DISEASE CONTROL 



METHODS 



Sample plots sown with known numbers of seed, nursery inventory data, and periodic 

 counts of dead and dying seedlings were used to evaluate the effects of soil fumigation 

 on the control of seedling diseases. Differences in germination and seedling survival 

 were judged to be caused primarily by treatment effects on pathogenic fungi, but effects 

 on nematodes and insects may have contributed to these differences. Plot design and 

 statistical analysis used in the disease control evaluation were the same as those used 

 in evaluating weed control. 



EFFECTS ON SEEDLING PRODUCTION 



In the 1961 tests, fumigated seedbeds had from 20 to 150 percent more seedlings 

 than unfumigated beds, based on a September inventory of the 1-0 stock. Average 

 increases were greatest for Douglas-fir (66%), followed by western white pine (57%), 

 Engelmann spruce (39%), and ponderosa pine (32%). Germination and post-emergence 

 mortality patterns indicate that fumigation reduced pre- and post-emergence mortality 

 about equally well in Douglas-fir, ponderosa pine, and Engelmann spruce. Western 

 white pine stand increases in fumigated soils, however, must be attributed largely to 

 control of pre-emergence mortality since post-emergence mortality was greatest in the 

 fumigated beds. Brozone applied at 340 pounds per acre produced the greatest average 

 yield increase (98%), followed by Trizone at 180 pounds per acre (48%), Trizone at 

 140 pounds per acre (32%), and Brozone at 170 pounds per acre (17%). 



A number of the 1963 fall fumigation treatments at Coeur d'Alene provided sub- 

 stantial and significant increases in seedling production of 2-0 stock (table 3) . The 

 production of western white pine was significantly increased by all of the methyl 

 bromide-based fumigants , except the lowest rates of Trizone and Brozone, and by both 

 application rates of Vapam. Increases in the 2-0 seedling stand, for effective treat- 

 ments, ranged from 50 to 97 percent, with Trizone at 200 pounds per acre providing the 

 largest increase. 



Douglas-fir production results were similar except that neither the highest rate 

 of Brozone (340 lb. /acre) nor the 40 gallon per acre Vapam treatments were effective 

 in increasing production. The effective treatments provided increases in Douglas-fir 

 production of 23 to 144 percent. MC-33 at 300 pounds per acre was outstanding with a 

 144 percent increase in the 2-0 stand. 



Engelmann spruce production was increased significantly by two fumigants (Trizone 

 at 140 lb. /acre and Brozone at 170 lb. /acre). Other production gains probably were 

 present although they are not statistically significant. Replications may have been 

 inadequate to remove the effect of the great variability in disease incidence in the 

 nursery fields. Percentage increases in spruce production ranged from 115 to 133 

 percent . 



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