Current Situation:  It has been hot this week as some cotton and peanut fields are starting to show  signs of stress.  Most of the area corn crop is past dent stage. White fly populations seem to be building in area cotton.  Lesser cornstalk borer is being noticed in some area peanut fields.  Cotton and peanut irrigation questions are common.  Peanut growers are trying to put out gypsum and soil borne fungicide applications and fields as start to dry out.

Managing Whitefly in Cotton..

I have been seeing an increasing populations of whitefly in the Colquitt County area.  Below is information about managing this pest in cotton thanks to Drs. Philip Roberts and Mike Toews.

 

Scouting Silverleaf Whiteflies in Cotton

Phillip Roberts and Mike Toews

University of Georgia

The goal in silverleaf whitefly (SLWF) management is to initiate control measures just prior to the period of most rapid pest population development.  Routine sampling is required to identify the rate of SLWF population increase.  IPM principles and practices such as conservation of beneficial insects should be employed to delay population buildup.  A well-timed initial SLWF insecticide application will pay significant economic dividends in reducing overall insecticide inputs and plant injury.

 

The goal in silverleaf whitefly (SLWF) management is to initiate control measures just prior to the period of most rapid pest population development.  Routine sampling is required to identify the rate of SLWF population increase.  IPM principles and practices such as conservation of beneficial insects should be employed to delay population buildup.  A well-timed initial SLWF insecticide application will pay significant economic dividends in reducing overall insecticide inputs and plant injury.

Steps for Efficient Sampling of Whiteflies

1.  Familiarize yourself with the general location of the 5th main stem leaf in each field.

2.  Select plants at random at least 25 paces into the field and at least 10 paces apart, being careful to keep your shadow from passing over the plant you plan to sample.

3.  Turn the 5th leaf over slowly by its tip or petiole and count the leaf as infested with adults if it has 3 or more adults on it.  Include in your counts any adults that fly up from the leaf as you turn it over.

4.  Detach the leaf by the petiole from the main stem.  If it fails to snap off easily, you have likely sampled a leaf that is too high on the plant.  Recheck your leaf position to make sure you are sampling the 5th leaf.

5.  Examine the bottom of the leaf for the presence of immature SLWFs.  Count the leaf as infested if it has 5 or more immatures on the underside of the leaf.  It is important that you are sampling the 5th mainstem leaf.  A hand lens will aid in counting immatures.

6.  Sample at least 30 plants (leaves) per field.

7.  Calculate the percentage of leaves infested with adults and the percentage of leaves infested with immatures.

8.  Treatment is recommended when 50 percent of sampled leaves are infested with immature SLWFs.

Following these guidelines, especially on a community basis, should result in better management of SLWF locally and areawide.

•Destroy host crops immediately after harvest; this includes vegetable and melon crops in the spring and cotton (timely defoliation and harvest) and other host crops in the fall.

•Scout cotton on a regular basis for SLWF adults and immatures.

•The presence of SLWF should influence insecticide selection and the decision to treat other pests.

•Conserve beneficial insects; do not apply insecticides for ANY pests unless thresholds are exceeded.

•Avoid use of insecticides for other pests which are prone to flare SLWF.

•Risk for SLWF problems:

•Hairy leaf > smooth leaf cotton.

•Late planted > early planted cotton.

•Hot and dry > rainy conditions.

•All efforts should be made to minimize the need to treat SLWF with insecticide.

Insecticide Use:

The goal of SLWF management is to initiate control measures just prior to the period of most rapid SLWF population development. It is critically important that initial insecticide applications are well timed.  If you are late with the initial application control will be very difficult and expensive in the long run.  It is nearly impossible to regain control once the population reaches outbreak proportions!

SLWF Threshold: Treat when 50 percent of sampled leaves (sample 5th expanded leaf below the terminal) are infested with multiple immatures (≥5 per leaf).

Insect Growth Regulators (Knack and Courier):  use of IGRs are the backbone of SLWF management programs in cotton.  Effects on SLWF populations are generally slow due to the life stages targeted by IGRs, however these products have long residual activity and perform very well when applied on a timely basis.

Use of other insecticide options which are active on all life stages have quicker effects on SLWF infestations but lack the residual of IGRs.

SLWF is an areawide cross commodity problem.  When all parties use sound SLWF management programs all will benefit.