Author Archives: Thomas Kuhar

About Thomas Kuhar

Professor and VCE-Vegetable Entomology Specialist Department of Entomology Virginia Tech Blacksburg, VA

Corn earworm pressure and recommendations for sweet corn in Virginia

OLYMPUS DIGITAL CAMERA

Corn earworm larva in mature sweet corn ear.

Corn earworm is the major pest attacking corn ears in the mid-Atlantic U.S. Moth activity has been high in some areas of Virginia such as the Eastern Shore based on pheromone trap catches and grower reports in fields. Sweet corn is one of the most preferred host plants for corn earworm, especially if fresh silks are available when female moths are ovipositing.

For control in sweet corn, it is recommended to begin treatment when the ear shanks emerge or the very first silks appear. Silk sprays should continue on a schedule based on pest pressure on the farm or area blacklight or pheromone trap counts, geographical location, and time of year. This time of year (August) it may be necessary to treat on a 2-3 day schedule.

Dr. Sally Taylor (Tidewater AREC) and I have seen increased levels of pyrethroid (insecticide class 3A) resistance in CEW populations throughout Virginia, and that these insecticides should be used with caution and rotated to other insecticide classes within a season.  See the list of recommended insecticides in the table.

During heavy populations and high temperatures, treatments will need to be made according to the legal “days to harvest” of the chemical. For best control during heavy infestations, maximize the gallonage of water per acre, use a wetting agent, and make applications during the early morning if possible. If irrigation or rains wash off the spray within 24 hrs after an application, repeat treatment as soon as the foliage dries.

 
Group Product Name Product Rate   Active Ingredient(s) (*=Restricted Use) PHI (d) REI (h) Bee TR
3A Lambda-Cy, LambdaT 1.92 to 3.84 fl oz/A lambda-cyhalothrin* 7 12 H
3A Mustang Maxx 2.24 to 4.0 fl oz/A zeta-cypermethrin* 1 12 H
3A Perm-UP 3.2EC 4.0 to 8.0 fl oz/A permethrin* 1 12 H
3A Tombstone 2EC 0.8 to 2.8 fl oz/A cyfluthrin* 0 12 H
3A Warrior II 1.28 to 1.92 fl oz/A lambda-cyhalothrin* 7 12 H
3A Asana XL 5.8 to 9.6 fl oz/A esfenvalerate* 3 12 H
3A Baythroid XL 0.8 to 2.8 fl oz/A beta-cyfluthrin* 0 12 H
3A Bifenture 2EC, Sniper 2.1 to 6.4 fl oz/A bifenthrin* 3 12 H
3A Hero EC 4.0 to 10.3 fl oz/A zeta-cypermethrin* + bifenthrin* 3 12 H
1A Lannate LV 1.0 to 1.5 pt/A methomyl* See label 48 H
5 Blackhawk 36WG 2.2 to 3.3 oz/A spinosad 1 4 M
5 Radiant SC 3.0 to 6.0 fl oz/A spinetoram 1 4 H
28 Coragen 1.67SC 3.5 to 7.5 fl oz/A chlorantraniliprole 1 4 L
Combo products containing a pyrethroid 3A          
Cobalt Advanced 11.0 to 42.0 fl oz/A lambda-cyhalothrin* + chlorpyrifos* (Group 1B) 21 24 H
Besiege 6.0 to 10.0 fl oz/A lambda-cyhalothrin*+chlorantraniliprole (Group 28) 7 12 H

Bt Transgenic Sweet Corn

Bacillus thuringiensis (Bt) sweet corn hybrids are available that express single or pyramided insecticidal proteins for protection against lepidopteran “worm” pests. Attribute® hybrids (Syngenta Seeds) expressing the cry1Ab protein (YieldGard trait) have been available since 1998, and these hybrids now express the Liberty Link herbicide tolerance trait. Performance Series™ hybrids (Seminis Seeds) expressing two Bt proteins (cry1A.105 and cy2Ab2) are also available and these have the RoundupReady gene as well. However, based on multiple years of field trials in Virginia and surrounding states, neither of these Bt traits/varieties provide effective control of CEW due to Bt resistance development to the Cry proteins.  Thus, fields planted in these Bt hybrids will need insecticide applications, depending on the insect pressure and level of resistance in the population. In addition, under moderate to high moth activity (early August-early September), many eggs are laid later in ear development after the expressed Bt protein has degraded in dead silk tissue. This loss of protein activity also is accelerated by hot, dry conditions, which cause rapid desiccation of the silk tissue. As a result, earworms and fall armyworms have a greater chance of surviving and invading the ear. Under high moth activity, up to 50% or more of the Attribute ears can become infested with larvae. In this situation, spray schedules of 3 or 4 applications starting 3-4 days after the first onset of silking and repeated 3-4 days apart may be required.

Attribute® II Bt corn hybrids (Syngenta Seeds) with pyramided genes expressing YieldGard and Viptera traits (Vip3A protein) and stacked with the Liberty Link trait are now available. This Bt pyramided gene technology currently provides outstanding nearly 100% control of all lepidopteran pests of sweet corn.

Fall armyworm outbreak in southwest Virginia – and management recommendations

Prepared By: Tom Kuhar, Adam Formella (Entomology graduate student), and Sally Taylor (TAREC)

Fall armyworm larva.

Over the past two weeks fall armyworm outbreaks have occurred in southwest Virginia with reports from Abingdon to Roanoke, VA in turfgrass and small grain crops. Some new plantings of rye have been completely destroyed and densities of armyworms have exceeded 10 per square foot in some areas.

Fall armyworm (Spodoptera frugiperda) is a tropical moth native to warm climate areas of the western hemisphere. It cannot successfully overwinter in Virginia. However, this armyworm moth (see Fig. 9) is a strong flier, and populations can migrate throughout the eastern United States in the late summer and fall months, sometimes in very high populations like what recently occurred in southwest Virginia. Phil Blevins (VCE ANR Agent in Washington Co.) was monitoring a fall armyworm bucket trap for us in sweet corn in Abingdon, VA, and 2-3 weeks ago detected a huge jump in moth catch.  This was a harbinger of things to come.  Female FAW moths can lay up to 10 egg masses (each with 100 – 200 eggs) (see Figs 1-2). So, it’s no surprise how quickly the densities of armyworms can build up from just a few egg laying moths in a field.
Fall armyworm can feed on a number of different host plants, but prefers grasses, small grains, corn, and sorghum.  Turfgrass has been particularly hit hard by this pest this week around the New River Valley.  In turf, FAW larvae can consume all above-ground plant matter causing noticeable damage and bare spots.  This can happen quickly.

Control
Insecticides recommended for control include most pyrethroids (such as bifenthrin, lambda-cyhalothrin, Mustang Max, Baythroid XL, etc..), Lannate LV, and many of the more selective (lepidopteran-targeting) insecticides such as the diamide Prevathon, Coragen, Acelepryn, Besiege), indoxacarb products like Steward, Avaunt eVo, Provaunt, spinosad (Blackhawk, Tracer, Matchpoint), Radiant, Intrepid Edge, as well others. Consult the relevant Pest management Guide for specific recommendations on the various commodities. Please note that control of large larvae is sometimes difficult with any insecticide. Link to the VCE Pest Management Guides for Field Crops, Vegetables, and Turf are provided below.

Links to Pest Management Guides
Turf:
http://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-017/turf.pdf
Field Crops:
https://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-016/insects.pdf
Vegetables:
https://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/AREC/AREC-66/AREC-234.pdf
https://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-420/456-420.pdf

Sources
http://entnemdept.ufl.edu/creatures/field/fall_armyworm.htm
Luginbill P. 1928. The fall armyworm. USDA Tech. Bull. No. 34.

 

Some late season activity by corn earworm and fall armyworm in parts of Virginia

Although most of our sweet corn has been harvested for 2018, there are still some late-planted fields that may still be at risk to insect attack.  While most of the remaining pheromone traps around the state had low catch numbers, Mark Sutphin VCE Frederick County saw a great jump in corn earworm catch this week at one of the farms still growing sweet corn.  Keep in mind that corn earworm is also a pest of many other crops that may still be at risk this fall including tomatoes and beans (See images below).

Please keep in mind, In an effort to fend off any more pyrethroid insecticide resistance development in our corn earworm populations, rotating to another insecticide than a Class 3 (pyrethroid) is highly encouraged for at least one spray. Diamide insecticides such as Coragen or Besiege, the carbamate Lannate LV, or the spinosyn Blackhawk, are all effective non-pyrethroid options.

Also, Phil Blevins VCE Washington County reported some of the highest fall armyworm catch of the year >200 moths in the bucket trap this week.  These moths showed up late to southwest Virginia and are probably not going to be much of a pest concern in the state, and they will not successfully overwinter here as they are a tropical moth.

Fig. 1. Corn earworm damage to snap bean pods.

Fig. 2. Corn earworm (=tomato fruitworm) damage to tomato fruit.

 

 

Sweet Corn IPM Moth Trapping in Virginia – Week Ending September 7, 2018

This will be final trap catch alert of the year for the sweet corn IPM program as most corn has been harvested. I want to thank all of the VCE Extension folks who monitored traps on farms in their respective counties this year: Phil Blevins (Washington Co.); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Helene Doughty (Eastern Shore AREC Entomologist, Accomack Co.); Roy Flanagan (VA Beach); Bob Jones (Charlotte Co.); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.).
Click on the table below to view the trap catch results (moths per night) for some of the locations around Virginia for this final week. We will send out a synopsis of the season this winter. We are still seeing some high corn earworm moth activity on the Eastern Shore of Virginia, Westmoreland County on the Northern Neck, and Frederick County in the northwestern portion of our state. With the hot weather that we’ve experienced the past 2 weeks, moth activity has probably been a little higher than usual for September. Sweet corn growers are advised to keep control measures (spray intervals) as they were during August in most counties.
We still have caught very few fall armyworm moths in our traps around Virginia; however, this insect could contribute to some infestations in the ears of late corn. In an effort to fend off any more pyrethroid insecticide resistance development in our corn earworm populations, rotating to another insecticide than a Class 3 (pyrethroid) is highly encouraged for at least one spray. Diamide insecticides such as Coragen or Besiege, the carbamate Lannate LV, or the spinosyn Blackhawk, are all effective non-pyrethroid options.

Corn earworm average moth catch per night at farms around Virginia for week ending September 7, 2018.

Fall armyworm larva.

Sweet Corn IPM Moth Trapping in Virginia – Week Ending August 24, 2018

Corn earworm moth catch data from sweet corn farms in Virginia can be found in the table below. In summary, corn earworm moth activity increased dramatically this week at several locations including lower Northampton County, Westmoreland County in the Northern Neck, Amelia County, Hanover County, and Frederick County.  Moth activity is quite variable right now, and should certainly be monitored carefully in the coming weeks. We still have caught very few fall armyworm moths in our traps around Virginia; however, it should be noted that the Amelia County Farm averaged 5.5 FAW moths per night, which is the highest of any trap this season so far. So, a late flight of this pest appears to have reached some part of Virginia.

In an effort to fend off  pyrethroid insecticide resistance development in our corn earworm populations, rotating to another insecticide than a Class 3 (pyrethroid) is highly encouraged for at least one spray. Diamide insecticides such as Coragen or Besiege (although it includes lambda-cy with the diamide), the carbamate Lannate LV, or the spinosyn Blackhawk, are all effective rotational insecticide options.

I want to once again thank Helene Doughty at the ESAREC and all of the VCE agents that are monitoring these pests on sweet corn farms in 17 different counties in Virginia: Phil Blevins (Washington Co. – See Photograph below); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Roy Flanagan (VA Beach); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.).

Corn earworm moth catch in pheromone-baited Heliothis traps around Virginia for week ending August 24, 2018.

Phil Blevins, Washington County VCE Agent – ANR, standing in front of his Bt sweet corn trial adjacent to a Heliothis trap for corn earworm and a bucket trap for fall armyworm monitoring.

Sweet Corn IPM Moth Trapping in Virginia – Week Ending August 17, 2018

Corn earworm moth catch data from sweet corn farm locations around Virginia can be found in the table below. In summary, corn earworm moth activity has dropped off this week at most locations with the exception of one of the farms in Frederick County where trap catch increased to 13 moths per night. Trap catch remained high at the Creeds location in Virginia Beach with over 20 moths per night being caught, which is high pest pressure still at that location. Moth activity is quite variable right now, and should certainly be monitored carefully in the coming weeks. We have caught very few fall armyworm moths in our traps around Virginia, which is good news. That insect can be quite devastating to late planted sweet corn. Keep an eye on brown marmorated stink bugs feeding on corn ears particularly on field edges (border rows). Fig. 2 below shows BMSB injury to sweet corn from feeding through the husk. Fig. 3 shows the same sweet corn ear after boiling in water. If more than 1 stink bug is found per 10 ears, a pyrethroid insecticide spray is recommended.

Corn earworm trap catch at sweet corn farms in Virginia – week ending August 17, 2018.

Fig. 2. Sweet corn damaged by brown marmorated stink bug.

Fig. 3. Sweet corn ear after being boiled in water. Note the appearance of stink bug feeding on the cooked corn.

Sweet Corn IPM Moth Trapping in Virginia – Week Ending August 10, 2018

Corn earworm moth catch data from sweet corn farm locations around Virginia can be found in the table below.  In summary, corn earworm activity has gone up this week in Accomack County, Virginia Beach, Amelia County, Frederick County, and Franklin County, but has dropped off in many other locations around Virginia.  Thus, moth activity is quite variable right now, but should certainly be monitored carefully in the coming weeks.

Corn earworm pheromone trap catch per night in Virginia.

Insecticide Options for Insect Control in Sweet Corn

Pyrethroids are the most commonly used insecticides in sweet corn.  They are relatively cheap, effective, and include many options such as (alphabetized):
Baythroid XL 1.6 to 2.8 fl oz/A
bifenthrin–2.1 to 6.4 fl oz/A Bifenture 2EC (Sniper, or others);
cyfluthrin–1.6 to 2.8 fl oz/A Tombstone 2EC (or OLF);
esfenvalerate–5.8 to 9.6 fl oz/A Asana XL;
lambda-cyhalothrin–1.28 to 1.92 fl oz/A Warrior II or 2.56 to 3.84 fl oz/A Lambda-Cy (LambdaT) permethrin–4.0 to 8.0 fl oz/A Perm-UP 3.2EC (or OLF)
zeta-cypermethrin–2.8 to 4.0 fl oz/A Mustang Maxx (or OLF)
zeta-cypermethrin+bifenthrin–4.0 to 10.3 fl oz/A Hero EC

Some drawbacks to pyrethroids are that they are broad spectrum contact poisons that are also quite toxic to natural enemies such as ladybeetles and minute pirate bugs, Orius spp., that frequent sweet corn in Virginia and which can destroy many eggs of CEW before the larvae can damage the ears. Pyrethroid insecticides are also toxic to bees.  Frequent use of pyrethroids can also cause outbreaks of corn leaf aphids, which can build up on the ears causing honeydew and sooty mold, which can reduce quality and marketability of the produce.  Corn earworm in Virginia is showing signs of resistance development to pyrethroids and therefore rotating different modes of action is recommended.

Other insecticide classes (different modes of action) that should be considered for use in sweet corn include:

  • Lannate LV methomyl –  Will not flare aphids.  HAs not provided as effective control of  corn earworm as the other products when used exclusively.  Is a good rotation or tank mix option.
  • Coragen 1.67SC  chlorantraniliprole–3.5 to 5.0 fl oz/A  – this diamide insecticide is virtually non-toxic to bees and natural enemies, and provides excellent control of corn earworm and other worm pests.  Only about two applications can be used per season.  It is an excellent choice during pollen shed.
  • Besiege lambda-cyhalothrin+chlorantraniliprole–6.0 to 10.0 fl oz/A  includes both the diamide and a pyrethoid.
  • Blackhawk 36WG spinosad–2.2 to 3.3 oz/A or Radiant SC spinetoram–3.0 to 6.0 fl oz/A are spinosysns that provide very good control of corn earworm and other worm pests and are less harmful to many natural enemies.

Sweetcorn IPM Moth Trapping in Virginia and Stink Bug Problems – Week Ending Aug 3, 2018

Corn earworm moth activity has increased in several Virginia locations this week including: Virginia Beach with some traps averaging over 20 moths per night, Hanover County with 16.6 moths per night, and Page County with 10.9 moths per night.  A trap catch exceeding 16 moths per night is quite high and control measures in sweet corn are recommended at short intervals 2-3 days apart (See table below for the trap catch data).

In addition to corn earworm, fall armyworm is another important Lepidopteran “worm” pest that attacks sweet corn.  So far, very few moths have been caught in traps around Virginia, but the some late-planted sweet corn on the Eastern Shore has gotten fall armyworms in the early whorl stage corn, where a lot of damage can occur.  In addition to corn earworm and fall armyworm, the invasive brown marmorated stink bug (BMSB) has occurred in large numbers in some sweet corn fields, including Virginia Beach.  The picture below is from Helene Doughty.  BMSB can feed through the husk and damage multiple kernels, reducing the quality of the produce.  To learn more about BMSB biology, pest threat and management in vegetable crops, click on the following link (pdf) BMSB-in-Vegetables-English

Brown marmorated stink bugs on sweet corn in Virginia Beach. Photo by Helene Doughty (ESAREC).

I’d like to acknowledge the 14 VCE agents that are monitoring moth pests on sweet corn farms in 17 different counties in Virginia: Phil Blevins (Washington Co.); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Helene Doughty (Accomack Co.); Roy Flanagan (VA Beach); Bob Jones (Charlotte Co.); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.).

Here are some trap catch results (moths per night) for some of the locations around Virginia for this week (note we are missing a lot of data this week from some locations):

Corn earworm moth catch at sweet corn fields in Virginia in 2018

Same trap catch data can be found here:

dataAug2

 

Sweet corn IPM – Moth Trap Catch in Virginia – Week Ending July 27, 2018

We’ve seen a jump in corn earworm moth activity this week in many sweet corn fields around Virginia with high levels being reported all around the state, specifically Virginia Beach, Accomack, Northampton, Amelia, Frederick, Page, Montgomery, and Carroll Counties. Fall armyworm moths are also being monitored with bucket traps and very little activity has been observed throughout Virginia.
A catch of >1 or >13 corn earworm moths per night means moderate and high pest pressure, respectively, and a more frequent spray interval is justified.

A big thank you to the 14 VCE agents that are monitoring these pests on sweet corn farms in 17 different counties in Virginia: Phil Blevins (Washington Co.); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Helene Doughty (Accomack Co.); Roy Flanagan (VA Beach); Bob Jones (Charlotte Co.); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.). Here are some trap catch results (moths per night) for some of the locations around Virginia for this week (note we do not have data for all locations yet):

Corn earworm moth catch in VA for week ending – July 27, 2018.

 

Sweet corn IPM Scouting – Week Ending July 20, 2018

Moth trap monitoring

We are monitoring corn earworm and fall armyworm moth activity levels on sweet corn farms in 17 different counties in Virginia. Moth Trap Catch Data are being recorded by: Kuhar Vegetable Entomology lab (Montgomery Co.); Phil Blevins (Washington Co.); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Helene Doughty (Accomack Co.); Roy Flanagan (VA Beach); Bob Jones (Charlotte Co.); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.). Data are posted weekly.

Trap Catch

Below are some trap catch results (moths per night) for some of the locations around Virginia for this week. In summary, we are observing a slight drop off in corn earworm moth activity at most locations, except Amelia County, which posted the highest corn earworm activity this week.  Very little fall armyworm activity has been observed at this point, and numbers are so low that they are not presented.