The objective of this study was to evaluate six green zucchini cultivars, three experimental cultivars, two grey zucchini cultivars (Amatista and Topazio), and one golden yellow cultivar (Sebring Premium) with resistance to powdery mildew by comparingthem to a susceptible cultivar that is an industry standard (Zucchini Elite). Romulus PM is open-pollinated. Some cultivars evaluated also have resistance to several viruses. A field experiment was conducted at the Long Island Horticultural Research andExtension Center in Riverhead on Haven loam soil. Seeds were sown on 8 Jun in the greenhouse. Seedlings were transplanted into beds covered with black plastic mulch on 18 Jun. Fertilizer (N-P-K 10-10-10) at 400 lb/A was broadcast and incorporated on 16May. Additional fertilizer (N-P-K 46-0-0) at 30 lb/A was injected through the drip irrigation system on 9 and 30 Jul. Water was provided as needed through drip irrigation. During the season weeds were controlled with Strategy (2 pt/A) applied on 1 Jun and RoundUp WeatherMax (1% solution) applied on 12 and 27 Jun between the rows of black plastic mulch with a shielded sprayer, and by hand weeding. Cucumber beetles were managed with Admire applied after transplanting as a soil drench around transplants (0.0007 fl oz/plant) on 21 Jun and with Asana XL (9.6 oz/A) applied to foliage on 16 Jul. No fungicides were applied specifically for powdery mildew. Kocide DF (2 lb/A) was applied preventively for bacterial leaf spot on 29 Jun. The following fungicides were applied preventively for downy mildew (Pseudoperonospora cubensis) and Phytophthora blight (Phytophthora capsici): Forum 4.16SC (6 oz/A) on 16 Jul, Ranman 400 SC (2.75 fl oz/A) on 12 Aug, Acrobat 50 WP (6.4 oz/A) on 19 Aug, and Previcur Flex 6 F (1.2pt/A) on 29 Aug. Neither disease was detected before the end of this experiment. Plots were two adjacent rows each with six plants spaced 24-in. apart. Rows were spaced 68-in. apart. One yellow summer squash plant of a susceptible cultivar (Multipik) wasplanted between each plot. A randomized complete block design with four replications was used. Upper and lower surfaces of 15 old and mid-aged leaves were assessed for powdery mildew on 26 Jul, 14 days after fruit were harvested for the first time. Tenold, 10 mid-aged, and 10 young leaves were examined on 9 Aug in each plot. Leaves were categorized based on leaf physiological appearance and position in the canopy. Powdery mildew colonies (spots) were counted; severity was assessed by visual estimationof percentage leaf area affected when colonies could not be counted accurately because they had coalesced and/or were too numerous. Colony counts were converted to severity values using the conversion factor of 30 colonies/leaf = 1%. Average severity for the entire canopy was calculated from the individual leaf assessments. A square root transformation was used when needed prior to analysis to achieve homogeneity of variance. Zucchini fruit were harvested and weighed a total of eight times on 12, 17, 20, 24, 27, and 31 Jul; and on 3 and 7 Aug. Fruit were separated into marketable and unmarketable grades based on length, then weighed. There were no unmarketable fruit with blemishes due to disease or insect feeding. Fruit characteristics were evaluatedand overall appearance was rated on a scale of 1 to 9; 1= poor, 5 = marginal, 7 = acceptable, and 9 = good. Average monthly high and low temperatures (oF) were 79/61 in Jun, 82/66 in Jul, and 82/65 in Aug. Rainfall (in.) was 3.37, 3.63, and 2.60 for these months, respectively.
展开▼
