Ponderosa pine production was, in general, the least affected by fumigation. Only 

 Vapam at 80 gallons per acre provided a significant increase (39%) in 2-0 seedling 

 production. None of the dichloropropene base compounds (Vidden-D, M-2441, or M-2467), 

 nor the lowest rate of Brozone, resulted in any significant changes in plant production. 



In seedbeds fumigated in the fall of 1963, the post-emergence mortality during the 

 first growing season was generally only slightly greater in unfumigated than in fumi- 

 gated seedbeds. Also, the magnitude of differences in the 1-0 stands in fumigated and 

 unfumigated beds was about the same as the 2-0 stand differences. Thus the treatment 

 effects on overall plant production seem to have been primarily the result of reductions 

 in pre-emergence losses. 



The effects of fumigation on the ultimate production, and therefore, by inference, 

 on the incidence of disease losses, were highly variable with significant block effects 

 as well as significant treatment effects. A particular treatment tended to look 

 effective or ineffective depending on whether it happened to fall in an area of high 

 disease incidence and virulence or in an area where conditions were naturally unfavor- 

 able for the pathogen. The design of the trials was generally not adequate to remove 

 the effect of such differences and provide good statistical information on the relative 

 effectiveness of the various fumigants . 



The effects of the 1963 fall fumigation at the Savenac nursery were similar to 

 those at Coeur d'Alene. Production of 3-0 Engelmann spruce stock was increased from 

 21 to 35 percent by MC-33 at 300 pounds per acre, Trizone at 200 pounds per acre, and 

 Brozone at 170 pounds per acre. Although sampling of other species was not sufficient 

 for a good statistical test, it was obvious that western white pine production was 

 greatly benefited by MC-33 at both rates, Trizone at 200 pounds per acre and by Vapam. 

 Savenac ponderosa pine was least benefited by fumigation but did display increases in 

 production with the better fumigants such as Trizone at 200 pounds per acre. 



Spring fumigation, unlike the fall fumigations, provided no detectable control of 

 disease losses. Neither post-emergence damping-off nor the 1-0 stand densities were 

 significantly different on fumigated and unfumigated soils. In fact, seedlings growing 

 in fumigated soils were often stunted and chlorotic. If fumigation provided some 

 disease control, it was masked either by fumigant toxicity or unknown secondary detri- 

 mental effects. KTiile there may be some advantage to sowing as soon after fumigation 

 as possible, Coeur d'Alene spring weather is generally not warm enough to bring the 

 soil temperature up to suitable fumigation levels until mid-May, which is generally 

 several weeks beyond the optimum sowing date. This delay in sowing, plus the additional 

 delay imposed by allowing time for the chemicals to dissipate from the soil, makes 

 spring fumigation impractical. 



SEED COST SAVINGS 



The higher seedling survival promoted in the nursery beds by fumigation can result 

 in appreciable savings through lower seed costs. The amount of savings depends not 

 only on the effectiveness of disease and insect control, but also upon the desired 

 seedbed density and upon seed costs. 



Using a final density goal of 40 seedlings per square foot, savings in seed cost 

 have ranged as high as $1,100 per acre for a fumigation investment of approximately 

 $400 per acre. This occurred in Douglas-fir seedbeds at Coeur d'Alene which have been 

 particularly subject to disease losses. Seed cost savings have been highest with 

 Douglas -fir, western white pine, and ponderosa pine. Savings with Engelmann spruce 

 and western larch have been relatively small due to the low cost per unit count of seed. 



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