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the samples. Fertilization had substantial negative effects. Mean dry weights of individual larvae from fertilized plots were
126.0 mg and 248.7 mg for 4th and 5th instars respectively, compared to 196.5 mg and 360.3 mg, respectively, tbr untreated
plots. These were 29.6% (p = 0.036) and 32.9% (p = 0.006) reductions, respectively, due to fertilization. Mean fresh weights
of treated and untreated pupae in September, 1990 were 290.1 mg and 30l .4 rag, respectively, but were not significantly
different (p = 0.56).
Foliage and Bud Weights
Foliage weight was consistently greater on the control plots from 1989 through 1992, but this difference was significant
(p = 0.03) only in 1990 (Fig. 2). The declining weights of all foliage from 1989 through 1992 was probably due to the
combined effects of chronic drought and repeated de|bliation. Visual defoliation ratings made in fall, 1990, were similar for
both fertilized and control trees. The trend of bud weight was similar to that found for foliage except in 1989 fertilized buds
were heavier than the controls (Fig. 3). Buds from control plots were significantly heavier in 1991 and 1992 than fertilized
buds (132.3 vs 120.8 mg, p = 0.053 and 69.5 vs 49.3 rag, p = 0.021, respectively). Again, the much smaller buds in 1992
probably reflect combined effects of 2 defoliation episodes and 5 consecutive years of subnormal precipitation.
60
50
"*" 40
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._
30
(D
03 : . . •
._ 20
0
LL :
1o / /
0 -/ /
1989 1990 1991 1992
Year
Figure 2.--Foliage per centimeter of shoot length. Each bar is an average of 10 plot means.
Foliage and Frass Chemical Analyses
Foliage from fertilized trees contained more total N in both 1989 and 1990 and more available N in 1989 (Table 1).
Statistical analysis was not possible because the samples were pooled. Other nutrients (P, S, and K), apparently were similar
in both fertilized and control foliage for both years (Table 1).
Larval frass collected in June 1990 was also analyzed for nutrients (Table 2). Available N was over 6 times higher in
frass from larvae feeding on fertilized trees. Total P and K in frass from fertilized trees was approximately half that from
unfertilized trees. Because the samples were pooled, a statistical analysis was not possible, but these differences were
striking.
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