EPIDEMIOLOGY AND CONTROL OF DEAD-ARM OF GRAPES

Abstract

Inoculation of pruning wounds on grape with spore suspensions of Phomopsis viticola Sacc. at different times of the year rarely resulted in more than 25% infection. In many cases, incipient lesions and even pycnidia developed shortly after inoculation, but infection did not progress further. Highest infection rates were obtained in the summer months with freshly cut wounds. Wounds that had dried out for several weeks were difficult to infect.Primary infections occurred on young, uninjured, succulent, green shoots. Their incidence and severity were dependent on the inoculum potential resulting from the previous year's infection and on the amount of precipitation in the latter half of May. Discrete primary lesions were nearly always superficial but coalescent ones were more deeply seated and often became perennial. Functional pycnidia were frequently observed in the mature layer of bark on the basal nodes and internodes of 1-year-old canes, the underlying tissues of which were not diseased. Green shoots are considered to be more important infection sites than the pruning wounds made during the dormant season in normal commercial practice.Control measures should include propagation and planting of clean nursery stock as well as a pre-bloom spray program. If the disease becomes established in arms or trunk it is more effective and economical to remove and renew the vine at ground level than to try to save part of an affected vine at a greater risk of reinfection.