Page 16 - 01 Cotton SA May 2013

Navorsing/Research

<< p15 without affecting yield or crop maturity. Harvesting cotton refereNceS
in time also prevents the stainers attacking the seeds from the opened L.D. Godfrey, P.B. Goodell, E.T. Natwick and D.R. Haviland. UC IPM Pest Management
bolls. This is essential to break the cycles of pest in the system as a whole. Guidelines: Cotton. UC ANR Publication 3444.
Natural insecticides and botanical sprays such as neem, custard apple, L. Wilson, M. Khan and T. Farrell. 2008. Pale cotton stainers, Dysdercus sidae. On Farm
garlic, sweet flag, and sweet basil can be used to control stainers. In small Series: IPM. Produced by Cotton CRC.
plots they may be hand-picked and destroyed. Strict adherence to cotton K. Kohno and B.T. Ngan. 2004. Effects of host plant species on the development of
Dysdercus cingulatus. (Heteroptera: Pyrrhocoridae). Appl. Entomol. Zool. 39 (1): 183–187.
crop destruction dates assists in keeping the pest numbers down between
growing seasons. By: L N Malinga, ARC-Institute for Industrial Crops, Tel: (+27) 014 536 3150.
Common insect pests and their

control on cotton in South Africa - 2

We continue with information on common insect pests found on cotton in South Africa – the first part was published
in the December issue of CottonSAKatoen, 2012.
Stink bugs imPortaNt uSe of PeSticiDeS
Stink bugs pierce small bolls and suck Chemical treatments should only be applied when the populations of
sap from the seeds. This may cause pests reach levels that correspond to the economic thresholds of each
small bolls to fall from the plants. Seed pest. Avoid treating infestations that are below thresholds because
coats collapse and the attached lint unnecessary disruptions to populations of beneficial species often
often acquires a yellowish to brownish result in plant injury by other insect pests. Pesticides must only be used
coloured stain. Lint beneath the feeding for the purpose for which they are registered and must not be used in
spot may be stained or reduced in grade. any other situation or in any manner contrary to the directions on the
Small, warty growths on the inside of a boll wall will generally mark label. Some chemical products have more than one retail name. All
the points of penetration. Water-soaked cuts are signs of more recent retail products containing the same chemical may not be registered
penetrations, where warts may not have had time to develop. Warts for use on the same crops. Always check carefully that the label on the
may never develop when a stink bug penetrates the boll wall, fails to retail product carries information on the crop to be sprayed. Pesticides
find a seed, and then quickly withdraws its beak. Damaged bolls may may contaminate the environment and when spraying, care must be
open prematurely. Boll damage is the main criterion used to evaluate taken to avoid spray drift on to adjoining land or waterways. Residues
infestations of stink bugs. When scouting for stink bugs, one should may accumulate in animals fed any crop product, including crop
randomly select young bolls, break them open, and check the inner residues, which have been sprayed with pesticides. In the absence
walls of the bolls for the damage symptoms indicated above. Care of any specified grazing withholding periods, grazing of any treated
should be taken to ensure that all bolls examined are of the same crop is at the owner’s risk. Disruption of beneficial insects with a broad
age class because these will provide the most reliable estimate of the spectrum of insecticides can increase the populations of other pests.
actual current damage in a field. When damage symptoms are present,
look for adults and large nymphs by shaking plants. It is possible that ScoutiNg
plant bugs or other sucking insects might damage small bolls, so A good scouting program is still the first line of defence against insect
identification is important before action is taken. Pyrethroids applied pests in cotton. Along with the development of this multi-tactic
for bollworm control will generally provide control of stink bugs as management system is an increased awareness of “in-field” insect and
well. Stink bugs seldom develop in large numbers on cotton. plant dynamics. This awareness is a result of constant crop monitoring
Cotton stainers of pests and beneficial insects and their effects on the cotton plant.
The adult cotton stainer is a “true bug” This is the basis of cotton scouting. Insect scouting should begin from
with piercing, sucking mouthparts. The seedling emergence and be done at least weekly. Cotton scouting, or
head and the neck are bright red; the crop monitoring, is not a suppression tool itself but rather a means
remainder of the body is dark brown of gathering information on pests which will aid in management
crossed with pale yellow lines. Immature decisions. There is more to cotton monitoring than just checking for
stages are smaller but resemble adults insects. It involves proper identification, a determination of pest and
without wings. Cotton stainer eggs are beneficial insect densities and their effects on the cotton crop as a
small, pale and laid singly on cotton whole. Insect numbers fluctuate a great deal. In cotton fields pests can
plants or dropped on the ground near cotton plants. The immature increase to a point where, if not suppressed, they will cause economic
insects are usually found congregating near the egg shell after damage to the crop.
emergence and the older ones feed on the bolls or wander freely over The economic threshold is determined by research and practical
the plant. The cotton stainer is mainly a pest of long staple cotton. experience. It has been approximated for most cotton pests but
It damages developing bolls by puncturing seeds and causing plant may vary with the area in which the crop is grown. Since evaluating
sap to exude from the feeding site. The plant sap stains the lint an the economic threshold involves observing a pest population that
indelible yellow colour. Feeding by the cotton stainer also interferes is truly dynamic and rises and falls periodically, there must be some
with the bolls’ natural development. The economic threshold for method of systematic scouting on a regular basis. Scouting results
cotton stainers is 6 focal points per hectare. Some of the insecticides should be recorded in an easy-to-understand method. It is also critical
that control cotton stainers include Bulldock®, Beta 125 SC Decis® and to monitor the effects of other factors such as weather, disease and
Forté Sevin® XLR Plus. herbicidal injury. >> p17

Katoen sa Cotton 16 Jan - Mei/May 2013