More aphids threaten virus spread in seed potatoes
Potato growers need to be on the lookout for a wider range of aphid species to avoid spread of virus in seed crops this season, warns SAC Entomologist, Andy Evans. Up to 15 species of aphids pose a risk of transmitting viruses in the early stages of crop growth, and should be controlled as soon as the crop emerges in susceptible varieties, he advises.
Dr Evans reports an increase in the incidence of Potato Virus A (PVA) over recent seasons, which is typically transmitted early in the season - often before the conventionally blamed culprits, Peach-Potato Aphid (Myzus persicae) or Potato Aphid (Macrosiphum euphorbiae), have been found in the crop.
"Growers need to be alert for a wider range of key aphid species, including several cereal and brassica crop aphids," he says. On the most susceptible varieties, such as Estima, Desiree, Kerr's Pink, Marfona and Russet Burbank, Dr Evans advocates growers start aphicide treatments as soon as the crop emerges to prevent the spread of PVA.
This season, SAC agronomists recommend growers start with a treatment containing lambda-cyhalothin, combined with pirimicarb, as in the preformulated Dovetail. This should be alternated with a tank-mix including lambda-cyhalothrin (Hallmark Zeon) plus a resistance busting insecticide, including Actara or Plenum.
For seed crops of other varieties, the recommendation is to follow the same product choice routine, but begin treatments when the key group of virus carrying aphids appear in traps or on the crop.
Dr Evans highlights that PVA, along with Potato Virus Y and V, are non-persistent viruses that will be transmitted rapidly when infected aphids probe plants to identify food sources. Non-potato aphids quickly move on to other plants, and can therefore rapidly spread infection across the field.
"The rapid knockdown of lambda-cyhalothrin is recommended to quickly kill aphids, along with being a deterrent to stop them probing treated leaves," he adds. "It will reduce the risk of virus being acquired and transmitted, specifically targeting the transmission of non-persistent viruses."
Systemic and translaminar aphicides, such as Plenum and Actara, kill aphids feeding on the leaf sap, and are especially effective in reducing spread of persistent viruses, including Potato Leaf Roll Virus. Furthermore, there is no resistance to these products among the primary virus vector – the Peach-Potato Aphid – making them an essential component of an anti-resistance strategy.
Syngenta Technical Manager, Michael Tait, reports that the new potato insecticide, Actara, combines persistent activity against all aphids with good knock-down properties, making it ideal for early season applications. "In practice, most growers aim to tie insecticide applications in with their blight spray programme," he reports. "In the early season, when blight applications may be less frequent, there is a risk of stretching insecticide intervals too far, at a time when crops are most susceptible to virus transmission. The persistent activity of Actara will offer valuable extra protection at this time."
