118 VEN Fungal Diseases Continued
Phomopsis Cane and Leaf Spot Phomopsis viticola Downy mildew Plasmopora viticola
Phomopsis Cane and Leaf Spot Phomopsis viticola
Phomopsis cane and leaf spot Phomopsis viticola
Spore germination: 1 37oC, optimum is 23oC Infection takes place within few hours in free water or near 100% RH Only very young tissue is infected Prolonged periods of rain and cool weather are prime factors in the development of an epidemic Spread within vineyard is localized, remaining in close proximity to inoculum source
P. viticola overwinters as mycelium and pycnidia in bark.
When wet,spores will excude from the pycnidia
and washed or splashed by rain to shoot tips
Phomopsis viticola disease cycle and epidemiology
Phomposis Damage/Control
Damage Infections will weaken shoots that can break in strong winds or due to other circumstances Control sanitation (remove as much diseased and dead wood as possible during pruning) Dormancy application of liquid lime sulfur will reduce viability of pycnidia Control fungicides (two applications of a protective chemical when shoots are 1-3 and 6-12 cm in length)
Final note on P. viticola
In a survey by Dr. Gubler of vineyards around the state of CA, Phomopsis viticola was the principal fungus found in cankers from Fresno and Tulare counties. They have yet to initiate a project there to evaluate the significance of this finding.
Downy mildew Plasmopora viticola
Downy mildew disease cycle and epidemiology
Over-winters mainly as oospores in fallen leaves but can survive as mycelium. Spores germinate in water in the spring as soon as temperatures reach 11oC. They produce a sporangium from which dispersal of zoospores occurs by rainsplash, with the zoospores landing upon green susceptible grape tissue
Downy mildew disease cycle and epidemiology
Zoospores will swim and encyst near stomata, which are entered by germ tubes The fungus enters the plant almost via exclusively the stomata. Under optimal conditions, the time from germination to penetration is less than 90 minutes.
Downy mildew disease cycle and epidemiology
Sporangiophores and sporangia are produced only through the stomata, a process that requires 95-100% RH and at least 4 hours of darkness. Optimal temperature for sporulation is 18 to 22oC. Detachment of sporangia from the fruiting structure, which requires moisture, occurs and they are carried by wind to leaves where they germinate in free water (optimal temp. = 22 to 25oC). The optimal temperature for development of the fungus is 25oC, extremes ranging from 10 to 30oC
Downy mildew symptoms
Fungus attacks all green parts of the vine, particularly the leaves. Sporulation occurs from the lower surface of the leaf blade. The upper leaf surface will turn yellowish and have anoily texture. Young berries are susceptible but they become less susceptible as they mature (however, rachis infections can spread to older berries). Infected berries may drop and fall from the cluster. Portions of the rachis or the entire cluster may drop from the vine.
Oil-spot symptoms of Downy mildew on leaf in spring.
Lower surface of grape leaf blade w/sporangiophores and mycelium of P. viticola.
Downy mildew symptoms on a leaf in autumn.
Shepherds Crook
Downy mildew - Plasmopora viticola
Damage can cause significant reductions in vegetative and reproductive (yield) growth of the vine if left uncontrolled.
Downey mildew - Plasmopora viticola
Control draining soils, reducing source of overwintering inoculum and pruning out infected shoots (generally not practical). Control - fungicides are the most important control measure and are either preventative or curative. The preventative fungicides (including copper compounds) must be applied before an infection. Most serious epidemics occur when wet winters are followed by wet springs and warm summers with intermittent rainstorms.