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Mycologia, MASTIGOMYCOTINA, PERONOSPORALES, PERONOSPORACEAE .
Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images
[R]Description
The fungus is already present at emergence, causing damping-off or yellowish colour in seedlings.
In the vegetative stage chlorotic spots occur on the upper leaf surface corresponding to purplish-grey cottony down on the lower surface. Leaflets turn bristle and gradually dry out. Plants become stunted. Attacks during the flowering stage can cause withering of the flowers. Pods become yellow, distorted and, in severe attacks, sterile.
Seeds are covered by a white cottony mycelial growth ; they are dwarfed and brown.
The disease mainly affects the spring pea.
[R]Biology
The fungus survives as oospores on seeds or in the soil.
Primary infection occurs in the soil.
The systemic mycelium infects the tissues of the young plant causing the stems and petioles to swallow.
Sporulation occurs on the lower surface of the leaflets.
The resulting sporangia cause the secondary contaminations to take place at different stages of the crop cycle.
Oospores form in the infected tissues at the end of the crop life cycle.
[R]Epidemiology
Mildiew develops mostly in cool weather (5 - 18 °C.) with RH over 85 %. Therefore, early sown plants are more susceptible to attacks than the later ones.
The rain and wind-borne sporangia germinate only at 4 - 8 °C.
Oospores are produced when the temperature reaches over 20 °C.
[R]Treatement
Use treated seeds containing specific active agents against downy mildew which can also control other diseases in order to reduce the infective effect of primary inoculum.
Proceed to chemical control during the vegetative stage as well in order to limit the extent of the epidemic.
HYP3 on line : Species (scientific name), Diseases (common names), Glossary, Crops.
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