IPM – Maryland Fruit & Vegetable Farm Blog

September Vegetable Insect Scouting Tips

Emily Zobel on September 10, 2024September 17, 2024

Alium crops: Scout fall leeks, garlic, and other Allium species from now until the first freeze for Allium leaf miner egg-laying damage. Damage consists of a row of several small round white dots 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. Row covers can be used to exclude this pest when Alliums are first planted. For organic production, spinosad works well in controlling the larvae. Two or three applications of the insecticide about ~2 weeks apart from each other once oviposition marks are seen should offer good control of this pest. Using a penetrant adjuvant such as neem oil is recommended for better control.

A photograph of a yellow-green caterpillar feeding on a cabbage leaf. The caterpillar is the same size as the plant veins. — Figure 2. ) Late instar diamondback moth larvae feeding. Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

Cole Crops/ Brassicas: Check young plants for flea beetles. The thresholds for flea beetles are one per transplant or five beetles per 10 plants. Downy mildew and Alternaria can be a problem in fall brassica crops. When the disease first appears, apply a fungicide every 7 to 10 days. Continue to scout all fields for caterpillar pests (armyworm, diamondback moth larvae (DBM) (fig 2), and cabbage looper larvae). Treat crops when 20% of the plants are infested during the seedling stage, then 30% infestation until the cupping stage. Use a 5% threshold from early head to harvest in cabbage and Brussels sprouts. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. If treatment is needed, adjust your spray pattern so the spray goes sideways and gets on the undersides of leaves, particularly when using BT and other contact materials. Bt and Copper are not compatible and should be apply 24 hour apart from each other. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for the control of diamondback moths. Re-scout treated fields within 3 days to assess the efficacy of the insecticide applications. Effective materials should eliminate DBM larvae within 48 hours.

Sweet Corn: CEW numbers have been declining due to cooler nights, but traps around us are still recommending a 3-4 day spray schedule for silking corn. This week’s predicted rain should also reduce their number.

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

A photo of a green caterpillar inside a fold over leaf with white webbing. — Figure 3.) Beet webworn in a fold over hemp leaf. Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

Swiss chard, Beets & Spinach: Check for beet webworm (fig 3). Its habit of enclosing itself in folded leaves protects it from insecticides and natural enemies. Insecticides are most effective in controlling small caterpillars instead of those that are nearly full-grown and not eating as much.

A photo of a green caterpillar with a yellow head and two white lines gong down it's back. — Figure 4.) Late instar melonworm larvae. A key characteristic is the two white lines running the length of the body. Photo: Alton N. Sparks, Jr., University of Georgia, Bugwood.org

Pumpkins: Continue to check for aphids, squash bugs, and mealworms. For melon worms (fig 4), check the undersides of partially shredded leaves and look at the rinds of pumpkins to determine if they are attacking the fruit.

Stinkbug Damage Found in Maryland Tomato Fields

Emily Zobel on September 9, 2022September 12, 2022

Stinkbug Damage Found in Maryland Tomato Fields

Jerry Brust, UME

There have been reports of stinkbug damage in tomatoes in Maryland for the last couple of weeks. Stinkbug feeding damage is called cloudy spot in tomato fruit (fig. 1). It occurs when the adult or immature stinkbug puts its needle-like mouth part into the fruit and removes material from a large number of cells. On green fruit the damage appears as whitish areas with a black dot in the center and indistinct borders (fig. 2) on ripe fruit the spots are golden yellow (fig. 1). Individual spots may be 1/16 -1/2 inch in diameter; or the spots may merge and encompass a large area of the fruit surface (fig. 2). Peeling back the skin shows these areas as white shiny, spongy masses of tissue (fig. 3). This damage is usually most common from mid-July until the end of the season.

Stinkbug feeding injury to tomato fruit. — *Fig.1) Stinkbug injury to tomato fruit. Photo by G. Brust UMD.*

The Green and Brown as well as the Brown Marmorated stinkbugs are often difficult to see and usually go unnoticed as they spend much of the day deep inside tomato plants, any disturbance and the stinkbugs will drop to the ground and move under the plastic, which results in monitoring difficulties. Only a few are necessary to cause the appearance of cloudy spot on many tomato fruit. Although stinkbug damage has been observed in slightly greater than usual amounts in tomato fields this year, observations of stinkbugs have been much less numerous.

Continue reading Stinkbug Damage Found in Maryland Tomato Fields

Corn Earworm numbers on the rise..

Emily Zobel on July 29, 2022July 29, 2022

Corn earworm moths counts in pheromone traps have been increasing over the past few days in some areas in Maryland and Delaware. Sweet corn growers should keep an eye out and consider shortening spray intervals to a 2 to 3-day spray schedule while others could still be around a 3 to 4-day spray schedule.

Continue reading Corn Earworm numbers on the rise..

Allium leaf miner

Emily Zobel on April 1, 2022

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).

Mowing: a casually thought of integrated weed management tool

Emily Zobel on March 16, 2022

By Cerruti R² Hooks^$ and Dwayne Joseph^*^$Professor and Extension Specialist, *Post-Doctoral Fellow, CMNS, Department of Entomology,

Mowing is a relatively inexpensive form of mechanical weed control that can reduce the use of tillage, herbicide and manual weeding. It may serve as an alternative to herbicide and cultivation or part of an integrated approach. However, mowing to manage weeds has not been well studied compared to other IWM tools and is more popular in habitats with perennial stands of vegetation. Consequently, limited information is available on mowing use in crops. As such, it is not adaptable to numerous cropping systems; and partially for this reason, it is used mainly for aesthetic reasons and preventing seed production in perennial stands of vegetation neighboring cropland. Still, research has shown that mowing can be used jointly with other weed management tools such as applying herbicides, cover cropping and growing competitive crops. Mowing may also be used to successfully manage perennial weeds by removing the aboveground plant parts and consequently reducing food reserves in their storage organs. This, however, may take multiple years and the integration of other weed management tactics. Some research has found that combining mowing with herbicides enhances perennial weed control. Still, there are advantages and disadvantages of using mowing as a weed management tool. Mowing generally does not have any negative environmental effects. However, many weeds especially those that grow close to the ground such as buckhorn plantain are naturally tolerant of mowing. As with any IWM program, it is important to “keep weeds guessing” by utilizing different management tactics; and mowing is no exception to this rule. For example, repeated use of mowing as a single weed management tactic may result in a selection pressure or shift to weed species or genotypes that can reproduce even if repeatedly mowed. These species may overtime become more difficult to manage. As such, in those situations where mowing is practical, one should consider making it part of an overall IWM program. Financial support for the publication of this article is via USDA NIFA EIPM grant award numbers 2021-70006-35384 and NESARE – Research for Novel Approaches (LNE20-406R).

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Blueberry IPM Post Bloom – Diseases Pathogens

Emily Zobel on May 24, 2021

By Haley Sater
Agriculture Agent, Wicomico County
University of Maryland Extension
HSater@umd.edu

( Article from May 2021 issues of UME Fruit and Vegetable Newsletter)

Most blueberry cultivars here in Maryland bloomed and green fruit are developing. Now is the time when a variety of pathogens and pest will begin to take up residence in your field which can harm your developing crop. It is important to perform routine scouting throughout your farm and make sure that you’re not seeing symptoms of some of
the common pests and pathogens. Below is a description of several of the most common diseases and pests you may find at this time in your blueberries.

Pathogens to be on the lookout for:
During the cool, wet days where temperatures do not reach above 70 degrees you may begin to see symptoms of several fungal pathogens including botryosphaeria canker or stem blight, botrytis, anthracnose and powdery mildew. These conditions make for an ideal environment for some of these fungal pathogens to grow or spread.

Blueberry Pathognes — A.) Botryosphaeria stem blight, Bill Cline NCSU. B.) Botrytis, Caleb Slemmons, National Ecological Observatory Network. C.) Anthracnose, Bruce Watt, University of Maine D.) Powdery Mildew, Florida Dept. of Agriculture. Bugwood.org

Botryosphaeria stem blight (A) will exhibit dieback symptoms. It is initially detectable as yellowing and reddening of leaves which will move down then stem as vascular tissue becomes blocked by the pathogen. Whereas, botryosphaeria canker will develop as stem lesions which will sometime become swollen resulting in the formation of a canker. If botryosphaeria stem blight or canker is observed the best method to prevent the spread is pruning the infected tissue and fruit clusters six inches below any infected stems. Then, remove pruned branches from the field.

Botrytis (B) also known as gray mold, affects both fruit and the plant. It infects the fruit from bloom. As with botryosphaeria, the best tactic to reduce the spread of this disease is by pruning out infected fruit clusters and wood, then removing clippings from the field.

Anthracnose (C) will appear as stem, bud and leaf lesions and may have orange spore masses. Infections will cause leaf browning and will move from top of the leaf to the bottom. If untreated, anthracnose will also cause fruit rot. Fungicides may be used to prevent further development of anthracnose during the green fruit
development stage.

Powdery mildew (D) will start as chlorotic discoloration spots and develop into powdery masses on leaves. The infection usually begins in the spring with young leaves and may become more severe throughout the season eventually causing defoliation. However, while unsightly, powdery mildew will not significantly damage the developing fruit crop and therefore no action is required.

Asparagus Beetle IPM

Emily Zobel on April 26, 2021

There are two beetle pests that feed on asparagus, the common or striped asparagus beetle (Crioceris asparagi) and the spotted asparagus beetle (Crioceris duodecimpunctata). Feeding on the spears results in scarring, browning, and hooked tips render the crop unmarketable. While both beetles can damage the emerging spears, the common asparagus beetle larvae and adults will also feed on the ferns, which can reduce the plant’s ability to build resources for a strong crop the following spring.

Fig 1. Adult Asparagus Beetle Photo by Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org

Fig 2. Adult spotted asparagus beetle.
Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

Adults: Adult beetles are about ⅓ inch in length. The adult common asparagus beetle is blue-blackish with six cream-colored square-shaped spots on its back (Fig 1). Adult spotted asparagus beetles are reddish-orange with twelve black spots on their back (Fig 2). Both the beetles overwinter as adults.

Fig 3. Asparagus Beetle Eggs. Photo by Ward Upham, Kansas State University, Bugwood.org

Eggs: Eggs take about a week to hatch. They are small, cylindrical, and dark-colored. The asparagus beetle lays eggs on the spear at a 90-degree angle in rows of 3 to 8 eggs (Fig 3.), while the spotted asparagus beetle oviposits eggs singularly on the fern.

Larvae: The larvae of both species are light gray with visible heads and legs. The common asparagus beetle larvae have blackheads (Fig 4.), while the spotted asparagus beetle larvae have an orange head. Larval feeding lasts for 10-14 days. Asparagus beetle larvae feed on the spear, while spotted asparagus beetles will burrow into the berry. Mature larvae crawl to the ground and burrow within the soil to pupate.

Scouting: Scouting should start at the end of April – early May or just after asparagus plants emerge and continue for the rest of the growing season. Check 10 plants in 5-10 different locations in a field, best on a warm, sunny afternoon when beetles will be most active. Treatment may be justified if 10% of spears are infested with beetles or 1-2% have eggs.

Cultural Controls & Prevention:

During harvest, harvest all spears every day to reduce the number of stems where eggs will survive for long enough to hatch.
Allow plants in one area to develop ferns so as to act as a trap crop. These plants can then be sprayed selectively.
Maintain a clean environment in asparagus fields in the fall to force adults to overwinter in field edges where natural predators reside.
Destruction of crop residues will eliminate overwintering sites for asparagus beetles.
The most important natural enemy of the common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. These parasitoids lay their own eggs inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs were killed by parasitoid feeding, and half of the surviving larvae were parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.

Chemical Control

Organic options on spears include Surround WP as a repellent, EC5.0, or products containing capsaicin (check for certification status).
If possible, spot spray along edges of planting where overwintering adults colonize the field and/or band insecticide over the row to help spare natural enemies. Use selective insecticides on ferns.
Daily harvest of asparagus makes chemical treatment difficult. 1 dh products are available and can be used immediately after picking to allow harvest the following day (see the Mid-Atlantic Commercial Vegetable Production Recommendations for current recommendations)

E. Zobel

Stinkbug Damage Found in Maryland Tomato Fields

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