Implications of Irrigation Method and Amount of Water Application on Phytophthora and Pythium Infection and Severity of Root Rot in Highbush Blueberry

Authors: Bryla, David; Linderman, Robert

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2007
Publication Date: 10/10/2007
Citation: Bryla, D.R. and Linderman, R.G. 2007. Implications of irrigation method and amount of water application on Phytophthora and Pythium infection and severity of root rot in highbush blueberry. HortScience.42:1463-1467.

Interpretive Summary: Irrigation is often critical for profitable production of blueberry, but when over-applied it can reduce root function, increase soil erosion and nutrient leaching, and potentially cause problems with fungal diseases such as phytophthora root rot. Northern highbush blueberry ('Duke') was planted in April 2004 and irrigated by overhead sprinklers, microsprays, or drip. Sprinklers and drip are the two most common methods used to irrigate blueberry in the U.S. Plants were irrigated by each system with optimum, excessive, or inadequate amounts of water. Excessive and inadequate irrigations were included to determine the consequences of over- or under-irrigating the crop. By the end of the first season, drip irrigation produced the largest plants while sprinklers produced the smallest; plant size with microsprays was intermediate. However, by the end of the second season, plants irrigated by drip were the smallest. Assessment of plants harvested destructively revealed that plants in each treatment were infected by both Phytophthora and Pythium root rot fungi. Root rot is a major disease in blueberry, with symptoms ranging from stunted growth to premature defoliation and plant death. Root infection significantly increased with over-irrigation and was highest when plants were irrigated by drip. Clearly, root rot had reduced growth, especially when plants were irrigated by drip. Based on analysis of plant-free soil samples, it appears that the fungi probably originated with the planting stock. Drip irrigation maintained wetter soil conditions near the base of the plant than sprinklers and microsprays, which probably increased spread and severity of the disease. We are now attempting to control the fungi with fosetyl-Al fungicide, and so far results look promising in all treatments except plants over-irrigated by drip.

Technical Abstract: Northern highbush blueberry (Vaccinium corymbosum L. 'Duke') was planted in April 2004 and irrigated by overhead sprinklers, microsprays, or drip. Irrigation was applied by each system at 50, 100, and 150% of the estimated crop evapotranspiration requirement (ETc). By the end of the first season, drip irrigation produced the largest plants (based on whip counts and pruning weights) while sprinklers produced the smallest; plant size with microsprays was intermediate. However, by the end of the second season, plants irrigated by drip not only had fewer whips and less pruning weight than those irrigated by sprinkler and microspray, they also had only half the shoot and root dry weight. Assessment of plants harvested destructively revealed that plants in each treatment were infected by both Phytophthora and Pythium root rot fungi. Root infection significantly increased with irrigation level and was highest when plants were irrigated by drip. Clearly, root rot had reduced growth, especially when plants were irrigated by drip. Based on analysis of plant-free soil samples, it appears that the fungi probably originated with the planting stock. Drip irrigation maintained higher soil water content near the base of the plant than sprinklers and microsprays, which probably increased spread and severity of the disease. We are now attempting to control the fungi with fosetyl-Al fungicide, and so far results look promising in all treatments except plants over-irrigated by drip (i.e., 150% ETc).