Thursday, May 10, 2018

Wireworms in Texas High Plains Cotton

I have received a few queries regarding wireworms lately. Here is some info to answer some of the common ones.

What are wireworms
Wireworms are a common cotton pest which feed on germinating seeds and emerging seedlings. Two types of wireworms feed on cotton: true wireworms and false wireworms. True wireworms, commonly called click beetles, are members of the Elateridae family, while false wireworms, or darkling beetles, are from the Tenebrionidae family.
Click beetle
Darkling beetle

Wireworm larvae (Photo: Pat Porter)
Overwintering larvae inflict the most damage as they become active in the spring. The larvae damage cotton by feeding on the root, hypocotyl (stem of the germinating seedling), and cotyledon (seed leaves) of plants before emerging from the soil. Root feeding can kill plants and reduce plant stand but usually results in stunting.

It’s hard to find crop worms that you can’t see! Soil-dwelling habit of larvae makes it very challenging to scout for. Baits with mixture of either wheat grain or oatmeal and honey may help detecting the presence of wireworms in field.

There are no rescue treatments. Minimize wireworm infestations through clean cultivation and fallowing. Infestations are most severe in no-tillage or reduced-tillage situations, particularly following grain crops. Planting shallow and under warm conditions allows cotton seeds to germinate rapidly and plants to outgrow wireworms. Insecticidal seed treatments and/or at plant insecticides are the most effective means of minimizing wireworm damage.

Can compost application make problem worst?
No, unless the compost is carrying any wireworms or their eggs. In general, compost can provide better environment for wireworms that already exist in the field but there are little or no data available on this.                                                                                                                          

Need more info?
Access our online fact sheet on wireworms at: http://agrilife.org/lubbock/files/2017/05/Wireworms_ENTO-068.pdf

Thursday, April 12, 2018

As Crop Threats, All High Plains Fall Armyworms Are Not The Same

We all respect fall armyworm as a significant threat to High Plains corn, sorghum and cotton, and that is why we run pheromone traps to assess the potential threat during the growing season. Last year we sent some of our moths to Ashley Tessnow, a graduate student working with Dr. Greg Sword in the Dept. of Entomology at College Station. She is looking at the population genetics of fall armyworm.

She sent some of her preliminary results this week, and they were a surprise; based on just 2017 moths, we seem to have a baseline level of around 30% "rice" strain. There are two strains of fall armyworm, and the rice strain feeds on rice, Bermudagrass and Johnsongrass (but can feed on corn). The "corn" strain feeds on corn, sorghum and cotton. In another surprise, the baseline level of about 70% corn strain jumped to 93% in the late June sample when we had a sudden influx of high numbers of moths for just a few days. 

I sent Ashley a draft of this text, and she wisely added the following comment. "An important caveat is that the corn versus rice strain determination is based on a single mitochondrial gene. It is possible that there could be hybridization between the moth strains that were originally pure corn and rice before beginning their migration from south Texas earlier in the year."Ashley’s more detailed genome-wide sequencing of these moths will help us know if this is occurring.

Ironically, Ashley's data arrived at the precise moment Blayne Reed, IPM Agent in Hale, Swisher and Floyd counties, and I were discussing a research trial to determine whether we could time insecticide sprays in corn based on fall armyworm pheromone trap captures. Spraying on trap captures is not a good idea in most cases, but fall armyworm eggs are difficult to scout for and the treatment window after they hatch is very short. Ashley's data told us that a) we might not know what proportion of the moths in a trap are a threat to corn, and b) the proportion that are a threat seems to vary significantly (and unpredictably) over the season. And, well, c) our assumption that High Plains fall armyworms are almost entirely corn strain is probably wrong, but that is really good to know. Suffice to say that it is not likely we can develop a treatment threshold based on trap captures. 

Our pheromone trapping project still has great value in telling us when moth activity is high and crops are at risk. However, thanks to a graduate student at Texas A&M we now know that we need to interpret our trap data cum grano salis, which, if you missed it in logic class, means with a grain of salt. 

Monday, February 5, 2018

All New Guide to Manage Cotton Insects is Now Available

Entomologists with Texas A&M AgriLife Extension Service have released a new statewide guide on managing insect pests of cotton.

The highlights of new guide include 1) description of economic arthropod pests of cotton in Texas, including their associated damage to crop growth stages, 2) description of the various sampling methods for these pests, 3) information on Bt traits available in market and their relative efficacy, and 4) description of action thresholds and management tools for each pest.

Here is a link to access online version of the guide.

It can also be downloaded from the Texas A&M AgriLife Extension bookstore at no cost.

Friday, February 2, 2018

Texas Receives Section 18 for Transform for Control of Plant Bugs in Cotton

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service

The EPA has approved the Section 18 Emergency Exemption for use of Transform WG in Texas to control plant bugs in cotton. This exemption is effective March 1, 2018 and expires October 31, 2018.

Pests and application rates: Plant bugs (1.5 – 2.25 oz Transform WG per acre)

Spray drift management: Applications are prohibited above wind speeds of 10 mph

-    Pre-harvest Interval: Do not apply within 14 days of harvest.
-    A restricted entry interval (REI) of 24 hours applies to all applications.
-    Minimum Treatment Interval: Do not make applications less than 5 days apart.
-    Do not make more than four applications per acre per year.
-    Do not make more than two consecutive applications per crop.
-    Do not apply more than a total of 8.5 oz of Transform WG (0.266 lb ai of sulfoxaflor) per acre per year.

Sunday, December 10, 2017

Bt Corn Update, and New Bt Trait Table Published

As final seed purchases are being made in the Texas Panhandle, here is a brief update on the status of Bt corn. But before your eyes glaze over from the discussion below of new Bts and resistance to older Bts, I want to highlight a publication that makes it easy to tell which toxin packages and herbicide traits are in which type of corn. Dr. Chris DiFonzo at Michigan State University publishes the annual "Handy Bt Trait Table for U.S. Corn Production", and the 2018 version was posted online today. (I am a contributor to this publication, but Dr. DiFonzo does the heavy lifting.)  In just two pages she lists the types of Bt present in all commercialized corn in the U.S.A., and the table presents the trade names for traits, Bt event, protein(s) expressed, targeted insects and herbicide traits.

The 2018 Trait Table also lists the insect x Bt combinations with documented field-failures, confirmed resistance, or cross-resistance. These statements are based on published lab assays and/or field research. The resistance column is intended to alert growers and consultants to potential management problems, influence seed selection, and encourage field scouting. It is important to note that the Trait Table is a national publication, so check with your local seed company or extension personnel for the types of Bt resistance present in your area.

For those looking at a printed version of this newsletter, the Handy Bt Trait Table can be found here: https://www.texasinsects.org/bt-corn-trait-table.html .

And now to the Bt corn update.

Monsanto is marketing Trecepta, its version of Vip3a pyramided with other toxins. I worked with Trecepta in 2017 and was impressed with its insect resistance and yield. For Vip3a corn we have Monsanto's Trecepta, DuPont Pioneer's Leptra, and Syngenta's Viptera. This type of corn is virtually immune to caterpillar damage whether the pest is western bean cutworm, fall armyworm or corn earworm. I have worked with Leptra for six years and Trecepta for one and, in that time, have seen only two live caterpillars in many thousands of ears I have examined.

On the resistance front, laboratory studies conducted primarily in Canada by Dr. Jocelyn Smith (with coauthors from academia and seed companies) have shown that western bean cutworm (WBC) is now resistant to Cry1F (often sold as Herculex). Control with Cry1F, even in the Texas Panhandle, has been slipping for several years, and it is now conclusive that resistance is a big part of the reason. All of the Cry1F registrants and licensees have removed WBC from the list of insects their non-Vip3a Bt corn will control. All of the companies correctly point out that the only Bt corn that will control WBC are the hybrids with Vip3a (combined with other ineffective toxins which vary by company). Bt hybrids that do not contain Vip3a should be scouted and treated according to extension recommendations.

Southwestern corn borer is known to be resistant to Cry1F in southeastern Arizona and southwestern New Mexico. The good news is that we have no indication that this resistance has come to Texas. DuPont Pioneer made significant efforts in 2017 to determine where the resistance does and does not occur. As part of this they funded John David Gonzales, IPM Agent in Bailey, Parmer and Castro counties, to make SWCB collections, and that project will be ongoing in 2018. The other good news is that in places where the resistance does exist, planting Bt corn with two toxins rather than just Cry1F has eliminated economic yield losses.

In the less than good news category, Dr. Ed Bynum, Extension Entomologist in Amarillo, and I have been in continuous corn fields in the Dalhart area that had unusually high amounts of corn rootworm damage in mCry3a hybrids. There have been many instances of western corn rootworm resistance to Bt toxins in other parts of the country, and is known that there is cross resistance between Cry3Bb1, mCry3a and eCry3.1Ab. It looks to me like we have resistance to these toxins in the Panhandle. However, resistance should be determined through laboratory analysis of the offspring of adults collected from fields, and that is why it is important to contact extension personnel or your seed dealer if you are seeing indicators of resistance. These indicators include fields that have been planted to the same Bt toxins for three or more years, the need to use soil applied insecticides on top of the Bt, high levels of root pruning, goosenecking or lodging of plants, or consistently high numbers of adult beetles in July or August. It is important to report suspected resistance while there are still plenty of adult beetles in the field to collect. Dr. Bynum and I would be glad to discuss resistance with anyone who thinks they might have a problem.

Thursday, October 26, 2017

Southern Bt Crops: Getting Boxed In

Insects have developed resistance to the older Bt toxins in cotton and corn on a local or regional scale. A quick look at the situation in the southern U.S.A. finds that in the last two years, resistance has been documented over a large geographic area in cotton bollworm/corn earworm (Helicoverpa zea) to the cotton Cry1Ab, Cry1Ac and Cry2Ab2 toxins. In corn, the limited efficacy of Cry1Ab, Cry2Ab2 and Cry1F has slipped from where it was years ago. This year in the mid-south, university personnel are reporting as much earworm damage in Bt corn as in non-Bt corn.

The "new" toxin, Vip3a, is highly effective on bollworm/earworm, and seed companies are putting it into new corn hybrids and cotton varieties alongside suites of the older toxins for which resistance has developed. Yes, readers can already see what is wrong with this picture; once Vip3a hybrids and varieties are widely planted, bollworm/earworm will be selected for successive generations on this toxin that now has only partial protection from the other toxins because they are already compromised. There will be two generations of Vip3a resistance selection on corn, and then another 1-2 generations of selection on cotton.

When bollworm/earworm becomes resistant to Vip3a, cotton will suffer economic damage because bollworm is a major pest. Resistance will be noticed in cotton first, in part because Vip3a toxin expression is lower in cotton than in corn. When Vip3a fails in cotton, growers will then begin to spray their crops 1-3 times per season with the diamide class of insecticides, the most effective class on bollworms. This in turn will select bollworm for resistance to diamides. Cotton production costs will rise and profits will decline. Any new toxins are seven to ten years away, so profitable cotton production depends on keeping bollworm susceptible to Vip3a for as long as possible.

On the other hand, on the vast majority of acres in the southern U.S., corn does not need the protection afforded by Vip3a. (The exceptions would be the few areas where fall armyworm is a pest, and in very small areas where fumonisin levels can increase due to insect damage to ears.) Corn earworm is not a significant pest in field corn; it damages the tips of ears and is not a major contributor to yield loss. This fact, however, has not stopped the seed companies from marketing Vip3a corn as a breakthrough solution to the corn earworm "problem". It is easy to sell technology that results, at least for a few years, in a completely undamaged ear, whether that technology is needed or not.

Unnecessary insect control aside, seed companies have put their most advanced genetics into Vip3a corn, so even without insects in the system these hybrids will probably yield more than older hybrids with compromised Bts or no Bt. Because they can't get advanced genetics in older, non Vip3a hybrids, growers will end up planting Vip3a corn for the yield potential rather than a need for Vip3a.

As a consequence, it is easy to predict that Vip3a corn acres will expand in the south and therefore hasten the demise of bollworm susceptibility in cotton. If this happens, the cotton industry will suffer major losses and corn growers will barely notice. Earworm/bollworm moths resistant to Vip3a (and perhaps the diamide insecticides) will fly north and threaten the sweet corn industry.

The older Bt toxins are failing, and Vip3a stands as the primary means of caterpillar control for some pests. There is already a field collected colony of fall armyworm that is resistant to Vip3a, but as yet bollworm/earworm is susceptible, although cotton varieties with Vip3a did suffer bollworm damage this season (which does not mean resistance).

I have long been a proponent of GM crops and still am. However, the current situation highlights the fact that we are just on a different version of the old Pesticide Treadmill. We are being boxed in; trying to come up with the next great thing before the last great thing loses effectiveness. I hope the next great thing comes along in time.


For a bit of background, older issues of this newsletter have discussed the convergence of Bt toxins in our crops and what it means for resistance evolution.

Is There Still Value in GM Crops? (9/16/16)
Bt Corn and Resistance Clouds (2/6/16)
Shuffling the Deck Chairs in Bt Crops (9/10/16)

Monday, October 9, 2017

Fumonisin Levels and Insect Damage in Corn

I am not smart enough to be a Plant Pathologist, and in fact had two courses in it in college and still don't understand it. The classic "disease triangle" taught in pathology says that disease occurs when there is a pathogen, susceptible host and conducive environment. This year we seem to have had a happy triangle for Fusarium species, the causative agents of fumonisins.

Not much is known locally about how these fungi interact with our corn, but it is thought that drought stress followed by warm, wet weather, especially at flowering, favor the fungi. Being just an entomologist, I tend to think there is a baseline risk for significant fungal infection based on the susceptibility of the host (hybrid genetics) and environmental conditions. Without insects in the system there will be a given level of fungal growth and fumonisin creation. In my simplistic entomologist's picture, the baseline level is what it is and can vary from year to year, but insect damage can add to this level by opening wounds on the ear and/or by insects carrying fungal spores into the ear.

Dr. Ed Bynum and I did some work at Lubbock in 2012 that looked at the amount of fumonisin in ears with three different levels of insect damage, and more fumonisin was found with higher levels of insect damage. This was one hybrid of non-Bt corn that we sprayed with different timings of insecticide so as to get the three damage levels.

Figure 1. Type of ear damage and fumonisin levels associated with that damage, 2012.
This year there is a need to try and determine to what extent insect damage might be contributing to fumonisin levels, but this is not easy to do unless the hybrids have the same genetic background (inherent susceptibility) and are grown in the same field under the same conditions. One seed company has a small plot field trial near Ralls, and they were kind enough to allow me to sample ears from their new hybrid that contains Vip3a and other toxins, and an older Bt type that has fewer toxins but still the same genetic background as the new type of corn. This is a fair comparison for determining the role of insects. The older type of Bt corn averaged 3.6 damaged kernels per ear, while the new corn with Vip3a was essentially undamaged. Even the silks on the new type of corn were intact. The photos below represent what I saw in the field today.

Figure 2. New hybrid with Vip3a and other toxins (top), and older Bt with two toxins (bottom). The new hybrid was essentially without insect damage. In the older hybrid the insect damage was only at the tip, but fungal growth could proceed through much of the ear. 

The same photo as above, but rendered in an infrared simulation that highlights the kernels damaged by fungi. The grain from these ears was sent for laboratory analysis of fumonisin content, and the relatively undamaged ears on the top of the photo had an average of 6.0 ppm fumonisin. The ears on the bottom row had an average of 208 ppm. 

It is common on the High Plains for nearly every ear of corn to have corn earworm damage, and this year was no different and not significantly worse. In the opinion of this entomologist, the problems we are having this year are primarily due to environmental conditions that favored Fusarium. Having said that, I have worked with Vip3a corn for six years, and in all that time have seen only two live caterpillars in thousands of ears examined. Vip3a corn is essentially bulletproof for now, and if the goal is to reduce caterpillar damage then this type of corn is the way to go. Of course it is more expensive than older Bt technologies. All of the seed companies put other Bt toxins in with Vip3a. Pioneer sells their Vip3a corn as Optimum Leptra or AcreMax Leptra, Monsanto is now beginning commercial sales for 2018 as Trecepta, and Syngenta calls it Agrisure Viptera or Agrisure Duracade 5222. This is not to say that these hybrids won't have fumonisin problems; the inherent susceptibility might be more or less. It is to say that they will have less insect damage, which our data suggest ultimately plays a role in fumonisin levels.

Update on 10/11/17: Erin Louise Bowers did her Ph.D. dissertation on the benefits of transgenic corn in reducing fumonisin levels. She found that Cry1Ab +Vip3a corn had lower fumonisin levels that other types of Bt corn and non-Bt corn. The work is here.