The Georgia Weekly Weather and Crops Report for the week ending
August 13th listed the crop as 94 percent setting bolls and 11 percent with open bolls. Hot and dry conditions are taking a toll on cotton this week. USDA recently released production estimates
for cotton and projected Georgia would harvest 1.3 million acres with an average yield of 620 lbs lint per acre. A few early fields have been defoliated, others are in the first week of bloom. There is a lot of
variation in crop development and crop conditions from area to area. INSECT SITUATION: As a whole caterpillar insects remain at low to moderate levels. Stink bug numbers and damage continued
to increase, especially in untreated fields. Stink bug management needs to be a priority for the remainder of the season. Silverleaf whitefly have been observed in Tift and Brooks Counties.
Silverleaf Whitefly: Silverleaf whitefly (SLWF) has been a troublesome pest of cotton during recent years, primarily in the Tift County vicinity. Infestations were much more intense and more widespread during 1999
and caused significant yield loss in some fields. Silverleaf whitefly has been observed in cotton for several weeks this year. However, when compared to last season, populations are significantly less as a whole, but
some fields have high populations. Correct identification is important. Many of us are more familiar with the banded winged whitefly which is much easier to control. The banded winged whitefly has faint but
visible grayish bands on the wings whereas the silverleaf whitefly is solid white. Silverleaf whitefly is a localized pest.
The silverleaf whitefly adult is small, about 1/20th
inch in length, and holds its solid white wings rooflike over a paleyellow body while at rest. Eggs are oblong, pointed, and yellowish brown. The first stage upon hatching is known as the crawler that moves about searching for a suitable site to attach itself on the underside of the leaf. Once becoming sessile, three more molts occur as a flattened, oval nymph. These scale like nymphs remain stationary, sucking plant sap. As the nymphs develop and molt, red eye spots will become visible on the yellowish scale like immature. The pupal stage has very prominent red eye spots. It requires as little as 18 days to develop from egg to adult under warm temperatures. The host range of silverleaf whitefly includes over 500 species of plants. Among these are weeds and cultivated vegetables, agronomic and ornamental crops.
Both adult and nymphal silverleaf whiteflies feed on the lower surfaces of leaves by sucking sap with their piercingsucking mouthparts. Whiteflies produce honeydew upon which sooty mold can grow; thus reducing light penetration;
hence, reducing yield and quality. Honeydew accumulation on open lint may also cause problems. Excessive feeding may also cause premature leaf defoliation
Silverleaf whitefly is not a predictable pest in
Georgia. Potentially significant damage may occur and infestations tend to be most severe during hot and dry conditions. Infestations can build to extremely high numbers in a short period of time. Cultural
practices such as destroying crop residues which harbor whiteflies will help reduce overall population buildup. Conserving beneficials, planting smooth leaf varieties, and avoiding late planting are also a means of reducing
the likelihood of whitefly problems. However, when and if the problem develops, control of silverleaf whitefly with insecticides is expensive and difficult. We basically have three options when faced with economic
infestations of silverleaf whitefly; 1) do nothing, 2) contact insecticides, or 3) insect growth regulator Knack. 1999 demonstrated to us that silverleaf whiteflies can significantly reduce yields. This pest is unpredictable,
but failure to control damaging infestations can be very costly.
Contact Insecticides: Thiodan or a tank-mix of the pyrethroids (Danitol or Capture) with Orthene, Ovasyn, or Provado can provide temporary relief. However,
multiple applications will be needed since we will probably have continued migration and emergence of whiteflies in severely infested areas. Control is difficult. A starting point for a threshold would be 5-10 adults
per leaf. To scout silverleaf whiteflies, gently turn leaves and count the number of whiteflies on the underside.
Insect Growth Regulator (Knack): Knack is the most consistent treatment for management of silverleaf
whiteflies. It is also the most expensive. Knack has a long residual (several weeks) and is slow acting in general. When females feed on foliage treated with Knack, her eggs will be sterile. Knack will
control immatures when they pupate (red-eye stage), thus established nymphs will continue feeding for several days. A starting point for a threshold when using Knack is 5 immatures found in an area the size of a nickel.
Management decisions concerning silverleaf whitefly are difficult and must be made on a field to field basis. Consideration must be given to the length of time the crop has to mature, yield prospects, and the potential for
numbers to increase. As we gain experience with this pest, hopefully our decisions can be more direct.
INSECT UPDATES: Check the Cotton Insect Hotline
(1/800-851-2847) for updates on current insect conditions. The Cotton Pest Management Newsletter is also posted on the Internet at www.gaipm.org" and then click on "cotton."
Sincerely
