Evaluation of resistance inducers and cover crops for management of Fusarium wilt in seedless watermelon, 2008

摘要

The experiment was established in a field of Norfolk “A” loamy sand soil at the University of Maryland’s Lower Eastern Shore Research and Education Center, Salisbury. This field has a history of severe losses to Fusarium wilt. The experiment was conducted as a split-plot design with four replications. Main plots consisted of three winter cover crop treatments (hybrid common vetch cv. ‘Cahaba White’, rye, and rye plus the fumigant K-pam); subplots consisted of 1) Actigard (acibenzolar-Smethyl), 2) CS20 (nonpathogenic F. oxysporum), 3) both Actigard and CS20, and 4) nontreated control. Vetch (45 lb/A) andrye (140 lb/A) were seeded on 18 Oct 07. On 22 and 28 May 08, vetch and rye cover crops were disked two times and incorporated into soil to a depth of 6 to 8 in. with a tractor-mounted rototiller. Before bedding, fertilizer at 750 lb/A of 16-0-18 (N-P-K) plus S (5%) and B (0.2%) was applied to rye plots; 369 lb/A of 16-0-18 plus S (5%) and B (0.2%) and 381 lb/A of 0-0-18 plus S (5%) and B (0.2%) were applied to vetch plots. K-pam (metam potassium) was injected into the soil to adepth of 7.9 in. and covered immediately with black polyethylene mulch. A single drip irrigation tube was placed under black polyethylene mulch in the center of each plot. Plots were 40 ft long and 3 ft wide and separated on 6-ft centers. The triploid(seedless) watermelon cv. ‘Sugar Heart’, susceptible to Fusarium wilt, was seeded in a greenhouse on 2 May. At the time of seeding and 1 week prior to transplanting, 3 ml of a conidial suspension of CS20 (2 x 106 microconidia/ml) was added intoeach plug cell (72 cells per tray). Inoculum of CS20 was prepared by harvesting microconidia from 10-day-old cultures grown in 1% soybean hull meal medium on a rotary shaker (150 rpm) at room temperature. Watermelon seedlings weretransplanted 36 in. apart within rows on 30 May. The pollenizer ‘SP4’, highly resistant to Fusarium wilt, was intertransplanted between every other seedless watermelon plant within each row. For pre-emergence weed control, Curbit 3E (3pt/A) and Sinbar WP (3 oz/A) were applied over beds prior to transplanting. Actigard 38WG was applied at 0.33, 0.5, 0.5 and 0.75 oz/A at 1, 3, 5 and 7 weeks after transplanting, respectively, using a tractor-mounted sprayer that delivered 45 gpa at 43psi. The boom was equipped with six D4-45 hollow cone nozzles. Foliar diseases were managed with Bravo Weather Stik 720SC (2 pt/A) and Pristine 38WG (15 oz/A) each applied on alternate weeks beginning 29 Jun until 1 week before harvest.The percent of plants showing symptoms of Fusarium wilt was assessed on 24 Jun and 22 Jul. Total fruit yield was weighed on 13 Aug, and sugar content in three fruit from each plot was determined with a hand-held refractometer.