A field study was conducted from 1999 through 2001 at Stoneville, MS, to determine the effects of bromoxynil-resistant (BR) and glyphosate-resistant (GR) cotton rotation systems under ultranarrow- (25-cm spacing) and wide- (102-cm spacing) row planting on weed control, weed density and shift, and cotton yield. The four rotations during 3 yr included BR–BR–BR, GR–GR–GR, BR–GR–BR, and GR–BR–GR, all with bromoxynil or glyphosate postemergence (POST) only or following fluometuron plus pendimethalin preemergence (PRE). Control of hemp sesbania, pitted morningglory, prickly sida, and hyssop spurge was ≥97% regardless of row width, rotation, and herbicide program. Control of common purslane, sicklepod, and smooth pigweed was higher with glyphosate POST in GR cotton than with bromoxynil POST in BR cotton. Broadleaf and yellow nutsedge weed biomass were higher with bromoxynil POST in BR cotton than with glyphosate POST in GR cotton. Continuous BR cotton system resulted in higher densities of common purslane, sicklepod, and yellow nutsedge (15.3, 1.5, and 373 plants/m2, respectively) compared with continuous GR cotton (0.7, 0.1, and 1.0 plant/m2, respectively). Seed cotton yield was consistently higher in wide- than in ultranarrow-row cotton. Seed cotton yield was lower in continuous BR cotton than in the other three rotation systems, and yields greatly improved when BR cotton was rotated with GR cotton. During a 3-yr period, seed cotton yields with glyphosate POST only (4,000 to 4,890 kg/ha) or after PRE herbicides (4,480 to 4,860 kg/ha) were similar in GR cotton, whereas in BR cotton, bromoxynil POST only (1,390 to 4,280 kg/ha) resulted in lower yield than did bromoxynil POST after PRE herbicides (2,550 to 4,480 kg/ha). The results indicated that the shift in spectrum of weeds toward more tolerant species and yield decline in continuous BR cotton can be prevented by rotating BR with GR cotton.

Field experiments were conducted in 1999 and 2000 at the Rice Research and Extension Center at Stuttgart, AR, on a DeWitt silt loam and at the Pine Tree Branch Experiment Station near Colt, AR, on a Calloway silt loam to evaluate the tolerance of 14 rice cultivars and four experimental cultivar lines to clomazone at 0.34 and 0.67 kg ai/ha applied preemergence. Early-season chlorosis 14 days after emergence (DAE) ranged from 1 to 21% in 1999 and 3 to 40% in 2000 when averaged over herbicide rate. The experimental cultivar line RU961096 was slightly more susceptible to clomazone than other cultivars and lines. However, RU9701041 was more tolerant to clomazone at 0.67 kg/ha 14 DAE than other cultivars and lines. By 28 DAE, all cultivars had <13% chlorosis in 1999 and <8% in 2000. The experimental cultivar line RU9601096 and cultivar Koshihikari did not recover as quickly as the other 16 cultivars and cultivar lines. Early-season chlorosis had no effect on days to 50% heading or yield for any of the cultivars evaluated.

Greenhouse studies were conducted to evaluate shoot number, shoot weight, rhizome weight, and root weight reduction of green and false-green kyllinga at three placement levels (soil applied, foliar applied, and soil + foliar applied) and five herbicide treatments (CGA-362622, halosulfuron, imazaquin, MSMA, and imazaquin + MSMA). Averaged over herbicide and placement level, false-green kyllinga shoot number 30 d after treatment (DAT) and rhizome weight 60 DAT were reduced more than those of green kyllinga. Furthermore, imazaquin, MSMA, and imazaquin + MSMA, averaged across placement levels, as well as CGA-362622 and halosulfuron, both foliar and soil applied, reduced false-green kyllinga shoot number greater than that of green kyllinga 60 DAT. Halosulfuron reduced false-green kyllinga shoot weight greater than that of green kyllinga 60 DAT; however, MSMA reduced green kyllinga greater. In general, foliar- and soil + foliar–applied treatments reduced shoot number (30 DAT), rhizome weight, and root weight of both kyllinga species greater than soil-applied treatments, whereas soil + foliar–applied treatments were more effective in reducing shoot weight 60 DAT. CGA-362622 and halosulfuron reduced kyllinga species shoot number (30 DAT), false-green kyllinga shoot weight (60 DAT), and root weight of both species greater than all other herbicides. However, CGA-362622 reduced green kyllinga shoot weight (60 DAT) and rhizome weight of both species greater than all other herbicides.

Field trials were carried out in organic soils to determine the effects of different phosphorus (P) fertilization programs and common lambsquarters duration of interference on lettuce. Phosphorus was either banded (125 kg/ha) or broadcast (250 kg/ha) before lettuce planting. A common lambsquarters population density of four plants per 6 m row interfered with ‘South Bay’ lettuce for 2, 4, 6, or 8 wk after lettuce emergence, along with a weed-free control. For banded P, lettuce fresh weight declined linearly (y = 14.82 − 0.97x; r2 = 0.96) as duration of common lambsquarters interference increased. The effect of broadcast P over common lambsquarters duration of interference fit a quadratic equation (y = 10.67 − 1.69x + 0.12x2; r2 = 0.98). The difference in the regression model intercepts for both P fertilization programs showed that in the absence of common lambsquarters interference, marketable lettuce fresh weight was higher by banding P than by broadcasting P. Based on predicted values, this difference is approximately 28% (+4.15 kg per 6 m row) in favor of banded P. Therefore, banding P at 125 kg/ha proved to be beneficial in raising lettuce fresh weight regardless of the duration of interference. For banded P, the model predicts that 10% yield reduction would be observed at 1.53 wk (10.5 d) of common lambsquarters interference. However, with broadcast P, this period declined to 0.67 wk (4.7 d).

Dryland rotations are changing in the semiarid Great Plains because of no-till systems. Producers now rotate summer annual crops such as corn with winter wheat and fallow, which can disrupt weed population growth because of diverse life cycles among crops. This study estimated changes in weed populations as affected by rotation design, with the goal of suggesting crop sequences that lower weed community density. We used an empirical life-cycle simulation based on demographics of jointed goatgrass and green foxtail to compare various rotations consisting of winter wheat, corn, proso millet, and fallow across a 12-yr period. The simulation indicated that designing rotations to include a 2-yr interval when seed production of either jointed goatgrass or green foxtail is prevented will drastically reduce weed populations. Arranging four different crops in sequences of two cool-season crops, followed by two warm-season crops was the most beneficial for weed management. Fallow, if used, serves in either life-cycle category. However, if the same crop is grown 2 yr in a row, such as winter wheat, the benefit of rotation design on weed density is reduced considerably. Impact of rotation design on weed density was enhanced by improving crop competitiveness with cultural practices. Rotations with balanced life-cycle intervals not only reduce weed density but enable producers to use alternative weed management strategies, improve effectiveness of herbicides used, and minimize herbicide resistance.

Corn and soybean were planted in narrow and wide row spacings to determine the effect of glyphosate application timing and row spacing on crop yield. Glyphosate was applied when average weed canopy height reached 5, 10, 15, 23, and 30 cm. Weeds present in these studies included velvetleaf, redroot pigweed, common ragweed, common lambsquarters, jimsonweed, barnyardgrass, fall panicum, giant foxtail, yellow foxtail, green foxtail, and eastern black nightshade. Under highly competitive growing conditions (below normal rainfall and high weed density), corn yield was first reduced when weeds reached 10 and 15 cm in height with corn planted in 38- and 76-cm rows, respectively. Under similar conditions, soybean yield was first reduced when weeds reached 15 and 23 cm with soybean planted in 19- and 38-cm rows, respectively. Yield losses occurred only in the untreated control when soybean was planted in 76-cm rows. When growing conditions were less competitive (adequate rainfall and lower weed density), yield losses occurred only when weeds reached 30 cm or more in corn and only in the untreated control in soybean. Corn and soybean yields were higher when planted in narrow rows in three of 4 yr but were more susceptible to early-season weed interference than corn and soybean in wide rows. Corn yield was affected more by weed interference than was soybean yield. The product of weed height by weed density, as the independent variable, resulted in the best linear fit for both corn and soybean yields. High weed densities increase the risk of yield loss and must be considered when determining the appropriate timing for total postemergence herbicide applications such as glyphosate. Sequential glyphosate applications in corn did not increase yield.

Corn and soybean were planted in narrow- and wide-row spacings to study the effects of glyphosate application timing and row spacing on light interception and subsequent weed growth. Corn planted in narrow rows (38 cm) had greater light interception than corn planted in wide rows (76 cm) from 35 to 55 d after crop emergence. Soybean planted in narrow rows (both 19 and 38 cm) had greater light interception throughout the growing season than soybean in 76-cm rows. At maximum canopy closure, narrow-row soybean (both 19 and 38 cm) intercepted more light than narrow-row corn. Biomass of weeds emerging after glyphosate application was greater when soybean was planted in 76-cm than in 19- or 38-cm rows. However, weed biomass was generally similar in both row spacings of corn. Sequential glyphosate applications reduced weed biomass in corn each year compared with a single glyphosate application at the 5-cm weed height. Sequential glyphosate applications that followed initial glyphosate application to 10- or 15-cm-tall weeds did not reduce weed biomass compared with a single application.

The difficulty of measuring fecundity of weeds with shatter-prone seeds can be overcome by postanthesis application of nontoxic glues to seedheads. Such glues reduced seed losses of redroot pigweed to <5% of total seed production compared with 12 to 14% for nontreated plants.

Maintaining crop residues on the soil surface has changed cropping practices in the Central Great Plains. Where previously winter wheat–fallow was the prevalent rotation, producers now grow warm-season crops in sequence with winter wheat and fallow. Controlling weeds during fallow with herbicides eliminates the need for tillage, thus conserving more crop residues. However, producers are considering subsurface tillage as an option to manage herbicide-resistant weeds. We reviewed the impact of subsurface tillage with the sweep plow on weed dynamics and crop growth compared with no-till systems. Cropping systems studies show that rotations can be designed to reduce weed community density severalfold; tillage lessens this rotational effect by burying weed seeds and prolonging their survival in soil. Crop residues on the soil surface reduce weed seedling establishment in no-till systems, but tillage eliminates this effect. Crops also yield less after tillage compared with no-till in this semiarid climate. Tillage may help in managing herbicide resistance, but it also may increase weed density as well as reduce crop yield.

Flights of pigeons were whirling over head, violets and stellarias were sprouting beneath the feet, and such was the January of Savannah.

Life in the South; from the Commencement of the War, C. C. Hopley, 1863.