Author Archives: Thomas Kuhar

About Thomas Kuhar

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

Beet armyworm infestations in central Virginia

This week I visited several vegetable farms in southside (southcentral) Virginia and found beet armyworm infestations at all of the farms. This is not good news as this insect pest can be difficult to control. One field of Brussels sprouts had been sprayed with a pyrethroid and with Lannate the spray before and had a healthy population of beet armyworms doing a lot of damage (see photo). I saw mostly young larvae and even some egg masses (see photo). Based on my experience, this pest is resistant to those two classes of insecticides.

Beet armyworm on Brussels sprouts in southside Virginia. September 2022.

History and Pest Status of the Beet Armyworm in the U.S.

The beet armyworm (BAW) is a widely distributed polyphagous insect pest of >90 species of plants and cultivated crops, including alfalfa, asparagus, bean, beet, broccoli, cabbage, cauliflower, celery, chickpea, corn, cotton, cowpea, eggplant, lettuce, onion, pea, peanut, pepper, potato, radish, safflower, sorghum, soybean, spinach, sugarbeet, sweetpotato, tobacco, tomato, and turnip.  The insect also feeds on fruit and ornamental plants.  The BAW is native to Southeast Asia, but has spread throughout much of the world.   It was first discovered in North America in the late 1800’s on the west coast, and reached the southeastern U.S. by the 1920’s.  As it is a tropical insect, it lacks a diapause and ability to overwinter in colder (temperate) climates.  High populations of BAW occur in the southeastern and southwestern states in the spring, and highly mobile migrants usually make their way northward each summer to the Mid-Atlantic states, Colorado, and northern California.  Occasionally the pest is found as far north as New York and even Canada. 

Damage

Beet armyworm egg mass.

BAW larvae feed on foliage and fruit.  When they are young, larvae feed gregariously, usually in great numbers, where they skeletonize and web leaves.  As they mature, larvae devour more foliage and may burrow into fruit or heads of plants.  When BAW outbreaks occur in a region, they are conspicuous and often become the primary pest control focus of growers of numerous field and vegetable crops because of the sheer numbers of larvae and their ability to move from crop to crop.  If they are not controlled, BAW infestations can sometimes result in total crop losses.  The insects have a high reproductive potential; eggs are laid in clusters of 50 to 150 eggs, and female moths can produce over 1300 eggs in a lifetime.  In addition, eggs are well protected from the environment and predators because they are usually deposited on the undersides of leaves and are covered with cottony scales deposited by the female moth.  This usually results in numerous larvae infesting a single plant after egg hatch. 

Insecticide Resistance in the Beet Armyworm

BAW has a high propensity for developing resistance to insecticides. In the southeast and southwestern states, the relatively high abundance of BAW coupled with large acreages of valuable crops has stimulated a long history of intense insecticide use . Not surprisingly, this has resulted in the development of resistance to a diverse array of pesticide classes, including chlorinated hydrocarbons, organophosphates, carbamates, pyrethroids, and benzoylphenylureas. Some recommended insecticide options include the diamides such as Coragen, Harvanta, Beseige, Elevest, etc.., spinosyns like Radiant or Blackhawk or Entrust for organic growers. Bt products like Dipel, Agree, Xentari, Javelin, Deliver, etc.. will provide very good control of small larvae. Proclaim and Avaunt are also effective products from past efficacy trials.

Monitoring Fall armyworm, Pickleworm, and Corn Earworm in Virginia – Week of August 19

By Kelly McIntyre1, Helene Doughty2, Lorena Lopez2, and Tom Kuhar1

This summer and fall, we are tracking moth flight numbers around Virginia using pheromone traps for three important pests, fall armyworm (FAW), which can attack most grasses, corn, sorghum, small grains, and even alfalfa; pickleworm, which is a late season pest of squash, pumpkins, and cucumbers, and corn earworm (CEW), which attacks over 300 host plants including many of the major crops in Virginia.  FAW and pickleworm do not overwinter in Virginia and typically are carried northward in late summer on storm fronts coming from the south. 

Fall armyworms.
Fall armyworm moth
pickleworm damage
pickleworm moth.
corn earworm
corn earworm moth

Researchers have demonstrated that certain trap types are better for certain moth species.  We are monitoring fall armyworm moths using the bucket trap baited with a Trece FAW pheromone lure and placed near corn fields.  We are monitoring the presence of pickleworm moths using the Trece Deltatrap baited with the pheromone lure and placed around pumpkin fields.  Corn earworm is monitored using the Heliothis mesh trap or the Hartstack wire mesh trap, which catches the most corn earworm moths among all trap types. 

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.
FW = fall armyworm; PW= pickleworm; CEW = Corn Earworm
namelocationdate checked# days since last check# FAW (if applicable)# PW (if applicable)# CEW (if applicable)
McintyreHomefield Farm – Whitethorne8/96905
McintyreWall Farm – Blacksburg8/96nana109
McintyreTurfgrass Center – Blacksburg8/96300
McintyreHomefield Farm – Whitethorne8/1781100
McintyreWall Farm – Blacksburg8/178nana
McintyreTurfgrass Center – Blacksburg8/178400
McintyreHomefield Farm – Whitethorne
McintyreWall Farm – Blacksburg
McintyreTurfgrass Center – Blacksburg
DoughtyESAREC, Painter, VA6/157nana30
DoughtyESAREC, Painter, VA6/227nana8
DoughtyESAREC, Painter, VA6/297nana7
DoughtyESAREC, Painter, VA7/67nana24
DoughtyESAREC, Painter, VA7/137nana5
DoughtyESAREC, Painter, VA7/2070na18
DoughtyESAREC, Painter, VA7/2770na39
DoughtyESAREC, Painter, VA8/372na19
DoughtyESAREC, Painter, VA8/129
DoughtyESAREC, Painter, VA8/175155
RomelczykMontross8/1240
RomelczykMontross8-1790
LopezESAREC, Painter, VA8/187na0na
FlanaganCullipher Farms, VB, VA8/18N/A340
LopezHRAREC8/187na0na
LopezSea Breeze Farm, Cape Charles8/187na042
DeitchArlington RD – Northampton Co.8/27na8
DeitchSeaview – Northampton Co.8/27na246
DeitchMachipongo – Northampton Co.8/27na43
DeitchNassawadox – Northampton Co.8/270na
DeitchTownsend – Northampton Co.8/270na
DeitchKendall Grove – Northampton Co.8/270na
DeitchRed Bank Road – Northampton Co.8/270na
DeitchExmore – Northampton Co.8/270na
DeitchArlington RD – Northampton Co.8/97na25
DeitchSeaview – Northampton Co.8/97na3
DeitchMachipongo – Northampton Co.8/97na66
DeitchNassawadox – Northampton Co.8/97na8
DeitchTownsend – Northampton Co.8/970na
DeitchKendall Grove – Northampton Co.8/971na
DeitchRed Bank Road – Northampton Co.8/970na
DeitchExmore – Northampton Co.8/970na
DeitchArlington RD – Northampton Co.8/167na16
DeitchSeaview – Northampton Co.8/167na4
DeitchMachipongo – Northampton Co.8/167na168
DeitchNassawadox – Northampton Co.8/167na4
DeitchTownsend – Northampton Co.8/1671na
DeitchKendall Grove – Northampton Co.8/1670na
DeitchRed Bank Road – Northampton Co.8/1670na
DeitchExmore – Northampton Co.8/1670na

Fall armyworm in southwest Virginia sweet corn – treatment evaluation and recommendations

By Kyle Bekelja (postdoc), Tom Kuhar (Professor), and Sally Taylor (Associate Professor) Department of Entomology, Virginia Tech

We installed our pheromone bucket traps for fall armyworm in late July at Homefield Farm in Whitethorne, VA and we caught moths the first week (8 per trap).  This alerted us that this tropical moth pest had already reached southwest Virginia.  Then, this week, August 16, 2022, we noticed a pretty bad infestation of FAW larvae in our sweet corn at this same location. 

Fig. 1. Fall armyworm in sweet corn at Homefield Farm, Whitethorne, VA, August 15, 2022.

The Pest.  Fall armyworm (FAW) is a moth pest that migrates northward during late summer and early fall. Be on the lookout for this pest especially during times of northerly winds (such as tropical storms) which can carry female moths to Virginia late in the season. Fall armyworms have a wider host range that includes more than 80 plants: vegetables include sweet corn, tomatoes, and peppers, field and forage crops such as alfalfa, cotton, and peanuts, and ornamental commodities, especially turfgrass. Last year, FAW hit turfgrass hard in Virginia; this year, we have already started seeing it in sweet corn.  Based on observations from Dr. Scott Stewart in Tennessee, we believe that this strain of FAW favors corn and is likely not going to be a huge turf pest like we saw in fall 2021. 

Identification

Be on the lookout for shotgun-patterned damage and lots of frass (i.e., poop) in the corn whorl, shown in Figure 1 (we noticed feeding that was concentrated on un-emerged tassels). If you dig deep inside the whorl, you’re likely to find a caterpillar with the telltale inverted “Y” on its forehead, and four black dots at the tail-end of the abdomen, shown in Figure 2.

Figure 2. Image credit: Department of Entomology, University of Nebraska-Lincoln

Treatment Evaluation. We collected FAW caterpillars from sweet corn at Homefield Farm in Blacksburg, VA on August 16, 2022, and assessed percent mortality using treatments listed in Table 1. We placed caterpillars in 1-ounce cups with corn tassels that were dipped into solutions of treatments, and assessed mortality after 24-hours. All treatments provided good control compared to a water check. Although the pyrethroid lambda-cyhalothrin resulted in over 83% mortality of FAW, the two products that combine the diamide chlorantraniliprole with pyrethroids (Beseige and Elevest) resulted in 100% mortality after 24 hours.

Insecticide bioassay Results of field-collected fall armyworm larvae.

Fig 3. Table Showing Fall Armyworm Larval Mortality After 24-hours exposure to treated corn tassel (conducted Aug 17, 2022, Whitethorne, VA).

 Control. Insecticides recommended for controlling FAW include pyrethroids (such as Lambda-Cyhalothrin, bifenthrin, and others) and more selective caterpillar-targeting insecticides such as Prevathon, Coragen, and Acelepryn. Consider using some of these more selective options during times when pollinators are more active (e.g., while sweet corn is tasseling). Consult the relevant pest management guides for specific recommendations on various commodities. Remember that control of large caterpillars is often difficult with any insecticide.

Squash vine borer is bad this year

In southwest Virginia we’ve seen a lot of squash vine borer problems this summer. More than usual. This moth pest lays its eggs (singly) at the base of squash or pumpkins, where the larva quickly bores into the plant after egg hatch and ultimately kills the vine or entire plant (as we’ve seen in our squash research plots in Whitethorne, VA).

Young squash vine borer larva in blue hubbard squash, Whitethorne, VA, July 20, 2022
Later instar squash vine borer larva.
Squash vine borer egg (dark red in color).
Squash vine borer adult (moth).

Control

Squash vine borer can be a major pest challenge for growers and home gardeners. If you only have a few plants to protect, then trying to cover the base of plants with aluminum foil or the cardboard can help as the moth prefers to deposit the egg at the base of plants. This acts as an oviposition deterrent. However, this is not practical for commercial growers and the best control option is an insecticide spray directed at the base of plants where the female moth may contact it and die before laying the egg, or, after egg hatch, the young neonate larvae may die from the insecticide residue before boring into the plant, where it will be protected. Pyrethroids such as Asana XL (esfenvalerate), Baythroid XL (beta-cyfluthrin), Brigade 2EC (bifenthrin), Danitol 2.4EC (fenpropathrin), Hero EW (zeta-cypermethrin + bifenthrin), Warrior II or Lambda-Cy 1EC (lambda-cyhalothrin), Mustang Maxx (zeta-cypermethrin), Permethrin 3.2EC, Tombstone (cyfluthrin), to name a few, are the most effective insecticides for quick contact control of the SVB. As always, please read the label before using any insecticide and be mindful that pyrethroids are toxic to pollinators and other beneficial arthropods. So avoiding spraying when flowers are open and in bloom, and directing sprays to the base of plants will help reduce nontarget impacts.

Be on the lookout for allium leafminer in your spring onions, garlic, or leeks

The allium leafminer (ALM), Phytomyza gymnostoma (Loew) (Diptera: Agromyzidae), is an invasive fly species that was first recorded in the U.S. in Pennsylvania in 2015. The pest attacks onions, garlic, and leeks where the larvae (maggots) feed on plant tissue by mining the plant causing wilting and possible death. This new pest to the mid-Atlantic area is a long grey-black fly with a distinctive yellow or orange patch on the top of its head, yellow sides and “knees” (femur-tibia junction), and white halteres (knobs as second pair of wings). The larvae are a typical whitish maggot. Adult females repeatedly puncture leaves with their ovipositor, resulting in a line of small white dots. Leaves can be wavy, curled and distorted. Larvae mine leaves and move into bulbs and leaf sheathes where they pupate. This invasive pest was recorded in southwest Virginia in 2021 and has been found in Montgomery, Carroll, Botetourt, and Bedford Counties in Virginia. Please pass this information on to VCE personnel and Master Gardeners so that we can track the spread of this invasive pest in The Commonwealth. The photos below show the life stages of this pest. The egg laying scars (perfect line of tiny circle marks on stems) are telltale sign.

Allium leafminer larva (photo by Sean Boyle, Virginia Tech)
Allium leafminer larva found in Blacksburg, VA in September 2021. (photo by Sean Boyle Virginia Tech)
Oviposition scars by allium leafminer. Photo by Tom Kuhar.

Control: Covering plants in April-May, or September-October, during the adult flights, can exclude the pest. A number of systemic and contact insecticides can provide effective control including neonicotinoids, diamides, spinosyns, and pyrethroids. Products registered for allium leafminer control include:

Mustang Maxx  2.88 to 4.0 fl oz/A           zeta-cypermethrin

Warrior 1.28 to 1.92 fl oz/A         lambda-cyhalothrin

Scorpion 35SL    8.75 to 10.5 fl oz/A         dinotefuran – soil

Scorpion 35SL    5.25 to 7.0 fl oz/A           dinotefuran – foliar

Venom 70SG      5.0 to 6.0 fl oz/A             dinotefuran – soil           

Venom 70SG      3.0 to 4.0 fl oz/A             dinotefuran – foliar        

Entrust SC (OMRI)           3.0 to 6.0 fl oz/A             spinosad           

Radiant SC          6.0 to 10.0 fl oz/A           spinetoram

Trigard 75WSP  2.66 oz/A           cyromazine

Exirel    13.5 to 20.5 fl oz/A         cyantraniliprole

Minecto Pro       7.0 to 10.0 fl oz/A           cyantraniliprole + abamectin

Chlorpyrifos (Lorsban) no longer allowed on food crops

From Daniel Frank (Virginia Tech Pesticides Program):

As of February 28, 2022, all food tolerances for chlorpyrifos were revoked and any new applications of chlorpyrifos will render any food treated as adulterated and ineligible to be distributed in interstate commerce. In issuing the final rule, EPA found that it could not determine that there is a reasonable certainty of no harm from aggregate exposure, including food, drinking water, and residential exposure, to chlorpyrifos, based on currently available data and taking into consideration all currently registered uses for chlorpyrifos. EPA has a dedicated webpage including information for anyone in possession of chlorpyrifos products for use on food when tolerances expire. According to EPA,
• Applicators should discontinue use on food. If the products label allows for use in other non-food settings, it may continue to be used for those non-food purposes.
• Chlorpyrifos products should not be disposed of in landfills for industrial or municipal solid waste.
• Current options for dealing with chlorpyrifos products labeled for use on food:
o Store chlorpyrifos products until there is an opportunity for appropriate disposal. Details on proper storage can be found using the following links:
 https://www.epa.gov/safepestcontrol/storing-pesticides-safely
 https://www.epa.gov/pesticide-worker-safety/requirements-pesticide-storage
o Appropriately dispose of these products as specified by the state.
Information regarding the VDACS pesticide collection program including the 2022 service area and dates/times of collection were previously sent out and are also available here. Should any additional information become available related to the rule including other options for final disposition of the product, I will be sure to share that information.

Regards,

Daniel


Daniel L. Frank
Director of Pesticide Programs
Virginia Tech
302 Agnew Hall
460 West Campus Drive
Blacksburg, VA 24061
540-231-3430
vtpp.org

Update on Fall armyworm outbreak in Virginia

By: Tom Kuhar, Alejandro Del Pozo, and Sally Taylor
Virginia Tech Department of Entomology

In the past week, many areas of Virginia have experienced severe outbreaks of fall armyworms (FAW), which have completely destroyed lawns, sod plantings, hayfields, and alfalfa fields. As you would imagine, we have gotten a lot of calls about these pests. We’ve included some of the FAQ below.

Fall armyworms collected from a sod farm in Virginia last week.
Lawn in Lancaster destroyed by fall armyworm, which fed upon the fescue grass only and left behind other grass and plant species.
  1.  Who’s being harmed the most by armyworms?

    Lawns with turf-type fescue grass are being hit the hardest across Virginia.  Alfalfa and hayfields are also being attacked.  
Alfalfa field in Virginia destroyed by fall armyworms last week.

2. What crops are at risk? 
While FAW are known to attack a number of crops such as grasses, small grains, corn, sorghum, soybean, and vegetables, this particular strain of FAW seems to be a bit more selective.  Several people have reported FAW only eating the fescue grass and leaving behind crabgrass and other plants and weeds. Kentucky bluegrass, and Zoysiagrass for example have not appeared to have been damaged.  There have also been very few reports of FAW in late-planted sweet corn, which is often a magnet for FAW.  So, we are not sure exactly what crops might be at risk from this current strain of FAW.  We are advising to keep a close watch on all susceptible host plants. 

3. Does climate change play a role in spreading armyworms? If so, how?
Fall armyworms are tropical moths.  They cannot survive cold winters.  With climate change, it is possible that these moths are overwintering a little further north than usual.  If climate change leads to dry (drought) conditions in the southern states, then high densities of these moths can build up.  When storm winds blow north, they carry the moths to the mid-Atlantic, northeast, and Midwestern states. 

4. What do you think the rest of the year will look like in terms of armyworms? Is the worst behind us or yet to come?
Great question.  The fall armyworm will complete a full generation of its life cycle (egg-larvae-pupa-adult moth) in about 30-40 days, depending on weather conditions.  This fall armyworm outbreak occurred early enough for the moth population to still cycle through another generation here in Virginia, meaning more eggs might be deposited on lawns and more devastation from larval feeding may occur.  However, FAW are very susceptible to disease that occurs after wet rainy conditions, which we’ve also experienced.  So, we may see things go either direction.  Still don’t know. 

5. Have there been previous years where we’ve seen a similar explosion in army worms? Is this going to be the ‘new normal’ having FAW every year?

We last had a fall armyworm outbreak in 2018.  It was not as severe.  This is the worst FAW devastation that I’ve seen in Virginia in my 30-year career in entomology.  We still do not know if we might have another huge outbreak of FAW in 2022. All we know that some insect pests have cycles between outbreak. It could be possible that with warmer and dryer conditions, we might see FAW being present in higher number during the upcoming years. Now we know that this creature can come in Virginia as early as late-August. Scouting for this pest will be still crucial.

6. What can you do about them? 

If lawns have been killed, the only recourse is to reseed the lawn this fall.  If new fall cover crop plantings have been devoured, then reseeding those also may be the only recourse.  For crop protection, insecticides recommended for control include most pyrethroids (active ingredients such as bifenthrin [in the products Talstar, Brigade, Sniper, and many others]), lambda-cyhalothrin, and commercial products such as Mustang Max, Baythroid XL, and others), the carbamate, Lannate LV, and many of the more selective (lepidopteran-targeting) insecticides such as the diamides Prevathon, Coragen, Acelepryn, Besiege, indoxacarb products like Steward, Avaunt eVo, Provaunt, the active ingredient spinosad (in products such as Blackhawk, Tracer, Matchpoint), and other products including Radiant, or Intrepid Edge.  Consult the relevant Pest management Guide for specific recommendations on the various commodities.  Please note that control of large larvae may be difficult with any insecticide.  Link to the VCE Pest Management Guides for Field Crops, Vegetables, and Turf are provided below.  On turf, we have gotten very good control of FAW larvae with pyrethroids, which are also one cheaper insecticide options.  Golf course turf treated with a systemic diamide insecticide like Acelepryn or Tetrino have shown no damage even after 50 days post-spray. 

Links to Pest Management Guides   https://resources.ext.vt.edu/

Turf:  

https://resources.ext.vt.edu/contentdetail?contentid=2377&contentname=2021%20Pest%20Management%20Guide%20-%20Home%20Grounds%20and%20Animals

Field Crops:      

https://resources.ext.vt.edu/contentdetail?contentid=2375&contentname=2021%20Pest%20Management%20Guide%20-%20Field%20Crops

Vegetables:  

https://resources.ext.vt.edu/contentdetail?contentid=2379&contentname=2020-2021%20Mid-Atlantic%20Commercial%20Vegetable%20Production%20Recommendations

Fall armyworm outbreak in Virginia – Turf, sod, small grains, late sweet corn, sorghum, and other crops at risk.

By: Drs. Tom Kuhar, Alejandro Del Pozo, and Sally Taylor (Dept. of Entomology, Virginia Tech)

Recently, some VCE agents as well as golf course superintendents in the northcentral and southwestern counties of Virginia have reported fall armyworm outbreaks (Fig. 1) on lawns and golf courses.  This outbreak is earlier than usual and potentially could lead to one of the heaviest pest problems that we’ve experienced from this pest in Virginia in recent years. Some lawns have completely been destroyed by these voracious feeders (Fig. 2 and 3).

Fig. 1. Fall armyworm larvae collected from a lawn in Richmond, VA. August 26, 2021. Photo courtesy of Jeff Sacks.

Fig. 2. Fall armyworm destroyed lawn in Henrico Co. August 26, 2021. Photo courtesy of Jeff Sacks.

Fig. 3. FAW damage to lawn in Richmond, VA. August 26, 2021. Photo courtesy of Tyler Green.

 

 It’s important to understand the biology of this polyphagus pest (Fig. 4).  Fall armyworm (Spodoptera frugiperda) is a tropical moth native to warm climate areas of the western hemisphere.  It cannot successfully overwinter in Virginia.  However, fall armyworm moths (see Fig. 9) are strong fliers, and populations can show up throughout the eastern United States in the late summer and fall months, sometimes in very high populations like we saw most recently in 2018 in Virginia, and now in 2021.  Female FAW moths can lay up to 10 egg masses (each with 100 – 200 eggs) (see Fig 4).  So, huge densities of armyworms can build up from just a few egg laying moths in a field.  This can completely destroy lawns or new plantings of grain cover crops.    


Fig. 4. Biology of the fall armyworm.  Photos courtesy of *cripts.farmradio.fm/radio-resource-packs/107-farm-radio-resource-pack/backgrounder-fall-armyworm/

Fall armyworm can feed on a number of different host plants, but prefers grasses, small grains, corn, and sorghum. 

Control

Insecticides recommended for control include most pyrethroids (such as bifenthrin, lambda-cyhalothrin, as active ingredients, and some commercial formulations such as Mustang Max, Baythroid XL, etc.), the carbamate (Lannate LV) and many of the more selective (lepidopteran-targeting) insecticides such as the diamide Prevathon, Coragen, Acelepryn, Besiege (as commercial formulations), indoxacarb products like Steward, Avaunt eVo, Provaunt, spinosad products such as Blackhawk, Tracer, Matchpoint, and additional insecticides such as 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.  On turf, we have gotten very good control of FAW larvae with pyrethroids, which are also one the cheaper insecticide options. 

Links to Pest Management Guides   https://resources.ext.vt.edu/

Turf:  

https://resources.ext.vt.edu/contentdetail?contentid=2377&contentname=2021%20Pest%20Management%20Guide%20-%20Home%20Grounds%20and%20Animals

Field Crops:      

https://resources.ext.vt.edu/contentdetail?contentid=2375&contentname=2021%20Pest%20Management%20Guide%20-%20Field%20Crops

Vegetables:  

https://resources.ext.vt.edu/contentdetail?contentid=2379&contentname=2020-2021%20Mid-Atlantic%20Commercial%20Vegetable%20Production%20Recommendations

Sources

http://entnemdept.ufl.edu/creatures/field/fall_armyworm.htm

Luginbill P. 1928. The fall armyworm. USDA Tech. Bull. No. 34.

Pickleworm found in Virginia – a pest threat to pumpkins, squash and other cucurbit crops

This week, my PhD student, Sean Boyle, observed pickleworm holes in our zucchini and squash in Whitethorne, VA near Blacksburg. This is the first that we’ve seen this pest in 2020. If you have noticed this pest in your area, please let me know – email tkuhar@vt.edu. The pickleworm, Diaphania nitidalis (Stoll) is a tropical moth pest of cucurbit crops including pumpkins, squash, and cucumbers (Fig. 1). It is typically a pest in the southern U.S. and does not overwinter in Virginia. The past few years, the pest has made its way northward in late summer on wind and storm fronts. Several pumpkins growers in Virginia have suffered damage from this pest in since 2017 usually following some August summer storms.   

This image has an empty alt attribute; its file name is Pickleworm-moth.png
Fig. 1. Pickleworm moth.
Fig. 2. Pickleworm larva and entrance hole on pumpkin.

Moths fly to flowering pumpkins, squash, or cucumbers and deposit their eggs. A single female moth can lay up to 400 eggs usually on cucurbit flowers.  Larvae feed on flowers (Fig. 2) and bore into fruit leaving a characteristic perfectly round hole often with sawdust-like fecal material around it as well.     

Management. Pickleworm is very difficult to predict or monitor for as eggs are very tiny, moths fly at night, but are not attracted to lights, and there is no commercially-available pheromone lure.  As a result, cucurbit growers in the South often apply insecticides weekly during the fruiting stages until final harvest.  Pyrethroid insecticides can be effective at controlling this pest if sprayed in a timely manner (i.e., lambda-cyhalothrin, permethrin, bifenthrin, Baythroid XL, Mustang Max, etc.). Pyrethroids are often used because of their low cost and because they also control squash bugs and cucumber beetles, but they are not IPM compatible and can result in outbreaks of secondary pests such as aphids.  Usually two or more sprays of pyrethroids in late summer can cause severe aphid problems leading to honey dew build up on plants. Other insecticides that control pickleworm include: the spinosyn productss, Radiant and Entrust, the diamide insecticides, Coragen and Harvanta, the insect growth regulator (IGR) Intrepid, and the lepidopteran-targeting insecticide Avaunt eVo.  All of these products will have less nontarget impacts than pyrethroids and will also control pickleworm.                                                                                           

Corn earworm moth trap catch around Blacksburg, VA and results of an insecticide evaluation on hemp

This article was co-authored by Virginia Tech Entomology Ph.D. student, Kadie Britt.

Here are the corn earworm moth catch numbers from a handful of pheromone traps that we have set up in hemp fields and one sweet corn field around Blacksburg, VA. Trap catch appeared to peak around mid-August with moths emerging from cornfields and has subsided a little toward the end of August. Crops such as soybeans, hemp, tomatoes, and sweet corn are still at risk to this important pest.

Corn earworm moth catch in Heliothis traps baited with corn earworm Hercon sex pheromone lures.

Corn earworm (CEW) is the insect pest of greatest concern to hemp grown outdoors in Virginia and other states. For more information about this pest’s biology and behavior in hemp, see this factsheet: https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ento-328/ENTO-328.pdf.

We have already started to see worms feeding on hemp throughout Virginia. CEW feeding on hemp causes mechanical damage to buds, allowing environmental pathogens to enter crop material, ultimately leading to bud rot. Bud rot is visible and present in hemp crops right now but is not prevalent just yet. Managing populations early on will be key to reducing crop injury this season.

Corn earworm larva on hemp plant in Virginia. Photo by Kadie Britt.

Strict regulations on pesticide applications to hemp prevent the use of many available insecticides. We have conducted a laboratory experiment to evaluate the efficacy of some products that are currently allowed for use in hemp in Virginia as well as Pyganic, which is not labeled on hemp, but is a widely used organic insecticide.

Treatments included in the August 19, 2020 bioassay included:

  1. Untreated control (UTC): water
  2. Agree: Bacillus thuringiensis subspecies aizawai strain GC-91
  3. Spear-Lep + Leprotec: GS-omega/kappa-Hxtx-Hv1a + Bacillus thuringiensis variety kurstaki
  4. XenTari: Bacillus thuringiensis subspecies aizawai strain ABTS-1857
  5. PyGanic: Pyrethrins
  6. PyGanic + PBO (insecticide synergist): Pyrethrins + Piperonyl butoxide

To conduct this bioassay, corn earworm larvae (3rd to 5th instars) were collected from untreated sweet corn grown at Kentland Research Farm in Whitethorne, VA. Untreated hemp seed heads were collected from grain hemp, variety ‘Joey’, grown at the Urban Horticulture Center farm in Blacksburg, VA. Seed heads were dipped in spray tank concentrations of each insecticide at the high labeled rate and placed into 1 oz. diet cups. Larval corn earworms were placed directly on top of treated material. Mortality was evaluated at 1, 2, 3, and 4 days after the experiment was set up (Figure 3). PyGanic + PBO provided significantly greater efficacy against CEW than all other products tested with only 6.5% of worms surviving after 4 days. The addition of the synergist is needed for effective control with Pyganic due to pyrethroid resistance development in this pest.  Unfortunately, Pyganic is not currently labeled for use on hemp in Virginia.  Agree, XenTari, and PyGanic without PBO all performed similarly with 50.3%, 53.5%, and 59.9% of worms surviving after 4 days, respectively.

Survival after 4 days of field-collected corn earworm larvae placed on hemp seed heads that were dipped in spray tank concentrations of various organic insecticides. All products except Pyganic are permitted for use on hemp in Virginia.

Looking ahead this season, insecticide research trials in CBD hemp will be conducted in Blackstone with all of the aforementioned products plus many more. We will continue doing lab bioassays with CEW and other insecticides that are allowed for use in hemp at this time. Results will be shared as they become available.