Trials focused on the sequencing of insecticides for the control of onion thrips found the new combinations being tested may provide better control than the current industry standard.
The Onions New Zealand-A Lighter Touch trials also showed some correlation between thrips numbers and the incidence of stemphylium leaf blight, with the more thrips present, the higher the percentage of incidence of the disease in some cases.
Both of these outcomes were found to be statistically significant in the 2022-23 growing season. Similar results were found in the 2023-24 season but were not statistically significant. Further research is required to confirm these results.
The trials took place on commercial grown crops in Pukekohe. They aimed to evaluate the effectiveness of different sequencing of insecticides compared to the industry standard. The current industry standard sequences the insecticides used by their residue profiles, with the product with the shortest withholding period being used closest to harvest, rather than by how effective each product is in controlling thrips at different life stages of the pest.
The trials involved weekly applications of three commercial insecticides in different combinations. The treatments included an industry standard plot and an untreated control plot.
The results from 2022-23 showed the industry standard provided the worst control, and identified a clear correlation between thrips number and Stemphylium leaf blight incidence.
The trials in 2023-24 were conducted on two Pukekohe crops, ELK (Early Long Keeper) sown in June, and PLK (Pukekohe Long Keeper) planted in July. However, low insect pressure in the ELK trial site meant the results from that trial were inconclusive.
The PLK trial site showed clear differences between treatments, with the sequence of products that showed the most efficacy in the 2022-23 trials again resulting in the lowest final numbers of thrips present in the crop.
The 2023-24 trials, which involved weekly thrips assessment, also found the severity and incidence of Stemphylium leaf blight was considerably higher within the untreated control plot than any of the insecticide treatment plots.
Onions New Zealand shared the trials results with growers at a workshop this month.
