Category: Scouting Tips

Monthly Insect & Disease Scouting Tips – Sept 2023

Emily Zobel on

September Insect & Disease Scouting Tips

By Emily Zobel, AgFS Agent, Dorchester County, UME
ezobel@umd.edu

 Cole Crops/ Brassicas: Continue to scout all fields for caterpillar pests (armyworm, diamondback moth larvae (DBM), and cabbage looper larvae). For fresh-market crops, treat when 20% of the plants are infested during the seedling stage, then 30% infestation till the cupping stage. Use a 5% threshold from early head to harvest for cabbage and Brussels sprouts. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest.

Good identification as early as possible is important because some products may not be labeled or as effective for all brassicas caterpillar pests. If treatment is needed, adjust your spray pattern so that the spray is getting sideways to the undersides of leaves, particularly when using Bt and other contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for controling DBM. Effective materials should eliminate DBM larvae within 48 hours. Make sure to re-scout treated fields within 3 days to assess the efficacy of the insecticide applications.

Check young plants for flea beetles. Thresholds for flea beetles are 1 per transplant or 5 beetles per 10 plants. They will lay eggs in the soil, and larvae can cause significant root injury. Downy mildew and Alternaria can be problematic in fall brassica crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears, apply a fungicide every 7 to 10 days.

Alium crops: Scout fall leeks, garlic, or other Allium species from now until the first freeze for Allium leaf miner damage. Egg-laying damage consists of several small round white dots (made by the female’s ovipositor) that appear on the leaf blades (fig 1). Larvae will live inside the leaves before moving down to the bulbs, where they feed and eventually pupate and overwinter. The feeding damage can open up the foliage and bulb to fungal infections. Row covers can be used to exclude this pest when Alliums are first planted. For organic production, spinosad (Entrust is OMRI-labelled) works well in controlling the larvae. Two or three applications of the insecticide used 2 weeks apart from each other, with the first one coming only after oviposition marks are seen, should offer good control of this pest. The use of a penetrant adjuvant such as neem oil is recommended for better control. 

Image of a Onion leaf blade showing linear white dots made by female Allium leaf miners.
Fig 1.) Onion leaf blade showing linear white dots made by female Allium leaf miners. Photo by Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org

Lima Bean: Check any latelima bean for soybean looper and stink bugs. Looper activity should decline once nighttime temperatures drop into the low 50s.

Swiss chard, Beets & Spinach: Check for beet webworm. They fold leaves and cause window-paning feeding damage. They also feed on pigweed.

Sweet Corn: Corn earworm (CEW) numbers have been declining across the state. Cooler night temperatures and shorter day lengths have triggered mature larvae to enter diapause as overwintering pupae.

Spider mites: Now is a great time to treat weeds growing in and around greenhouses. Winter annual weeds such as chickweed, henbit, dead nettle, and speedwell serve as spider mites and thrip habitats, allowing them to overwinter. Treating now will reduce the possibility of having early-season pest activity on transplants next year.

 

September Insect & Disease Scouting

Emily Zobel on

September Insect & Disease Scouting

Emily Zobel, UME

Remember to rotate modes of action out every 30 days. Always read the label since not all materials are labeled for all crops, insects, or application methods. See the Mid-Atlantic Commercial Vegetable Production Recommendations Guide for more information (https://go.umd.edu/MidVegGuide).

Cole Crops/ Brassicas: Continue to scout all fields for beet armyworm, fall armyworm, diamondback moth larvae ((DBM)and cabbage looper larvae.  DBM seem to be the main species seen across the regain this fall.  For fresh-market crops treat when 20% of the plants are infested during seedling stage, then 30% infestation from early vegetative to cupping stage. From early head to harvest in cabbage and Brussels sprouts use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. If treatment is needed make sure to adjust your spray pattern such that spray is getting sideways to the undersides of leaves, particularly when using Bacillus thuringiensis and contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for control of diamondback moths. Rutger’s is reporting that DBM is not responding to chlorantraniliprole (Coragen) in many parts of the state. It is important to return to treated fields within 2-3 days to assess the efficacy of the insecticide applications.  Effective materials should eliminate DBM larvae within 48 hours.

Check young plants for flea beetles Thresholds for flea beetles are 1 per transplant or 5 beetles per 10 plants. They will lay eggs in soil and larvae can also cause significant root injury.  Downy mildew and Alternaria can be a problem in fall brassica crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears, apply a fungicide every 7 to 10 days.

Sweet Corn: Scout any whorl stage sweet corn for fall armyworm (FAW). FAW can infest plants at any growth stage. Injury from newly hatched larvae shows up as “window panes.”  As larvae gain size, they begin creating ragged holes in leaves with lots of droppings. FAW can be tough to manage because it is resistant to synthetic pyrethroid insecticides (IRAC 3A). Treat when 15% early whorl infestation, 30% mid whorl, and 15% infestation at tassel push. CEW number are currently active but low across that state, so unless temperatures rise again a 4-5 days spray schedule would be suggested for corn that’s tasseling or silking. Pyrethroid (Group 3A) resistance has been reported in populations of CEW.

Pumpkins and Late Melons: Scout for cucumber beetles and rind feeding lepidopteran worms, such as melon worms and fall armyworm. Look at the undersides of leaves that have been partially shredded and look at the rinds of pumpkins to determine if they are attacking the fruit.  Due to our recent wet warm weather  scout for Downy Mildew.

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

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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

Mid-July Vegetable Insect Scouting Tips

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By Emily Zobel
 Ag Agent Dorchester County

General Tips: Check > 50 plants throughout the whole field when making treatment decisions. Localized infestations can be spot treated to save time and money. For up-to-date chemical recommendations, check the Mid-Atlantic Commercial Vegetable Production Guide.  Read all labels carefully for rates and restrictions. 

Cucurbits: Continue to scout for aphids, cucumber beetles and spider mites. Early detection is critical since these pest populations can quickly explode during hot, dry weather. Watch for rind feeding pests such as beet armyworm, yellow-striped armyworm, cabbage loppers, and cucumber beetle adults in melon fields. 

Sweet Corn: Sample pre-tassel stage for whorl feeders (corn borer, corn earworm, and fall armyworm).  Treatment should be applied when 15% of plants are infested with larvae and should be directed into the whorls. 

Lima Beans and Snap Beans: Scout fields for aphids, leafhoppers, and spider mites. The leafhopper threshold is an average of 5 per sweep. As soon as pin pods are present, check for plant bugs and stink bug adults and nymphs. As a general guideline, treatment should be considered if you find 15 adults and/or nymphs leafhopper per 50 sweeps. Continue to scout for bean leaf beetles and Mexican bean beetles—Control when there is an average of 20% defoliation or 1 beetle per plant. 

Potatoes: Scout fields for Colorado potato beetle, leafhoppers, and aphids. Controls will be needed for green peach aphids if you find 2 aphids per leaf during bloom and 4 aphids per leaf post-bloom. This threshold increases to 10 per leaf at 2 weeks from vine death/kill. If melon aphids are found, the threshold should be reduced by half.