Fire blight is a major threat to apple production in USA. It can destroy thousands of high density trees per farm in epidemic conditions. Our priority is to address this threat by development of pest risk assessment through quantifying survival of fire blight bacterium Erwinia amylovora in wood cankers as main sources for infection. We will determine its survival in relation to apple and pear cultivar susceptibility, tree drought stress, and winter cold. Current fire blight prediction models assume successful fire blight survival in cankers every year. This can lead models to report false infection periods in bloom when bacteria in cankers might have died and risk of infection is low or nonexistent. Using digital (d)PCR, a new diagnostic and quantification method, to determine survival rate of the bacteria, we will quantify carryover risk by cankers from one to the next season. Long-term benefit to growers is new knowledge which will provide new fire blight IPM tools, enable creation of more accurate models for disease prediction, enable development of new tools for pre- and post-infection management, and modify recommendations for sprays in bloom. By working with growers, we predict project data will allow reducing production costs by eliminating unnecessary sprays in certain years and summer-long labor use for fire blight removal by pruning on certain tolerant or resistant cultivars. We will intensively disseminate project results to growers at various meetings, in journals, and through on farm visits, blogs and field days.
