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Photos and text by Debbie Roos, Agricultural Extension Agent.
Phytopthora Caused by Infected Worm Castings
A group of four organic growers who all shared the same lot of custom-blended soilless mix are all having problems with their transplants. They order the custom blend without the synthetic wetting agents and starter fertilizer, and then they add worm castings and bloodmeal. The first grower had problems with a wide variety of crops including tomatoes, peppers, eggplants, and brassicas (not pictured). The seedlings were very stunted with marginal leaf necrosis and death. The problem was diagnosed as high soluble salts and pythium. Two weeks later, another grower started seeing transplants die. The symptoms appeared to be damping-off, where the the stem gets pinched off at the soil line and the seedling falls over (see photos below). The problem affected cucumber, tomato, peppers, and eggplant.
By this time the grapevine was working and we knew that the growers had the soilless mix in common. A sample was sent to the NCDA for a waste analysis and the report did not indicate anything too out of the ordinary nutrient-wise.
The next suspect was the worm castings. The four growers used the same source of worm castings, and it was not their ususal source. Extensive testing led by Dr. Frank Louws at North Carolina State University’s Plant Disease and Insect Clinic revealed that the worm castings were infected with Phytopthora capsici which causes damping off. The castings were from a commercial vermicompost producer in western North Carolina who used culled vegetable plants as part of his feedstock. The plants were infected with the Phytophthora fungus and contaminated the castings. The casting producer has been advised to avoid using culled vegetable plant matter as feedstock.
New Photos Added April 23, 2007:
Heirloom tomato transplanted into hoophouse. One hoophouse was planted in the hybrid varieties Bush Celebrity, Big Beef, and Pink Girl – about 45 out of 150 of the Pink Girls and Big Beef plants have died (but none of the Bush Celebrity!).
Another hoophouse is planted in the heirloom varieties Cherokee Purple, Mortgage Lifter, and Mexico – 72 out of 120 of these plants have died.
Leah purchased transplants from another source to replace dead plants in both houses and many of these have died as well (now that the disease is in the soil).