Additional reports of economic spider mite infestations
continue to come in, particularly from central and south Alabama. The heaviest
infestations are already causing significant leaf shed in early square cotton. Fieldmen
have reported that the lower leaves that show the greatest damage do not always
have high mite numbers. Mites will continue to move up the plant to fresher
leaves as the older leaves get ready to drop. Fieldmen should look a couple of
nodes above the most damaged leaves in order to get a good handle on the number
of mites present.
Several materials are recommended for mite control. However,
some of these materials only seem to work in some locations. Examples are:
bifenthrin, chlorpyriphos, dimethoate and propargite. One product in our 2014 recommendations
is no longer on the market – dicofol. That leaves the newer mite chemistry as
our best choice for control. These are abamectin (Agri-Mek), extoxazole (Zeal),
fenpyroximate (Portal), and spiromesifen (Oberon). Abamectin is the most
economical and has been the most widely selected for mite control. Ag suppliers
are encouraged to have some on inventory since spider mites appear to be a
growing problem.
Plant bugs continue to be reported in cotton that is
squaring or approaching bloom. Plant bug immatures are now present in some of
our oldest cotton. This indicates that adults deposited eggs a couple of weeks
ago. Plant bug eggs are deposited into the stems of the plant in the more rapid
growing areas. Therefore TPB eggs are not visible to fieldmen.
Adult plant bugs feed on tiny pin head squares in pre bloom
cotton. Therefore pin head square retention is a good survey technique. Adult
TPB’s can best be quantified with a sweep net. Once cotton begins to bloom,
plant bugs seem to prefer feeding down in the canopy on the older squares. This
results in “dirty blooms”. At this point (blooming cotton) a pin head square
retention count is not the most reliable survey technique. It is also at this
time that we begin to focus on the immature plant bugs instead of just the
adults. The best tool for measuring immatures is the drop cloth. Therefore, in
normal maturity cotton, we switch from a sweep net to a drop cloth about July
1-10 each season. Early instar nymphs are very small with long antennae and
pale green in color. They move about more rapidly on a drop cloth than other
insect species that may appear on the drop cloth in July.
The next few weeks should be focused on adult and immature
plant bug numbers by fieldmen. While doing plant bug counts, aphids and spider
mites can be observed. After July, or about the 3rd or 4th
week of bloom, our primary focus should be on stink bugs. This would be true
for the lower southeastern area of the cotton belt.
Ron Smith