Insect Strip

Insect Strip

Monday, November 19, 2018

Updates on Bt corn for caterpillars and rootworms

Dr. Pat Porter has recently post two excellent articles to "Focus on Entomology"about Bt traits in corn. One article titled " Good News: Some Single Toxin Bt Corn Being Withdrawn from the Market" was posted on Wednesday, November 14, 2018. He provides a good summary for why seed companies are withdrawing corn hybrids with a single Bt toxin and the implications of resistant development with single a Bt toxin compared to having a pyramid of multiple Bt toxin in a corn hybrid.

The most recent article posted is today, Monday, November 19, 2018. This article is titled "Bt Corn Seed Selection in Light of Resistance in Corn Rootworm". This is a follow-up posting on August 25th where he discusses the possibility of field populations of corn rootworms developing resistance and cross resistance to Cry3-type toxins in corn hybrids with Bt corn traits specific for corn rootworms. So, in the most recent article Dr. Porter outlines what options are available for corn rootworm management. He addresses several situations that may occur when making purchase decisions for the coming year. These situations are:

  • Rotation to a non-corn crop
  • Is there a difference between a hybrid with only Cry34/35 toxin and one that has both Cry34/35 and a Cry3-type toxin?
  • Will corn roots be protected if using a Cry34/35 Bt corn without a Cry3-type toxin?
  • What if I have resistance but have to plant a Cry3-type (only) toxin?
  • How much protection is provided by insecticidal seed treatments, soil applied insecticides, and beetle sprays?
  • Does corn without a rootworm Bt toxin have a place?
Also, he provides a table summarizing which trait packages are available from seed companies and which of these packages contain Cry34/35 toxin, Cry3-type toxin, or a combination of Cry34/35 and Cry3-type toxins.

Additional information on caterpillar and rootworm Bt toxins in every type of corn hybrid from each of the seed companies is available in the Handy Bt Trait Table

Wednesday, November 7, 2018

Insecticidal Virus Products for Pest Control: What are the Latest Facts

The arsenal of insecticides and acaricides that we have to select from for controlling arthropod pests is extremely important. Our arsenal may be limited due to cost of the product, which pesticide class will be effective, pests developing resistance, and the impact of a pesticide on beneficial populations or possible flaring of other pests. Therefore, we are always looking for new pesticides to add to our arsenal. 

Toward the end of our growing season this year there was talk of a new insecticide for control of corn earworm/headworm/cotton bollworm. The active ingredient in this product is the nucleopolyhedrovirus (NPV) that is being used in Australia. What is interesting is that this “new insecticide” was studied as early as 1960’s and extensively during the 70’s and 80’s as the nuclear polyhedrosis virus.  And, it was first registered in 1975 by EPA and marketed as Elcar©, Biotrol VHZ©and Viron/H© for Heliothis zea control in beans, corn, lettuce, peanuts, sorghum, soybeans, strawberry, tomato, and cotton. (Yes, I am dating myself). Registration for all of these old products has been cancelled. 

Now new products of the same NPV are being marketed as Heligen©, Helicovex©, and Gemstar©. Are these new products any different from the older products? The virus itself is the same, but how the product is formulated or processed may or may not be different. So, what facts are available about NPV and these products.

Numerous NPVs have been identified for different lepidopteran insects, but each NPV is specific to a particular insect host or narrow range of hosts.These above NPV products are specific to larval stages of Helicoverpa (aka corn earworm, cotton bollworm, tomato fruitworm, soybean podworm, and sorghum headworm) and Heliothis virescens (tobacco budworm). There is an NPV marketed as Fawligen©that is specific to Spodopteralarvae (fall armyworm and beet armyworm). Another NPV product (Loopex©) is specific to the cabbage looper, Trichoplusia ni. These few examples of NPVs will not infect other insects or arthropods, including pests and beneficial predators and parasites. 

Figure 1. Old world cotton bollworm, Helicoverpa armigera, cadaver from NPV infection. Photo: O.P. Sharma,
As a simple illustration of how the virus works, a larva feeds on NPV treated plants where the virus infects the cells of the gut lining and begins to replicate throughout other cells in the larva. These infected cells rupture causing the larva to die. Viral particles are released from the larval cadaver onto the host leaves where healthy larvae can become infected when eating on the plant. 

Figure 2. Top, Dead Beet armyworm from NPV infection. Photo: David Nance, USDA-ARS,
Larval infection and mortality are dependent on the amount of NPV consumed and the larval size at infection. The infection rate of the target pest to the NPV in larvae is age-dependent (Engelhard et al. 1995, Virology). As with any biological insecticide, it may take a few days to a week for larvae to die. Often times dying larvae will climb to the top of the plant.  One great virtue of NPV insecticides is that they target a very narrow pest range, have no direct effect on beneficial insects, and offer little disruption to the arthropod complex in the field. These biological insecticides could be an alternative control method when the target pest has developed resistance to other available insecticides. However, with any product for controlling a pest there is a potential with increased exposure for the pest to develop resistance to the product over time, even NPV. For example, velvetbean caterpillars developed resistance following multiple generation exposure to NPV (Abot et al. 1996, Biological Control).

We do not have any current data on the effectiveness of NPV product applications for control of the above listed pest species with field crops in the Texas High Plains. There was a trial this past summer conducted by Dr. Katelyn Kesheimer, former Extension agent–IPM (Lubbock, Crosby counties), with Heligen©for control of sorghum headworm. At the time of application, the headworm population was very low, below economic threshold, which prevented any measurable results of the effectiveness for control of headworms in sorghum. However, she occasionally found diseased dead larvae when scouting the plots. Since we do not have any definitive results, we (Texas A&M AgriLife Extension) are hesitant to suggest the use of these products, but that does not mean that the products could not provide effective control under the right conditions. If you are interested in trying any of the NPV products the following are facts about the products and general guidelines to help obtain optimum results:

Application volume
Ground rig – 10 gal/ac
Aerial – use only water with > than 3 gpa 

Applied through ground sprayers, chemigation or by airplane. Use sufficient water to obtain thorough, uniform coverage.

Aerial – minimum 5 gpa spray solution.
Applied using standard ground, aerial application, and overhead sprinkler chemigation.
Apply in sufficient water to obtain thorough coverage without excessive runoff. 
Sorghum only – can be aerially applied at 1 gpa with 3 fl. oz of anti-evaporation additive (emulsifieable oil/mineral oil)
Use of non-ionic or oil-based spreader/sticker and ultraviolet screening agent may enhance performance.

Silicone-based spreaders should not be used
Performance may be enhanced with Pinolene or related sticker, latex, methylated seed oils, humic acid, and powdered skim milk.

Avoid silicone-based adjuvants intended only as “spreaders”.

In organic crops, performance may be improved by addition of a feeding stimulant such as sugar or molasses at 5 pounds per acre.
Nozzle selection and boom setup
Avoid flat fan nozzles, unless in row crops with multiple nozzles per row

Prefer use of TwinJet or hollow cone nozzles

Spray solution pH
Spray water pH should be neutral (7). pH above 8 may damage the virus and performance will be reduced.
pH of 5 - 8.5
If pH is 9 or higher, buffer to pH of 7
Environmental conditions
Best to apply in humid (above 50% RH) and warm (77-95oF) for good coverage and for larvae to actively feed

Ideal conditions often before 8 am.
Temperatures above 100oF will degrade the virus and result in a loss of quality
Short term exposure at temperatures above 90oF (a few days) will not immediately deactivate the virus. Avoid spraying in intense sunlight. 

Effectiveness may be increased by spraying in the late afternoon or early evening.
Original container out of direct sunlight at or below 40oF or in a freezer at 0oF
Store at temperatures below 41oF. 
Store at room temperature for up to two months. Refrigeration or freezing will extend shelf life to one year or longer. Store in original container in cool, dry place, out of direct sunlight
60% - 90% control depending on conditions

When to Apply
Sorghum – In fields with even flowering apply when 50% of heads have reached 100% flowering. For uneven flowering fields apply earlier than 50% flowering.

0.7 fl. oz/ac for larvae smaller than 0.3 inches.

1.4 fl. oz/ac for larvae between 0.3 inches to 0.5 inches).

Do not treat if larvae are larger than 0.5 inches.

Cotton – only be applied when larvae are less than 0.3 inches and actively feeding.

Soybeans – 1.0 fl. oz/ac used pre-podding of pre-threshold larval populations.

1.6 fl. oz/ac when populations reach economic threshold – the addition of a molasses-based additive is for threshold sprays of soybeans.
Target smaller larvae and eggs that are about to hatch. If applied on large larvae, damage might not be avoided.

Lower rates may be used during vegetative stage/before fruit set or when tank mixed with other insecticides. Preferable to apply several smaller doses than a single high dose.

For most crops apply 1 – 2.5 fl. oz/ac with reapplication after 6-8 days.  

If the plant tissue is growing fast, such as sweet corn silks, apply 0.5 – 1.25 fl. oz/ac in an interval of only 3 days.
Application should be targeted against first or second instar larvae (smaller than 0.3 inches).

Application rate – 4 to 10 fl. oz/ac

Lower rates may be used during vegetative stages or when tank mixed with other insecticides also effective against Heliothis or Helicoverpa.

When flowers, fruit, or other harvested structures are present use higher rates and/or increased frequency of sprays, or tank mix with other insecticides having contact knockdown activity.

Sweet corn: Application should be made from early vegetative growth stage to tasseling and before emergence of silks. Retreatment may be required at 2 - 3 day intervals depending on egg counts and crop growth rate due to short residual activity of the virus.
REI – 4 hours

PHI – not restrictions on applying up to the time of harvest.
REI – 4 hours

PHI – can be applied up to and including the day of harvest.
REI – 4 hours

PHI - Can be applied up to and including the day of harvest and storage.
The information in this table is for informational purposes only and does not include all information that is available on the product label. Read and follow the label before use. 

The following links were used to obtain information from company brochures, technical bulletin, fact sheet, and product labels about each of the above NPV products for control of larval stages of Helicoverpa zea) and Heliothis virescens (tobacco budworm).

Tuesday, September 4, 2018

Approaching Corn Harvest and Moldy Corn

This is a jointly issued article from Dr. Jourdan Bell (Extension Agronomist – Amarillo) and myself. 

As corn harvest approaches on the Texas High Plains, producers should be evaluating corn fields for visual symptoms of Fusariumear rots.

What are preharvest decisions that can be made to minimize the risk of fumonisin development?
1)   Specifically, producers should identify potential “hot” areas in their fields. If Fusariumis only present in areas with the greatest stress such as the southwest corner, the producer should consider strategic combining. Rather than mixing contaminated corn into several loads, it may be beneficial for the producer to segregate the clean and moldy areas to minimize risk of contaminating multiple loads from the field. 
2)   Additionally, the producer may consider adjusting the fan speed to blow out light weight, moldy corn, cob pieces, and fines that are often highly contaminated with fumonisin. In some regions, it is recommended to leave tip kernels attached to the cob because the tip kernels are often at the greatest risk for Fusariumand fumonisin. To leave tip kernels attached to the cob, it is suggested to run the combine at full capacity with the concave settings open and the cylinder speed at a low setting. 
3)   If the producers suspect high levels of fumonsin present based on visual observations of Fusarium, the producer needs to contact his or her insurance agent prior to harvesting the com.

What are pre-plant decisions that can be made to minimize the risk of fumonisin development?
While producers cannot control environmental stress, some pre-season decisions can help producers minimize their risk for Fusariuminfection and ultimately fumonisin development. Hybrid selection is one of the most important pre-plant decisions a producer can make. While yield potential is often the deciding factor for hybrid selection, other important characteristics are:
1)   Irrigation Capacity and Plant Population: Producers should evaluate their well capacity prior to planting corn. Because irrigation mitigates drought and heat stress, corn grown on low well capacities is often at a greater risk for Fusarium infection. Additionally, producers should also manage plant populations to minimize stress. High populations planted on low water can compound plant stress. 
2)   Maturity Class:Newer, earlier maturing corn hybrids provide producers the opportunity to potentially save several inches of irrigation; however, it is observed that earlier maturing hybrids often have poor kernel integrity. As the corn pericarp prematurely dries in the field during late grain fill, the kernel splits further predisposing the ear to fungal pathogens.
3)   FusariumEar Rot Resistance Ratings: Many hybrids are screened for Fusariumresistance, but it is important for producers to inquire with seedsmen about ratings unique to each hybrid.
4)   Insect Traits:Above ground Bt traits target worms in corn ears. Damage from corn earworms, fall armyworms, and western bean cutworms is strongly correlated with Fusariumear rots and fumonisin. So, producers should consider Bt insect traits for managing ear worms and reduce feeding damage to minimize Fusariumdevelopment. However, we are beginning to see more unexpected survival and damage with the Bt corn hybrids currently used for our corn ear pests. Producers may want to look at planting corn hybrids with the Bt Vip3A trait. This trait is showing good protection against the three lepidopteran ear pests.
5)   Husk Coverage:On the Texas High Plains, few elevators use driers; consequently, it is necessary for corn to air dry in the field until a grain moisture of approximately 14% is reached. Many hybrids grown on the Texas High Plains are open husk hybrids because, the open husk permits the kernels to dry more quickly. However, the ear with an open husk is at a greater risk for bird and insect damage. 
6)   Ear Orientation:Most of the hybrids currently grown on the Texas High Plains have a short shank, which results in an upright corn ear. An upright ear with an open husk will dry down more quickly under dry conditions, but an upright ear with an open husk will hold water during moist conditions, which magnifies Fusarium ear rot infection and the risk for fumonisin development. While precipitation is responsible for water accumulation in the husk in most fields, poorly placed irrigation nozzles may also result in corn ears being repeatedly hit with water later in the season. Consequently, downward facing ears allow for water to drain away from the ear during the later stages of grain development. 

Wednesday, August 8, 2018

Evidence of Bollworms Damaging Bt cotton in the Texas Panhandle

I received a text last night from Cameron McAnally, FMC Retail Market Manager, about bollworms damaging a Bollgard 2 cotton field near Wellington, TX. This is the first report I am aware of where there is bollworm damage in Bt cotton in the Texas Panhandle. I forwarded the information to Dr. David Kerns, Cotton Entomologist at Texas A&M College Station, and he stated that Bollgard 2 fields around the Altus, OK area had been sprayed for bollworms. This would indicate that Bt cotton traits are not holding up to bollworm infestation pressure or bollworms may not be as susceptible to the traits. Either way Bt cotton fields across the Texas Panhandle may be subject to bollworm damage.

In a previous newsletter on July 28, 2018, I wrote about bollworms being sprayed in non-Bt cotton on the Texas Panhandle. However, at that time I was not aware of bollworms damaging Bt cotton varieties such as Bollgard 2, WideStrike, or TwinLink. Now that we have reports of bollworms in Bt cotton, scouting these cotton varieties become more critical. Sampling for bollworms in Bt cotton varieties becomes more tedious because bollworms can be found throughout the plant in squares, white blooms, pink blooms, bloom tags (dried flower in bracts still on small boll, Fig. 1), and bolls. Do not include flared or yellow squares when sampling. And, do not overlook checking bloom tags as larvae can be under the tag burrowing into the tip of the boll (Fig.2). Thoroughly inspect all of these fruiting locations and record the number of damaged and undamaged fruit in order to calculate percentage of damage. The following table contains the action threshold for making control decisions.

Figure 1. Bloom tag, photo: UTcrops.

Figure 2. Bollworm damage to boll under a bloom tag. Photo: M. Carter.

Bollworm and Tobacco Budworm Action Threshold Based on Boll Damage
Cotton Stage
Action threshold (both Bt and non-Bt cotton
Before bloom
> 8 worms (>1/4 inch) per 100 plants or when populations threaten to reduce square retention below 80 percent
After boll formation
>6% damaged squares and/or bolls and worms are present
Fields that have accumulated 350 DD60s beyond 5 NAWF are no longer susceptible to first or second instar bollworm/tobacco budworm larvae. Action threshold should be adjusted according to yield potential and production system (dryland vs irrigated).

I spoke with a Monsanto rep and Monsanto currently has a rebate program if Bollgard 2 and Bollgard 3 cotton has to be treated for bollworm control. The program provides a $2 rebate/acre for Prevathon application to Bollgard 2 and Bollgard 3 cotton. This program was initially for south Texas and southeastern states that will expire August 15. Contact local seed reps or dealers for more information about the possibility of this rebate program for the Texas High Plains.