Efficacy of Proline 480 SC (prothioconazole) for control of Phoma betae in table beet and Swiss chard seed crops in western Washington, 2016

摘要

The maritime region of western Washington and Oregon is the only area of the USA with suitable conditions for table beet and Swiss chard seed production. Mild temperatures and rainy conditions over ~7 months of the 14- to 15-month duration of these biennial seed crops can be conducive to Phoma betae, which can be seedborne and seed transmitted. Proline 480 SC was evaluated for managing P. betae in table beet and Swiss chard seed crops. In each trial, five replicate plots of each of two treatments were set up in a randomized complete block (RCB) design on 15 Apr with: i) a control treatment (water + R-11 surfactant at 2 fl oz/100 gal); and ii) Proline 480 SC applied three times at 5.70 fl oz/acre withR-11 surfactant at 2 fl oz/100 gal. Each plot in the beet trials was 20' x 2 rows (a female row and adjacent male row of the hybrid crop). Proline 480 SC and the control treatment were applied with a CO2-pressurized backpack sprayer with a single-nozzle boom. The first applications were made on 19 Apr in Trials 2 and 3, and 4 May in Trial 1, at 20 psi, 2 mph, and 31.19 GPA with the nozzle 12 in. above the ground for a 20-in. spray width, using a TJ 8003XR nozzle tip and 50 mesh screen. above the ground to deliver 34.65 GPA in a 30-in. spray width. The third applications were made on 1 Jun in Trials 2 and 3, and 17 Jun in Trial 1. The chard plants were much larger than the beet plants by Jun, so the application in Trial 3was with a 3-nozzle boom fitted with TJ8002 nozzle tips with 2 nozzles on drop legs 30 in. apart, and the nozzle held 60 in. above the soil to deliver 50.49 GPA in a 30-in. spray width at 30 psi. Plants in Trials 2 and 3 were rated on 7 Jun for leaf spot and phytotoxicity; and plants in Trial 1 were rated on 24 Jun. The seed crop trials could not be inoculated with P. betae, so two table beet trials and two Swiss chard trials were completed in a greenhouse. One trial for each host was with vegetative plants, and the second trial for each host used bolted (flowering) plants. For the vegetative beet and chard trials, seed of cvs. Red Ace and Silverado, respectively, were planted in RediEarth Starter Mix in 72-cell flats, and seedlings transplanted 3 weeks later into Sunshine Mix No. 1 in 4-in.-diameter pots (1 plant/pot). For the flowering beet trial, vernalized seedlings of the male parent in field Trial 2 were transplanted into Sunshine Mix No. 1 in 0.5-gal pots (1 plant/pot) on 15 Apr. Similarly, vernalized Swiss chard seedlings of the cultivar in Trial 3 were planted into 0.5-gal pots for the flowering chard trial on 15 Apr.The plants were maintained in a greenhouse at 21-24oC with supplemental lighting from 6 am to 10 pm daily. For each trial, six replicate plants were subjected to six treatment combinations of a 3 x 2 factorial treatment design arranged in a RCB design. Three Proline treatments included: i) control plants sprayed with water + R-11 surfactant at 2 fl oz/100 gal, ii) Proline 480 SC at 5.0 fl oz/acre + R-11 at 2 fl oz/100 gal, and iii) Proline 480 SC at 5.70 fl oz/acre + R-11 at 2 fl oz/100 gal. Inoculationtreatments included: i) non-inoculated plants, and ii) plants inoculated with P. betae by atomizing a spore suspension (4 x 106 spores/ml). Plants were treated with Proline 480 SC on 9 May using a CO2 backpack sprayer, enclosed in plastic bags on 10 Mayfor 24 h, unbagged, inoculated with a spore suspension of isolates Phb032 and Phb035 of P. betae (prepared by flooding plates of each isolate on ^-strength potato dextrose agar amended with chloramphenicol at 100 ppm), enclosed in plastic bags again for48 h, and unbagged. Plants were rated 7 and 14 days after inoculation (dai) for severity of Phoma leaf spot (% of foliage with spots) and phytotoxicity (% of foliage with symptoms of chemical injury). Severity of Phoma leaf spot was severe in the boltedbeet and chard trials, so plants in those trials were cut at the soil line on 26 May, dried, and weighed.