Abstract:
Green manures, soil solarization, and long rotations with crops not
susceptible to Verticillium wilt are among the disease management tactics currently
under investigation as alternatives to chemical fumigation of soil. The effect of a
broccoli green manure on soil microsclerotial populations of three isolates of
Verticillium dahliae and on Verticillium wilt of peppermint, potato, and red maple
was evaluated in a field study. Compared to the fallow control, soil populations of
V. dahliae declined by at least 30% (P=0.0405) following the incorporation of a
broccoli green manure (3.87-4.63 kg/m²). Disease severity of potato was reduced
by up to 40%, (P=0.0001); however, disease severity of peppermint was not
affected by the broccoli green manure treatment. No symptoms of Verticillium wilt
were observed in red maple. Potato tuber yield was up to 38% greater following the
broccoli green manure compared to the fallow treatment (P=0.2484).
The effects of a broccoli green manure and of soil solarization, individually
and in combination, on soil populations of V. dahliae and on Verticillium wilt of
royal purple smokebush and amur maple were examined in a field study. Following
incorporation of the broccoli green manure (2.65 kg/m²) and 2 mo of soil solarization, soil populations of V. dahliae were 40% less (P=0.0377) in plots that received the broccoli green manure treatment compared to fullowed plots, however, the solarization treatment did not affect soil populations on any sampling date. Disease severity of smokebush soon after symptom onset was 35% less (P=0.0264) in plots which were solarized compared to nonsolarized plots; however, the broccoli green manure treatment did not affect disease severity.
Aggressiveness of three isolates of V. dahliae on potato, eggplant, and peppermint were evaluated in three field studies. An isolate recovered: from potato was more aggressive on potato than was an isolate recovered from maple (P=0.0329) and more aggressive on eggplant than were isolates obtained from maple and mint (P=0.0001). Mint and potato isolates were more aggressive on the host from which they were isolated than the mint isolate was to potato and vice versa. Inoculum density of the mint and potato isolates as a predictor of disease severity was significant only in the host: from which the isolate was recovered.
