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.

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.

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.

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.

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.

What is raspberry anthracnose? Anthracnose is a common disease that causes significant reductions of yield and fruit quality on raspberries in the United States. Black and purple raspberries (oftentimes misidentified as blackberries) are particularly susceptible to anthracnose, while red raspberries are less susceptible to the disease. True blackberries are also occasionally affected by anthracnose.

What does raspberry anthracnose look like? Anthracnose can affect any part of a raspberry plant; however, canes are most commonly affected. Watch for scattered, purple, roundish spots (up to ⅜ inch in diameter) that are characteristic of the disease. Over time, the spots develop ash-colored, sunken centers and raised purple margins. When anthracnose is severe and develops early in the growing season, these sunken spots can merge and girdle raspberry canes, resulting in cane death. When anthracnose develops later in the season spots may not develop sunken centers, but will overlap and merge. If a large enough portion of a cane is affected, the bark may split. This symptom is called “gray bark”. Canes severely affected by anthracnose are more prone to winter injury. On leaves, anthracnose symptoms typically appear in early to mid-summer as irregularly-shaped, yellow spots that are approximately ¹/₁₆ inch in diameter. These spots enlarge and develop gray centers with reddish-purple borders. Over time, the gray centers may fall out, giving the spots a “shot-hole” effect.

Where does raspberry anthracnose come from? Anthracnose is caused by the fungus Elsinoe veneta. The fungus can be introduced into a raspberry patch on infected plants or by spores that are blown from other raspberry patches or from wild raspberry relatives (such as brambles). Once established in a raspberry patch, E. veneta can overwinter on diseased raspberry canes. In the spring, spores of the fungus spread to new canes (which are more susceptible to infection due to their lack of a hard bark) and leaves by wind, rain splash, and insects. Infections are more likely to occur during long periods of wet weather. Additional spores produced as a result of these early season infections can lead to additional infections late in the summer (e.g., in late August and September).

How do I save a plant with raspberry anthracnose? Anthracnose is difficult to manage once symptoms have developed. Pruning symptomatic canes as they appear may provide some benefit, but only when disease levels are relatively low. Prune four to six inches below where symptoms have appeared and decontaminate pruning tools between cuts by treating them for at least 30 seconds with 10% bleach or preferably (because of its less corrosive properties) 70% alcohol. Rubbing alcohol and many spray disinfectants typically contain approximately 70% alcohol and are easy to use. Canes can be burned (where allowed by local ordinance) or buried. Fungicides are not effective for controlling anthracnose once infections have occurred and should be only be used preventatively (see below).

How do I avoid problems with raspberry anthracnose in the future? When establishing your raspberry patch, choose a sunny, open area with a well-drained soil. Remove plants related to raspberries (e.g., brambles) from the vicinity of your patch as these plants can potentially be a source of the anthracnose fungus. Purchase disease-free raspberry plants from a reputable nursery or other raspberry supplier, and space these plants in rows that are 12 to 18 inches apart to promote good air flow, and rapid drying of plants. Fertilize your raspberries appropriately [see University of Wisconsin-Extension Bulletin A1610, “Growing Raspberries in Wisconsin” (available at http://learningstore.uwex.edu) for details], but DO NOT overfertilize with nitrogen. Heavy nitrogen fertilization will stimulate excessive growth of tender canes that are more susceptible to infection by the anthracnose fungus. When watering, DO NOT use a sprinkler; instead use a soaker or drip hose that applies water to the soil rather than to onto leaves and canes. Keep weeds under control so that they do not block air movement.

Once your raspberry patch is established, prune raspberries routinely (see Bulletin A1610 for details) to remove diseased and winter-injured canes as well as to promote better air flow. If anthracnose has been a chronic problem in your raspberry patch, consider using a preventative fungicide treatment for control. Use a single application of liquid lime sulfur (1⅓ cups per gallon of water) when leaf buds show ¼ to ½ inch of green tissue. Be sure to read and follow all label instructions to ensure that you use the fungicide in the safest and most effective manner possible.

For more information on raspberry anthracnose: Contact your county Extension agent.

What is peach leaf curl? Peach leaf curl is a common disease on peach and nectarine trees throughout the Midwest and eastern U.S. Where the disease is severe, tree vigor and fruit quality and yield are diminished. Reports of peach leaf curl have increased in recent years, possibly because relatively mild winters have been favorable for the survival of the organism that causes the disease. A related disease, plum pockets, affects plums.

What does peach leaf curl look like? Diseased leaves are distorted with puckered, thickened, twisted areas that are reddish to purple in color. Leaves later turn brown and fall from the tree. Diseased shoots are stunted with small, yellowish leaves, or have leaves arranged in tight whorls (rosettes). Diseased flowers may abort, leading to reduced fruit set, while diseased fruit are bumpy, reddish in color, and fall prematurely.

Where does peach leaf curl come from? Peach leaf curl is caused by the fungus Taphrina deformans, which overwinters in bark and bud scales of peach and nectarine trees. Fungal spores infect leaves and shoots during spring while leaves are still in the bud, and as they just begin to emerge. Mild (50-70°F), wet weather during this period favors infection. As the fungus grows in plant tissues, it disrupts normal cell development resulting in distorted, off-color leaves, shoots, and fruit. Additional spores form on the surface of diseased tissue, and these spores cause new infections if the weather remains mild and wet.

How do I save trees that have peach leaf curl? Peach leaf curl is unlikely to kill a peach or nectarine tree on its own. However, if significant premature leaf drop occurs, trees will be susceptible to drought stress and winter injury. To help maintain tree vigor, irrigate during dry periods, fertilize with nitrogen (but not later than August 1), and thin fruit if the crop load is heavy. Avoid late summer fertilization as this will prevent trees from hardening off thoroughly before winter.

How do I avoid problems with peach leaf curl in the future? Because Taphrina survives in bark and bud scales, removal of diseased leaves in the fall will not reduce disease. In addition, no peach varieties are immune to peach leaf curl. However, varieties derived from Redhaven are more resistant than varieties derived from Redskin. In addition, a single fungicide spray in the fall after leaf drop, or in the spring before buds begin to swell will control peach leaf curl (as well as plum pockets). Effective fungicide active ingredients include chlorothalonil, copper (e.g., Bordeaux mixture), and ferbam. Be sure when selecting a fungicide that you choose one that is labeled for use on edible food crops. Also, 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.

For more information on peach leaf curl: Contact your county Extension agent.