Field resistance to yellow aphids in Pecan

Putative resistance to the blackmargined aphid (Monellia caryella Fitch) in 'Pawnee' pecan [Carya illinoinensis (Wangenh.) K. Koch] was first noted in greenhouse tests by rating cultivars for relative amounts of honeydew on adaxial leaf surfaces. This resistance was confirmed in two field tests monitored from mid-June to mid-October. 'Pawnee' supported significantly lower aphid populations during every rating period when relatively large numbers of these insects were present. 'Navaho' also showed resistance, with 'Desirable') having intermediate resistance and 'Stuart' being very susceptible. Insect populations were also monitored on the four quadrants of each tree, with quadrant effect being significant in only one test. This test had the highest populations on the western quadrant and lowest populations on the eastern quadrant. In determining individual clone resistance, it is recommended that the general orchard aphid infestation level be determined so that only two or three well-timed clonal ratings are needed. We also recommend that all sides of the tree be monitored.