Velvetleaf (Abutilon theophrasti Medik.) is a troublesome broadleaf weed that competes with crops for resources such as soil moisture. Water stress can affect the ability of weed species to grow and produce seeds. The objective of this study was to determine the effect of degree of water stress on the growth and fecundity of A. threophrasti using soil moisture sensors under greenhouse conditions. Abutilon threophrasti seeds collected from a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] field were grown in silty clay loam soil, and plants were maintained at 100%, 75%, 50%, and 25% soil field capacity (FC) corresponding to no, light, moderate, and high water-stress conditions, respectively. Water was added daily to pots based on soil moisture levels detected by a Meter Group 5TM sensor to maintain the desired water-stress level required by treatment. Plants maintained at 100% FC had the maximum number of leaves (28 leaves plant−1), followed by 21 and 15 leaves plant−1 at 75% and 50% FC, respectively. Abutilon threophrasti at 100% and 75% FC achieved maximum plant height (108 to 123 cm) compared with 83 cm at 50% FC. Abutilon threophrasti maintained at 75% FC had the greatest growth index (79,907 cm3) followed by 72,197 cm3 at 100% FC and 64,256 cm3 at 50% FC. Seed production was similar at 100%, 75%, and 50% FC (288 to 453 seeds plant−1) compared with 2 seeds plant−1 at 25% FC. This is because the majority of plants maintained at 25% FC did not survive more than 77 d after transplanting. Seed germination was 96% to 100% at 100%, 75%, and 50% FC compared with 20% germination at 25% FC. Abutilon threophrasti can survive ≥50% FC continuous water-stress conditions, although with reduced leaf number, plant height, and growth index compared with 75% and 100% FC.

Common bean and azuki bean are poor competitors with weeds and demonstrate sensitivity to herbicides used for weed control in soybean. S-metolachlor, flufenacet, and acetochlor are categorized as Group 15 herbicides and provide control of multiple annual grass and select small-seeded broadleaf weeds. By way of field trials near Exeter and Ridgetown, Ontario, in 2019, 2020, and 2021, four dry bean market classes (azuki, kidney, small red, and white bean) were evaluated for their tolerance to 1× established label rates and 2× rates of S-metolachlor (1,600 and 3,200 g ai ha−1), flufenacet (750 and 1,500 g ai ha−1) and acetochlor (1,700 and 3,400 g ai ha−1) applied preplant incorporated (PPI). Injury was evaluated by assessing visible injury symptoms, density, shoot biomass, height, seed moisture content, and seed yield. Azuki bean was more sensitive to the Group 15 herbicides than other dry bean market classes; the Group 15 herbicides caused a 12% reduction in azuki bean growth at 2 wk after emergence; growth reduction was ≤2% in the other bean classes. Flufenacet (2× rate) was the most injurious treatment, causing a 27% reduction in azuki bean yield. This study concludes that kidney, small red, and white bean have a sufficient margin of crop safety to flufenacet, acetochlor, and S-metolachlor applied PPI. Azuki bean was sensitive to flufenacet; additional research is needed to investigate azuki bean tolerance to acetochlor and S-metolachlor applied PPI.

Plant height in chickpea is a multivariate, dynamic trait, and shows differences in growth rate at different stages of plant development in different genotypes. In the majority of plant-breeding experiments, the phenotypic data on a quantitative trait measured at a fixed time point (generally at maturity) are used for quantitative trait loci (QTL) mapping. However, this method can result in missing important/major QTLs which are expressed at different time points and are not expressed at maturity. In the current study, using a set of 49 desi chickpea genotypes sown at three different durations for two successive years, we observed that heritability for plant height was highest at the 2 month stage in the normal sown trial, and at the 1 month stage in late-sown trials. However, heritability drastically declines at maturity, particularly due to heat stress with an increase in temperatures during the growing period. In the association analysis, it was also observed that almost all the marker–trait associations (MTAs) identified using endpoint phenotypes were identified using data obtained at different intervals. In addition, some novel and stage-specific MTAs were identified using phenotypic data recorded at monthly intervals. The results highlight the importance of multistage phenotyping for dynamic traits like plant height in germplasm characterization programmes.

Rapid growth of Palmer amaranth (Amaranthus palmeri S. Watson) poses a challenge for timely management of this weed. Dose–response studies were conducted in 2017 and 2018 under field and greenhouse conditions near Garden City and Manhattan, KS, respectively, to evaluate the efficacy of dicamba to control ≤10-, 15-cm, and 30-cm-tall A. palmeri, which mimics three herbicide application timings: on-time application (Day 0) and 1- (Day 1) and 4-d (Day 4) delays. Visual injury rating and reduction in shoot biomass (% of nontreated), and mortality were assessed at 4 wk after treatment using a three- and four-parameter log-logistic model in R. Increasing dicamba doses increased A. palmeri control regardless of plant height in both the field and greenhouse studies. The results suggest that delaying application 1 (15 cm) and 4 d (30 cm) resulted in 2- and 27-fold increases in the effective dose of dicamba on A. palmeri, respectively, under field conditions. However, in the greenhouse, for the same level of A. palmeri control, more than 1- and 2-fold increases in dicamba dose, respectively, were required. Similarly, the effective dose of dicamba required for 50% reduction in A. palmeri shoot biomass (GR50) increased more than 4- and 8-fold or more than 1- and 2-fold when dicamba application was delayed by 1 (15 cm) and 4 d (30 cm), in the field or in the greenhouse, respectively. To understand the basis of increased efficacy of dicamba in controlling early growth stages of A. palmeri, dicamba absorption and translocation studies were conducted. Results indicate a significant reduction in dicamba absorption (7%) and translocation (15%) with increase in A. palmeri height. Therefore, increased absorption and translocation of dicamba results in increased efficacy in improving A. palmeri control at early growth stages.

Sensitive cotton varieties planted into soil treated with 2,4-D or dicamba utilized in burndowns can result in stunting and stand loss if use rate is too high and the plant-back interval is too short. The objective of this study was to evaluate cotton stunting and yield responses resulting from 2,4-D or dicamba residues in soil after preplant burndown applications at three locations in 2016 and 2017. Treatments with 2,4-D included 532 and 1,063 g ae ha−1 applied 3 wk before planting (WBP) and 53, 160, 266, 532, 1,063 g ae ha−1 applied at planting. Dicamba treatments included 560 and 1,120 g ae h−1 applied 3 WBP and 56, 168, 280, 560, 1,120 g ae ha−1 applied at planting. Dicamba or 2,4-D treatments applied 3 WBP resulted in no adverse effects on cotton stand, plant height, or yield. Dicamba 560 g ae h−1 applied at planting reduced cotton stand by 36% at 21 to 24 d after planting (DAP) over all locations in 2016. In 2017, stands were reduced by dicamba at 168, 280, 560, and 1,120 g ae ha−1 by 17% to 25% at 20 to 23 DAP. Moreover, cotton stands were not affected by 2,4-D in 2016, and only 266, 532, and 1,063 g ae ha−1 of 2,4-D caused stand reductions of 26% to 36% at 20 to 23 DAP over all locations in 2017. Dicamba at 560 g ae ha−1 at planting was the only treatment in this study that reduced plant height. Although stand losses were observed in both years, no yield loss occurred. The data suggest that stunting and stand reduction may occur if susceptible varieties are planted soon after burndown applications with 2,4-D or dicamba, but yield may not be affected after a full growing season. Dicamba showed greater potential to cause stunting and stand reduction than 2,4-D.

Crop plants have been used as mimic weeds to substitute for real weeds in competition studies. These mimic weeds have the advantages of availability of seed, uniform germination and growth, and the potential to confer better experimental controllability and repeatability. However, the underlying assumption that the competitive effects of mimic weeds are similar to real weeds has not been tested. We compared a range of morphological traits (plant height, node and leaf number, leaf area, leaf size, and dry weight) between the mimic weeds and real weeds: Japanese millet vs. junglerice, mungbean vs. bladder ketmia, and common sunflower vs. fierce thornapple. The impact of these mimic and real weeds on cotton was also assessed. There were similarities and differences between the mimic and real weeds, but impact on cotton lint yield was most closely associated with weed height and dry weight at mid-season. Mimic weeds may be satisfactorily substituted for real weeds in competition experiments where seasonal and environmental conditions are not limiting, such as with fully irrigated cotton, provided the plants have similar dry weight and height at mid-season. Alternatively, one can account for the differences in dry weight and height. We define here a generalized relationship estimating the yield loss of high-yielding, irrigated cotton from weed competition over a range of weed dry weights and heights, allowing extrapolation from the results with mimic weeds to the competitive effects of a range of weeds.

The influence of ammonium sulfate on the activity of sethoxydim on wild oats and barley was examined under field conditions in 1989 and 1990. A chlorophyll assay, together with plant height and dry weight determinations, was used to quantify the visual ratings for sethoxydim activity. Ammonium sulfate enhanced the activity of 75 and 150 g ai ha-1 sethoxydim in 1989. In 1990, ammonium sulfate increased the activity of the lower rate of sethoxydim only. Of the three quantitative assays, chlorophyll concentration alone differentiated the more rapid development of injury symptoms with added ammonium sulfate that was observed in the visual ratings. The chlorophyll assay was not better than the visual rating assessment, however, and appears to offer no advantages that would justify the time required.

Yellow nutsedge (Cyperus esculentus L. # CYPES) was hoed in two cotton (Gossypium hirsutum L. ‘Acala SJ-2′) fields each year (1979 to 1981) for 2 to 12 weeks after crop emergence to evaluate the influence of several nutsedge-free periods on the growth and reproduction of nutsedge and yields of seed cotton. Compared to the control (plots cultivated but not hoed), a 2-week nutsedge-free period reduced the average number of nutsedge shoots at harvest by 52% (61 vs 29 shoots/m2). Additional hoeings for 4 to 12 weeks further reduced populations by 67 to 87%. Compared to tubers counted in the spring, populations of tubers in control plots increased 3- to 12-fold by harvest. However, compared to control plots, two weekly hoeings reduced tuber populations at harvest by 70 to 90% (treatment average of 884 vs 221 tubers/m2), and additional hoeings tended to reduce, or reduced, tuber populations further (75 to 98% reduction). When cotton yields were reduced in control plots in 1979 and 1980, a 2- to 6-week nutsedge-free period substantially decreased yield losses. Averaged over six locations, yields in plots with a 4- to 12-week nutsedge-free period were greater than yields of control plots.

Field studies at Arlington, WI, and LeSueur, MN, were conducted in 1996 and 1997 to evaluate tolerance of six sweet corn hybrids to RPA 201772 applied preemergence at 79 to 210 g/ha. Both years the most sensitive hybrid at the Wisconsin site was ‘Zenith,’ with yield reductions of 14 and 22% at 210 g/ha (twice the labeled rate). ‘Excellency,’ ‘Green Giant 43,’ and ‘Jubilee’ tolerated RPA 201772 at 158 g/ha or less. The least tolerant hybrids in Minnesota were ‘Green Giant 6′ and Jubilee, and the most tolerant hybrids were Green Giant 43 and ‘Rogers 9056.’ Injury from RPA 201772 increased as application dose increased. The greatest risk of injury from RPA 201772 appear to be with Green Giant 6, Zenith, and Jubilee, especially on coarser textured soils with low organic matter. Excellency, Green Giant 43, and Rogers 9056 appeared to be the most tolerant. Because of the differential hybrid response to RPA 201772 across sites and years, more hybrid response data needs to be generated before RPA 201772 is labeled in sweet corn.

Greenhouse and field research evaluated yellow nutsedge growth, vegetative control, and tuber production after application of glyphosate, various acetolactase synthase (ALS)–inhibiting herbicides, and tank mixtures thereof. Yellow nutsedge was controlled by the herbicides halosulfuron at 35 g ai/ha, chlorimuron at 12 g ai/ha, and imazethapyr–imazapyr at 62 g ai/ha (> 70% control); imazethapyr at 70 g ai/ha, glyphosate at 840 g ae/ha, cloransulam at 17.5 g ai/ha, and rimsulfuron at 17.5 g ai/ha (40 to 70% control); and imazamox at 45 g ai/ha (< 40% control). Compared with the untreated control, tuber fresh weight in the field was reduced 45 to 91%, and tuber density was reduced 33 to 90% by all herbicide treatments 42 wk after treatment (WAT) except imazamox and rimsulfuron. Tuber sprouting was reduced to 19% in plots treated with halosulfuron and pyrithiobac compared with untreated yellow nutsedge 42 WAT. Chlorimuron and imazethapyr–imazapyr controlled yellow nutsedge at least 90%, prevented panicle formation, and reduced tuber density and fresh weight by 90% or more 14 WAT in the greenhouse. The addition of glyphosate to cloransulam or imazethapyr increased yellow nutsedge control and reduced tuber density and fresh weight when compared with either ALS-inhibiting herbicide or glyphosate applied alone. Tuber density data indicated that there were 8 tubers for every gram of tubers harvested. Yellow nutsedge height was 15 to 20 cm 4 to 5 wk after tillage, using growth analysis data. Long-term yellow nutsedge management may be aided with treatments that reduce tuber production.

The effects of MT-101 and its herbicidally active form, NOP, on the germination and seedling growth of hemp sesbania and rice were investigated. MT-101 decreased the germination of hemp sesbania by 57 and 90% at 0.05 and 0.5 mM, respectively, 1 d after treatment (DAT) in petri dishes. The germination, however, recovered such that there was no significant difference between treatments 4 to 6 DAT. NOP completely inhibited the germination of hemp sesbania at both 0.05 and 0.5 mM 1 DAT. However, germination also similarly recovered, and there was no difference between treatments 4 to 6 DAT. Neither MT-101 nor NOP decreased the germination of rice 3 to 6 DAT. In greenhouse trials preemergence (PRE) application of MT-101 at 2.25 kg ai ha−1 decreased the density (number of plants pot−1), plant height, and dry weight of hemp sesbania by 85, 67, and 91%, respectively. When applied postemergence (POST), MT-101 at 2.25 kg ha−1 decreased the density, plant height, and dry weight by a maximum of 58, 61, and 82%, respectively, indicating that MT-101 may have greater activity when applied PRE. NOP had greater activity than MT-101 on hemp sesbania. NOP at 2.25 kg ai ha−1 decreased the density, plant height, and dry weight of hemp sesbania 99, 78, and 97%, respectively, with PRE application. A POST application of NOP at 2.25 kg ha−1 decreased the dry weight of hemp sesbania 91 to 94%. A PRE application of NOP at 2.25 kg ha−1 decreased the dry weight of rice by 58%. Rice was not affected by POST applications of MT-101 but was affected slightly by NOP. These results suggest that MT-101 is a possible weed control agent in rice.

A field experiment was conducted in 1996 and 1997 to determine snap bean tolerance to halosulfuron based on crop injury, height, and yield. Halosulfuron was applied preemergence (PRE), postemergence (POST), and sequentially PRE followed by (fb) POST at 35, 53, and 70 g ai/ha, respectively. For comparison, a hand-weeded check was included. When data were averaged across years and halosulfuron rates, halosulfuron PRE, POST, and PRE fb POST provided similar yellow nutsedge control (74 to 82%) at snap bean harvest. Halosulfuron PRE resulted in 4% snap bean injury at harvest. Similarly, halosulfuron PRE fb POST resulted in 5% injury, while halosulfuron POST caused the most damage at 8%. Snap bean height at harvest was reduced 14% with halosulfuron POST compared to the weed-free check, with only 5 and 6% reduction caused by halosulfuron PRE and PRE fb POST, respectively. Halosulfuron POST reduced yield 39% compared to the weed-free check, while the PRE and PRE fb POST application timings produced yield similar to the check. When averaged across years and halosulfuron application timings, an increase in halosulfuron rate had no effect on yellow nutsedge control or snap bean yield. A linear trend was found for snap bean injury and plant height at harvest with snap bean injury increasing with an increase in halosulfuron rate while snap bean plant height decreased with an increase in halosulfuron rate. Application of halosulfuron PRE is the safest means to control yellow nutsedge in snap bean in North Carolina.

Field studies were conducted in 1998 and 1999 at Simcoe and Exeter, ON, to evaluate the tolerance of nine sweet corn cultivars, representing a range of genotypes, to RPA 201772 applied preemergence at 105 and 210 g ai/ha. The location × year interaction was significant for visible plant injury, plant height, and yield. All cultivars showed significant injury at Simcoe in 1999, especially at 210 g/ha. Calico Belle was the most sensitive cultivar, with RPA 201772 resulting in severe injury at Simcoe in 1999. Increased injury in 1999 was due to significant rainfall (48.5 mm) within 10 d of RPA 201772 application at Simcoe. Calico Belle also showed injury at Exeter in 1999 and at Simcoe in 1998. Plant height of all cultivars was reduced at the Simcoe location in 1999. Yield of five cultivars was also reduced at Simcoe in 1999. Sensitivity to RPA 201772 increased as application rate increased. Plant height and yield was not reduced at Exeter.

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.

Field studies were conducted in 1999 and 2000 at Simcoe, Ridgetown, and Exeter, Ontario, to evaluate the tolerance of nine sweet corn cultivars to mesotrione, applied preemergence (PRE) at 140 and 280 g ai/ha and postemergence (POST) at 100 and 200 g ai/ha. Urea ammonium nitrate fertilizer (28%) at 2.5% (v/v) and crop oil concentrate at 1% (v/v) were added to POST applications of mesotrione only. All cultivars were tolerant to mesotrione applied PRE. There was no injury, or reductions in plant height or yield with PRE applications of mesotrione at any location in either year. POST applications of mesotrione, particularly at 200 g/ha, caused significant phytotoxicity to ‘Calico Belle’ and ‘Del Monte 2038’. Other cultivars also showed phytotoxic symptoms; however, this injury was much reduced and did not occur at all locations each year. Sweet corn injury by mesotrione increased as rate increased. Del Monte 2038 also had significantly reduced plant height and yields. Other cultivars had no plant height or yield reductions because of POST applications of mesotrione.

This study was conducted to evaluate the tolerance of two black bean cultivars, AC Harblack and Midnight Black Turtle, to preplant incorporated (PPI) and preemergence (PRE) applications of S-metolachlor at 1.6 and 3.2 kg ai/ha, imazethapyr at 0.075 and 0.15 kg ai/ha, and S-metolachlor plus imazethapyr at 1.6 plus 0.075 and 3.2 plus 0.15 kg ai/ha, respectively, at Exeter and Ridgetown, Ontario, Canada, in 2001 and 2002. There were generally no differences between the two cultivars in their responses to the herbicide treatments. PPI and PRE applications of S-metolachlor did not reduce black bean growth or yield. The PPI and PRE applications of imazethapyr alone or in tank mixture with S-metolachlor at the low and high rates did not have a significant effect on plant height, dry weight, seed moisture content, or yield at Ridgetown but caused as much as 14% visual crop injury at Exeter and reduced plant height, dry weight, and yield as much as 25, 40, and 49%, respectively. The higher rate of either herbicide alone or in tank mixture generally caused greater crop injury than the lower rate. At sites where there was a significant difference, the PPI application caused less crop injury than the PRE application. On the basis of these results, the PPI and PRE applications of S-metolachlor can be applied safely at the recommended label rate for the control of annual grass in black beans. However, the PPI and the PRE applications of imazethapyr alone and in tank mixture with S-metolachlor require careful application to avoid spray overlaps because there is potential for crop injury and yield reduction under some environmental conditions.

Studies were conducted to evaluate density-dependent effects of tropic croton on weed and peanut growth and peanut yield. Tropic croton remained taller than peanut throughout the growing season, yet tropic croton density did not affect peanut or tropic croton heights. Tropic croton biomass per plant decreased linearly with increasing plant density. Peanut pod weight decreased linearly 4.7 kg/ha with each gram of increase in tropic croton biomass per meter of crop row. The rectangular hyperbola model was used to describe effects of tropic croton density on percent peanut yield loss. Estimated coefficients for a (maximum yield loss) and i (yield loss per unit density as density approaches zero) were 81 and 26 in 1988, 41 and 33 in 1989, and 33 and 61 in 1998, respectively. Although a and i values varied between years, yield loss predictions were stable between years at weed densities below two plants per meter of crop row. Even though the results show that tropic croton is less competitive than many broadleaf weeds in peanut, it has potential to substantially reduce yields and subsequently reduce economic return.

We conducted a series of field experiments to determine the role of several factors that might contribute to the inconsistent control of common lambsquarters with glyphosate. Experiments in 2006 and 2007 determined common lambsquarters response to glyphosate under a wide range of measured environmental conditions. Glyphosate was applied at 0.84 kg ae ha−1 plus 3.8 kg ha−1 ammonium sulfate (AMS) to 10-cm-tall plants on 18 dates in each year and to 20-cm-tall plants on 18 dates in 2007. Control was less for six application dates relative to control for 48 other dates. Poor control was attributed to rainfall on one of these six dates, but for the other five dates, regression analysis did not identify any significant relationships between environmental conditions (relative humidity, temperature at time of treatment, or minimum and maximum temperature pre- and posttreatment) and control, even though a wide range of conditions occurred. To determine the effects of plant growth stage on control, glyphosate was applied at 0.1 to 3.2 kg ha−1 plus 3.8 kg ha−1 AMS to 10- and 20-cm-tall plants at four sites. The glyphosate ED50 value (the effective dose that reduced shoot mass by 50% relative to nontreated plants) was 1.9 to 3.0 times greater for 20- than 10-cm-tall plants in three site-years, but was not affected by plant height in one site-year. We also conducted experiments to determine the effect of rainfall on glyphosate efficacy. Across years, common lambsquarters control increased from 44 to 75% as the interval between glyphosate application (0.84 kg ha−1 + 3.8 kg ha−1 AMS) and simulated rainfall increased from 0.5 to 4.0 h, respectively. Our results did not identify environmental conditions that explained reduced glyphosate efficacy in all cases, but they suggest that rainfall after application and plant height can be important factors contributing to the inconsistent control of common lambsquarters.

Amaranthus species, commonly referred to as “pigweeds,” are among the most troublesome weeds in many crop production systems. Effective control of these species often begins with an understanding of their biological and reproductive characteristics. At two sites in Missouri, six pigweed species (redroot pigweed, common waterhemp, spiny amaranth, tumble pigweed, smooth pigweed, and Palmer amaranth) were established in 60-m rows spaced 1.5 m apart. At biweekly intervals, plant heights and dry weights were recorded for each species; seed numbers were estimated at the end of the growing season. Dry weight of Palmer amaranth was up to 65% greater than those of all other species 2 wk after planting (WAP). Palmer amaranth biomass accumulation remained greater than those of the other species throughout the season and at the end of the season was 1.2- and 2.7-fold greater than those of redroot and tumble pigweed, respectively. Palmer amaranth was approximately 10 cm tall 2 WAP (37% taller than the next tallest species, redroot pigweed) and approximately 24 cm tall 4 WAP (45% taller than redroot pigweed). In contrast, common waterhemp had not emerged 2 WAP, and plant dry weight 4 WAP was approximately 11 and 26% those of Palmer amaranth and redroot pigweed, respectively. Final plant height ranged from 58 (tumble pigweed) to 208 cm (Palmer amaranth). Redroot pigweed, smooth pigweed, common waterhemp, and Palmer amaranth plants each produced over 250,000 seeds plant−1. Spiny amaranth and tumble pigweed produced approximately 114,000 and 50,000 seeds plant−1, respectively. Common waterhemp produced 535 seeds g−1 of total plant dry weight; this seed production was 1.4-, 1.4-, 2.0-, 3.4-, and 3.4-fold greater than those of redroot pigweed, smooth pigweed, Palmer amaranth, tumble pigweed, and spiny amaranth, respectively. Because the timing for many postemergence herbicides depends on weed height, rapid growth shortly after emergence reduces the time frame for optimum control of species such as Palmer amaranth. Delayed emergence also could result in escaped common waterhemp. Escape of only a few plants could result in a rapid increase in seed populations in the soil seed bank and may select for late-emerging biotypes.