sustainability through science & innovation

General aphid warning

Summer and early autumn rainfall in many regions has resulted in significant growth of weeds and volunteer crop plants which can act as alternative hosts for many aphid species. A good ‘green bridge’ enables aphids to survive between cropping seasons, and can result in high numbers of aphids present around the time of crop emergence. At this time winged aphids move  into crops, and when aphid numbers build up they can damage crop plants directly by feeding on plant sap and nutrients. Aphids that arrive in crops in autumn and persist in low numbers over winter can also lead to large, damaging populations that peak in late winter and early spring.

Importantly, aphids are also vectors of several important plant viruses and the potential severity of these is greatly increased when they are transmitted to plants early in the season. Effectively controlling weeds and crop volunteers well in advance of sowing is a good way to reduce the risk of aphids moving into newly established crops. At this time of year it is important to inspect green weeds, volunteer plants and roadside verges for the presence of aphids which will indicate the likely occurrence in nearby crops in the coming months. Farmers, particularly those in virus prone areas, are also advised to pay close attention to crops, looking for signs of wilted or stunted growth.

If chemical control is required, selective insecticides (e.g. pirimicarb) are available, which are aphid specific and less harmful to other invertebrates including beneficial natural enemies of aphids. If spraying in autumn, insecticides are often most effective if applied soon after aphids begin moving into crops from surrounding vegetation. If detected early, a border spray may be all that is necessary. Waiting too long could result in some plant infestation and issues with virus control later in the year. Another option is to use insecticide-based seed dressings, as they can delay aphids from entering crops for up to six weeks after emergence and delay the need for foliar sprays.

PestFacts is supported by