All posts by hudelson

Wisconsin Lawn Care Calendar

Regular care and maintenance will yield a lawn that is lush and beautiful.
Regular care and maintenance will yield a lawn that is lush and beautiful.

The following lawn care calendar provides an overview of home lawn maintenance. Not all lawns require every maintenance activity. Be sure to customize the care of your lawn to its specific problems and needs. For details on specific activities listed below, check out the University of Wisconsin-Extension bulletins (available at http://learningstore.uwex.edu) and University of Wisconsin Garden Facts (available at http://hort.uwex.edu) that are referenced at the end of this fact sheet. Finally, be sure to read and follow all label instructions of any pesticides that you select to ensure that you use these products in the safest and most effective manner possible.

April

  • Rake and clean up winter debris as weather allows.
  • Reseed bare spots, and establish a new lawn, if you desire.
  • Apply a pre-emergent crabgrass herbicide to your established lawn.
  • Mow your lawn to remove 1/3 of the current grass height. Grass should be 21/2 to 31/2 inches tall after mowing.

May

  • After your grass is actively growing, core aerate your lawn if the thatch layer is over one inch thick.
  • Late in May (e.g., around Memorial Day), fertilize your lawn using a controlled-release or slow-release formulation. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate.
  • Apply an herbicide to your established lawn to control actively growing broadleaf weeds. DO NOT use herbicides on newly seeded areas. If possible, apply the herbicide to weeds when they are blooming. Many fertilizer products also contain herbicides for broadleaf weed control, so combining fertilizer and herbicide applications may be possible.

June

  • If you have not applied one previously, apply an herbicide to your lawn for broadleaf weed control.
  • Begin watering your lawn as needed for the summer. Or alternatively, do not water and allow the lawn to go dormant (i.e., turn brown) if natural rains are insufficient.
  • Watch for insect pests, diseases, and other lawn problems.

July

  • Water your lawn as needed. If you do not water, your lawn will naturally go dormant.
  • Early in July (e.g., around Independence Day), fertilize with a controlled-release or slow-release fertilizer. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate. If your lawn has been consistently fertilized for 10 to 15 years, if you leave clippings on your lawn when you mow, or if your lawn has gone dormant, skip this application.
  • Apply a grub control product to your lawn if there is a history of grub problems and/or your lawn is a high maintenance (i.e., regularly watered) lawn.
  • Avoid seeding and spraying for weeds.
  • Watch for insect pests, diseases, and other lawn problems.

August

  • Water your lawn as needed.
  • Establish a new lawn or renovate your current lawn. Note that mid-August to mid-September is the best time to establish a lawn in Wisconsin.
  • Watch for insects, diseases, and other lawn problems.

September

  • Early in September (e.g., around Labor Day), fertilize your lawn using a controlled-release or slow-release formulation. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate.
  • Apply an herbicide to your established lawn to control broadleaf weeds. Fall is the best time to apply herbicides for weed control. DO NOT apply herbicides to lawns planted in August or September.
  • Core aerate actively growing lawns if the thatch layer is over one inch thick, or if the soil is compacted.

October

  • Apply a broadleaf herbicide to your lawn if you did not apply one in September and the weeds are still growing.
  • If you have removed clippings from your lawn all season, fertilize your lawn in early October using a controlled-release or slow-release formulation. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate.

November

  • Continue to mow your lawn until it goes dormant for the winter.

For more information on lawn care and lawn pests: See University of Wisconsin-Extension bulletins A1990, A2303, A3179, A3237, A3271, A3275, A3434, A3435, A3700, A3710, and A3714 (available at http://learningstore.uwex.edu), and University of Wisconsin Garden Facts XHT1018, XHT1023, XHT1062 and XHT1114 (available at http://hort.uwex.edu), or contact your county Extension agent.

Wireworms

Wireworms are the larvae of several species of click beetles that feed primarily on grasses, including grass crops such as corn and small grains. Row crops that are attacked include beans, beets, cabbage, carrots, lettuce, onions, peas, potatoes, and radishes. Asters, phlox, gladioli, and dahlias are some of the more commonly infested herbaceous ornamentals.

A wireworm larva.
A wireworm larva.

Appearance: Wireworms are thin, shiny, jointed, yellow to reddish-brown, worm-like larvae. They range in length from 14 to 112 inches and are approximately 18 wide. The different species of wireworms are distinguished by the ornamentation on the last body segment. Adults are hard-shelled, brown or black “streamlined” beetles that flip into the air with an audible click when turned upside down.

Symptoms and Effects: Wire-worms feed on seeds, hypocotyls, or developing cotyledons. This feeding activity results in reduced germination, snakehead seedlings, and wilted or stunted plants. Dead spots scattered in a planting may be an indication of wireworm activity. If the seedlings in affected areas are dug, they will be riddled with holes and larvae may be found feeding on the roots of wilted plants. Wireworms tend to be most damaging one to four years after plowing up sod, or in poorly drained lowlands, but they are not exclusive to these areas.

Life Cycle: Wireworms have an extended life cycle, taking from one to six years to complete one generation. They overwinter as either adults or larvae. Larvae inhabit the upper six inches of soil where they migrate only short distances and feed on seeds and plant roots. They are sensitive to moisture and may burrow deeply into the soil in dry conditions. Adults become active in spring and begin laying eggs. Adult females may live 10 to 12 months, spending most of this time in the soil where they may lay up to 100 eggs in sod, and grassy weedy areas in row crops. Egg hatch occurs over several days to weeks. The tiny larvae immediately begin to feed on the roots of grasses, weeds, and other crops. Because of their extended life cycles, larvae of some wireworm species will feed for two to three years before pupating. Adult wireworms that emerge from these pupae remain in the pupal chambers until the following spring.

Scouting Suggestions: Scheduled scouting is not recommended and no thresholds for wireworms have been developed. If wireworm damage is suspected, dig up several ungerminated seeds or damaged plants along with a four to six inch core of surrounding soil and check for wireworms in and around roots, or in the underground portion of stems. Larvae may be extracted from soil by washing. Bait stations may be buried in fall or spring and recovered to check for wireworm larvae.

Control

Non-Chemical: Crop rotations that avoid susceptible crops and clean cultivation may reduce wireworm numbers. Some species of wireworms thrive in poorly drained soil and can be reduced by improving drainage. Clean summer fallowing of infested fields has been effective in some areas. Certain soil types (e.g., silt loams) are particularly susceptible.

Several natural enemies of wireworms have been described, but they are not effective in reducing populations.

Chemical: Insecticides registered for wireworm control are rarely recommended since outbreaks are infrequent. If treatment is necessary, applications should be made at the time of planting and incorporated into the soil prior to planting. Refer to University of Wisconsin-Extension publication A3422 “Commercial Vegetable Production in Wisconsin” for a list of recommended products.

For more information on wireworms: See UW-Extension Bulletin A3422, or contact your county Extension agent.

 

Winter Burn

What is winter burn? Winter burn is a common problem of evergreens including those with broad leaves (e.g., boxwood, holly, rhododendron), needles (e.g., fir, hemlock, pine, spruce, yew) and scale-like leaves (e.g., arborvitae, false cypress, juniper) grown in open, unprotected locations and exposed to severe winter conditions. Evergreen plants that are marginally hardy in a location (i.e., not well-adapted to local winter conditions) are at increased risk for winter burn. Winter burn can be so severe that affected plants may die and/or require replacement.

Browning due to winter burn on dwarf Alberta spruce.
Browning due to winter burn on dwarf Alberta spruce.

What does winter burn look like? Winter burn symptoms often become apparent as the snow melts and spring temperatures rise. Foliage starts to brown at the tips of branches with browning progressing inward toward the center of the plant. On broad-leaved evergreens, leaf edges typically brown first, followed by browning of entire leaves. Foliage facing south, southwest or west is most often affected. Symptomatic foliage often begins to drop off starting in spring and continuing through mid-summer as new foliage is produced. In extreme cases, entire plants can brown and die.

What causes winter burn? There are many factors that can contribute to winter burn. In general, plants with shallow or poorly-developed root systems that do not efficiently take up water (e.g., recent transplants) are more prone to winter burn. Warm fall temperatures that delay the onset of plant dormancy can also contribute to winter burn. Under such conditions, plants are not prepared for the subsequent rapid onset of freezing winter temperatures, and as a result damage to foliage occurs. Similar cold injury can occur mid-winter when temperatures drop sharply at sunset causing foliage that has warmed during the day to rapidly cool and freeze. In addition, on sunny winter days, foliage (particularly foliage facing the sun) can begin to transpire (i.e., naturally lose water through the foliage). Because the ground is frozen, plant roots cannot take up water and replace the water that has been lost from the foliage. As a result, foliage dries and browns. Foliage under snow or facing away from the sun and direct winds is usually not damaged. Strong winter winds can lead to additional water loss making winter burn more severe. Colder than normal winter temperatures and longer than normal winters can also be factors in the development of winter burn, especially if below normal temperatures occur into April (the time of year when plants normally come out of dormancy and are most susceptible to winter injury). Finally, exposure of plants to salt used to deice roads, driveways and sideways during the winter can make plants more prone to winter burn injury.

How do I save a plant with winter burn? For evergreens such as arborvitaes, boxwoods, junipers and yews, prune out dead, brown, damaged or dying tissue in mid-spring after new foliage is produced. If new foliage has not yet emerged by spring, scratch the bark on affected branches and look for green tissue underneath. Also gently peel back the bud scales to look for inner green bud tissue. If the stem or bud tissue is green, buds on the branch may still break to form new foliage. If the tissue is brown, the branch is most likely dead and you should prune the branch back to a live, lateral bud or branch. Such buds and branches may be far back inside the canopy and pruning may remove a substantial amount of the plant. Pines, spruces and firs typically produce new growth at branch tips in spring that will replace winter burn-damaged needles, and thus pruning may not be required on these evergreens. After a couple of growing seasons, new foliage will fill in the areas that were damaged. If an entire evergreen is brown, recovery is unlikely and the plant should be replaced with something (e.g., a deciduous shrub or tree) that is better-suited to the site.

How do I avoid problems with winter burn in the future? Use a variety of strategies to prevent winter burn before winter arrives.

Plant the right plant in the right place. Buy plants that are rated as cold hardy for your location and are well-adapted to local growing and soil conditions. Plants exposed to drying winter sun and winds are more likely to be injured. Therefore, avoid planting winter injury sensitive evergreens, particularly those that require shade or that are marginally cold-hardy, in exposed, sunny, windy areas. Plant them on the northeast or east side of a building or in a protected courtyard. Plant boxwoods, hemlocks, rhododendrons, and yews in partial shade to provide them added protection from winter sun and wind.

Plant evergreens at the right time of year. Optimally plant evergreens either in early spring (before buds break) or in late summer (i.e., August through September). Evergreens can be planted in the summer if you provide supplemental water. Avoid planting after early October in northern Wisconsin and after mid-October in southern Wisconsin as this will not allow sufficient time for roots to grow adequately before the ground freezes.

DO NOT prune evergreens in late summer or early fall. Late season pruning of some non-native evergreens may encourage a flush of new growth that will not harden off properly before winter. See University of Wisconsin Garden Facts XHT1013 “How to Properly Prune Evergreens” for details on when and how to prune specific evergreen trees and shrubs.

Mulch evergreens properly. Apply two inches (on clay soils) to four inches (on sandy soils) of loose mulch (e.g., shredded hardwood, pine, or cedar bark; leaf compost; or wood chips) around the base of evergreens out to at least the drip line (e.g., the edge of where the branches extend). Keep mulch at least three inches away from the trunks of trees and the bases of shrubs. Proper mulch insulates roots from severe fluctuations of soil temperatures and reduces water loss. It also helps protect roots from injury due to heaving that occurs when soils go through cycles of freezing and thawing during the winter. Heaving can especially be a problem for shallow-rooted and newly planted evergreens. DO NOT mulch excessively or too close to plants as this can lead to damage by providing shelter for mice and voles (which can girdle trunks and branches) and by providing a favorable environment for disease development as well as insect activity and feeding.

Water plants properly. Plants that are well-hydrated are less prone to winter burn. In particular, newly planted or young evergreens, especially those planted in open, exposed sites, those planted under eaves, or those planted in dry falls may suffer severe moisture loss during the winter and consequently severe winter burn. Established evergreens should receive approximately one inch of water per week and newly transplanted evergreens up to two inches of water per week during the growing season up until the soil freezes in the autumn or there is a significant snowfall. If supplemental watering is needed, use a soaker or drip hose to apply water near the drip lines of plants rather than using a sprinkler.

Avoid late summer or fall fertilization. Applying quick-release, high-nitrogen fertilizers in late summer or fall could potentially stimulate growth of new foliage (particularly on some non-native evergreens) as well as inhibit proper onset of dormancy which can lead to damage over the winter. If you are concerned that your evergreens may need to be fertilized, submit a soil sample from around your plants to a professional soil testing lab that can provide specific information on what fertilizer to use and when to fertilize.

Protect plants during the winter. Use burlap, canvas, snow fencing or other protective materials to create barriers that will protect plants from winter winds and sun. Install four to five foot tall stakes approximately two feet from the drip lines of plants especially on the south and west sides (or any side exposed to wind) and wrap protective materials around the stakes to create “fenced” barriers. Leave the top open. These barriers will deflect the wind and protect plants from direct exposure to the sun. Remove the barrier material promptly in spring. DO NOT tightly wrap individual plants with burlap as this can collect ice, trap moisture and make plants more susceptible to infection by disease-causing organisms. Use of anti-transpirant products to prevent water loss from foliage over the winter has been shown to have limited benefit. These materials degrade rapidly, require reapplication after each significant rain or snow event, and may not be effective in preventing water loss that can lead to winter burn.

For more information on winter burn: Contact your county Extension agent.

Wild Parsnip

What is wild parsnip? Wild parsnip (Pastinaca sativa) is an aggressive Eurasian member of the carrot family that grows in sunny areas and tolerates dry to wet soil types. It is often found along highways, in prairies or bordering farmed fields. The plant spreads primarily by seed. Sap from the plant can cause phytophotodermatitis, a light sensitive reaction on your skin. If the juice from broken stalks, leaves or flowers contacts your skin and then is exposed to sunlight, a skin rash will result 24-48 hours later. Symptoms range from slightly reddened skin to large blisters. The blisters may produce a sensation similar to a mild to severe sunburn. The blisters do not spread or itch, as poison ivy rashes do, but they are uncomfortable and leave brown scars that last for a number of months to two years. See your doctor if you develop burn symptoms.

A wild parsnip plant.
A wild parsnip plant.

What does wild parsnip look like? At maturity, wild parsnip is about four to five feet tall. It bears many large flat clusters of yellow-green flowers on a thick stem. Flowers appear from the first of June through July in southern Wisconsin. Seeds form around the end of July. The plant will often have both flowers and seed capsules at the same time. Seeds are flat, oval and about the size of a sunflower seed. After flowering and producing seed, the plant turns brown and dies. The plants have a rosette of basal leaves, as well as leaves arranged alternately on the stem. The leaves are branched into leaflets and have heavily toothed margins. The plant can be confused with prairie parsley (Polytaenia nuttallii), an endangered native species in Wisconsin. Prairie parsley has sparse, light yellow flowers, and long leaves branched into leaflets with few teeth.

How can I control wild parsnip? Prevention is the best way to control wild parsnip. When wild parsnip is first detected in an area, it can be cut below ground level with a sharp shovel. Be sure to wear long sleeves, long pants and gloves when working with plants. Also, try to work after sunset so that exposure to sunlight does not occur. Plants can also be pulled by hand, if you wear protective gloves. If the wild parsnip population is fairly large, you may use a brush-cutter just after peak bloom and before the plant sets seed. Remove all the cut material. A few weeks later, repeat the treatment to prevent plants from re-sprouting. Treatments may need to be repeated over several years. Herbicides containing the active ingredient glyphosate are also effective against wild parsnip. In high quality natural areas such as prairies, the Department of Natural Resources recommends burning the site and then applying spot treatments of a 1-3% glyphosate solution to wild parsnip rosettes if they re-sprout after burning.

For more information on wild parsnip: See the DNR publication ER-090-97 – “Wisconsin Manual of Control recommendations for Ecologically Invasive Plants”, or contact your county Extension agent.

 

Whiteflies

Whiteflies are not true flies although they look fly-like. They actually belong to the same order of insects as scales, aphids, and mealybugs: the order Homoptera. There are several species of whiteflies that can infest greenhouses including the greenhouse (Trialeurodes vaporariorum), sweet potato (Bemisia tabaci), silverleaf (Bemisia argentifolia), and bandwing (Trialeurodes abutilonea) whiteflies. Of these, the greenhouse whitefly is the most common in northern areas. The silverleaf whitefly is responsible for causing phytotoxemia in poinsettia as this species extracts more sap than the other species. Bandwing whiteflies can enter the greenhouse in late summer or early fall but are not as much of a problem as previously mentioned species. Host plants include fuchsia, geranium, hibiscus, gerbera daisy, and poinsettia. Vegetable hosts include cucumbers, tomatoes and eggplant.

An adult whitefly.
An adult whitefly.

Appearance: Whitefly adults resemble tiny moths and are covered with a whitish powder. Species identification can be made by examining the wing markings. The first instar nymphs resemble scales, but they become a transparent yellow-green and settle once they reach the second and third instar stages.

Symptoms and Effects: Like all other Homopteran insects, whiteflies have piercing-sucking mouthparts and feed on plant juices. Damage consists of yellowing and wilting of the foliage. In severe cases, plant death may occur. Whitefly infestations in vegetable crops will produce a noticeable yield reduction. Honeydew and sooty mold may also be present if populations are large enough. Whiteflies are capable of transmitting viruses to some hosts, but at the present time, this is not a major concern.

Life Cycle: Female whiteflies lay six to 20 eggs per day on the lower leaf surface of host plants. The eggs are white initially, but become dark brown as they mature. Eggs hatch in seven to 10 days and the mobile, first instar crawlers resemble scales. Within several hours of hatching, these crawlers will seek out a suitable place to settle, where they will pass the next two instars. The final instar is often referred to as a pupa although the whiteflies go through simple metamorphosis in which a true pupal stage is absent. There can be several generations of whiteflies per year, with each generation taking one to three months to develop depending on the temperature of their environment. At 82°F, whiteflies develop from egg to adult in 18 days.

Scouting Suggestions: Check hanging baskets frequently and monitor any weeds that may be growing beneath greenhouse benches. Begin monitoring susceptible crops such as fuchsia and poinsettia at planting. Yellow sticky traps placed just above the crop canopy will help you monitor adult whiteflies, as will a gentle shaking of the foliage. A more thorough visual inspection of the foliage is necessary to detect whether immature nymphs are present. Placing trap crops such as fuchsia near doors and air-intake vents can signal when whiteflies are moving into the greenhouse.

Control:

Non-Chemical: There are no established treatment thresholds, but plants can handle more whiteflies than greenhouse managers can tolerate. Typically a mature poinsettia plant can tolerate up to 50 whiteflies per leaf before damage occurs.

Good sanitation and exclusion are critical for whitefly management. Eliminate all plants including weeds and “pet” plants for at least one week before starting a new crop. Inspect all new plant shipments. Screen vents to keep bandwing whiteflies from entering the greenhouse in the fall. Avoid excessive fertilization and irrigation.

There are several parasitic wasps that control whiteflies. The most common is Encarsia formosa which is commercially available. Other available natural enemies are Encarsia luteola, Eretmocerus eremicus, Chrysoperla comanche, Chrysoperla rufilabris, Delphastus pusillus, and several minute pirate bugs (Orius spp.).

For additional information on biological control, refer to NCR publication 581, “Biological Control of Insects and Other Pests of Greenhouse Crops”.

Chemical: There are several insecticides available for control of whiteflies. Refer to UW-Extension publication A3744, “Insect Pest Management for Greenhouses”, for a complete listing of available products. Whitefly management is difficult without pesticide use. It is critical that you rotate chemical classes to prevent an outbreak of insecticide-resistant populations. Start any chemical control program early and treat every five to seven days for a total of three treatments to control all stages of overlapping generations. Watch closely and evaluate for the development of resistant whitefly populations. If you find you aren’t getting suitable control with one class of insecticide, switch to another.

For more information on whiteflies: See UW-Extension Bulletin A3744, or contact your county Extension agent.

White Pine Blister Rust

What is white pine blister rust? White pine blister rust is a serious, tree-killing disease of eastern white pine and its close relatives (pines with needles in bundles of five). This disease is caused by the exotic (not native) fungus Cronartium ribicola, which was introduced into North America in the early 1900’s. This pathogen is now found in most regions where pines grow in the United States, including Wisconsin. White pine blister rust affects trees of all ages, but perhaps most frequently and severely damages seedlings and saplings.

White pine blister rust cankers on branches and stems often have a cracked or blistered appearance and may bear yellow to orange spores in fruiting bodies of Cronartium ribicola.
White pine blister rust cankers on branches and stems often have a cracked or blistered appearance and may bear yellow to orange spores in fruiting bodies of Cronartium ribicola.

Where does white pine blister rust come from? The white pine blister rust fungus Cronartium ribicola requires two different plant hosts to complete its complex life cycle. Spores of the fungus produced on white pine are blown to alternate host plants in the genus Ribes (gooseberries and currants). After infecting gooseberry and currant bushes the fungus multiplies rapidly throughout the summer, repeatedly producing spores that germinate to result in additional gooseberry and currant infection. Spores produced in late summer on gooseberries and currants are spread by the wind to white pines, where needles that are moist from rain, fog, or dew are infected.

What does white pine blister rust look like? Infection of needles by Cronartium ribicola results in development of yellow to brown spots and bands. The fungus slowly grows through pine needles and bark to eventually form cankers on twigs, branches, and trunks (main stems) of trees. A canker is a localized diseased area, which may be swollen or sunken, that is surrounded by healthy tissues. A typical white pine blister rust canker has resinous margins, and may appear “blistered” before rupturing to expose fruiting bodies (reproductive structures) with yellow to bright orange spores of Cronartium ribicola. As a canker expands to completely encircle stems, all portions beyond the canker are killed. Dead white pine branches may temporarily retain orange to red dead needles to form a bright “flag” that is a common symptom of this disease.

Can I save a tree affected by white pine blister rust? There is no “cure” for a tree with a white pine blister rust canker on its main stem. As the canker expands to completely encircle the trunk, all parts above the canker will die. Branch cankers that extend to within four inches of the trunk, probably indicate that the trunk already is colonized by the fungus and future development of a main stem canker is likely. Pruning off branches on which cankers are located farther from the trunk, however, can prevent the fungus from growing into the trunk. These branch cankers can be removed by pruning at least six inches beyond any visible symptoms on the trunk side of the cankered branch. Removal of branch cankers and trees with main stem cankers prevents production of spores that are spread to gooseberries and currants. The fungus quickly dies in discarded branches and trunks and presents no further danger to either of its hosts.

How do I avoid future problems from white pine blister rust? Infection of pine is most frequent in proximity to diseased gooseberries or currants. Therefore, removal of these alternate hosts (especially within 200 feet) can greatly reduce incidence of white pine blister rust. Gooseberries or currants can be killed by uprooting them or by application of herbicides in accordance with label directions.

Conditions that promote or prolong needle wetness should be avoided. These include use of sprinklers that wet the needles of ornamental trees, dense plantings, growth of weeds surrounding young trees, or planting white pines in low-lying, chronically moist areas near water or sites that lack good air movement. Growing white pines under a hardwood overstory that will intercept evening dew can help keep needles dry and reduce infection.

Regular inspection allows prompt detection and removal of cankered branches on young trees. Also, because infection very often occurs on needles of low branches, pruning to remove healthy branches (if aesthetically acceptable) will reduce the likelihood of this disease. When trees are five to seven years old, starting close to the ground, prune off all branches up to no more than one-third to one-half the height of the tree. Branch pruning can be continued every other year until the lower eight to nine feet of trunk is free of branches.

Planting or measures to encourage natural regeneration of conifer species other than white pines (including red or jack pines, spruces, firs, arborvitae, hemlock, and junipers) might be considered, especially in the presence of gooseberries or currants and where moisture conditions favor infection.

Use of protectant fungicides may be a management practice in white pine production nurseries. Nursery stock should be carefully inspected, because the planting of diseased white pine seedlings is one way Cronartium ribicola has been spread into previously disease-free locations.

For more information on white pine blister rust: Contact your county Extension agent.

 

 

White Mold

What is white mold? White mold, also known as Sclerotinia stem rot, is a serious and often lethal fungal disease that affects over 400 species of plants in many plant families. White mold causes severe damage in commercial snap, kidney and lima bean production, as well as commercial sunflower production. White mold also can be a serious problem in home vegetable gardens on tomatoes, potatoes, cucurbits (e.g., cucumber, pumpkin and squash), carrots, lettuce, celery, brassicas (e.g., cabbage, broccoli, and cauliflower), basil, and rosemary. White mold is a common disease on many annual and perennial ornamentals as well.

Stem cankers, cottony mycelia and sclerotia (see arrows) of white mold on snap beans.
Stem cankers, cottony mycelia and sclerotia (see arrows) of white mold on snap beans.

What does white mold look like? Symptoms of white mold vary depending on the plant infected. White mold can lead to crown and stem cankers, root rots, wilts, damping-off of seedlings, and blossom and fruit rots. Plants affected by white mold can wilt rapidly due to stem-girdling cankers at or near the soil line. Brown spots can appear on flower petals and buds. Cottony masses of fungal threads (called mycelia) may appear on stems or on nearby soil. Hard, irregularly-shaped masses (called sclerotia) develop within or on the surface of infected plants. The sclerotia are white at first and then turn dark brown or black as they mature.

Where does white mold come from? White mold is caused by several species of the fungus Sclerotinia, most commonly Sclerotinia sclerotiorum. White mold fungi overwinter as sclerotia in dead plant material or in infested soil. Sclerotia can survive in soil for at least 3 years. During periods of cool, wet or humid weather, sclerotia germinate to form either fungal threads (called hyphae) or tiny, mushroom-like spore-producing structures (called apothecia). Apothecia can release millions of spores over a period of several days. Spores are dispersed primarily by wind, but also by rainsplash and insects. Both spores and hyphae can infect plant tissue, with infection often occurring through dead or declining plant parts (e.g., flowers and leaves), and then spreading to healthy tissue. Infections may also occur through healthy plant parts that are growing near or in contact with the soil. In some plants, seeds can be contaminated by sclerotia or mycelia of white mold fungi.

How do I save plants with white mold? White mold is difficult to manage once infections have occurred. Prune four to five inches below obviously disease tissue or remove entire plants if they are severely affected. DO NOT compost these materials because of the risk of spreading white mold fungi via long-lived sclerotia. Burn these materials instead.

White mold can be destructive on ornamentals such as Liatris.
White mold can be destructive on ornamentals such as Liatris.

How do I avoid problems with white mold in the future? Check seed for sclerotia and remove these structures if you find them. Make sure your soils are well-drained, and avoid overwatering as well as frequent, light watering. DO NOT overhead water (e.g., with a sprinkler). Instead water deeply early in the day with a drip or soaker hose. Promote good air circulation in your garden so that plants more rapid dry when they do get wet (e.g., from natural rain). Better air circulation can be achieved by choosing cultivars or varieties of plants that have a more open growth form, by spacing plants farther apart, by avoiding excessive use of nitrogen fertilizers (which can promote excessive production of lush, thick foliage), and by keeping weeds under control. Weed control also eliminates potential alternate hosts that white mold fungi can infect. As leaves and flowers or your plants naturally wither and die, remove them, as well as any other plant debris that may harbor white mold fungi. Finally, in beds where severe cases of white mold have occurred, remove and replace infested soil.

For more information on white mold: Contact your county Extension agent.

White Grubs on Christmas Trees

White grubs (i.e., larvae) of the common May/June beetle or “Junebug” (Phyllophaga spp.) are an important pest of Christmas trees in Wisconsin. This soil-dwelling pest feeds on the roots of pines, firs, and spruces, and can cause damage severe enough to kill small trees in Christmas tree production fields.

A typical white grub (left) and an adult May/June beetle (right).  (Adult photo courtesy of Phil Pellitteri)
A typical white grub (left) and an adult May/June beetle (right). (Adult photo courtesy of Phil Pellitteri)

Appearance: Adult May/June beetles are typically ½ to one inch long and vary in color from reddish-brown to almost black. Adults are active in late May and early June, often flying near house lights at night. May/June beetle white grubs have a distinctly C-shaped, cream-colored body with a reddish brown head and three pairs of legs. Grubs vary in size (depending on their stage of development), and can be up to 1¼ inches long when fully mature. Larvae have strong mandibles (i.e., mouth parts) that they use to chew on the roots of small trees.

Symptoms and Effects: Adult May/June beetles occasionally cause damage to trees by feeding on leaves and needles. In contrast, May/June beetle larvae can be extremely damaging to young conifers. White grubs damage young trees by feeding on their roots and interfering with the uptake and transport of water and nutrients within the trees. The initial symptoms of grub damage appear similar to those of drought stress: mild yellowing and wilting of trees. When feeding damage to roots is severe, trees turn brown, often shed needles and typically can be pulled easily from the ground. Small conifers (e.g., 2-2 or 3-0 trees) in Christmas tree production fields are often most susceptible to white grub damage due to their small root systems. In contrast, larger trees with more developed root systems can tolerate some white grub activity without major consequences.

Life Cycle: May/June beetles typically have either a two- or three-year life cycle in Wisconsin depending on species. Adults emerge in late May to early June and are active in the evening hours. Adults mate, and females lay eggs in the soil. After emerging from eggs, white grubs begin to feed below-ground on plant roots. Larvae pass through three stages (called instars) and become progressively larger and more damaging. Depending on the species of May/June beetle, larvae begin pupating in the soil in the late summer and fall of the either the second or third year of their life cycle. The next generation of adults emerges the following year.

Heavy feeding activity by white grubs can destroy the root system of small conifers.
Heavy feeding activity by white grubs can destroy the root system of small conifers.

Control: An integrated approach to control that includes cultural, physical and chemical practices can help prevent or at least minimize the effects of white grubs. Control practices should include the following:

Scout fields prior to planting to identify potential white grub problems. Not all fields have problems with white grubs. If you sample with a hand trowel and find average grub densities of ½ to one or more grubs per square foot, grub control measures are warranted. Similarly, if you sample with a tree planter and find grub densities of approximately 1½ to three or more grubs per ten linear feet, grub control measures are warranted.

Apply insecticides when white grub densities are high to help prevent root damage to small trees. Grub control products for Christmas tree farms include products containing bifenthrin, imidacloprid, and thiamethoxam. You can directly apply these insecticides into the root zone of trees via soil incorporation or root dipping, or apply them as banded sprays. If you opt for a spray treatment, be sure to use a relatively high spray volume (i.e., 44 to 220 gallons/acre), and apply the insecticide prior to a forecasted rain to ensure proper movement of the product into the soil profile.

Manage weeds in production fields using a chemical herbicide. This will deter May/June beetles from laying eggs in the treated area. Female May/June beetles prefer to lay eggs in weedy or mowed grassy areas.

For more information on white grub control on Christmas trees: Contact your county Extension agent.

Western Conifer Seed Bug

Western conifer seed bugs belong to the leaf-footed bug family Coreiidae. Adults are 34 of an inch long, elongate, reddish to dull brown with a faint, white zigzag straight line across the center of the wings. They have long, thin antennae and hind legs that are flattened (leaf-like). Western conifer seed bugs can fly readily and may make a buzzing noise if disturbed. Western conifer seed bugs also have well developed scent glands that emit strong pine-like odors. For that reason they are sometimes incorrectly called stink bugs. Western conifer seed bugs are also often mistakenly identified as assassin bugs.

A Western conifer seed bug.
A Western conifer seed bug.

Western conifer seed bugs have become more numerous in Wisconsin during the last five years. They can become a nuisance when they crawl up the sides of buildings during September and October. Sometimes they cluster in small groups and enter buildings at the onset of cold weather as they seek a protected site to spend the winter. If they can crawl under siding or through other openings into the home, these insects will overwinter in the house and re-emerge on warm, sunny days during the winter and spring months. Western conifer seed bugs do not bite or cause damage in the home.

Life cycle: Usually a single generation of Western conifer seed bugs occurs each year. Western conifer seed bugs have a piercing, sucking moth part, and nymphs (immature insects) feed by sucking nutrients from the seed cones of white, red, Scots, Austrian, and mugo pine, white spruce, Douglas fir and hemlock. This feeding damage does not hurt the tree, but reduced seed production may result from heavy infestations.

Control: The first line of defense against Western conifer seed bugs is to prevent their entry into the home. Screen attic, overhang, and wall vents to mechanically block points of entry for the insect. Eliminate or caulk gaps around door and window frames and soffits, and tighten loose-fitting screens, windows or doors. Insecticidal soap sprays or general insecticides can be used to kill insects clustered on the outside during the fall. When adults find their way indoors, simply vacuum or hand-remove them.

For more information on Western conifer seed bugs: Contact your county Extension agent.

Weir’s Cushion Rust of Spruces

What is Weir’s cushion rust? Weir’s cushion rust is a needle disease that disfigures and reduces growth of spruce trees (Picea spp.) of all ages. This disease has been known in both eastern and western regions of the United States, but was recognized in Wisconsin for the first time in 2002.

Yellow spots and bands in winter on spruce shoots affected by Weir's cushion rust.
Yellow spots and bands in winter on spruce shoots affected by Weir’s cushion rust.

What does Weir’s cushion rust look like? Needles on current year’s shoots affected by Weir’s cushion rust may develop yellow spots or bands in summer and fall. These spots and bands may intensify to give needles a bright “green and gold” appearance during the following spring, when tiny blister-like pustules also may develop in the yellow areas. Microscopic examination of these pustules is required for diagnosis of this disease. Affected one-year-old needles continue to yellow, turn brown, and fall off as spring and summer progress. Trees badly damaged by Weir’s cushion rust will have thin crowns due to repeated loss of the previous year’s needles.

Where does Weir’s cushion rust come from? Weir’s cushion rust results from colonization of spruce needles by the fungus Chrysomyxa weirii. This fungus overwinters in needles infected during the previous growing season. In late summer, or more typically the next spring, Chrysomyxa weirii produces spores in tiny, blister-like pustules that develop on these needles. These spores can be blown by wind or splashed by rain to newly emerging needles on the same tree or other trees. Spore germination is followed by infection of young needles.

Can I save a tree affected by Weir’s cushion rust? Fungicides containing chlorothalonil may be applied to trees affected by Weir’s cushion rust to prevent new needle infections. The first application should be made when 10% of the buds have broken and two additional applications should be made at seven to 10 day intervals thereafter. Fungicide applications do not kill the fungus in needles that are already infected, so it is important to begin applications promptly and to complete the spray program, to ensure thorough coverage of foliage. Please be sure to read and follow all fungicide label instructions to ensure that the fungicide is used in the safest and most effective manner. Needles infected by Chrysomyxa weirii the previous year will die, and the fungus will not continue to live or produce spores on dead needles. Therefore, destruction of dead needles is not necessary.

How do I avoid Weir’s cushion rust in the future? Growers and homeowners should be careful not to accept nursery stock affected by Weir’s cushion rust, which may be present in wholesale or retail nurseries. Spruces in nurseries and the landscape should be carefully inspected in late summer and fall for yellow spots and bands on current year’s needles and in spring for these symptoms and pustules on the previous year’s needles. Affected trees should not be moved to areas where the disease is not already present. Preventative application of fungicides may prevent establishment of the fungus on new trees or in previously unaffected nurseries.

For more information on Weir’s cushion rust: Contact your county Extension agent.