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Mohammad Babadoost

Phytophthora blight, caused by Phytophthora capsici, is a widespread problem of many vegetables including bell peppers. Four bell pepper cultivars marketed as resistant/tolerant to P. capsici include `Paladin' (resistant), `Alliance' (tolerant), `Aristotle X3R' (tolerant), and `Revolution' (tolerant). These cultivars, along with four other widely grown cultivars (`Commandant', `King Arthur', `Legionnaire', and `Red Knight X3R') and a susceptible control (`California Wonder'), were evaluated for their performance in a commercial field highly infested with P. capsici. `Paladin' had the lowest incidence of Phytophthora blight and the greatest yield compared to all other cultivars. `Alliance', `Aristotle X3R', and `Revolution' (the tolerant cultivars) also had lower Phytophthora blight incidence and greater yields compared to the other five cultivars evaluated. Results indicated that in fields that historically have high incidence of Phytophthora blight, `Paladin' could be a reliable choice for commercial production.

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Abbasali Ravanlou and Mohammad Babadoost

This study was conducted to assess occurrence of bacterial spot, incited by Xanthomonas cucurbitae, on pumpkin leaves and fruit. Development of the disease was monitored in 9, 14, and 15 commercial pumpkin fields in 2009, 2010, and 2011, respectively, in Illinois. Bacterial spot was observed from 4-leaf growth stage until the green leaf tissue was unavailable. Three types of lesions were observed on leaves, which were described as Type I, Type II, and Type III lesions. Type I lesions were small (1 mm), angular, brown necrotic spots, and numerous on each leaf. Type II lesions were angular, beige in the center with brown halo, numerous on each leaf, and measured 1 to 4 mm. Type III lesions were angular, translucent spots with a narrow chlorotic halo, only a few spots on each leaf, and measured 4 to 8 mm. Incidence and severity of bacterial spot on leaves were the greatest when fruit began to turn to orange. Bacterial lesions were observed on fruit from 1 week after fruit set until harvest. Lesions on fruit were circular, water-soaked, sunken, with beige centers and chlorotic halo, and measured 1 to 3 mm. Occurrence of bacterial spot on fruit was assessed in 17, 50, and 65 commercial pumpkin fields in 2009, 2010, and 2011, respectively. The disease on fruit was observed in 100%, 80%, and 88% of the fields surveyed in 2009, 2010, and 2011, respectively. The incidence of fruit with bacterial spot in all fields surveyed was 46%, 35%, and 24% in 2009, 2010, and 2011, respectively.

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Anas Eranthodi, Mohammad Babadoost and Bernhard Trierweiler

This study was conducted to develop a reliable method for control of set-borne inoculum of Verticillium and Fusarium species that cause the internal discoloration of horseradish roots. Horseradish propagative root stocks (sets), 0.5 to 3.0 cm in diameter and 20 to 25 cm long, were treated by immersing them into water at 44, 45, 46, 47, 48, 49, and 50 °C for 10, 20, and 30 min. Treated and untreated sets were cultured on acidified potato dextrose agar to determine the presence of the pathogens in the sets. Treatments at temperatures lower than 46 °C did not control the set-borne inoculum of the pathogens. Treated and untreated sets were also planted in the greenhouse and fields to assess the effects of the thermotherapy on germination of the sets and vigor of the plants. Treatments at 48 °C or greater either delayed or reduced set germination and reduced plant vigor. The most effective treatment for control of the set-borne pathogens without adverse effects on set germination or plant vigor was determined to be 47 °C for 20 min.

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Guirong Zhang, Mohammad Babadoost, Alan De Young, Eric T. Johnson and David A. Schisler

Basil downy mildew (Peronospora belbahrii) is a destructive disease that occurs in sweet basil (Ocimum basilicum). Foliar fungicide treatments could reduce infection and the severity of foliar symptoms over the course of the growing season. Multiple fungicides in variable combinations, application rates, and sequences were applied to basil foliage weekly over the course of a field season in Illinois (14 July to 8 Sept. 2014), and the treatment effects on basil downy mildew were evaluated three times. The evaluated treatments included mixtures and different rotations of azoxystrobin, potassium phosphite, mandipropamid, cyazofamid, oxathiapiprolin, experimental compound A18269SE, dimethomorph, zoxamide + mancozeb, fluazinam, fluopicolide, mefenoxam + copper hydroxide, fenamidone, mancozeb, and ametoctradin + dimethomorph. Potassium phosphite, which is known to be effective against other downy mildew pathogens, was included in combination with other fungicides or in fungicide application sequences. Disease severity was rated in fungicide-treated plots (0% to 20%) and compared with the control (73% to 80%) at each evaluation time. All fungicide treatments significantly reduced the area under the disease progress curve values compared with the untreated control. Adding a nonionic surfactant did not improve the efficacy of any of the chemical treatments evaluated for reducing downy mildew. Organic basil growers need novel, effective products to minimize damage from basil downy mildew. To aid organic basil growers, two novel, effective biocontrol agents were evaluated, Bacillus amyloliquefaciens AS 43.3 and Papiliotrema flavescens OH 182.9 3C (formerly Cryptococcus flavescens). Greenhouse experiments were conducted with the fungicides quinoxyfen and azoxystrobin serving as negative and positive fungicide treatment controls, respectively. Azoxystrobin reduced downy mildew according to the greenhouse tests, but neither quinoxyfen nor the biocontrol agents reduced downy mildew severity compared with the untreated control. This study identified 13 fungicide regimens that resulted in less than 10% basil downy mildew disease severity. More studies are needed to identify effective control products for basil downy mildew on organic basil.

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Jamie R. Stieg, S. Alan Walters, Jason P. Bond and Mohammad Babadoost

Management strategies for Phytophthora blight (caused by Phytophthora capsici) in bell pepper production are limited and there is no single method that will consistently provide adequate control. Twelve bell pepper cultivars (including four marketed as resistant/tolerant to P. capsici) were transplanted into a P. capsici-infested field and were managed with or without fungicide applications. The fungicide applications consisted of: i) Mefenoxam (Ridomil Gold EC, 1.2 L/ha) at transplant; and ii) a spray application of Dimethomorph (Acrobat, 0.45 kg/ha) + Copper (Tenn-Cop, 3.6 L/ha) alternated with Manganese ethylenebisdithiocarbamate (Maneb, 2.8 kg/ha) + Copper (Tenn-Cop; 3.6 L/ha) at 10- to 14-day intervals. Regardless of cultivar, the standard fungicide program reduced the incidence of Phytophthora blight and resulted in greater yields and farm-gate revenues when compared to the no fungicide program. Across all cultivars, total farm-gate revenues per hectare were $6,773 and $3,674 for the standard fungicide program and the no fungicide program, respectively. For P. capsici-tolerant cultivars, farm-gate revenues improved with the use of the standard fungicide program by $1,316, $4,427, and $5,447 per hectare for `Aristotle X3R', `Revolution', and `Alliance', respectively, compared to no fungicide applications. Furthermore, farm-gate revenue for P. capsici-resistant `Paladin' was improved by $3,240 per hectare when a standard fungicide program was used. Results indicate that although plant resistance is an important component of a P. capsici bell pepper management program, the use of recommended fungicides could improve disease control and increase farm-gate revenues.

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Emily E. Braun, Sarah Taylor Lovell, Mohammad Babadoost, Frank Forcella, Sharon Clay, Daniel Humburg and Sam E. Wortman

Weeds are a top management concern among organic vegetable growers. Abrasive weeding is a nonchemical tactic using air-propelled abrasive grit to destroy weed seedlings within crop rows. Many grit types are effective, but if organic fertilizers are used, this could integrate weed and nutrient management in a single field pass. Our objective was to quantify the effects of abrasive grit and mulch type on weed suppression, disease severity, soil nitrogen availability, and yield of pepper (Capsicum annuum L. ‘Carmen’). A 2-year experiment was conducted in organic red sweet pepper at Urbana, IL, with four replicates of five abrasive grit treatments (walnut shell grits, soybean meal fertilizer, composted turkey litter fertilizer, a weedy control, and a weed-free control) and four mulch treatments (straw mulch, bioplastic film, polyethylene plastic film, and a bare soil control). Abrasive weeding, regardless of grit type, paired with bioplastic or polyethylene plastic mulch reduced in-row weed density (67 and 87%, respectively) and biomass (81 and 84%); however there was no significant benefit when paired with straw mulch or bare ground. Despite the addition of 6 to 34 kg N/ha/yr through the application of soybean meal and composted turkey litter grits, simulated plant N uptake was most influenced by mulch composition (e.g., plastic vs. straw) and weed abundance. Nitrogen immobilization in straw mulch plots reduced leaf greenness, plant height, and yield. Bacterial spot (Xanthomonas campestris pv. Vesicatoria) was confirmed on peppers in both years, but abrasive weeding did not increase severity of the disease. Pepper yield was always greatest in the weed-free control and lowest in straw mulch and bare soil, but the combination of abrasive weeding (regardless of grit type) and bioplastic or polyethylene plastic mulch increased marketable yield by 47% and 21%, respectively, compared with the weedy control. Overall, results demonstrate that when abrasive weeding is paired with bioplastic or polyethylene mulch, growers can concurrently suppress weeds and increase crop N uptake for greater yields.