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The benomyl fungicide, rersan, applied at 7 and 14 pounds active ingredient
per acre, on April 26 and July 25, 1973, was ineffective in reducing
mortality in 2-0 Engelmann spruce seedlings derived from two different
seed sources growing in three different nursery sections at the USFS
Coeur d'Alene Nursery.
Percent mortality in plots monitored over the entire summer was 8.6, 3.6
and 8.0 in sections 31, 36, and 37 respectively, and ranged from 0 to
as high as 21.9 in individual mortality plots. Percent mortality in
sections 31 and 37 was similar and significantly greater than in section
36, indicating variation in conditions associated with individual sections.
Percent mortality combined for sections 36 and 37 (seed source 72-180)
was significantly less than that for section 31 (seed source 72-144)
indicating variation in host or seed lot susceptibility or tolerance.
Higher rates of application, 28 and 42 pounds active per acre, applied
during a second treatment period were ineffective. Because of experimental
design inadequacies, however, the results are inconclusive.
Bioassay studies to determine chemical distribution in soil and within
seedlings were generally negative. Reasons for lack of control and
negative assays are discussed.
Isolation studies did reveal a high frequency of occurrence of Fusariuin
spp. in dead seedlings, and disease expression increased with increasing
summer temperatures, implicating fusarial pathogens in the causal complex. |
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