Black light trap catches of AGB per 3 to 4 nights in Sussex County, Virginia were 500 on June 7 and 487 on June 10, 2024. Producers have reported seeing adult AGB just by kicking over the top inch or so of soil in infested areas. I heard of 5 acres of cotton in Suffolk with very heavy AGB defoliation, but there are more reports where injury is not as severe. I look forward to learning when our AGB population will finally decline.
Captures of Asiatic garden beetle (AGB) in our black light trap climbed this past week, with 300 adults caught between May 31 and June 3, 2024. We do not know if we have reached peak emergence yet for this sporadic pest. Johnny Parker (Commonwealth Gin) reported three Virginia seedling cotton fields with AGB injury so far this season, with defoliated areas reaching 2 acres. Check for these insects under weeds such as pigweed, marestail, or volunteer soybean–focus especially on sandy soils. You may see round adult emergence holes in the ground. Or, a visit to the field at night (when adult AGB are active) may confirm the problem.
In a June 4, 2024 Pest Alert, Dr. Dominic Reisig and Dr. Guy Collins (North Carolina State University) provide AGB scouting and management information which is also applicable for Virginia cotton growers. Contact insecticides would need to be applied during peak emergence, and at night.
In 2023 there were multiple, scattered reports of severe defoliation and/or death to cotton seedlings caused by Asiatic garden beetle (AGB) in Virginia and northeast North Carolina. Infested cotton areas varied in size, with some reaching 10 acres. AGB feed on roots (as grubs) and foliage (as adults) of many different host plants. The adults hide in the soil during the day and feed at night. AGB prefer sandy soil over heavier soil. When we visited the infested cotton fields, we often found AGB in the soil below weeds (e.g., marestail) and volunteer soybean plants.
This April the Tidewater Agricultural Research and Extension Center’s entomology program began sampling field “hotspots” from the 2023 season using soil samples, pitfall traps, and a black light trap. We found AGB grubs in soil samples from fields in Wakefield and Sussex County, VA, but did not find them in a northeast North Carolina field infested last year. AGB grubs can be differentiated from other white grubs by their “puffy cheeks.”
The black light trap is being operated in Sussex County, VA; it had a peak of 114 AGB adults (total per 3 nights) on May 9, 2024, followed by a sharp decline in captures. Other states have reported a single generation of AGB per season, but we plan to keep monitoring for several more weeks. We are still finding grubs and pupae in our soil samples. Pitfall traps placed in the field, designed to capture crawling adults (not flying due to cool temperatures), have not captured any AGB so far.
Cotton infestations and seedling injury from 2023 may have been due in part to cool May temperatures, keeping AGB adults on the ground, feeding in the cotton fields where they emerged; the cooler weather also limited cotton seedling growth.
We’ll provide further updates as we learn more. If you suspect an AGB problem in your seedling cotton, please feel free to reach out to me, or contact your county Extension Agent.
Acknowledgements: We are grateful for the financial support provided by Cotton Incorporated and the Virginia State Cotton Support Committee, and for the assistance provided by local cotton growers.
Observations from the field this week indicate that there are spider mite infestations at some level in most, if not all, peanut, cotton, and soybean fields in the drought-stressed Virginia regions. Drying of corn and weeds is contributing to this problem. Let’s all hope we get the rain we need to make a good crop this season. Rainy, humid weather will favor fugus that kills mites, but its effect may be mitigated by extremely hot conditions. Just in case, and since our last bad mite year was 2011, see below for a refresh about spider mites and how to treat them in each crop…
Soybean
Concentrate on the field borders and look for the early signs of white stippling at the bases of the leaves. Do not confuse mite damage with dry weather injury, mineral deficiencies, and herbicide injury. Mite infestations will have some pattern, usually originating from field margins. Consider applying a miticide if more than 50 percent of the plants show stippling, yellowing, or defoliation over more than one-third of the leaves. Recommended products include Zeal and Agri-mek (other abamectin products are available, but not labeled for soybean). Lorsban and dimethoate are labeled and may require a second application. Bifenthrin will offer some suppression, but mite infestations will come back stronger.
Peanut
Heavy infestations usually occur first around the borders of peanut fields; then they spread inward throughout the fields. Avoid harvesting spider mite infested cornfields or mowing weedy areas next to peanut fields until peanuts are harvested. Spider mites will readily move into peanuts when corn dries down or is harvested. Be prepared to treat peanuts if adjacent corn is infested. Use adequate pressure and GPA to ensure penetration of the canopy. Comite is our only registered product that works. See graph below from Dr. Mark Abney at UGA.
Cotton
Mite damage first appears as a slight yellowing of the leaves, which later changes to a purplish or bronze color and is usually associated with webbing. Damage occurs especially in spots or on field edges but widespread defoliation is not uncommon if favorable conditions persist. I recommend abamectin (10 oz/A rate is usually sufficient) or Zeal for control. Bifenthrin, other pyrethoids, and especially acephate, will flair mites. If you are treating for plant bugs, I recommend Transform at 2-2.25 oz/A until wetter conditions prevail. Be mindful of the bollworm flight next week and do not make automatic sprays for worms until you confirm a problem in your field. Worm specific products (Prevathon, Intrepid Edge, Blackhawk) are better options than broad-spectrum insecticides (pyrethroids).
Our annual post-bloom survey starts next week. If you need help learning how to scout insect pests, call or text me on my mobile (919) 801-5366.
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The much needed rain earlier this week also heralded the start of the moth flight in southeastern VA. Both eggs and adult moths are being picked up by scouting teams. So far, only a handful of fields are over recommended thresholds. I recommend scouting 2-gene cotton (Bollgard II, Widestrike, Twinlink) for eggs and applying Prevathon or Besiege when you find 25 or more per 100 terminals and/or leaves. If you planted 3-gene cotton, you are likely protected. We have measured very little benefit to spraying Widestrike 3, Bollgard III, and Twinlink Plus varieties for bollworm. In these varieties, finding 3 or more live second-stage larvae in one trip (or two worms in two consecutive trips, or one worm in three consecutive trips) triggers an application.
Other insecticides can control bollworm in cotton, but timing is critical. If you are using a pyrethroid, for example, target small worms. No product will clean up a problem field once worms are inside bolls.
Our team, lead by PhD student Seth Dorman, ANR Agent Josh Holland, and Dr. Sean Malone are scouting fields this week for lygus. Few problems fields were detected in southern counties today. However, fields were observed over recommended thresholds. At this point, many people have sprayed. Some may need to spray again and some may not. The only way to know is to scout.
Northern counties will be scouted this Friday and I will update the blog with our findings.
As always, you can reach out to me with your questions and concerns.
The entomology program recognizes the logistic difficulty in scouting. We know that you have to cover a large acreage in a limited amount of time, you manage multiple crops, and some weeks, frankly, you would rather spend the time with your family. We get it.
So, let’s chat about how to scout cotton for plant bugs, and the amount of money that it will make you, in the fewest possible bullet points:
Figure 1. Comparison, in terms of lint yield, of different sampling methods for tarnished plant bug (sweep net, drop cloth, and sweep net until 2nd week of bloom combined with drop cloth after) and different thresholds (low, medium or recommended, high, and very high). Favoring the low threshold (1 per drop cloth sample) was profitable when using a drop cloth alone, but this did not make money over using a medium threshold in the combined method. Regardless, you make money if you sample and spray by any method. Not every Virginia field will experience this high pressure.
Table 1. Net economic returns (per hectare) for threshold trial in 2018 above the untreated control. Cotton was priced at $0.77 per acre for 2018; nitrogen (32-0-0) was priced at $49.18/acre (120.0 lb/acre); bifenthrin (6.4 oz) was priced at $2.90/acre; acephate (8 oz) was priced at $3.12/acre; sulfoxaflor (2.25 oz) was priced at $13.80/acre; thiamethoxam (2 oz) was priced at $15.61/acre; chlorantraniliprole (27 oz) was priced at $26.35/acre
As always, best wishes for a profitable 2019. Please reach out to Sally or myself if you have questions or concerns. I hope that you have the opportunity to spend this weekend with the people and activities that you value most. Happy 4th y’all!
Plant bug populations have been spotty, and lower overall than this time last year (click to see map). 10% or fewer of Virginia fields need insecticide applications this week, but, unfortunately, a much higher percentage will end up treated. Before making a decision to spray without scouting consider several things:
Spraying for plant bugs at or exceeding threshold will pay off. Keep in mind that sprays during flowering typically yield higher returns. These two Focus on Cotton presentations by NCSU (click here) and VT (click here) will tell you what you need to know about plant bugs in our region (follow links).
If you need help scouting, ANR agents Josh Holland (Southampton) and Elizabeth Pittman (Suffolk) will be hosting scouting clinics in July. More information coming soon. Beat sheets are available to you free of charge at these events and at the Taylor lab at the Tidewater AREC. Stop by anytime Monday through Friday 8 am – 4 pm. We are closed next Thursday and Friday.
A big thank you to FMC, BASF, and Corteva for sponsoring this round of beat sheets!!
A big thank you to Josh Holland for his help scouting this week!
Click this link for interactive map with insect density and square retention data (click points for summary data).
Early season scouting (pre-bloom cotton)
We recommend scouting for plant bugs as soon as cotton begins squaring. We encourage everyone to scout for plant bugs, especially those that saw high numbers last year. Early in the growing season (pre-bloom) we are scouting for adult plant bugs immigrating into cotton from flowering weedy hosts and other cultivated hosts nearby (corn, wheat, soybean). Plant bug adults (pictured below) are approximately 5-6mm in length (quarter inch) and can be identified by their yellowish brown body color, conspicuous “Y” shape on their scutellum or upper back, and two yellow dots on their cuneus or lower back. For pre-bloom cotton, we recommend sweep net sampling with an action spray threshold of eight plant bugs (adults and nymphs) per 100 sweeps. This can be done by conducting four to eight random 25-sweep samples throughout each field. We also recommend measuring square retention before bloom by sampling 25 random plants in each field and calculating the percentage of missing or black squares from all first positions on whole plants or the top five nodes. Consider a spray application for plant bugs if the insect threshold is reached (8 plant bugs per 100 sweeps) and square retention is below 80 percent.
Click on this video link to see sweep net sampling technique in cotton.
Plant bug pre-bloom action threshold in cotton.
Mid- to late-season scouting (flowering cotton)
For mid- to late-season scouting, when cotton is flowering, we are mainly sampling for plant bug nymphs using a black drop cloth. The action threshold for triggering sprays in flowering cotton is 2-3 plant bug nymphs and adults per drop cloth sample. For drop cloth sampling, we recommend placing the drop cloth in between two rows and vigorously beating plants onto the drop cloth. We also recommend taking at least four samples per field.
Click on this video link to see drop cloth sampling technique in cotton.
Plant bug action threshold in flowering cotton.
Insects often mistaken for plant bugs
Common insects in cotton fields that are often confused with plant bugs include big-eyed bugs, aphids, and stink bug nymphs (pictured below). Big-eyed bugs head and eyes are wider than their body. Aphids are a secondary pest and are generally smaller and slower than plant bug nymphs with two tailpipes or cornicles on their lower back. Stink bug nymphs have a more shield-like body shape with three black stripes on their antennae.
Insects that are often confused with plant bugs include big-eyed bugs, aphids, and stink bug nymphs.
Economic benefits of managing plant bugs in cotton
The single most important management strategy for plant bugs in cotton is applying insecticides at the recommended action thresholds described above. The bar graph below highlights lint yield gained when applying insecticides at various thresholds (low, medium/recommended, high, very high) using sweep net only, drop cloth only, or both (as described above). We see that the highlighted recommended threshold using sweep net sampling pre-bloom and drop-cloth sampling during flowering was one of the highest yielding treatments with the highest economic returns among treatments with five or fewer spray applications. The major take-home from these data is that any scouting technique (sweep net and or drop cloth sampling) at any threshold, is going to significantly increase lint yield and economic returns when plant bug infestations are present!
Bar chart highlighting lint yield gained above the untreated control using various sampling techniques and spray thresholds for plant bugs.
Economic returns above the untreated control when properly managing cotton for plant bugs.
