Susceptibility of 15 cultivars of watermelon, melon, squash, pumpkin, and bottle gourd to gummy stem blight, 2009

摘要

Experiments were conducted at the Clemson University Coastal Research and Education Center in Charleston, SC. The soil type was Yonges loamy fine sand with a pH of 6.0. The field was cropped to rye the preceding fall and was fallow the preceding spring. Prior to bedding, the field was disked twice. On 1 Jul, raised beds were shaped 3 ft wide on 6-ft centers, 500 lb/A of 10-10-10 fertilizer was broadcast over the field, and beds were cultivated lightly with a rotovator to incorporate fertilizer. Bedswere covered with white-on-black polyethylene mulch. Prior to planting, alleys were sprayed with the herbicides Strategy at 6 pt/A and Makaze at 2% v/v on 13 Jul. Fifteen cultivars of cucurbits were transplanted into every other row on 23 Jul in plots arranged as a randomized complete block with four replications. Plots were 40 ft long with 10 ft of non-planted space between plots within rows; plants were spaced 4 ft apart within plots. Cultivars were selected to represent a variety of cucurbit taxa; cultivars with resistance to powdery mildew were selected whenever possible. Insects were managed by applications of Sniper 2EC at 6.4 fl oz/A on 27 Jul, 27 Aug, and 8 Sep; Sevin XLR at 1 qt/A on 6 Aug; Warrior at 1.92 fl oz/A on 14 Aug; Spintor 2SC at 8 fl oz/A on 27 Aug and 10 Sep; Coragen at 5 fl oz/A on 20 Aug, 3 Sep, and 25 Sep; and Fulfill 50WDG at 2.75 oz/A on 17 Sep. Downy mildew and powdery mildew were managed with the fungicides Previcur Flex 6F at 1.2 pt/A plus Quintec 2.09SC at 6 fl oz/A on 8Aug; Tanos 50WDG at 8 oz/A plus Rally at 5 oz/A on 14 Aug, 27 Aug and 10 Sep; Presidio at 4 fl oz/A plus Quintec on 20 Aug, 3 and 17 Sep; Presidio plus Rally on 23 Sep and 9 Oct; and Ranman 3.3SC at 1.25 fl oz/A plus Rally on 10 and 25 Sep. On 17 and 31Aug all plants in each plot were inoculated with a suspension of 1 x 106 D. bryoniae conidia per 0.03 fl oz. Plants were misted 30 minutes in the morning and evening with an overhead mini-wobbler mist system to promote leaf wetness and spread of gummy stem blight. Gummy stem blight severity on leaves was rated with a 16-point modified Horsfall-Barratt type scale on 9 Sep, 18 Sep, 8 Oct and 30 Oct. Necrosis due to downy mildew and anthracnose was excluded from gummy stem blight ratings. Disease incidence counts were done on 21 Oct. Average max/min temperatures for Jul, Aug, Sep, and Oct were 89.1/68.5, 89.0/72.5, 84.9/66.8, and 76.2/57.1 deg F, respectively. Rainfall for Jul, Aug, Sep, and Oct was 4.15, 4.3, 1.54, and 2.88 in., respectively.