Field experiments were conducted to evaluate placement techniques for preemergence applications of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] in grain sorghum [Sorghum bicolor (L.) Moench.]. The first technique consisted of row shields mounted behind the planter units. Shields maintained an untreated strip over the crop drill and allowed successful crop establishment with pendimethalin at 1.1 kg ai/ha, despite a simulated, intense rainfall of 3.8 cm within 24 h after planting. A second technique, which consisted of a special nozzle arrangement, was evaluated in no-till grain sorghum. The nozzle arrangement allowed a broadcast herbicide application but maintained an untreated strip over the crop drill. No stand reductions occurred using this technique at pendimethalin rates of 1.1 and 2.2 kg/ha. In a growth chamber experiment, preemergence applications of pendimethalin severely injured grain sorghum when the soil was wet at the time of emergence, but injury was reduced under hot, dry conditions.

Field experiments were conducted in 1988, 1989, and 1990 in Greece to investigate the combination of cultural and chemical methods for weed control in soybean. The selectivity of herbicides or the combination of herbicides used was dependent on application rate. Imazaquin applied PRE was selective on soybean even at 0.18 kg/ha, whereas imazethapyr was safer on soybean than imazaquin at 0.22 kg/ha. Metribuzin at 0.37 kg/ha tank-mixed with alachlor, metolachlor, imazaquin, and SAN 582H were not phytotoxic at their recommended rates. All herbicides satisfactorily controlled the weeds in the experiments. The early-season period threshold level for a mixed population of Amaranthus spp. occurred 3.0 to 3.5 wk after weed emergence. Density of Amaranthus spp. of about 270 to 470 plants/m2 caused soybean yield reduction equal to 11 to 35%, respectively. The treatments did not influence the oil content of the soybean seed but in one experiment the protein content was influenced slightly by some of the treatments. The results emphasize the importance of using chemical, cultural, and competition threshold levels of cultural practices for an integrated approach for weed control in soybean.

Field experiments were carried out from 1987 to 1990 to develop an integrated weed control management system for the control of blackgrass in winter wheat in Greece. The weed control treatments included both herbicides and cultural measures. The performance of preemergence (PRE) herbicides against blackgrass was better than postemergence (POST) herbicides; selectivity was dependent on application rate. Late timing of wheat sowing resulted in significant reduction of the blackgrass population competing with wheat. The critical period for blackgrass infestation occurred 4.0 to 5.5 wk after wheat emergence. Blackgrass density of 170 to 1,170 plants/m2 caused wheat yield reduction equal to 10 and 30%, respectively. A quadratic relationship describing the percent reduction of wheat yield due to competition with different blackgrass densities was developed. The economic threshold level for blackgrass varied between 100 and 125 plants/m2. The results emphasize the importance of using a combination of chemical and cultural controls, including critical periods for herbicide application in maintaining an integrated approach for blackgrass control in wheat.

Rhizome johnsongrass [Sorghum halepense (L.) Pers.] in late-planted soybeans [Glycine max (L.) Merr. ‘Forrest’] was effectively controlled with glyphosate [N-(phosphonomethyl)glycine] applied twice by a rope-wick applicator at 0.1 kg/ha each time. At crop maturity, wick-applied glyphosate controlled an average of 92% of the johnsongrass over a 2-yr period as compared to 51% where 2.2 kg/ha of glyphosate was applied conventionally to rhizome johnsongrass prior to planting. There was no difference in soybean yields and no visible injury to soybeans. Rhizome johnsongrass and volunteer corn (Zea mays L.) were effectively controlled in soybeans planted at the proper time with glyphosate applied by either the rope-wick applicator or recirculating sprayer. Soybean yields were reduced more when volunteer corn was treated with glyphosate that was applied with a recirculating sprayer than with a rope-wick applicator. This reduction in yield was attributed to splattering of the herbicide.

Commercially available cabinet sprayers are not well suited for making low volume applications (<30 L/ha) of herbicides to woody forest species that can be up to 1.5 m tall. A simple, inexpensive laboratory sprayer that overcomes some limitations of commercial cabinet sprays can be built from materials readily available at local building and electronic suppliers. The only specialized equipment required is a positive displacement pump and a rotary disk atomizer. The atomizer is attached to the end of a variable height arm mounted on a laboratory cart. A positive displacement pump ensures controlled flow. The operator pushes the cart along a metal rub rail which keeps the cart tracking in a straight line. Travel speed is regulated by the operator following a marker on a clothesline-like loop of fishing line and is driven by a variable-speed drill attached to a variable voltage power supply.

Water and paraffinic oils were used to determine variables that affect positive displacement pumps used to meter liquid flow in an air-assist spray system. Components needed to construct an air-assist spray system were described for use in spray chambers and on a tractor for field application of herbicides in ultralow volume (ULV). The flow rate of the pump varied less than 2% for the water and oil as the pump setting was varied from 0 to 100% of the pump's capacity. Linear relationships were shown for both liquids as the voltage input varied from 4 to 13 volts. Air pressures to 100 kPa and liquid temperatures to 35 C did not affect flow rate of the pump. Volume median diameter of the spray droplets decreased from 295 μm to 77 μm and 159 μm to 85 μm for water and paraffinic oil, respectively, as the air pressure was adjusted from 14 to 110 kPa.

An air-assist spray nozzle was constructed to apply herbicides in oil or water at volumes as low as 2.3 L/ha. The spray was metered through a disc orifice inside the nozzle and forced into an airstream which atomized the liquid. The nozzle produced 16 to 54 spray droplets/cm2 with air pressures from 3.4 to 62 kPa from a 2-mm outlet using a lightweight paraffinic oil. The number of spray droplet deposits produced with a paraffinic oil at 34 kPa increased from 7 droplets/cm2 with a 0.8-mm outlet to 48 droplets/cm2 with a 2.4-mm outlet. The nozzle was designed primarily to apply herbicides in oil at 2.3 to 4.7 L/ha, but it has the capability of applying 150 L/ha of oil or water.

In 1991 and 1993, tolerance of ‘Zenith’ and ‘Merit’ sweet corn to 35 g ai/ha nicosulfuron post-directed (PDIR) 0, 5, 10, and 15 cm up the corn stalk or applied POST was determined. In 1991, nicosulfuron applied POST to Zenith caused approximately 30% visible injury, 30% height reduction, and 50% reduction of U.S. No. 1 marketable ear weight. In 1991 no visible injury was observed in the PDIR treatments. Zenith was not injured by any treatment in 1993. Both years, Merit was killed by nicosulfuron applied POST. In 1991 and 1993, nicosulfuron PDIR 0 and 5 cm up the corn stalk of Merit caused approximately 5% and 65% visible injury, respectively, and resulted in yield loss. PDIR application increased nicosulfuron tolerance of moderately tolerant Zenith but did not improve that of least tolerant Merit.

Protoporphyrinogen oxidase (protox)-inhibiting herbicides damage cell membranes, resulting in electrolyte leakage. A whole-plant dose-response study and a rapid assay that measured electrolyte leakage was used to determine the response of wild mustard, soybean, and protox inhibitor–susceptible and protox inhibitor–resistant common waterhemp to increasing doses of three protox inhibitors: acifluorfen, fomesafen, and sulfentrazone. For the dose-response study, whole plants were treated with the three protox-inhibitor herbicides. Electroconductivity assay 1 consisted of cutting discs from leaf tissue and submerging them in an incubation medium containing concentrations of acifluorfen, fomesafen, or sulfentrazone. In electroconductivity assay 2, the entire leaf was treated with solutions containing acifluorfen, fomesafen, or sulfentrazone. The whole-plant dose-response study showed increasing visible injury with increasing herbicide rates for all species and all herbicides. The order of visible injury was wild mustard > susceptible common waterhemp > resistant common waterhemp > soybean. In assay 1, electrolyte leakage from leaf discs treated with acifluorfen or fomesafen increased with increasing herbicide concentrations, and was similar for all species. In contrast, electrolyte leakage from leaf discs treated with sulfentrazone did not increase with increasing herbicide concentrations for any species. In assay 2, only wild mustard leaf discs increased in electrolyte leakage with increasing herbicide rates of acifluorfen, fomesafen, and sulfentrazone and followed the regression curves established by the whole-plant dose-response study. However, assay 2 was not able to distinguish between susceptible wild mustard and tolerant soybean, or between susceptible and resistant waterhemp.

Field studies were conducted from 2000 to 2002 to determine whether glyphosate applied during periods of low temperature (< 10 C) provides effective control of garlic mustard without injury to nontarget native herbs. A 1% glyphosate solution was applied on three dates between November and March in 2000 to 2001 and 2001 to 2002, when average daily temperatures ranged from −4.2 to 7 C. Glyphosate reduced the population density of prereproductive springtime garlic mustard infestations, regardless of application timing. During the primary bolting period (April to June), mortality of garlic mustard rosettes in sprayed plots was 87 to 94%, whereas mortality in nontreated plots was 12% in the first year and 41% in the second. Nontarget native herbaceous species were not injured by the cold-weather herbicide applications and exhibited higher springtime densities than in the nontreated plots. By targeting garlic mustard rosettes during the part of the year when most other plant species are dormant, managers can selectively control garlic mustard without damage to native herbs and, thereby, increase forest restoration success.

Rice cutgrass is encroaching into rice fields from ditch banks and canals, especially into continuous rice fields where tillage is limited in the Mississippi Delta region of Arkansas. Experiments were conducted to evaluate the effectiveness of various herbicides applied alone on rice cutgrass and to determine if the effectiveness of bispyribac on rice cutgrass is influenced by number of applications, adjuvant type, and adjuvant rate. Glyphosate, glufosinate, and clethodim were the most effective herbicides when applied alone; however, none of these are labeled for over-the-top application in rice. Of those herbicides that can be applied over the top of rice, imazethapyr and bispyribac were the most effective, providing 52 to 62% rice cutgrass control, albeit imazethapyr can be used only in imidazolinone-resistant rice. The addition of an adjuvant to bispyribac improved rice cutgrass control, and sequential bispyribac applications were generally superior to a single application. Methylated seed oil/organosilicone/urea ammonium nitrate adjuvant increased rice cutgrass control with bispyribac, especially when bispyribac was applied as a single application. A single application of imazethapyr, bispyribac, halosulfuron, penoxsulam, clomazone, thiobencarb, cyhalofop, propanil, quinclorac, and fenoxaprop provided less-than-acceptable control, which partially explains the difficulty that growers are experiencing in controlling rice cutgrass, especially in continuous rice production.

In 2004 and 2005, glyphosate + diuron and flumioxazin + MSMA were applied POST-directed to cotton at 20, 30, 40, and 50 cm in height. Herbicides were directed to either the lower 2 cm of the cotton stem or to the lower 50% of the cotton stem to determine the impact of application timing and placement on cotton response. Glyphosate + diuron resulted ≤ 22% injury when applied high on the stem and ≤ 8% injury when applied low on the stem. Regardless of application placement or timing, no yield reductions were observed as a result of glyphosate + diuron application. Conversely, flumioxazin + MSMA applications resulted in 93 and 64% injury when applied high POST-directed (HPD) to 20- and 30-cm cotton, respectively. Low POST-directed (LPD) applications caused 33 and 23% injury to 20- and 30-cm cotton, respectively. In both years, HPD applications of flumioxazin + MSMA on 20-cm cotton resulted in excessive yield loss (94 to 87%), whereas yield loss was only noted in 30-cm cotton in 2004. No yield loss was observed in 40- or 50-cm cotton. Additionally, LPD applications of flumioxazin + MSMA, though causing significant visual injury, did not result in a yield reduction at any application timing. Although cotton became more tolerant to flumioxazin + MSMA as the season progressed, the research suggests that applications of flumioxazin should be made with precision or delayed until cotton reaches 40 cm in height.

Field experiments were conducted at Warooka and Rudall on the Yorke and Eyre Peninsula of South Australia during 2004 and 2005 to investigate the effectiveness of metribuzin for the selective control of rigid brome in no-till sown barley. Metribuzin (135 to 203 g ai/ha) incorporated by sowing (IBS) was more effective in controlling rigid brome (> 67%) than the same herbicide dose applied POST. Although IBS metribuzin at the highest rate (270 g/ha) provided effective weed control (82 to 90%), it was more phytotoxic to barley, reducing crop density by 23% relative to the nontreated control at Rudall. Soil at Rudall had low clay and organic matter content. In contrast, tank mixtures of metribuzin (203 g/ha) with pendimethalin, applied IBS, provided reliable rigid brome control (89 to 93%) and resulted in little crop damage (< 5%). Over the site-by-year combinations studied, all herbicide-treated barley at Warooka and Rudall yielded 6 to 50% more grain than the nontreated crop. Although metribuzin provides growers with an opportunity to selectively control rigid brome in no-till barley, high rates (≥ 203 g/ha) of this herbicide on sandy textured soils can result in significant crop damage.

Site-specific herbigation using a linear-move irrigation system equipped with an automated irrigation control system was evaluated in a series of field trials conducted at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. In the first study, the experimental area was divided into site-specific management zones that were randomly assigned herbigation treatments of metolachlor at 0, 1.8, 2.7, or 3.6 kg ai/ha. In a second study, site-specific herbigation treatments of metribuzin at 0, 0.28, 0.42, or 0.56 kg ai/ha were applied. The tests covered a range in system flow rate from 29 to 90% of maximum design flow. Average metolachlor rates applied were within 1, 2, and 4% of the target 1.8, 2.7, and 3.6 kg/ha rates, respectively, and average metribuzin rates were on target at the 0.28 kg/ha rate and within 5 and 2% of the 0.42 and 0.56 kg/ha target rates, respectively. In a third study, potato (Solanum tuberosum) fields were divided into management zones, and low, medium, or high populations of Indian mustard (Brassica juncea) and foxtail millet (Setaria italica) were seeded in each zone. Different rates of a metolachlor plus metribuzin mixture were herbigated in each zone—higher rates in zones with high populations and lower rates in zones with low populations. Weed control was excellent in all zones. Results suggest good potential for site-specific herbigation when linear-move or center-pivot irrigation systems are equipped with the automated irrigation control system.

The intensification of farming practices has reduced weed infestations, but it has also led to a reduction in weed diversity and changes in species composition. These effects are well described for aboveground flora; however, it is less clear how these effects might be expressed in the soil weed seedbank. We evaluated the effects of different long-term farm management strategies on the weed seedbank abundance, diversity, and community composition in the DOK (bioDynamic, bioOrganic, and Konventionell) field trial established in 1978 at Therwil, Switzerland. The trial compares biodynamic, organic, and conventional farming systems, which mainly differ in fertilization, weed control strategies, and pest control. The species richness and seed abundance of the weed seedbank were higher in the organic and biodynamic systems compared with the conventional ones. The different farming systems favored shifts in species assemblages, because specific management practices, such as herbicide application and type of fertilization, acted as filters that selected against certain species but promoted others that were more adapted.