are effective for four to six weeks.

Monitor for crawlers by wrapping two-sided sticky electrical tape (coated with a thin layer of petroleum jelly) around infested tree limbs at both ends of the infested area.  Start checking tape for crawlers approximately four to six weeks after bloom.

A San José scale pheromone trap.
A San José scale pheromone trap. (Photo courtesy of S. Schoof, North Carolina State Univeristy)

Control:  The best strategy for managing San José scale is to prevent serious infestations.  The best cultural control is to prune out infested branches.  This reduces scale numbers and opens up the tree canopy so that if spray treatments are used, there is better penetration.  Several parasites and predators attack San José scale; however, use of these alone does not provide enough control to prevent damage.

The most effective spray control for San José scale is the use of 2% horticultural oil with or without an insecticide just before or right after bud break, but before flowers open.  During this period San José scale resumes its development after being dormant during the winter and the sprays will smother the insects.  After applying horticultural oil, continue to monitor for adults and crawlers (as described above) and if you still find active San José scale, consider using chemical insecticides for additional control.  Insecticides containing insect growth regulators (e.g., pyriproxyfen or buprofezin), neonicotinoids, organophosphates, or spirotetramat can be effective.  Start applications when you find the first adults in pheromone traps or the first crawlers on sticky tapes (usually around early to mid-June).  Apply another spray approximately 10 days later if you continue to find active crawlers.  When using two applications, be sure to use two products with active ingredients in different Insecticide Resistance Action Committee (IRAC) chemical classes (i.e., with different modes of action) to delay development of insecticide resistance.  See http://www.irac-online.org/modes-of-action/ for guidance.  Note that late-fall and postharvest applications are NOT effective for San José scale control.  Also, remember that whenever you use insecticides, you should consider the effects of products on non-target and beneficial insects.  Check the current year “Midwest Fruit Pest Management Guide” (available at https://learningstore.uwex.edu/) for additional insecticide recommendations.

For more information on San José scale:  Contact your county Extension agent.

Disease - Vegetable, Fact Sheet

Hot-Water Seed Treatment for Disease Management

Growing vegetables from seed is a common practice for many home gardeners.  Unfortunately, vegetable seed (even though it appears perfectly healthy) can sometimes be contaminated with disease-causing organisms, particularly disease-causing bacteria.  Bacterial speck (see University of Wisconsin Garden Facts XHT1250, “Bacterial Speck of Tomato”), bacterial spot (see University of Wisconsin Garden Facts XHT1244, “Bacterial Spot of Tomato”), and stem canker of tomato, as well as bacterial spot of pepper and black rot of crucifers such as cabbage and broccoli (see University of Wisconsin Garden Facts XHT1225, “Black Rot of Crucifers”) are common bacterial diseases where pathogens can be introduced into a garden via contaminated seed.  Making sure your vegetable seed is pathogen free is an important first step in preventing these diseases from being a problem.

Hot-water treatments can eliminate disease-causing organisms from seed.
Hot-water treatments can eliminate disease-causing organisms from seed.

Hot-water seed treatment is one method that you can use to eradicate, or at least reduce the level of pathogens (particularly bacterial pathogens), in vegetable seed.  Some commercial vegetable seed companies routinely use this method (as well as other more stringent decontamination methods) to eradicate pathogens.  Hot-water seed treatments are effective because hot water soaks into the seed for a brief time and kills disease-causing organisms, without killing the seed itself.  Other common seed treatments (e.g., fungicide treatments) can also help reduce disease, but typically do not eliminate pathogens that have penetrated the seed coat.

Hot-water seed treatment works best for small seed.  It is not as effective for large or extremely fragile seed, pelleted seed, primed seed (i.e., seed treated to speed germination), fungicide-treated seed, and old seed.  When using hot water seed treatments, treat only the amount of seed that you plan on planting.  Treatment temperatures and durations will vary depending on the particular crop (see Table 1).

To most effectively hot-water treat seed, use a water bath (in home cooking often referred to as a “water oven”) with precise temperature and timing control.  Such equipment will provide the most consistent and uniform heating, but unfortunately can be very expensive.  Alternatively, you can use a large pan heated on a stove.  In order for this method to work, you will need to use a precise thermometer to accurately and frequently measure any changes in temperature.  In addition, you must mix the water thoroughly, adjust the stove settings appropriately and submerge the seed completely during the treatment process to ensure that the seed receive a constant and uniform temperature at all times.  Water that is too hot may injure the seed; water that is too cold will not eradicate pathogens.

To hot-water treat seed, use the following steps:

  •  Wrap seed in a permeable cloth (e.g., cheesecloth);
  • Thoroughly soak (removing any air) and pre-warm seed in 100°F tap water for ten minutes;
  • Transfer seed to tap water heated to the crop-specific prescribed temperature (see Table 1);
  • Place seed in cold tap water for five minutes to quickly end the heat treatment;
  • Apply fungicide seed treatments according to the manufacturer’s instructions (optional).  Spread seed out on a paper towel or screen to air dry;
  • Apply fungicide seed treatments according to the manufacturer’s instructions (optional).

Table 1.  Hot-water treatment temperatures and timings by crop*

Crop Temperature (°F) Time (minutes)
Brussel Sprouts 122 25
Broccoli 122 20
Cabbage 122 25
Carrot 122 20
Cauliflower 122 20
Celeriac 118 30
Celery 118 30
Chinese Cabbage 122 20
Collards 122 20
Coriander 127 30
Cress 122 15
Cucumber 122 20
Eggplant 122 25
Kale 122 20
Kohlrabi 122 20
Lettuce 118 30
Mint 112 10
Mustard 122 15
New Zealand Spinach 120 60-120
Parsley 122 30
Pepper 125 30
Radish 122 15
Rutabaga 122 20
Shallot 115 60
Spinach 122 25
Tomato 122 25
Turnip 122 20

*Table modified from http://vegetablemdonline.ppath.cornell.edu/NewsArticles/HotWaterSeedTreatment.html.

For more information on hot-water seed treatment:  Contact your county Extension agent.

 

Disease - Vegetable, Fact Sheet

Bacterial Spot of Tomato

What is bacterial spot?  Bacterial spot of tomato is a potentially devastating disease that, in severe cases, can lead to unmarketable fruit and even plant death.  Bacterial spot can occur wherever tomatoes are grown, but is found most frequently in warm, wet climates, as well as in greenhouses.  The disease is often an issue in Wisconsin.

Sunken, scabby bacterial spot lesions on ripening tomato fruit. (Photo courtesy of Mary Ann Hansen, Virginia Polytechnic Institute and State University)
Sunken, scabby bacterial spot lesions on ripening tomato fruit. (Photo courtesy of Mary Ann Hansen, Virginia Polytechnic Institute and State University)

What does bacterial spot look like?  Bacterial spot can affect all above ground parts of a tomato plant, including the leaves, stems, and fruit.  Bacterial spot appears on leaves as small (less than ⅛ inch), sometimes water-soaked (i.e., wet-looking) circular areas.  Spots may initially be yellow-green, but darken to brownish-red as they age.  When the disease is severe, extensive leaf yellowing and leaf loss can also occur.  On green fruit, spots are typically small, raised and blister-like, and may have a yellowish halo.  As fruit mature, the spots enlarge (reaching a maximum size of ¼ inch) and turn brown, scabby and rough.  Mature spots may be raised, or sunken with raised edges.  Bacterial spot symptoms can be easily confused with symptoms of another tomato disease called bacterial speck.  For more information on this disease, see University of Wisconsin Garden Facts XHT1250.

Where does bacterial spot come from?  Bacterial spot of tomato is caused by Xanthomonas vesicatoria, Xanthomonas euvesicatoria, Xanthomonas gardneri, and Xanthomonas perforans.  These bacterial pathogens can be introduced into a garden on contaminated seed and transplants, which may or may not show symptoms.  The pathogens enter plants through natural openings (e.g., stomates), as well as through wounds.  Disease development is favored by warm (75° to 86°F), wet weather.  Wind-driven rain can contribute to more severe disease as the pathogens are splashed and spread to healthy leaves and fruit.  Bacterial spot pathogens can survive well in tomato debris, but they survive very poorly in soil when not associated with debris.

How do I save plants with bacterial spot?  A plant with bacterial spot cannot be cured.  Remove symptomatic plants from the field or greenhouse to prevent the spread of bacteria to healthy plants.  Burn, bury or hot compost the affected plants and DO NOT eat symptomatic fruit.  Although bacterial spot pathogens are not human pathogens, the fruit blemishes that they cause can provide entry points for human pathogens that could cause illness.

On tomato leaves, bacterial spot leads to small, angular (i.e., straight-edged) spots with yellow haloes. (Photo courtesy of Michelle Grabowski, University of Minnesota Extension)
On tomato leaves, bacterial spot leads to small, angular (i.e., straight-edged) spots with yellow haloes. (Photo courtesy of Michelle Grabowski, University of Minnesota Extension)

How can I prevent bacterial spot in the future?

Plant pathogen-free seed or transplants to prevent the introduction of bacterial spot pathogens on contaminated seed or seedlings.  If a clean seed source is not available or you suspect that your seed is contaminated, soak seeds in water at 122°F for 25 min. to kill the pathogens.  To keep leaves dry and to prevent the spread of the pathogens, avoid overhead watering (e.g., with a wand or sprinkler) of established plants and instead use a drip-tape or soaker-hose.  Also to prevent spread, DO NOT handle plants when they are wet (e.g., from dew) and routinely sterilize tools with either 10% bleach solution or (better) 70% alcohol (e.g., rubbing alcohol).  Where bacterial spot has been a recurring problem, consider using preventative applications of copper-based products registered for use on tomato, especially during warm, wet periods.  Keep in mind however, that if used excessively or for prolonged periods, copper may no longer control the disease.  Be sure to read and follow all label instructions of the product that you select to ensure that you use it in the safest and most effective manner possible.  Burn, bury or hot compost tomato debris at the end of the season.  Wait at least one year before planting tomatoes in a given location again, and remove and burn, bury or hot compost any volunteer tomatoes that come up in your garden.

For more information on bacterial spot of tomato:  Contact your county Extension agent.

Disease - Vegetable, Fact Sheet

Bacterial Speck of Tomato

What is bacterial speck?  Bacterial speck is a common disease of tomato that occurs worldwide wherever tomatoes are grown.  The disease can substantially reduce yield when it severely affects leaves early in the growing season.  The disease can have an even greater impact on quality (and marketability for commercial tomato producers) when symptoms occur on tomato fruit.

Small, brown/black spots on a green tomato characteristic of bacterial speck. (Photo courtesy of S. T. Koike)
Small, brown/black spots on a green tomato characteristic of bacterial speck. (Photo courtesy of S. T. Koike)

What does bacterial speck look like?  Leaf symptoms of bacterial speck consist of small black spots (approximately ⅛ to ¼ inch in diameter) that often are more prominent on the undersides of leaves.  As the spots age, a yellow halo may develop around the edge.  Spots on fruit are very small (almost pinpoint-like) and do not penetrate very deeply into the tissue.  The spots can be raised, flat or sunken, and range in color from brown to black.  On unripe, green fruits, the spots often have darker green haloes, while on ripe fruits the spots can have subtle, yellow haloes.  Leaf symptoms of bacterial speck can be hard to distinguish from other tomato diseases.  Bacterial spot, (see University of Wisconsin Garden Facts XHT1244, “Bacterial Spot of Tomato”) and tomato spotted wilt (a viral disease) may cause similar leaf symptoms.  Laboratory testing may be needed to determine which disease is affecting your tomatoes.

Where does bacterial speck come from?  Bacterial speck of tomato is caused by the bacterium Pseudomonas syringae pv. tomato.  The bacterium is typically brought into a garden on contaminated tomato seeds or transplants, and thrives in cool (63oF to 75oF), wet weather.  It can be moved from plant to plant via splashing water (e.g., from rain or overhead watering with a sprinkler) or on hands and gardening tools when working with contaminated, and then healthy plants.  The bacterium can overwinter in dead tomato debris or on porous materials such as wooden plant stakes or trellises.

How do I save tomatoes with bacterial speck?  Once tomatoes are infected, there is no cure.  You may be tempted to cut off affected leaves as symptoms develop, but this will likely not do much to minimize or slow disease development, and may actually promote spread of the pathogen.  Often the best course of action is to allow the disease to run its course and simply salvage any unblemished fruit as they ripen over the summer.  DO NOT eat symptomatic fruit.  Although the bacterial speck pathogen is not a human pathogen, the fruit blemishes that it causes can provide entry points for human pathogens that could cause illness.

On tomato leaves, bacterial speck leads to small, angular (i.e., straight-edged) spots with yellow haloes. (Photo courtesy of Alan Collmer, Cornell University)
On tomato leaves, bacterial speck leads to small, angular (i.e., straight-edged) spots with yellow haloes. (Photo courtesy of Alan Collmer, Cornell University)

How can I prevent bacterial speck in the future?  Start by using high quality, pathogen-free seed or transplants from a reputable seed supplier or garden center.  If you have seed that you believe is contaminated with the bacterial speck bacterium and would still like to use it (e.g., it’s a favorite variety with difficult-to-find seed), consider treating the seed in hot water prior to planting to eliminate the pathogen.  Treat seed with 122°F water for 25 minutes.

To prevent spread of the bacterial speck pathogen from plant to plant in your garden, DO NOT use a sprinkler to water; instead use a soaker or drip hose to water at the bases of plants.  Also, only work with tomato plants when they are dry and consider routinely disinfecting garden tools with 10% bleach or (better) 70% alcohol (e.g., rubbing alcohol).  Spray disinfectants that contain approximately 70% alcohol can also be used for this purpose.

If you have a problem with bacterial speck, remove contaminated tomato debris from your garden at the end of the growing season.  This material can be deep buried, burned (where allowed by local ordinance) or hot composted.  DO NOT replant tomatoes in the same area the following growing season; instead grow a nonsusceptible vegetable crop.  This approach is referred to as non-host crop rotation.  For more information on this technique, see University of Wisconsin Garden Facts XHT1210, “Using Crop Rotation in the Home Vegetable Garden”.

As a last resort, consider chemical treatments for bacterial speck control.  If you decide to go this route, use a product that is labeled for use on tomatoes and that contains copper as the active ingredient.  To be most effective, the first treatment must be applied before symptoms have developed.  Apply additional treatments every 10 to 14 days as long as cool, moist conditions continue.  Keep in mind however, that if used excessively or for prolonged periods, copper may no longer control the disease.  Be sure to read and follow all label instructions on the product that you select to make sure you use it in the safest, most effective manner possible.

For more information on bacterial speck of tomato:  Contact your county Extension agent.

Disease - Deciduous Woody Ornamental, Fact Sheet

Eastern Filbert Blight

What is Eastern filbert blight?  Eastern filbert blight is a potentially serious fungal disease found throughout the United States, including Wisconsin.  It affects only Corylus species, commonly known as hazelnuts or filberts.  On hazelnuts native to Wisconsin such as American hazelnut (Corylus americana) and beaked hazelnut (Corylus cornuta), the disease causes little significant damage, but on the commonly grown European hazelnut (Corylus avellana), including Harry Lauder’s walking stick (Corylus avellana ‘Contorta’), the disease is lethal.  Turkish filbert (Corylus colurna) also appears to be highly susceptible.

Eastern filbert blight can cause small black cankers that form in rows, or deep gouges in the bark of severely infected trees/shrubs.
Eastern filbert blight can cause small black cankers that form in rows, or deep gouges in the bark of severely infected trees/shrubs.

What does Eastern filbert blight look like?  Eastern filbert blight causes cankers (i.e., dead, collapsed areas of bark) on branches or main trunks.  Easily visible within the cankers are black, football-shaped stromata (the reproductive structures of the causal fungus).  The stromata often form in rows of two.  Cankers first appear on new twigs and expand over time.  American hazelnut trees/shrubs are able to live almost indefinitely with Eastern filbert blight, forming a small number of slowly-expanding cankers (if any cankers form at all) that lead to limited branch dieback.  On European hazelnut however, cankers will expand anywhere from one inch to three feet in a year, and can eventually form long, deep gouges or grooves on severely affected trees/shrubs.  European hazelnuts typically die due to girdling from Eastern filbert blight within five to 10 years.

Where does Eastern filbert blight come from?  Eastern filbert blight is caused by the fungus Anisogramma anomala.  Stromata formed by the fungus produce spores that are spread short distances by water splash and over longer distances by wind.  Humans also can spread Anisogramma anomala on their hands and clothing, on gardening tools, and by transporting wood from infected trees/shrubs.  Unlike other canker fungi that can infect through wounds, the Eastern filbert blight fungus primarily infects through immature tissue on actively growing shoots.  Cankers appear 12 to 18 months after infection.  Eastern filbert blight does not affect hazelnut leaves, fruits or nuts.

How do I save trees/shrubs with Eastern filbert blight?  There is no cure for Eastern filbert blight.  If only a few branches on a tree/shrub are affected, prune these branches two to three feet below each canker.  Disinfest tools after each cut by dipping them for at least 30 seconds in a 10% bleach solution or (even better) a 70% alcohol solution.  Alternatively, use a spray disinfectant containing roughly 70% ethanol, spraying tools until they drip and then allowing them to air dry.

If a tree/shrub is severely affected by Eastern filbert blight (e.g., when there are so many cankers on multiple branches that the tree/shrub would look ugly if pruned, when branch pruning would require removing part of the trunk, or when trunk cankers are present), removal of the tree/shrub is the preferred management strategy.

Pruned branches and removed trees/shrubs should be burned (where allowed by local ordinance), deep-buried, or chipped (as long as the chips are allowed to dry to kill the fungus).

How do I avoid problems with Eastern filbert blight in the future?  Consider planting native species of hazelnut (e.g., American and beaked hazelnut) that are naturally resistant to the disease.  If you decide to plant European hazelnut, select cultivars that have been bred for resistance.  ‘Jefferson’, ‘Santiam’, ‘Yamhill’, and ‘Theta’ are resistant, nut-bearing cultivars.  ‘Red Dragon’ is a resistant, ornamental cultivar.  Note that these cultivars are not hardy in all hardiness zones in Wisconsin.  Hybrid hazelnuts (crosses between American and European hazelnut) are becoming increasingly available, but should be used with caution because their susceptibility to Eastern filbert blight has not been adequately tested.

Once hazelnut trees/shrubs are established in your yard, routinely inspect the plants for infection and remove infected branches as they occur.  Watch for dying branches in the summer and cankers (particularly on or near the youngest growth) in the winter.  Inspecting trees during the winter is very important, because cankers are more visible at that time.

Fungicides can be used for management, but should only be used as a last resort.  Not all fungicides that are approved for Eastern filbert blight control are particularly effective, but chlorothalonil has been shown to be an effective preventative treatment, although it will not cure existing infections.  Note that not all formulations of chlorothalonil are approved for use on nut-bearing hazelnuts; many formulations can only be used on ornamental hazelnuts.  Therefore, if you decide to use chlorothalonil, be sure to select the appropriate formulation for your particular situation.  Apply the first treatment at bud break (i.e., when half the buds show a separation of leaves) and additional treatments (up to three) every two weeks thereafter.  If you plan to eat nuts from your hazelnut tree, make sure that your last fungicide treatment is applied at least 120 days before anticipated nut harvest.  For further details about recommended fungicides, spray rate recommendations, and diagrams of bud stages, see “Pest Management Guide for Hazelnuts in the Willamette Valley”, Oregon State University Extension Bulletin EM8328 available at https://catalog.extension.oregonstate.edu/em8328.

For more information on Eastern filbert blight:  Contact your county Extension agent.

Fact Sheet, Turf

Fairy Rings

Type 1 (top), Type 2 (middle) and Type 3 (bottom) fairy rings.
Type 1 (top), Type 2 (middle) and Type 3 (bottom) fairy rings.

What are fairy rings?  Fairy rings are circular areas of abnormal turf growth that are most commonly found on lawns and golf courses where soils have high levels of organic matter, and in areas where trees have recently been removed.  Due to their mysterious, circular appearance, fairy rings have been of interest since ancient times.  According to medieval lore, they were thought to appear after a band of fairies had danced in an area.

What do fairy rings look like?  Fairy rings are rings of grass up to 15 feet in diameter that have a distinctly different color or texture than the grass inside or outside of the ring.  Half- or other partial ring patterns occur as well.  Depending on conditions, grass within fairy rings can be denser, greener, and faster growing, or alternatively browner and drier than surrounding grass.  During wet weather, rings of mushrooms may form at the edge of the discolored grass.

Where do fairy rings come from?  Fairy rings are caused by certain fungi that feed on decaying organic matter (e.g., tree stumps, logs, leaves or roots) buried in the soil.  Growth of fairy ring fungi begins in the center of the ring, expanding outward in a relatively uniform, circular pattern.  Three different types of fairy rings can form depending on soil type, the specific fungus involved, and environmental conditions.  Type 1 fairy rings occur most commonly on golf course putting greens, and occur less commonly on home lawns.  The fungi involved produce compounds that reduce the amount of water that the soil can absorb, leading to drought conditions that cause the grass in the ring to brown and die.  Type 2 fairy ring fungi efficiently decay organic matter releasing nitrogen that promotes lush growth and leads to a dense green ring of grass.  Finally, Type 3 fairy rings have rings of mushrooms that appear during wet periods, particularly in the fall.

What do I do with fairy rings in my lawn?  Fairy rings in home lawns do not typically cause turf death and thus are primarily cosmetic problems.  They often disappear naturally following a change in environmental conditions.  Therefore, waiting for fairy rings to naturally disappear is often the simplest option for management.

If you want to be more proactive in managing fairy rings, consider routine core aeration for your lawn.  Core aeration reduces the buildup of thatch which can harbor fairy ring fungi and make fairy ring development more likely.  If you are having a problem with Type 2 fairy rings, also consider applying a nitrogen fertilizer to the rest of your lawn to green up the surrounding grass to match the color of the fairy rings.  For Type 3 fairy rings, consider hand removing (wearing gloves) or raking up the mushrooms and disposing of them in your garbagethe mushrooms as they may be poisonous.  Finally, DO NOT use fungicides for control, as products labeled for use in managing fairy rings are typically not effective in preventing fairy ring development or reducing the severity of symptoms.

For details on core aeration and proper lawn fertilization rates and timings, see University of Wisconsin-Extension bulletin A3435, “Lawn Maintenance”.

For more information on fairy rings:  Contact your county Extension agent.

Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Vegetable, Fact Sheet, Misc

Cucumber Mosaic

What is cucumber mosaic?  Cucumber mosaic is a viral disease of worldwide distribution that affects over 1200 plant species.  Hosts include a wide range of fruits, vegetables, herbaceous and woody ornamentals, and weeds.  The disease has perhaps its biggest impact in vegetable production where it can cause significant losses in yield and vegetable quality.

Cumber mosaic on pepper (left) showing yellowing and ring spots, and on broad bean (right) showing mosaic and puckering of leaf tissue. (Photos courtesy of Russ Groves)
Cumber mosaic on pepper (left) showing yellowing and ring spots, and on broad bean (right) showing mosaic and puckering of leaf tissue. (Photos courtesy of Russ Groves)

What does cucumber mosaic look like?  Symptoms of cucumber mosaic can vary widely depending on host species, host variety, and time of infection.  Typical symptoms include stunting of entire plants, mosaic or mottling (i.e., blotchy white, yellow, and light green areas) and ring spots (i.e., ring-like areas of discolored tissue) on leaves and fruits, and a variety of growth distortions such as cupping, puckering and strapping (i.e., elongation and thinning) of leaves as well as warts on fruits.  In extreme situations, parts of an affected plant or even an entire plant may die from the disease.

Where does cucumber mosaic come from?  Cucumber mosaic is caused by Cucumber mosaic virus (CMV) which can overwinter in susceptible biennial or perennial weeds, as well as in perennial agricultural crops (e.g., alfalfa) and perennial herbaceous and woody ornamentals.  Seeds and even pollen from certain host plants can carry the virus, and thus the virus can be spread via these plant parts.  More commonly, CMV is spread by aphids [see the University of Wisconsin Garden Facts XHT1043 (“Aphids”) for details on these insect pests] which can pick up the virus from infected plants and transmit it to healthy plants as they feed.  Over 80 species of aphids can potentially transmit CMV.  The severity of cucumber mosaic oftentimes depends on the size and activity of aphid populations in an area, as well as on the number infected plants in an area serving as reservoirs for the virus.

How do I save plants with cucumber mosaic?  There is no known cure for cucumber mosaic.  Infected plants should be removed and destroyed to eliminate the plants as potential reservoirs for the virus (which can subsequently be spread to other nearby healthy plants).  Infected plants can be burned (where allowed by local ordinance), deep buried or hot composted.  Killing infected plants with herbicides can also be an effective management strategy.

Cumber mosaic on hibiscus (left) showing mosaic and puckered leaves, and on bluebell (right) showing mosaic and line patterns. (Photos courtesy of Brian Hudelson)
Cumber mosaic on hibiscus (left) showing mosaic and puckered leaves, and on bluebell (right) showing mosaic and line patterns. (Photos courtesy of Brian Hudelson)

How do I avoid problems with cucumber mosaic in the future?  Buy certified, virus-free seeds and plants.  Consider using CMV-resistant varieties of lettuce, spinach, cucurbits (e.g., cucumber, melon and squash) and other vegetables where available.  Seed catalogs often contain information on CMV resistance that can be useful for variety selection.  Remove weed hosts whenever possible around your garden and mulch vegetable and ornamental gardens to inhibit weed growth.  Consider using floating row covers where possible to prevent aphids from reaching susceptible plants.  DO NOT use insecticides to control aphids because such treatments are unlikely to act fast enough to prevent aphids from transmitting CMV, and may actually stimulate aphids to move and feed more widely, thus leading to increased spread of the virus.

For more information on cucumber mosaic:  Contact your county Extension agent.