SEASONAL INFECTION OF NONWOUNDED PEACH BARK BY BOTRYOSPHAERIA-DOTHIDEA

Conidial suspensions of Botryosphearia dothidea were applied at variou s concentrations to the nonwounded stems of 1-yr-old peach trees maint ained under wet conditions for periods that varied. Bark necrosis incr eased with spore concentration and the duration of bark wetness. Simil ar inoculations made at 3-wk intervals during 1987 and 1989 revealed t hat infection occurred from March through August with a peak period fr om about late April through July or early August. A significant correl ation was found between disease severity and temperature for a 3- to 6 -wk period after inoculation. In two commercial orchards, stems of new ly planted peach trees were periodically exposed to natural inoculum o f B. dothidea. At 1-mo intervals from April 1988 through December 1989 , water-excluding covers were removed from preselected trees for a 1-m o period. Infections occurred more frequently in the second season of growth (particularly during June and July) than in the season after pl anting. Disease severity was positively correlated with the availabili ty of water-borne spores of B. dothidea. Nonwounded bark of 1- to 2-yr -old peach trees is susceptible to invasion by B. dothidea during most of, if not the entire, growing season. The amount of infection during this period depends on inoculum availability and environmental condit ions.