Weed control continues to be a major concern of farmers considering adoption of no-till technology. Many believe that satisfactory weed control in no-till is either too expensive or is unattainable. Fear of crop failure due to poor control of weeds is probably justified for certain weed problems in some crops; In many other situations, however, co -effective control measures for no--till are currently available. This paper will examine the economics of weed control in soybeans, wheat, and sunflowers using no-till versus conventional till methods.

The economic analyses developed below will focus on cost estimates of certain variable inputs such as herbicides, herbicide adjuvants, spraying, and tillage which represent the primary cost differential between conventional and no-till systems. Other input costs associated with fertilization, land rental, seed, labor, insecticide or fungicide spraying, etc. generally are similar for both tillage systems and will not be considered here. It is recognized that many variables not accounted for in the following analyses can radically alter the outcome of the comparison. Growers are encouraged to "factor in" costs of additional known or anticipated variables to develop economic analyses that custom fit particular situations.

Considerable research over the last 20 years has compared crop yields under conventional and no-till practices. In general, the picture emerging from these studies is that many of our important field crops respond well under no-till conditions and yield comparably with conventional till. Corn, soybeans, wheat, barley, sunflowers, and sorghum are among crop species that have fairly consistently yielded well in no-till studies where production practices were such that weeds, diseases, and insects were controlled. And while it is recognized that successful no-till cropping may be more challenging on heavy soils, several studies have indicated that no-till and conventional till crop yields also can be comparable even on these heavy soils, assuming pests are controlled. The ensuing discussion will present the economics of different weed control approaches in a soybean-wheat rotation experiment conducted at Fargo, and hypothetical cost analyses for wheat and sunflowers grown under no-till or conventional till conditions.

In 1988, a long-term soybean-wheat rotation was established at Fargo on a silty clay with 4% organic matter and pH 7.8. On one area, soybeans were planted in 1988 and wheat in 1989. On an adjacent area, wheat was seeded in 1988 with soybeans in 1989. Soybeans in 30-inch rows were planted using a Hiniker no-till planter. Wheat and 7-inch-row soybeans were seeded with a Haybuster drill. The treatments consisted of five herbicide approaches in each of three soybean systems: minimum till (fall chisel plowing with spring field cultivation for seedbed preparation) with soybeans in 30-inch rows, no-till with 30-inch-rowsoybeans, and no-till with soybeans in 7-inch rows. Following application of planned herbicide treatments in the soybean crop; other herbicides or cultivation were used as needed, with the aim of maximizing profit. As the soybean area of 1988 was rotated to wheat in 1989, tillage practices and the identity of individual plots was maintained so that herbicides could be applied to specific plots as needed. Thus, management decisions were exercised and Input costs were recorded so as to develop an economic outcome for each treatment.

Table 1 shows the five-planned herbicide treatments that were applied to each of the three tillage systems in soybeans. For most treatments, a follow-up postemergence treatment was required. In no-till systems, a burndown herbicide also was needed as shown. Planned herbicide treatments were selected as the most likely candidates available f r achieving cost-effective weed control in each tillage system and are therefore different between tilled and no-till situations. All soil-applied herbicides in tilled plots consisted of preplant incorporated Treflan in combination With a broadleaf herbicide. By contrast, the planned soil-applied treatments in no-till consisted of a broadleaf herbicide applied either preemergence or 4 weeks prior to planting, followed by postemergence Poast as needed for foxtail control. Both tilled and no-till systems also received a "total post" treatment of Poast followed by Basagran plus Blazer.

A follow-up treatment of Poast was required in tilled plots even though Treflan had been applied (Table 1).

See Table 4 for information on spray adjuvant used.

EPP = early preplant (applied 4 weeks prior to planting); PPI = preplant incorporated;

Pre = preemergence; Po = postemergence;

HWC = hand weeded check.

Inadequate control of foxtail by Treflan probably resulted from especially dry soil conditions. A follow-up application of Blazer was used for control of redroot, pigweed and common lambsquarters, while follow-up Basagran plus Blazer was used where pigweed, lambsquarters, and kochia were not adequately controlled by the soil-applied treatment. Sencor applied in no-till provided the least control of these broadleaf weeds and required the greatest inputs of follow-up broadleaf herbicides.

Among no-till treatments, early preplant Bladex or Pursuit provided essentially complete at-planting broadleaf control, allowing a low rate of Roundup as a burndown for yellow foxtail control (Table1). Other no-till treatments required a Gramoxone burndown due to infestations of kochia, common lambsquarters, and foxtail.

Yields of no-till soybeans grown in 30-inch rows (Ave. = 11.2 BU/A) were higher than yields of tilled soybeans grown at the same row spacing (Ave. = 9.3Bu/A) (Table 2).