Thrips, Grasshoppers and Slugs

I’d like to mention several pests today, these being thrips, grasshoppers, and slugs.

1. Thrips- The heaviest pressure encountered this season was from about May 1-20. From monitoring 5 thrips trials, it appeared to me that thrips were later than normal moving from wild hosts and wheat to cotton. In addition, thrips pressure was not uniformly heavy. In some fields it seemed only low to moderate pressure was encountered. Cotton is growing very rapidly now and once it reaches the fourth leaf stage should be safe from economic thrips injury. Cotton planted on or about May 15^th, with seed treatments, should not need a foliar overspray. Remember that seed treatments give adequate protection under most conditions until about 21 days after plant.

2. Grasshoppers- We lost another 45 ac. field in Talladega County to grasshoppers last week. The cotton was in the “crook” stage of emergence when attacked by grasshoppers. The strange thing about grasshopper feeding is that you can never predict when they will turn to cotton to feed. Grasshopper numbers do not mean much as far as thresholds. Sometimes a low number will cause a lot of damage and other times high numbers will result in no feeding. The usual damage from grasshoppers to cotton is in the form of stem feeding. They will feed on and cut the stem of the plant anytime from the crook stage up to about the 2-3 true leaf stage. Most grasshoppers in the system now are adults and are rather difficult to control. A max labeled rate of a pyrethroid or .75-1.0 lb. acephate is the usual grower choice in May. Back in March and April, a low rate of most any cotton insecticide will do a good job when the grasshoppers are still immatures.

3. Slugs- We have had two more locations last week where slugs were damaging stands of cotton or soybeans. This brings a total of five or more locations with loss of stands to slugs this season. These fields are always in no-till, high crop residue situations. Usually the grower/consultant looks in day time and sees pillbugs or snails and not slugs- only when observing at night do we find the real culprit, slugs. They bury deep in the residue during the day and only feed at night. Snails and pillbugs normally do not feed on cotton or soybeans. There is not much a grower can do about slugs. Metaldehyde at 10-40#/ac. is the only recommended chemical. At $2.25/lb. this would cost $25-85/ac. and controls, even then, may not be 100%. Seems to me that replanting would be the best alternative to slug damaged stands. Slug damage seems to usually be when cotton or soybeans are following corn.

Be prepared to scout corn for stinkbugs during the early ear formation stage!

We are fast approaching the early ear formation stage with our earliest planted corn. This is the time when stinkbugs do the most significant damage to corn. Early ear formation occurs about 10-12 days before silking, and is the stage when the ear shoot is less than ¾ inch long. In fact, you will not see the tiny ear shoot on the plant unless you pull back the leaf sheaf. Stinkbug damage at this time will result in ears being aborted or severely deformed. The deformed ears are C-shaped and are often called banana ears or cow horn ears. Note stinkbug damaged ears below. The direction of the curve is the side of the ear in which the damage occurred. Growers with corn fields located close to wheat fields or any small grains should especially be prepared to scout, as stinkbugs will migrate from maturing small grains into green corn. Also, fields located close to pine plantations often experience severe stinkbug damage as stinkbugs will over-winter under the bark of pine trees. We typically see more stinkbug damage in south Alabama and the Florida panhandle than north Alabama, but I would still encourage growers in north Alabama to scout their corn for stinkbugs. Pyrethroids work well on the green species while an organophosphate material, such methyl parathion, works best on the brown species. Auburn University recommends treatment when 5 percent of the plants have stinkbugs during the early ear formation stage. Be still when scouting, as stinkbugs will often try to hide behind the stalk.

By: Rob Duffield, Area Agronomist, Pioneer "Walking Your Fields Newsletter"
May 7, 2012

Abundant Numbers of Thrips in Seedling Cotton Requiring Foliar Applications Across North Alabama

Many cotton acres in north Alabama are being treated for thrips as large numbers move from grass to cotton plants in the first to second true leaf stage. Thrips collected from a cotton field in Lawrence county on May 15 were mainly Tobacco thrips ( Frankliniella fusca) and Flower thrips (Frankliniella tritici) (usually called Eastern flower thrips). Soybean thrips (Neohydatothrips variabolis) and Western flower thrips (Frankliniella occidentalis) were also present but in much lower numbers. However, the proportion of each species in other fields could be different. Pyrethroids and organophosphates are the primary classes of chemistry being applied this week for thrips control in cotton. Spider mites are present in many fields and the foliar applications of these two types of chemicals for thrips may flare spider mites and farmers and consultants should monitor fields closely. Foliar chemicals for thrips are frequently being applied in a tank mix with a herbicide and growers/consultants should read the herbicide label carefully to insure that the insecticide and herbicide can be tank mixed. Adverse interactions between some tank mixed insecticides and herbicides can result in crop injury.

Written By Tim Reed and Barry Freeman, Extension Entomologists.

Thrips Damge in Cotton

Thrips pressure is quite variable based on the location and field. The two most significant factors affecting thrips damage seem to be planting date and rainfall. Thrips trials at Prattville, AL, planted on April 16, are showing low to moderate thrips injury even without a foliar application on top of seed treatments at planting. Trials planted a week earlier, April 9, are showing heavy thrips injury behind all seed treatments. Rainfall occurred on all trials during 5 of the first 10 days of May.

Most April-planted cotton should be out of the thrips damage window within 10 days or less. Cotton planted in April had three true leaves or more with the fourth or fifth emerging on May 11.

Growers planting behind the rainfall that occurred between May 7 and May 11 will likely not have to be concerned about making a foliar spray for thrips at the first true leaf stage. Seed treatments alone should provide adequate thrips control.

Cotton up and growing should be beyond grasshopper damage. The concern about pill bug damage in the one field in Talladega County this week turns out to be primarily damage from slugs and not pill bugs.

Grasshoppers and Pill Bugs in Cotton

The most common concern in cotton insects continues to be grasshoppers. The most significant change in the past 2-3 weeks is the fact that a percent of the population now are adult grasshoppers. Adults are much more difficult to control so current recommendations call for higher rates of whatever insecticide chosen. Several consultants are now applying one of the least expensive pyrethroids at higher labeled rates. Even then, a small percent of the adult population will escape controls.

Growers should be reminded that cotton planted in April with seed treatments will profit from foliar insecticides at the 1^st true leaf stage. This is especially true in conventional tillage dry land situations.

A rare question was received today about controlling pill bugs in cotton. This situation usually occurs when cotton is planted in reduced to no-tillage behind corn. Pill bugs seem to only occur in high residue, high organic matter conditions. Little research or experience is available to base a pill bug recommendation on. After several phone calls, the best chemical options seem to be: Bidrin at 0.25-0.33; Orthene at 0.5; or Sevin at 0.5-0.75 lbs per acre. This is a question that will likely occur again on an infrequent basis. Dry weather and high temperatures should help solve this infestation. However, the next 48-72 hours may not present this situation.