Page 21 - 21 Cotton SA February 2020

/ PRODUCTION AND TECHNOLOGY

Leafhoppers (left), and damage on cotton (right).

Some of these stinkbugs also occur in mid- Red spider mite can easily be spotted as red
season, and can be found in the lower plant dots on the underside of a leaf, while nymphs
parts where the bolls form on the lower are often present in higher numbers. Too many
branches closest to the main stem, in the latter insecticide applications aimed at aphids earlier
half of the mid-season. in the season, and at stainers during this time
The leaf-sucking pests can occur during of the season, can result in an increase in red
other plant growth periods but are particularly spider mite populations. If 12 out of 24 plants
evident in the late season and difficult to scouted have a heavy infestation of spider mites
control. Leafhoppers and spider mites occur on three leaves from the bottom, middle and top
on the underside of leaves, and the increase in leaves, it usually indicates spraying, according
their numbers is usually due to the application to the late SW Broodryk. Alternatively, make use
of too many insecticides, usually pyrethroids, of the guidelines given in the Management guide
earlier in the season. for the cotton producer to calculate a population
Leafhopper damage, as discussed under mid- index, and spray accordingly.
season pests, appears as the red-purple staining
of leaves, and the curling of leaf margins, which
appear dry and discoloured. Leaves are weakened, Red spider mite adults (Tetranychus cinnabarinus).
the plants appear stressed, and the dead leaf
matter can be a factor during the harvesting or
de-leafing period, resulting in too much dead leaf
matter in seed cotton being harvested.
Leafhoppers can appear at any time from 14
weeks onwards, and are sprayed when 12 out
of 24 plants have leafhoppers on at least three
leaves in total from the bottom, middle and top of
the plant. Only use registered products to control
these pests at this late stage, such as a systemic in-
secticide on its own, or in combination with a con-
tact insecticide. Two sprays per season directed at
leafhoppers should be effective for control.
Red spider mites, occurring mainly from
18 weeks onwards, occur commonly, and are Red spider mite eggs and nymphs.
usually controlled by insect predators, spiders,
or predatory mites. A heavy red spider mite The boll-piercing pest group, which includes
infestation usually occurs together with a leaf- cotton stainers, is usually the culprit at this time
hopper infestation. of the season.

Volume 22 No 1 February 2020 | 21