Tomato Spotted Wilt Virus
Tomato Spotted Wilt Virus is a plant virus that was detected in Australia in the early 1900s and rapidly spread to other areas. It is now common in temperate, subtropical, and tropical regions around the world. The disease affects around 800 different plant species, and has become a major issue for tomato growers.
There is no treatment for this virus, but fortunately, we describe some great precautions and preventative measures here.
Causes and Symptoms
Spotted wilt is caused by thrips, which are small insects that feed on a variety of plants by puncturing the leaves and sucking the plant’s contents. Thrips contract the virus while they are in the larval stage and feed on infected plants, such as weeds. They then transmit the virus as adults, flying from infected plants to healthy plants.
An infected tomato has a number of visible characteristics. Symptoms include bronze-colored or dark-spotted leaves, stunted growth, dark streaking in the plant’s terminal stems, and possible die-back of the plant’s growing tips. The fruit may be deformed or wilted, with a reduction in fruit quality and yield. Ripe fruit has a distorted shape and may be covered with red and yellow ring-like markings.
Treatments and Control
There is no treatment for spotted wilt once a plant is infected, but there are steps you can take to control and reduce the incidence of the virus.
It is not easy to control in field tomato plants because of the virus’s wide host range, which includes perennials and weeds. If the disease appears, infected plants should be removed and destroyed immediately. This is not always effective, however, as oftentimes the virus has spread before symptoms ever appeared.
If you live in an area with either a high occurrence of spotted wilt or a high thrips population, resistant tomato varieties are an option. You should also be sure keep your tomato plants away from susceptible plants wherever possible, especially home gardens and flower and grain fields.
At the end of each crop you should remove sources of thrips, such as weeds, then plow and let lie fallow. In three to four weeks, thrips should have had time to emerge and disperse, but reduce cultivation to avoid moving thrips from infected plants.
Tomatoes grown in the controlled environment of a greenhouse present slightly less challenge in controlling the virus. Yellow sticky cards allow early detection of a thrips infestation, increasing chances of removing infected plants before the disease has spread. Place the cards above the crop canopy. You may also reduce thrips exposure through the application of a fine mesh cloth to doors and air vents.
Controlling thrips with insecticides is not effective, whether in the greenhouse or the field, as the insects quickly develop resistance to common insecticides. Pesticide rotation helps to retard thrips resistance. More than one application is necessary and the applications should be made in five-day intervals.