Spot Blotch (wheat) - Rotations and Crop Management

Rotations and Crop Management

Clearing or ploughing in the stubble, grass weeds and volunteer cereals reduce inoculum as does crop rotation (Diehl et al., 1982). Reis et al. (1998) indicate that eradicant fungicide treatment of the seed and crop rotation with non-host crops can control spot blotch. In the rice-wheat system of South Asia, little work has been done on the epidemiology of HLB and how management of the rotation crops affects spot blotch and tan spot, except as noted earlier. More quantitative information is required on the role of alternate rotations, soil and plant nutrition, inoculum sources and climate. In the rice-wheat system, there is a need for timely planting of wheat, better stand establishment and root development, increased soil organic matter, sufficient levels of macro- and micronutrients, and water and weed management (Hobbs et al., 1996; Hobbs and Giri, 1997). Crop rotation and organic manures will play a major role in HLB. This should favour beneficial soil organisms as well as better plant nutrition. In the rice-wheat system, it will be necessary to break the rotation with other crops to make it more sustainable, and this should help reduce disease problems in general. The use of oilseed rape in South Asia is common in mixture with wheat or in rotation. Since rape is known to have some fungitoxic effects upon decay, its effects on HLB would need research (Dubin and Duveiller, 2000). In the HLB complex, rotations would need to be sufficiently long to reduce the amount of soil inoculum. Cook and Veseth (1991) note that the kind of rotation crop may not be so important to root health as the length of time out of wheat. The rotation crops and length of rotation would have to be studied in relation to HLB.

Apparently, sound management recommendations may antagonize specific diseases as in the case of tan spot. Tan spot has been controlled largely by cultural practices, such as rotation with non-host crops and removal or burial of stubble (Rees and Platz, 1992). Bockus and Claassen (1992) observed that rotation to sorghum was as effective as ploughing for control of tan spot, and under certain conditions, crop rotations as short as one year controlled tan spot. In South Asia, recent work by Hobbs and Giri (1997) indicates that minimum tillage may be the best way to reduce turnaround time from rice to wheat and thus permit the planting of wheat more timely. Since this probably increases inoculum of tan spot, it highlights the need for integration of disciplines to determine how best to achieve attainable yields.