By: Kelly McIntyre and Tom Kuhar

This week FAW adults were observed at 3 of 5 monitoring locations throughout the state. The West Central region (Montgomery county) had sites with 2-4 individuals while and more eastern regions of the state (Hampton Roads) experienced increased numbers with 22 individuals at Virginia Beach. See table for all locations and counts.

I have received a lot of questions regarding leaf spot fungicide treatments in the past two weeks. A lot of this is driven by either: 1) fungicide failures in fields with high disease pressure; or 2) fields under heavy drought stress. In both cases I have advised growers and consultants to look at low cost options. I’ll cover both situations below.

Fields with high late leaf spot pressure Late leaf spot outbreaks have shown up in fields that have been sprayed with Miravis that has traditionally performed well in past years. In each case the fields were in a 4 year or less rotation, most of these fields were irrigated, and growers were using the 4 week extended spray interval to take advantage of the residual activity provided by Miravis. What growers and consultants are interested in now is what to do to hold the leaves on until digging. I try to reduce fungicide costs this close to digging while providing late leaf spot management that reduces excessive defoliation. My “go to” has been Microthiol Disperss (dry sulfur formulation) mixed with a Group 3, DMI fungicide. University researchers, including myself, have observed favorable results with this combination in field trials. The hesitancy in using this program is the added complexity of using a dry formulation and sourcing Microthiol Disperss. Some grower opt for liquid formulations of sulfur because of the two reasons just mentioned, but most of the positive results reported have been with Microthiol Disperss and the amount of sulfur provided by liquid formulations is variable depending on each product, and often the amount of sulfur used with liquid formulations is less than what is provided with Microthiol Disperss. I prefer Microthiol Disperss because it has proven effective in managing high levels of late-season late leaf spot and because it is inexpensive (about $1 per pound which is $5/acre at the recommended 5 lb rate). The sulfur provides instant reduction in leaf spot inoculum but little to no residual activity. That’s why I recommend mixing it with a DMI fungicide like Provost Silver or less expensive Alto. DMI’s provide some curative activity, but most importantly residual activity. Group 7 (SDHIs) and Group 11 (strobilurins) don’t provide curative activity and are most active when applied preventively when little-to-no leaf spot is present.

Fungicide decisions on drought stressed peanuts In many areas peanuts are under severe drought stress with many fields exhibiting wilting 24 hours a day with growers being reluctant to apply leaf spot fungicides due to dry conditions. In many cases these fields are 10-14 days away from digging. This is really a situation where I tend to favor no fungicide applications or at least one application of a very inexpensive fungicide. During dry conditions we often avoid using chlorothalonil (Bravo) due to it’s propensity for flaring spider mites. In my opinion the fungus that parasitizes spider mites to keep them in check is already absent due to the severe drought which is why many growers are seeing outbreaks of spider mites in certain areas. Since the fungus that keeps spider mites at bay (and that chlorothalonil reduces) is already absent, if chlorothalonil is chosen I see that as a low-risk application. Another less expensive option would be Alto which shouldn’t flare spider mites. My personal favorite is to not apply a fungicide at all because: 1) there is little to no leaf spot in these wilted peanuts; and 2) leaf spot outbreaks take a good bit of time to get going and by the time you see any leaf spot in these fields it will be too late for the disease to cause yield damage by the time they are dug. In Suffolk, VA the extended forecast shows no rain chances over 20% for 9 days, at least with the weather app I use. So leaf spot pressure will be low until digging in most cases which further decreases the chance of outbreaks occurring. Deciding not to spray a fungicide is a low risk option in my opinion.

Aflatoxin potential It’s been many years since growers have had to think about dry conditions leading to aflatoxin-contaminated peanuts, which is a good thing. This year is different due to the drought stress near harvest. I recommend keeping peanut field harvests separate between fields with low and high risks of aflatoxin contamination. In other words, avoid mixing peanuts from severely drought-stressed and fields that have not had as much drought stress (possibly irrigated). If peanuts that have had drought stress are to be used for seed, they should receive a quality seed treatment to reduce poor stand due to the aflatoxin fungus in peanuts planted next spring.

By: Kyle Bekelja, Kelly McIntyre, and Thomas Kuhar

We have spotted pickleworm in Blacksburg, VA! It’s not hard to see how this pest can be economically severe. An infestation of just one caterpillar on a fruit is enough to render it entirely unmarketable. Who wants to cut into a squash to find a big juicy caterpillar living inside? I don’t…actually, as an entomologist I might find this exciting, but we aren’t growing veggies just for entomology enthusiasts. Notice the circular, tunnel-like feeding hole caused by the caterpillar (in Figure 1 and Figure 2), which burrows its way inside the fruit where it will live and feed, evading all efforts to kill it with insecticides.

Management
To manage this pest, scout fields and look for caterpillars in flowers, before fruit set. If one is spotted, this means your crop is infested and caterpillars need to be killed before they enter fruit. Once they enter the fruit, insecticides are useless since damage is already done, and caterpillars are protected by the fruit. See the current Mid-Atlantic Commercial Vegetable Production Recommendations (VCE Publication 456-420) for management of pickleworm on crops other than those provided here. If you’re interested in getting involved in our pickleworm monitoring network, send an email to any of the authors of this post and we will be sure to send you trapping supplies.

Biology
This insect is a member of the genus Diaphania, which contains both “pickleworm” and “melonworm.” We will need to rear these caterpillars to adults to determine which species they are, but management recommendations remain the same, regardless. This insect cannot overwinter in Virginia; it is a migratory pest that moves northward, hence arrival is usually late-summer. Adult moths will lay eggs on flowers of cucurbits. Larvae hatch and begin feeding on fruit and may eventually tunnel inside. Once inside, insecticides are useless to kill caterpillars. Caterpillars will emerge into adults after spending 8 or 9 days as pupae.

By Lorena Lopez and Tom Kuhar 

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. 

By: Kelly McIntyre and Tom Kuhar

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.

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.

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

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

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.

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.

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!

By: Kelly McIntyre and Thomas Kuhar

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.