Click on any
image for a more
detailed view

Disease Management

No single method is available to provide adequate control of Phytophthora blight. Various disease control practices can be integrated to manage Phytophthora blight, including: exclusion, cultural practices, and chemical control.

Exclusion

The most effective method of control for Phytophthora blight is to prevent P. capsici from moving into a non-infested field. Phytophthora capsici spreads by soil, water, and/or plant material. It is highly recommended to thoroughly clean all farm equipment that is used in an infested field before moving it to another field. Also, avoid using water sources (i.e. ponds or reservoirs) that receive run-off water from an infested field. Water sources can be tested for the presence of the pathogen by baiting techniques. Phytophthora capsici is not considered a seed-borne pathogen, however, saving seed from a field where Phytophthora blight occurred should be avoided.

Cultural practices

The following cultural practices can help to manage Phytophthora blight in cucurbit fields. Because P. capsici can survive in soil for several years, fields without a history of Phytophthora blight should be selected for planting. Although no cropping rotation period has been established for effective management of Phytophthora blight of cucurbits, it is recommended to select only fields that have not had a history of cucurbits, eggplant, peppers, and/or tomatoes for at least 3 years. Fields should be selected that are well isolated from fields infested with P. capsici. High soil moisture favors the development of Phytophthora blight, thus well-drained fields should be selected and excessive irrigation should be avoided. Also avoid planting cucurbit crops in areas of the field that have poor drainage.

Non-vining cucurbit crops (e.g. summer squash) should be planted on dome-shaped raised beds [approximately 25 cm (10 in. high)]. The field should be scouted regularly for Phytophthora symptoms, especially after major rainfalls, and particularly in low areas of the field. When symptoms are localized in a small area of the field, the infected plants should be plowed into the soil. Plants should be sprayed with effective fungicides at the first sign of the disease. Healthy fruit should be removed from the infested area as soon as possible, and they should be checked for disease development routinely. Growing cover crops and/or mulching with plant materials including straw and rye vetch can also be used to manage the dispersal of the pathogen.

Chemical control

Fungicide seed-treatment and spray-application can prevent seedling death and reduce foliar blight and fruit rot. Seed treatment with either mefenoxam [Apron XL LS at the rate of 0.42 ml /kg (0.64 fl oz/100 lb) seed] or metalaxyl [Allegiance FL at the rate of 0.98 ml /kg (1.5 fl oz/100 lb) seed] can protect seedlings of cucurbits against P. capsici for up to 5 weeks after planting. Spray applications of dimethomorph [Acrobat 50WP at the rate of 448 g /ha (6.4 oz/A)] plus copper sulfate [e.g. Cuprofix Disperss 36.9F at the rate of 2.25 kg/ha (2 lb/A)], at weekly intervals, can provide effective protection against foliar blight and fruit rot caused by P. capsici in cucurbit fields. Combining Apron XL LS seed-treatment with spray-applications of Acrobat plus copper can minimize crop losses to Phytophthora blight in cucurbit fields. It is important to note that resistance to both mefenoxam and metalaxyl has occurred in some areas of the US, so the sensitivity of P. capsici populations should be tested before fungicide applications are chosen.