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.

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.

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.

Registration is open for the 2018 Mid-Atlantic Crop Management School for Certified Crop Adviser, Nutrient Management, and Pesticide Applicator Credits for Virginia, Delaware, Maryland, West Virginia, and Pennsylvania. The venue is the Princess Royale Oceanfront Hotel and Conference Center in Ocean City, MD on November 13-15, 2018. Register early so you can enroll in your preferred classes!

Registration: https://app.certain.com/profile/2876563
Schedule: https://sites.udel.edu/agronomy/cropschool/

Soybean loopers have reared their ugly heads across southeastern and coastal Virginia this week. With many of us busy hauling corn, it is reasonable to ask  – when can we stop spraying beans?

In a normal year, we could safely ignore mid-September infestations. This year, the majority of double crop Virginia fields are completing pod fill. Research indicates that R3-R5 beans benefit from a spray when defoliation reaches 15% and you find more than 1 looper per sweep. I recommend that you at least double, and can safely triple, this threshold in R6 beans (i.e., 35-50% defoliation is acceptable). It benefits you to exercise restraint when treating fields after R5.5. There is no scenario when you need to spray R7 beans for loopers. Cooler evening temperatures will work in our favor when they arrive.

In Virginia, Intrepid Edge and Steward have been our most consistent treatments (see image below from 2017). Looper populations in Virginia have tested diamide resistant the past two years (e.g., Besiege, Prevathon). Spraying pyrethoids  will only make the problem worse.

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.

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.

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.