The study of phenological events and purple blotch incidence of Ilocos white garlic involves the observation, recording and interpretation of their occurrence. This study considers the occurrence of purple blotch based on weather conditions and phenophases of the plants. The different weather parameters that influence the timing of the occurrence and intensity of damage of this disease are discussed.

Results show that the emergence of each leaf requires an average of 5 to 6 days. All throughout its growing period, the plant produced up to 17 leaves. Purple blotch was evident as early as in the later part of the vegetative stage or the development of 8th leaf (40-45 days after planting) when there was an occurrence of rainfall or when relative humidity was >88 %. The disease spread rapidly reaching a very high damage when the relative humidity was consistently higher than 90% but did not progress rapidly when the relative humidity was below 85%. There was no occurrence of the disease during the initial and early vegetative stages of the plants even if there was high relative humidity (>90%) and occurrence of rainfall. The intensity of purple blotch damage affect the yield of the plants. Likewise, the yield decreased when the minimum temperature was more than 20^oC.