This week, pickleworm larvae have been detected in the Virginia Beach area, Chesapeake, and Portsmouth. If you have late plantings of squash beware of the presence of this pest in the area. Also, pumpkins could be infested by pickleworms borrowing into the fruit or feeding on the surface of the fruit. Here is a brief description of pickleworm larvae and adults, as well as options for management.
Pickleworms feed on wild and cultivated cucurbit species. Adults are not active during the day, only at night when females lay their eggs close to flowers or flower buds. The larvae burrow into the fruit where it feeds and develops. Larva color varies from light green to translucent with multiple dark spots and varies in size from 0.05 to 0.6 inches long.
Management: Pyrethroid insecticides can be effective at controlling this pest if sprayed in a timely manner (i.e., lambda-cyhalothrin, permethrin, bifenthrin, Baythroid XL, Mustang Max, etc.), but they are not IPM compatible and can result in outbreaks of secondary pests such as aphids. Usually two or more sprays of pyrethroids in late summer can cause severe aphid problems. Other insecticides that control pickleworms include Radiant and Entrust (spinosyns), the diamide insecticides like Coragen and Harvanta, the insect growth regulator Intrepid, and the lepidopteran-targeting insecticide Avaunt eVo (Indoxacarb). These products will have less non-target impacts than pyrethroids and also control pickleworm.
Pickleworm larva inside a zucchini in Virginia Beach.Adult pickleworm moth.
This week FAW adults were observed at 7 of 14 monitoring locations throughout the state. The West Central region (Carroll and Montgomery counties) maintained FAW presence at some sites (5-6 individuals) and more eastern regions of the state (Hampton Roads and Eastern Virginia) experienced increased instances and counts of FAW (1-49 individuals). See table for all locations and counts.
Corn earworm (=bollworm) moth captures from southeast Virginia black light traps this week were 5 per night at Templeton (Prince George Co.) and 4 per night at Disputanta (Prince George Co.); Suffolk numbers averaged 45 per night. Here is the Table. In our pyrethroid resistance monitoring tests, the seasonal average is at 33% survival (n=565 moths tested).
This week I visited several vegetable farms in southside (southcentral) Virginia and found beet armyworm infestations at all of the farms. This is not good news as this insect pest can be difficult to control. One field of Brussels sprouts had been sprayed with a pyrethroid and with Lannate the spray before and had a healthy population of beet armyworms doing a lot of damage (see photo). I saw mostly young larvae and even some egg masses (see photo). Based on my experience, this pest is resistant to those two classes of insecticides.
Beet armyworm on Brussels sprouts in southside Virginia. September 2022.
History and Pest Status of the Beet Armyworm in the U.S.
The beet armyworm (BAW) is a widely distributed polyphagous insect pest of >90 species of plants and cultivated crops, including alfalfa, asparagus, bean, beet, broccoli, cabbage, cauliflower, celery, chickpea, corn, cotton, cowpea, eggplant, lettuce, onion, pea, peanut, pepper, potato, radish, safflower, sorghum, soybean, spinach, sugarbeet, sweetpotato, tobacco, tomato, and turnip. The insect also feeds on fruit and ornamental plants. The BAW is native to Southeast Asia, but has spread throughout much of the world. It was first discovered in North America in the late 1800’s on the west coast, and reached the southeastern U.S. by the 1920’s. As it is a tropical insect, it lacks a diapause and ability to overwinter in colder (temperate) climates. High populations of BAW occur in the southeastern and southwestern states in the spring, and highly mobile migrants usually make their way northward each summer to the Mid-Atlantic states, Colorado, and northern California. Occasionally the pest is found as far north as New York and even Canada.
Damage
Beet armyworm egg mass.
BAW larvae feed on foliage and fruit. When they are young, larvae feed gregariously, usually in great numbers, where they skeletonize and web leaves. As they mature, larvae devour more foliage and may burrow into fruit or heads of plants. When BAW outbreaks occur in a region, they are conspicuous and often become the primary pest control focus of growers of numerous field and vegetable crops because of the sheer numbers of larvae and their ability to move from crop to crop. If they are not controlled, BAW infestations can sometimes result in total crop losses. The insects have a high reproductive potential; eggs are laid in clusters of 50 to 150 eggs, and female moths can produce over 1300 eggs in a lifetime. In addition, eggs are well protected from the environment and predators because they are usually deposited on the undersides of leaves and are covered with cottony scales deposited by the female moth. This usually results in numerous larvae infesting a single plant after egg hatch.
Insecticide Resistance in the Beet Armyworm
BAW has a high propensity for developing resistance to insecticides. In the southeast and southwestern states, the relatively high abundance of BAW coupled with large acreages of valuable crops has stimulated a long history of intense insecticide use . Not surprisingly, this has resulted in the development of resistance to a diverse array of pesticide classes, including chlorinated hydrocarbons, organophosphates, carbamates, pyrethroids, and benzoylphenylureas. Some recommended insecticide options include the diamides such as Coragen, Harvanta, Beseige, Elevest, etc.., spinosyns like Radiant or Blackhawk or Entrust for organic growers. Bt products like Dipel, Agree, Xentari, Javelin, Deliver, etc.. will provide very good control of small larvae. Proclaim and Avaunt are also effective products from past efficacy trials.
By: Kyle Bekelja, Kelly McIntyre, and Thomas Kuhar
Figure 1. Striped and spotted cucumber beetles feeding on a pie pumpkin (Image credit: Thomas Kuhar)
Insecticides It’s late in the growing season, which means many cucurbit growers, especially those growing pumpkins, need to start thinking about how they’re going to keep their fruit looking pretty for the coming weeks! Table 1 shows a list of insecticides and their effectiveness against a few key pests of cucurbits based on insecticide evaluations, their preharvest-intervals (PHI), and their relative bee toxicity rating (i.e., high, medium, low).
Table 1. Insecticides for managing key pests of cucurbits. Effectiveness rating scale: E = excellent; G = good; F = Fair; P = poor (credit: Thomas Kuhar)
Insecticide Evaluation In the lab, we tested Assail 30SG at four rates (0.44, 0.88, 1.75, and 2.50 dry oz/acre) for its effectiveness against cucumber beetles. We looked at percent mortality and percent damaged leaves for each treatment.
Figure 2. Bar graph showing percent mortality of cucumber beetles at 2, 3, and 4 days after treatment (DAT).
Although the percent mortality was relatively low for Assail at the 1.75 rate, as shown in Figure 2, it still seemed to have prevented beetles from feeding on plant material, shown in Figure 3.
Figure 3. Bar graph showing percent damaged leaves at 2, 3, and 4 days after treatment (DAT) with insecticides targeting cucumber beetles.
Assail 30SG prevented cucumber beetle feeding, and outperformed Bifenture DF four days after treatments were applied at the 1.75 and 2.50 rate (Figure 3). Although % mortality was low at the 1.75 rate (Figure 2), it appears that feeding was still prevented.
Assail 30SG has the added benefit of being less toxic to bees than many other options, and has a short preharvest interval. Regardless of your chemistry, try to avoid spraying while pollinators are active!
This week FAW adults were observed at 5 of 20 monitoring locations throughout the state. The West Central region (Carroll and Montgomery counties) had greater counts (5-63 individuals) though adults were also observed (1 individual) in Central Virginia (Henrico and Hanover counties). See table for all locations and counts.
Corn earworm (=bollworm) moth captures from southeast Virginia black light traps this week were 7 per night at Templeton (Prince George Co.) and 9 per night at Disputanta (Prince George Co.); Suffolk numbers reached 60 per night. Here is the Table. In our pyrethroid resistance monitoring tests, the seasonal average is at 33% survival (n=502 moths tested).
This week FAW adults were observed at 5 of 15 monitoring locations throughout the state. Western regions (Carroll and Montgomery counties) of the state had greater counts (4-26 individuals) though adults were also observed (1 individual) in eastern Virginia (Williamsburg and Northampton County). See table for all locations and counts.
Last year, we at Virginia Tech started a pickleworm and melonworm monitoring program consisting of information exchange between cucurbit growers and extension agents across the state that looked for these pests’ damage to cucurbit blossoms or fruits. In 2021, we recorded up to 80% of squash fruits or flower buds infested with either pickleworms or melonworms. This year we continued with the monitoring efforts by monitoring closely summer squash fields in the Eastern Shore, Blacksburg, and Chesapeake area and no pickleworms nor melonworms have been detected.
Additionally, we set up traps with pickleworm pheromone lures in squash and pumpkin fields in Montross, Hillsville, Cape Charles, Painter, Hampton Roads, and Madison County. If these moths are present in the area, they will be attracted to the lure at night when they are active. After two weeks of trapping, no pickleworms or melonworms have been caught in the traps. We will continue to trap these pests as the summer squash season finishes and the pumpkin season continues and will keep you updated.
This week’s corn earworm (=bollworm) moth captures from local black light traps were: Sara Rutherford (Greensville ANR Agent) reported a nightly average of 20 moths; Scott Reiter (Prince George ANR Agent) had 8 per night at Templeton and 10 at Disputanta; the Spiers reported 5 per night in Dinwiddie; and we averaged 28 in Suffolk. Here is the Table. In our pyrethroid resistance monitoring tests, the seasonal average is at 30% survival (n=395 moths tested).
