Late blight has been detected on tomato transplants in Somerset County and in a community garden outside of Hollidaysburg, Tom Ford, educator at the Penn State Cooper-ative Extension office in Blair County, said.
The pathogen that causes late blight, Phytophthora infestans, infects tomatoes, potatoes, tomatillos, petunias and other members of the nightshade family when temperatures are cool and when there is ample moisture to nurture their wind-blown spores.
Gardeners and commercial growers should examine susceptible plants daily for signs of infection.
The disease wiped out plants in three to five days last year after the detection of the first lesion on a tomato or potato leaf.
It starts out as a greenish gray to black spot or lesion on the leaf surface, then black to brown lesions develop on the plant's stems.
If it continues, gray spores will develop on the undersides of the leaves. When mature, the spores can be spread by people, animals or tools.
Once detected on tomato plants, home gardeners should cover the infected plant with a large black plastic trash bag and pull the plant up roots and all. Tie the bag up and allow it to sit out in the sun for several days to kill the material. Once the refuse has dried in the bag, dispose of it through trash service.
Do not compost infected plants. Spores will continue to develop and could spread.
If trash service is not available, bury the infected plants under 12 to 18 inches of soil far away from the vegetable production area.
Gardeners who note symptoms in potato plants need to react very quickly to save underground tubers.
At the first sign of infection, mow the tops of the potato plants off at ground level and allow the plant tissues to dry for a couple of weeks.?Then begin digging the tubers. Infected potato tubers can look perfect but will begin to rot in storage.
Inspect all tubers carefully and discard one that display any obvious black or brown lesions on the skin.
Do not compost infected potato tubers or you may increase the risk of infection in your area in 2011. Bury them 12 to 18 inches below the soil or have them removed through a trash service.
Gardeners who have tomato or potato plants which display no visible signs of infection can apply a properly labeled fungicide like chlorothalonil, mancozeb or a fixed copper to plants on a five to seven day schedule.
For more information, contact Ford at 940-5989.
