CAUSAL AGENTS OF SILVER TOP AND OTHER TYPES OF DAMAGE TO GRASS SEED CROPS

Abstract

AbstractStudies during 1962–64 showed that the mites Siteroptes graminum (Reut.) and Aceria tulipae Keifer, thrips, and the fungus, Fusarium poae (Pk.) Wr., were not causal agents of silver top in the Peace River region, and indicated leafhoppers were probably not involved. The fact that silver top is controlled with insecticides, but not with miticides, constituted strong evidence for insects as causal agents. In 1963, extensive examination of grasses with silver top revealed minute, inconspicuous punctures, 0.01 to 0.04 mm in diameter through leaf sheaths which were typical of chose made by insects with piercing and sucking mouthparts such as plant bugs. In 1964, attempts to produce silver top by infesting grass plants with plant bugs, leafhoppers, and spittlebugs were unsuccessful for reasons in-explainable. Non-appearance of silver top in either infested or uninfested plants, however, indicated the causal agent was not present in the plants or attached soil when collecred from fields in mid-May. Further studies in 1965 showed that grasses affected by silver top were infested with the plant bugs Stenodema trispinosum Reut., S. vicinum (Prov.), Litomiris debilis Uhl., Capsus simulans Stal., and Trigonotylus ruficornis (Geof.). Experimental infestation of plants with these bugs showed that they fed on stems by puncturing through leaf sheaths and so damaging stem tissue as to cause silver top. In 1966, examination of grasses with silver top from southern Alberta, Saskatchewan, and Oregon revealed punctures in leaf sheaths opposite areas of stem injury, indicating that plant bugs probably cause silver top in these regions.