Leopold Center
U.S. Department of Agriculture



At the Iowa State University Horticulture Farm near Ames, the research team evaluated survival, yield, and fruit quality of 13 apple cultivars that are genetically highly resistant to scab. The cultivars were selected from the Purdue-Rutgers-Illinois breeding program and the Cornell University program.

The trial orchard, planted in 1993 on M7 rootstock, included 13 scab-resistant cultivars and one scab-susceptible cultivar (Empire). Eight scab-resistant cultivars were commercially available but not widely grown in Iowa, while five scab-resistant cultivars have not yet been released commercially. Each cultivar had 9 single-tree replications. Conventional disease and pest control tactics were used in the trial orchard, since the objective was to evaluate horticultural characteristics. The trees were trickle-irrigated as needed.

Table 1 summarizes survival and growth of the cultivars after 7 years (1993-2000). Tree mortality was low; only 4 trees died in the planting year and only one tree thereafter. Williams Pride, Dayton, and Co-op 29 were among the most vigorous cultivars in terms of tree growth, while Gold Rush and Coop 28 were among the least vigorously growing cultivars.

The highest-yielding cultivars over four harvest seasons (1997-2000) were Williams Pride, Liberty, Co-op 31, Gold Rush, and Redfree (Table 2). On the other hand, Co-op 28, Empire, CLR13T40, and Co-op 27 had the lowest yields. Freedom,Williams Pride, Enterprise, and Co-op 29 produced relatively large-size fruit, while Co-op 28 and Liberty produced the smallest fruit. Pre-harvest fruit drop averaged more than 20% for CLR13T40, Jonafree, Williams Pride, and Enterprise.

Email: mgleason@iastate.edu Telephone: (515) 294 0579 Address: 312 Bessey Hall, Iowa State University, Ames IA 50011