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.   

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.                                                                                           

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 (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.

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 (3^rd to 5^th 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.

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.  

Over the past couple of weeks our fruiting vegetable crops at Kentland Farm in Whitethorne, Virginia have been invaded by abundant numbers of leaf-footed bugs (Leptoglossus spp.). These bugs that are in the same bug family Coreidae as the squash bug Anasa tristus. They are piercing sucking feeders that have killed entire cucumber and zucchini plants from their feeding on stems and leaves or have caused numerous puncture wounds on fruit, which result in a little fluid oozing from the fruit.

These insect pests can be controlled using the same insecticides that are labeled for use on stink bugs and squash bugs, namely, pyrethroids or neonicotinoids for conventional growers. Organic growers can achieve some suppression of bugs with the use of products containing pyrethrins such as Pyganic or Azera, or with the use of Surround (kaolin clay powder), which also works to prevent sunscald on fruit.

To learn more about this pest, please see the following VCE fact sheet that we produced a decade ago. Wow has it been that long? https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/3012/3012-1522/3012-1522_pdf.pdf

Since early July, we have been monitoring Heliothis traps baited with corn earworm pheromone at on 4 hemp fields and one sweet corn field in and around Montgomery, Co., Virginia. Below are the trap catch results. After a week or two of low catch, the moth activity has picked up especially at the Wall sweet corn.

Corn earworm moths per trap per week

FMC Corp. just released a new insecticide Elevest WITH RYNAXYPYR® ACTIVE and BIFENTHRIN. This new insecticide should be available in late season 2020. According to the label, Elevest is registered for use on corn, soybean, edible bean, sweet corn, peanut, cotton, potato and a few other crops. Similar to the product Besiege, Elevest is a mixture of a Group 3A pyrethroid (bifenthrin) with the diamide Group 28 insecticide chlorantraniliprole, which is found in the popular products Coragen or Prevathon. Thus, it will be effective on a wide range of insect pests.

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.

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.

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.