A quick way to rate citrus gall wasp infestation in the orchard
Dr Jianhua Mo, October 2022
Have you ever asked yourself how severe the gall wasp infestation is in your orchard?
If you do, here is a simple and easy way to rate the severity. Just randomly select 50 or more galls and count the number of galls that are 50 mm or longer. If the answer is less than 3%, the infestation rate is low. If the percentage is over 25%, rate the infestation as high. If the percentage is between 3 and 25%, the infestation can be rated as low, moderate, or high, depending on its exact value.
A ‘rule of thumb’ is that if the percentage is much closer to 3% than to 25%, rate the infestation as moderately low. If the percentage is much closer to 25% than to 3%, rate the infestation as moderately high. If the percentage is neither close to 3% nor 25%, rate the infestation as moderate. These ratings are summarised in Table 1.
Table 1. Rating the infestation level of citrus gall wasp.
Percentage of galls ≥ 50 mm | |||||
≤ 3% | ≥ 25% | 3–25% | |||
Gall size category | Closer to 3% | Closer to 25% | Close to neither | ||
Infestation rating | Low | High | Moderately low | Moderately high | Moderate |
To minimise human bias in selecting galls to measure and count, it is better to select galls by branch, e.g. randomly selecting terminal branches and measure and count all galls, big or small, in selected branches. More galls will give you more reliable ratings.
The above rating method was based on gall size distribution data collected in the southern citrus regions from 2015 to 2018. Other gall size categories (other than 50 mm or longer galls used here) can also be used in rating the infestation level.
Contact: Jianhua.mo@dpi.nsw.gov.au
