. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. i 6/19 6/26 7/11 7/24 1986 DATE 8/7 8/20 Figure 2.—The development of current season needle ne- crosis on branches in the top, middle and bottom portions of 10 Grand fir Christmas trees. In the plantings of smaller Grand fir and noble fir examined in 1986, initial current season needle necrosis symptoms were observed on 9 June and symptom devel- opment occurred most rapidly during the next 4-week period. The incidence of trees with cu
. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. i 6/19 6/26 7/11 7/24 1986 DATE 8/7 8/20 Figure 2.—The development of current season needle ne- crosis on branches in the top, middle and bottom portions of 10 Grand fir Christmas trees. In the plantings of smaller Grand fir and noble fir examined in 1986, initial current season needle necrosis symptoms were observed on 9 June and symptom devel- opment occurred most rapidly during the next 4-week period. The incidence of trees with current season needle necrosis was slightly higher for the Grand fir and there were no differneces between the two Noble fir seed sources in the percentage of trees with symptomatic needles (fig. 3). T R E E S A F F E C T E D 100 80 60 40 - 20 GRAND FIR ? 053 NOBLE FIR I 440 NOBLE FIR r. 6/9 6/18 6/25 7/9 7/23 8/6 1986 DATE Figure 3.—Development of current season needle necro- sis on 480 Grand fir and 230 and 250 Noble fir from 053 and 440 seed sources, respectively. Isolation and examination of needles.—No evidence of a pathogen was detected upon examination of the sec- tions of symptomatic needles. Except for one piece of needle, no growth developed on the 100 pieces of Noble and Grand fir needles plated onto the PDA. Factors affecting symptom development.—Slightly more than 20% of the needles on the nontreated check trees had symptoms of current season needle necrosis on 9 August. Applications of Folicote, Bravo 500 and basal irrigation during shoot elongation had no effect on the incidence of symptomatic needles, while covering trees with shade cloth during shoot elongation significantly re- duced the incidence of symptomatic needles (table 1). Applications of calcium chloride significantly reduced the incidence of symptomatic needles and there was a negative correlation between the incidence of sympto- matic needles and the concentration of calcium chloride applied d
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