August 11, 2000
COTTON SITUATION: The Georgia Weekly Weather and Crops Report for the week ending August 6th listed the crop as 88 percent setting bolls and 4 percent with open bolls. Thirty percent of the
crop is rated poor or very poor due primarily to the ongoing drought. It is possible we will see some fields defoliated in the next week or two. In some areas, late-April and early- May planted irrigated fields have
cuttout.
INSECT SITUATION: The insect situation has not changed much from recent weeks and this newsletter may sound like a broken record. Tobacco budworm, corn earworm, and stink bugs are the
primary insects of concern. A few areas have reported spider mites and sporadic beet armyworms have been observed. Whiteflies continue to be observed in the Tift County vicinity.
When is a boll relatively safe from insect damage? A percentage of cotton in the state is approaching or at the stage at which a decision concerning terminating insecticide applications arises. These decisions were
made on some dryland fields several weeks ago. Fortunately, the insects themselves often answer this question for us. Once plants cuttout and few squares remain on the plant, tobacco budworm and corn earworm moths will
often look for more suitable host sites such as later planted or lush cotton. However, number and size of larvae must be considered when terminating corn earworm and tobacco budworm sprays. Will larvae be able to size
on developing squares and move down the plant to feed on developing bolls? Historically, bollworm larvae have difficulty becoming established in fields when squaring rates drop below 100,000 per acre (approximately two to
three squares per plant). In fields where bollworms do become established, we must be concerned about losing bolls already set on the plant. Until bolls are about 20 to 25 days old, they remain susceptible to bollworm
damage. Damage is less likely to occur on these older bolls but they are not immune from bollworm damage. Control of fall armyworm may be needed for a more extended period of time. This is evidenced by damage
observed to bolls low in the plant canopy during past years. Falls generally penetrate the softer basal area of bolls and thus are capable of damaging more mature fruit. Excessive defoliation by foliage feeders such as
loopers and beet armyworm can affect a developing boll's ability to fill properly. Thus, foliage which is feeding these developing bolls must be protected until bolls are physiologically mature. Honeydew producing
insects such as whiteflies and aphids must also be monitored and controlled if necessary until it is time to defoliate the crop. Treatments for these sucking pests may be needed if excessive honeydew is accumulating on open
bolls. As stink bugs have become more of a concern, questions concerning termination of stink bug controls have arisen. At this point in time we have limited data. However, one year of research suggested that
bolls which were 21 days from white bloom were not significantly impacted by stink bug feeding. We still need more data and at this point in time would be more conservative and suggest protecting bolls for 30 days past white
bloom. To use these rules, we must identify the last harvestable boll which will significantly contribute to yield. This position will vary from field to field and thus these decisions will need to be made on a
field by field basis.
Tobacco Budworm and Corn Earworm: Tobacco budworm and corn earworm infestations are very erratic. Variability in populations and species make-up varies from field to
field. When looking at the state as a whole, populations have generally been light to moderate.
Armyworms: Fall and beet armyworm populations are generally low and few fields have required
insecticide treatment.
Silverleaf Whitefly: Silverleaf whiteflies continue to be observed on cotton in the Tift County vicinity. In general, in fields I have observed, populations are not
building but potentially these numbers could increase and cause some problems. Scattered showers have helped suppress whiteflies, but if we encounter dry conditions in coming weeks, the risk of whitefly buildup will
increase.
Stink Bugs:
Stink bugs are at threshold levels in many parts of the state. Be sure scouts are monitoring stink bug populations and/or damage. If threshold levels are exceeded, treatment with an OP (Bidrin or methyl parathion) or a pyrethroid would be recommended.
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,
