Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in various formulations and placements was applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG), huisache [Acacia farnesiana (L.) Willd. # ACAFA], live oak (Quercus virginiana Mill. # QUEVI), Macartney rose (Rosa bracteata J. C. Wendl. # ROSBC), and Texas whitebrush [Aloysia gratissima (Gillies & Hook.) Troncoso # ALYLY]. There was little difference in a species response to the various tebuthiuron formulations. Pellets (20%) at 2 g ai/tree base reduced the canopy 85% and killed 50% of the honey mesquite. At 1 g ai/plant, two briquettes at 0.5 g ai each or pellets (5.14 g, 20%) killed 37 and 80% of the huisache, respectively. Pellets were no more effective at 2 g than at 1 g ai on huisache. Basal treatments of 0.25, 0.5, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 8 to 22, 48 to 62, 62 to 85, and 92% of the live oak, respectively. Pellets at 2 g ai placed at the base reduced the canopy 83% and killed 59% of the Macartney rose. On Texas whitebrush, 0.25, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 68 to 85, 75 to 100, 90, and 100% of the plants, respectively. Tebuthiuron persisted mainly in the upper 30 cm of soil for at least 15 months.

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied alone and in mixtures with propanil [N-(3,4-dichlorophenyl)propanamide] reduced rough grain yield of rice (Oryza sativa L. ‘Lebonnet’ or ‘Bond’) by 7% when applied at the late-booting or heading growth stages, averaged over several rates of application. Earlier applications did not reduce rice yield. The highest rate (0.6 kg ai/ha) of acifluorfen alone and in mixtures with propanil at 3.4 kg ai/ha reduced grain yields more than lower rates (0.1 or 0.3 kg ai/ha). Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} alone and in mixtures with propanil reduced rough grain yields of rice by 18% when applied at the late-booting growth stage, averaged over several rates of applications, but did not affect yields when applied at the early-tillering, jointing, or early-booting growth stages. Whole-grain milling yield and germination of rice seed were not affected by acifluorfen or triclopyr alone or in mixtures with propanil, regardless of rate or growth stage of application.

This research was conducted near North Platte, NE, over an 18-yr period to determine the feasibility of using herbicides to replace tillage as the weed control method in a winter wheat (Triticum aestivum L.)-sorghum [Sorghum bicolor (L.) Moench.]-fallow rotation. Five tillage treatments [two tillage and three reduced or no-till treatments] were used on the same plots during the duration of this experiment on a Holdrege silt loam (Typic Argiustolls). Herbicides effectively replaced tillage for weed control. The no-till plots treated with atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] after wheat harvest had higher sorghum and winter wheat yields, higher crop residue remaining on the soil surface, and lower weed yields than tilled plots. The most difficult weeds to control were volunteer wheat and barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG]. Soil surface pH decreased over time because of increased use of nitrogen. The pH in nontilled plots was significantly lower than in tilled plots due to lack of soil mixing. Exchangeable calcium was the predominant cation leached from the top 5 cm but showed accumulation between the 5- to 12.5-cm depth. Organic matter content showed little change over time.

An experiment involving six winter wheat (Triticum aestivum L.) cultivars, an early-April herbicide application on wheat and on four dates after wheat harvest, and the growth of a subsequently planted corn (Zea mays L.) crop was conducted at North Platte, NE. ‘Centurk 78’ suppressed barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] more than ‘Bennett’ and ‘Eagle’ in the growing wheat and after wheat harvest in July, but there were no differences in weed yield among cultivars in corn planted 11 months later. Herbicides applied to the tillering wheat in early April improved weed control in wheat and the subsequent corn crop. Also, herbicides were applied 5, 25, 45, and 300 days after wheat harvest. Weed growth increased and soil water decreased as spraying dates were delayed. Herbicides applied 5 days after harvest did not maintain adequate weed control in the corn planted 11 months after wheat harvest and low corn yield resulted. Plots receiving herbicides 300 days after wheat harvest had the least soil water in the fall after wheat harvest but the best weed control in corn and highest corn yields because of better weed control in corn.

Broadcast applications of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] pellets and foliar sprays were tested at four rates for hardwood control and safety to loblolly pine (Pinus taeda L.) at each of eight study locations differing in soil characteristics. Reduction in the number of hardwoods in the stand (hardwood density reduction) was greater with the pellet on soils with more than 60% sand, while the liquid formulation was most efficacious for finely textured soils. Hardwood density reduction with the pellet was negatively correlated with percent silt, clay, soil organic matter, and cation exchange capacity, and positively correlated with percent sand. With foliar sprays, hardwood density reduction was positively correlated with hexazinone rate and negatively correlated with soil pH. Pine mortality was positively correlated to percent sand with the pellet and negatively correlated to soil pH with broadcast sprays. Regression models incorporating pine height, herbicide rate, soil texture, cation exchange capacity, soil organic matter, and acidity could explain up to 78% of the variation in hardwood density change and 77% of the variation in pine mortality. Selective control of hardwoods in young loblolly pine stands is a function of hexazinone rate, formulation, and various soil factors.

The precise delivery of small quantities of herbicide solutions to leaf surfaces is difficult to achieve, yet most absorption research has this requirement. An atomizer for delivering microliter quantities of herbicide solutions has been designed, constructed, and tested. The function of the atomizer is to quantitatively apply low-volume (1-to 10-μl) solutions of herbicides, especially radioactive herbicides, to plant surfaces. The appearance of droplets from the atomizer and a flat-fan nozzle were similar and both yielded deposits that were much smaller than a 1-μl droplet applied by syringe. There was no splatter loss of herbicide when applied with the atomizer, and the bio-activity of the herbicide was equal to that applied as a single droplet. The atomizer yielded drops similar to those from a flat-fan nozzle and should produce absorption results more representative of those found under field conditions.