Early action to target aphid activity in brassicas
Dry conditions conducive to aphids has resulted in early pest activity this season, even ahead of the predicted start to migration into brassica crops. Furthermore, insect pest monitoring has already identified a high proportion of the Myzus persicae caught in traps are carrying Turnip Yellows Virus (TuYV).
Myzus was first picked up in the south west in February, with further catches in the south, eastern and western counties before the end of April. Earlier this month, 64% of Myzus tested nationally were found to be carrying TuYV.
Max Newbert, Syngenta Field Technical Manager, highlighted the key concern was that populations could start to build up quickly from the initial infestations.
“Furthermore, the early transmission of virus would have more severe effects on plants over the course of the season, including depressed yield and quality issues, such as tip burn and leaf colour,” he added.
Seed treatment follow-up
Andy Richardson (below) of the Allium & Brassica Centre, reported that where aphid spread of virus is a potential risk, Cruiser 70WS seed treatment is a standard for any long-season brassica crops, such as cauliflower, Brussels sprouts or storage cabbage.
He believed that Cruiser 70WS provided eight to 10 weeks control of aphids, which could in itself prove sufficient, but typically needed to be supplemented with two or three foliar insecticides - according to the crop and the seasonal pressures. Shorter season crops, including broccoli, however, are still frequently grown without the seed treatment, and frequently require a full foliar programme, he advised.
Whilst aphids are actively feeding in warmer conditions, Andy would advocate an insecticide with ingestion take up, such as Plenum, and then switch to contact products when conditions cool down in the autumn, if aphids are still active.
“Crop planting has been bang on schedule this season, but establishment and growth has been slow where seedbed conditions have been very dry and water availability limited,” he added.
“Preventing the early infection of TuYV whilst plants are small is crucial for both yield and to limit storage losses. If we can delay aphid activity through to late summer, there’s a good chance of minimising problems.”
Max Newbert added that where aphids are found on plants, Plenum WG has been shown to be very effective at reducing virus transmission. “Plenum stops aphids feeding quickly and, in the case of persistent viruses such as TuYV, can completely protect plants from virus infection,” he pointed out.
“Growers and agronomists need to be monitoring crops regularly for the first signs of aphid migration, particular the presence of Myzus persicae and Cabbage Aphid, which are typically slightly later to arrive.
“Plenum enables growers to target both species, as well as other aphids feeding on the crop,” he advised.
To further assess risk, Max pointed out that growers should regularly watch results of the Rothamsted Insect Survey, to build up a picture of migration pressure. The latest data from the BBSRC/HAPI project, including levels of Myzus infection with TuYV, can be found by visiting the AHDB Pest Bulletin.
Andy Richardson’s recommendation for foliar applications in established brassicas, including Plenum, is to use an angled nozzle to spray in a water volume of 300 l/ha. Andy pointed out that the variable pressure Syngenta Potato Nozzle enables operators to adjust the droplet spectrum to minimise risk of drift and better target the crop, whilst also stressing that slowing down and maintaining the boom height at no more than 50 cm will further reduce potential drift.