Month: April 2022

Strategies for Effective Management of Botrytis and Anthracnose Fruit Rot in Strawberries

Emily Zobel on

Strategies for Effective Management of Botrytis and Anthracnose Fruit Rot in Strawberries

Dr. Mengjun Hu, Univ. of Maryland, and Kathy Demchak, Penn State Extension

Managing gray mold (Botrytis) on strawberries is increasingly challenging because of fungicide resistance development, plus a new Botrytis species that is less susceptible to fungicides is becoming common in the mid-Atlantic region. Resistance to certain fungicides is also a problem in management of anthracnose fruit rot.  This article describes disease management strategies designed to slow further resistance development, while also providing specifics for managing our two most common fruit rots.

Gray mold on strawberry. Photo: Kathy Demchak, Penn State Extension

First, what’s new with Botrytis.  There are at least 4 species of Botrytis that can infect strawberries, but only two of them have been commonly found in the region. Botrytis cinerea, the species traditionally infecting strawberries, is present nearly everywhere and affects many horticultural crops.  Recently another species, Botrytis fragariae, has also been found and as its name indicates, is more specific to strawberry plants. It appears to overwinter on strawberry plant tissue, and preferentially colonizes blossoms early in the spring, causing them to “turn brown and dry up”.  While sometimes only one of these species is present, both can be present at the same time in a field and even in the same blossom.  Using certain fungicides selects for resistant strains of either species, and also preferentially selects for one species over the other.  This means that both species have resistance to multiple fungicide groups, and both species can survive in fungicide-treated fields.

How can you tell if the newer species of Botrytis might be present in your fields?  While B. cinerea (the traditional species) is often isolated from both flowers and fruit, B. fragariae (the new one) is often isolated from flowers, and it has been shown that B. fragariae infection was much more aggressive on strawberry flowers than fruit. If you see larger-than-usual numbers of blossoms turning brown and shriveling (not to be confused with frost damage, which blackens the center of the flower), it may be prudent to choose fungicides as if B. fragariae presence had been confirmed in your field.  If you see no more symptoms on the flowers or buds than usual, you may be able to assume that the new species isn’t present, or at least not to a great extent.

Continue reading Strategies for Effective Management of Botrytis and Anthracnose Fruit Rot in Strawberries

Apple Scab Alert!

Emily Zobel on
Despite cooler temperatures during the past few days, apple scab (Venturia inaequalis)  spores continue to mature. A significant apple scab infection event is forecasted April 5 to 7, 2022, in Pennsylvania and surrounding area. For those with green tissue present on their apple trees, protection is necessary for this event.
The apple scab fungus overwinters in infected leaves.  As it warms up in the spring they mature and produce spores that are discharged into air currents and carried to developing apple buds. The disease negatively affects fruit size and quality (due to blemishes and poor ripening). Over time, repeated defoliation from the disease reduces tree vigor, growth, and yield. 
Apple scrub leaf lesions.
Photo by Penn State Department of Plant Pathology & Environmental Microbiology Archives , Penn State University, Bugwood.org
Apple scab produces gray-to-olive green lesions on the leaves ( as seen above), but may also be seen on blossoms, sepals, petioles, pedicels, and fruit. On leaves, lesions first appear on the undersides of young leaves in the spring as they unfold and are exposed to infection. Leaves are susceptible to infection for about 5 days after they unfold. Fruit may become infected at any time in its development. Typical fruit lesions are distinct, almost circular, rough-surfaced, olive-green spots up to ¾ inch in diameter. 
Control information can be found on Penn State Extension website:  https://extension.psu.edu/2022-disease-update-apple-scab-infection-event-april-5-7-2022 

Allium leaf miner

Emily Zobel on
Adult allium leaf miners.

Allium leaf miner Phytomyza gymnostoma is a pest on chives, scallions, garlic, onions, and leeks. Overwinter ALM across the Mid-Atlantic will be emerging soon. Start scouting for ovipositor markings made by female ALM over the next few weeks on food and ornamental Allium crops. These markers will be neat rows of white spots descending from the upper tips of allium leaves. These marks will be typically be seen on the tallest leaves first. ALM Larvae mine leaves and moves towards and into bulbs and leaf sheathes. The leaf punctures and mines serve as entry routes for bacterial and fungal pathogens.

Spring crops are usually not as hard-hit as fall crops, especially when looking at leeks, but this pest has steadily increased its geographical range each year and its damage potential. If you had some infestation last year, you will especially want to look for this pest’s signs.

Yellow sticky cards or yellow plastic bowls containing soapy water can be used for monitoring but are not affected control independently. 

 

Onion leaf blades showing round white dots made by female Allium leaf miners. Photo by Jerry Brust

 

Cultural Control: Covering plants in February, prior to the emergence of adults, and keeping plants covered during spring emergence, can be used to exclude the pest. Avoiding the adult oviposition period by delaying planting (after mid-May we think) has also been suggested to reduce infestation rates. Covering fall plantings during the 2nd generation flight can be effective. Growing leeks as far as possible from chives has been suggested. Organic

 

Chemical Control: Azadirachtin (Aza-Direct or other formulations) or spinosad (Entrust or other formulations) follow label instructions for leaf miner.

Synthetic Chemical Control: Systemic and contact insecticides can be effective. EPA registrations vary, however, among Allium crops. Check labels to ensure the crop is listed, and for rates and days-to-harvest intervals. Options that may be effective include cyromazine (Triguard), dinotefuran (Scorpion), spinetoram (Radiant), lambda-cyhalothrin (Warrior II or other formulations), and abamectin (Agri-Mek or other formulations).