Wk After Planting Research Articles

Live and Killed Hairy Vetch Cover Crop Effects on Weeds and Yield in Glyphosate-Resistant Corn

A 2-yr field study was conducted from 2002 to 2003 on a Dundee silt loam soil at the Southern Weed Science Research Unit Farm, Stoneville, MS (33°26′N latitude), to examine the effects of hairy vetch cover crop (hairy vetch killed at corn planting [HV-K], hairy vetch killed in a 38-cm-wide band centered over the crop row at corn planting [HV-B], hairy vetch left alive [HV-L], and no hairy vetch [NHV]) and glyphosate postemergence (broadcast, banded, and no herbicide) application on weed control and yield in glyphosate-resistant corn. Two applications of glyphosate at 0.84 kg ae/ha were applied 3 and 5 wk after planting (WAP) corn. Hairy vetch dry biomass was higher in HV-L (4,420 kg/ha) and HV-B (4,180 kg/ha) than in HV-K (1,960 kg/ha) plots at 7 WAP. Hairy vetch reduced densities of pitted morningglory, prickly sida, and yellow nutsedge in HV-B and HV-L compared with NHV plots, but hairy vetch had no effect on densities of barnyardgrass, johnsongrass, and large crabgrass at 7 WAP regardless of desiccation. Total weed dry biomass at 7 WAP was lower in HV-B and HV-L than in HV-K and NHV plots. Corn yield was higher in HV-K (10,280 kg/ha) than in HV-B (9,440 kg/ha) and HV-L (9,100 kg/ha), and yields were similar between HV-K and NHV (9,960 kg/ha). Glyphosate applied broadcast resulted in the highest corn yield (11,300 kg/ha) compared with a banded application (10,160 kg/ha). These findings indicate that hairy vetch cover crop has the potential for reducing the density of certain weed species in glyphosate-resistant corn production systems; however, optimum weed control and higher yield were obtained when glyphosate was used.

Residual Effect of 2,4-D on Whole-Stalk– and Billet-Planted Sugarcane

Field studies conducted for two growing seasons evaluated the effect of 2,4-D applied at 1.6 kg ai/ha to ‘LCP 85-384’ sugarcane 7, 5, 3, and 1 wk before planting (WBP). Sugarcane was planted in mid September using both whole stalks and billet (45 cm) stem sections. When 2,4-D was applied 5 wk or closer to planting, sugarcane shoot emergence and population averaged across planting methods and years were reduced up to 28 wk after planting (WAP) relative to the nontreated control. By 52 WAP, sugarcane had compensated and stalk population was equivalent among treatments. Sugarcane height in response to 2,4-D varied between years, and only in 2001 at 52 WAP was a height reduction observed when 2,4-D was applied 1, 3, or 5 WBP. Crop injury in 2001 was further reflected in reduced sugarcane yield (at least 11%) and sugar yield (at least 12%) more than 1 yr after 2,4-D had been applied 5 wk or closer to harvest of sugarcane for seed. Sugarcane and sugar yields were equivalent for the nontreated control and the 7 WBP 2,4-D treatment in 2001, but 2,4-D application in 2002 did not negatively affect yield. Even though sugarcane shoot populations across the growing seasons were consistently higher for the billet planting system, yields averaged across 2,4-D application timings were greater for billets (18%) compared with whole stalks only for the first year. Because 2,4-D can have a residual effect on sugarcane yield more than 1 yr after the initial foliar application, a 7-wk period should be allowed between herbicide application and harvest of LCP 85-384 for billet or whole-stalk planting.

Manual Control of Thorny Mimosa (Mimosa invisa) in Cassava (Manihot esculenta)1

The optimum weeding regime for thorny mimosa control in cassava established at 10,000 plants/ha was studied at Ibadan, Nigeria (7°22½′N, 3°50½′ E), a humid tropical environment. The study compared six weeding regimes, each comprising manual removal of thorny mimosa three times at different intervals within 13 wk after planting (WAP). Cassava vegetative growth recovered from thorny mimosa interference when the first weeding occurred within 5 WAP, but interference for more than 5 WAP reduced storage root yield. Allowing thorny mimosa infestation after 11 WAP had no effect on cassava growth or root yield. Manual removal of thorny mimosa at 4, 7, and 11 WAP consistently gave the highest cassava root yield. Nomenclature: Thorny mimosa (or giant sensitive plant), Mimosa invisa Mart.; cassava, Manihot esculenta Crantz ‘TMS 30572’. Additional index words: Canopy closure, cassava vegetative growth, storage root yield, weed interference. Abbreviations: IAR & T, Institute of Agricultural Research and Training; MAP, ...

Weed Management in Strip Tillage Corn

Field studies were conducted in 2000 and 2001 to determine if differences exist in weed emergence patterns, weed control, corn (Zea mays L.) plant population, and grain yield in strip tillage, conventional tillage, and no‐tillage production. Weed emergence peaked at 2 and 4 wk after planting (WAP) in 2000 and 2001, respectively. Weed emergence at 2 WAP in 2000 was greater in conventional tillage compared with no‐tillage and strip tillage. Tillage system did not affect total weed species emergence in 2001. In both years, lower control of giant foxtail (Setaria faberi Herrm.) and common waterhemp (Amaranthus rudis Sauer) occurred following acetochlor {[2‐chloro‐N‐(ethoxymethyl)‐N‐(2‐ethyl‐6‐methylphenyl)acetamide]} plus atrazine {[6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine]} applied pre‐emergence in no‐tillage compared with conventional tillage. Control of common waterhemp in 2001 and giant foxtail in both years was similar with glyphosate [N‐(phosphonomethyl)glycine] applied postemergence regardless of tillage system. Corn population was greater in conventional tillage compared with no‐tillage in 2000 and greater than the population in no‐tillage and strip tillage in 2001. When averaged across weed management strategies, corn yield was greatest in strip tillage in 2000 and conventional tillage in 2001.

Competition and control of smellmelon (Cucumis melo var. dudaim Naud.) in cotton

Smellmelon is becoming a problem weed in southern Texas and Louisiana cotton-producing areas. Experiments evaluating the density and duration of smellmelon competition are necessary for the recommendation of appropriate control practices to minimize yield loss. In 1999 and 2000, field experiments were initiated to determine the density, critical period of competition, and potential control measures for smellmelon in cotton. Although the degree of competition differed between the years, similar trends were observed with respect to smellmelon density. As few as 2 or 3 smellmelon plants 10 m−1 row reduced yield at least 17% each year. When densities were increased to 5 or 10 plants 10 m−1 row, yield reductions increased to at least 34%. Results from the duration of smellmelon competition in 1999 and 2000 indicated that cotton should remain smellmelon free for 1 to 7 wk after planting (WAP) and 2.5 to 6 WAP, respectively. Results from the control studies indicate that smellmelon size at application influences control. Early-season control strategies are necessary to reduce yield losses associated with smellmelon competition.

Comparative growth of six Amaranthus species in Missouri

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.

Rice (Oryza sativa) Response to Rotational Crop and Rice Herbicide Combinations1

A 2-yr field study was conducted to evaluate the response of rice to rotational crop herbicides in combination with rice herbicides in water-seeded culture. Fluometuron, imazethapyr, metolachlor, and norflurazon were applied at 0.5, 0.25, 0.125, and 0.063 times the recommended use rates preplant incorporated (PPI) to simulate herbicide carryover from previous crops. Molinate and thiobencarb at 4.5 kg ai/ha were applied PPI, and quinclorac at 0.43 kg ai/ha postemergence. No interaction between rice herbicides and rotational crop herbicides was observed for rice injury at 4 wk after planting (WAP), plant dry weight, stand, and height at 8 WAP, or rice grain yield. However, rice heading was delayed with some rotational crop herbicide and rice herbicide combinations. Fluometuron at the 0.5 and 0.25× rates injured rice 64 and 21% at 4 WAP, and reduced rice yield 96 and 20%, respectively. At 4 WAP, metolachlor at the 0.5 and 0.25× rates injured rice 93 to 29%, and reduced rice yield 85 to 20%, respectively. An ...

Horsenettle (Solanum carolinense) Control With a Field Corn (Zea mays) Weed Management Program1

Field studies were conducted at three sites in Delaware from 1997 to 1999 to evaluate fall glyphosate applications followed by postemergence (POST) field corn herbicides on horsenettle control and shoot densities. The fall treatments were either no fall treatment or 2.2 kg ai/ha glyphosate as a preharvest treatment in soybean at least 2 wk prior to frost. POST treatments were applied the following spring in no-tillage field corn 4 wk after planting (WAP) and included glyphosate, CGA 152005 plus primisulfuron plus dicamba, halosulfuron plus dicamba, atrazine plus dicamba, nicosulfuron plus rimsulfuron plus atrazine plus dicamba, or nicosulfuron plus dicamba. The fall glyphosate application delayed horsenettle shoot emergence in the spring and resulted in > 90% control at the time of POST in-crop applications. At 11 WAP, the highest horsenettle control was observed with a fall glyphosate application followed by POST in-crop treatments of CGA 152005 plus primisulfuron plus dicamba, halosulfuron plus dicamba,...

Effects of Cereal and Legume Cover Crop Residues on Weeds, Yield, and Net Return in Soybean (Glycine max)1

A 2-yr field study was conducted during 1998 and 1999 at Stoneville, MS, on a Dundee silt loam to determine weed control, yield, and net return associated with winter cover crops in soybean. Cover crop systems included Italian ryegrass, oat, rye, wheat, hairy vetch, crimson clover, subterranean clover, no-cover crop conventional tillage (CT), and no-cover crop no-tillage (NT), all with standard preemergence (PRE), postemergence (POST), PRE POST, and no-herbicide weed management. Oat (11.1 Mg/ha) had highest dry biomass compared to all other cover crops (6.0 to 7.6 Mg/ha) at soybean planting. Biomass decreased 9 wk after planting (WAP) compared to the respective biomass at soybean planting in all cover crops. Italian ryegrass and rye biomass decay was slow and about two-thirds of plant residue persisted at 9 WAP. Cover crops had no effect on densities of barnyardgrass, prickly sida, and yellow nutsedge, but altered the density of browntop millet. Total weed biomass was higher in rye, wheat, and subterranean clover than in Italian ryegrass cover crop systems, and higher with the PRE-only vs. POST-only or PRE POST programs at 10 WAP soybean. Soybean yield decreased in the order of no-cover crop NT ≥ no-cover crop CT ≥ hairy vetch ≥ crimson clover ≥ rye ≥ oat ≥ wheat ≥ subterranean clover > Italian ryegrass. None of the cover crop systems gave soybean yield higher than the no-cover crop CT system in the absence of herbicides. Under a PRE-only program, all cover crop systems had lower yield compared to the no-cover crop CT system. When late-emerged weeds were controlled with POST applications (POST-only or PRE POST programs), all cover crops, except Italian ryegrass, had no detrimental effect on soybean yields, which were not different from no-cover crop CT plots. In cover crops, input costs were high due to additional cost of seeds, planting, and desiccation. Net return was highest in no-cover crop NT ($105/ha) followed by no-cover crop CT ($76/ha) system. Net returns were negative for all cover crops and losses were highest in crimson clover (−$62/ha) and subterranean clover (−$161/ha).Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; browntop millet, Brachiaria ramosa (L.) Stapf # PANRA; prickly sida, Sida spinosa L. # SIDSP; yellow nutsedge, Cyperus esculentus L. # CYPES; crimson clover, Trifolium incarnatum L. ‘Dixie’; hairy vetch, Vicia villosa Roth; Italian ryegrass, Lolium multiflorum Lam. ‘Gulf’; oat, Avena sativa L. ‘Bob’; rye, Secale cereale L. ‘Elbon’; soybean, Glycine max (L.) Merr. ‘DP 3588’; subterranean clover, Trifolium subterraneum L. ‘Mount Barker’; wheat, Triticum aestivum L. ‘Cocker 9803’.Additional index words: Allelopathy, conventional tillage, herbicide, integrated weed management, mulch, net return, no-tillage, weed emergence, weed biomass.Abbreviations: ANOVA, analysis of variance; CT, conventional tillage; NT, no-tillage; POST, postemergence; PRE, preemergence; WAP, weeks after planting soybean.

Tolerance of Direct-Seeded Paprika Pepper (Capsicum annuum) to Clomazone Applied Preemergence1

Field experiments were conducted from 1997 to 1999 at Ejea and at Valdegon (Spain) to study weed control and tolerance of direct-seeded pepper ‘Agridulce SIA’ to clomazone alone or with linuron, napropamide, or pendimethalin. The main weeds at Ejea were redroot pigweed, Diplotaxis erucoides, common purslane, and ivyleaf speedwell, while at Valdegon they were Solanum physalifolium and common purslane. Pepper was tolerant to clomazone applied at 0.18 kg ai/ha, but weed control was less than 77%. Increasing the rate of clomazone to 0.36 kg/ha controlled weeds at least 85% and did not injure pepper. Clomazone at 0.54 and 0.72 kg/ha injured pepper 6 wk after planting (WAP), but plants recovered and the dry weight and yield of paprika were not affected. Napropamide at 2.03 kg ai/ha applied with clomazone improved the control of D. erucoides. Addition of pendimethalin at 0.17 to 0.25 kg ai/ha to clomazone did not improve weed control and increased pepper injury 6 WAP in 1 of 2 yr, but yield was not affected. Linuron at rates ranging from 0.08 to 0.13 kg ai/ha used in combination with clomazone provided complete weed control but injured pepper the most (34 to 88%) and reduced pepper stand by 50% in 1 yr.Nomenclature: Clomazone; linuron; napropamide; pendimethalin; common purslane, Portulaca oleracea L. #3 POROL; Diplotaxis erucoides (L.) DC.; ivyleaf speedwell, Veronica hederifolia L. # VERHE; redroot pigweed, Amaranthus retroflexus L. # AMARE; Solanum physalifolium Rusby; paprika pepper, Capsicum annuum L., ‘Agridulce SIA’.Additional index words: Weed control, Convolvulus arvensis, CONAR.Abbreviations: PRE, preemergence; WAP, weeks after planting.

Weed Management Systems Utilizing Glufosinate-Resistant Corn (Zea mays) and Soybean (Glycine max)1

Abstract: Field studies were conducted from 1996 to 1998 at Queenstown, MD to evaluate weed management programs utilizing single and multiple applications of glufosinate, with and without preemergence (PRE) and postemergence herbicides in both glufosinate-resistant (GR) corn and soybean. No herbicide treatment resulted in corn or soybean injury greater than 10% at 7 d after treatment (DAT). No injury was visible at 14 DAT for both GR corn and soybean. In corn, all treatments provided 72% or greater giant foxtail control 14 wk after planting (WAP). With soybean, in 1996 and 1998, few differences in giant foxtail control were observed, with all treatments providing at least 93% giant foxtail control 12 WAP. For common lambsquarters control in GR corn, there were no differences in control among treatments for 1996 and 1997. Over 80% common lambsquarters control was observed both years with all treatments 14 WAP. Glufosinate + atrazine at 0.4 kg/ha + 1.7 kg ai/ha, respectively, provided 100% season-long commo...

Use of preplant sulfentrazone in no-till, narrow-row, glyphosate-resistantGlycine max

Abstract Field studies were conducted in 1998 and 1999 to evaluate crop response, weed control, Glycine max yield, and economic returns with sulfentrazone alone and tank-mixed with glyphosate, cloransulam, or chlorimuron at two preplant application timings in no-till, narrow-row, glyphosate-resistant G. max. No significant crop injury was observed. Setaria faberi and Polygonum pensylvanicum control 5 wk after planting (WAP) was generally greater with sulfentrazone applied early preplant (EPP) than with sulfentrazone applied at planting (AP). When applied AP, glyphosate plus sulfentrazone provided greater S. faberi control than sulfentrazone alone. Control of Amaranthus rudis, Ambrosia artemisiifolia, and Ipomoea hederacea was greater in 1998 than in 1999 because of more timely early-season precipitation. Sulfentrazone-based programs provided 80 to 100% control of A. rudis in 1998, but control in 1999 ranged from 72 to 95% at Columbia and 46 to 83% at Novelty. Cloransulam alone, at either application timin...

ALS-resistantHelianthus annuusinterference inGlycine max

Field studies were conducted to determine the effect of early-season and early- plus late-season acetolactate synthase–resistant Helianthus annuus interference on Glycine max and H. annuus growth and yield at two sites in Missouri. Helianthus annuus densities of 3 plants m−2 were established shortly after G. max emergence in all plots except the weed-free check. To study early-season interference, H. annuus were removed with postemergence glyphosate (0.84 kg ae ha−1) 2, 4, 6, and 8 wk after planting (WAP) and kept weed-free for the rest of the growing season. Glycine max yields were not different with 2, 4, 6, or 8 wk of early-season interference at either location. To study early- plus late-season interference, H. annuus densities were established at 3 plants m−2. They were then removed 2, 4, 6, or 8 WAP with glyphosate and subsequently reestablished at the same density within 2 wk after removal by newly emerging and transplanted H. annuus. These H. annuus were allowed to remain in the field for the remainder of the growing season. This provided a weed-free period of approximately 2 wk during the growing season beginning 2, 4, 6, or 8 WAP. Season-long interference and no-interference treatments were also included. Glycine max yields were reduced 47 to 72% with season-long interference. Helianthus annuus vegetative dry matter was approximately 56% lower at Columbia than at Miami. Glycine max yields tended to increase as the weed-free period was delayed into the growing season. Early-season weed-free periods (2 to 4 and 4 to 6 WAP) allowed H. annuus to become re-established before G. max formed a canopy and resulted in larger amounts of H. annuus biomass and seed production as well as G. max yield losses of 15 to 80%. Re-establishment of H. annuus in 6 to 8 WAP and 8 to 10 WAP weed-free treatments generally resulted in the plants surviving for only a few weeks after establishment and not producing seed or reducing G. max yield.

Effect of Seed Bank Augmentation on Herbicide Efficacy1

Abstract: Seeds of giant foxtail (Setaria faberi, 4,000 seeds/m2) or velvetleaf (Abutilon theophrasti, 3,000 seeds/m2) were added to the seed bank to determine the effect of increases in weed density on herbicide efficacy in corn (Zea mays). A herbicide program consisting of SAN 582 applied preemergence followed by a postemergence application of dicamba plus atrazine was evaluated at four levels (0.0, 0.3, 0.7 and 1.0 times the label rates). At a site with low initial weed densities, the addition of velvetleaf or giant foxtail seed to the seed bank did not influence herbicide efficacy at the 1.0× rate at 9 wk after planting (WAP). Giant foxtail densities were greater 9 WAP in augmented areas than in the native seed bank plots at both the 0.3× and 0.7× rates, whereas with velvetleaf, higher densities in augmented plots were seen only at the 0.3× rate. In areas with high native weed densities, addition of seed of either species resulted in an increase in final weed densities at all herbicide rates. Nomencla...

Effect ofGlycine maxcanopy characteristics,G. maxinterference, and weed-free period onSolanum ptycanthumgrowth

Additive and replacement series studies were conducted to investigate the effect of Glycine max cultivar canopy characteristics, interference, and weed-free period on the vegetative and reproductive growth of Solanum ptycanthum. Solanum ptycanthum established 0, 2, and 4 wk after planting (WAP) did not reduce seed yield of either Group II (Pioneer 9273) or Group IV (Asgrow 4715) varieties. The Group IV variety intercepted a greater percentage of light throughout the season. However, both varieties reduced growth of S. ptycanthum established 2 and 4 WAP, suggesting no disadvantage of Group II in suppressing S ptycanthum growth. The greenhouse and field replacement series experiments indicated that S. ptycanthum plants experienced greater intraspecific than interspecific competition; that is, S. ptycanthum grew more in mixed species competition than in monoculture. Under field conditions, G. max grew equally well in competition with S. ptycanthum or in monoculture. However, in the greenhouse G. max accumulated more biomass and fruit weight in monoculture vs. competition with S. ptycanthum. Relative yield total values (RYT) in the field supported greater productivity per unit area for mixed species competition when compared to G. max or S. ptycanthum grown in monoculture. Data from both studies suggested that S. ptycanthum did not reduce G. max yield when grown in the field. Regardless of maturity group, a fully developed G. max canopy reduced S. ptycanthum growth.

Evaluation of Several Herbicides for Burcucumber (Sicyos angulatus) Control in Corn (Zea mays)

A postemergence (POST) timing study was conducted on established populations of burcucumber (Sicyos angulatus) in corn (Zea mays), and a second study examined the residual activity of several herbicides for burcucumber control under greenhouse conditions. In the field study, flumiclorac, halosulfuron, primisulfuron, CGA 152005, and CGA 152005 + primisulfuron (45, 71, 40, 40, and 20 + 20 g ai/ha, respectively) were applied at two POST timings. CGA 152005, primisulfuron, and the combination provided greater than 85% control of burcucumber 14 wk after planting (WAP). Flumiclorac and halosulfuron provided 60% control or less by 8 WAP. Timing of the POST applications did not influence burcucumber control by 11 WAP with any herbicide. In the greenhouse, germinated burcucumber seeds were placed in soil treated with atrazine, chlorimuron, primisulfuron, or CGA 152005 at normal field use rates. All treatments provided similar residual control early; however by 4 wk after treatment (WAT), control from atrazine was less than 10% compared to 69% for chlorimuron and about 50% for primisulfuron and CGA 152005. This research suggests that CGA 152005 and primisulfuron can both be effective for managing burcucumber in corn, whereas flumiclorac and halosulfuron proved ineffective.

Broadleaf Weed Control with Sulfentrazone and Flumioxazin in No-Tillage Soybean (Glycine max)

Field trials were conducted at two sites in 1996 and 1997 to evaluate weed control and crop response to herbicide programs in no-till soybean that include flumioxazin or sulfentrazone alone and each herbicide tank-mixed with either chlorimuron or imazaquin. A prepackaged mixture of metribuzin plus chlorimuron also was included for comparison. Cool, wet conditions after herbicide application in both years were conducive to soybean injury up to 21% at 3 wk after planting (WAP). Flumioxazin and sulfentrazone alone provided ≥ 89% control of velvetleaf, Pennsylvania smartweed, and common cocklebur. Sulfentrazone alone provided greater control of common waterhemp, common cocklebur, and ivyleaf and pitted morningglories than flumioxazin. Flumioxazin provided greater control of common ragweed than sulfentrazone. The addition of chlorimuron to flumioxazin or sulfentrazone provided greater control of velvetleaf than flumioxazin or sulfentrazone alone. The addition of imazaquin or chlorimuron to flumioxazin provided greater control of common cocklebur than flumioxazin alone. The addition of imazaquin or chlorimuron to sulfentrazone provided greater control of common ragweed than sulfentrazone alone. The addition of chlorimuron or imazaquin to sulfentrazone or flumioxazin provided little or no additional control of pitted morningglory, common waterhemp, or Pennsylvania smartweed. Metribuzin plus chlorimuron provided control of velvetleaf, Pennsylvania smartweed, common ragweed, and common cocklebur that was equal to or better than the control provided by sulfentrazone or flumioxazin plus chlorimuron or imazaquin.

Time of hilling and interseeding affects weed control and potato yield

The current emphasis on reducing pesticide use has led to increased interest in alternative weed control methods. The purpose of this study was to evaluate the potential of hilling, in combination with subsequent interseeding of cover crops, to control weeds in potato and to determine the impact of these actions on potato yield and insects. Each cover crop, either hairy or lana vetch, oats, barley, red clover, or a combination of oats and hairy vetch, was interseeded, following hilling, 3, 4, or 5 wk after planting (WAP). Hilling and interseeding treatments were compared to a no-cover treatment and a chemical standard, metolachlor (1.7 kg ai ha−-1) plus linuron (1.7 kg ai ha−-1). Cultivation associated with the interseeding operation and cover crops reduced weed density 20 to 27% by 3 wk after interseeding. To prevent excessive competition, cereals interseeded 3 or 4 WAP and vetches interseeded 3 WAP were controlled at a height of 25 to 35 cm using fluazifop (0.22 kg ai ha−-1) plus metribuzin (0.28 kg ai ha−-1). Because of slow growth, it was necessary to control red clover (interseeded 3 WAP), only in 1996, at a height of 15 cm. Control of cereals resulted in a dead mulch that provided 0 to 95% weed control, whereas legumes regrew after herbicide application and provided 45 to 70% weed control. However, an adequate minimum of 70% weed control was achieved only with the chemical standard, cereals (1995 and 1996), and legumes (1996) interseeded 3 WAP when controlled with herbicides. In a dry season (1995), potato yields were highest with the chemical standard, whereas in a season with adequate precipitation (1996), potato yields equivalent to those of the chemical standard were obtained with early interseeding (3 WAP) of cereals. The observed changes in the densities of potato leafhopper and of its natural enemies were unlikely to have any effect on potato yield because of low overall insect populations. Thus, the results suggest that in good growing conditions, early (3 WAP) interseeding of cover crops supplemented with postemergence herbicides may both suppress weeds with 70% less herbicide (ai ha−-1) and provide yields comparable to those associated with conventional potato production.

Variety and Maturity Affect Amaranth Forage Yield and Quality

Little information is available on the forage potential of improved amaranth (Amaranthus sp.) cultivars. Our objectives were to determine the effect of maturity on forage yield and forage quality of A. cruentus L. and A. kypochondriacus L. and to evaluate forage quality of leaf, stem, and inflorescence fractions at two maturity stages. Field experiments were conducted on a Waseca silt loam (fine-loamy, mixed, mesic Cumulic Haplaquolls) and on a Waukegan silt loam (fine-silty over sandy skeletal, mixed, mesic Typic Hapludoll). Amaranth dry matter yield was 1.3 tons/acre at 8 wk after planting (WAP), increased with each subsequent harvest, and peaked at 4.4 tons/acre and 4.1 tons/acre at 16 and 14 WAP in 1988 and 1989, respectively. Forage quality decreased as maturity increased from bud to flowering. Crude protein (CP) was greatest (average of 23%) at 8 WAP when amaranth was vegetative and decreased with maturity to about 13%. Forage neutral detergent fiber (NDF) and acid detergent fiber concentrations (ADF) were about 36 and 26% at 8 WAP and increased as plants matured. Amaranth had nearly equal proportions of leaf and stem material when vegetative. When harvest was delayed until inflorescence development, the leaves averaged only 13.4% of the total forage and stems averaged 42.9%. Leaves had greater CP and less fiber concentration than stems. The decline in whole plant quality with maturity was associated with a decrease in CP concentration of leaf and stem fractions and an increase in both NDF and ADF concentrations of stems. Amaranth entries differed in forage quality, but vegetable types were not superior to grain types.

Mowing as a Weed Control Supplement to Herbicides and Cultivation in Peanut (Arachis hypogaeaL.)

A 3-yr field study was conducted in peanut in which weed control systems with varying levels of herbicides, cultivation inputs, or both were supplemented with mowing to remove weeds extending above the crop canopy. Highest yield and net returns were consistently obtained with the highest level of herbicide/cultivation inputs, and mowing was of no value. However, mowing was consistently beneficial to yield and net return when the only other weed control inputs were paraquat and 2,4-DB applied at 4 wk after planting (WAP) and cultivation at 10 WAP. In the absence of any other weed control inputs, mowing was detrimental in a drought stress year, but beneficial in years with near-normal growing conditions. Although disease incidence was aggravated by the lack of weed control inputs, it was generally independent of mowing.