Category Archives: Cotton

Cotton insect pest update—bollworms are here.

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At this point in the season, many cotton fields have been treated once for mid-season plant bug/stink bug. The next decision will be focused on bollworm control—whether it is needed, and if so, what insecticides to use. We are seeing a general increase in bollworm moth activity at TAREC and have gotten recent reports of some pretty large worm infestations in a couple of peanut fields in the cotton area, and outbreaks in a couple of soybean fields in the Suffolk area. Caution: if the earlier applied mid-season plant bug/stink bug spray included a pyrethroid (e.g., bifenthrin), the beneficial populations in those fields will have been depleted—which makes them more susceptible to bollworm.

We have plenty of data that shows that cotton varieties with bollworm protection traits can be damaged by worms. Some escape the toxin, survive, and feed on bolls. We have seen as much as 9% or more boll damage in some varieties which is 3 times our working threshold of 3% live worms/fresh boll damage.  But, that was in years when bollworm pressure was high.  In years like 2014 and 2015 when bollworm populations were very light, we saw essentially no boll damage in any of the varieties.  So what is the 2016 situation?  So far it looks like we may be looking at heavier pressure than last year, light to moderate depending on the field—but—we won’t know for sure for another few weeks—as the main flight out of field corn has not kicked in yet. The corn crop is generally a little behind and a little less mature than normal for this time of year because of later planting and good rainfall.

The best approach for managing bollworm in cotton is to scout fields for worms by inspecting small bolls, the terminals, and under flowers (boll tags) for live worms or damage. As mentioned, our current threshold is 3% of the fruit or positions inspected with either live worms or damage.

We have a history of bollworm resistance to pyrethroids in Virginia and this year is no exception. Of the 650 or so moths tested so far, we are seeing about 40+% survival. This is high. So for the best control results we suggest using a non-pyrethroid (e.g., Prevathon, Belt, Blackhawk, or Intrepid Edge). Note that Belt is not widely available this season due to the registration being canceled by EPA. Distributors and growers can use existing stocks according to label, but when that is gone, that will be it—at least as far as we know.

We also recommend adding a pyrethroid to the worm product to clean up any plant bugs/stink bugs that may be in the cotton. There are several pyrethroid options, and I would use the highest labelled rate for stink bugs—for better kill and longer residual. Besiege is the only product that contains both the non-pyrethroid (= Prevathon) with a pyrethroid (= Karate). With all the other non-pyrethroids, you will have to do the tank mixing on the farm. And, it is past time to include any of the insecticides in the neonicotinoid class as they do not provide good control of either bollworms or stink bugs.

Stakeholder input on Virginia’s State Pollinator Protection Plan

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The following advisory is posted on behalf of Dr. Hunter Frame:

I want everyone to check out this letter for stakeholder input on the pollinator protection plan that is being developed by VDACS. So for the cotton producers the nearest meeting will be on February 22 from 6-8 pm at the Tidewater Agricultural Research and Extension Center in Suffolk, VA. This is an important issue that needs to be discussed and solutions need to be developed so no tools for producers are lost and bees/beekeepers are able to thrive next to cotton and other crops! Look forward to seeing everyone there!

http://www.vdacs.virginia.gov/pdf/pollinatorprotectionplanletter.pdf

26th Annual Eastern Shore of Virginia Ag Conference & Trade Show

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The Eastern Shore of Virginia Ag Conference & Trade Show is on! We are snow free, and looking forward to a great event on January 26 and 27, 2016. The event will take place at the Eastern Shore Community College Workforce Development Center in Melfa, VA. The full program can be found at: http://issuu.com/esarec/docs/flipbookfinal/1. We have been approved for Certified Crop Adviser (CCA) CEU credits (details at: https://www.dropbox.com/s/f34f3spg4quni7a/CCA_Credits_Handout_2016.pdf?dl=0), Virginia Nutrient Management Credit (1 credit), and Virginia Pesticide Recertification credits (information in the program). See you there! Directions can be found at: http://es.vccs.edu/about/mapdirections/.ESCC

Bollworm treatments may be needed in Virginia cotton

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As of last week, we found bollworm eggs in cotton fields in numbers high enough to indicate that fields may need to be treated. The bollworm (= corn earworm) moth flight from corn is light and spotty, but it does not take many moths to cause concern in cotton.

In the old days before Bt cotton, we relied on the two spray system to control bollworms—the first spray applied at egg threshold followed by an automatic second spray 5 to 7 days later. This system worked very well to protect cotton from economic levels of boll damage.

With the advent of Bt cotton varieties (now TwinLink, BG2 and WideStrike) we found that even with these technologies, there were enough worm escapes (worms not killed by feeding on the plant toxins) to warrant a single insecticide spray. And—we determined that the best time for that single worm spray coincided with the second of the original two spray system—i.e., 5 to 7 days after the egg threshold.

Egg thresholds were found towards the end of last week in fields near the Tidewater AREC. The same is likely happening in fields across the region. So now is the time for applying a bollworm treatment. Based on our history of bollworm resistance to pyrethroids, the best control results will be obtained using a non-pyrethroid (e.g., Steward, Belt, Prevathon, Blackhawk). But we also recommend adding a pyrethroid to clean up any stink bugs that may be in the cotton. There are several pyrethroid options, and I would use the highest labelled rate for stink bugs—better kill and longer residual. Besiege is the only product that contains both the non-pyrethroid (= Prevathon) with a pyrethroid (= Karate). With all the other non-pyrethroids, you will have to do the tank mixing on the farm. And, it is past time to include any of the insecticides from the neonicotinoid class as they do not provide good control of either bollworms or stink bugs.

Black flag seen in some Virginia cotton fields

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As you may have heard, reports out of northeastern North Carolina are talking about infestations of plant bugs (Lygus) causing a symptom called “black flag” by feeding on presquare cotton.  This is very rare in US cotton.  This symptom is termed “black flag” due to the death and blackened appearance of the expanding terminal leaves.  The danger is creating “crazy cotton”, which is loss of apical dominance, causing multiple terminals per plant, delayed squaring, or yield loss.  Terminals can be destroyed from only 20 minutes of feeding.

But it is important to remember that given good conditions, cotton can recover later in the season without yield loss.  We did research earlier in Virginia that showed that even this far north, cotton can easily compensate from removal of squares—even up to 20 percent—so this black flag injury may not be as big a threat as you may be thinking it is.

The plant bugs that are causing this problem are from a generation that developed on weeds and is moving through the system.  It is important to keep in mind that plant bug infestations are very erratic. Some fields may be infested, or even some areas within a field—but not every field. We and others have checked a lot of cotton fields in Virginia and are finding just a few with very limited amounts of black flag.

We don’t want to overreact to this and spray all of our cotton just because we have seen this problem in a few plants in one area. If you do see these symptoms you should use a sweep net to see if plant bugs are still present (see recommendations below). Overreacting could certainly help flair other problems as well as waste money if plant bugs are not present at damaging levels.

Management on presquare cotton (borrowed from NCSU)

1.  Use a sweep net to make 25 sweep samples and count the adults.  Realize that bug numbers will be higher in field edges, so move around.  A sample of 25 sweeps per location (one set of 25 “swooshes”) should be adequate.

2.  Where you sweep, look for black flag, wilted leaves, or injured terminals.  If you see this injury, and have plant bugs present, spray if the number of injured terminals is greater than 1 plant in 10 feet of row (borrowed from Mississippi State).  If you do decide to spray, use a neonicotinoid at the highest labeled rate at this point in the season.  They tend to be less effective as the season goes on, but should do the trick, while preserving some beneficials.  Examples include Admire Pro, Belay and Centric. DO NOT use an organophosphate or pyrethroid this early in the season.  These will kill the beneficials and could help flare spider mites and/or aphids. We are seeing some of both in a few fields so the risk of flaring these pests is pretty high—and would be very costly.

3.  Monitor the situation after the spray.  A visit and sweeping 24 hours following the spray should give you a good idea of knockdown.  Since you’ve swept and know the plant bug numbers prespray, another good visit would be 4-5 days later.  See if plant bugs have migrated in again and if the terminal injury is holding steady or increasing.

4.  Once the plants start squaring, you need to use a threshold that incorporates plant bug numbers with square retention measurements.  You can find scouting recommendations and the threshold for squaring cotton in the Virginia Cotton Production Guide, http://www.pubs.ext.vt.edu/AREC/AREC-124/AREC-124.html.