Pre-plant Dipping of Strawberry Transplants for Control of Colletotrichum acutatum

Abstract

Strawberry anthracnose caused by Colletotrichum acutatum may kill strawberry plants or reduce plant vigor and marketable yield, resulting in multimillion dollar losses to strawberry industry. The fungus is often carried with transplants from nurseries to production fields undetected. The studies in one summer and two winter seasons near Oxnard, Calif., evaluated 30-second pre-plant dipping in ten fungicide solutions or water washing of transplants inoculated with C. acutatum as a means of reducing infection and improving fruit yield. In summer-planted `Baeza,' the pathogen caused severe die-back and reduced marketable fruit yield 89% in inoculated, untreated controls compared to non-inoculated plants while plants dipped in Switch (cyprodynil + fludioxynil) at 0.38 g/L had 33% yield reduction. Other fungicides provided even less protection, resulting in 53% to 89% yield losses. During cooler winter seasons the pathogen remained latent and lesions appeared on `Camarosa' when the day-night air temperatures reached 16 °C or more, 7–14 days after rain. None of the treatments reduced fruit lesion development, however, among plants dipped in strobilurin fungicides only 3% had C. acutatum symptoms (including early die-back) as opposed to 26% in inoculated, untreated controls. Plants dipped in Switch, Quadris (azoxystrobin), or Pristine (pyraclostrobin + boscalid) yielded similar to non-inoculated, untreated controls in 2003 and 10% to 12% more in 2005. These studies showed that strobilurin fungicides did not prevent fruit infection (indicating need for foliar in-season control) but improved marketable yield compared to the inoculated, untreated plants. Temperatures over 16 °C and precipitation may significantly increase disease development.