Inhibition of oomycetes by the mixture of maleic acid and copper sulfate

After the discovery of the protective activity of Bordeaux mixture against plant disease caused by oomycetes, copper compounds have been used for over a century as a significant plant protection strategy. However, application of excessive copper can cause adverse effects through long-term heavy metal accumulation in soils. Therefore, it is necessary to develop new strategies to reduce or replace copper in pesticides based on organic and low-input farming systems. Organic acids are eco-friendly in nature. In this study, we tested the antifungal and anti-oomycete activity of maleic acid (MA) and copper sulfate (CS) against thirteen plant pathogens. Treatment of MA and CS mixture showed strong anti-oomycetes activity against Phytophthora cambivora, P. capsici and P. cinamomi. Moreover, the concentration of CS in the activated mixture of MA and CS was lower than that in the activated CS only, and the mixture showed synergy or partial synergy effects on the anti-oomycete activity. Application of a wettable powder formulation of MA and CS mixture (MCS 30WP; 26.67 % MA and 3.33 % CS) exhibited excellent protective activities in pot experiments with control values of 73 % Phytophthora blight on red pepper, 91 % damping-off on cucumber, and 84 % Pythium blight on creeping bentgrass, which are similar to those of the CS wettable powder formulation (6.67 % CS) containing two times the CS content in MCS 30WP. These observations suggest that the synergistic effect of the MA and CS combination is a sustainable alternative for effective management the destructive oomycete diseases.

A field evaluation of jalapeño and non-jalapeño chile pepper resistance to Phytophthora blight caused by Phytophthora capsici

Phytophthora capsici is a destructive soilborne pathogen, which causes Phytophthora blight in many vegetable crops including chile pepper (Capsicum sp.). Our research was aimed at evaluating the resistance of jalapeño cultivars in field conditions and identifying the factors associated with reduction of Phytophthora blight caused by P. capsici. Six jalapeño (NuMex Orange Spice, NuMex Pumpkin Spice, NuMex Jalmundo, TAM Jalapeño, Early Jalapeño, and NuMex Vaquero) and two non-jalapeño (CM-334 and NM 6-4) cultivars were inoculated with P. capsici at the fruiting stage. Disease severity index (DSI), disease incidence (DI), and area under the disease progress curve (AUDPC) for each cultivar were measured. The most susceptible jalapeño cultivars with the highest DSI, DI, and AUDPC were NuMex Orange Spice, NuMex Jalmundo and NuMex Pumpkin Spice, whereas the least susceptible jalapeño cultivars were Early Jalapeño, TAM Jalapeño, and NuMex Vaquero, with the lowest DSI, DI, and AUDPC. The identified jalapeños with reduced susceptibility to Phytophthora blight can be planted in infested fields, combined with other control methods which may help in soil disinfestation by reducing the inoculum level in soil over time.

Detection of Phytophthora capsici from irrigation ponds in South Georgia

Phytophthora capsici, the causal agent of Phytophthora blight, is a prominent and economically damaging oomycete pathogen in South Georgia. P. capsici causes crown, root, leaf, stem, and fruit infections on a wide range of vegetable crops. Oomycete pathogens such as P. capsici are dispersed in water as their zoospores are flagellated and can move through runoff. Irrigation ponds are often reservoirs for different pathogens and reusing the captured runoff is increasing in popularity to decrease irrigation costs. This combination allows for unintended outbreaks of diseases by pumping the contaminated runoff onto susceptible crops. Detection and identification of these pathogens is a crucial step in disease management and rapid detection can ensure timely application of disease control measures. In this study, 42 irrigation ponds in nine counties from South Georgia were surveyed for the presence of P. capsici using a novel filtration method in conjunction with a LAMP assay specific for P. capsici. Ten ponds in five counties were found to have P. capsici as detected from the assay, suggesting that testing of irrigation ponds for P. capsici and other pathogens should be conducted to assist in preventing disease outbreaks.

Efficacy of Pecan Husk and Shell Phenolic Extracts Against Phytophthora Blight in Chile Pepper

Phytophthora blight, caused by Phytophthora capsici, is detrimental to chile peppers (Capsicum spp.). In this study, phenolics extracted from pecan (Carya illinoinensis) husk and shell, were foliarly applied to chile pepper (Capsicum annuum L., cultivar NM 6-4) to induce a resistance response against plant infection by P. capsici. Several pecan metabolite extractions were tested, and an acetic acid (2%) in aqueous methanol (80%) solution was the best extraction solvent, yielding total polyphenolic content of 290 mg/g dry weight from husk and 641 mg/g from shell. The phenolic extracts from husk and shell were applied as foliar sprays at different concentrations to chile plants inoculated with a virulent isolate of P. capsici. Chile plants treated with 1% phenolic husk or shell extracts or 0.1% salicylic acid remained alive throughout the study while plants subjected to all other treatments (including a water control treatment) died. Analyses of the extracts through spectrophotometry and high performance liquid chromatography indicated that the phenolic content in the extracts was largely made up of proanthocyanidins also known as condensed tannins. Pecan byproducts may be used as additional options for management of Phytophthora blight.

Applying Drone-based Spatial Mapping to Help Growers Manage Crop Diseases

Phytophthora blight (Phytophthora capsici) is one of the major soilborne diseases threatening many vegetable crops including squash. The disease results in severe epidemics and yield losses due to a rapid spread of the pathogen associated with wet weather and soil waterlogging. Implementing drone-based spatial mapping with software elevation tools can assist growers in evaluating land levelling for uniform distribution of water to mitigate potential disease incidence. The technology has great advantages: rapid, precise, and labor-cost effective. Our result can implicate Extension professionals with application of spatial mapping to assist growers in managing their land and crops for disease control efficiently.