The EPA is soliciting public comment on a petition from several organizations to cancel remaining organophosphate (OP’s) insecticide registrations. OP’s are widely utilized in Tennessee row crop agriculture and are critical components of IPM programs. Cancelling an important crop protection product would place increased pressure on a limited number of control options available to producers. We are encouraging agricultural professionals to comment to the EPA on the impacts OP’s have on your production systems. If you need assistance with comments please contact your UT extension specialist. The link to comment is below. Deadline for comments is August 11, 2022.
As of this week, bollworm trap catches across West TN are beginning to increase and moths are making their way into many cotton fields.
Bollworm Moth on Cotton Leaf (Photo by D. Jones)
UT’s threshold for dual gene cottons (Bollgard 2) is 20% of plants have eggs present. That is 2 plants out of 10 have at least one egg present. Bollworm resistance to Cry proteins is increasing across much of the Midsouth and the egg threshold doesn’t give dual gene cottons an opportunity to fail. Insecticide timing at this stage is more critical than rate. A 1.4 fl oz/a rate of Vantacor (equivalent to 16.0 fl oz/a Prevathon) or 8.0 fl oz/a rate of Besiege sprayed on egg lay will work as well as higher rates of the same products. However, if live worms (2-3 day old and older) are present in the plant canopy or have bored into bolls or squares the lighter rates of Vantacor, Besiege won’t cut it for control. Chasing worms in the plant canopy with lower rates often doesn’t end well. Vantacor rates of 1.50 fl oz/a or 9 fl oz/a of Besiege or higher will provide better, more consistent control on worms in the canopy.
Bollworm Moth on Cotton Flower (Photo by D. Jones)
Triple gene cottons (Bollgard 3, Widestrike 3, Twinlink Plus) have a much more robust insect package that is centered on the Vip3a toxin that does most, if not all, of the heavy lifting in controlling bollworms. The threshold for 3 gene cotton is 4 or more larvae are present per 100 plants or 6% or more fruit injury is occurring. So far, the 3 gene cottons are holding up well in West TN; however, I have experienced break through infestations in triple gene cottons under severe drought stress or fields that are at or near cutout (NAWF <5). Bt expression is often negatively affected by environmental stressors and heavy worm infestations coupled with poorly expressing Bt cotton can equal unexpected damage. We still don’t need to spray on egg lay in triple gene cottons but if worms are surviving past a day or so in 3 gene cotton, an application may be necessary. Diamides (Vantacor, Besiege, Elevest) are still the best options for worm control. Orthene plus a pyrethroid is an option but residual efficacy is limited to 5-7 days and the potential for worms to rebound is a real risk.
I’ve gotten a few phone calls inquiring about our bollworm moth trap catches and what the populations are doing. To date, we’ve only had one trap catch that was in the double digits and that was on the WTREC research station. Our trapping runs began in May and will continue through August across West TN. We are still on the early side for bollworms to appear in cotton and once we begin to see consistent numbers across our catches, I’ll update our numbers on the blog. Keep a look out for eggs and kicking up moths as you scout cotton and soybeans. The drought situation and overall poor condition of corn may have an impact on the bollworm generation migrating out of corn, we’ll see the results of that in the coming weeks.
I’ve received a few calls about twospotted spider mite infestations in soybeans in West Tennessee. Spider mites usually are a minor issue in soybeans and I’ve only seen two instances in 10 years that warranted treatments for mites in beans, both were in severe droughts. Spider mite infestations in soybeans, like cotton, often start from the edge of fields. Unlike cotton, infestations don’t result in reddening leaves but a gradual transition from green to light green to yellow to brown. In a normal year, soybeans have the ability to compensate for spider mite injury and most infestations often go unnoticed or mites never gain a foothold due to ample rainfall, predators or entomopathogens that control them before they become a problem. In drought years, when alternative weed hosts have been killed with herbicides or desiccated by lack of water, soybeans become an attractive host for spider mites.
Spider Mite Hotspots in Soybeans (Photo by T. Baute OMAFRA)
Mite populations, in soybeans, often reach very large numbers before they are discovered. This is, in part, due to people not looking and assuming that desiccated brown leaves are a bad spot in the field, charcoal rot or generally poor area that beans are struggling in. Under West Tennessee’s current conditions, brown/yellow patches of soybeans should be investigated for presence of mites and not just assumed its from drought. Thresholds for spider mites are not well established in soybean. Consider treatment when spider mites are present on the majority of plants and premature defoliation is occurring. The decision to treat mites in beans is often difficult but mites can absolutely defoliate infested plants and move on to others. Ignoring spider mites in beans, especially during a drought, can be a costly mistake.
Fortunately we have a few dedicated miticides that are now labelled for control of mites in beans, several years ago this what not the case. Abamectin (Agri-Mek SC 0.7) at 1.75 fl oz/a and etoxazole (Zeal SC, Stifle SC) at 2.0 fl oz/a are both excellent products for spider mite control in beans. Etoxazole is mite growth regulator that will have significantly longer residual control than abamectin; however, a well timed application of abamectin is often enough to get mite populations under control in soybeans. If recurring or severe populations become apparent, etoxazole may be the better choice.
Severe Spider Mite Infestation (Photo by MSU)
Insects/arachnids do weird things during severe drought. Major pests we always assume will be there don’t always appear and secondary pests we never see can sneak in and cause crop injury. The take home is check your soybeans. Don’t just assume that the brown patch by the tree line or yellowing is caused by a sand blow or the beans are just burning up.
