Timing crucial in controlling Citrus Gall Wasp

Timing crucial in controlling Citrus Gall Wasp

The timing of Citrus Gall Wasp (CGW) control methods is crucial in controlling population growth.

NSW DPI and Riverina Biosecurity Incorporated, who are concerned about the progress of CGW in the region, held workshops at Griffith and Yanco late last month to discuss CGW and red scale management.

Michael Johns, Southern Cross Farms, Nericon, NSW, attended and said with no option for completely eradicating CGW, growers needed to improve management techniques to minimise it.

“Monitoring is important to know how much is there, but when you do find it, a lot of if comes back to timing,” he said.

“There are multiple things you can do, but with all of them, it seems getting timing right is as important as anything else.”

Mr Johns said CGW had become more of a focus for growers in the region in the last five years.

Growers were advised by Dr Jianhua Mo, research entomologist with NSW DPI, to review their cultural practices, as they would achieve better control results with timing.

CGW adults are most abundant between late-October to mid-November and are present for about four weeks. Most adult wasps stay near the same tree of emergence. An online prediction tool has been developed and is available from the NSW DPI website.

“Monitoring is essential as low levels of CGW infestation may not require chemical intervention,” Dr Mo said.

“Applying soil systemic chemical controls every season is not recommended as it can lead to other pest problems and increase the risk of insecticide resistance.”

Adult CGW are only present in the orchard in spring and early summer and predominately lay eggs into spring flush.

Dr Mo said in orchards where CGW is restricted to isolated trees, gall-bearing branches should be pruned off and destroyed if within six weeks of emergence.

Galls are often more abundant on rootstock suckers. De-suckering trees following CGW emergence will allow the rootstock suckers to act as a trapping site and will assist in slowing the establishment of CGW in new incursion areas.

In heavily infested orchards trees can be pruned (heavy hedging) to rejuvenate trees.

“CGW can still emerge from cut galls if left in the shade for less than six weeks,” Dr Mo said.

“Mulching these prunings after hedging will help to dry out galls and kill the wasp before emergence.

“Be aware that heavy pruning will encourage vigorous regrowth which will be highly attractive to remaining CGW adults when they emerge and should be protected.”

Galls appear to be more abundant in the lower parts of the tree canopy, which could be a result of shading and a more humid micro-climate. CGW also favour under-tree sprinklers, compared with the dryer conditions of drip irrigation.

Dr Mo said involving neighbours in an area wide management approach will provide the best results.

Controlling CGW on the farm could require a number of strategies:

• Monitoring will help identify low and high infestation blocks.
• Prioritise treatment areas and develop a plan which leaves some areas untreated (i.e. low priority) to provide a repository for beneficial insects. Occasional and strategic chemical applications (for example, two years of chemical application followed by two or more years of no treatment depending on monitoring) will reduce the risk of chemical resistance and encourage biological control.
• Encourage neighbours to control their CGW populations and annually discuss planned strategies with each other.
• Multiple strategies may be needed to control severe infestations (for example,. pruning and systemic or spring and autumn controls).

Monitoring

Monitoring of citrus gall wasp (CGW) is best done from autumn onward when galls are easily seen.

Galls tend to be more abundant in the lower canopy close to the skirt line. A good monitoring technique is to check underneath the canopy and look for shoots growing at a right angle from the main branch. Galls are commonly seen on rootstock suckers and they can be targeted for monitoring.

An updated fact sheet on CGW will be released this month.