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
Our first confirmed identification of white sugarcane aphid occurred this week. A BIG thanks to Laura Siegle in Amelia County for her vigilance and sharp eye. What does this mean for sorghum growers? It is time to scout. At least once per week until aphids are spotted in the field. Following that and until threshold is met – scout twice per week. Numbers can increase quickly. Start scouting on the borders of fields. Aphids will infest borders first. Check the underside of leaves. Not every aphid you find is a sugarcane aphid. You can bring samples to me or your local agent.
Corn earworm are likely found in sorghum this time of year. The same products will not kill both sugarcane aphids and corn earworm. Only Transform and Sivanto Prime are labeled for white sugarcane aphids in Virginia. Scout for earworms by beating sorghum heads into a 10-gallon bucket. A rough threshold is 2-4 worms per head. A threshold that includes costs of application and sorghum prices can be found here.
I made an error this week in my Southeast Ag Fax post and referred to the last spray date in cotton as “cutout.” What I should have said is, cotton should be sprayed for an above threshold plant bug population until the bolls that you anticipate harvesting are past susceptibility (~250dd). This may or may not coincide with cut-out (4 nodes above white flower). Keep in mind that, as the season progresses, sprays will offer less of a yield benefit. In Virginia, our critical window of protection is early to mid-bloom. There is a small and real yield benefit in spraying until week 5 or 6, but the lint gain may not offset the cost of applications. Late planted cotton is at high-risk because it overlaps longest with large bug populations and the plants have less time to compensate.
This season, there has been very poor performance of pyrethroids against plant bugs. Bifenthrin (Brigade and generics) performs better than other active ingredients including lambda-cyhalothrin (Karate, Besiege, Warrior II, Lambda-Cy) and beta-cyfluthrin (Baythroid). Acephate (Orthene 97) and sulfoxaflor (Transform) are better products. Diamond, an insect growth regulator that targets nymphs, should be tank mixed with either acephate at 8 oz. or bifenthrin at 6.4 oz. Currently, I do not recommend Diamond with other products without consulting your Amana representative. Diamond is added to prevent infestation and kill nymphs. It may not have quick knock-down. We have tested Diamond’s residual until two weeks post spray. Acephate alone works well at 8 oz. and is not rain fast. I have concerns with acephate and aphid populations that I will discuss this in another post. Both Bidrin and acephate are effective against plant bugs and stink bugs. For bollworms, I recommend Prevathon or Besiege. A well-timed pyrethroid spray may work and it will need to target small worms before they move inside of squares and bolls. Overall, stink bug pressure is moderate and bollworm pressure is light to moderate. Eggs and small worms have been spotted in low numbers in two-gene cotton. Please keep in mind that I am rarely called when insecticides work well. Keep me posted if your specific combination looks terrific!
Our cotton field day is on August 16th at the Tidewater Research Station. Seth Dorman and I will cover insect sprays, scouting techniques, and other topics. Josh Holland, ANR Southampton, and I will provide portable summary tables of product performance (as we have measured in 2019 on-farm trials).
Thanks to Stan Winslow from Tidewater Ag for his advice and video evidence that big-eyed bugs eat plant bugs. Thanks to Josh, Seth, and the TAREC team for their continued scouting efforts.
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.
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.
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.
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).
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!
Large aphids populations have been observed in alfalfa this year following insecticide applications targeting alfalfa weevil. If you haven’t scouted for alfalfa weevil in Virginia, you should. See the bottom of this post for a weevil summary.
Aphids, typically pea aphids, can be problematic when their natural enemies are disturbed. They can reduce vigor and cause wilting in first cuttings. If early cutting is not an option, several insecticides (mostly pyrethroids) are labeled for their control. Low label rates are generally effective as long as you ensure good coverage. Scout for aphids by pulling 30 random stems per field and counting the number of aphids. This guide from Iowa State can help you make treatment decisions.
Most of the aphids I have seen in Virginia alfalfa are pea aphids (left) and cowpea (right). If you think you have another species, please give me a call or send an email.
Photos Erin Hodgson, Iowa State
My thanks to Lane Grow from Southern State Cooperative for his ongoing efforts to scout and report problems in western Virginia.
Alfalfa weevil information
Scout fields by pulling 30 random stems and inspecting foliage for weevils. Weevil larvae are small, can be white, yellow, or green, and have black heads. They are often tucked tight into new growth. It’s possible to dislodge larger larvae so be careful or collect stems into some container that catches these. I use a plastic freezer bag and insect stems in the shop or truck. This guide from Penn State can help you make spray decisions. Cutting alfalfa is an option if you don’t want to use pesticides. I recommend using clorpyrifos based on spray tests in 2018 and 2019. Some people have been successful with indoxacarb (Steward) or pyrethroids (many brand-name and generic options). Coverage is essential with any product.
Soybean loopers have reared their ugly heads across southeastern and coastal Virginia this week. With many of us busy hauling corn, it is reasonable to ask – when can we stop spraying beans?
In a normal year, we could safely ignore mid-September infestations. This year, the majority of double crop Virginia fields are completing pod fill. Research indicates that R3-R5 beans benefit from a spray when defoliation reaches 15% and you find more than 1 looper per sweep. I recommend that you at least double, and can safely triple, this threshold in R6 beans (i.e., 35-50% defoliation is acceptable). It benefits you to exercise restraint when treating fields after R5.5. There is no scenario when you need to spray R7 beans for loopers. Cooler evening temperatures will work in our favor when they arrive.
In Virginia, Intrepid Edge and Steward have been our most consistent treatments (see image below from 2017). Looper populations in Virginia have tested diamide resistant the past two years (e.g., Besiege, Prevathon). Spraying pyrethoids will only make the problem worse.
Plant bugs continue to be a problem in some Virginia fields with ¼ of those scouted by the entomology team above threshold for the first two weeks of bloom. In anticipation of the upcoming bollworm flight, Monsanto sponsored a meeting last week at the TAREC to discuss mid-season insect management in cotton. Here is a summary of our discussion:
For 2 gene cotton (Widestrike, Bollgard II, Twinlink): scouting for eggs is recommended. Sample 100 terminals and leaves. Aim for 10 in 10 locations in the field. If you find 25 eggs, spray an insecticide. I recommend Prevathon unless stink bugs or plant bugs are an issue in your field. In that case, use Besiege. Bollworm (Helicoverpa zea aka corn earworm) and tobacco budworm (Heliothis virescens) eggs are indistinguishable and budworms are 100% controlled by Bt cotton. There is some risk that you are spraying unnecessarily. Very low numbers (<3%) of larvae sampled in non-Bt cotton were budworms in 2016 and 2017.
For 3 gene cotton (Widestrike 3, Bollgard III, and Twinlink Plus): scouting for 2nd stage larvae (1/8″ or larger) is recommended. This gives in-plant toxins time to kill small worms. Sample 100 bolls, blooms, and/or squares. Aim for 10 in 10 locations per field. If you find three larvae in one trip, two larvae in two consecutive trips (two larvae in each trip), or one larva in three consecutive trips (one larva in each trip), spray insecticides. I do not anticipate damage in 3 gene cotton unless we have very high pressure.
Pyrethroids have performed poorly in cotton in 2016 and 2017 tests (15-50% control). I think that pyrethroids are too risky in cotton. Some growers are satisfied with the control that they have been achieving. Last year, worm specific products ran out in some Virginia locations. I recommend Steward as an alternative to Prevathon and Besiege for bollworm control in cotton.
Weekly scouting is recommended for all pests. Bollworm eggs hatch fast (2-3 days) and worms cannot be controlled by any product once they are inside of the boll.
Spray bugs only at threshold. Bloom threshold for plant bugs is 2-3 per drop cloth sample. For stink bugs, use damaged fruit thresholds: Week of bloom 1 = 50% internal boll damage; week 2 = 30%; weeks 3, 4 and 5 = 10%; week 6 = 20%; week 7 =30%; week 8 = 50%. About a dozen beneficial insects are common in Virginia cotton. Ambush bugs, big-eyed bugs, minute pirate bugs, green lacewings, two species of ladybird beetles, and several types of spiders are examples. They are of two types: 1) predators that prey upon an insect pest (see examples below), or 2) parasites that live within the host insect. These insects, particularly the predators, reduce the number of eggs and larvae of bollworms, plant bug nymphs and aphids. Because these allies lessen the impact of pest insects, common sense dictates that producers use them as a management tool. Their presence often means that growers can delay and, on occasion, eliminate some insecticide applications. However, the rapid increase in pest populations will often overwhelm the beneficial population and applications become necessary. Do not hesitate to spray pest insects at recommended thresholds.
A big thank you to Seth Dorman and his scouting crew and to Glenn Roundtree for initiating and organizing our recent pest management discussion.