Proso millet (Panicum miliaceum L. # PANMI) was controlled in corn (Zea mays L. ‘Pioneer 3747’) with postemergence-directed herbicides applied following a standard preplant-incorporated application of butylate [S-ethylbis(2-methylpropyl)carbamothioate] plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) plus cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile}. Postemergence-directed applications of ametryn [N-ethyl-N′-(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine], cloproxydim {(E,E)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, butyl ester of fluazifop-p {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, glyphosate [N-(phosphonomethyl)glycine], methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in 40-cm-tall corn gave greater than 90% control of 5- to 15-cm-tall proso millet while causing little or no corn injury at selected rates. Season-long proso millet control was obtained with sethoxydim at rates as low as 56 g ai/ha with no visible corn injury. Unacceptable injury to 40-cm-tall corn occurred with all but the lowest rate of sethoxydim (56 g ai/ha) when a crop oil concentrate was used. Sethoxydim applied as a directed spray at rates up to 110 g ai/ha plus 1.25% (v/v) crop oil concentrate did not injure 60-cm-tall corn.

Proso millet occurs both as a crop and a weed in North America. In 1970, an olive-black seeded biotype called ‘wild proso millet’ was found as an aggressive weed in row crops in Minnesota and Wisconsin and has since spread over a large area. We used Random Amplified Polymorphic DNA (RAPD) to assess genetic relationships among biotypes, measure genetic variation within wild proso millet across its range, and detect hybridization between wild proso millet and crop biotypes of proso millet. We found 97 RAPD genotypes among 398 individuals: 69 wild proso millet genotypes, 26 crop and crop-like weed genotypes, and two hybrid genotypes. Five RAPD markers consistently differentiated wild proso millet from crop cultivars and crop-like weeds. About 10% of the genotypes had at least one marker of the other type, suggesting possible hybridization between wild proso millet and crop biotypes. Most genotypes occurred in only one or two of the over 100 populations tested. The most widespread wild proso millet genotype occurred in 12 populations distributed in North Dakota, Minnesota, Illinois, and Wisconsin. More genetic variation exists among populations of wild proso millet than expected for a plant that presumably experienced a severe genetic bottleneck only 20 generations ago. Hypermutation rates and crossing between wild proso millet and crop cultivars could not account for the degree of genetic variation found in wild proso millet. The pattern of genetic variation among wild proso millet populations suggests multiple introductions of wild proso millet to North America.

Wild-proso millet control in furrow-irrigated corn was evaluated in Colorado and Nebraska in 1986 and 1987. No single herbicide alone controlled wild-proso millet all season. In Colorado, EPTC applied preplant incorporated followed by cyanazine plus pendimethalin applied early postemergence controlled 94% of wild-proso millet. Acetochlor applied preemergence followed by cyanazine plus pendimethalin applied early postemergence controlled wild-proso millet better all season (93%) than alachlor (81%) or metolachlor (71%) followed by the same early postemergence strategy. Successful Colorado wild-proso millet management treatments (>85% season-long control) increased corn yields an average of 3260 kg ha-1 compared to the untreated control. To obtain wild-proso millet control of 90% or more in Nebraska in 1986, alachlor, cycloate, EPTC, and metolachlor applied had to be combined with cyanazine plus pendimethalin applied early postemergence. Average corn yields in herbicide-treated areas in Nebraska were 2980 kg ha-1 higher than those recorded in the untreated control.

Laboratory studies were conducted to determine the ability of the extenders dietholate and SC-0058 to prevent enhanced biodegradation of EPTC and butylate applied to Wisconsin soils with different histories of carbamothioate herbicide use. Enhanced EPTC and butylate biodegradation occurred in soils previously treated with those herbicides. Enhanced biodegradation of dietholate occurred on soils previously treated with that extender plus either EPTC or butylate. Enhanced dietholate biodegradation was observed when applied alone or in combination with butylate or EPTC. Application with dietholate prevented enhanced biodegradation of butylate but not EPTC even though enhanced biodegradation of dietholate was occurring. Enhanced biodegradation of SC-0058 did not occur. SC-0058 prevented enhanced EPTC and butylate biodegradation even in soils previously treated for three consecutive years with the respective herbicide plus SC-0058. Application of either 1.1 or 2.2 kg/ha SC-0058 plus 6.7 kg/ha EPTC provided equal or better wild proso millet control and sweet corn yields than applications of EPTC alone or EPTC plus dietholate.

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] is a potent synergist of atrazine for postemergence control of weeds such as giant foxtail (Setaria faberi Herrm. ♯ SETFA) and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA]. We determined whether: a) tridiphane could syngergize the activity of other herbicides known to be detoxified via enzymatic conjugation to glutathione, and b) differential toxicities of the synergized herbicides could provide control of proso millet (Panicum miliaceum L. ♯ PANMI) in corn (Zea mays L. “PAG SXIII”). Four herbicides were used in this study: EPTC (S-ethyl dipropylthiocarbamate), atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], CDAA (N-N-diallyl-2-chloroacetamide), and alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide]. Herbicides and herbicide-synergist combinations were applied postemergence. In corn, tridiphane synergized the activity of EPTC at 2 and 4 kg ai/ha, causing 22 to 25% growth reduction. Atrazine was ineffective and CDAA only slightly effective in combination with tridiphane in causing growth reduction. However, alachlor was markedly synergized by tridiphane at both 2 and 4 kg ai/ha, resulting in 36 to 54% growth reduction compared with plants treated with herbicides alone. Proso millet followed a similar trend to corn: EPTC and alachlor were effectively synergized by tridiphane, while atrazine and CDAA were ineffective. Importantly, however, the rates of herbicide used for proso millet control were much lower than those used for corn. Our data suggest that tridiphane used in combination with EPTC or alachlor could provide improved control of proso millet in corn.

Efficacy of primisulfuron and reduced rates of nicosulfuron on woolly cupgrass, wild-proso millet, and giant foxtail in field corn was evaluated in 1994 and 1995. Nicosulfuron was applied at 18, 27, and 36 g ai/ha alone and with 20 g ai/ha primisulfuron. Woolly cupgrass control from nicosulfuron at 18 and 27 g/ha was less than control from 36 g/ha (79% and 84% vs. 90%, respectively). Woolly cupgrass control was 5% greater when primisulfuron was combined with nicosulfuron at 27 and 36 g/ha than when nicosulfuron was applied alone. Corn grain yields were similar among all nicosulfuron plus primisulfuron treatments applied to control woolly cupgrass in 1994. In 1995, corn grain yield was increased 900 kg/ha when primisulfuron was combined with nicosulfuron at 18 g/ha compared to nicosulfuron applied at the same rate alone. Wild-proso millet control 3 WAT with nicosulfuron at 18 g/ha was less than control with nicosulfuron at 36 g/ha. Wild-proso millet control 8 WAT with nicosulfuron alone was greater than when nicosulfuron at any rate was applied with primisulfuron. No differences in corn grain yields were observed across nicosulfuron rates or combinations with primisulfuron to control wild-proso millet either year. Giant foxtail control and corn grain yield were not affected by nicosulfuron rate or combined applications of nicosulfuron and primisulfuron either year.

Effects of proso millet interference with irrigated dry beans were evaluated in Nebraska over a 2-yr period. Dry bean yield reduction ranged from 12 to 31% from a wild proso millet density of 10 plants m-2. As density increased, dry bean yield reduction could be predicted with a rectangular hyperbola regression model. Ten wild proso millet plants m-2 growing with dry beans produced 14 780 to 21 420 seed m-2. Dry bean yields were reduced 41 and 11% in 1990 and 1991, respectively, when wild proso millet removal was delayed 6 wk after dry bean planting. Four weeks of weed-free maintenance were sufficient to provide dry bean yields comparable to plots kept weed free all season.

Several precision postemergence-directed sprayers with different nozzle designs and arrangements were evaluated for potential use in sweet corn for wild-proso millet (PANMI) control in field trials from 1987 to 1989. Ametryn at 2270 g ha-1 plus oil-emulsifier mixture (OEM) at 1.3% v/v and sethoxydim alone or plus OEM applied postemergence-directed selectively controlled PANMI in sweet corn. Sethoxydim at 220 g ha-1 plus OEM controlled PANMI best when averaged over the 3-yr period. Ametryn plus OEM did not injure corn and sethoxydim at 110 g ha-1 plus OEM caused little or no corn injury and no yield reductions when applied with any of the sprayers. Generally, only sethoxydim at 220 g ha-1 plus OEM injured corn. The amount of injury was different among sprayers, with the nozzle designs and arrangements responsible for corn injury. Injury was minimized when sethoxydim was applied with a sprayer equipped with 150 degree dual orifice nozzles spaced 38 cm apart and mounted on skids that contacted the soil to assure constant nozzle height. This sprayer, or sprayers of similar nozzle design, show the most potential for use by sweet corn growers.

Seedlings of proso millet usually were killed by discing and rototilling in field experiments but populations were not reduced by mowing or by compressing under tractor wheels. In greenhouse experiments, recently emerged seedlings had the greatest mortality after raking and desiccation treatments but were less affected by shoot and/or root damage. In contrast, seedlings treated several weeks after emergence suffered greater mortality from shoot damage and less from desiccation. Two weedy proso millet biotypes, black and Crown, were used in the field experiments, and up to six biotypes were used in the greenhouse. Few significant differences among biotypes were found. Young (emerging) seedlings were extremely resilient to all treatments.

Wild and cultivated proso millet (Panicum miliaceum L. ♯ PANMI) showed increased height and dry mass with increasing photoperiod and flowered under all photoperiods. Increasing planting density decreased height and dry mass and slowed seedhead development in both types. Shading increased plant height and decreased dry mass of both millets and increased germination compared to unshaded treatments. Planting date did not affect germination of freshly collected seed of either millet. Wild proso millet seed had a low germination rate until 8 weeks after panicle emergence, and the rate increased to 22% after 10 weeks. Germination of cultivated proso millet seed was low for 5 weeks after panicle emergence and increased to 92% after 10 weeks.

Nicosulfuron and rimsulfuron are two selective postemergence sulfonylurea herbicides commercialized, respectively, in Europe and USA for weed control in maize. They are under development in Canada as a 1:1 premix (DPX-79406). The objective of the present study was to investigate the effects of these herbicides and their interactions on acetolactate synthase (ALS) activity of selected annual weed species. Each nicosulfuron and rimsulfuron treatment used over a concentration range of 0.01 to 10 μM produced a distinct pattern of ALS inhibition for common ragweed, proso millet, redroot pigweed, smooth crabgrass, and wild oats. Based on ALS specific activity, I50 values for each herbicide differed slightly among the five weed species. However, rimsulfuron was much more inhibitory to ALS than was nicosulfuron. Common ragweed ALS activity increased linearly from 30 to 120 min, even in the continual presence of both herbicides in the assay buffer. This suggests the reversibility of their interaction with ALS. Delaying nicosulfuron (1 μM) or rimsulfuron (0.1 μM) additions to the assay buffer, after initiating the reaction with the enzyme, resulted in a quadratic increase of common ragweed ALS activity. In the continual presence of 0.1 μM of rimsulfuron, addition of 0.1 or 1 μM nicosulfuron did not affect ALS activity any further. However, in the continual presence of 0.1 μM of nicosulfuron, delaying rimsulfuron addition caused an increase in ALS activity. This increase was lower in the presence of 1 μM of nicosulfuron. Inhibition of common ragweed ALS by nicosulfuron and rimsulfuron was not independent of each other, suggesting some competition between the two herbicides for a common binding site on ALS.

DPX-79406 was evaluated for POST annual grass weed control in both controlled environment and field experiments. In controlled environment experiments, green foxtail was most susceptible to DPX-79406; whereas yellow foxtail was least susceptible of the species evaluated. DPX-79406 at 12 g/ha completely controlled six leaf black-seeded proso millet, yellow foxtail, green foxtail, and barnyardgrass. In the field, DPX-79406 at 3.0 to 25.0 g/ha effectively controlled annual grass weeds without injury to three- to six-leaf corn. There was more variation in the effectiveness of DPX-79406 applied in the field. Early POST applications provided less weed control than the late application, especially for barnyardgrass, because of weeds emerging after application. As a result, higher doses were sometimes needed for effective control. In weed-free field trials at two sites in 1990 and 1991, corn tolerated doses up to 75 g/ha of DPX-79406 applied at the three- to six-leaf growth stage. However, doses as low as 18.8 g/ha applied at the six- to nine-leaf growth stage reduced grain yield. In 1991, corn tillering increases and height and yield reductions were related linearly to the dose of DPX-79406 applied during later growth stages. DPX-79406 should be applied early POST in order to avoid crop injury while providing effective weed control.

The effect of sequential hexane, ethyl acetate, and aqueous methanol extracts of ‘Regal’ sweetpotato periderm on seed germination of sweetpotato, proso millet, and seven weed species was studied. The hexane extract, which contained the nonpolar components of the periderm tissue, was least inhibitory. It inhibited velvetleaf, proso millet, black nightshade, and redroot pigweed germination, and maximum inhibition was 56% for black nightshade at 200 mg of periderm extracted ml–1. The ethyl acetate fraction was inhibitory to proso millet, velvetleaf, black nightshade, goosegrass, tall morningglory, coffee senna, and redroot pigweed. The estimated I50 for ethyl acetate ranged from 17 mg periderm extracted ml–1 for black nightshade to 201 mg ml–1 for coffee senna. Sweetpotato, tall morningglory, and eclipta germination was not inhibited by this extract at the concentrations tested. The aqueous methanol extract was much more inhibitory than the hexane or ethyl acetate extracts, and there was considerable variation between species in response to this extract The I50 estimates for the aqueous methanol extract were 0.5, 0.6, 2.8, 4.4, 5.1, 9.6, 15.7, 21.0, and 25.8 mg ml–1 for velvetleaf, proso millet, black nightshade, goosegrass, sweetpotato, tall morningglory, eclipta, coffee senna, and pigweed, respectively.

Under simulated no-till conditions in the greenhouse, rye (Secale cereale L. ‘Wheeler’) residues reduced emergence of lettuce (Lactuca sativa L. ‘Ithaca’) and proso millet (Panicum miliaceum L. # PANMI) by 58 and 35%, respectively, over that obtained with a wood shaving control mulch. Rye shoot tissue inhibited lettuce germination 52% more than root tissue. Petri dish bioassays of residue in soil confirmed phytotoxicity on cress (Lepidium sativum L. ‘Curly’), lettuce, barnyardgrass (Echinochloa crus-galli L. Beauv. # ECHCG), and proso millet. Radicle elongation was a more senstive measure of phytotoxicity than germination per se. Phytotoxicity increased as the distance from seeds to rye residues decreased. While rye shoot residues caused 40% greater inhibition of cress radicle elongation in sterile soil than nonsterile soil, barnyardgrass was equally inhibited in both soil regimes. Phytotoxicity decreased in nonsterile soil, indicating that the compounds were degraded by microorganisms. Phytotoxic compounds in shoots were water extractable. Cress and barnyardgrass responded similarly to both aqueous rye extracts and to residues added to soil.

Thirty-six postemergence-directed (PDIR) herbicide treatments, applied with a precision PDIR sprayer, were evaluated for wild-proso millet (PANMI) control in sweet corn field trials in Wisconsin from 1987 to 1990. The performance of butylate and cyanazine (B + C), applied to suppress PANMI early in the season and to provide a height differential between corn and PANMI, greatly influenced PANMI control with PDIR treatments. PDIR treatments controlled PANMI greater than 90% when PANMI was effectively suppressed by B + C, but poor PANMI suppression reduced PDIR herbicide efficacy. Generally, PDIR treatments of paraquat or sethoxydim most effectively controlled PANMI. Paraquat alone at 545 g ha–1 or combined with simazine or sethoxydim at 57 and 114 g ha–1, and sethoxydim at 170 and 227 g ha–1 plus an adjuvant controlled PANMI greater than 95%. PDIR applications of ametryn, linuron, sethoxydim at 57 to 227 g ha–1 alone, sethoxydim at less than 114 g ha–1 plus an adjuvant, and sethoxydim at 114 g ha–1 tank mixed with either of four other herbicides controlled less than 86% of PANMI. Tank mixing a photosynthetic inhibitor or sethoxydim with paraquat did not improve PANMI control compared with paraquat alone. PANMI control with sethoxydim plus an adjuvant at 114 g ha–1 was similar to 227 g ha–1. There was no difference in PANMI control with sethoxydim applied with crop oil concentrate or BCH-815. With the exception of glyphosate at 318 g ha–1 and sethoxydim at 227 g ha–1 plus an adjuvant, PDIR treatments did not injure sweet corn in 1987, 1988, or 1990. However, sethoxydim in 1989 at all rates severely injured corn.

Field studies were conducted at Arlington, WI, in 1996 and 1997 and at Georgetown, DE, and LeSueur, MN, in 1997 to determine weed control efficacy, crop injury, and yield response of PAT-transformed sweet corn to glufosinate-based weed management. Sequential applications of glufosinate 10 to 18 d apart at 0.4 and 0.3 kg ai/ha controlled common lambsquarters, common ragweed, velvetleaf, wild-proso millet, and fall panicum 90% or better at all locations. Weed control varied little among 0.3, 0.4, or 0.3 and 0.3 (sequential) kg/ha glufosinate rates. Glufosinate applied alone, with, or following atrazine controlled velvetleaf 90% or greater but was less consistent on common ragweed and common lambsquarters (73 to 100%). Atrazine plus metolachlor applied preemergence (PRE) and glufosinate applied alone postemergence (POST) provided inconsistent wild-proso millet and fall panicum control (43 to 99%). Metolachlor followed by glufosinate improved consistency of grass control (> 76%). Glufosinate followed by cultivation provided 80% or greater control of velvetleaf and wild-proso millet. Glufosinate did not injure or delay maturity of PAT-transformed sweet corn. Sweet corn treated with glufosinate resulted in yields greater than or equal to the sweet corn that was hand-weeded or received a standard herbicide treatment.

Giant foxtail, woolly cupgrass, and wild-proso millet infest millions of hectares of land devoted to corn production in the midwestern U.S. Control of these species and effects on corn grain yield were evaluated at various timings using POST applications of nicosulfuron vs. applications of various PRE herbicides at 17 locations across the midwestern U.S. in 1992 and 1993. Nicosulfuron applied to 5 to 10 cm giant foxtail and woolly cupgrass provided greater control than that observed with selected PRE herbicides. Giant foxtail control with nicosulfuron averaged 88%, and control of woolly cupgrass averaged 77% across all sites. Nicosulfuron, applied to 5 to 10 cm wild-proso millet, provided a level of control similar to that of selected PRE herbicides. Corn grain yield was greater when giant foxtail was controlled POST with nicosulfuron vs. PRE control with selected soil-applied herbicides. Corn grain yields were similar when nicosulfuron was applied POST to 5 to 10 cm woolly cupgrass or wild-proso millet vs. PRE control of these grass weeds. Across a broad range of geographical locations, nicosulfuron, applied POST to 5 to 10 cm tall grass, provided greater or similar levels of weed control vs. the selected PRE herbicides, with no deleterious effect on grain yield.

Herbicide efficacy trials in field corn, sweet corn, and soybean were conducted at three locations in Wisconsin over a 6-yr period. Percent weed pressure (WP) was determined by visually estimating the contribution of all weed species present to the total crop and weed volume in each plot. Crop yields in each plot were measured. Percent crop yield reduction (YLDRED) was calculated by comparing mean yields of individual treatments with those of the highest yielding treatment in each trial. Linear regression analyses of YLDRED and WP data from 1640 field corn and 138 sweet corn treatments were significant. Nonlinear regression analysis of YLDRED and WP data from all 1374 soybean treatments was significant; however, a linear regression of those 1154 soybean treatments with WP ratings of 30 or less produced a more easily interpreted regression equation.

Field studies evaluated the effects of crop, crop rotation, planting date, row spacing, no-till planting, and herbicides on wild-proso millet control. Benefin and EPTC reduced wild-proso millet biomass in new seedings of alfalfa, and the combination of herbicides and forage harvest prevented wild-proso millet seed production in that crop. Wild-proso millet seedling populations were reduced and corn yields increased when corn followed 1 to 4 yr of alfalfa. Apparent effectiveness of herbicides in corn increased after cropping with alfalfa. Germination of buried wild-proso millet seed decreased approximately 90% after 54 months which is equivalent to 4-yr prior cropping to alfalfa. Wild-proso millet control and field and sweet corn yields increased when the crops were planted late season (May 17) rather than early season (April 27). Planting sweet corn in rows spaced 76 cm rather than 108 cm apart also increased sweet corn yields. EPTC plus dichlormid (EPTC+) plus cyanazine always controlled wild-proso millet equal to or better than EPTC+ alone. When field corn was planted no-till into killed alfalfa sod, combinations of pendimethalin plus simazine and pendimethalin plus cyanazine provided the best wild-proso millet control and corn yields. But the following year when corn was no-till planted into corn stubble of the identical plots, wild-proso millet control from the same treatments tended to be lower and corn yields were reduced.

A curved-linear Fresnel lens was investigated to test the effect of concentrated solar radiation on surface and buried weed seed. The lens produced a line focus 1 by 150 cm with a mean temperature of 309 C. A 20-s exposure to seed on the soil surface was 100% lethal to green foxtail, kochia, common lambsquarters, common purslane, and wild buckwheat. In a separate study, emergence from kochia and yellow foxtail seed was reduced 100% at 10 mm soil depth after 15 min in soil of 35 and 93 g/kg moisture and 20 to 40% at 178 g/kg moisture content. Concentrated solar radiation from a Fresnel lens has the greatest potential for affecting weed seed on the soil surface. A series of Fresnel lenses and/or larger lenses may be required for many practical field applications.