Meetings of the Royal Botanical Society of The Netherlands

The ‘Rhizoctonia disease’ in tulip and iris, caused by Rhizoctonia solani, occurs in patches. In order to develop alternative means of control, the dynamics of these patches in space and time was studied in a field trial and a bioassay. Tulip fields on three soil types, i.e. a sandy soil (Lisse), a loamy clay (Creil) and a clay soil (Zwaagdijk), were artificially infested with a coldpreferring isolate of R. solani (Doomik, A.W. 1981. Neth. J. PI. Path. 87: 139-147), belonging to the AG-2 complex. The increase of patches was measured by estimating sprout affection from April 1992 to June 1992 every 2 weeks. Disease progress of patches was less on the clay soil compared to disease progress on the sandy and loamy clay soil. At harvest (June) the number of bulbs affected by R. solani inside and outside patches was counted. Disease incidence (measured as % affected bulbs per row) depended on soil type, but also differed within fields.