THIS year growers need to strengthen their strategies for aphid control as the incidence of aphid-transmitted viruses such as potato leaf roll virus (PLRV) and PVY are on the increase, especially in seed crops, according to Andrew.
Once a plant is infected, the virus alters its defence mechanisms, affecting the movement of carbohydrates and sugars.
The virus challenge forms part of a general trend in yellows viruses in a potato crops.
Potato leaf roll virus can affect tuber numbers, size and quality characteristics, and therefore impact on marketability and profitability. Virus in ware crops causes between 30 -80 % yield loss, as well as affecting quality – and fry colours in processing varieties, he warns.
“PLRV vectors settle on potato plants to feed from the phloem and acquire the virus which can take up to four hours to be absorbed. The virus eventually enters the salivary gland and is transmitted through the probe into the leaf, so it takes a few days for aphids to become infective.”
The main aphids involved in transmission of PLRV in potato are the colonising aphids, such as the peach potato aphid (Myzus persicae), the potato aphid (Macrosiphum euphorbiae), and the glasshouse potato aphid (Aulacorthum solani).
Non-persistent viruses, such as mosaic viruses, are vectored by a wide range of non-colonising aphids.
“Transmission is very rapid – between 30 minutes and two hours – and as the virus is held in the mouth parts of the aphid, so just a short probe by the aphid can result in the plant becoming infected.”
“Symptoms of these mosaic viruses can be similar, showing lack of plant vigour, smaller leaves, leaf distortion and mottling, and cracking on the tuber surface. This is a real challenge for growers to deal with, as transmission to a potato crop is really fast and there are times when the aphid has already transmitted the virus before the insecticide kills it.
“The main factor for Virus Y infection is location, and the only way to stop this virus is to grow in an area where there are no other potatoes.”
