EFFECTS OF A COVER CROP ON SPLASH DISPERSAL OF COLLETOTRICHUM-ACUTATUM CONIDIA

A rain simulator, with generated rains of 11 and 30 mm/h, was used to determine the effect of a cover crop or intercrop on the splash disper sal of Colletotrichum acutatum conidia. Dispersal through sudangrass, which can be used as a 'living mulch', was tested at two planting dens ities (140 or 280 kg/ha) and two heights (5 and 20 cm) and compared wi th a control consisting of a bare soil. Dispersal of C. acutatum conid ia was assessed by counting colonies formed from spore-bearing splash droplets deposited in sheltered petri plates containing a selective me dium. Both a cover crop and rain intensity significantly affected spla sh dispersal as measured by the interpolated total number of colonies (denoted by Sigma) from 0 to 72 cm from the inoculum source and in a t ime span of 61 min of generated rain (P < 0.001). However, there was n o significant interaction of cover crop and intensity (P > 0.90). Disp ersal with a 30-mm/h rain was higher than dispersal with a 11-mm/h rai n, and presence of a cover crop significantly reduced dispersal compar ed with bare soil (P < 0.001). Of the treatments with sudangrass, cove r crop planting density did not affect dispersal overall, but there wa s greater spore dispersal with the taller sudangrass at the higher pla nting density, due in part to the higher rate of water splashing with the tall grass compared with the short grass. Spore deposition in the petri plates could be functionally related to distance and time using a diffusion-type model, and parameter estimates could be used to expla in the effects of cover crop on C. Although the relationship between c over crop properties and splash dispersal is complex, results show the potential beneficial effects of the cover crop on disease management.