Gall wasp control in autumn
Gall wasp in young larva stage
Systemic insecticides the only larva control option
Adult wasps likely to lay eggs in the same tree they emerged from
Researchers from the NSW Department of Primary Industries and FruitDoctors update citrus growers on autumn control of citrus gall wasp and wasp movements.
Gall wasp is now in the young larva stage feeding inside newly formed galls. The larvae are well protected from natural elements and contact chemicals. The only control options from now until adult wasp emergence in the following spring are systemic insecticides.
We completed four field trials in the southern citrus regions over the last two seasons to determine optimal autumn control options. The research is funded by Hort Innovation, using the citrus research and development levies and contributions from the Australian Government. The results showed Samurai® and Movento® provided consistent control of gall wasp larvae.
A single soil application of Samurai® at 8g/tree or foliar application of Movento® at 40ml/100l plus Hasten® at 50ml/100l in March/April both reduced emergence of adult wasps in the following spring by over 60% (Figures 1 and 2). Due to their late timing, autumn applications of the two chemicals did not affect gall size. Please check permit requirements, withholding periods (WHP) and maximum residue limits (MRL) before applying chemicals.
FIGURE 1 Reduced wasp emergence with autumn Samurai® application
FIGURE 2 Movento® timing research trial – Griffith 2016-17
Gall wasp movement
To find out how far adult gall wasps would normally fly, we conducted a mark-recapture experiment in a block of Valencia orange trees in Leeton from 17 October to 7 December 2017. Adult gall wasps were marked with fluorescent powder upon emergence and their subsequent movements were monitored with yellow sticky traps. The traps were placed in four concentric, rectangular rings around the release tree at a minimal distance of 5, 10, 20 and 40m.
Of all the marked wasps caught on the sticky traps, 95% were caught in the tree where the wasps emerged and 5% in a neighbouring tree 5m away. Traps placed further away did not catch any marked wasps. The results confirmed our earlier observations that citrus gall wasps do not fly far and are happy to lay eggs in the same tree they emerged from. It is likely though the wasps may move over long distances in the wind.
This research is part of the project Development of national strategies to manage citrus gall wasp (CT15006) which is a strategic levy investment under the Hort Innovation Citrus Fund. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.
To find out more about the project contact Dr Jianhua Mo, NSW DPI on (02) 6951 2537 or email@example.com