Effect of Sprinkler Irrigation on Bacterial Soft Rot and Yield of Broccoli.

The effect of amount of applied water under two irrigation frequencies (once versus three times per week) on the incidence of bacterial soft rot, caused by Erwinia carotovora subsp. carotovora, and yield of broccoli was investigated in field studies conducted in 1987 and 1988. At head initiation, the amount of applied water was varied by utilizing a line source irrigation system. Incidence of soft rot was higher in the OSU breeding line 86-3 plots, followed by cv. Citation and then cv. Gem. Soft rot was not consistently affected by amount of applied water. Differences in amount of disease were apparent, however, between the separate irrigation frequency studies in 1988; disease incidence more than doubled under the high- compared with the low-frequency irrigation. Further studies on the effects of frequency and timing of sprinkler irrigation on soft rot and yield of Gem broccoli were undertaken in 1993 and 1994. Six sprinkler irrigation regimes, a factorial combination of frequency (irrigation every 2, 4, or 8 days) and timing (morning or evening), were established. Total water applied did not differ by treatment. Incidence of soft rot was negligible at the first harvest in both years. At the last harvest, the incidence of soft rot was significantly reduced, from 22 to 10% in 1993 and from 30 to 15% in 1994, by the change in frequency of irrigation from 2 to 8 days. In contrast, timing of irrigation had no effect on disease incidence. Yield of broccoli was not affected by either frequency or timing of irrigation.