The infection cycle starts when spores are spread by rain or overhead irrigation from leaves or canes infected from the previous season. The conidia must be wet for several hours to infect plant tissues. Symptoms begin to appear in three to 16 days after infection. Mature conidia can be produced 10 to 18 days after infection and initiate a new cycle. Conidia are colorless and two-celled (Fig. 2b). A temperature of 64°F is optimal for black spot development, but conidia germination still occurs from 59 to 81°F. This wide temperature range allows the disease to continue to develop as long as the moisture is adequate during the season.