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Category Archives: Cotton
Spider mites in many crop fields
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…
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.
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.
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.
Herbicide Resistant Weeds Workshops
CANCELLED! Due to Virginia Tech’s response to COVID-19 and out of concern for everyone, we are cancelling all of these workshops. We will reschedule after field season in Nov. or Dec.
- Herbicide Resistance- What is it and how did we get here?
- Creating Effective Herbicide Plans
- Integrated Weed Management of Palmer amaranth, common ragweed, and horseweed/marestail
- Local Perspective on Weed Management
- Putting It All Together: Creating a Weed Management Plan
CCA credits will be offered
Free lunch to start or end the program!
If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in this activity, please contact the Extension office listed above or TDD* during business hours of 8:00 a.m. and 5:00 p.m. to discuss accommodations 5 days prior to the event. *TDD number is (800) 828-1120.
Virginia Cooperative Extension programs and employment are open to all, regardless of age, color, disability, gender, gender identity, gender expression, national origin, political affiliation, race, religion, sexual orientation, genetic information, veteran status, or any other basis protected by law. An equal opportunity/affirmative action employer.
Plant bug / bollworm update for VA cotton
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 value of scouting for plant bugs
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:
- Decisions can be quick and easy – if scouting multiple locations in a field (either by quadrant or on the diagonal) results in numbers over threshold (8 per 100 sweep or 2-4 per beat sheet sample), spray the field. Likewise, if you are seeing consistently below threshold numbers, don’t spray. The only scenario where more time is warranted is when you capture near-threshold numbers in multiple spots. In this scenario, you must decide: 1) how much yield you want out of this field, 2) whether you have time to revisit this field in 3 to 5 days to scout again, and 3) how spraying right now fits into your schedule. Remember two things: 1) it always pays to spray on threshold, and 2) spraying in this hot, dry year increases your risk of secondary pests with any insecticide application. I favor treating the problem that I have and dealing with the problem that may occur, but this is entirely up to you and your operation. An additional 15 minutes of scouting may be more profitable than spraying an entire field. It’s ultimately your choice.
- Any sampling method works. Our data (below) from 2018 show that when you scout with a sweep net, a beat sheet, or both combined, you are profiting over not scouting at all. This is why we are distributing beat sheets free of charge at the Tidewater AREC. The companies that have paid for your beat sheets (Corteva, BASF, and FMC) agree. No one wants you to spend money unnecessarily – especially in this difficult time.
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 bugs in cotton update
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:
- Your risk of aphids and spider mites increases, especially if it does not rain soon.
- Your risk of subsequent plant bug infestations increases.
- You spend money that you did not have to spend.
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).
Plant bug spray thresholds in cotton
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.
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.
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.
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!
Scouting and spraying plant bugs in pre-bloom cotton
Virginia cotton fields are a mixed bag when it comes to plant bug infestations this week – some fields will require sprays and most will not. The only way to know what is in your field is to look in your field. It is time to scout when cotton starts squaring.
Spray cotton for plant bugs when square retention drops below 80% and you capture 8 or more plant bugs per 100 sweeps. Inevitably, there will be fields where bug numbers exceed threshold and square retention is >80%. In this case, I favor spraying to prevent bugs from reproducing in the field, but only if numbers exceed threshold.
As far as I’m concerned, all Virginia cotton fields are at risk for plant bugs. This animal has over 200 known hosts and you will find one in any field if you look hard enough. There are fields that are predisposed to higher populations. These field, in general, are:
- In Eastern cotton growing counties. Plant bugs populations benefit from warmer low temperatures. Abundant water in the landscape contributes to warmer lows and cooler highs.
- Near corn or double crop wheat/soybeans.
- In areas with high deforestation and new growth forests.
Results from our 2018 survey are below. Note that infestations cluster in the eastern region. However, fields in all regions are at risk.
I recommend a neonicotinoid insecticide pre-bloom. This class includes Belay, Centric, and Admire Pro. There is a lot of debate on using Admire Pro. In field tests, sometimes it is as good as Centric/Belay and sometimes it is not. This is why I recommend Centric or Belay. However, spraying Admire Pro will be better than not treating if you are over threshold. If you are not over threshold, do not spray any product. You will put yourself at high risk for infestations. This cannot be overstated.
As always, call me with your questions and concerns. If you do not know how to sample for plant bugs, I will show you. My program has beat sheets for you – free of charge. We will be distributing them at scouting clinics and field days this summer. If you need one before then, please stop by the Tidewater AREC. Please thank your sales reps from Corteva, BASF, FMC, Amana, and Bayer for funding this program. Cotton Inc. and the Virginia Cotton Board also generously provided support. Please thank Seth Dorman and his awesome plant bug scouting crew for generating data specific to our region.
Section 18 Emergency Exemption approved for Virginia cotton
Virginia cotton growers can now use Transform to control tarnished plant bug in cotton in 2019 (June 1 – Oct 1). This product will allow us to rotate modes of action and reduce our dependence on acephate and pyrethroids to manage this potentially destructive pest. Transform is softer on beneficials too, but you must notify beekeepers within 1 mile of cotton fields and, if there are known hives, apply before 7am or after 7pm when cotton is flowering. Transform is applied at 1.5-2.25 oz/A. Follow all label directions and keep a copy of the label with you when applying.
Based on early sampling numbers, we will have another high pressure year. Spray test results from the Tidewater AREC (shown below) can help you chose insecticides. Neonicotinoids (Admire, Belay, Centric, Endigo) should not be used after first bloom and are less effective during this time. Diamond is a growth regulator and is more effective against nymphs. There is evidence that it suppresses adult reproduction.
The single most important thing you can do to protect cotton from plant bugs is to spray at extension recommended thresholds (8 per 100 sweeps or 2-3 per drop cloth sample). As always, the only way to know what is in your field is to scout.
Call/text/email me if you have questions.
Thrips dispersal and foliar sprays
Virginia cotton requires a thrips control product at planting to preserve yield and avoid maturity delays. This is especially true since the arrival of tarnished plant bugs. Any maturity delay early-season will likely magnify plant bug injury. Cotton planted at the end of April and first week of May has put on 1-2 true leaves. It is time to scout for thrips injury and make foliar applications when necessary.
Levels of injury to cotton seedlings rated from ‘0’ (no damage) to ‘5’ (dead terminal
or plant) from thrips. Injury at ‘2-3’ or above approximates a threshold for intervention with an
insecticide application. (Photo and caption from Kerns et al., 2018)
Using a seed treatment alone will likely require a foliar spray based on research from the Tidewater AREC. In-furrow aldicarb and in-furrow imidacloprid with a seed treatment should not need a foliar spray. Scout cotton planted with in-furrow imidacloprid alone and determine if a foliar application is necessary (often it is not – saving you time and money).
All cotton planted in Virginia is under high risk for thrips injury. NCSU prediction model shows risk increasing in later-planted cotton. This model was highly accurate in 2018.
Tips for foliar applications: Consider plant-date and growing conditions. Cotton planted late-May into warm soil may not need a foliar spray. Do not apply foliar acephate if plants are growing fast with no to minimal thrips injury. Thrips injury is likely for all cotton planted in Virginia and risk will be high until plants are no longer susceptible. The three diagrams below from the NCSU model show when seedling susceptibility declines based on planting date (May 1, May 8, May 15). The blue line on these diagrams shows you when risk for thrips injury is highest.
Spraying is most effective when the first leaf is the size of a pencil tip to a mouse ear. I recommend a 6-8 oz. rate of acephate. Several scenarios may be responsible for reduced efficacy of sprays:
1. Rain. Acephate is not a rain fast product. Consider reapplying if necessary.
2. Resistance. Acephate at 3 oz. per acre has become less effective in spray tests. Rotate to Radiant if another spray is required or use a higher rate.
3. Species composition. Tobacco thrips are most common in VA, but western flower thrips can co-infest. Acephate is less effective on this species. Rotate to Radiant if another spray is required.
As always, call/text/email me with any questions. Good luck and happy planting!