Pre- and Post-Infection Activity of Pyraclostrobin for Control of Anthracnose Fruit Rot of Strawberry Caused by Colletotrichum acutatum

Strawberry anthracnose, caused by Colletotrichum acutatum J. H. Simmonds, is one of the most serious diseases in commercial strawberry production. Even in well-managed fields, losses due to the fruit-rotting phase can exceed 50% when conditions favor disease development (10). Historically, the disease has been thought of as a “southern” disease (16), occurring primarily in the warmer production regions of North America. Over the last 20 years, however, losses due to anthracnose fruit rot have increased in fields across North America, including California, New York, Massachusetts, Pennsylvania, Ohio, and Ontario, Canada. Although several species of Colletotrichum cause anthracnose on strawberry (6), C. acutatum is the most prevalent fruit-rotting pathogen. C. acutatum was first reported on strawberry in the United States in 1986 (25) and appears to be well established in the temperate and subtropical strawberry-growing regions in the United States. The fungus can attack virtually all parts of the plant, including the crown, leaves, petioles, and immature and mature berries (19), and also causes a root necrosis leading to stunting and chlorosis of the plant (5). The disease probably is introduced into plantings on contaminated nursery plants (2,5,10). Once established, C. acutatum can overwinter under a wide variety of conditions in mummified fruit (31) or in soil with or without strawberry plant debris (2–4,7). However, in warmer climates, it does not oversummer in association with crown tissue (29). C. acutatum can survive and reproduce on the surface of leaves without causing symptoms through a process called microcyclic conidiation (15,32). This means of survival may have serious implications for disease management because infested plants can escape inspection prior to planting and the pathogen may build up to high levels in the field undetected. Conidia of C. acutatum are dispersed locally by splashing water, and droplets may be disseminated further with the aid of wind (33). A number of factors influence the efficiency of dissemination and the intensity of disease that results. Plastic ground cover facilitates the spread of disease manyfold relative to bare soil or straw mulch (20,34). Yang et al. (34) showed that for plants grown on plastic mulch, as little as 15 min of rainfall was sufficient to achieve 100% infection of fruit lying within a 60-cm radius of an infected source fruit. However, plastic ground cover is essential for weed management in annual production systems and its elimination is not a realistic option currently. In annual production systems, additional dispersal occurs when pickers spread spores from infected to healthy fruit when brushing their hands through the canopy searching for ripe fruit (16). Wilson et al. (30) found that optimal temperatures for infection on immature and mature fruit were between 25 and 30oC on cv. Midway, with greater than 80% incidence occurring after 13 h of leaf wetness. They found that no infection occurred on immature or mature fruit below 4oC, nor was any infection observed on immature fruit above 35oC. Predictive curves for estimating the incidence of fruit infection as a function of the duration of berry wetness and temperature were developed and these adequately predicted infection in experimental field plots, with about 75% of the variation in disease incidence explained by these equations (20). Most commercial management programs rely on calendar-based protective applications of fungicides for disease management. Under ideal management, fungicides would be applied only when necessary and, preferably, only in response to an infection event. However, this recommendation is difficult to follow, mainly because wetting events during fruit set and ABSTRACT Turechek, W. W., Peres, N. A., and Werner, N. A. 2006. Preand post-infection activity of pyraclostrobin for control of anthracnose fruit rot of strawberry caused by Colletotrichum acutatum. Plant Dis. 90:862-868.