The objective of this project is to evaluate the benefits of precision guidance systems as a means of using tillage to kill weeds, and to confine herbicide applications to narrow bands. In cotton, a precision guided close cultivation with a directed spray of MSMA significantly reduced a purple nutsedge stand early on. However this reduction was not significant by the end of the season. For controlling woolly morningglory, the use of a precision guided cultivator equipped with in -row weeding devices resulted in much lower numbers of morningglory weeds, although the differences were not significant at the 95% confidence level. The guidance system kept the implement precisely aligned to the drill rows at a higher speed than was possible with the cooperator's non - precision cultivator. This higher productivity more than offsets the cost of the guidance system and the in-row weeding devices.

Late emerging summer annual grassy weeds such as Mexican sprangletop can stain cotton lint resulting in price discounts for color at harvest. Cyanizine (Bladex) is commonly applied layby for grassy weed, morningglory, and pigweed control, however use of this herbicide will be phased out by 2002 with rate reductions beginning in 1998. Clethodim (Select) herbicide was evaluated as an alternative to cyanizine for layby grassy weed control, plus the antagonistic effect of tank mixing Select with Staple herbicide was examined in Parker Valley, AZ during the 1997 cotton growing season.

A study was conducted at the Maricopa Agricultural Center to compare various cotton weed control programs that combined the use of the over-the-top herbicides Buctril, Roundup Ultra and Staple with reduced or eliminated preemergence herbicide applications in dry planted cotton. Roundup Utra provide superior large seedling Palmer amaranth control compared to Buctril or Staple. The yield and end of the season weed control data showed that BXNBuctril and Staple weed control strategies require the application of a dinitroaniline herbicide prior to planting. The data also suggest that a band application of Prowl in combination with timely postemergence Buctril or Staple applications would be just as effective as preplant incorporated application of Prowl. In contrast to the Buctril and Staple herbicide treatments, the end of the season weed control ratings and seed cotton yield were the same for all of the Roundup Ready cotton treatments suggesting that Roundup Ready cotton weed control strategies do not necessarily require a dinitroaniline herbicide (Prowl or Trejlan) application prior to planting.

The distribution of weed species and the herbicides and cultural practices used to control weeds in Arizona cotton fields were surveyed in 1995 and 1996. The most common weeds were purple nutsedge, bermudagrass, annual morningglory, Palmer amarnath, Wright groundcherry, common purselane, yellow nutsedge and Johnsongrass. The average statewide cost for hand weeding in 1995 was reported as $27.87 per acre in addition to other weed control costs. Statewide, most growers used preemergence herbicides before or at planting and used pre- and post-emergence herbicides later in the season. Most of these applications were broadcast applications suggesting that many of the postemergence herbicide applications were layby applications. Preemergence herbicides (usually applied preplant incorporated) such as Treflan, Prowl, and Prometryn were more commonly used than postemergence herbicides. Statewide, few growers banded preemergence herbicides or used electro- hydraulic quick-hitch guidance systems and in-row weeding tools with their cultivators.

The efficacy of Roundupm herbicide for the control of common Arizona weeds in Roundup Ready® cotton was evaluated in field studies conducted at the Maricopa Agricultural Center in 1995. Promising results were obtained with 1 lb a.i./A (1 quart/A) over-the-top band applications of Roundup when cotton had 1 to 2 true leaves followed by a second, "sloppy", post-directed application ofRoundup at 1 lb a.i./A when cotton had 4 to 5 true leaves. Excellent control of small Palmer Amaranth, Wright Groundcherry, and annual morningglory seedlings was obtained with each 1 lb a.i./A Roundup application in the broadleaf weed study. The two sequential 1 lb a.i./A Roundup applications kept plots free of broadleaf weeds until layby. In the nutsedge weed control study, it was found that nutsedge plants treated with a single 1 lb a. i./A application of Roundup were stunted and exhibited leaf chlorosis, but efficacy was marginal with weed control ratings of only 40 to 50 percent. Nutsedge control ratings for an application of norflurazon (i.e., Zorial) alone or combined with Roundup applied at the 1 to 2 true leaf stage of cotton were 63 and 75 percent, respectively. Two sequential applications of Roundup at 1 lb a.i./A, both with or without norflurazon, resulted in about 90 percent nutsedge control. Roundup Ready cotton exhibited good tolerance to two sequential early season 1 lb a.i./A Roundup applications, as made in these studies, with no apparent seed cotton or lint yield reductions.

This article offers practical advice on in-row weeding techniques and tooling setups.

Close cultivation (within 1.5 inches of the cotton drill row) accomplished with an electro-hydraulic machine guidance system and an early season application of the herbicide DSMA were evaluated for purple nutsedge suppression in cotton. There were no significant differences in the cotton plant mapping data collected mid - season except that there was significantly less boll retention on the second fruiting branch in the precision cultivator treatments that may have been caused by root pruning during the second precision cultivation that could have shocked the cotton. There were significant differences in seed cotton yield with the precision cultivator treatments yielding more than the standard cultivator treatments. There was an opposing yield trend with the use of DSMA; DSMA tending to be beneficial with the precision cultivator and detrimental with the standard cultivator. We cannot explain this opposing trend. We regard our results as preliminary until we gain more experience with precision-guided cultivators in dense stands of nutsedge.

This article explains the operation of the two types of quick hitch guidance systems on the market. Techniques for farming with precision guidance are offered.

The effect on cotton stand establishment and seed cotton yield of various rates of norflurazon applied in combination with pendimethalin or both pendimethalin and prometryn was determined in field studies conducted at the Maricopa Agricultural Center in 1994 and 1995 in a sandy loam soil. Cotton stand counts were highest when only pendimethalin was applied or when no herbicide was used. Tank mixing prometryn with pendimethalin did not significantly reduce plant populations. Tank mixing increasing amounts of norflurazon with pendimethalin resulted in decreasing plant populations in both the wet and the dry plant experiments. Tank mixing increasing rates of norflurazon with both pendimethalin and prometryn caused a similar decline in plant populations in both the wet and the dry plant experiments. The symptoms of dying cotton seedlings and the stand count data indicated that notflurazon was the component of the tank mixtures that caused seedling mortality. The effect of the herbicide treatments on seed cotton yields was much less than on stand counts, but the same trends discussed above were evident. However, at the label rate for norflurazon in coarse textured soils, 0.5 lb a. i./A, seed cotton yields were not significantly reduced. The smaller effect of the herbicide treatments on seed cotton yields was due to the bush type nature of DPL 5415 and increased growth of surviving plants when plant populations were reduced. The data indicates that yield losses were not significant unless plant populations were reduced below about 20,000 to 25,000 plants /A.

Monitoring of whitefly resistance in the major cotton producing areas of Arizona confirmed the presence of an over 100 fold resistance to the mixture of Danitol® + Orthenem (fepropathrin + acephate). Strong evidence was found of cross-resistance affecting the other principle pyrethroid insecticides used to control whiteflies (Asana®, Capture® Karate®). Susceptibility to Ovasyn® varied widely in leaf -disk bioassays; lesser variation was observed in whitefly susceptibility to endosulfan. A provisional resistance management strategy (IRM) for Arizona whiteflies was formulated and evaluated in a 200 acre field trial in 1995. A key element of the strategy was diversifying as much as possible the insecticides used against whiteflies. Contrasts of this (rotation) strategy with a more conventional (less diverse) regime showed that rotation slowed but did not prevent resistance from developing. By seasons end both the IRM and conventional plots had very high and comparable levels of resistance to Danitol® + Ortliene®. This large field trial illustrated clearly the seriousness of the whitefly resistance problems faced in Arizona. It showed that whitefly populations cannot be managed effectively solely with the products currently registered for this purpose in Arizona. The large shift to lower susceptibility took place with as few as 3 insecticide treatments. In concert, our field art laboratory results indicated unequivocally that Arizona growers will be forced by resistance to greatly reduce reliance on pyrethroid insecticides in the future. This underscores the urgency for obtaining approval of novel new insecticides for whitefly control and for deploying new products within the framework of a resistance management strategy that limits their use.