Phaseout of Most Bt Corn Hybrids Proposed

 My recent post discussed the proposal by EPA to drastically change the resistance management regulations around Bt corn and cotton. You can submit a comment here before November 9th. The proposal is hard to find on the EPA website, so I have reposted it here.  Part of the plan is to phase out all single toxin Bt corn hybrids within three years, and all pyramid (multi-toxin) hybrids that do not contain Vip3a within five years. 

Assuming we don't get any wonderful new technology in the next few years, this would leave southern corn growers with two choices; grow a pyramid hybrid that had Vip3a, or grow non-Bt corn. (It would also leave cotton growers with just the 3rd generation varieties containing Vip.) There are some implications for resistance management of corn earworm/cotton bollworm that are being discussed should this come to pass, like having all Bt corn and Bt cotton in the south expressing Vip, while at the same time the older toxins are failing and less able to provide any protection against resistance developing to Vip in the pyramid with older toxins. Essentially, Vip would become a single toxin because the pyramid could not protect it. The same EPA proposal is attempting to fast-track the removal of old single toxin corn hybrids because they pose a very clear danger for resistance evolution. I explained why this is so back in 2018.

Another outcome would be that corn growers would have a drastically shortened list of hybrids from which to choose. The EPA proposal simply listed the hybrids to be removed by their registration numbers, which is regulatory-speak and rather foreign to most of us. However, yesterday, Emily Unglesbee at DTN/Progressive Farmer posted an article that put common names on these corn and cotton hybrids. The title of the article is Bt on the Chopping Block, and I encourage you to read it. 

Chris DiFonzo at Michigan State University is lead author of our "Handy Bt Trait Table For US Corn Production", and she has created a new table that shows what will be left for caterpillar control after the proposed phaseout. Here is a pictorial representation of the bottom line.

The 8 survivors. 

The 34 types of Bt corn currently sold.

The Handy Bt Trait Table will give you a high resolution view of hybrids currently sold. 

Tighter Regulations Around Bt Corn Are Pending

This week the EPA released a draft plan that essentially overhauls many of the regulations around insect resistance management (IRM) in Bt crops grown in the "cotton belt". 

There are many major changes proposed, one of which is that field failures are presumed to be cases of "practical resistance" if certain criteria are met. (Like 6% boll damage in third generation (Vip) cotton and second instar bollworm larvae are present, which is basically the treatment threshold we use now.) Seed companies can then make collections and do the insect rearing and testing to refute the determination of resistance, if they want to do so. This is totally opposite of the way things have been done for 25 years. In the past, field failures were presumed to be from susceptible insects, and only laboratory testing could determine whether the insects were resistant. 

Seed blend corn refuge will be approved for southern planting. However, a 20% structured (block) refuge will also be required with fields planted to seed blends. This block refuge is basically insurance until we can figure out whether seed blends are a good thing or a bad thing, as some of the data say they might accelerate resistance. In the last four years there has been an all out effort by the seed industry and Land Grant Universities to answer this question, and if it turns out that seed blends are safe then the requirement for a block refuge could be dropped in the future. ABSTC (the Agricultural and Biological Stewardship Technical Committee, a consortium funded by Bayer, Corteva (Pioneer) and Syngenta), sponsored a very expensive and detailed seed blend trial that Dr. Suhas Vyavhare and I conducted near Olton this year. Bayer sent a large crew of people to help on the days we could not possibly have done all of the work ourselves. I am grateful that Bayer and their excellent people stepped in at their own expense to help us answer this important question; we could not have done it without them. We are all trying to answer the seed blend questions as quickly as possible. 

The new rules, if enacted as currently proposed, will change things at the farm level. I am quoting from the document directly.

• "Sales of Bt corn products requiring block refuges must be followed up with on-farm visit by the seed industry for compliance monitoring by ABSTC during the growing season. This will be conveyed to growers at the point of sale and be included in the grower agreement. Visits will be reported to the Agency [EPA].
• For farmers out of compliance with block refuge standards in the cotton belt for one year, the registrant [seed company] will withhold all the company's Bt corn products, including RIB and block refuge for two years.
• Registrants must ensure that seed dealers obtain signed grower agreements that set forth the terms of the IRM program. If a seed dealer fails to ensure that at least 95% of the customers sign grower agreements, registrants will restrict the availability of the Bt seed to that dealer. Registrants must ensure that seed dealers keep a record of signed grower agreements for a period of at least three years from sale. 
• Industry must ensure availability of non-Bt elite corn hybrids for refuge."

Why is EPA doing this? Basically it is because corn earworm/cotton bollworm is now resistant to all but one Bt toxin, Vip3a. Refuge rules were not well followed in the past, and now resistance has come home to roost. If we are to prevent resistance to Vip3a, the last effective toxin for bollworm, things need to change. Prior to this we were operating under the set of rules mostly set forth in 1996, and there were some major problems with them. The new guidelines correct several of the mistakes made in the past.

The EPA document is not final, and in several places it goes out of the way to ask for input from producers and consultants. I know the woman who wrote the document and is in charge of changing it, and she sincerely wants to hear from you on how these proposed changes will affect you, and whether there is a better way to accomplish the objectives. I trust her to listen to you. You can be assured that the anti-Bt crop lobby will be submitting comments, so here is your chance.

The 24-page draft document is here: https://beta.regulations.gov/document/EPA-HQ-OPP-2019-0682-0007. The docket where you can submit your comments is here: https://beta.regulations.gov/search?filter=EPA-HQ-OPP-2019-0682. I would be glad to answer any question about the proposed changes, and you can write me at p-porter@tamu.edu. 

Pat Porter

Bollworms per acre coming off of corn (or why we had fewer bollworms this year)

Dr. Suhas Vyavhare and I are conducting a very detailed experiment this year on some aspects of Bt corn. Part of the experiment involves putting 120 emergence cages on the ground under corn after corn earworm larvae (cotton bollworms) have left the corn ears and entered the soil for pupation. This lets us determine the number of moths being produced per square foot or acre under actual field conditions. After they emerge as moths, these insects will then fly to other crops, and their eggs become the late season bollworm infestations in cotton and headworm infestations in sorghum. 

2020 was a fairly light year for corn earworm infestation in corn; only 54% of the ears were infested with larvae at our Olton trial. In most years this would have been nearly 100%.

Here is the math: 

This year we had 3,398 moths emerging per acre from irrigated non-Bt corn, or 407,760 moths per 120 acre field.

In a "normal" year when almost every ear had a corn earworm, this would have been 6,292 moths per acre, or 755,040 moths per 120 acres of irrigated corn. 

My work with the older Bts like Cry1Ab, Cry2Ab2, Cry1F and Cry 1A.105 suggest these Bts are no longer killing as many earworms as they once did, so one could expect them to produce a significant number of moths. Vip3a corn is highly effective at killing corn earworm, so it will not contribute significantly to a moth flight (until we get resistance). 

This is the first chance we have had to estimate the number of cotton bollworm moths coming off of corn on the High Plains, and the numbers are impressive, at least in their contribution to localized bollworm populations in nearby cotton. The lower number of bollworms this year in cotton seem to be directly linked to the lower number of bollworm moths that laid eggs in corn.