SUMMARY

Erysiphe necator overwinters as mycelium or conidia in dormant buds and/or as cleistothecia, but the impor-tance of the two forms as sources of primary inoculum varies in different viticultural areas. The present study summarizes the observations made over 2001-2003, in 29 vineyards of southern Italy, on the occurrence and frequency of the two overwintering forms. Flag shoots were found in one-third of the vineyards, with a fre-quency highly variable between year and vineyard, be-ing more frequent in vineyards for wine-grape than for table-grape production. An average of 20 % flag shoots were present on the same vine and arm as the previous year, and 75 % of them originated from the three proxi-mal buds of the canes. Cleistothecia were found in 46% of monitored vineyards, in the leaves and bark, but not in the soil. In spring there were between 3 and 856 cleistothecia/g of leaf tissue with a viability of 7%, whereas in the bark between 2 and 464 overwintering cleistothecia/g of bark were found, with an average via-bility of 14%