THE USE OF SOIL STERILANTS FOR CONTROLLING VERTICILLIUM WILT OF STRAWBERRY IN BRITAIN

The potential of this technique for commercial wilt control in Britain were re-examined recently at the Institute of Horticultural Research East Malling. A field artificially infested with Verticillium dahliae was prepared for fumigation by deep ploughing and cultivation and in September/October 1985 replicated (x 5) plots (8.5 m x 4 m) in a randomised block design were treated with chloropicrin at 420 or 210 l/ha, Basamid (dazomet) at 450 kg/ha or were untreated. A Laminaria seaweed meal soil amendment (1 400 kg/ha) was included in this experiment. All plots were covered immediately after treatment with a polythene/nylon laminate. In December 1985 in the same infested field, adjacent to the main trial, 5 similar plots were treated with formalin at 5 000 l/ha in 25 000 l/ha water. In April 1986 all plots were planted with the wilt susceptible cv. Hapil. The incidence and severity of wilt in these plants were recorded (scale 0–4 where 0 = healthy and 4 = severely diseased) in October 1986 and in September 1987 and plant yields were recorded in 1987 and 1988.

Wilt records in 1986 showed no reduction by the seaweed meal amendment (index = 2.02) over control (index = 2.02) while 420 l chloropicrin (index = 0.06), 210 l chloropicrin (index = 0.03) and Basamid (index = 0.12) all gave excellent control. Formalin (index = 0.21) also markedly reduced wilt compared with adjacent untreated plots (indices = 1.09, 1.05). In 1987 wilt indices increased only slightly in all treatments so that high standards of control were maintained. Comparative fruit yields in 1987 and 1988 reflected the levels of wilt control : treatment with soil sterilants resulted in yields from 1.6 to 2.8 times those of untreated plots. These results demonstrate that with good soil preparation and sealing chloropicrin and Basamid may be employed in Britain at economic rates for the control of strawberry wilt. Formalin also shows promise for this purpose.

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