About Potato Spotted Wilt
Spotted wilt on potato plants is often mistaken for early blight, another common ailment amongst the Solanaceous plant family. The upper leaves are affected first. The disease spreads through infected seed, insects and weed hosts, especially those in the nightshade family. Tomato spotted wilt virus, or TPWV, was first described around 1919 in Australia. It is now in almost every region of the world, with the exception of very cold climates. The culprit and instigator of the disease is a tiny insect called the western thrip. Don’t let the directional descriptor fool you, this little pest gets around in most zones. In greenhouse situations, heavy crop losses have occurred due to the presence of the thrips. The virus is transmitted during the insect’s feeding. The thrips also feed on common weeds such as those in the chickweed, purslane, clover, and legume families. These plants will harbor and overwinter spotted wilt of potatoes.
Symptoms of Potatoes with Spotted Wilt
The virus causes dark dead spots on the upper leaves. These are ring shaped and brown to black with dry edges separated by green tissue. Leaves and some stems of plants with severe potato spotted wilt will die. If the seed tuber is initially diseased, the plant will be malformed and stunted with a rosette form. In plants that do form tubers, these are distorted and may have black, corky spots. Tubers may show no external symptoms until they are cut into. The thrip feeding damage will also cause plant cell collapse, deformed stems and leaves and silvery stippling on leaves. Effective control of the thrips can be difficult due to their unusual and rapid life cycle.
Controlling Spotted Wilt on Potato
Use organic insecticides recommended for the control of thrips. Some pyrethrin based formulas are very effective against the pests. Sticky cards are also useful to keep the population down. Control of weeds, especially broad leaf weeds and those in the nightshade family, can help reduce the spread of the disease. In a crop situation, any plants that are symptomatic should be removed and destroyed. Use certified seed that is TPWV free and plant varieties such as Coliban, which are less likely to carry the disease over. Good management of the insect population is the number one way to effectively prevent potatoes with spotted wilt.
