Dr Jianhua Mo, NSW DPI Research Entomologist and technical staff have found trials with kaolin clay or Surround® applied twice, just before and during the middle of gall wasp emergence greatly reduced the number and size of galls.
The white kaolin clay, applied with a wetter and a good coverage sprayer, might deter citrus gall wasp egg laying in spring.
Results from a trial conducted in a Sunraysia orchard in 2015 showed a >90% reduction of total gall weight in kaolin-treated plots compared with unsprayed control plots. The size and number of galls were also greatly reduced in kaolin-treated plots.
Mr Craig Swanbury and staff from Fruit Doctors in the Riverland managed a second kaolin clay trial in Star Ruby grapefruit.
Craig’s team are currently compiling the results from several different Riverland trials this season. Craig reported that ‘the galls on the Surround® treated plots were clearly smaller and fewer in number compared to the galls on the unsprayed trees’.
It is promising that both the Riverland and Murray trials showed similar results. Next year the research focus with kaolin is to determine whether this effect in plot areas of 50 trees remains true when whole blocks are treated.
The citrus gall wasp project team will meet in Mildura with a project steering group this month to discuss these results and plan project work for next season. The research results will be shared with growers at later meetings.
Citrus Australia is pursuing emergency use chemical permits from the APVMA so growers could have management options in spring.
The graphs below show the gall weight and size in Kaolin-treated and untreated plots in the Sunraysia trial.