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Abstract
Factors affecting natural infestation of flowering dogwoods (Cornus florida L.) by the dogwood borer, Synanthedon scitula Harris (Lepidoptera: Sesiidae), were studied in an urban cemetery in Louisville, Kentucky. Two tree characteristics, severity of trunk wounding and exposure to sun, were most important in determining the probability of borer attack. Degree of crown dieback or color of bloom did not significantly affect the rate of infestation. There was no correlation between tree diameter and probability of attack, but height of attack sites increased linearly with increasing tree size.
Abstract
Resistance to the twospotted spider mite (Tetranychus urticae Koch) of 18 cultivars of ivy geranium [Pelargonium peltatum (L.) L’Her ex Ait.] was evaluated under greenhouse conditions by mass screening, by measuring fecundity on isolated leaves, and by paired leaf tests for selected cultivars. ‘Sybil Holmes’, ‘Yale’, and ‘Cornell’ were among the most susceptible, whereas ‘Double Lilac White’, ‘Sunset’, and ‘Salmon Queen’ were relatively mite-free. ‘Madeline Crozy’ and ‘Cornell’ were preferred for oviposition over the resistant ‘Double Lilac White’. Mite resistance was not related to density of simple or glandular leaf trichomes, but there was an apparent relationship between mite susceptibility and severity of oedema.
Abstract
Three genetically diverse Kentucky bluegrasses (Poa pratensis L. cvs. Kenblue, Vantage, and Adelphi) and 6 other turfgrasses were evaluated for susceptibility to the greenbug, Schizaphis graminum Rondani. Nine common lawn weed species were also tested as potential alternative hosts. Heavy greenbug populations and feeding damage occurred on all 3 bluegrasses and on tall fescue (Festuca arundinacea Schreb. cv. Kentucky 31) and chewings fescue (Festuca rubra var. cummutata Guad. cv. Jamestown). Creeping bentgrass (Agrostis palustris Huds. cv. Penncross), bermudagrass (Cynodon dactylon L. cv. Midiron), perennial ryegrass (Lolium perenne L. cv. Derby), and zoysia grass (Zoysia japonica Steud. cv. Meyer) were not suitable hosts. No greenbugs survived on the 9 weed species tested.