Category Archives: Insect

Corn earworm pest problems on hemp and results of recent insecticide tests

By: Tom Kuhar (Entomology Professor, Virginia Tech), Kadie Britt (Ph.D. student researching hemp IPM), and Helene Doughty (Entomologist, Eastern Shore AREC, Painter, VA)

Fig. 1. Corn earworm damaging CBD hemp in Virginia. Photo by Kadie Britt.

Corn earworm has become one of the most important pests of hemp, Cannabis sativa, in Virginia and many other states (Fig. 1).  Please see our factsheet on this insect as it relates to hemp:

Corn earworm can be quite damaging to the seed heads of hemp grown for grain (Fig. 2), but, as we’ve seen recently in Virginia, the pest can also damage hemp grown for CBD oil.  Over the past few weeks, corn earworm densities and damage to CBD hemp has reached very high levels throughout Virginia, and their presence in fields has been associated with increased flower bud rot (Fig. 3). This can result in significant economic damage to that crop. 

Due to strict regulations on pesticide use on hemp, insecticide recommendations for managing this pest are quite limited at this time.  Recently, we evaluated the efficacy of some naturally-derived pesticides that can be legally applied on hemp in Virginia and one naturally-derived (OMRI-certified) insecticide that currently is not allowed to be applied on hemp (Spinosad).    

Fig. 1. Corn earworm damage to grain hemp. Photo by Helene Doughty, Eastern Shore AREC.
Fig. 2. Bud rot on CBD hemp. Photo by Kadie Britt.

Eastern Shore Insecticide Field Trial:

Treatments included:

  1. Gemstar (5 fl oz/A) – which is a nuclear polyhedrosis virus that is specific to the corn earworm species.  The virus causes corn earworm to become sick and die.  Fig. 4. Shows a corn earworm killed by the virus. 
  2. Javelin WG (8 oz/A)Bacillus thuringiensis (Bt) strain kurstaki – bacterial crystalline proteins that kill caterpillars.
  3. Dipel DF (16 oz/A) – Bt kurstaki different formulation
  4. BoteGHA (32 fl oz/A) Beauveria bassiana – entomopathogenic fungi
  5. Entrust (5 oz/A) – Spinosad derived from soil microbes. *cannot legally be applied on hemp in Virginia. 
Fig. 4. Corn earworm killed by virus (Gemstar insecticide). ESAREC 2019. Photo by Helene Doughty.

We evaluated their efficacy in the field on the Eastern Shore of Virginia in a randomized complete block small plot trial.  Hemp plots were sprayed twice (1 week apart) and numbers of live CEW larvae and damage was assessed.  Results are shown in Figs. 5 & 6.  Entrust was the only product that provided effective control of CEW.  Unfortunately, this is the one product that we evaluated that is not allowed to be applied on hemp.  The insecticide Entrust is OMRI-certified however.    

Fig. 5. Numbers of live corn earworm larvae on hemp plants after insecticide treatments at the ESAREC, Painter, VA.
Fig. 6 Corn earworm damage to hemp seeds in the field after insecticide treatments.

Virginia Tech bioassay trial:

Treatments included:

  1. Gemstar (5 fl oz/A) – which is a nuclear polyhedrosis virus that is specific to the corn earworm species.  The virus causes corn earworm to become sick and die.  Fig. 3. Shows a corn earworm killed by the virus. 
  2. Javelin WG (8 oz/A)Bacillus thuringiensis (Bt) strain kurstaki – bacterial crystalline proteins that kill caterpillars.
  3. Dipel DF (16 oz/A) – Bt kurstaki different formulation
  4. Xentari (16 oz/A) – Bacillus thuringiensis , subsp. aizawai , Strain ABTS-1857
  5. BoteGHA (32 fl oz/A) Beauveria bassiana – entomopathogenic fungi
  6. Entrust (5 oz/A) – Spinosad derived from soil microbes. *cannot legally be applied on hemp in Virginia. 

In order to evaluate the efficacy, untreated hemp seed heads were collected from Kentland Farm and dipped in each of the treatments.  Approximately 1 oz of seeds was placed per diet cup and four reps of 10 cups each were set up for the aforementioned six insecticide treatments.  CEW larvae (3rd instar (medium sized) were collected from sweet corn planted at Kentland Farm and were immediately placed 1 larva per cup.  Mortality was evaluated 1, 2, 3, and 4 days after treatment (Fig. 7).  Similar to the Eastern shore field trial, Entrust provided the most effective control of CEW.  However, this trial also included the Bt aizawai product Xentari, which also provided significant control (better than the other products except spinosad.  Xentari is allowed for use on hemp in Virginia.  For best management of corn earworm during this time, apply Bt products on hemp every few (2-3) days in early morning or late evening. Corn earworm must consume the insecticide for the application to be effective, so ensure good spray coverage on plants. Dead worms may not be noticed until 48 hours after first application.

Fig. 7. Percentage mortality of corn earworm larvae placed on treated hemp seeds in a controlled laboratory experiment. DAT refers to days after treatment (insecticide dip).

EVAREC Soybean Field Day is This Tuesday

The Eastern Virginia Agricultural Research and Extension Center (EVAREC) Soybean Field Day is this Tuesday, Sept. 24. The field day begins at 8:45 am and tours will begin promptly at 9:00 am. There are a number of different topics to be discussed, all supported by the Virginia Soybean Checkoff. The 2019 full-season soybean variety test will also be available for viewing. Lunch will be served by Nixon’s Catering. We look forward to seeing you there.

The EVARE is located at 2229 Menokin Road, Warsaw, VA 22572. For more information, contact Dr. Joseph Oakes, EVAREC Superintendent at 804-333-3485.

Group 1 Field Tour Schedule

  • 8:45 – Welcome & Introductions; Load Trailers to ACR 2
  • 9:00-9:20 – Integrated Pest Management Approach for Soybean
  • Dr. Sally Taylor
  • 9:25-9:45 – Food Grade Soybean Breeding
    • Mr. Nick Lord
  • 9:45 – Load Trailers to Y1
  • 9:55-10:15 – The Best Maturity Group for Your Farm
    • Dr. David Holshouser
  • 10:15-10:30 – The Use of UAV in Crop Research and Production
    • Dr. Joseph Oakes
  • 10:35-10:55 – Roundup-Ready and Conventional Soybean Breeding
    • Dr. Bo Zhang
  • 11:00-11:20 – Weed Management in Soybean
    • Dr. Michael Flessner
  • 11:20 – Walk to Seed Lab

Program & Speakers in the Seed Lab

  • 11:40 – Begin Indoor Program
    • Dr. John Fike: VT Forage Extension Specialist – Hemp Production
    • Dr. Mike Evans: VT School of Plant and Environmental Sciences
  • 12:00 – Lunch is Served: Nixon’s Catering

Thank You to Our Field Day Sponsors!

Crabbe Aviation                       Ryan Ellis

Frazier Quarries                      UniSouth Genetics

James River Equipment            Virginia Crop Improv. Assoc.

Montague Farms

Corn earworm update for September 5, 2019

Average nightly black light trap captures of corn earworm moths this week were: Chesapeake=33; Greensville=13; Southampton=10; Suffolk=27. Hanover had 12 per night if averaged over the past 2 nights, but 3 if averaged over the entire week. Here is the table:

In our corn earworm pyrethroid resistance monitoring experiment (adult vial tests), the seasonal average is 36% survival to a 24-hour exposure of 5 micrograms of cypermethrin per vial.

Corn earworm update for August 29, 2019

Nightly corn earworm/bollworm moth averages for reporting black light trap stations this week were: Greensville=22; Prince George (Templeton)=12; Prince George (Disputanta)=10; Southampton=13; Suffolk=32. Please see the link to the table below and also compare this year’s Suffolk, VA numbers to the past several years.

I have seen a large number of corn earworm moths in our soybean at the Tidewater Agricultural Research & Extension Center in Suffolk this week. Remember to scout for larvae and use the threshold calculator for soybean:

Our pheromone trap catches at Suffolk have also increased and we were able to conduct more adult vial tests for resistance monitoring using the pyrethroid cypermethrin. The average survival for this season is now 37%.

Corn earworm update for August 8, 2019

Black light trap catches of H. zea (corn earworm/bollworm) moths increased at most locations this week. Please see the data table for more information.

We have tested 168 corn earworm moths in our cypermethrin vial tests so far this season, with a seasonal average of 39.5% survival. Here are the results by month (we’ll be conducting more tests throughout August):

We have updated our corn earworm survey of field corn (as a predictor of infestation risk in other crops such as soybean) to include Rockingham County’s 10.8% infested ears. Thanks to all cooperators for their efforts. Statewide average infested ears was 15.3% for 2019. The updated table and map are here:

Corn earworm update, including field corn survey results, for August 1, 2019

Corn earworm moth catches are increasing for most black light stations; nightly averages this week were: Greensville=25.1; Prince George (Templeton)=5.7; Prince George (Disputanta)=3.7; Warsaw=46.4; Southampton=9.0; Suffolk=14.6.

Preliminary results from our annual survey of field corn show the following percent infested ears (based on sampling 5 corn fields/county, 50 ears per field, for evidence of corn earworm larvae): Accomack=16.0 percent infested ears; Amelia=15.6; Chesapeake=5.6; Dinwiddie=19.6; Essex=11.6; Greensville=32.8; Hanover=32.8; Isle of Wight=17.6; King & Queen=13.6; King William=24.4; Lancaster=4.8; Northampton=11.2; Northumberland=4.0; Prince George=12.8; Southampton=11.2; Virginia Beach=17.6; Westmoreland=12.8. Thanks to the following for collecting data from their counties: Eastern Shore AREC entomology; Laura Siegle; Watson Lawrence; Mike Parrish; Robbie Longest and Brittany Semko; Sara Rutherford; Laura Maxey-Nay; Livvy Preisser; Trent Jones; Scott Reiter; Joshua Holland; Roy, Bailey, and Fletcher Flanagan; and Stephanie Romelczyk and Amerah Thompson.

We have found bollworm eggs and small larvae in our cotton experiment in Suffolk. Please be sure to scout your fields.

Plant bug / bollworm update for VA cotton

The much needed rain earlier this week also heralded the start of the moth flight in southeastern VA. Both eggs and adult moths are being picked up by scouting teams. So far, only a handful of fields are over recommended thresholds. I recommend scouting 2-gene cotton (Bollgard II, Widestrike, Twinlink) for eggs and applying Prevathon or Besiege when you find 25 or more per 100 terminals and/or leaves. If you planted 3-gene cotton, you are likely protected. We have measured very little benefit to spraying Widestrike 3, Bollgard III, and Twinlink Plus varieties for bollworm. In these varieties, finding 3 or more live second-stage larvae in one trip (or two worms in two consecutive trips, or one worm in three consecutive trips) triggers an application.

Other insecticides can control bollworm in cotton, but timing is critical. If you are using a pyrethroid, for example, target small worms. No product will clean up a problem field once worms are inside bolls.

Our team, lead by PhD student Seth Dorman, ANR Agent Josh Holland, and Dr. Sean Malone are scouting fields this week for lygus. Few problems fields were detected in southern counties today. However, fields were observed over recommended thresholds. At this point, many people have sprayed. Some may need to spray again and some may not. The only way to know is to scout.

Northern counties will be scouted this Friday and I will update the blog with our findings.

As always, you can reach out to me with your questions and concerns.


Corn earworm report for July 18, 2019

Very low numbers of corn earworm moths were reported by our network of black light trap operators this week. Nightly averages ranged from 0.3 to 1.0 moths. Here are this week’s numbers (trap operators listed in parentheses):

Greensville (Sara Rutherford): 0.7 per night

Hanover (Laura Maxey-Nay): 0.9 per night

Prince George-Templeton (Scott Reiter): 0.8 per night

Prince George-Disputanta (Scott Reiter): 0.5 per night

Richmond County-Warsaw (Mary Beahm): 0.3 per night

Southampton (Josh Holland): 0.3 per night

Suffolk (Sally Taylor and crew): 1.0 per night

Here is a pdf of the data table: BLT_18_Jul_2019

We will be conducting vial tests to monitor insecticide resistance in corn earworm/bollworm again this year, but so far we have only captured and tested a handful of moths.