Citrus gall wasp is expected to emerge from about early October so growers should prepare a control strategy to suit their situation.
Gall wasp has infested many blocks throughout the southern regions, however, there are significant differences in infestation levels and varieties affected.
This will affect the type of control required for your situation.
The first step is to find out which blocks are infested and the level of infestation.
Galls in newly infested blocks are small and difficult to spot. Check for light-green coloured shoots coming out at right angles from the main stem in the lower canopy (pictured).
If the block is infested, galls are more easily found at the base of the light-green coloured shoots.
For blocks known to have gall wasp infestation, a rough estimate of the infestation level can be made based on the size of the galls.
The following table provides a rough guide to infestation level.
Table 1: Quick gall wasp orchard assessment method
Observation of galls
Most galls <3 cm
>3 cm galls easily seen, >5 cm galls rare
>5 cm galls easily seen, 10 cm galls rare
>10 galls easily seen
Note: For a more accurate classification, gall data per canopy volume is required (i.e. by using a counting frame).
NSW DPI in collaboration with Fruit Doctors is currently undertaking a Horticulture Innovation Australia project to develop management strategies against citrus gall wasp.
The first year findings suggest that the calcined kaolin clay (Surround®), applied at least twice during gall wasp emergence, disrupts egg laying (pictured) and provides a significant reduction in galls.
This can be an effective control in moderate infestations where suppression is required, and/or in higher infestation levels where chemical control is not possible.
The cost of application using ‘sunburn’ rates is about $600/ha. However, this year research will focus on using lower rates that are sufficient to disrupt egg laying to reduce the cost by more than half.
In addition to Surround®, two systemic insecticides showed equal promise in gall wasp control. One is a soil-applied chemical with a lengthy withholding period commonly used in spring to control red scale. The other is Samurai®, produced by Sumitomo, which is available under a recent APVMA permit to control citrus gall wasp.
Samurai® is another soil-applied insecticide with a lengthy withholding period. Initial trials indicate that the two-soil applied insecticides can both significantly reduce galling. However, in high infestation blocks, many galls will still develop next season.
The cost of each systemic insecticide varies considerably (e.g. $150/ha vs $600/ha) and growers need to consider their action on other pests (i.e. Fullers rose weevil and red scale control on fruit) to get value for money for their specific requirement.
In heavy infestations, hedging is a good option to bring the tree back to healthy branches. Vigorous regrowth from heavily hedged trees is attractive to gall wasp and will probably require spray protection.
Gall wasp seminars were recently held in the southern citrus production regions of Riverina, Sunraysia and the Riverland.