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Published online by Cambridge University Press: 12 June 2017
Greenhouse studies were conducted to determine the following: if treating henbit or downy brome with glyphosate increased populations of Fusarium solani f. sp. pisi and Pythium ultimum in soil and rhizosphere soil; if treating henbit or downy brome with glyphosate increased root colonization and infection by F. solani f. sp. pisi or P. ultimum; and, if henbit and downy brome are hosts of F. sohni f. sp. pisi or P. ultimum. Pythium ultimum populations increased only in soil containing glyphosate-treated henbit. Fusarium solani f. sp. pisi and P. ultimum populations increased in rhizosphere soil from glyphosate-treated henbit, while only P. ultimum populations increased in rhizosphere soil from glyphosate-treated downy brome. These results suggest that peas planted in soil where either downy brome or henbit had been treated with glyphosate could be exposed to higher populations of F. solani f. sp. pisi and P. ultimum. Root colonization and infection, plant height, and root weight data indicated that henbit and downy brome are alternate hosts of P. ultimum. F. sohni f. sp. pisi colonized, but did not readily infect roots of downy brome and henbit.