Category Archives: Cotton

Plant Bug Distribution Map

Twenty-three representative cotton fields in eight Virginia counties were scouted weekly for plant bug abundance and square retention. Data for the June 28th through July 13th sampling period is represented in the distribution map below (follow link to view). We will continue to post updates to the map through peak plant bug abundance in cotton. Sweep net and drop cloth samples were taken for each field to account for sampling bias associated with sweep net sampling towards adult captures and drop cloth sampling towards nymphal captures. When sampling cotton fields for plant bugs, look carefully for nymphs (pictured below). Since nymphs are flightless, they may spend more time feeding in an isolated area and cause more damage than adults because their movement in and out of fields is limited. The action threshold for plant bug in Mid-Atlantic cotton is generally eight plant bugs (i.e., adults and nymphs) per 100 sweeps in addition to square retention below 80 percent.

Plant bug nymph feeding on weedy host, buckhorn plantain (Plantago lanceolata).

When viewing the distribution map in full-screen mode, click on the left arrow icon to view map legend. Click on sampling labels on the map to view square retention and number of samples taken from each site. Mean plant bug densities were calculated by sampling four sweet net samples (25 sweeps per sample) and four drop cloth samples across each field. Total adults and nymphs in a single visit were totaled and averaged for each visit within the sampling period.

Click here to view full-screen distribution map

Plant bug distribution map in Virginia cotton sampled from 28 June to 13 July 2017.

Corn earworm and fall armyworm trap catch numbers in Virginia – Week of July 10, 2017

 

Corn earworm larva in sweet corn.

Corn earworm and fall armyworm are two important pests of a number of agricultural crops in Virginia.  Sweet corn, in particular, is extremely vulnerable to attack by the larvae (or caterpillars) of these moth pests.  Monitoring moth catch numbers in pheromone-baited traps can help IPM decision-making.  See at the end of this post the Action threshold for spraying insecticides on sweet corn based on corn earworm trap catch.  In general trap catch less than 1 per night means relatively low pest pressure and sprays can probably be spaced 5-6 days apart during silking.  However, a catch of >1 or >13 moths per night means moderate and high pest pressure, respectively and a more frequent spray interval is justified.

In 2017, we are monitoring these pests on sweet corn farms in 11 different counties in Virginia.  Moth Trap Catch Data are being recorded by:  Katlyn Catron & John Few (Montgomery Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Helene Doughty (Virginia Beach); Kenner Love (Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk  (Westmoreland Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.)

Here are the trap catch results (moths per night) for several locations around Virginia for this week (note we do not have data for all locations):

Region County Field CEW  moths/night FAW moths/night
Eastern Shore Accomack ESAREC 1.1 0
Eastern Shore Virginia Beach Pungo 1 1.6 0
Eastern Shore Virginia Beach Pungo 2 3.9 0
Eastern Shore Northampton Bridge Tunnel 6.6 0
Eastern Shore Northampton Capeville 1 3.6 0
Eastern Shore Northampton Capeville 2 0.0 0
Eastern Shore Northampton Eastville 0.6 0
Eastern Shore Northampton Nassawaddox 1.0 0
Piedmont Amelia Field 1 2.7 0
Piedmont Hanover Field 1 2.1 0
Piedmont Hanover Field 2 1.0 0
Northern Neck Westmoreland Field 1 3.0 0
Shenandoah Valley Rappahannock Field 1 1.0 0
Shenandoah Valley Frederick Field 1 2.3 0
Shenandoah Valley Frederick Field 2 3.5 0
New River Valley Montgomery Whitethorne 1.9 0
New River Valley Montgomery Wall field corn 1.1 0
New River Valley Montgomery Wall sweet corn 20.8 0

 

Action threshold: Number of Corn Earworm Moths Caught in Pheromone trap
Per Day Per 5 Days Per Week Spray Interval for sweet corn
<0.2 <1 <1.4 No Spray
0.2 – 0.5 1.0 – 2.5 1.4 – 3.5 6 Day
0.5 – 1.0 2.5 – 5.0 3.5 – 7.0 5 Day
1.0 – 13.0 5.0 – 65.0 7.0 – 91.0 4 Day
>13.0 >65.0 >91.0 3 Day

 

 

Tarnished Plant Bug Update

My name is Seth Dorman, and I’m a graduate student with Dr. Sally Taylor in the Virginia Tech Department of Entomology. My research focuses on tarnished plant bug (Lygus lineolaris) management and distribution in Virginia cotton. In recent weeks, large numbers of tarnished plant bug have been active throughout southeastern Virginia in fallow fields and ditch banks with an abundance of flowering, weedy hosts as well as in corn. Plant bugs have begun migrating into some early-planted cotton fields and were observed in cotton fields in Suffolk and Southampton counties last week.

Tarnished plant bug feeding on weedy host, daisy fleabane (Erigeron annuus).

Tarnished plant bug may move from preferred alternative hosts into cotton fields as flowering weeds senesce, and cotton plants begin to develop small, pinhead squares and subsequent flowers. Feeding during early squaring can cause plants to abort squares. Feeding on larger squares and small bolls may cause anthers in flowers to turn brown (“dirty bloom”), and small bolls to shed. Sustained feeding by tarnished plant bug from first square to early bloom can delay maturity and result in substantial losses. Scouting cotton fields once or twice a week is highly recommended after squares become visible on plants. The best indirect method for sampling plant bug is estimating square retention. Square retention can be measured by calculating the percentage of squares in the top two or three nodes of 25 randomly selected plants in a given field. If square retention drops below 80%, direct sampling for plant bugs with a sweep net is recommended. For sweep net sampling, conduct a minimum of eight 25-sweep samples randomly throughout your cotton field. We recommend using Admire Pro or other neonicotinoid products until bloom. Adult plant bugs can reinfest quickly following applications. Use restraint when treating early in the season when plants have time to compensate for injury.

Scar of an aborted square at the fruiting site on a cotton plant.

More updates on plant bug activity throughout Virginia’s cotton regions will be posted soon!

Save the date: Virginia/Northeastern North Carolina Cotton Field Day on July 20, 2017

You are invited to attend our cotton field day at the Virginia Tech Tidewater AREC on Thursday, July 20, 2017. The tour will begin promptly at 8:00 am, ending with lunch. The location is our research farm at 1045 Hare Road, Suffolk, VA. The event is free and open to the public, but pre-registration is required–please contact Gail White by phone at 757-657-6450 extension 430, or by email at guwhite@vt.edu by July 10th. Private Pesticide recertification credits (cat. 90, 91) are being offered. More information will be made available in the upcoming weeks. Thank you.

Warrant and Cool, Wet Soils

Charlie Cahoon

Extension Weed Specialist, Virginia Tech

Warrant is an encapsulated formulation of the herbicide acetochlor and has widely become a part of our postemergence (POST) herbicide program in cotton.  Although Warrant does not control emerged weeds, it does provide excellent residual control of pigweed, other small seeded broadleaves, and annual grasses (with the exception of Texas panicum).  This makes it an excellent tank mix partner for glyphosate (Roundup) or glufosinate (Liberty) in our first, second, or both POST sprays, especially in fields heavily infested with glyphosate-resistant Palmer amaranth.  However, because of its encapsulated formulation, Warrant can also be applied preemergence (PRE) to cotton.  You may remember the days of using the EC formulation of acetochlor, known as Harness, in corn.  This formulation was not encapsulated and significant injury would result if applied PRE or POST to cotton.  This is not the case with Warrant.  The encapsulated version affords much more cotton safety that the old EC formulation.  In my experience, PRE applied Warrant has been very safe on cotton.  As is the case with all residual herbicides, environmental conditions influence cotton response to PRE applied Warrant.  Unfortunately, conditions we are currently experiencing in Virginia and northeast North Carolina; cool, wet soils and overall less than ideal weather for planting cotton are conducive to Warrant injury.

I saw this in my on research trials during the spring of 2016.  Our cotton planted at the Tidewater AREC (near Holland, VA) on May 15, 2016 took approximately 9 days to emerge whereas cotton planted May 26, 2016 emerged in roughly 5 days.  The weather was mostly to blame for the differences in vigor of the two plantings, but Warrant compounded the problem.  So why the difference?  We all know that cotton planted into cool wet soils is slow to emerge.  Cotton tolerance to Warrant all hinges on the breakdown of the tiny capsules used to encapsulate acetochlor versus the time it takes for cotton to emerge.  The key to avoiding injury from PRE applied Warrant is for cotton to emerge prior to the majority of these capsules breaking down and subsequent release of acetochlor.

Nontreated check plot.

Under ideal planting conditions this is not an issue.  On the other hand, if cotton is slow to emerge, giving the capsules more time to breakdown and the seedlings have to push through a higher concentration of acetochlor, the potential for injury is greater.  This is exactly what I saw in 2016 and have heard complaints about in years prior.  Cotton that laid in the ground longer than usual and received Warrant PRE was stunted about 25%.

Weed control by Warrant alone.

My cotton eventually recovered and by the end of the season no yield differences were observed.  Cotton that emerged quickly showed no injury in response to PRE applied Warrant and was one of the safest and cleanest treatments.

Weed control by Warrant plus 10 oz/A Reflex.

I routinely recommend Warrant PRE especially where Palmer pigweed is a problem.  The fact is that all of our residual herbicides are capable of injuring cotton if the weather does not cooperate.  As the planting progresses, I would advise you to factor in the planting conditions when choosing your PRE herbicides.  Any conditions delaying emergence of cotton is conducive to injury from Warrant PRE.  With that said, it may be wise to leave Warrant out of the tank until planting conditions improve.  Do not let this stop you from using a residual herbicide all together.  Alternatives to Warrant include Cotoran, Direx, Prowl, Reflex, and fluridone containing products (Brake FX and Brake F16).  With all the herbicide resistance issues knocking on our door, it is imperative that we continue to use residual herbicides early burndown, around planting, and in-season.  Once cotton land dries out and soil temperatures rise, Warrant will again be one of our best residual options.

Cotoran in Short Supply; What Are My Options for Ragweed?

Alan York, NC State Extension Weed Specialist

Charlie Cahoon, Virginia Tech Extension Weed Specialist

In the past few days, several people have told us that Cotoran is unavailable.  Naturally, the conversation turned to alternatives.

Cotoran was once used almost universally on cotton.  Prior to the mid-90’s, we basically told growers to buy the Cotoran first, and then buy the cotton seed.  We felt Cotoran was that important.  But, things have obviously changed in the past two decades, primarily because of Roundup Ready and LibertyLink.  And, we have some additional PRE (preemergence) herbicides today.  Although some growers still like and use Cotoran, the percentage of acres receiving Cotoran has decreased substantially.

A shortage of Cotoran is probably nothing to be highly concerned about.  For most growers, glyphosate-resistant Palmer amaranth is the driver weed.  And, frankly, Cotoran is not our best PRE herbicide for Palmer amaranth.  However, in northeastern North Carolina and Virginia, glyphosate-resistant common ragweed is often more problematic than Palmer amaranth.   And, as we have been saying in winter grower meetings, Cotoran is the material of choice for PRE ragweed control.

In the absence of Cotoran, what are the alternatives where common ragweed is an issue?  Prowl, Staple, and Warrant have little to no activity on ragweed (see table below).   Brake F16, Direx, and Reflex, on the other hand, may not be quite as effective on ragweed as Cotoran, but they should still provide good control.  And, a mixture of Direx plus Reflex should be as good as Cotoran on ragweed.  Brake F16 contains a mixture of fluridone plus the active ingredient in Reflex.  Brake FX contains a mixture of fluridone plus the active ingredient in Cotoran.  Brake FX is registered for sale in Virginia and North Carolina although Brake F16 seems to be the material being most promoted by the manufacturer.  Brake FX should do a very good job on ragweed.

Poor common ragweed control by Caparol. Painter, VA 2016.

We had a trial in 2016 at a site heavily infested with common ragweed.  The weatherman cooperated, and we could not have asked for better herbicide activation.  Nevertheless, we had essentially complete ragweed control with Brake F16 and with combinations of Reflex + Direx, Reflex + Warrant, Direx + Warrant, and Direx + Staple.  Knowing that Staple and Warrant are poor on ragweed, that leads us to believe that either Direx or Reflex would be good alternatives to Cotoran.  If used alone, we suggest 1 pint of Reflex or 1.5 pints of Direx.  If tank mixed, we would suggest 1 pint of Direx plus 12 to 16 ounces of Reflex.

Good common ragweed control by 1 pint/A Reflex. In the absence of Cotoran, Direx plus Reflex would be a wise choice for common ragweed control while also delaying PPO-resistance. Painter, VA 2016.

In this age of herbicide resistance, we routinely recommend at least two herbicides (two mechanisms of action) applied PRE.  The exception is high organic matter soils where Warrant, and to a lesser extent Staple, are the only products that work.  For mineral soils, and especially where Palmer amaranth is a problem, we will continue to recommend two or three mechanisms of action PRE.  The goal is to hopefully prevent resistance to our PRE herbicides, especially Reflex, and to improve overall control.

Reflex is one of many PPO inhibitors being used in multiple crops.  You have probably read in the farm press about the issues they are having in the Mid-South with PPO-resistant Palmer amaranth.  At least some of their populations are resistant to PPO inhibitors applied PRE or POST.  Obviously, we want to avoid that or at least delay its occurrence as long as possible in our area.  To do that, we need multiple mechanisms of action PRE followed by an effective POST program.

Table 1. Weed response to preemergence cotton herbicides

So, what does that have to do with common ragweed?  A ragweed population on the Virginia/North Carolina border has been confirmed as having multiple resistance to glyphosate, ALS inhibitors, and POST-applied PPO inhibitors.  Brandon Schrage, a graduate student at NC State, is in the process of determining if that population is also resistant to PPO inhibitors applied PRE.  Preliminary findings suggest it is.  That should encourage us to use a tank mix of Direx + Reflex if common ragweed is our problem.

After the PRE application, we can control glyphosate-resistant ragweed escapes with timely applications of Liberty, XtendiMax or Engenia (XtendFlex cotton only), or Enlist Duo (Enlist cotton only).  Envoke is also an option unless you expect ALS resistance.

 

Scout now for marestail/horseweed

Recent mild temperatures and the mild winter are setting the stage for rapid development of marestail/horseweed (Conyza canadensis) this spring.  Marestail was particularly troublesome last year in soybeans.  Marestail can germinate in both the fall and the spring. It is more likely to overwinter in the rosette stage during mild winters.  If you wait until your typical burndown the marestail may start bolting and therefore be more difficult to control. Adding to this difficulty, many marestail populations are resistant to Roundup (and other glyphosate containing products). You should scout your fields targeted for soybeans now to identify overwintering marestail.  Marestail control can be achieved with 2,4-D  or dicamba now and still offer plenty of time to avoid plant back restrictions (up to 15 days for 2,4-D or up to 28 days for dicamba). Glyphosate resistant weeds and the difficulty in controlling more mature weeds underscore the need to scout fields earlier and use some alternative herbicides in your program.  Always consult the product label for specific instructions.

Virginia Cooperative Extension logo

Virginia Eastern Shore Ag Conference and Trade Show

Join us in Melfa, VA for the 27th Annual Eastern Shore Agricultural Conference and Trade Show on January 25-26, 2017. This event is free, open to the public, and will be held at the Eastern Shore Community College Workforce Development Center. We will offer Virginia Pesticide Recertification credits for categories 1A, 10, 60, and 90. We will also offer Certified Crop Adviser Credits for nutrient management (2), soil and water (1), integrated pest management (4.5), crop management (6), and professional development (0.5). Click on the following link for topic areas being presented: ag-conf-press-release-2017

Dicamba Registered for Cotton and Soybean

Last week Monsanto received EPA registration for XtendiMax with Vapor Grip Technology for use on XtendFlex cotton and Roundup Ready 2 Xtend soybean.  Attached is an article authored by Dr. Alan York at NC State pertaining specifically to cotton.  I share Dr. York’s sentiments concerning this technology and will echo these same points at winter meetings.

york-dicamba-article

 

Cotton insect pest update—bollworms are here.

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.