English name: Mildew Downy
The scientific name: Plasmopara viticola
The type of disease: Fungal disease
family: Peronosporaceae
Symptoms
Downy mildew can affect all green tissues of grapes, including leaves, shoots and clusters. On the leaves, it appears as irregular yellow or reddish-brown spots on the upper surface with fine white growth on the underside. These spots may collect, causing the paper to curl or become distorted. Severely infected leaves may turn brown and fall off. On fruit, the disease can cause brown discoloration, cracking and premature drop.
Reasons
Downy mildew is caused by the fungal pathogen Plasmopara viticola, high temperatures and is an obligate parasite that requires live host tissue to survive.
Propagation conditions
Downy mildew thrives in warm, humid conditions with temperatures between 80°F (15°C and 27°C) and long periods of leaf wetness. The pathogen produces sporangia that can be spread by wind, rain or water spray.
Disease course
The pathogen overwinters as eggs in leaf litter or soil. In the spring, when temperatures are favorable and humidity is present, the eggs germinate and release spores that infect sensitive young tissue. The pathogen then produces sporangia on the underside of infected leaves, which can spread and start a new infection. The disease cycle continues throughout the growing season as long as suitable conditions persist.
The walker
Severe downy mildew infections can result in significant defoliation, reduced photosynthesis, and poor fruit set, ultimately resulting in yield and quality losses.
Control strategy
An integrated approach including cultural practices, resistant varieties and fungicide applications is recommended for downy mildew management.
Preventive measures
Plant resistant or tolerant varieties, ensure good air circulation in the vineyard, and avoid excessive nitrogen fertilization.
Organic/chemical control
For organic control, copper-based fungicides (such as copper hydroxide and copper sulphate) can be effective when applied preventatively. Chemical fungicides containing active ingredients such as mandipropamide, dimethomorph, or cyazofamide may also be used according to label instructions.
reference
https://www.crop.bayer.com.au/news-and-insights/news/news-
container/2022/08/05/02/55/downy-mildew-concern-in-grapevines
Oregon State University - Grape Downy Rot https()catalog.extension.oregonstate.edu/pnw/642//
https //www.vineloverswineclub.com/wp-content/uploads/2020/05/Downy-
Mildew-on-Grape-Leaves-2.jpg
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