Cotton Growing and Thrip and Grasshopper Treatments

Some of the April planted cotton is finally beginning to grow since the nights have become warmer. April 17 planted cotton at Prattville, AL now has 4-6 true leaves and is about 5 inches high. Thrips pressure is still heavy enough to cause a moderate level of visible injury to true leaves when no foliar insecticide was applied. Most cotton planted in April 2013 definitely needed a foliar spray at the 1-2 true leaf stage. Plants that emerged after May 15 likely will not need this foliar application.

I have had several calls this week about making a combination spray to target thrips and grasshoppers as an over the top herbicide is applied. My comment was positive to do this but realizing that some of the grasshopper population is now adults and will be difficult to control without going to the highest labeled rates of whatever insecticides are applied. I suggest staying with a lower rate and just targeting the thrips and immature grasshoppers.

I will come back in a few days to look ahead at out next potential cotton insect – tarnished plant bug. It has been my experience that wet springs, with delayed planting, have the potential to be bad plant bug years.

Grasshopper Control with Winter Weed Burn Down

Several calls have been received from consultants, advisors and Extension agents this week concerning grasshopper control. Reports indicate that numerous early instar grasshoppers and nymphs are present in reduced tillage fields that are receiving burn down herbicides. There are also reports of large adult grasshoppers present in wheat in the southern area of the state.

Based on experiences during the past 10 or so years, it is suggested that where grasshoppers have been a concern in reduced tillage fields of seedling cotton, the best time to control is when applying winter weed burn down.

 Grasshoppers are a “risk” insect when cotton is in the seedling stage. With today’s seed and technology costs at planting, we must manage this risk just as we manage our in-season insects. I do not know of any established thresholds. This problem is much greater in reduced tillage in the central and southern areas of Alabama. The immature stage of grass hoppers are much easier to control in March and April than the adults will be in May. Most all labeled cotton insecticides, at the lower labeled rates, give good control of immature grasshoppers. Control can be achieved for as little as 50 cents to $1.00 per acre with some chemistries by mixing with the burn down herbicides. If that window is missed, broadcast applications behind the planter would not be too late if planting in April.

The addition of Dimilin, at 2 oz. per acre, would give residual control when applications are made in March or early April. Dimilin would provide control of later emerging grasshoppers or those that might migrate from field borders.

No highly effective controls have been found for adult grasshoppers that may be present in May. Cotton is susceptible to grasshopper chewing on the stalk, just above the soil line, until plants reach the fifth to seventh true leaf stage.

More comments about early season thrips control will follow in a week or so.

Follow me on Twitter for updates throughout the season @Ron_Smith23

Immature Grasshoppers in Winter Cover Wheat

Cotton planting is underway in a significant way in some south Alabama counties. A question was received today from that area about what to do with the grasshoppers in winter cover wheat that is currently being burned down prior to planting cotton. Immature grasshoppers are present at thousands per acre in the wheat. My recommendation would be to control these grasshoppers at the same time wheat is being burned down or prior to the time the cotton begins to emerge. They pose a significant risk to stands if allowed to remain in fields. Based on our research of several years ago, immature grasshoppers can be easily controlled with a low-to-mid range rate of most any insecticide labeled for cotton. The pyrethroids do an excellent job and are very economical. Adding 1 oz. of Dimilin per acre to the mix would provide residual control of immatures for weeks down the road. Since we are still early in the spring, there could be some additional migration into fields from hedgerows and field borders. The problem with waiting until later to make an application is eventually these immature grasshoppers will become adults, which is much more difficult to control.