Page 15 - 01 Cotton SA May 2013

Navorsing/Research

Stainers and their control on cotton in

South Africa

It is generally known that a wide range of secondary pests occur on cotton and the cotton stainer is one of the most
important pests. Cotton stainers are one of the main secondary pests that are of economic importance on South
African cotton. Cotton stainers occur generally on both the conventional and genetically modified cotton varieties.
This article provides information on description, damage and management of the pest.

DeScriPtioN of tHe PeSt and attractiveness to insects, therefore random selection of the plants
must be done. It is important to include an assessment of plant damage
ggs of the cotton stainers are about 1.5 mm in diameter, pale,
and are laid in the soil, or under decaying plant material, or in when making pest management decisions because insect numbers alone
the cotton plant. Nymphs are found together in the area where may not give an accurate indication of the need for control.
the eggs had been laid and later disperse to look for food. The Plant monitoring in conjunction with regular insect monitoring allows an
Enymphs, lacking the wings that hide their bodies, look similar to assessment of the effects of stainers that might be difficult to detect in
their adult but with bright red colour. The younger nymphs that hatch regular sampling. Plant monitoring can assist in decision making where
develop through five instars and they feed on droplets of dew and plant pest levels are just below threshold or where there are combinations of
fluids. From the third instar on, they will start damaging cotton plants pests present. Thresholds provide a rational basis for making decisions
because their mouthparts have developed sufficiently to pierce young and are a means of keeping decisions consistent. Acceptable damage
bolls. The adult cotton stainers are about 15 mm long and true bugs levels will vary depending on yield expectations and climatic conditions.
with piercing and sucking mouthparts. Their colours vary from bright It is important only to apply chemicals to control pest when they are
red, yellow, and orange and they commonly have a distinctive yellow present in numbers that can damage the crop. When adults and nymphs
cross on black wing cases with red bodies and black legs. A characteristic are observed in the crop and damage to developing bolls is detected,
stance in which these bugs are seen is running around back-to-back in an action threshold of more than six stainer groups of between three or
mating pairs. Adults can tolerate a wide range of climatic conditions and more insects present on 24 plants is recommended.
can disperse and fly up to 15 km. The adults remain inactive through the
winter until suitable hosts like okra and native grass become available in coNtrol of cottoN StaiNerS
spring and summer. Insecticide applications must be based on predetermined economic
threshold levels. Any decision to use broad spectrum insecticides should
Damage oN cottoN take into account their impact on beneficial insects and the subsequent
There are two types of feeding damage that the cotton stainers cause. risk of increasing other secondary pests should also be considered.
The first is purely by mechanical feeding, destroying the immature fibre Stainers can be controlled chemically by pyrethroid sprays, once the
and seeds inside the boll. The other type of damage is the staining and economic threshold has been reached.
yellowing of the cotton lint and destruction of the seeds by a fungus Selecting an insecticide can be a complex decision based on trade-offs
which is introduced by mouthparts of contaminated stainers. between preventing pest damage and conserving beneficial insects, or
Although the stainers can attack cotton early in the season, the population reducing one pest but risking the outbreak of another. All pests have
usually increases after the flowering stage and square formation. Usually survival strategies that allow them to live and breed in cotton farming
cotton becomes infested by adults that fly into fields around the time of systems. Knowing the survival strategies that are employed by the
first open boll. Cotton stainers suck sap from flowers, buds, and seeds pest can help with decision making at the farming systems-level (e.g.
from open bolls. If infestation is high the bolls open insufficiently and choice of rotation crops like sorghum and some legumes) and also can
the lint quality is reduced. Heavy infestations on the seeds affect the crop help to anticipate pest outbreaks. Controlling of ratoon cotton and
mass, oil content, germination capacity of the seed and marketability of cotton volunteers is also important for limiting cotton stainers access to
the crop. More mature bolls may be less affected by the infection of the alternative food source. There are few products registered for the control
introduced fungus. Cotton plants can recover from a degree of damage, of cotton stainers. Cotton stainers are influenced by their susceptibility to
especially early season damage with no reduction in yield or delay in insecticides used for other pests.
maturity. A vigorous, healthy crop can tolerate more damage from pests, A cotton crop is not often sprayed specifically to control cotton stainers.
without yield or maturity being affected, than a crop with poor vigour. The synthetic pyrethroids like Bulldock Beta 125 SC are registered for
the control of bollworms; however cotton stainers may be incidentally
moNitoriNg of cottoN StaiNerS controlled by them. It is crucial to carefully follow all label directions when
Assessments of cotton stainers include scouting for the pest starting from applying any insecticide. Records of chemical use and weather conditions
the formation of the first cotton squares. Scouting is done according to at the time of spraying must be always kept. Over-reliance on synthetic
a specific method which is used throughout Southern Africa. Weekly insecticides may create insecticide resistance of the target and other
scouting must commence at approximately 8 weeks up to approximately pests, disruption of natural enemies of the pests leading to outbreaks of
16 weeks after cotton emergence. Twenty four random plants per secondary pests and other environmental consequences. Frequent soil
hectare may be scouted. The pattern to be followed should cover a cultivation to destroy the eggs and removal of cotton stalks after last
representative area of the field. Crops should be checked frequently for picking should be practised. For an IPM system to work, the conservation
pests, beneficial insects and for damage and fruit retention. Regular and of beneficial insects is critical.
frequent checking provides an overview of what is happening in a field in Cotton stainers can also be avoided by encouraging birds and beneficial
relation to pest and beneficial insects’ abundance and development. This insects like spiders, parasitic wasps and assassin bugs. Minimising early
involves looking at the entire plant, including under leaves, along stems, season sprays helps to conserve the beneficial insect population. The
in squares and around bolls. Since fields are rarely uniform in crop growth cotton plant has the ability to tolerate a level of damage >> p16

Katoen sa Cotton 15 Jan - Mei/May 2013