RESPONSE OF CONIFER SEEDLINGS AND WEEDS TO SEEDBED FUMIGANTS
Four soil fumigants at three rates each were field-tested in nursery seedbeds as pre-sowing treatments for effectiveness in controlling weeds and for tolerance of Scots pine (Pinus sylvestris L.), Colorado spruce (Picea pungens Engelm.) and white spruce (Picea glauca (Moench) Voss). The fumigants were: allyl alcohol, dazomet (3,4,5,6-tetrahydro-3,5-dimethyl-2-thio-2H-1,3,5-thiadiazine), metam (sodium N-methyldithiocarbamate) and methyl bromide containing 2% chloropicrin.Most of the fumigant treatments, especially at medium and high rates, provided 80 to 90% control of weeds, irrespective of the weed density. However, the weeds that escaped the treatment grew well. Hand-weeding stimulated the germination of more weed seeds.Most of the fumigant treatments, in 1963 or 1964, did not affect the emergence and stands of the three conifer species. The fresh weight of conifer seedlings in most instances was equal to or better than the weight of seedlings in the hand-weeded check plots. However, the emergence of the two spruce species tended to be reduced in non-weeded as well as in hand-weeded check plots when the weed density was high, and this was attributed to competitive effect of high weed-seedling emergence.