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Update on Louisiana cotton pests


High densities of snails (less than 40 per plant) have been reported in cotton fields this season. Due to the high numbers, this has resulted in many calls about insecticide recommendations for control of these infestations. These infestations will occasionally occur when environmental conditions favor their development. In nearly every report, snail infestations are associated with reduced tillage practices and heavy plant residue on the soil surface. If soil moisture is available, nitrogen has been applied, and the plants have not been stressed, cotton seedlings should rapidly grow. Under these conditions there is usually little cause for concern.

Snails do not normally feed on the cotton plant. If the seedlings are being fed upon and leaves are injured, then it is likely that another pest is present. In most instances, the snails are moving up the cotton plant to avoid adverse conditions at the soil surface. Herbicide applications, cultivations, or high moisture conditions can cause this upward movement in the cotton plant. Heavy concentrations will usually be seen in areas of weak seedlings that have experienced some stress. Stress may have occurred from herbicide applications, poor fertility, low areas with water saturated soil conditions, or injury by thrips.

There are no insecticide recommendations for control of snails in cotton. We realize that several growers have become alarmed and tried multiple treatments such as MSMA, foliar fertilizers, Prowl, Lorsban, and Furadan. However, We repeat there are no recommended insecticides for snails in cotton. Time will take care of this, as the snails move and cycle out.

Tarnished Plant Bugs

Spring conditions appear to be very conducive to tarnished plant bug population development. Several areas of the state are already reporting 25 to 30 percent infestations in cotton near large acreages of alternate hosts. We would anticipate that tarnished plant bug populations will continue to develop in cotton and have the potential to be a major problem during the late-season.

If late-season tarnished plant bugs problems materialize, insecticide selection right now could have a major impact on control late-season. Resistance has been documented for several insecticides (most notably, acephate and pyrethroids) currently used to control tarnished plant. If any of the insecticides used for tarnished plant bug control have been used extensively (3 or 4 applications for any pest), alternate to another insecticide chemistry or class. By alternating now, late-season resistance should be lower product performance will be improved.

Recommended insecticides for tarnished plant bug control include:

1. Acephate 90S: 0.25 to 0.5 lbs (AI)/a

2. Bidrin 8E: 0.25 to 0.5 lbs (AI)/a

3. Centric 25WG 0.0469 lbs (AI)/a

4. Dimethoate 4EC: 0.25 lbs (AI)/a

5. Lorsban 4E: 0.25-0.5 lbs (AI)/a

6. Monitor 4E: 0.25-0.5 lbs (AI)/a

7. Orthene 97SP: 0.25-0.5 lbs (AI)/a

8. Provado 1.6: 0.047 lbs(AI)/a

9. Vydate 3.77C-LV: 0.25-0.47 lbs (AI)/a

Also, several questions have been raised about malathion ULV for tarnished plant bug control. Malathion ULV is not very efficacious against tarnished plant bugs (50 to 60percent control at best). The reason that it worked so well during boll weevil eradication applications was that there were very few non-treated areas. The Boll Weevil Eradication Program sprayed every field and the borders, plus drift from these sprays was treating alternate hosts adjacent to cotton fields. Malathion essentially overwhelmed tarnished plant bug populations.

False Chinch Bugs

The false chinch bug rarely is a problem in cotton but we do have this species in sufficient numbers to warrant concern this season. Most of the feeding observed has been in no-till or minimum till fields. Don’t confuse false chinch bugs with chinch bugs. This insect is about 1/8 inch in length, grayish with clear wings that lack the black “spots” of the chinch bug’s wing covers. It resembles the big-eyed bug but is more slender. False chinch bug nymphs are brownish-gray with tiny reddish spots on the tan abdomen, and lack the white band found across the middle of chinch bug nymphs. The most potential for damage is in fields or areas that are slow growing. Be on the lookout for dying plants in no-till or minimum till fields and then look for the insect. Populations tend to have a clumped distribution in fields. Field observations suggest that areas of injured plants look similar to spots in fields that have been injured by lightning.

Several control measures have been tried with limited success. All of the products tested to date have resulted in inconsistent and unsatisfactory control this year. Lorsban at 1 pint, Methyl parathion at 1 pint, Acephate at 1 pound, or Bidrin at 6 ounces may reduce populations. Rainfall and/or irrigation seem to be the most effective at reducing injury from this pest.

Bollworm/Tobacco Budworm Oviposition during June

Cotton fields in Louisiana have been experiencing a moderate to heavy egg-lay. This is a mixed population. If most of your cotton is Bollgard, then wait until the eggs hatch. Do not spray during June based solely on infestations of eggs. If they are tobacco budworm, then no control is warranted on Bollgard cotton. If they are bollworm, then there are no flowers for these insects to infest. The highest bollworm mortality on Bollgard occurs during this time of the year. Unless scouts find infestations greater than 25 to 30% live worms in terminals, then control measures should not be considered. On non-Bollgard cottons, use the same threshold to trigger treatments and assume that the population is tobacco budworm and not bollworm. Pyrethroids should not be used against tobacco budworm, and alternative chemistry such as Tracer 4F, Steward 1.25SC, or Denim 0.16 EC should be the core treatments for tobacco budworm on non-Bollgard cotton.

Late Fruiting Cotton

Cotton usually starts squaring from the 5th through the 7th node. However, this will vary a lot depending on moisture, fertility, variety, and several other factors. Several fields in the state have experienced conditions that have delayed squaring until the 7th or in a few cases 8th node. Some of this is due to stress by unfavorable conditions. Dry conditions have prevailed in some fields and been the problem. The recent rainfall across much of the state should help with the later planted cotton.

One factor that is sometimes a problem but can be managed is herbicide applications. It is critical that over the top applications of glyphosate not go out past the 5th leaf being the size of a quarter. Cotton beyond this stage of growth should be treated with direct sprays to avoid the possibility of delaying fruiting.

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