Wednesday, April 25, 2012

Be on the look-out! Garden diseases to watch for in May and June

With summer swiftly approaching, we are seeing quite a few more diseases out and about in the landscape and in the home garden. We wanted to take a few minutes and go over some common diseases you should look out for in your own vegetable garden. 

Tomato Spotted Wilt Virus 
A few days ago we received the second TSWV sample of the season on greenhouse tomato. TSWV is a virus spread by at least 7 different kinds of insects called thrips. TSWV has a very broad host range that includes a variety of ornamental plants, along with tomatoes, peppers, tobacco, and peanuts. Early symptoms of this disease include cupping or bronzing of the foliage and pale ring-spots/ mottling on the fruit. As the disease progresses, necrotic spots/lesions can be seen on the foliage, stems, petioles, and fruit. Infected plants are usually severely stunted and new growth is often deformed. Infected plants will not recover and should be removed from the garden. Detailed information can be found here
Early TSWV symptoms on tomato (Photo: E.C. Lookabaugh)
Ringspot symptoms on pepper (Photo: E.C. Lookabaugh)
Symptoms on tobacco (Photo: E.C. Lookabaugh)
Fruit Symptoms (Photo: F.J. Louws)
Septoria Leaf Spot of Tomato 
Septoria leaf spot is a very destructive fungal disease of caused by the fungus Septoria lycopersici. Usually this disease shows up on the lower foliage after the first fruit set. Necrotic spots can be seen on the foliage. As the spots age, the centers turn gray and tiny black dots (fruiting bodies of the fungus) can be seen in the center of the spots. The fungus survives the winter on infected tomato debris or nearby weeds. Controlling this disease in the home garden can best be achieved by removing all crop debris at the end of the growing season or by tilling it under the soil. In commercial situations, control can be achieved through the use of resistant cultivars and fungicides. 
Septoria foliar symptoms (Photo: E. C. Lookabaugh)
Southern Blight 
Southern blight is a serious and frequent disease in the Piedmont and Coastal Plain regions of North Carolina. This disease is caused by the fungus Sclerotium rolfsii, which attacks many vegetable crops including tomato, bean, cantaloupe, carrot, pepper, potato, sweetpotato, watermelon, and several field crops such as peanut, soybean, and tobacco. This disease is easily recognized by the white fan-shaped growth of the fungus at the base of the plants. Over time, tiny round tan to brown sclerotia are formed on soil and infected plants. These sclerotia can survive in the soil for MANY years. Rotation is not very effective because this pathogen has more than 1,000 reported hosts. Corn and some other members of the grass family are not hosts and are safe to plant in problem areas. In gardens, planting on a raised bed filled with sterile soil is the best way to avoid contact with native soil that may contain the pathogen. The disease is more active in warm, wet weather and can be seen every year in North Carolina. Watch for a more comprehensive post on this disease coming soon! 
Southern Blight (Photo: Kurt Taylor)
Southern Blight up close (Photo: F.J. Louws)
Southern Bacterial Wilt 
Here in North Carolina, southern bacterial wilt is one of the most commonly diagnosed diseases of tomatoes in the home gardens and production fields. This disease is found throughout the Piedmont and Coastal Plain regions of the state. It is caused by the soilborne bacterial pathogen Ralstonia solanacearum, and is most commonly found on tomatoes, peppers, potatoes, tobacco and other members of the nightshade family. Brown discoloration of the vascular tissue in stems and leaves is a distinctive symptom of bacterial wilt. The discoloration is caused by bacteria colonizing the plant’s vascular tissue, plugging it up. The plant loses its ability to conduct water, which results in yellowing and wilting, especially during the hottest part of the day. Infected plants quickly collapse and die. Diseased plants should be removed and susceptible species should not be planted back into infested areas. More detailed information on this disease can be found here
Complete collapse caused by bacterial wilt (Photo: F.J. Louws)

Vascular discoloration (Photo: M.J. Munster)
Root-knot Nematodes 
Root-knot nematodes (Meloidogyne sp.) attack a wide variety of vegetable and field crops, including tomato, peanuts, spinach, carrots, and many others. Usually root-knot nematodes are more common in eastern North Carolina where we have more sandy soils. Symptoms are worse is hot, dry summers. The most obvious symptoms are galls and swellings on the roots and stunting and yellowing of the above-ground portion of the plants. Control can be achieved through the use of resistant cultivars and crop rotation.
Root-knot nematodes on tomato, notice galls on roots (Photo: F.J. Louws)
Female nematodes under dissecting scope (Photo: F.J. Louws)