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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #333097
Title: Nonchemical, cultural management strategies to suppress phytophthora root rot in northern highbush blueberry

Author
item YEO, JOHN - Oregon State University
item Weiland, Gerald - Jerry
item SULLIVAN, DAN - Oregon State University
item Bryla, David

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2017
Publication Date: 6/1/2017
Citation: Yeo, J.R., Weiland, G.E., Sullivan, D.M., Bryla, D.R. 2017. Nonchemical, cultural management strategies to suppress phytophthora root rot in northern highbush blueberry. HortScience. 52(5):725-731. doi: 10.21273/HORTSCI11437-16.

Interpretive Summary: Phytophthora root rot of highbush blueberry, caused by Phytophthora cinnamomi, is often managed with fungicides, but organic growers cannot use fungicides and need nonchemical methods for managing this disease. Left untreated, root rot can reduce establishment, yield, and profitability for growers. A field experiment was established to evaluate whether combinations of mulch type (sawdust versus plastic weed mat, drip irrigation line placement (narrow versus wide), and gypsum incorporation (amended or not) reduced disease in comparison to fungicide treatment (control). Initially, disease was lower in plots mulched with sawdust, with wide drip irrigation line placement, and amended with gypsum than in all other treatments except the fungicide control. However, by the second growing season, plant biomass was similar between the two mulch types. The combination of widely-spaced drip irrigation with gypsum amendment resulted in the largest plant biomass of all the cultural treatments. However, plants treated with fungicide always had at least twice as much biomass as plants grown in any of the cultural treatments without fungicide. Therefore, although less effective than fungicide, this study suggests that gypsum soil amendment coupled with widely-spaced irrigation lines can help suppress root rot and increase growth of blueberry at sites where root rot is present.

Technical Abstract: Phytophthora cinnamomi causes root rot of highbush blueberry and decreases plant growth, yield, and profitability for growers. Fungicides can suppress root rot, but cannot be used in certified organic production systems and fungicide resistance may develop. Alternative, non-chemical, cultural management strategies were evaluated to reduce root rot in a field infested with Phytophthora cinnamomi and planted with a susceptible blueberry cultivar, Draper. Treatments included conventional sawdust mulch or weed mat combined with either narrow or wide drip irrigation line placement, and with the soil either amended or not with gypsum. A fungicide control treatment included application of two conventional fungicides with narrow drip line placement, sawdust mulch, and no gypsum. Initially, root infection was lower in plots amended with gypsum, mulched with sawdust, and with wide drip irrigation than in all other treatments except the fungicide control. However, after two growing seasons, plant biomass was similar between the two mulch types. The effects of irrigation line placement and gypsum incorporation were interactive, and the combination of widely-spaced irrigation lines with gypsum incorporation produced the most plant biomass of the cultural treatments. Irrigation lines placed adjacent to the plant crown negated the disease-suppressive effects of gypsum by moving zoospore-inhibiting Ca2+ away from the plant root zone. Plots with irrigation lines adjacent to the plant crown were also wetter in the center of the bed, which may facilitate infection by zoospores. Despite greater plant biomass with gypsum amendment and widely-spaced irrigation lines, plants treated with conventional fungicides had at least twice the biomass of plants grown in any of the cultural treatments without fungicide. Therefore, while less effective than the fungicides, this study suggests that pre-plant soil amendment with gypsum coupled with widely-spaced drip irrigation lines can help suppress root rot and increase growth of blueberry at sites where the pathogen is present.