Wednesday, February 8, 2017

Cotton Variety Selection: More Bt Traits to Choose From

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

Variety selection is the most important decision made during the year. Selecting Bt vs non-Bt or the kind of insect trait package is an important consideration in selecting cotton varieties.
Bt cotton is genetically altered to produce certain proteins which are toxic to specific groups of insects. For example, currently available Bt traits in cotton specifically target worm pests such as cotton bollworm, tobacco budworm, and beet armyworm. On the other hand, conventional, or non-Bt cotton does not produce such insecticidal proteins and as a result it is more vulnerable to worm damage.

Since the introduction of Bt cotton into US agriculture in 1996, the technology has transformed from a single-gene trait to multi-gene trait packages. The 1st generation Bt cotton had only a single Bt gene. The second generation Bt technologies, such as Bollgard 2, TwinLink, and WideStrike produce two Bt toxins. While the most recent 3rd generation Bt is a three-gene trait—Phytogen brand varieties with WideStrike 3 have already been in the market for the last couple of seasons. Recently, Monsanto (Deltapine brand) and Bayer CropScience (FiberMax and Stoneville brands) announced the availability of some of their varieties with Bollgard 3 and TwinLink Plus technologies, respectively.

Bt Technologies
Proteins expressed
Second generation

Bollgard 2
Cry1Ac + Cry2Ab
Cry1Ac + Cry1F
Cry1Ab + Cry2Ae
Third generation

WideStrike 3
Cry1F + Cry1Ac + Vip3A
Bollgard 3
Cry1Ac + Cry2Ab + Vip3A
TwinLink Plus
Cry1Ab + Cry2Ae + Vip3Aa19

Over the years, Bt technologies have been fairly effective controlling worms in cotton. The second generation Bt was more effective than the first one, and the third generation technology is more effective than the second generation due to the addition of toxin(s). Newer traits usually come with additional costs, so if you don’t need these traits, varieties with older trait packages are still competitive in yield and quality.

Some farmers may choose to go with non-Bt cotton to avoid paying tech fees. With non-Bt cotton, field scouting becomes even more important to stay on top of the game. In 2016, worm pressure on the Texas High Plains was so low that many of our non-Bt cotton fields got away without spraying for worms. This doesn’t mean we will have a similar situation in 2017---we may face higher worm pressure—therefore, there is higher risk associated with the non-Bt crop compared to Bt. However, with a good scouting program in place and timely insecticide applications, non-Bt cotton can perform well.

Finally, insect trait is an important consideration in selecting varieties but it should not take priority over agronomic characteristics such as yield, maturity, and fiber quality. I have seen some of the non-Bt cotton varieties performing as well as Bt cotton and sometimes even better (especially on the Texas High Plains where worm pressure is usually light). Therefore, it’s not the transgenic insect trait but the inherent yield potential of a variety which should come first in the decision making.

Monday, December 12, 2016

Sorghum Stalk Nutritional Quality and Sugarcane Aphid Damage

(Because FOCUS on Entomology has a different readership than our Sugarcane Aphid Newsletter, this is a reprint of an article recently posted on the sugarcane aphid news site.)

One of the questions as we end the season is what kind of affect does sugarcane aphid damage have on the nutritional quality of sorghum stalks that are used for stover. We conducted two experiments this season, and both were designed to look at leaf damage and its affect on grain yield. However, in conducting these experiments we ended up with many plots with discreet levels of leaf damage, and The United Sorghum Checkoff Program asked us to harvest stalks from the various plots and send them for nutritional analysis.

To be clear, the results that appear below are for grain sorghum, not forage sorghum. One experiment was conducted at the Lubbock Research and Extension Center using a sugarcane aphid-susceptible hybrid grown under moderate furrow irrigation, and the other was conducted at the Helms Farm near the Halfway Experiment Station. This experiment was conducted on a sugarcane aphid resistant hybrid grown under drip irrigation that supplied relatively more water than was available at Lubbock. Data from the two trials showed very similar trends, so they were combined to generate the following charts.

The Leaf Damage Rating System developed by Blayne Reed goes from 0 to 10, with 1 being very little damage on the lower leaves, to 10 being all the leaves on the plant with observable damage. Sugarcane aphid damages lower leaves first and then moves up the plant, so a leaf damage rating of 5 would suggest the leaves in the lower 50% of the canopy are damaged.

Each dot on a graph represents at least 4 stalks harvested from a plot at a given leaf damage rating. The nutritional analyses were performed at Servi-Tech Labs in Amarillo. A sample report from Servi-Tech is here.

Figure 1. There was a highly significant decrease in Total Digestible Nutrients with increasing levels of leaf damage.

Figure 2. Crude Protein was not significantly different between plots with different levels of leaf damage. 

Figure 3. There was a highly significant increase in Acid Detergent Fiber (non-digestible components) with increasing levels of leaf damage.

Figure 4. There was a highly significant decrease in Digestible Energy with increasing levels of leaf damage.

Figure 5. There was a highly significant decrease in Metabolic Energy, Beef with increasing levels of leaf damage.

Figure 6. There was a highly significant decrease in Net Energy, Lactating with increasing levels of leaf damage.

Thursday, November 3, 2016

Stink Bug Outbreak in Texas High Plains Cotton: What Can We Do Better Next Season?

Suhas Vyavhare and Katelyn Kowles, Texas A&M AgriLife Extension Service

Stink bug infestation in cotton during August-September
Rotten bolls in stink bug infested field 

This season we experienced unusually high numbers of conchuela stink bugs in Texas High Plains cotton (parts of eastern Lubbock and Crosby counties in particular). Stink bug numbers peaked during August-September when plants were loaded with tender bolls that stink bugs feed on with their piercing-sucking mouthparts. Farmers who spotted stink bugs early and took timely action are now reaping the benefits. However, those who missed an insecticide application in infested fields are seeing severe stink bug damage now that bolls have opened. A few infested fields we visited last week have very little to harvest due to the extent of boll damage by stink bugs. During August-September, stink bug numbers were overwhelmingly high in spots—in some fields numbers were over 2-3 stink bugs per boll. When stink bugs feed on tender bolls, it can result in lint staining or allow pathogens to enter and cause boll rot; smaller bolls may be aborted altogether. As we are now towards the end of the growing season, there are many who want to know what can be done differently for the next season.

The fact is there is not much we can do beforehand when it comes to stink bugs as there are no specific effective cultural practices or resistant varieties available. The best thing farmers can do is regular field scouting. Bolls that have been fed on by stink bugs will typically have a black mark on the outside. It is critical to scout fields for stink bugs especially in areas with the known history of this pest. Our field observations indicate that stink bug population build-up started on grain sorghum and as the grain became too hard for the bugs to pierce with their mouthparts, they moved to adjacent cotton. We will provide more information on stink bug scouting and management when we approach the next growing season. Meanwhile, as we wrap up the current season, the best thing we can do is learn from our experience and scout better next time. 

Stink bug infestation in grain sorghum (photo: Pat Porter)

Wednesday, October 5, 2016

Cry1F No Longer Effective Against Western Bean Cutworm

Western bean cutworm is a serious corn pest in the northern Texas Panhandle and occurs in lower numbers as far south as Hale County. Several years ago the insect underwent a major range expansion and is now the primary corn caterpillar pest in several Midwestern states to as far east as New York and as far north as Canada. This year there have been major field failures of Cry1F in these areas, and the Land Grant entomologists have written an open letter to the transgenic seed industry to prompt them to stop claiming that Cry1F corn controls western bean cutworm. Laboratory data confirming resistance to Cry1F are in the scientific publication process.

Given these new developments, we will be modifying our suggestions for Bt corn to control western bean cutworm to include primarily those that contain Vip3a in combination with other toxins. Our now outdated suggestions are in Table A20 (page 32) of Managing Insect and Mite Pests of Texas Corn, 2016. You will easily find the hybrids with Vip3a.

An open letter to the Seed Industry regarding the efficacy of Cry1F Bt against western bean cutworm: October 2016

This open letter was prepared by the undersigned extension entomologists from the Great Lakes Region regarding the efficacy of the Cry1F (Herculex 1, TC1507) trait on western bean cutworm (WBC; Striacosta albicosta). We strongly urge seed companies to remove the designation of “control” for this pest with regard to this toxin.

At the time Cry1F received regulatory approval in 2001, western bean cutworm was found in the far western Corn Belt (Colorado, Idaho, Nebraska, and Wyoming), with occasional movement into western Iowa. Indeed, EPA’s original Biopesticide Registration Action Document (BRAD) for Cry1F Bt corn, published in August 2001, did not even mention WBC. Instead, the following language was used: “The registrant-submitted data indicate that Cry1F protected corn offers excellent control of European corn borer, southwestern corn borer, fall armyworm, black cutworm, and suppression for the corn earworm.” References to Cry1F giving “excellent protection” against WBC began to appear in marketing literature only after Iowa State University entomologists documented its eastward range expansion and the first economic damage in that state. Presumably this rating was based on a limited number of lab assays and field trials done in pure Bt stands, not Refuge-in-a-Bag hybrids.

The rapid eastward range expansion of WBC across the central Corn Belt into the Great Lakes Region resulted in a dramatic increase in the number of WBC-infested acres in a short time period. This created a large-scale ‘efficacy test’ of Cry1F hybrids to (as stated in the BRAD) “provide highly efficacious control of key Lepidopteran pests”, “reduce the use of more toxic chemical insecticides” and “reduce levels of mycotoxin in corn”. In all these regards, Cry1F has failed in our states. This season in particular, the level of larval infestation and damage is troubling in both single and pyramided Refuge-in-a-Bag hybrids from multiple seed companies. Wherever Cry1F is challenged by WBC, it fails to provide observable benefit to producers. We have collectively fielded dozens of phone calls and emails, and visited numerous fields; we know that our agribusiness contacts and seed industry agronomists have responded to many more, and corn acres were sprayed with both insecticides and fungicides (most too late and with little hope of benefit). People are frustrated and angry and, more importantly, yield was lost. Growers purchased Cry1F hybrids with the understanding that the trait provides “control”, thus negating the need to scout for egg masses or larvae in those fields. When the visible manifestations of damage became apparent late in the season, such as the intense ear-feeding we witnessed, it was far too late for rescue treatments. As the fall progresses and damaged corn is harvested, additional issues are sure to arise regarding quality and mycotoxin levels. The severity of the latter will largely be dependent on weather conditions favorable for ear mold development. What is certain is that many damaged ears are primed for fungal colonization and quality loss.

As extension educators and specialists, we can no longer refer to Cry1F as providing WBC control. In fact the opposite is true, and our extension recommendations (including the Handy Bt Trait Table) will be changing to classify Cry1F hybrids for WBC the same as non-Bt, Cry1Ab, or double/ triple pro hybrids, all of which provide no control. In other words, we believe that Cry1F fields must be scouted for egg masses and sprayed with foliar insecticides if needed, the same as a non-Bt corn. Western bean cutworm is now the PRIMARY Lepidopteran ear pest in many parts of the Great Lakes region. For growers in our states, the costs of scouting and spraying Cry1F corn nullifies a major reason they purchased and planted a hybrid with the trait in the first place.

Before growers make seed choices for 2017, we again urge the seed industry to acknowledge the reality of what is happening in the field, and to reclassify Cry1F in hybrid fact sheets, technical use agreements, and other educational materials. This would reduce grower expectations of Cry1F and allow local agricultural professionals to deal with their customers in a more truthful manner, in a way that allows for protection against yield loss. We also urge the industry to regard western bean as a primary, not a secondary, pest. Doing nothing risks alienating those close to the situation, including field agronomists, consultants, university extension staff and (most importantly) corn growers themselves who have a vested interest in finding effective pest management solutions for a growing world.

Dr. Chris DiFonzo, Michigan State University
Dr. Christian Krupke, Purdue University
Dr. Andy Michel, The Ohio State University
Dr. Elson Shields, Cornell University
Dr. Kelley Tilmon, The Ohio State University
Dr. John Tooker, Pennsylvania State University

BRAD Document:  http://www.ceragmc.org/files/cera/GmCropDatabase/docs/decdocs/brad_006481.pdf)

Friday, September 16, 2016

Is There Still Value in GM Crops?

The day after the Bayer/Monsanto agreement was announced this week, The Wall Street Journal had an article entitled "Behind the Monsanto Deal, Doubts About the GMO Revolution" (subscription required or article can be purchased). The paragraph that best summarizes the article was, "Today, farmers are finding it harder to justify the high and often rising prices for modified, or GMO, seed, given the measly returns of the current farm economy. Spending on crop seeds has nearly quadrupled since 1996, when Monsanto Co. became the first of the companies to launch biotech varieties. Yet major crop prices have skidded lower for three years, and this year, many farmers stand to lose money."

The article contained a graphic that showed that since 1996, the year GM soybeans were introduced on a commercial scale, soybean seed prices have risen 305% to $60.75 per acre, but commodity prices have risen only 31% to $9.79.  It is a bit puzzling why the Wall Street Journal did not choose to plot the yield increases per acre since 1996; we all know that higher yields are good but reduce prices, all other things being equal.

This is an entomological newsletter and I won't discuss the benefits to growers that have come from having herbicide tolerant GM crops that allowed greater yields through less weed competition while using a simpler and less expensive herbicide regimen. I will also not discuss the yield losses later incurred when weeds became resistant to those herbicides, or the additional expense of having to go back to a more complicated and expensive herbicide regimen. And I will not discuss the latest generation of herbicide tolerant GM crops that are tolerant to one of two types of older herbicides that have been reformulated to reduce off-target drift. These new crops are being sold in part as the answer to the resistance problem that was caused by the first generation of herbicide tolerant crops. The seed companies will charge on the order of $6 per acre for this trait ($25 - 30 per bag of seed) over and above the cost of current technology, and will additionally profit by selling growers the specific herbicides that must be used on these crops.

GM crops with toxins for insects (Bt crops) have reduced insecticide use and provided environmental benefits. In the Midwest, Bt corn with toxins for European corn borer has reduced the populations of that pest to the point that non-Bt corn can be grown without the need for an insecticide application. Similarly, in my part of the country we no longer fear southwestern corn borer; the planting of Bt corn has greatly reduced the size of the population. Obviously the widespread planting of Bt crops toxic to some insects has resulted in significant benefits.

However, 2016 has been a year of frustration for some farmers who plant GM corn, soybean and cotton. As the Wall Street Journal article said, this is in part because the price of seed seems to be high compared to the value of the commodity at the grain elevator or gin. It is also because some of our insect toxin traits in corn and cotton no longer work as well (or at all) on some of the insects that damage crops and reduce crop quality. This is not the first year for such frustration; resistance to corn rootworm Bt crops was first scientifically documented in 2011 and has spread geographically and to all four Bt toxins used in corn. At least two caterpillar toxins (probably three) have failed due to resistance, as corn growers in the Midwest and Canada are finding out this season due to extensive western bean cutworm damage in their Cry1F corn. This year cotton farmers found themselves having to spray GM crops with insecticides to prevent yield loss.

Our insect-protected Bt crops never were "bulletproof". In fact they never worked very well at all on some pests and were not intended as the sole control for other pests. In the latter case, the word "suppression" or some similar word was usually mentioned in company literature, or no mention was made at all and the grower was left to come to his or her own conclusion.  The job of selling seed being what it is, the nuances between the ability to control one pest and suppress others was often lost and these technologies competed with each other in the sales arena based on being oversold in their abilities. Sales material showed perfect ears of corn and growers were led to believe in the invincibility of the product.

The current frustration then is a result of resistance development in the pests the technologies were meant to control, and resistance in pests for which the technologies formerly provided suppression. In both cases it has become necessary to use traditional insecticides on top of the Bt technologies or suffer significant yield loss. And even when traditional insecticides are used there is often yield loss after the increased expense.

Why are seed prices so high? The Wall Street Journal article said that when GM crops were introduced Monsanto came up with a formula that was quickly adopted by the rest of the industry. "For every dollar that biotech seeds saved farmers in pesticides and labor, Monsanto would keep about 33 cents, in the form of a “technology fee” charged on top of each bag of seed." Seed prices keep going up, but GM crops are no longer saving growers as much in pesticides and labor as they once did. This is to say that in many places GM crops have less value now in terms of insect and weed control. It is not hard to understand the frustration at paying higher prices for something of lesser value.

However, our GM crops are not just herbicide tolerance and insect resistance traits, they are also improved genetics for yield and drought and disease tolerance. These qualities are expensive to produce, and the regulatory system in the US adds significant cost to some of them.

On the surface it would seem that growers could choose to buy non-GM seed and go back to the way we handled insect and weed control prior to 1996. This might work for insects, especially in places Bt crops have driven down populations of major pests. Unfortunately, non-GM crop breeding slowed considerably in the age of GM breeding, and the yield potential of many non-GM crops, even in the absence of pests, is not competitive with GM crops. (This is more true in corn than in cotton.) Another difficulty is that the introduction of GM crops coincided with the Food Quality Protection Act. This was convenient for the EPA because one could rationalize that Bt crops could replace many of the insecticides that would be cancelled. Today there are fewer insecticide options for use in non-Bt crops (or Bt crops with resistant insects), and many of the newer insecticides carry high price tags.

For sure there is still value in GM crops, but right now that value does not seem to be what it once was. It is unclear whether 2016 is the year we will look back on and point to as the start of a movement away from GM crops, or whether improved technologies and higher commodity prices in the future will make them look like a more valuable proposition.


(A  2013 USDA publication called Genetically Engineered Crops in the United States provides a concise summary of the number of GM traits introduced and the economic returns from them. Unfortunately, the publication is somewhat outdated because it does not address the weed and insect resistance to GM crops that has occurred in the last four years.)

Saturday, September 10, 2016

Shuffling the Deck Chairs in Bt Crops

2016 has been a challenging year for our Bt crops. Cotton bollworms did an unusually high amount of damage in many fields of Bt cotton, and corn earworms (which are bollworms by another name) caused a significant amount of damage to corn crops from Texas through Kansas. Western bean cutworm caused severe damage in fields of Cry1F corn in the Midwest and Canada where once the toxin provided a reasonable level of control. Fall armyworm is known to be resistant to Cry1F corn in parts of the country. Corn rootworm is resistant to toxins that once did a good job of control.

One question this fall is whether we have resistance to our Bt toxins targeted at caterpillars and, if so, how far it has spread. Field observations suggest that we do have resistance, but we will have to wait for the results of the laboratory tests on the progeny of the insects collected from the field. We don't have a magic genetic test to detect resistance, so we do things the old fashioned way by crossing field collected insects with laboratory insects and seeing how their offspring survive known doses of Bt toxins as compared to progeny from a colony we know to be susceptible to the toxins.

This article is not about whether we have resistance, it is about why we will have more resistance. When Bt crops were originally registered and deployed some 20 years ago, the seed companies each had their own unique toxins that worked more or less well on specific pests. Effectively the percentage of the pest insect population exposed to any particular toxin depended to a great extent on the market share held by each company.

Over time, however, seed companies began licensing their toxins to their competitors. In addition to financial gain there was a good reason for this; two or three different toxins were far better than one for delaying resistance. If an insect had an allele to survive on toxin 1, it probably did not have different alleles to survive on toxins 2 and 3. The insect would be killed and its allele to survive toxin 1 would die with it and not be passed to the next generation.

This strategy of multiple toxins targeted at the same pest (a pyramid of toxins) was successfully employed when corn rootworm in the Midwest became resistant to Cry3Bb1; the answer was to make plants that expressed both Cry3Bb1 (from company A) and Cry34/35 (from company B). Rootworms resistant to Cry3Bb1 were still exposed to Cry34/35 and many of them died. However, because they were already resistant to one toxin they were really only being challenged by the remaining effective toxin, so they were back to having to overcome one toxin and not two. Astute readers will note that we have four toxins for corn rootworm, so why not add one or both of the other two? The answer is cross resistance; rootworms that are resistant to Cry3Bb1 are also resistant to mCry3a, even if their ancestors never encountered mCry3a. Researchers in Iowa have recently confirmed resistance to the fourth toxin, eCry3.1Ab. A good article on this problem is here, and it says, "Cry3Bb1, mCry3A and eCry3.1Ab all appear fairly similar to the rootworm, and resistance to one is likely to confer resistance to the other two."

The example above illustrates that there is a finite limit to the addition of new Cry toxins and, because companies are licensing their technologies to their competitors, essentially our whole arsenal of Bt toxins is being planted on the vast majority of our corn and cotton acres. On a national level we are effectively selecting several generations of insects, even on different crops, on the same or similar toxins. (Corn rootworm is only on corn, but many of the caterpillar species infest both crops.)

If you want to see an example of cross licensing of toxins, look at Chris DiFonzo's Handy Bt Trait Table for corn. For each company, the products listed toward the bottom of their offerings are the newer types of Bt. Regardless of company they all look pretty much the same. (Cry1A.105 is just a synthetic stack of Cry1Ab, Cry1F and Cry1Ac. Cry1F and Cry1Ac are also used in cotton.)

The newest silver bullet is Vip3a for caterpillars. It is fairly high dose and does a good job of controlling many species. In their latest generation of Bt corn and cotton, all of the seed companies are now adding Vip3a as a pyramid with older toxins. Once again the insects will have adapted, or partially adapted, to the older toxins, so selection for resistance will be on Vip3a.

There does not seem to be a way out of the box with corn rootworm toxins, and increasingly we are relying on Vip3a to protect yield while the other caterpillar toxins are failing. Cry toxins had a good run and will hang on for a while longer, but the era of the Cry toxin seems to be ending.

Thursday, September 8, 2016

Green cloverworms in alfalfa and soybeans

If you are growing soybeans or alfalfa on the Texas High Plains it would be a good idea to scout for green cloverworms. I was in a soybean field near Ralls earlier in the week that had approximately 8 larvae per plant, and I just got a call about soybeans near Clarendon that were heavily infested.

In both cases the people making the reports thought the worms were soybean loopers. It is easy to tell the two caterpillars apart because loopers have two pairs of prolegs on the abdomen while the green cloverworm has three pairs. Loopers are fairly lethargic, but green cloverworms hop around quickly when disturbed.

Green cloverworm larvae near Ralls

Typical defoliation in soybean caused by green cloverworm

Fortunately the green cloverworm is only a leaf feeder in soybean and it does not damage pods. For alfalfa here is a quote the Oklahoma guide, "These defoliators are rarely a significant problem in established alfalfa, although seedling stands can be heavily damaged by their feeding." However, if there are enough of them present they can cause defoliation, which in turn will reduce the amount of nutrients the plants can store for overwintering.

For soybeans, University of Tennessee has good list of insecticides in their publication here. Oklahoma State University has control suggestions for alfalfa here.