Category Archives: Corn

EPA Requests Comments on Organophosphate Cancellation Petition

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.

Organophosphate registrations Regulations.gov

EPA–HQ–OPP–2022–0490

 

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Bollworm Control in Cotton

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)
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)
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.

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Nutrient Management in Cotton During Drought Conditions

Due to the ongoing drought, I’ve recently received questions along the lines of, “how much N is still available after the prill sits on the soil surface without rain for 35 plus days?” and, “should I begin a foliar fertilizer regiment to meet plant N/K/S/B demands?”  In this blog, I tackle both of these questions and share N response curves generated from Tennessee data over the past 5 years.

“I applied urea and it didn’t rain for a month.  Will my cotton crop have the N required to make close to maximum yields?”

For growers that have applied 60-90 lb as urea, the simple answer is yes; the amount of soil nitrate released from the urea you applied will likely meet cotton N demand without additional N fertilizers given plant available water increases significantly in the coming week. Generally, if surface applied urea fertilizer is not incorporated into the soil, some of the N may be lost as ammonia into the atmosphere depending on weather, soil properties and management practices. Continue reading

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Bollworm Trap Catches

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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.

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Spider Mite Numbers Increasing in Cotton

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I’ve received several phone calls about spider mites increasing in cotton around West Tennessee. Spider mites favor hot, dry weather and will often become an issue after plant bug applications are initiated. UT recommends treatment when 30-50% of plants are showing signs of injury and spider mites are still present.  This may be too aggressive under low stress conditions, but most of the crop is currently under substantial heat and drought stress. Treatment options are fairly limited and most are mite specific. Abamectin based products are typically the first option because they are economical and effective. There are a couple different formulations of abamectin that are different lb/ai per gallon products.  Below is a rate conversion of 0.15 lb ai/gallon formulations (Willowood Abamectin 0.15 EC, etc)  to 0.7 lb ai/gallon formulations (Agri-mek SC 0.7, Willowood 0.7 SC, etc).

5.0 fl oz/a = 1.0 fl oz/a

7.0 fl oz/a = 1.5 fl oz/a 

8.0 fl oz/a =1.75 fl oz/a

10.0 fl oz/a = 2.0 fl oz/a

Abamectin rates below 7.0 fl oz/a or 1.5 fl oz/a should be avoided due to potential resistance issues and the increased likely hood of retreatment.

Other mite products such as etoxazole (Zeal, Stifle) are mite growth regulators that work very well but are more expensive and somewhat slower than traditional miticides.  Fenpyroximate (Portal) is a contact miticide that has a shorter residual than abamectin or etoxazole but  works very well. Bifenthrin alone is not an adequate miticide and should be avoided.

Products used for controlling plant bugs, bollworms and stink bugs (OPs, pyrethroids) exacerbate mite populations and their use, especially during hot dry conditions, should be delayed until after bloom if possible. Mite populations can rebound quickly after miticide applications so diligent scouting is critical to slowing the spread of mites across a field.

 

 

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Is it time to irrigate corn?

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Corn is not sensitive to water limitations in early vegetative stages, but it’s important to watch the growth stages and soil type when timing irrigation. After V8, corn undergoes rapid vegetative growth and ear size determination begins (Table 1).  A corn plant’s irrigation requirement will drastically change with the onset of hot and dry conditions such as are being experienced this month (Figure 1). Continue reading

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