Category Archives: Pest Group

Insect update for July 20, 2017

This week, our black light trap operators reported a range of zero to 8.5 corn earworm/bollworm moths per night and zero to 2.7 brown marmorated stink bugs per night. The tables are in this pdf file: BLT_20_Jul_2017

The corn earworm/bollworm pyrethroid resistance monitoring program is averaging about 36% moth survival. These are pheromone trap-collected moths from Suffolk, Virginia. The pyrethroid is cypermethrin at 5 micrograms per vial.

Virginia Cooperative Extension ANR Agents, Virginia Tech personnel, interns, and others have started our annual field corn survey for corn earworm/bollworm larvae. It can be an indicator of the pressure that we’ll see in other crops (e.g., soybean) when the moths emerge and fly out of corn fields. We’ll have a full report in the beginning of August (including data from many more counties), but here are the average ear infestations from those surveys already completed (based on sampling 50 ears per field, 5 fields per county): Accomack=29%; Henrico=37%; Southampton=53%; Amelia=18%; Westmoreland=6%.

 

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.

Insect report for July 13, 2017

Virginia Cooperative Extension ANR Agents and Virginia Tech faculty/staff have started up their black light traps to monitor corn earworm moths (aka bollworm) and brown marmorated stink bugs for the season. CEW and BMSB catches have been low in the black light traps; however, our pheromone traps in Suffolk, VA are catching moderate numbers of CEW moths–averaging about 5 per night. We tend to pick up more CEW moths in the pheromone than in the black light traps during this time of year. Dr. Taylor’s cypermethrin vial tests are showing about 35% of CEW moths surviving the 5 microgram rate (the moths were collected from the Suffolk pheromone traps). Watson Lawrence reported 26 brown stink bugs in his Chesapeake black light trap this week.

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!

Herbicide Resistant Common Ragweed Plot Tour

Having trouble controlling herbicide resistant common ragweed? Make plans to attend the field tour, this coming Thursday (June 22nd, 2017) near Lawrenceville, Virginia. Complete information is below. Please RSVP as soon as possible.

View a complete spectrum of preemergence and postemergence herbicides in soybeans in the field to see what works best for yourself. Also, learn about integrated weed management approaches that work within our cropping systems. 

Potato Late Blight in North Carolina

The following advisory is posted on behalf of Dr. Steve Rideout:

Late blight was found on potato in Camden and Pasquotank counties in North Carolina over the weekend. We will be processing the samples to determine more information on race/fungicide sensitivity. In the meantime, growers are encouraged to scout their tomato and potato fields for the disease.  Preventative fungicide applications are recommended, particularly near the outbreak area in NC.

If you have questions please let us know.  You can access current recommended materials for late blight in the commercial and homeowner vegetable production guides.  Also, you can visit the following web page for more information on this disease:

https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ANR/ANR-6/ANR-6_pdf.pdf

This is a serious threat to potato and tomato production in the Commonwealth.  Please let us know if we can help.

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.

Failed Corn Stand: Starting Over

Charlie Cahoon and Michael Flessner

Virginia Tech Weed Science

Over the past few days we have had several questions concerning replanting corn behind an already failed corn stand.  Our biggest concern in this situation is how to terminate emerged corn from the first planting.  The best option for small corn (4-8 inch) is clethodim (Select Max or generics).  The label for Select Max (0.97 lb active ingredient/gal) specifies 6 oz/A must be applied at least 6 day prior to replanting.  Clethodim products that contain 2 lb active ingredient/gal and are labeled for this situation should be applied at 3 oz/A, while adhering to the same plant-back restriction.  As is the case with many weeds, timeliness is critical.  Control of larger corn by clethodim is variable (> 8 inches).

Poor corn stand as a result of bird damage. Painter, VA 2017.

Producers not wanting to wait 6 days before replanting should use paraquat (at least 3 pt/A of a 2 lb/gal product or 2 pt/A of a 3 lb/gal product).  Paraquat should not be used alone; adding atrazine (1 pt/A) and suggested adjuvants to paraquat will enhance control.  Research conducted by Dr. Kevin Bradley (University of Missouri) and Larry Steckel (University of Tennessee) concluded Liberty did not consistently control Roundup Ready corn.  Although not listed on the bag, many corn hybrids are tolerant to glufosinate (active ingredient in Liberty).  For these reasons, producers should be wary of using Liberty to terminate a failed corn stand.

Another common question when replanting corn is whether to reapply residual herbicides such as atrazine. Atrazine and other residual herbicides should not be reapplied. If additional atrazine is desired in a postemergence application, just note that the cumulative total atrazine for your first and second planting of corn cannot exceed 2.5 lb active ingredient per acre per year.  Other products have similar restrictions.

On a normal year, growers are usually asking if soybean can be planted behind corn.  And our answer to this is usually no.  This is mostly due to the fact that most everyone uses atrazine preemergence and planting soybean following atrazine if very risky.  The label of most atrazine products says “Do not rotate to any crop except corn or sorghum until the following year, or injury may occur” and “If applied after June 10, do not rotate with crops other than corn or sorghum the next year, or crop injury may occur”.

 

Wheat Disease Update – May 2, 2017

Following last week’s rain, the risk for Fusarium head blight (FHB or scab) infections has increased, and the risk is very high even for moderately resistant varieties in certain portions of the state (see FHB Risk Map). Much of the wheat crop is beyond the early flowering stage, but for fields where wheat is currently flowering a fungicide may be needed to protect the crop from FHB infection and DON contamination. Recommended fungicides include Caramba, Prosaro, and Proline. Fungicides are most effective when applied at the start of flowering and up to a week later. The greatest coverage of the heads can be achieved by applying fungicides in 5 gal/A by air and 15 gal/A by ground with a 300-350 um droplet size and nozzles angled forward at least 30 degrees.

FHB risk on May 2, 2017 for moderately resistant wheat varieties. Susceptible wheat varieties that are currently flowering are at high risk for FHB infection throughout Virginia.