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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #193619


item ABLES, C. B. - USDA, ARS
item Rosskopf, Erin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2011
Publication Date: 10/1/2007
Citation: Ables, C., Rosskopf, E.N., Lamb, E. 2007. Control of phytophthora rot in pumpkin and zucchini with phosphonates. Plant Disease. 91:1651-1656.

Interpretive Summary: Phytophthora root rot in cucurbits was first reported in the US in the late 1930s. The causal organism was identified as Phytophthora capsici, a species that attacks many other crops including pepper and eggplant. In addition to root rot, P. capsici can cause seedling damping off, stem lesions, foliar blight, leaf spots, and fruit rot. Most of the cultivated species of cucurbits are susceptible to P. capsici, most especially summer squash. Phytophthora root rot is a problem in fields with heavy, poorly drained soils. The losses due to this disease are periodic; but when the disease occurs, it can result in total devastation of the cucurbit crop. Throughout the United States, Phytophthora blight is considered a serious threat to cucurbit production. At present, there is no cucurbit cultivar with known resistance to this pathogen and crop rotation has not been effective due to the pathogen’s ability to persist in the soil for many years and to infect more than 50 plant species, including weeds. While fungicides can be a valuable component of a disease management scheme, there is no single fungicide that can provide high levels of efficacy, especially during periods of excessive soil moisture. Best management practices include water management, selection of well drained areas for planting and the application of fungicides. Phosphorous acid and related compounds have been shown to be effective against several Phytophthora diseases. However, some studies have also shown that application of phosphorous acid or related compounds may not always be effective in controlling Phytophthora spp. Possible reasons for variable efficacy include differences in the uptake and translocation by different crop species, application rate, timing of application, and environmental factors. This study was conducted to determine the efficacy of phosphonates, specifically a mixture of dipotassium phosphonate and dipotassium phosphate, against Phytophthora capsici infection in pumpkin and zucchini and to investigate the effect of concentration, application method (drench or foliar spray) and crop variety on the level of disease suppression by these materials.

Technical Abstract: Experiments in the greenhouse were conducted to determine the efficacy of two products containing potassium phosphate/dipotassium phosphonate (FNX-100 and FNX-2500) against Phytophthora root and stem rot in pumpkin and zucchini. Experiments were designed to determine the effects of crop variety, application method, and varying concentration of material on the severity of Phytophthora rot in pumpkin. In the pumpkin experiments, variety, treatment, concentration, and application method significantly influenced the severity of rot. Drench application of 3.0% FNX-100 consistently suppressed rot in variety Phantom. For variety Spooktacular, all three concentrations of FNX-100 significantly reduced the severity of rot. Experiments with zucchini compared the effect of the two products applied as drench and their concentration on Phytophthora rot. Rot was only controlled with FNX-100 regardless of variety or concentration. In both pumpkin and zucchini, only FNX-100 provided satisfactory disease control. FNX-2500, a foliar fertilizer comprised of the phosphate/phosphonates and copper, manganese and zinc, did not offer any benefit in terms of disease control.