Diseases Pests
Downy Mildew

Downy mildew is one of the major diseases of the grapevine. It is caused by the fungus Plasmopara vitícola, which attacks all of the grapevine’s green organs. Downy mildew develops in climates characterised by average temperatures, rain and high relative humidity. Usually, temperatures above 30ºC are harmful to the fungus.
In winter, this fungus has the form of oospores, which are found in fallen dead leaves. When the temperature starts to rise (above 10ºC) and a significant precipitation occurs for a day or two, macroconidiums are formed, which release zoospores - ciliated spores capable of moving in the water and responsible for primary contamination. Zoospores enter the plant through the stomas.

Leaves:

- Oil spots on the upper page of the grapevine’s leaves
- White fructifications on the lower page (conidiophores)
- If the leaves dried, they are brown and brittle
- In autumn, mosaic necrosis spots may occur

Inflorescences:

- Flowers with white/brownish mould
- Crozier-shaped inflorescence

Bunches:

- White powder coating the berries’ surface
- Crozier-shaped bunches (rot gris): become dark-coloured and dry

Cultural control:

- Drainage of soils with a high potential to retain water, in order to avoid the formation of water puddles.
- Remove the affected organs.
- Promote the aeration of the grapevines through training systems and green interventions.
- Avoid techniques that lead to excessive vigour (grape varieties, vine training systems, rootstocks and fertilisations).  

Chemical control:

The chemical control may have several effects, such as: preventive (performed outside the leaf to prevent the development of zoospores and germination hyphae), curative (performed inside the leaf to stop the development of mycelium and haustoriums) and antisporulating (action, necrosis of conidiophores and conidia formed outside the leaf).

In chemical control one uses:

- Contact fungicides (cuprics; dithiocarbamates; N-trihalomethyls), which act outside the plant on zoospores and respective germination tubes, preventing infection before contamination. 

- Penetrant fungicides (cymoxanil; azoxystrobin; dimethomorph), which, besides having contact action, also have lateral diffusion with translaminar movement. They also have a curative action that suspends the development of mycelium and haustoriums.

- Systemic fungicides (fosetyl; anilides; benalaxyl; metalaxyl; ofurace; oxadixyl), which have an antisporulating effect and interrupt the action of anilides. Moreover, they stimulate the plant’s defence mechanisms.

A animação “Comportamentos de acasalamento e postura da traça da uva, Lobesia botrana, faz parte de uma colecção intitulada “Ciclo de Vida da Traça da Uva Lobesia botrana e modo de acção de auxiliares”.

Estes materiais multimédia foram desenvolvidos sob a coordenação científica da Professora Ana Aguiar, e produzidos pela Universidade do Porto para integrarem os materiais de apoio ao processo pedagógico de disciplinas de Protecção de Culturas.

Neste momento, esta e outras animações, integram um curso on-line de formação contínua da U.Porto intitulado “Protecção Integrada da Vinha U.Porto – curso on-line”.


 
Português