MANAGING ANTHRACNOSE BLIGHT AND BOTRYOSPHAERIA AND PHOMOPSIS CANKERS OF WALNUT PART 2: LIFE CYCLE OF WALNUT ANTHRACNOSE AND DISEASE MANAGEMENT

In 2012, we sampled surveyed several orchards for anthracnose and we found that the disease is not only a problem of black walnut but also several cultivars of the English walnut can be infected. These include but are not limited to Ashley, Chandler, Hartley, Serr, Payne, Livermore, and Mountner. We also have diagnosed the disease on black walnuts and to a limited extent on paradox foliage. All, leaves, leaf petioles, shoots, fruit and peduncles can be infected by the pathogen, which easily produces fruiting structures (acervulli) full of conidia. The presence of these dark brown to black fruiting structures in the leaf, shoot, and fruit lesions is a distinguishing feature from the lesions caused by the walnut blight bacterium. The fungus also produces a second type of fruiting structures (perithecia) on leaves on the ground over the winter. These structures are the perfect (sexual) stage of the fungus Gnomonia leptostyla that has been reported in other states and countries where the walnut anthracnose occurs. Presumably the ascospores produced in the perithecia serve as the initial infection of emerging leaves in the spring. That is the reason why the first fungicide spray should be applied in the spring (early to mid April) as leaves emerge (about ½ of their final size) to prevent infections. Several fungicides that are listed in this report and registered in walnut show good to excellent efficacy against the anthracnose disease of walnut.