Red sorrel management and potential effect of red sorrel pollen on Botrytis cinerea spore germination and infection of lowbush blueberry (Vaccinium angustifolium Ait.) flowers

Red sorrel is a common weed in lowbush blueberry fields in Nova Scotia, Canada. Grower experience suggests that high red sorrel density necessitates fungicide applications to control Botrytis cinerea, a major fungal pathogen in lowbush blueberry. Specific interactions between red sorrel, lowbush blueberry, and B. cinerea, however, remain unclear. Experiments were conducted in Nova Scotia to determine the (1) presence or absence of red sorrel pollen on lowbush blueberry flowers in the field, (2) impact of red sorrel pollen on in vitro B. cinerea spore germination and infection of immature and mature blueberry flowers, and (3) effect of pronamide applications on red sorrel and lowbush blueberry growth. Red sorrel pollen grains were found on blueberry flowers in the field. In vitro B. cinerea spore germination increased with increasing red sorrel pollen concentration, with the relationship adequately explained by a 3-parameter exponential rise to a maximum equation. Red sorrel pollen increased B. cinerea disease incidence on immature, but not mature, blueberry flowers in the greenhouse. Pronamide applications reduced red sorrel density in three out of four site years, but did not reduce red sorrel biomass or increase harvestable blueberry yield. Red sorrel pollen may increase B. cinerea disease incidence in lowbush blueberry, and growers should expect variable results when using pronamide for red sorrel management.