Category Archives: Fact Sheet

Spotted Lanternfly

Spotted lanternfly (SLF) is an invasive planthopper native to China, India, and Vietnam.  It was first detected in the U.S. in Pennsylvania in 2014, most likely arriving up to two years earlier as egg masses on materials imported from China.  As of February 2016, SLF has been confirmed in five Pennsylvania counties, but due to its highly invasive nature, it appears to be spreading rapidly.  SLF has a large host range (in Korea, over 70 plant species have been reported as hosts) and potentially could greatly impact the grape, tree fruit, plant nursery and timber industries in the U.S.

Spotted lanternfly adult (left) and nymph (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)
Spotted lanternfly adult (left) and nymph (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)

Appearance:  Adult SLFs are approximately 1 inch long and ½ inch wide when resting.  The insects’ forewings are light brown to grey with black spots at the base and have a grey net-like pattern at the tips.  The hindwings are red with black spots at the base, have white bands near the center, and have a black net-like pattern at the tips.  The heads and legs of SLF adults are black, while their abdomens are yellow with broad black bands.  When resting, adults fold their wings over their bodies and appear light brown to grey with black spots.  Adult female SLFs have a red spot at the tip of their abdomens.  SLF egg masses are 1 to 1½ inches long and ½ to ¾ inches wide, greyish-brown, covered with a grey, waxy coating, and contain 30 to 50 eggs.  First stage immature SLFs (i.e., nymphs) are wingless and black with white spots.  As nymphs mature, they eventually develop red patches, but retain their white spots.

Host Range:  SLF has a wide host range and nymphs appear to feed on leaves and branches of virtually any plant they encounter, often gathering in large numbers.  In the fall, adult SLFs gather in large numbers on tree of heaven/paradise tree, willow, maple, birch, poplar, tulip poplar, ash, oak, grape, apple and stone fruit trees (e.g., cherries and plums).  Tree of heaven/paradise tree (Ailanthus altissima) is a preferred fall feeding host for SLF adults, as well as a preferred mating and egg laying site.  This plant is an invasive species native to China that grows in disturbed sites and along roadsides.  SLF damage on grape, apple and stone fruit trees is of particular concern because these plants are important agricultural crops.

Symptoms and Effects:  SLF adults and nymphs feed on a plant’s phloem (i.e., food conducting tissue), sucking the sap from young stems and leaves, and reducing the plant’s ability to photosynthesize.  Affected plants often have weeping/oozing wounds on their trunks that eventually result in greyish-black discolorations.  Damage can lead to weakened, withered plants, and potentially even plant death.  In addition, SLFs excrete large amounts of honeydew (i.e., sugar-rich feces) which can cover stems and leaves and build up on the ground at the base of plants.  Honeydew can become colonized by sooty mold fungi (see University of Wisconsin-Extension bulletin A2637, “Sooty Mold”, available at http://learningstore.uwex.edu) giving leaves and branches a blackish coating that can further reduce photosynthesis and contribute to plant decline and death.  Oozing sap and honeydew also attract other insects such as wasps, hornets, bees, and ants.

Life Cycle:  SLF has only one generation per year and overwinters as eggs in egg masses.  In the spring and early summer, eggs hatch and SLFs go through four nymphal stages (called instars).  Adults begin to appear in July and August.  Males and females mate multiple times and females can produce one or two egg masses between September through November (or until they die from the onset of winter).  Female SLFs lay egg masses on smooth-barked trunks, branches, and limb bases of medium to large-sized trees, as well as on smooth stone and other natural surfaces, and on man-made items such as yard furniture, cars, trucks, and farm equipment.

A cluster of adult spotted lanternflies on tree of heaven (left), and egg masses of spotted lanternfly covered by waxy deposits (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)
A cluster of adult spotted lanternflies on tree of heaven (left), and egg masses of spotted lanternfly covered by waxy deposits (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)

Scouting Suggestions:  SLF adults are poor fliers, but strong jumpers, and prefer to walk.  Nymphs and adults gather in large numbers on host plants and are easy to find at dusk or at night when they migrate up and down tree trunks.  SLFs are harder to find during the day as they tend to stay near the base of the host plants.  Beginning in late April to mid-May, watch for nymphs on smaller plants and vines, and on any new growth on trees and shrubs.  Watch for adult SLFs in late August through September, when they can be found in large numbers.  Sticky tree bands can be helpful for monitoring for young SLFs, but less useful in detecting later stage immature and adult SLFs.  From October through spring, watch for SLF egg masses (which can be very inconspicuous), particularly on tree of heaven.

Control:  To date, SLF has not been found in Wisconsin, and has been found in only five counties in eastern Pennsylvania.  These counties are under quarantine and there is an active monitoring and eradication program underway to prevent the spread of SLF.  Because SLF has great potential to adversely affect the grape, tree fruit, plant nursery, and timber industries, preventing introduction of SLF into Wisconsin is very important.  Accidental movement of egg masses poses the greatest risk for introduction.  Therefore, be sure to watch for egg masses (as well as adults and nymphs) on any item that has come from areas where SLF is established.  If you suspect that you have found SLF, please contact the University of Wisconsin-Madison/Extension Insect Diagnostic Lab at (608) 262-6510, idl@entomology.wisc.edu or http://labs.russell.wisc.edu/insectlab/contact-us/.

For more information on spotted lanternfly:  Contact your county Extension agent or see http://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/spotted_lanternfly/Pages/default.aspx.

Common Leaf Spot of Strawberry

What is common leaf spot?  Common leaf spot of strawberry (also known as Mycosphaerella leaf spot, Ramularia leaf spot, strawberry leaf spot, bird’s-eye spot, gray spotness, and white spot) is a common fungal leaf disease that affects both wild and cultivated strawberries throughout the world.  Common leaf spot was once the most economically important strawberry disease, but the use of resistant strawberry varieties/cultivars and improvements in methods for growing strawberries have been effective in managing the disease and reducing its impact.  Today, the disease is often a cosmetic problem and typically has little impact on yield or fruit quality.

Typical common leaf spot symptoms: tan to gray spots with reddish purple margins. (Photo courtesy of Dr. Patricia McManus, Department of Plant Pathology, University of Wisconsin)
Typical common leaf spot symptoms: tan to gray spots with reddish purple margins. (Photo courtesy of Dr. Patricia McManus, Department of Plant Pathology, University of Wisconsin)

What does common leaf spot look like?  Symptoms of common leaf spot can occur on leaves, fruits, berry caps, petioles, and runners.  The most noticeable symptoms of the disease are small, round, necrotic (i.e., dead) spots on strawberry leaves.  Initially, these spots develop on the upper leaf surface and are deep purple to red in color.  The spots eventually develop tan, gray or almost white centers with distinct reddish-purple to brown borders.  During warm, humid weather, uniformly rusty-brown spots without purple margins or light colored centers may develop instead.  Spots can occur on the undersides of the leaves as well, but these spots tend to be less vibrant in color.  As the disease progresses, spots enlarge to ⅛ to ¼ inch in diameter and may merge together, in extreme cases leading to leaf death.  Spots on berry caps, petioles, and runners resemble those produced on upper leaf surfaces.  Shallow, black spots (¼ inch in diameter) may develop on infected fruits, and are often surrounded by brown or black, leathery tissue.

Where does common leaf spot come from?  Common leaf spot is caused by the fungus Mycospharella fragariae, which can enter a garden on infected strawberry plants or via windblown spores from nearby strawberries.  Once introduced into a garden, the fungus is spread predominantly by splashing water from rain or sprinklers used for watering.  M. fragariae is most active when temperatures range from 65°F to 75°F, with periods of high rainfall and humidity.  M. fragariae survives the winter on dead strawberry leaves and other plant parts, and is moved to new foliage in the spring by early season rains.

How do I save strawberry plants with common leaf spot?  Once common leaf spot develops on strawberry plants, the plants cannot be cured.  If the disease is detected early, its development may be slowed using fungicides.  Keep in mind however, that common leaf spot is often merely a cosmetic issue and the use of fungicides may not be warranted.  If you decide that fungicide treatments are needed, select a product that is labeled for use on strawberries and that contains captan, myclobutanil or copper as the active ingredient.  Use copper-containing fungicides only prior to flowering.  If you decide to use a myclobutanil-containing product, alternate applications of this product with applications of a second fungicide containing another active ingredient.  This will help prevent selection of myclobutanil-resistant variants of the common leaf spot pathogen.  Be sure to read and follow all instructions on the label(s) of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.

How can I prevent common leaf spot in the future?  When establishing your strawberry patch, consider planting resistant strawberry varieties and use certified, disease-free nursery stock.  Examples of resistant varieties include ‘Crimson King’, ‘Earliglow’, ‘Glooscap’, ‘Ogallala’, and ‘Ozark Beauty’.  Plant strawberries in full sunlight, in well-drained soils, and with proper spacing to optimize air circulation and create a drier environment that is less favorable for the common leaf spot pathogen.  See University of Wisconsin bulletin A1597 (“Growing Strawberries in Wisconsin”) available at http://learningstore.uwex.edu for additional details on proper planting.

Once plants are in the ground, avoid overhead watering (i.e., DO NOT use a sprinkler) as this will splash the common leaf spot pathogen from plant to plant, and provide a wet environment that is more favorable for the fungus to infect.  Instead, use a drip or soaker hose for watering.  For similar reasons, DO NOT work in your strawberry patch (e.g., weeding, thinning plants or harvesting fruit) when it is wet; wait until the patch is dry.

For June-bearing strawberries, bed renovation techniques (in particular mowing) can be useful in managing common leaf spot.  See University of Wisconsin bulletin A1597 (mentioned above) for details on proper renovation techniques.  At the end of the growing season, remove strawberry plant debris to minimize sites where the fungus can survive the winter.  Deep bury, burn (where allowed by local ordinance) or hot compost this material.

For more information on common leaf spot of strawberry:  Contact your county Extension agent.

Stinkhorns

What are stinkhorns?  Stinkhorns are mushrooms that are found from the tropics to more temperate regions such as Wisconsin.  They can suddenly appear in mulch, lawns, and areas with bare soil.  These visually-shocking fungi get their common name from their characteristic, unpleasant odor.  Although they are often unwanted additions to home gardens, stinkhorns do not cause plant disease.  Because stinkhorns can grow on dead organic material, they actually are beneficial in that they contribute to the recycling of plant debris into nutrients that improve soil fertility and can be used by garden plants.

Stinkhorns
Stinkhorns come in many shapes and sizes. They produce foul odors and slimes that attract flies. [Photos (clockwise from the upper left) courtesy of Tom Volk (http://TomVolkFungi.net), Ted Geibel, Troy Bartlett and Gloria Schoenholtz]
Stinkhorns Photo 2
In their immature “egg” stage, stinkhorns can be found below ground. Cutting the “eggs” in half, reveals the developing stinkhorn mushroom. [Photo courtesy of Tom Volk (http://TomVolkFungi.net)
What do stinkhorns look like?  Stinkhorns grow into various shapes, but they are best known for looking like horns or penises.  A few species grow several appendages, resulting in an octopus-like appearance.  Some species have a veil attached below the cap that resembles a lacey skirt flowing from the mushroom’s hollow stalk.  Stinkhorns can range in color from white, beige, and olive to bright orange or red with black accents.  The tips of mature stinkhorns are usually coated in a spore-containing slime.  Gardeners often discover immature stinkhorns as they dig in the soil.  The immature forms appear as whitish to pink or purple, egg-shaped masses.  Stinkhorns develop rapidly sometimes growing up to four to six inches per hour, and can generate enough force to break through asphalt.

Where do stinkhorns come from?  Stinkhorns are often first introduced into a garden in organic materials (e.g., soils and mulches) that contain microscopic hyphae (i.e., fungal threads) of stinkhorn fungi.  Once stinkhorns mature, they produce a pungent, off-putting odor that is reminiscent of rotting flesh or dung.  This smell may disgust people, but it attracts insects, particularly flies.  Flies and other insects eat the slimy material at the tips of stinkhorns and carry spores in this slime to new locations as they move around in the environment.  In many ways, this process is comparable to the distribution of pollen by bees (but of course without the more appealing scents associated with most flowers).

How do I control stinkhorns?  Stinkhorns are short-lived and will naturally disappear quite rapidly.  If stinkhorns are too unsightly, if their smell becomes too putrid, if they attract too many insects, or if there is concern about small children or pets eating them, pluck them from the ground and discard them as they appear.  Keep in mind however, that removing stinkhorns will not eradicate them.  Stinkhorn hyphae will remain in the soil or mulch and will eventually produce other stinkhorn mushrooms.  In addition, flies and other insects carrying stinkhorn spores can introduce these fungi to new locations.

How can I prevent problems with stinkhorns in the future?  No fungicide treatments or other methods are available to prevent stinkhorns from appearing in a garden.  Removing organic matter (e.g., mulch) or reducing soil moisture may reduce the number of stinkhorns that appear.  However, these strategies are unlikely to eradicate stinkhorn fungi.  Therefore whenever stinkhorns appear, consider embracing their unique beauty and enjoy their brief time in your garden.

For more information on stinkhorns:  Contact your county Extension agent.

Basil Downy Mildew

Basil Downy Mildew
Leaf curling and yellowing, as well as a gray-purple fuzz on the bottoms of leaves, is typical of basil downy mildew. (Photo courtesy of Debbie Roos)

What is basil downy mildew?  Basil downy mildew is a devastating disease that affects the leaves, branches, and stems of many types of basil (i.e., plants in the genus Ocimum) commonly used for cooking.  Green-leafed varieties of sweet basil are particularly susceptible to the disease, while purple-leafed varieties of basil, Thai basil, lemon basil, and spice basil are less susceptible.  Certain ornamental basils (e.g., hoary basil) appear to be highly resistant to the disease.  Basil downy mildew was first reported in the United States in 2007 and has since spread widely to wherever basil is grown, including Wisconsin.

What does basil downy mildew look like?  Symptoms of basil downy mildew typically develop first on lower leaves, but eventually an entire plant will show symptoms.  Initial symptoms include leaf yellowing (which gardeners often think is due to a nitrogen deficiency) followed by leaf browning.  Affected leaves also curl and wilt, and on the undersides of the leaves, a gray-purple fuzzy material will develop.

Where does basil downy mildew come from?  Basil downy mildew is caused by the fungus-like organism, Peronospora belbahrii.  This pathogen can be easily introduced into a garden each year via contaminated seed, on infected transplants, or via wind-borne spores (technically called sporangia).  Once introduced into a garden the pathogen can spread by wind, by rain splash, or via items (e.g., hands, clothing, garden tools) that come into contact with infected plant and then are used to work with healthy plants.  The pathogen thrives in humid, warm environments and can spread rapidly, decimating an entire basil crop.

How do I save plants with basil downy mildew?  There is no known cure for basil downy mildew.  If you see basil downy mildew, harvest any asymptomatic leaves on infected plants, as well as other healthy basil plants in your garden.  Use these materials immediately (e.g., to make pesto).  Remove and bag any symptomatic plant remains and dispose of this material in your garbage.

How do I avoid problems with basil downy mildew in the future?  Avoid planting sweet basil if possible.  Instead, plant other types of basil that are more resistant to basil downy mildew.  If you decide to grow sweet basil, try growing the variety ‘Eleonora’ which has been bred for at least some resistance to the disease.  If you grow basil from seed, check to see if the seed you are buying has been steam-treated to kill the downy mildew pathogen.  Be aware however, that this information may be difficult to find, because steam treatment of basil seed is relatively new and the use of this technique is not widely advertised (at least to home gardeners).

Whatever type of basil you choose, try to grow your plants in a manner that will keep them as dry as possible, thus creating an environment that is less favorable for the downy mildew pathogen to develop and infect.  Plant basil in a sunny location, space plants as far apart as possible and orient rows in the direction of prevailing winds to promote good airflow and rapid drying of plants when they get wet.  Avoid overhead watering (e.g., with a sprinkler) that will wet leaves and spread the pathogen; instead, use a drip or soaker hose to water.

Use of fungicide treatments to control basil downy mildew is NOT recommended.  Products that currently are available to homeowners, even when applied in the best manner possible, will likely not control the disease adequately, if at all.  Thus using these products would be a waste of time, effort and money.

For more information on basil downy mildew:  Contact your county Extension agent.

Cane Blight

What is cane blight? Cane blight is a fungal disease that affects the health of canes (i.e., stems) of cultivated and wild Rubus species (e.g., raspberries and blackberries), wherever they are grown. Black and purple raspberries appear to be more susceptible to cane blight than red raspberries, but all commonly cultivated raspberry cultivars can get the disease. Although cane blight is not typically fatal, it may cause significant fruit yield losses if left unmanaged.

Cane death on a thornless blackberry caused by cane blight.  Look for a dark brown infection line and dead/dying shoots above the point of infection.  (Photo courtesy of Michael Ellis, The Ohio State University)
Cane death on a thornless blackberry caused by cane blight. Look for a dark brown infection line and dead/dying shoots above the point of infection. (Photo courtesy of Michael Ellis, The Ohio State University)

What does cane blight look like? Symptoms of cane blight usually first appear in early summer after blossoming and leaf emergence, and in association with wounds caused by pruning or harvesting of fruit. Look for sudden death of side branches and tips of fruit-bearing canes, as well as dark brown or purple spots (called cankers) on the canes below the dieback. In wet weather, cankers may produce a grey ooze. In dry weather, the cankers may appear fuzzy or powdery. Dead canes may become brittle and snap off in windy conditions.

Where does cane blight come from? Cane blight is caused by the fungus Leptosphaeria coniothyrium which survives the winter in infected canes. During wet periods, the fungus produces windborne spores and infects through open wounds on canes caused by pruning, harvest damage, insect damage, or abrasions from canes rubbing together. As the disease develops, the fungus produces additional spores that can spread to other wounds by wind and splashing water, leading to additional infections.

How do I save plants with cane blight? DO NOT prune infected canes during the growing season as pruning wounds will provide the cane blight fungus easy entry into healthy tissue. Label symptomatic canes as you see them and prune the canes to the ground during the dormant season (i.e., mid- to late winter). Also prune any older cane stubs at this time to remove them as a source of abrasion and wounding for newer canes. Pruning when plants are dormant allows ample time for wounds to close at a time of year when spores of the cane blight fungus are not being produced. Use only sharp tools for pruning, and disinfest pruning tools after each cut by dipping them for at least 30 seconds in 10% bleach or 70% alcohol (e.g., rubbing alcohol). Spray disinfectants that contain approximately 70% alcohol can also be used. Dispose of any canes that you prune by burning them (where allowed by local ordinance), deep burying them, or arranging to have them hauled away through municipal brush collection. Be patient as you attempt to get cane blight under control; it may take two or more years of pruning and good sanitation to reduce cane blight to negligible levels.

How can I prevent cane blight in the future? When establishing a new raspberry patch, choose a site that is well-drained and sunny, and make sure that the distance between rows is approximately 18 inches. Also be sure to keep weeds under control. Proper site selection, row spacing and weed control will promote good airflow and drainage, and will reduce excessive moisture that is favorable for spore production by the cane blight fungus.

In addition, maintain optimum soil fertility. If you underfertilize plants, they will produce weak canes that are less able to fend off infections by the cane blight fungus. If you overfertilize plants (particularly with nitrogen), they will produce succulent new growth that is more prone to breakage and more prone to wounding by certain insects that will use the new growth as food. Remember that wounds of any kind can provide entry points for the cane blight fungus. For details on properly fertilizing raspberries, see University of Wisconsin-Extension bulletin A1610, “Growing Raspberries in Wisconsin” (available at http://learningstore.uwex.edu/Growing-Raspberries-in-Wisconsin-P750.aspx).

Cedar-Apple Rust – Juniper

What is cedar-apple rust? Cedar-apple rust is the name of a group of closely related diseases caused by fungi that infect both junipers and woody rosaceous plants such as apple, crabapple, hawthorn and quince.

Cedar-apple rusts form slimy, orange  fruiting body on junipers in early spring.
Cedar-apple rusts form slimy, orange
fruiting body on junipers in early spring.

What does cedar-apple rust look like? On junipers, the cedar-apple rust fungus causes formation of irregularly-shaped brown galls (roughly 1∕2 to two inches in diameter). During moist periods in spring, these galls produce a distinctive orange, gelatinous slime. Symptoms on rosaceous hosts appear in late May as circular, yellow-orange areas on leaves. The undersurfaces of these diseased areas often have a fringed appearance.

Where does cedar-apple rust come from? Several fungi in the genus Gymnosporangium cause cedar-apple rust. These fungi overwinter as galls on junipers.

How do I save a tree or shrub with cedar-apple rust? Junipers can easily be treated for cedar-apple rust by pruning branches about four to six inches below the galls. Clean
pruning shears between cuts by dipping them for at least 30 seconds in a 10% bleach solution or alcohol (spray disinfectants that contain at least 70% alcohol can also be used). This will prevent movement of the fungus from branch to branch, or from plant to plan during pruning. To prevent future infections, you can apply fungicides containing triadimefon or ferbam every seven to 21 days from early July through August. You can control cedar-apple rust on rosaceous hosts using fungicides containing chlorothalonil, ferbam, dithiocarbamates, mancozeb, metiram, sulfur, thiram, triadimefon, triforine, or zineb. Apply treatments when flower buds first show color, when half of the flowers are open, at petal-fall, seven to 10 days after petal fall and again 10 to 14 days later. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

How do I avoid problems with cedar-apple rust in the future?  The best way to avoid cedar-apple rust is to plant trees and shrubs that are resistant to the disease. Check at your local nursery for resistant varieties of juniper, apple, crabapple, hawthorn, and quince that are available in your area and that will satisfy your landscaping needs.

For more information on cedar-apple rust:  See UW-Extension Bulletins A2598 and A8KS711 or contact your county Extension agent.

How to Properly Prune Deciduous Trees

Why should I prune my trees? Pruning is important for a variety of reasons. Pruning can help control the size of a tree, direct growth, influence flowering or fruiting, or maintain plant health and appearance. Pruning can also increase the safety of a tree by removing broken, diseased, dead, or dying branches. In addition to pruning, selecting plants that are suited to your environment and location are very important. The ultimate height and spread, in addition to location of overhead power lines, should be taken into account when selecting trees for landscaping.

The three step method of pruning large limbs.
The three step method of pruning large limbs.

What should I prune?

  • Newly planted trees: Newly planted trees should not be pruned unless a branch is broken, diseased or dead. These trees need foliage to produce carbohydrates (sugars) that are then transported to the root system for initiation of new roots.
  • Young trees: After a young tree is established for two to five years, the tree can be pruned to encourage a well-branched canopy. Lower branches can be removed to raise the canopy, if desired. Scaffold branches to be maintained in the tree should be selected such that they are 12-18 inches apart, are evenly distributed around the trunk and have wide crotch angles. Remove no more than 13 of the total crown of a tree at one time. Young trees also need corrective pruning to remove crossing branches, double leaders, watersprouts, and root suckers.
  • Older trees: Older, established trees, if properly trained when young, require little pruning. These trees should never be topped as this leads to poor branch structure and increased limb breakage. Use the three-point method of limb removal for pruning large branches (see diagram above and description below). This method ensures proper pruning and closure of wounds. Contact a certified arborist to prune larger limbs and remove trees, particularly if the tree is close to power lines or buildings.

The 3-point method of proper pruning of large limbs

When doing any type of pruning, always use a sharp pruning saw for making pruning cuts. Also, be sure to disinfect your pruning tools with alcohol or a 10% bleach solution after each pruning cut to avoid spreading diseases.

  • Step one: Select the branch that you want to remove. On large limbs, the first cut should be 12 to 18 inches from the limb’s point of attachment. The pruning cut should be an undercut made 12 way through the branch (see diagram). This pruning cut is very important because it relieves weight from the branch collar and prevents accidental tearing of bark from the tree’s trunk when the limb is removed.
  • Step two: The second pruning cut should be made on the outside of the first cut (i.e., farther from the trunk). Cut all the way through the limb from the top down, thus removing the weight of the branch.
  • Step three: The final cut should be made next to the tree’s trunk outside of the branch collar. Cut from the top down and cut all the way through the remaining branch stub. The branch collar should be left intact. DO NOT cut the branch flush with the tree’s trunk. A proper cut avoids large wounds, and allows the tree’s wound to close quickly.

Should I use wound treatments? In general, wound treatments, such as tree paint or wound dressing, are not recommended. These compounds slow down wound closure and promote decay. One exception when wound treatments are recommended, is the case of oak trees that are pruned during the growing season. Using wound treatments on oaks is important to keep out insects that transmit the oak wilt fungus (see University of Wisconsin Garden Facts X1075).

When should I prune trees? Most deciduous trees should be pruned in late fall to winter. At this time of year, you can see the overall branch structure easily, and most insects and disease causing organisms are not active. Late fall/winter pruning is especially important for oak trees to help prevent spread of the fungus that causes oak wilt (see University of Wisconsin Garden Facts X1075). Late spring and summer are usually not good times of year to prune because disease pathogens are present and wound closure is slower. If you prune in late winter, some trees may bleed or ooze sap excessively in the early spring. The bleeding may be unsightly, but does not harm the tree. Examples of trees that bleed excessively are maple, willow, birch, walnut, beech, hornbeam, elm, and yellowwood.

Definitions:

  • Branch collar: the ring of trunk tissue that surrounds a lateral branch at the point of attachment to the stem.
  • Double leaders: two major, terminal growing points located at the top of the tree.
  • Root suckers: vigorous, upright, adventitious shoots that arise from latent buds below the graft union or at the base of the tree.
  • Scaffold branches: the large branches that form the main structure of the crown of a tree.
  • Topping: an improper pruning technique that reduces the height of a tree by removal of large branches back to larger primary branches. This technique is not recommended.
  • Watersprouts: vigorous, vertical, adventitious shoots that arise from latent buds above the ground or graft union on older wood.

For more information on pruning: See UW-Extension bulletins A1817, A1771, A1730 and University of Wisconsin Garden Facts XHT1013, XHT1015, or contact your county Extension agent.

Viburnum Leaf Beetle

The viburnum leaf beetle (VLB), Pyrrhalta viburni, is an invasive insect that feeds exclusively on and can significantly damage Viburnum species. VLB is native to Europe and was detected in Canada in 1947. The first report of VLB in the United States was in New York State in 1996. VLB is now found scattered across much of the northeastern US. In Wisconsin, an isolated infestation of VLB was discovered in Dane County in 2009, but was successfully eradicated. In 2014, VLB was detected on a mature viburnum bush in northern Milwaukee County and other nearby infestations were detected in June 2015. At present, all active infestations of VLB in Wisconsin are in northern Milwaukee County and southern Ozaukee County.

Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University, Bugwood.org)
Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University, Bugwood.org)
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine; Bugwood.org)
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine; Bugwood.org)

Appearance: Adult VLB’s are approximately ¼ inch long and yellowish-brown in color. VLB larvae can be up to ⅓ inch long and range in color from yellowish-green to light brown with a series of black spots and dashes on their bodies.

Symptoms and Effects: VLB larvae chew holes in viburnum leaves in the spring creating a lace-like (i.e., skeletonized) pattern. VLB larvae feed individually or in small groups and can cause significant damage to viburnum shrubs. This damage can resemble the feeding damage of Japanese beetles (see University of Wisconsin Garden Facts XHT1062 “Japanese Beetle”). In late June and early July, VLB adults begin to feed, chewing oblong holes in leaves. Severe VLB infestations can cause complete defoliation of a viburnum shrub, which weakens the plant over time and can eventually lead to death.

Life Cycle: There is only one generation of VLB per year. VLB’s overwinter as eggs and development from eggs to adults takes approximately eight weeks. Larvae typically appear in early to mid-May and feed for several weeks, passing through three stages (instars) as they grow. In early to mid-June, larvae pupate in the soil and adults emerge by late June or early July. VLB females lay eggs during the summer and into October. They chew small pits in twigs, deposit five to eight eggs into each pit, and then cover the pits with tiny pieces of chewed wood to protect the eggs. Each female can deposit up to 500 eggs. Eggs remain in place through the winter until they hatch the following spring.

Control:

Cultural: When selecting viburnum plants for the landscape, DO NOT use arrowwood viburnum (Viburnum dentatum), European cranberrybush viburnum (Viburnum opulus), or American cranberrybush viburnum (Viburnum opulus var. americanum) as these types of viburnums are strongly preferred by VLB. Instead use resistant viburnums such as doublefile viburnum (Viburnum plicatum f. tomentosum), Judd viburnum (Viburnum x juddii), or Koreanspice viburnum (Viburnum carlesii). In addition, between October and the following spring, examine viburnums for twigs where VLB’s have laid their eggs. Prune and destroy these twigs to reduce VLB numbers. During the growing season encourage natural VLB predators in your area (e.g., lady beetles, spined soldier bugs, assassin bugs, green lacewings) that can reduce VLB numbers.

Chemical: Prior to bud break, apply horticultural oil to twigs where VLB eggs have been laid. This will significantly reduce the number of eggs that will hatch. Control any surviving larvae with contact insecticides such as acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin. Horticultural oil, insecticidal soap, pyrethrins and spinosad can also be effective. To achieve the best results, apply insecticides when larvae are small and before they have caused significant damage. VLB adults can be managed with contact insecticides, if needed, but are mobile and more challenging to control. Systemic products (e.g., clothianidin and imidacloprid) applied as soil drenches can also be effective, but apply these products after flowering (to minimize any risks to pollinators), but before VLB damage occurs to achieve the best protection.

For more information on viburnum leaf beetle: Contact your county Extension agent.

Zinnias

What are zinnias? Zinnias are one of America’s most popular annual bedding plants, but have humble origins as descendants of nondescript wildflowers native to the southwest U.S., Mexico and Central America. The zinnia was named after the 18th century German botanist Dr. Johann Gottfried Zinn, who wrote the first description of small, weedy plants that he discovered in the Mexican deserts. These plants had dull purplish-red, daisy-like flowers with single petals surroundng a protruding cone. Early varieties of garden zinnias were introduced in the U.S. in 1796, with double forms appearing in the mid-1800’s. Interest in zinnias increased in 1920 when Bodger Seeds Ltd. introduced the dahlia-flowered varieties ‘Giant Dahlia’ and ‘California Giant’. These varieties had large, flat-flowered heads and multiple colors. ‘California Giant’ eventually won a gold medal from the Royal Horticulture Society of England.

Zinnias can be a bright-colored addition to any garden, particularly when planted in mass.
Zinnias can be a bright-colored addition to any garden, particularly when planted in mass.

Today, zinnias come in a wide variety of flower forms: single, semidouble, or double. Single-flowered zinnias have one row of petals and the center of the flower is exposed. Semidouble-flowered zinnias have many rows of petals and the center can still be seen. Dahlia-type zinnias (typically semidouble) have large, flat blossoms. Double-flowered zinnias have so many rows of petals that flower centers are hidden. There are several types. Beehive-types have small blooms with stacks of flat petals resembling small beehives. Button-types are similar but have flatter flowers. Cactus-types have twisted, bent petals with rolled edges.

Although there are more than a dozen species of zinnias, only a few species are regularly planted in gardens. Zinnia elegans is the most common. It grows up to three feet tall and has single or double flowers in pink, rose, red, cherry, lavender, purple, orange, salmon, gold, yellow, white, cream or light green. Flowers range in size from one to seven inches in diameter and can be solid-colored, multicolored or zoned. Flower shapes include round, domed or ball-shaped, as well as dahlia-like or chrysanthemum-like. Tetraploid varieties (having four sets of chromosomes, rather than the normal two) were developed in the 1950’s, and these varieties produce larger flowers on stronger stems, grow more vigorously and have increased disease resistance. Hybrid varieties were developed soon thereafter. There are many varieties of Z. elegans available at garden stores, including the following.

  • The Border Beauty series has plants that grow up to 20 inches tall and have 3½-inch-wide semidouble to double, dahlia-like flowers.
  • The Peter Pan series has dwarf hybrids that grow up to 12 inches tall and have very large (up to five-inch-wide), slightly curled, double flowers. Seven separate colors in this series have been recognized as All-American Selections (AAS) winners.
  • The Ruffles series was developed for cut flower production. Plants grow up to 30 inches tall and have 2½-inch-wide, ball-shaped flowers with ruffled petals on stiff, upright stems. ‘Scarlet Ruffles’ was named an AAS winner in 1974, ‘Cherry Ruffles’ and ‘Yellow Ruffles’ AAS winners in 1978.

Z. angustifolia (synonym Z. linearis) has small, single, golden-orange flowers with yellow stripes, and narrower foliage than Z. elegans. These compact plants grow eight to 12 inches high, and can spread to two feet. The variety ‘Crystal White’ has pure white flowers with yellow centers and was an AAS winner in 1997. A cross of Z. elegans and Z. angustifolia yielded the Profusion series of zinnias which has compact plants with two to three-inch-wide, single flowers. Members of this series have superior heat and humidity tolerance, and tend to be disease resistant. Two members of this series ‘Cherry Profusion’ and ‘Orange Profusion’ won gold medals from AAS in 1999 (the first awarded to flowers in 10 years).

Z. haageana (Mexican zinnia) grows up to 18 inches tall and has small 1½ to two-inch-wide flowers on long stems. Flowers may be single or double, solid or bicolor, in red, mahogany, yellow and orange. Two popular varieties may be available at your local garden center.

  • ‘Persian Carpet’ (an AAS winner in 1952) grows up to 15 inches tall and has two-inch-wide, double, bicolored flowers of gold, maroon, purple, chocolate, pink or cream;
  • ‘Old Mexico’ (an AAS winner in 1962) has bushy, compact, 18-inch-tall plants with double, 2½-inch-wide blooms of deep, rich mahogany highlighted with yellow-gold.

Z. pauciflora (synonym Z. peruviana) grows up to 30 inches tall and produces 1½-inch-wide, single, red or yellow flowers with button-like centers. This zinna is good for cutting and drying, and has powdery mildew resistance. Only varieties ‘Bonita Red’ and ‘Bonita Yellow’ are readily available.

Zinneas can be effectively used in gardens as an edging plant.
Zinneas can be effectively used in gardens as an edging plant.

Where do I get zinnias? Zinnias can be purchased as bedding plants, but local garden centers often have only a limited selection of varieties. As an alternative, zinnias can be started from seed, either indoors four to six weeks before the last expected spring frost, or directly in the garden when the soil warms sufficiently. Germination takes five to seven days. Many references warn that zinnias do not like being disturbed and should not be moved after seeding. However, plants can be seeded individually in cells of seed-starting trays or even transplanted into these cells from mass plantings. When transplanting into trays, wait until the first true leaves have emerged. Separate roots as carefully as possible and place seedlings into their new cells up to the first set of leaves (the seedling leaves). Select appropriately sized tray cells based on the predicted size of the varieties being grown. Otherwise, tall varieties may outgrow their cells before it is time to plant them outdoors. Once the danger of frost has passed, zinnias can be transplanted outside. However, do not expect substantial growth until temperatures are above 50°F.

How do I grow zinnias? Zinnias do best in full sun in fertile, well-drained soil. Space plants four to 24 inches apart depending on variety. When growing zinnias for cut flowers, crowd plants to encourage longer stems. To produce bushier plants, pinch the tops out of plants when they are four to six inches high. Remove faded blossoms to encourage new blooms. Plants should be kept well-watered and fertilized two times per month for optimum bloom. Most varieties begin to bloom when very young and continue to bloom until frost.

Zinnias have few insect pests, but occasionally can have problems with aphids (see University of Wisconsin Garden Facts XHT1043), four-lined plant bugs (see University of Wisconsin Garden Facts XHT1101) and spider mites. Common diseases of zinnias include powdery mildew (see University of Wisconsin Garden Facts XHT1005), Alternaria leaf spot and bacterial leaf spot.

How do I use zinnias most effectively in my garden? Zinnias make good edging plants, but are also effective when grown in masses. Taller varieties make good background plants in flowerbeds, while smaller varieties are suitable for container plantings. Zinnias are great additions to butterfly gardens and many varieties make excellent cut flowers.

For more information on zinnias: Contact your county Extension agent.

Zimmerman Pine Moth

Zimmerman pine moth (Dioryctria zimmermani) was first detected in the US in 1879, and has subsequently been found and is established throughout the northern US east of the Rocky Mountains. Austrian and Scots pines are preferred hosts of Zimmerman pine moth. However Eastern white and mugo pines are also attacked.

Symptoms of Zimmerman pine moth.  Tunneling by larvae in branch whorls leads to formation of masses of pitch (left).  Sap from feeding sites often runs down branches and trunks (right).  Left photo courtesy of the Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org
Symptoms of Zimmerman pine moth. Tunneling by larvae in branch whorls leads to formation of masses of pitch (left). Sap from feeding sites often runs down branches and trunks (right). Left photo courtesy of the Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org

Appearance: Adult Zimmerman pine moths are midsized with gray and red-brown wings, marked with zigzag lines. Larvae are generally dirty white to light grey and up to one inch long. They can only be found in pitch masses, under bark or in new shoots.

Symptoms and Effects: Zimmerman pine moth larvae tunnel into new growth causing shoot dieback, or into whorl areas causing masses of pitch to form at the wound site. Repeated attacks by the larvae cause a weakening at the area of the infestation and make the branches and trunk susceptible to breakage.

Life Cycle: Zimmerman pine moth has a one-year life cycle and spends the winter as a young caterpillar underneath bark scales of infested trees. In mid to late April, larvae become active and they migrate to the base of branches or shoots and burrow inside. Larvae continue to feed into July and then pupate within a chamber in a mass of pitch. Adult moths emerge from infested trees in late July and August, and lay eggs near wounds or preexisting masses of pitch. Eggs hatch in approximately one week and larvae feed for only a brief time before preparing to overwinter under bark scales.

Zimmerman pine moth pupa (left) and larva (right) embedded in masses of pine pitch.
Zimmerman pine moth pupa (left) and larva (right) embedded in masses of pine pitch.

Control: Avoid plant injury (e.g., construction injury) and environmental stresses (e.g., drought stress) that can make trees attractive to Zimmerman pine moth adults. Also, consider removing heavily infested trees before July to reduce the number of adults that will emerge in the vicinity of, and potentially infest, healthy trees. If opting to use insecticides to control Zimmerman pine moth, applications must be made in the spring, before larvae migrate into tree trunks. Preventive insecticide sprays should be applied as a drenching spray to trunks in mid to late April. Spraying branches and foliage is not necessary. Permethrin or bifenthrin are preventative sprays that are available for use by homeowners. Chlorpyrifos (sold as Dursban) can be used in nurseries and Christmas tree plantations. Sprays applied in early September to kill small larvae are not recommended as they tend to have only spotty success.

For more information on Zimmerman pine moth: Contact your county Extension agent.