![]() Oilspots are known to survive the high summer temperatures in WA. These oilspots (and surfaces of other diseased tissue) produce sporangia (seen as white down) on suitable warm wet nights. Secondary infection (leaf to: leaf, shoot, inflorescence, berries, stalk)Īctive oilspots need to be present before secondary infections can occur. Hence, primary infections are very difficult to find if only a few germination events have occurred at the beginning of the season. Primary infection levels are usually low with only 1-3 oilspots developing per 50m of vine row per germination event. At warmer or cooler temperatures the incubation period is longer. The development of oilspots is quickest in warm weather (18-27☌). These hyphae grow inside the leaves to form oilspots that appear 5-17 days (but more often 5-10 days) after infection has occurred. The zoospores released during primary infection that establish on the underside of the leaf begin to grow hyphae. A combination of rainfall and irrigation together can be sufficient for germination to occur. Soil moisture levels are important for the germination of oospores. ![]() For this, the foliage must remain wet for at least 2-3 hours at 20☌ (or 4-5 hours at 10☌) for the spores to infect the leaf and complete the primary infection cycle. This process usually requires another 3-5mm of rain (and/or irrigation) to ensure sufficient splash and leaf wetness for infection on the underside of the leaves. The germinated oospores then release zoospores (that swim in free water) which then need to be splashed by rain or irrigation to the vine canopy before the end of the 24 hour period.
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