DISTRIBUTION OF METHYLISOTHIOCYANATE AND CHLOROPICRIN IN BOLES OR ROOTS OF DOUGLAS-FIR TREES

The distribution of the fumigants methylisothiocyanate (MITC), Vorlex, and chloropicrin, used to control Phellinus weirii (Murr.) Gilb., was assessed 10 years after application to sites near the bases of living Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). MITC was detected up to 8 m above the original application site, and fumigants were pre sent at the highest levels near the pith of the tree. MITC was detecta ble as far as 2.1 m down the roots in trees treated with the largest d osage, and Vorlex was detectable 1.5 m from the application site. Leve ls of chloropicrin were generally greater than levels of MITC or Vorle x, but chloropicrin was detected only up to 3 m above the application site; lower water solubility probably accounted for the restricted dif fusion of this chemical. The results indicate that fumigants can diffu se for considerable distances through Douglas-fir boles and roots. Fur ther studies are underway to establish the efficacy of the concentrati ons measured in these trees.