Friday, January 27, 2012

Sample of the Week: Tomato Triple Whammy

Tomato Sample, notice the puckered leaves (Photo: E. Lookabaugh)
This week’s Sample of the Week came packing a triple threat! A client brought in two tomato plants from their greenhouse. As soon as we opened the bag, a cloud of whiteflies flew out, alerting us to culprit number 1. Whiteflies damage the foliage when they feed, resulting in yellowing and curling of the leaves. In heavy infestations, whiteflies can cause stunting of the plant, reduced vigor, and leaf drop. Prevention is the best management option for whiteflies. All incoming plants should be checked before they are introduced into the greenhouse. Once the whiteflies are established in the greenhouse, you can starve them out by removing all host plants for at least two weeks, or a more practical option is the use of sticky traps. Whiteflies are attracted to bright colors like yellow and white so hanging white or yellow sticky traps above susceptible plants can reduce population numbers. 
Whitefly damage, look closely and you can see the whiteflies (Photo: E. Lookabaugh)
Upon examining the foliage, we noticed the leaves seemed stunted and distorted. Some of the leaves appeared puckered. We also saw light green etching or mottling on some of the foliage. Distorted foliage in combination with stunted new growth and mosaic or mottling of the leaves usually points toward a virus infection. We ran assays for the common viruses associated with greenhouse tomatoes and determined Tobacco Mosaic Virus (TMV) was culprit number 2. TMV is a serious threat to greenhouse plants. It is spread through contact with tools, workers’ hands, or infected plants. Pruning, tying, and transplanting are great ways to accidentally spread TMV to healthy plants in the greenhouse. TMV has a very wide host range and can survive on root and plant debris for long periods of time. Virus particles can also survive in cigarettes or chewing tobacco so workers who smoke or dip should wear gloves when handling TMV-susceptible plants. Strict prevention and sanitation programs provide the only means of controlling the disease. Use disease-resistant varieties and disease free seed/ transplants whenever possible. Encourage workers to dip hands in milk, wear gloves, or wash hands with soap and water before and after handling plants. Do not touch healthy plants after handling infected plants. Remove any nearby weeds that could harbor the virus. Infected plants and plant debris should be removed immediately. 
TMV Symptoms (Photo: E. Lookabaugh)
TMV Symptoms (Photo: E. Lookabaugh)
Finally, we checked the roots to provide a complete diagnosis. Amazingly, we noticed swollen and knotted roots caused by root knot nematodes, culprit number 3! Above ground, root-knot nematodes can cause yellowing, stunting, and wilting. Usually root-knot nematodes are not a problem in greenhouse tomatoes and other plants grown in treated potting mixes. These particular plants were being used in a research study so they were being grown in soil intentionally infested with nematodes. 
Root knot nematode, notice the galls on the roots (Photo: E. Lookabaugh)
Unfortunately, these tomato plants probably won’t make it. Whiteflies, TMV, and root knot nematodes can pack a serious punch to tomato plants individually-- imagine having all three!

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