Greenhouse studies were conducted to evaluate 14C-glufosinate absorption, translocation, and metabolism in glufosinate-resistant corn, goosegrass, large crabgrass, and sicklepod. Glufosinate-resistant corn plants were treated at the four-leaf stage, whereas goosegrass, large crabgrass, and sicklepod were treated at 5, 7.5, and 10 cm, respectively. All plants were harvested at 1, 6, 24, 48, and 72 h after treatment (HAT). Absorption was less than 20% at all harvest intervals for glufosinate-resistant corn, whereas absorption in goosegrass and large crabgrass increased from approximately 20% 1 HAT to 50 and 76%, respectively, 72 HAT. Absorption of 14C-glufosinate was greater than 90% 24 HAT in sicklepod. Significant levels of translocation were observed in glufosinate-resistant corn, with 14C-glufosinate translocated to the region above the treated leaf and the roots up to 41 and 27%, respectively. No significant translocation was detected in any of the weed species at any harvest timing. Metabolites of 14C-glufosinate were detected in glufosinate-resistant corn and all weed species. Seventy percent of 14C was attributed to glufosinate metabolites 72 HAT in large crabgrass. Less metabolism was observed for sicklepod, goosegrass, and glufosinate-resistant corn, with metabolites composing less than 45% of detectable radioactivity 72 HAT.

Experiments were conducted at the Upper Coastal Plain Research Station near Rocky Mount and at the Peanut Belt Research Station near Lewiston-Woodville in 2002 and 2003. Peanut injury was minimal (< 5%) with all soil-applied programs. S-Metolachlor PRE alone or in mixture with sulfentrazone, diclosulam, or flumioxazin controlled annual grasses similarly (66 to 87%). The addition of imazapic plus 2,4-DB POST increased annual grass control (> 93%). Sulfentrazone or diclosulam in mixture with S-metolachlor were the best PRE options, with 94% and 92% control of yellow and purple nutsedge, respectively, with flumioxazin being least effective at 70%. Diclosulam and flumioxazin in mixture with S-metolachlor were the best PRE options, with 99% and 93%, respectively for common ragweed control, whereas sulfentrazone was the least effective at 65%. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin PRE were similar (87 to 90%) for common lambsquarters control. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin provided similar levels of entireleaf, ivyleaf, pitted, and tall morningglory control (87, 86, and 87%, respectively) and better than S-metolachlor alone at 64%. Flumioxazin in mixture with S-metolachlor was the best PRE option for control of Palmer amaranth at 96%, whereas diclosulam with S-metolachlor was the best PRE option for control of eclipta at 100%. The prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST and imazapic plus 2,4-DB POST were similar for all morningglory species (> 96%) and Palmer amaranth control (93 and 97%, respectively). Peanut treated with S-metolachlor plus diclosulam PRE numerically yielded the highest at 3,210 kg/ha, but were statistically equivalent to S-metolachlor plus flumioxazin PRE at 3,040 kg/ha. Peanut treated with imazapic plus 2,4-DB POST yielded the most at 3,400 kg/ha, while peanut treated with a prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST yielded less (3,070 kg/ha).

Field trials were established in 2005 and continued in 2006 to evaluate a conventional broadcast herbicide sprayer compared to a variable spray (sensor-activated) weed-sensing sprayer (WSS). The computer-based Herbicide Application Decision Support System (WebHADSS™) was used to determine a portion of the herbicides applied (based on herbicide efficacy and economics). Weed control, herbicide usage, crop yield, and net returns were compared across treatments. The broadcast applications were usually the most effective at controlling weeds. A PPI herbicide did not always improve weed control compared to treatments in which no PPI herbicide was applied. Variable treatments used less herbicide than the broadcast system in both years. Cotton lint yields in broadcast applications were similar to the weed-free check in both years of the study. Variable treatments often provided equivalent net returns (gross yield revenue less weed control cost) to the broadcast treatments. Although herbicide savings were observed in the variable treatments when compared to a broadcast system, a reduction in weed control was observed, indicating the need for future improvements of this system. A site-specific weed management program used in conjunction with WebHADSS™ may have potential in cotton production systems in the Texas Southern High Plains where weed densities are low.

Greenhouse studies were conducted to evaluate absorption, translocation, and metabolism of 14C-glufosinate in glufosinate-resistant cotton, nontransgenic cotton, Palmer amaranth, and pitted morningglory. Cotton plants were treated at the four-leaf stage, whereas Palmer amaranth and pitted morningglory were treated at 7.5 and 10 cm, respectively. All plants were harvested at 1, 6, 24, 48, and 72 h after treatment (HAT). Absorption of 14C-glufosinate was greater than 85% 24 h after treatment in Palmer amaranth. Absorption was less than 30% at all harvest intervals for glufosinate-resistant cotton, nontransgenic cotton, and pitted morningglory. At 24 HAT, 49 and 12% of radioactivity was translocated to regions above and below the treated leaf, respectively, in Palmer amaranth. Metabolites of 14C-glufosinate were detected in all crop and weed species. Metabolism of 14C-glufosinate was 16% or lower in nontransgenic cotton and pitted morningglory; however, metabolism rates were greater than 70% in glufosinate-resistant cotton 72 HAT. Intermediate metabolism was observed for Palmer amaranth, with metabolites comprising 20 to 30% of detectable radioactivity between 6 and 72 HAT.

Field studies were conducted at Lewiston–Woodville and Rocky Mount, NC in 2001 and 2002 to evaluate weed control and peanut response to POST treatments of diclosulam at various rates and application timings. Diclosulam controlled common ragweed and entireleaf morningglory when applied within 35 d after planting (DAP). Common ragweed 61 cm tall was controlled ≥92% with 4 to 13 g ai/ha diclosulam and larger common ragweed (107 to 137 cm tall) were controlled ≥97% with 27 g/ha diclosulam. Common lambsquarters was controlled 62% or less with all diclosulam POST treatments following metolachlor applied PRE, which provided 48% control. Peanut injury was less than 15% with all diclosulam POST treatments and was transitory. In separate studies, POST diclosulam treatments did not affect peanut yield in a weed-free environment. Peanut yield in weedy environments was reduced as the diclosulam application timing was delayed because of early season weed interference. A linear relationship was observed between yield and application timing with yield decreasing as application timing was delayed. This yield response documents the importance of early season weed management for maximizing peanut yield potential. Virginia peanut varieties were not affected by different POST rates of diclosulam; however, early season peanut injury showed a linear and quadratic relationship with diclosulam rate and was less than 14% at rates as high as 71 g/ha, and was not apparent by late season.

Four field studies were conducted in 2004 to evaluate corn tolerance, weed control, grain yield, and net returns in glufosinate-resistant (GUR), glyphosate-resistant (GYR), imidazolinone-tolerant (IT), and nontransgenic (NT) corn with various herbicide systems. No significant differences between hybrid systems were observed for weed control. Limited corn injury (< 5%) was observed for all herbicide treatments. A single early POST (EPOST) system without S-metolachlor and sequential POST over the top (POT) herbicide systems, averaged over corn hybrids and PRE and late POST-directed (LAYBY) herbicide options, provide 93 and 99% control of goosegrass, respectively, and at least 83 and 97% control of Texas panicum, respectively. A single EPOST system without S-metolachlor, averaged over corn hybrids and LAYBY treatment options, provided at least 88% control of large crabgrass. When averaged over corn hybrid and PRE herbicide options, a sequential POT herbicide system alone provided at least 98, 99, 98, and 100 control of large crabgrass, morningglory species, Palmer amaranth, and common lambsquarters, respectively. The addition of ametryn at LAYBY to a single EPOST system without S-metolachlor was beneficial for improving control of morningglory species, common lambsquarters, and Palmer amaranth, depending on location. However, the observed increases (7 percentage points or less) are likely of limited biological significance. Grain yield was variable between hybrids and locations because of environmental differences. Consequently, net returns for each hybrid system within a location were also variable. Any POT system with or without ametryn at LAYBY, averaged over corn hybrid and PRE herbicide options, provided at least 101, 97, 92, and 92% yield protection at Clayton, Kinston, Lewiston, and Rocky Mount, NC, respectively. Net returns were maximized with treatments that provided excellent weed control with minimal inputs.

Experiments were conducted from 1998 to 2000 at Rocky Mount, NC, in weed-free environments to determine soybean tolerance to preplant (PP) applications of trifloxysulfuron and the potential for trifloxysulfuron applied preemergence (PRE) and postemergence (POST) to cotton to injure soybean grown in rotation the following year. Trifloxysulfuron at 3.75 and 7.5 g ai/ha applied PP 2 wk before seeding injured conventional soybean less than 5%, whereas no injury was observed when seeding was delayed 4 or 6 wk after PP treatment. No injury to sulfonylurea-resistant soybean (SR) was observed for any treatment. Soybean yields were not influenced by trifloxysulfuron treatment. Cotton injury was 7% or less with trifloxysulfuron applied PRE or POST at 3.75 and 7.5 g/ha. Trifloxysulfuron at 15 g/ha PRE or POST injured cotton a maximum of 14 to 18%. Trifloxysulfuron did not reduce cotton lint yields regardless of method or rate of application. Both conventional and SR soybean were not injured nor were yields influenced by trifloxysulfuron applied PRE or POST the previous year to cotton.

Field observations of morningglory (Ipomoea spp.) showed that many plants grew out from places of comparable competitive advantage (alleys in field experiments with little or no vegetation) into neighboring plants or structures that provided climbing support. Of 223 native morningglory plants growing in rows and row middles in a 121-m2 area within established corn research plots that contained no other weeds, 68% of the mature plants climbed up corn. More significant, of the 152 climbing morningglory plants, 96% grew toward and climbed the row in its closest proximity instead of growing across the row middle. Greenhouse and field experiments were initiated to determine whether morningglory grew preferentially toward certain colored structures or corn plants. Greenhouse-grown ivyleaf morningglory displayed varying frequency in locating and climbing toward black (17%), blue (58%), red (58%), white (67%), green (75%), and yellow (75%) stakes or corn (92%). Pots containing black stakes had the fewest climbing morningglory plants. In the field study, fewer ivyleaf morningglories climbed black structures compared with white- or green-colored structures or corn. The morningglory initial planting distance from colored structures or corn was also significant in the percentage of ivyleaf morningglories that exhibited climbing growth and in its final weight; morningglories that successfully located and climbed structures or corn weighed more and produced more seed than morningglories that remained on the ground. Ivyleaf morningglory appears to respond to spatial distribution of surrounding objects and possibly uses reflectance to preferentially project its stems toward a likely prospective structure for climbing.

Laboratory and greenhouse studies were conducted to determine the effect of temperature, solution pH, water stress, and planting depth on cutleaf eveningprimrose germination and emergence. Field studies were conducted to measure growth parameters of cutleaf eveningprimrose throughout the fall season. When treated with constant temperature, cutleaf eveningprimrose germinated over a range of 15 to 32 C, with the optimum germination occurring at 24 C. Onset, rate, and total germination were greatest in an alternating 20/35 C temperature regime. Germination decreased as solution pH increased, with greatest germination occurring at solution pH of 4. Germination decreased when cutleaf eveningprimrose seed was subjected to increased water stress. Emergence was optimum when seed were buried at depths of 0.5 cm. Germination decreased with increasing burial depth, and no seed emerged from a depth of 10 cm. Cutleaf eveningprimrose control was maximized when 2,4-D was applied in mixture with glyphosate or paraquat. These data suggest that cutleaf eveningprimrose can germinate and gain biomass from early March to late October. These attributes could contribute to poor control before cotton planting if preplant control applications are delayed after early March.

Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5×, 1×, and 2× rates, with 1× rates of 0.84 kgae/ha, 0.5 kgai/ha, and 2.2 kgai/ha, respectively. Glyphosate and glufosinate provided similar levels of control for most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared with either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2× rate of either herbicide alone. MSMA is not a compatible tank-mixture partner with glyphosate or glufosinate for weed control in cotton.

Field studies were conducted near Clayton, Lewiston, and Rocky Mount, NC in 2005 to evaluate weed control and cotton response to preemergence treatments of pendimethalin alone or in a tank mixture with fomesafen, postemergence treatments of glufosinate applied alone or in a tank mixture with S-metolachlor, and POST-directed treatments of glufosinate in a tank mixture with flumioxazin or prometryn. Excellent weed control (> 91%) was observed where at least two applications were made in addition to glufosinate early postemergence (EPOST). A reduction in control of common lambsquarters (8%), goosegrass (20%), large crabgrass (18%), Palmer amaranth (13%), and pitted morningglory (9%) was observed when residual herbicides were not included in PRE or mid-POST programs. No differences in weed control or cotton lint yield were observed between POST-directed applications of glufosinate with flumioxazin compared to prometryn. Weed control programs containing three or more herbicide applications resulted in similar cotton lint yields at Clayton and Lewiston, and Rocky Mount showed the greatest variability with up to 590 kg/ha greater lint yield where fomesafen was included PRE compared to pendimethalin applied alone. Similarly, an increase in cotton lint yields of up to 200 kg/ha was observed where S-metolachlor was included mid-POST when compared to glufosinate applied alone, showing the importance of residual herbicides to help maintain optimal yields. Including additional modes of action with residual activity preemergence and postemergence provides a longer period of weed control, which helps maintain cotton lint yields.

Field studies were conducted near Clayton, Goldsboro, Kinston, and Rocky Mount, NC in 2003 to evaluate weed control and cotton response to postemergence (POST) treatments of glufosinate applied alone or in tank mixtures with s-metolachlor, pyrithiobac, or trifloxysulfuron. Late-season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, purple nutsedge, and sicklepod with glufosinate early postemergence (EPOST) was ≥90%. The addition of S-metolachlor to glufosinate EPOST improved control of all weeds except sicklepod, ivyleaf morningglory, and entireleaf morningglory. When applied POST, glufosinate provided ≥90% late season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, large crabgrass, pitted morningglory, purple nutsedge, and sicklepod. Control of goosegrass and Palmer amaranth was 81 and 84%, respectively. When pyrithiobac or trifloxysulfuron were added in POST tank mixtures, control of Palmer amaranth improved 6 and 9 percentage points, respectively. Control of goosegrass remained near 80% regardless of herbicide treatment used. The addition of a late post-directed (LAYBY) tank-mixture of glufosinate plus prometryn provided ≥88% late season control of all weeds. Reduced control of goosegrass and Palmer amaranth was observed with the LAYBY tank mixture of glufosinate plus MSMA when compared to other LAYBY tank mixtures. Cotton lint yields in plots receiving any herbicide application were significantly higher than plots receiving no herbicide application for all application timings. Cotton lint yields were ≥ 740 kg/ha where an EPOST was applied and ≥ 680 kg/ha when a POST herbicide was applied. Cotton lint yields were at least 200 kg/ha greater on plots receiving a LAYBY application when compared to plots where no LAYBY treatment was applied.

Field experiments were conducted at three locations in North Carolina in 1998 and 1999 and one location in Virginia in 1998 to evaluate weed management systems in peanut. Treatments consisted of diclosulam alone preemergence (PRE), or diclosulam plus metolachlor PRE alone or followed by (fb) bentazon plus acifluorfen postemergence (POST). These systems were also compared with commercial standards of metolachlor PRE fb bentazon plus acifluorfen POST or imazapic POST. Our data indicate that diclosulam PRE plus metolachlor PRE in conventional tillage peanut production usually controlled common lambsquarters, common ragweed, prickly sida, and entireleaf morningglory. But control of spurred anoda, goosegrass, ivyleaf morningglory, large crabgrass, and pitted morningglory by this system was inconsistent and may require additional POST herbicide treatments. Systems that included diclosulam plus metolachlor PRE consistently provided high yields and net returns.

Field studies were conducted near Lewiston–Woodville and Rocky Mount, NC to evaluate the effects of mixed weed species on peanut yield. A combination of broadleaf and grass weeds were allowed to interfere with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. These periods were then combined to determine the critical period of weed control in peanut. The effects of various weedy intervals on peanut yield were also investigated. The predicted critical period of weed control, in the presence of a mixed population of weeds, was found to be from 3 to 8 wk after planting (WAP). Peanut yield decreased as weed interference intervals increased, demonstrating the need for weed control throughout much of the growing season in the presence of mixed weed populations.

Studies were conducted at three locations in North Carolina in 2004 to evaluate density-dependent effects of glufosinate-resistant (GUR) corn on GUR cotton growth and lint yield. GUR corn was taller than GUR cotton as early as 11 d after planting, depending on location. A GUR corn density of 5.25 plant/m of crop row reduced late-season cotton height by 38, 43, and 43% at Clayton, Lewiston-Woodville, and Rocky Mount, NC, respectively, compared with weed-free cotton height. GUR corn dry biomass per meter of crop row and GUR corn seed biomass per meter of crop row decreased linearly with increasing GUR corn density at all locations. The relationship between GUR corn density and GUR cotton yield loss was described by the rectangular hyperbola model with the asymptote (a) constrained to 100% maximum yield loss. The estimated coefficient i (yield loss per unit density as density approaches zero) was 7, 5, and 6 at Clayton, Lewiston-Woodville, and Rocky Mount, respectively. Percentage of GUR cotton lint yield loss increased 4, 5, and 8 percentage points at Clayton, Lewiston-Woodville, and Rocky Mount, respectively, with each 500 g increase in weed biomass/m of crop row. The examined GUR corn densities had a significant effect on cotton yield but not as significant as many other problematic grass and broadleaf weeds.

Research was conducted to evaluate root uptake, translocation, and metabolism of 14C-sulfentrazone alone or in a mixture with clomazone in solution in flue-cured tobacco transplants. Uptake and translocation of sulfentrazone was rapid and was not affected by the addition of clomazone. Fifty-nine and 65% of the 14C absorbed by the plant was translocated to the leaves within 24 h with sulfentrazone alone and in the clomazone plus sulfentrazone mixture, respectively. Differences in plant metabolism were observed between sulfentrazone alone and sulfentrazone plus clomazone. After 3 h, 66% of the 14C recovered from the leaves was metabolized when sulfentrazone was applied alone, compared to 91% when sulfentrazone was applied with clomazone. The difference could indicate that metabolism of sulfentrazone by tobacco transplants was enhanced by the presence of clomazone.

Experiments were conducted during 2000 and 2001 at a total of 13 locations throughout Alabama, Georgia, Florida, North Carolina, and Texas to evaluate efficacy of herbicides at or below the manufacturer's suggested use rate. Herbicide applications included diclosulam and flumioxazin applied PRE alone or followed by imazapic applied early postemergence (EPOST). All possible combinations of diclosulam at 0, 13.5, or 27 g ai/ha and flumioxazin at 0, 53, or 105 g ai/ha applied PRE were included. Imazapic was applied at 35 g ai/ha. Ivyleaf morningglory was controlled more than 87% when imazapic was applied EPOST regardless of PRE herbicide. Pitted morningglory control > 67% was observed with applications of diclosulam (27 g/ha) followed by imazapic, diclosulam (13.5 g/ha) plus flumioxazin (53 g/ha), diclosulam (13.5 g/ha) plus flumioxazin (105 g/ha), and diclosulam (27 g/ha) plus flumioxazin (105 g/ha). Sicklepod was controlled more than 74% with flumioxazin (53 g/ha) followed by imazapic and diclosulam (27 g/ha) plus flumioxazin (105 g/ha) followed by imazapic. Florida beggarweed was controlled more than 84% by all PRE herbicide combinations except flumioxazin (53 g/ha) alone or diclosulam (27 g/ha) alone or with imazapic. Yellow nutsedge was controlled at least 90% with diclosulam at either rate followed by imazapic and by diclosulam plus flumioxazin followed by imazapic regardless of rate. Pod yield was generally higher when herbicides were applied regardless of herbicide combination or rate. Peanut yield was maximized with the lowest rates of flumioxazin or diclosulam PRE followed by imazapic EPOST.

Previous research has shown that flumioxazin has the potential to cause peanut injury. In response to this concern, laboratory and greenhouse experiments were conducted to investigate the influence of temperature on germination of flumioxazin-treated peanut seed and the effect of interval between flumioxazin application and irrigation on peanut emergence and injury. Laboratory experiments using 14C-flumioxazin were also conducted to investigate differential tolerance exhibited by peanut, ivyleaf morningglory, and sicklepod to flumioxazin. Flumioxazin treatments containing either water-dispersible granular or wettable powder formulation at 1.4 μmol L−1 did not influence germination compared with nontreated peanut across all temperature regimes (15 to 40 C). Peanut treated with either formulations of flumioxazin preemergence and receiving irrigation at emergence and 2 and 4 d after emergence were injured between 40 and 60%. Peanut treated at 8 and 12 d after emergence were injured between 25 and 15%, respectively. Total 14C absorbed by ivyleaf mornigglory was 57% of applied whereas sicklepod absorbed 46%, 72 h after treatment (HAT). Peanut absorbed > 74% of applied 14C 72 HAT. The majority of absorbed 14C remained in roots of sicklepod, ivyleaf morningglory, and peanut at all harvest times. Ivyleaf morningglory contained 41% of the parent herbicide 72 HAT whereas sicklepod and peanut contained only 24 and 11% parent compound, respectively. Regression slopes indicated slower flumioxazin metabolism by ivyleaf morningglory (a susceptible species) compared with sicklepod and peanut (tolerant species).

Studies were conducted to evaluate the effects of grass and broadleaf weeds on peanut growth and peanut yield. In separate studies, grass or broadleaf weeds were allowed to compete with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. Hand-weeding and selective herbicides were used at appropriate times to remove and terminate weed growth. These periods were then used to determine the critical period of weed control. The effects of various weedy intervals on peanut yield were also investigated. The critical period of grass weed control was found to be from 4.3 to 9 wk after planting (WAP), whereas the critical period of broadleaf weed control was from 2.6 to 8 WAP. Peanut yields decreased as weed interference intervals for both grass and broadleaf weeds increased, demonstrating the need for control of both grass and broadleaf weeds throughout much of the growing season.

The influence of herbicide placement and plant growth stage on the absorption and translocation patterns of 14C-glyphosate in glyphosate-resistant cotton was investigated. Plants at four growth stages were treated with 14C-glyphosate on a 5-cm2 section of the stem, which simulated a postemergence-directed spray (PDS) application, or on the newest mature leaf, which simulated a postemergence (POST) application. Plants were harvested 3 and 7 d after treatment and divided into the treated leaf or treated stem, mature leaves, immature leaves and buds, stems, roots, fruiting branches (including the foliage on the fruiting branch), squares, and bolls. The PDS versus POST application main effect on absorption was significant. Absorption of 14C-glyphosate applied to stem tissue was higher in PDS applications than in POST applications. Plants receiving PDS applications absorbed 35% of applied 14C-glyphosate, whereas those receiving POST applications absorbed 26%, averaged over growth stages at application. Absorption increased from the four-leaf growth stage to the eight-leaf stage in POST applications but reached a plateau at the eight-leaf stage. Plants with PDS applications showed an increase in absorption from the four- to eight- to twelve-leaf stages and reached a plateau at the 12-leaf stage. Translocation of 14C-glyphosate to roots was greater at all growth stages with PDS treatments than with POST treatments. Herbicide placement did not affect translocation of 14C-glyphosate to squares and bolls. Squares and bolls retained 0.2 to 3.7% of applied 14C-glyphosate, depending on growth stage. Separate studies were conducted to investigate the fate of foliar-applied 14C-glyphosate at the four- or eight-leaf growth stages when harvested at 8- or 10-leaf, 12-leaf, midbloom (8 to 10 nodes above white bloom), and cutout (five nodes above white bloom, physiological maturity) stages. Thirty to 37% of applied 14C-glyphosate remained in the plant at cutout in four- and eight-leaf treatment stages, respectively. The concentration of 14C-glyphosate in tissue (Bq g−1 dry weight basis) was greatest in mature leaves and immature leaves and buds in plants treated at the four-leaf stage. Plants treated at the eight-leaf stage and harvested at all growth stages except cutout showed a higher concentration of 14C-glyphosate in squares than in other plant tissue. Accumulation of 14C-glyphosate in squares reached a maximum of 43 Bq g−1 dry weight at harvest at the 12-leaf stage. This concentration corresponds to 5.7 times greater accumulation of 14C-glyphosate in squares than in roots, which may also be metabolic sinks. These data suggest that reproductive tissues such as bolls and squares can accumulate 14C-glyphosate at higher concentrations than other tissues, especially when the herbicide treatment is applied either POST or PDS during reproductive stages (eight-leaf stage and beyond).