Comparison of Plastic Mulch and Nitrogen Form on the Incidence of Verticillium Wilt of Eggplant

Eggplants (cv. Midnite) were grown during 1996 to 1998 in soils naturally infested with Verti-cillium dahliae. Experimental plots were either mulched with black plastic or grown on bare ground and fertilized with either (NH 4 ) 2 SO 4 or Ca(NO 3 ) 2 at 224 kg of N per hectare each season. Compared to bare ground, mulch resulted in a 42 and 68% increase in 1996 and 1997, respectively. Compared to Ca(NO 3 ) 2 , (NH 4 ) 2 SO 4 fertilization increased yield by 22 and 18% in 1996 and 1997, respectively. In both years, there were no significant interactions between the mulch and fertilizer treatments on yield or on integrated estimates of the plant canopy growth curve or disease severity. However, the treatment effects were additive. When compared to bare ground, mulching increased the plant canopy 3 weeks after planting and reduced the percentage of symptomatic foliage 8 weeks after planting. Compared to Ca(NO 3 ) 2 , fertilization with (NH 4 ) 2 SO 4 increased the plant canopy after 6 weeks, but did not affect the percentage of symptomatic foliage. Mulching or (NH 4 ) 2 SO 4 fertilization increased the number of flowers compared to no mulching or Ca(NO 3 ) 2 fertilization, respectively. The rate of nitrogen fertilizer at planting or as a side-dress application did not affect growth or disease, but plants treated with (NH 4 ) 2 SO 4 were larger and had less symptoms than Ca(NO 3 ) 2 -treated plants. The use of black plastic mulch with (NH 4 ) 2 SO 4 fertilization complements one another and may reduce damage from Verticillium wilt on eggplant.