Foliar and drip applications of biopesticides evaluated for managing Phytophthora blight on pumpkin, 2006

摘要

The objective of this study was to evaluate the efficacy of a combination treatment schedule of foliar and drip applications of seven EPA-classified biopesticides that are at the advanced or demonstration (labeled) level of development for Phytophthora blight onpumpkin. Phytophthora blight is a devastating disease for which there have been no adequately efficacious control options, and growers have stated that they would use chemigation as a means to control this pathogen if it was found to be effective. Threebiological fungicides, Actinovate (Streptomyces lydicus WYEC 108), Kodiak (Bacillus subtilis GB03), and Yield Shield (Bacillus pumilis GB34),were evaluated along with a combination treatment of Promax (thyme oil) applied through the drip and Proud-3 (thyme oil) applied to the foliage. Two phosphorous acid products, ProPhyt and Fosphite, were also evaluated because a similar product, Phostrol,was foundto be effective in controlling Phytophthora blight in pumpkin in a previous experiment at LIHREC. All treatments were compared to a current grower standard fungicide program of weekly alternating foliar applications of three EPA-registered, conventionalfungicideslabeled for this use (Forum, Gavel, and Tanos) and a second combination program with two conventional fungicides not registered that have performed well in other experiments (Maestro 80 DF and Revus 250L) plus two registered, labeled fungicides (conventionalRanman and biopesticide ProPhyt). Some applications in these programs included Cuprofix Disperss for resistance management. A field experiment was conducted at LIHREC on Haven loam soil where Phytophthora blight had developed in 1991 to 1993, 1995 to1999, and 2003 to 2005. The field was plowed on 18 Apr and tilled on 2 May. Fertilizer (N-P-K 10-10-10) at 500 lb/A was broadcast and incorporated on 12 Jun. Eleven rows of black plastic mulch each with two strips of Aquatraxx drip tape were laid on 14 Jun.‘Munchkin’ pumpkin seed was planted in a greenhouse on 14 Jun and seedlings were transplanted on 30 Jun into the plastic mulch between the two strips of drip tape. On 29 Jun, the day before transplanting, plants to be treated with ProPhyt or Fosphite received adrench application of 20 ml/seedling of a 0.5% solution of each fungicide into their growing cells in the greenhouse. During the season weeds were controlled by cultivation, roto-tilling, and hand weeding. Asana XL (9.6 fl oz/A) was applied for cucumberbeetle control on 7 Aug. Plots were single 20-ft rows spaced at least 11 ft apart. There was 5-ft between plots. A randomized complete block design with four replications was used. Average monthly high and low temperatures (oF) were 77/62 in Jun, 84/69 in Jul, 82/67 in Aug, 73/58in Sep, and 64/48 in Oct. Rainfall (in.) was 5.83, 3.79, 5.48, 3.66, and 5.53 for these months, respectively. Foliar treatments were applied preventatively beginning on 26 Jul and continuing bi-weekly for most treatments on 9 Aug, 23 Aug, 7 Sep, and 21 Sep with atractor-mounted boom sprayer operated at 120 psi and 85 gal/A and equipped with D5-25 hollow cone nozzles spaced 17 in. apart. Drip applications were applied bi-weekly on alternate weeks of the foliar applications on 2 Aug, 15 Aug, 1 Sep, and 13 Sep. Thetape had 12-in. emitter spacing and a flow rate of 0.45 gal/min. The injection period for each drip application was 45 minutes using a separate Mazzei~R injector for each treatment. Drip tape in the four plots for each treatment was connected with blankirrigation tubing. SincePhytophthora blight did not develop on its own, likely due to low rainfall and high temperatures, the field was artificially inoculated with 1 tsp (10-15 seeds) of beet seed infested with P. capsici to the soil around the first and last plant in each plot on 15 Aug. All plots were examined on 1 Sep and no infection was found on any plants. On 5 Sep, one orange fruit at the beginning and end of each plot was inoculated with a 1-in.2 piece of an infected pumpkin