Cane & Fruit Rot Botrytis
(Botrytis cinerea)
Diseases
Symptoms
Botrytis fruit rot is found on overripe and bruised fruit and is more common in the ‘Evergreen’ cultivar. It is more prevalent in fields where overhead irrigation is used, or where fruit is allowed to become ripe enough to be harvested mechanically. Most infections occur on the flower during bloom; however, symptoms usually go unnoticed until harvest. Infected flowers turn brown and shrivel when dry conditions exist. Under moist conditions, grey tufts of fungus can be seen on blighted blossoms. Fruit infections initially appear as soft, light brown, rapidly enlarging areas on the fruit. Berries become shriveled and covered with grey tufts when the fruit matures. One to several berries in a cluster may show blasting (browning and dying) that may extend down the pedicle. Occasionally, fruit may appear healthy at harvest but become severely rotten within a short time when conditions are favorable for disease development.
Cane infections first appear as brown lesions on new green canes, often encompassing more than one node. The lesion becomes tan as the infected cane matures. Cane lesions exhibit typical concentric “watermark” patterns from fall through late winter. Sclerotia may be visible on canes as shiny, black, blister like structures. Cane botrytis can be very destructive during the wet season and in plantings where the growth is lush and dense.
Life History
The pathogen, Botrytis cinerea, is the fungus that causes blossom blight, fruit rot and cane botrytis. It overwinters as minute, black, fungal bodies (sclerotia) on bleached appearing canes or as mycelium in dead leaves and mummified berries. In early spring, under humid conditions, sclerotia produce conidia (spores), which are dispersed by wind, rain, and overhead irrigation. Disease develops under moist conditions and when temperatures are between 70º and 80º F. Disease will develop under cooler temperatures, but requires a longer wet period. The spores can infect mature or senescent leaves, resulting in primocane infections through petioles. Infected new canes wilt, die and may be covered with grey mold. During bloom, the fungus colonizes healthy or senescing flower parts and turns blossoms brown. The fungus is then able to establish within the receptacle of the young fruit as a latent infection. Infections generally remain dormant until fruit is nearly ripe or after harvest. Infections can recur throughout the season by sporulation of the fungus on unpicked, leaky, overripe fruit left on the vine.
Monitoring
Watch for infections in the spring, which appear as bleached-out, whitish areas on the cane. These overwintering infections are a primary source of spores for flower infections, which may develop into fruit rot symptoms. Monitor leaves and canes in mid to late summer for new infections, which first appear as brown lesions on new green canes. Monitoring is particularly important when wet conditions occur during bloom and harvest and/or in fields containing heavy foliage. During harvest, check fruit for over ripeness, which may show beginning stages of infection. Scout 3-5 sites per field, depending on field size, and evaluate 10-20 hills spaced 3-5 hills apart at each site. Record severity on a scale of 0-3 for each site scouted.
Thresholds and Management
No threshold or tolerance level available.
Examine canes in the spring to determine the level of overwintering fungus and plan a control program accordingly. If chemical treatment is required, fungicides can be applied as a protectant spray at 7-14 day intervals from early bloom up to harvest to combat the onset of fruit rot.
Promote air circulation and proper drying of plant tissue through pruning and trellising to keep plant canopy open. Maintain a narrow row by burning back early primocanes and controlling weeds. Minimize or adjust irrigation to prevent plants from being wet for extended periods of time. Avoid excessive use of nitrogen fertilizer in the spring because the Botrytis fungus will readily infect succulent green growth. Pick fruit before reaching full maturity to prevent postharvest fruit rot. Pick fruit often and early in the day when temperatures are cool. Move harvested fruit to cold storage as soon as possible.
Resources
Ohio State University Extension, Botrytis Fruit Rot “Gray Mold” of Strawberry, Raspberry, and Blackberry
http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3017_08.pdfOregon State University Extension, Plant Disease Control: Blackberry Fruit Rot
http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=164University of California, IPM Online: Caneberries, Botrytis Fruit Rot
http://www.ipm.ucdavis.edu/PMG/r71100211.html
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