Two orchards that both had a history of spider mite problems were used for a trial in 2014. After tunnel covering, when temperatures were adequate for predator survival, releases of either one A. andersoni Gemini sachet per tree or one sachet per five trees were made and compared to an untreated control. Assessments were made in June prior to harvest.
The numbers of A. andersoni in the plots treated with the sachets were significantly higher on the leaves in the trees than in the untreated plots. There was no difference between treatments where every tree was treated or only one every five trees.
However, the numbers of pest mites were low in the selected orchards in 2014 and statistics did not reveal any significant differences in pest numbers. The average numbers of both pest species was 0.17, 0.21 and 0.5 per leaf - for one Gemini sachet per tree, one Gemini sachet per five trees and no added predators, respectively.
Hence the trend was for fewer pest mites where Gemini sachets were added. The ongoing work is now exploring the impact of predatory mites on cherry trees in controlled caged studies.
The full grower summary for project TF 219 can be found online on the AHDB Horticulture website at www.horticulture.ahdb.org.uk.
For details on all AHDB Horticulture activity, see horticulture.ahdb.org.uk.