Due to impending rain Tuesday and Wednesday and already saturated soils, the Eastern Shore AREC field day scheduled for Wednesday, September 13, 2017 has been canceled. Let’s hope Hurricane Irma keeps tracking further west. We certainly do not need any more rain!
Please join us for Virginia Tech’s Eastern Shore Agricultural Research and Extension Center (ESAREC) 2017 Research Field Day on Wednesday, September 13th. Registration is free, open to the public and will begin at 8:00 AM at the ESAREC complex located at 33446 Research Drive, Painter, Virginia 23420. The field tour will begin at 9:00 AM and conclude with lunch at 12:30 PM. See the attached flyer for specific projects to be highlighted and more information.
If you would like more information or are interested in sponsoring this event, please contact Lauren Seltzer at 757-414-0724 ext. 11 or email at firstname.lastname@example.org.
Twenty-three representative cotton fields in eight Virginia counties were scouted weekly for mean plant bug density. Data for the July 17th to August 3rd sampling period is represented in the distribution map below (follow link to view). Red dots on the map represent fields that have averaged at or above the spray threshold for plant bug during the sampling period. Plant bug densities for multiple fields has increased substantially since the last update in mid-July. Nineteen of the 23 sampled fields have reached the spray threshold at least once this season since sampling began in late-June. Plant bugs are present in every county sampled and are likely present in at least low numbers in all cotton growing counties in the state. Therefore, we recommend scouting your cotton fields regularly for plant bug.
The spray threshold for plant bug in Mid-Atlantic cotton is eight plant bugs (i.e., adults and nymphs) per 100 sweeps in addition to square retention below 80 percent. We recommend conducting four to eight random 25-sweep samples throughout each field. Once flowering begins, we recommend continuing sweep net sampling and also looking for dirty blooms (pictured below) or sample dime to quarter size-bolls from 25 random plants for internal feeding damage (e.g., warts, stained lint, punctures). Spray treatment may be warranted if dirty blooms and or internal damage exceeds 15 percent and plant bugs are also active in the field. Please refer to the Virginia Cotton Production Guide (pg. 23) or Pest Management Guide (sect. 4, pg. 88) for spray recommendations if spray threshold is reached.
When viewing the distribution map in full-screen mode, click on the left arrow icon to view map legend. Click on individual fields represented by colored dots on the map to view mean plant bug density for the sampling period as well as total mean density for the season. 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.
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.
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.
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||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|
|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 – 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|
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 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.
More updates on plant bug activity throughout Virginia’s cotton regions will be posted soon!
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 email@example.com 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.
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.
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%.
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.
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.
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.
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.
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.
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.
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.