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In 1922, Phytophthora capsici was described by Leon Hatching Leonian as a new pathogen infecting pepper (Capsicum annuum L.), with disease symptoms of root rot, stem and fruit blight, seed rot, and plant wilting and death. Extensive research has been conducted on P. capsici over the last 100 years. This review succinctly describes the salient mile markers of research on P. capsici with current perspectives on the pathogen’s distribution, economic importance, epidemiology, genetics and genomics, fungicide resistance, host susceptibility, pathogenicity mechanisms, and management.

This research was conducted to identify species causing powdery mildew on cucurbits and to determine genetic variations among isolates of the pathogen. We collected 109 isolates from six cucurbit species hosts (Cucumis melo, Cucumis sativus, Cucurbita maxima, Cucurbita moschata, Cucurbita pepo, and Lagenaria siceraria) in California, Illinois, Indiana, Michigan, New York, Texas, Washington, and Wisconsin in the United States and in Italy. By sequencing the internal transcribed spacer region of the nuclear rDNA of these 109 isolates, Podosphaera xanthii was found as the only species causing powdery mildew on cucurbits in the United States. Genotyping-by-sequencing was applied to these 109 isolates to investigate their genetic diversity, which showed a trend of isolates clustering from New York and Italy. In addition, the virulence of 36 isolates was compared and a significant difference (P < 0.0001) was found among them. Furthermore, results of the virulence tests of 28 isolates from Illinois showed significant effects of collection years, hosts, and locations on the virulence of the isolates.

This study was conducted to evaluate the sensitivity of cucurbit powdery mildew fungus (Podosphaera xanthii) to major fungicides used for managing this pathogen in the Midwestern United States. Fungicides azoxystrobin from the quinone outside inhibitors group, cyflufenamid from the phenylacetamide group, penthiopyrad from the succinate dehydrogenase inhibitors group, quinoxyfen from the quinolines group, and triflumizole from the demethylation inhibitors group were tested for their effectiveness for preventing infection of cucurbits by P. xanthii. In 2015 and 2016, 37 isolates of P. xanthii were evaluated for their sensitivity to azoxystrobin (Quadris 2.08SC), cyflufenamid (Torino 0.85SC), penthiopyrad (Fontelis 1.67SC), and triflumizole (Procure 480SC) on cucumber ‘Bush Crop’ cotyledon leaves. The number of isolates sensitive to tested concentrations of Quadris 2.08SC, Torino 0.85SC, Fontelis 1.67SC, and Procure 480SC was 8 (22%), 21 (57%), 20 (54%), and 23 (62%), respectively. During 2015 to 2018, Quadris 2.08SC, Torino 0.85SC, Fontelis 1.67SC, quinoxyfen (Quintec 250SC), and Procure 480SC were tested for their effectiveness for managing powdery mildew on pumpkin ‘Howden’ in the field. The results showed that powdery mildew was effectively managed in the plots treated with Procure 480SC and Quintec 250SC. However, management of the disease was less successful in the plots treated with Quadris 2.08SC, Torino 0.85SC, and Fontelis 1.67SC.

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.

Bacterial spot, caused by Xanthomonas cucurbitae, is an important disease of cucurbits worldwide. Considering the absence of resistant cultivars, along with the limited effects of chemical treatments, we evaluated the use of potential biocontrol agents for management of the disease. We collected 1,134 bacterial isolates associated with bacterial spot symptomatic leaves and fruits and screened in vitro for their antagonistic activity against X. cucurbitae. A total of 271 isolates inhibited colony formation of X. cucurbitae in a disc diffusion assay. Species of these antagonistic isolates were identified based on 16S rRNA primers and phylogenetic analysis using four housekeeping genes. Based on results from the in vitro assays, the strong inhibitors of X. cucurbitae were selected for greenhouse and field evaluations. We found that Bacillus amyloliquefaciens, Bacillus velezensis, Pantoea agglomerans, and Pseudomonas putida were able to prevent or limit development of bacterial spot on pumpkin plants in the greenhouse and field studies. Additionally, Bacillus amyloliquefaciens and Pseudomonas putida increased growth of ‘Howden’ pumpkin (Cucurbita pepo). Our results suggest that these biocontrol agents can be used for managing bacterial spot disease and enhancing the growth of pumpkin plants.

Studies by Hagler et al. (1987) from 1981-1985 revealed that much of the grain sorghum grown in North Carolina was, except in 1983, contaminated at - harvest with zearalenone (ZE), deoxynivalenol (DON), and toalesser degree, aflatoxins (AF) B1 and B2. These studies defined some factors controlling occurrence of these mycotoxins in grain sorghum. Rainfall during flowering and early maturation was associated with the Increased incidence and concentration of ZE and DON. In 1983, there was a drought during this critical period which apparently prevented ZE and DON contamination (Bowman et al. , 1986; Hagler et al. , 1987). Zearalenone had been reported in grain sorghum previously (Schroeder and Hein, 1975; Bennett and Shot well, 1979; Shotwell et al. , 1980; M c Millian et al. , 1983). Deoxynivalenol, which frequently occurs with ZE in corn ( Thiel et al. , 1982), had not been previously reported as a contaminant of sorghum until 1981 (Hagler et al. , 1987).