Late season pests of pulses and cotton

Go soft early
Go soft early is a basic integrated pest management (IPM) strategy to avoid using non selective pesticides for as long as possible. This approach encourages a build up of predators and parasites to keep early pests in check and buffer the crop against attack later in the season. This strategy is particularly important in soybeans because of the risk of flaring whitefly. With no registered pesticides against whitefly in soybeans the going soft early approach maximises the chances of whitefly parasitism by the recently released wasp Eretmocerus hayati.

Green Vegetable Bugs (GVB) in soybeans
Intervention with non-selective pesticides may be required during pod-fill to control pod-sucking bugs. The most abundant pod sucking bug in soybeans is the green vegetable bug.

GVB are often found in the crop prior to pod-fill, but at this stage they are not causing economic damage. By delaying insecticide use untill pod-fill reduces the risk of flaring whitefly, because as pod-fill progresses, the leaves become progressively less attractive to this pest.

GVB is primarily a pod feeder with a preference for pods with well-developed seeds. Summer pulses remain at risk until pods are too hard to damage (very close to harvest). Damaging populations are typically highest in late summer crops during late pod-fill (when nymphs have reached or are near adulthood).

While many cultivars can compensate for yield loss caused by moderate bug populations, seed quality is adversely affected, particularly for culinary beans which have very low damage tolerances (a maximum of 2% damaged seed). Bug damaged seeds have increased protein content but a shorter storage life (due to increased rancidity). In soybeans, bug damage also reduces seed oil content.

The only effective registered pesticides for pod-suckers are non-selective and include deltamethrin (Decis) and trichlorfon (Dipteryx). Of these, deltamethrin is the most effective. Note that dimethoate and methomyl are also registered but were found to be ineffective against pod-sucking bugs.

To mitigate the impact of non-selective insecticides, delay spraying podsuckers until early podfill.

Green Vegetable Bugs (GVB) in cotton
Cotton is susceptible to damage from GVB from flowering through until one open boll per metre. Damage symptoms from GVB cannot be distinguished from damage done by mirids which include warty growths and brown staining of lint in developing bolls.

Thresholds for GVB in cotton are 1 adult/metre from flowering through to harvest. For insecticide options please refer to the cotton pest management guide which can be found on the Cotton Catchment Communities CRC website.

http://www.cottoncrc.org.au/content/Industry/Publications

Grass blue butterfly
Large populations of grass blue butterfly have been observed in soybeans this season. The green slug-like caterpillars feed mainly on leaves. They may be confused with the larvae of the hoverfly which is a beneficial insect and often found near aphid colonies on which they feed.

While control is rarely needed, high numbers can damage terminals resulting in plant branching and pods being set closer to the ground. This can indirectly impact on yield as low-set pods are more difficult to harvest. There are no insecticides registered for this pest specifically but anecdotal evidence (from a leading Goondiwindi grower) suggests they are readily controlled with Bt (Dipel).

Pale cotton stainers
Cotton stainers are occasional pests of cotton that feed on developing and mature cotton seed. While previously controlled by broad spectrum insecticides for other pests in cotton, the reduction in chemical use, especially on Bollgard II®, may lead to increased populations which may need to be managed.
For more information about pale cotton stainers click on the link provided below:

http://www.cottoncrc.org.au/content/Industry/Publications/Pests_and_Beneficials/Sucking_Pests.aspx

Article by Kate Charleston and Hugh Brier