All posts by Sebe Brown, IPM Extension Specialist

Soybean Looper Numbers Increasing

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I’ve received several calls about looper numbers increasing in soybeans across West Tennessee. Numbers range from 3 per 25 sweeps to 25 per 25 sweeps. Treatment is recommended when defoliation exceeds 20% from R1 to R6 or if looper numbers exceed 19 per 25 sweeps. It’s often suggested to ignore small worms (<1/2 inch) in these counts due to predators and entomopathogens taking a substantial toll on their survival.

Pyrethroid additions, at R3 fungicide timing, can exacerbate looper numbers and shouldn’t be included unless they are needed. This is one of the reasons I caution against including an automatic pyrethroid with fungicides at R3 and those applications won’t have any measurable impact on stink bug numbers when the beans hit R5. Loopers are one of the top pests encountered in late planted soybeans and are the most expensive to control. Further, I received word from my colleagues in Mississippi that low rates of diamides (1.2 fl oz/a Vantacor, 7.0 fl oz/a Besiege, 14.0 fl oz/a Prevathon) are providing unacceptable levels of control in large populations of loopers. This isn’t a surprise but take caution when utilizing diamides. Reports of diamide slippage on loopers has occurred for several years and more often than not, it occurs when low rates are utilized against high numbers (>1.5X threshold). Another product, Intrepid 2F (methoxyfenozide), has also had some control issues in Arkansas and Mississippi. Rates of 4.0 and 6.0 fl oz/a did not provide satisfactory control of loopers 7 days after application; however, Intrepid Edge (methoxyfenozide + spinetoram) performed very well. We have several insecticide options available at our disposal but if you’re facing large numbers, low rates of any product (especially the diamides) probably won’t cut it.

One final comment, don’t confuse soybean loopers with green cloverworms. Loopers have 2 pairs of prolegs cloverworms have 3 (see images below). Cloverworms are much easier to control than loopers and pyrethroids, as well as other insecticides, work well. Information on insecticide options for loopers can be found here: https://guide.utcrops.com/soybean/soybean-insect-guide/soybean-looper/

Soybean Looper Larva
Soybean Looper Larva
Green Cloverworm Larva
Green Cloverworm Larva

Fall Armyworm Update

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I’ve been asked several times over the past week if armyworms are beginning to appear in Tennessee.  There are a FEW isolated cases of fall armyworms infesting crops planted for wildlife, mainly millet. The instance and number of worms being found thus far is normal. Tennessee will still have armyworms that migrate North and infest pastures, food plots and the occasional yard.  However, the wormageddon that happened in 2021 was a very unique event and will not occur yearly.

Fall Armyworms in Sweep Net
Fall Armyworms in Sweep Net

Fall armyworms don’t overwinter in Tennessee and populations migrate North from Texas and Florida every year. The difference in 2021 vs 2022 is the conditions that were occurring in April and May in South Texas. Texas experienced a warm and unseasonably wet spring that allowed for the proliferation of extremely large numbers of armyworms. Large numbers of moths plus ample food supply in pasture grasses, fallow grasses, yards and pretty much anywhere that had grass allowed this “army” to make its way North. Texas experienced outbreaks first followed by Louisiana, Arkansas, Mississippi then Tennessee with the moth flight culminating, in Canada, in November. I ask my colleagues, in Southern states, weekly if they are seeing any armyworms or anything resembling what happened in 2021 and the answer has consistently been no.

If we do see armyworms it shouldn’t be assumed that pyrethroids won’t be effective. We don’t fully understand why pyrethroids provided inconsistent control last year. Resistance is a possibility but overlapping generations causing mixing of various worm sizes resulting the appearance of poor control is another possibility. Finally, since armyworms don’t overwinter in Tennessee and there is no evidence of reverse migration, the armyworms we experienced last year won’t be the same ones we see this year.

One final note to homeowners, don’t fall for companies trying to sell you an “armyworm preventative” lawn treatment. Most products that are utilized for fall armyworm outbreaks, in lawns, have limited residual efficacy and shouldn’t be applied if armyworms aren’t present. Insecticide residual, even in a systemic product, grows out with your grass. If you mow your lawn on a regular basis any residual insecticide is mowed off and new growth isn’t protected. Applying an insecticide for an insect that isn’t there in the first place or may never show up, isn’t IPM and is a waste of money. Your county agent is an excellent resource for information pertaining to armyworm control in home lawns and pastures and won’t try to sell you anything.


Insect Numbers Increasing in Soybeans

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Insect infestations have been generally mild in soybeans thus far, but I am starting to get more calls about stink bugs and a few other pests. As other crops mature, including early maturing soybean fields, late season insect populations often concentrate in the green islands of soybeans in the field. This may include corn earworm infestations in our latest maturing fields.

Stink Bugs are the topic of most calls at this time.  Here are a few points to consider.

  1. Populations often start building rapidly at about R5.  It really doesn’t matter if you already sprayed a few weeks ago when applying a fungicide. Infestations often continue to build up to and past R7.
  2. Treatment for stink bugs is recommended when you average 9 or more insects per 25 sweeps until R6 (full seed in the top of the plant). The only caveat to this is the redbanded stink bug which has a threshold of 4/25 sweeps. I highly doubt we will experience redbanded stink bug infestations this year or if we do, it will be in the southern most counties in very late beans.
  3. You should double this threshold (18/25 sweeps) in next 7-10 days after fields reach R6.
  4. Green stink bugs have composed the majority of stink bugs we’ve found thus far. Pyrethroid insecticides such as Brigade and other bifenthrin products, Karate/Warrior, Mustang Max provide good control of green stink bugs. I would be more inclined to use Orthene/Acephate if brown stink bugs are usually common.

I’ve also received a few calls about worms in beans. So far, soybean loopers haven’t shown up on a large scale and most fields have a mix of loopers, cloverworms and other assorted worms. With worms in beans, coverage is typically more important than insecticide rate. Corn earworms respond to lower rates of diamides (Vantacor, Elevest, Besiege) in soybeans than in cotton. Similarly, Intrepid Edge is effective for corn earworms in beans but not particularly effective in cotton. Green cloverworms and velvetbean caterpillars are susceptible to pyrethroids and will often be removed by applications for stink bugs or other insects.  Soybean loopers may require higher rates of diamides due to resistance issues.  Soybean looper populations migrate from South/Central America every year and resistance levels are hard to predict, control level/duration often decreases with lower rates of diamides.

Like our stink bug threshold, the defoliation threshold in soybean should be relaxed from 20% to 30-35% once fields reach R6. Making an insecticide application for defoliating pests once you are 7-10 days past R6 is not recommended. Don’t spray for defoliators if fields are beginning to turn color and naturally defoliate.

 


Wrapping Up Insect Control in Cotton

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The bollworm flight has been in decline in several areas. Our trap catches have returned to single digits in several counties. A general decline in plant bug populations is also being observed, but stink bugs continue to linger. Some fields of cotton have now reached a maturity where we should and have terminated insecticide applications for plant bugs, stink bugs and bollworms. For later maturing fields, it may still be necessary to manage pest infestations for a couple of more weeks.

Keep in mind that the average last effective bloom date is upon us (August 15-20th). This is the average date that a white flower has a 50% chance of making a harvestable boll. It is a roll of the dice whether bolls set after this date have time to mature before a frost. For late maturing fields that are just now or have not reached NAWF5, it is still advisable to continue to good insect management practices for 2-3 weeks to allow these last bolls to accumulate enough heat units to be relatively safe from insect attack.

  • Insecticide applications for plant bugs can be terminated when cotton has accumulated 250-300 DD60s past NAWF5 (NAWF5 = average of 5 nodes above a first position white flower).
  • Insecticide applications for stink bugs can be terminated when cotton has accumulated 400-450 DD60s past NAWF5. However, fields free of stink bugs at 350 DD60s past NAWF5 are unlikely to develop economically damaging infestation after this point.

With the above considerations in mind, producers can potentially relax thresholds since we’ve reached the last effective bloom date.

  1. The last effective bloom date mentioned above represent a 50% chance that a new boll will make it into the picker. Thus, there is a pretty good chance these bolls will not contribute to yield.
  2. The upper, less mature bolls typically are smaller in size and number and represent a relatively small proportion of the overall yield. This assumes average or better boll retention on the bottom two-thirds of the plants.

My suggestion from this point forward is to pay better attention to stink bug and active bollworm infestations than to plant bugs. Stink bugs and bollworms are more likely to injure bolls. Spending a lot of money to protect squares and small bolls from plant bugs at this late date is a questionable decision. Of course, we have some built in protection from bollworm because almost everything is Bt Cotton. However, Bollgard 2 cotton in particular does not always provide adequate protection against moderate to heavy infestations, and insecticide applications may be justified. Bollgard 3 and Widestrike 3 cotton varieties have held up well this year, however; Bt expression can also decrease at cutout and beyond. Keep an eye on fruit damaged potentially damaged by bollworms out to NAWF5 + 400 DD60’s. Final clean up shots need to have a pyrethroid, OP or combination of the two to take care of stink bugs, plant bugs and potentially catch a stray worm in the top.


Bollworm/Budworm Moth Trap Catches (8/12)

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Weekly Moth Trap Data
Date: 8/12
Location Bollworm Tobacco Budworm
Hardeman (Bolivar) 2 1
Fayette (Whiteville) 3 0
Fayette (Somerville) 0 0
Shelby (Millington) 13 16
Tipton (Covington) 0 0
Tipton (North) 0 0
Lauderdale (Goldust) 53 14
Haywood (West) 3 0
Haywood (Brownsville) 1 0
Madison (WTREC) 23 0
Madison (North) 1 2
Crockett (Alamo) 0 1
Crockett (Maury City) 1 0
Dyer (Kings Rd) 13 3
Dyer (Newbern) 1 4
Lake (Ridgely) 3 35
Gibson (Kenton) 11 2
Gibson (Milan REC) 3 1
Carroll (Atwood) 29 3

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

 


Bollworm/Budworm Moth Trap Catches (8/5)

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Weekly Moth Trap Data
Date: 8/5
Location Bollworm Tobacco Budworm
Hardeman (Bolivar) 1 1
Fayette (Whiteville) 10 0
Fayette (Somerville) 1 0
Shelby (Millington) 12 15
Tipton (Covington) 2 0
Tipton (North) 1 0
Lauderdale (Goldust) 40 20
Haywood (West) 6 0
Haywood (Brownsville) 0 0
Madison (WTREC) 50 2
Madison (North) 3 1
Crockett (Alamo) 0 0
Crockett (Maury City) 6 10
Dyer (Kings Rd) 35 1
Dyer (Newbern) 2 0
Lake (Ridgely) 19 15
Gibson (Kenton) 30 1
Gibson (Milan REC) 0 1
Carroll (Atwood) 23 2

Bollworm Control in Cotton

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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.