A comparison of four pre-plant soil treatments for control of Verticillium wilt in field-grown trees.

摘要

Verticillium wilt is a serious disease of several high-value ornamental tree species grown as field crops. The causal fungus Verticillium dahliae is widespread in UK soils. Until 2006, land was generally treated with methyl bromide before planting species susceptible to Verticillium wilt in order to reduce risk of the disease. A field experiment was done to determine effectiveness of four potential alternative pre-plant soil treatments for control of Verticillium wilt in Acer platanoides and Tilia cordata. The experiment was established in 2005 on land naturally infested with V. dahliae at a mean level of 15 cfu (microsclerotia)/g, as determined by a soil-plating test. Pre-plant soil treatments were: 1. Untreated fallow (control); 2. Sudan grass grown on site and incorporated as a green manure; 3. Biological Soil Disinfestation (BSD) using Italian rye-grass; 4. K&S Chlorofume (chloropicrin) injected to 35 cm depth; 5. Basamid (dazomet) incorporated to 20 cm depth applied simultaneously with Sistan 51 (metam sodium) injected at 25-35 cm depth. Basamid/Sistan 51, K&S Chlorofume and BSD significantly reduced levels of V. dahliae in the soil to <1, 3 and 10 cfu/g respectively; sudan grass was ineffective. In spring 2006, the land was planted with two Verticillium susceptible species, A. platanoides 'Emerald Queen' and T. cordata 'Greenspire'. Bark cracking in Acer first occurred in 2007, the second growing season after planting. This symptom of Verticillium wilt was significantly reduced by Chlorofume (8%) and Basamid/Sistan 51 (6%) soil treatments compared with the untreated control (22%). No definitive symptoms of Verticillium wilt occurred in Tilia at this time. In autumn 2007, one-third of the trees were cut down and the stem bases tested for V. dahliae by isolation onto agar. The fungus was recovered from 35% of Acer and 18% Tilia trees on untreated land. The incidence of infection in Acer was significantly reduced by Chlorofume (16%) and Basamid/Sistan (17%); the incidence of infection in Tilia was reduced by the two chemical treatments (nil infection) and BSD (9%). Levels of infection in Tilia were greater in 2008 than in 2007, with some diseased trees in all treatments. The incidence of tree infection is discussed in relation to the level of soil infestation with V. dahliae at planting.