Wednesday, May 30, 2012

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 15th, 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.