Progress of White Rot on Garlic Cultivars Planted at Different Times

In the region of Amarantina, Minas Gerais state, Brazil, four annual experiments with garlic (Allium sativum) were established in fields infested with Sclerotium cepivorum, causal agent of garlic white rot, to investigate the effect of time of planting on the day when disease was first noticed (t_onset), incidence at harvest (y_f), duration of epidemics (t_f - t_onset), and the response of five cultivars to white rot. Most epidemiological parameters were similar among cultivars. In 1986 to 1988, no white rot was observed on garlic planted during the warm temperatures in January. The average onset of white rot occurred at different times dependent on the day of planting as average temperatures decreased from January to May. That is, for February plantings, onset occurred after 93 to 140 days (between 1 June and 5 July); for March plantings, about 90 days (15 to 28 June); for mid-April plantings, about 77 days (1 July); and mid-May plantings, about 66 days (20 July). Because of these different times of onset, the average duration of epidemics was shorter for crops planted in February (30 days) compared to crops planted in March (48 days) or April to May (54 to 69 days). In general, most disease (highest incidence and longest duration) occurred on crops planted in March to May. Therefore, severe losses to white rot would be expected when garlic is planted at the traditional times (March and April) in areas infested with sclerotia of S. cepivorum. The early planting of garlic is recommended as an important management strategy to avoid white rot in areas with these infested soils.