Weed Control for Conservation Tillage

Introduction Conservation tillage systems using sweep plows or field cultivators leave a high percentage of crop residues on the soil surface, which protects the soil from wind and water erosion (Johnson, 1950; Jones and Johnson, 1982; Allen and Fenster, 1986; Johnson et al., 1974). These systems have been successful in semiarid areas because meager rainfall after plowing does not allow weeds to reestablish. In wetter areas, acceptable weed control has been obtained only where weeds were uprooted or inverted with disks or plows (Davidson and Santelmann, 1973). In conservation tillage systems for semiarid areas where soil water storage during fallow periods is essen­ tial for profitable crop production, weeds must be plowed before they are 150 mm tall or storage of soil water will be depleted compared to weed-free areas. Under the same conditions, weeds had to be sprayed with herbicides before they exceeded 50 mm (Lavake and Wiese, 1979). No-tillage, where weeds and volunteer crops are controlled with herbicides during fallow periods, is a relatively recent innovation for maintaining crop residues on the soil surface. This technique has been suc­ cessful when suitable herbicides are available that con­ trol weeds between and in crops without injuring subse­ quent crops in the rotation (Wiese and Staniforth, 1973). In the future, as new herbicides are developed and marketed, no-tillage will become feasible in an increas­ ing number of cropping sequences. However, from a practical standpoint, conservation or no-tillage systems that work are not adopted unless there is an economic advantage over conventional tillage. Texas is a large and diverse state, and, consequently, cropping sequences, weed control, and conservation tillage systemsvary. Figure 1shows locations in the state where research is being conducted on conservation tillage and cropping systems. Research information is available from the Rio Grande Valley, Coastal Bend, Northern Gulf Coast, Central Texas Peanut Production area, Southern and Northern Blacklands, Rolling Plains, and the Southern and Northern High Plains. Because of limited time, only weed control research in conserva­ tion tillage systems from the Coastal Bend, Northern Gulf Coast, Central Texas, Blacklands, Rolling Plains, and High Plains will be discussed.