Can. Ent. 99: 660-670 (1967) Studies during 1962-64 showed that the mites Siteroptes graminurn (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 puncmres, 0.01 to 0.04 mm in diameter through leaf sheaths which were typical of those made by insects with piercing and sucking mouthparts sncli as plant bugs. In 1964, attempts to produce silver top by infesting grass plants with planr hugs, leafhoppers, and spittlebugs were unsuccessful for reasons inexplaitmhle. Yon-appearance of silver top in either infested or uninfested plants, ho\vct.er. indicated the causal agent was not present in the plants or attached soil when collected from fields in mid-Clay. Further studies in 1965 showed that grasses affected by silver top were infested with the plant bugs Stenodema trispinosunz Reut., S. vicinzm (Prov.), Litomiris debilis Uhl., Capus simlans Stal., and Trigonotylus ruficom's (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 shearhs opposite areas of stem injury, indicating chat plant bugs probably cause silver top in these regions.

not available