© 1975 by Institute of Chartered Foresters
Testing Dosage Rates of Methoxychlor Applied by Helicopter for Control of Dutch Elm Disease
Forestry Commission, Forest Research Station Wrecclesham, Farnham, Surrey
During April 1973 various doses and concentrations of methoxychlor were applied to healthy elms by helicopter on farmland near Warwick. Bioassays showed that only the highest rate, five gallons of 6 per cent methoxychlor per tree achieved good control of maturation feeding by Scolytus scolytus (Fab.) for six weeks after spraying. The bioassays indicated that the efficacy of this treatment declined markedly between six and ten weeks after spraying. None of the treatments prevented beetle-borne infectionof the treated test elms, though trees sprayed with five gallons of 6 per cent methoxychlor showed the least amount of Dutch elm disease at the end of the summer
Separate tests of aerial spray deposits using a standard quantity of methoxychlor at varying dilutions in water showed that tree coverage was generally good, though none of these treatments satisfactorily controlled elm beetle maturation feeding. Residue analyses of methoxychlor deposits indicate that the original residues declined by about 50 per cent thirteen weeks after spraying