Shattercane Control Research Articles

Mutations in the acetolactate synthase (ALS) enzyme affect shattercane (Sorghum bicolor) response to ALS-inhibiting herbicides

BackgroundShattercane [Sorghum bicolor (L.) Moench ssp. Arundinaceum (Desv.)] is a competitive weed in North America's corn, soybean, sorghum, and other agronomic crops. Control of shattercane with POST herbicides in corn became possible with the introduction of acetolactate synthase (ALS)-inhibiting herbicides in the 1980s, and their extensive use resulted in the evolution of ALS-inhibitors resistant shattercane.ResultsShattercane seeds were collected from 16 south-eastern and south-central Nebraska fields that were treated with primisulfuron for three consecutive years. Three resistant plants were found in greenhouse evaluations of more than 30,000 plants. Results from a greenhouse bioassay conducted to assess the response of each shattercane biotype to ALS-inhibiting herbicides showed a differential response to ALS inhibitors within and between chemical classes. Biotype P8-30 was resistant or partially resistant to all ALS-inhibiting herbicides applied and displayed a unique amino acid sequence substitution (Trp574 to Leu) relative to the other two resistant biotypes, P2-205 and P9-102. Whole plant dose–response studies confirmed a 4- to the 12-fold level of primisulfuron resistance in three shattercane biotypes compared with the known primisulfuron-susceptible shattercane biotype. The ALS gene was sequenced using primers designed from the corn ALS sequence to identify mutations in the ALS gene that confer resistance. A total of seven nucleotide substitutions were detected in the three herbicide-resistant biotypes P2-205, P8-30, and P9-102. These biotypes are being crossed to adapted sorghum lines (grain, sweet, and forage) to broaden germplasm with resistance to ALS-inhibiting herbicides.ConclusionThe discovery of these mutants should accelerate the development of sorghum genotypes that tolerate ALS-based herbicides, which provide additional choices for sorghum farmers to control weeds, especially grasses, in their fields.

Confirmation and Control of Imazamox-Resistant Shattercane

Shattercane is a summer annual grass weed species commonly found in grain sorghum producing regions, including Kansas. Recent development and commercialization of grain sorghum hybrids with tolerance to acetolactate synthase (ALS) and acetyl-CoA-carboxylase (ACCase) inhibiting herbicides will allow producers to use these herbicides for in-season control of shattercane. In a recent field survey, three shattercane populations (DC8, GH4, and PL8) collected from sorghum fields in northwestern Kansas survived the field-use rate (6 fl oz/a) of postemergence (POST) applied IMIFLEX (imazamox). The main objectives of this research were to (1) confirm and characterize the level of resistance to imazamox in those suspected imazamox-resistant (IMI-R) shattercane populations, and (2) determine the effectiveness of alter-native POST herbicides for controlling IMI-R shattercane populations. Imazamox dose-response experiments were conducted in greenhouse conditions at the Kansas State University Agricultural Research Center near Hays, KS. A susceptible shattercane population (SUS) collected from sorghum field in Rooks County, KS, was included for comparison. Dose-response analysis revealed that all three populations exhibited a 3.5- to 5.3-fold resistance to imazamox as compared to SUS population. In a field study, POST treatments of nicosulfuron (Zest), quizalofop (Aggressor), clethodim (Select Max), glyphosate (Roundup PowerMax), and glufosinate (Liberty) provided an excellent control (92 to 100%) of IMI-R population at 21 days after treatment (DAT). These results report the first case of imazamox-resistant shattercane in Kansas. Growers should adopt effective alternative POST herbicides tested in this research for managing IMI-R shattercane.

The Impact of Spray Droplet Size on the Efficacy of 2,4-D, Atrazine, Chlorimuron-Methyl, Dicamba, Glufosinate, and Saflufenacil

Herbicide applications often do not reach their full potential because only a small amount of the active ingredients reaches the intended targets. Selecting the appropriate application parameters and equipment can allow for improved efficacy. The objective of this research was to evaluate the effect of droplet size on efficacy of six commonly used herbicides. Atrazine (1.12 kg ai ha−1), cloransulam-methyl (0.18 g ai ha−1), dicamba (0.14 kg ae ha−1), glufosinate (0.59 kg ai ha−1), saflufenacil (12.48 g ai ha−1), and 2,4-D (0.20 kg ae ha−1) were applied to seven plant species using an XR11003 nozzle at 138, 276, and 414 kPa and a AI11003 nozzle at 207, 345, and 483 kPa. Each herbicide, nozzle, and pressure combination was evaluated for droplet size spectra. Treatments were applied at 131 L ha−1to common lambsquarters, common sunflower, shattercane, soybean, tomato, velvetleaf, and volunteer corn. Control from 2,4-D was observed to increase approximately 12% on average for all species except common lambsquarters as droplet size increased from medium to very coarse (Dv0.5303 to 462 μm;Dv0.5is droplet size such that 50% of spray volume is contained in droplets of equal or smaller size). Control with atrazine was near 95% for common lambsquarters, common sunflower, and soybean. Atrazine provided the greatest shattercane control using a medium (Dv0.5325 μm) droplet, whereas the same droplet size provided the lowest tomato control. Control of common lambsquarters, shattercane, and tomato with cloransulam-methyl increased 79% when decreasing droplet size from extremely coarse to fine (Dv0.5637 to 228 μm). Dicamba control of common lambsquarters increased 17% using a medium droplet compared with a fine droplet (Dv0.5279 to 204 μm). Dry weight of common sunflower and soybean was reduced 21% using dicamba when using a very coarse spray compared with a fine spray classification (Dv0.5491 to 204 μm). Common lambsquarters control using glufosinate increased 18% using a fine spray classification (Dv0.5186 μm) compared with medium (Dv0.5250 μm) and both very coarse droplet sizes (Dv0.5470 and 516 μm). Conversely, tomato and velvetleaf control with glufosinate was maximized using a very coarse (Dv0.5470 and 516 μm) or extremely coarse droplet (Dv0.5628 μm) with increases of 11 and 25% compared with a fine spray (Dv0.5186 μm). Saflufenacil control of volunteer corn was 38% greater using extremely coarse droplets (Dv0.5622 μm) than fine, medium, and very coarse spray classifications (Dv0.5257 to 514 μm). Overall, spray classifications for the herbicides evaluated play an important role in herbicide efficacy and should be tailored to the herbicide being used and the targeted weed species.

Efficacy of Anthem, Anthem ATZ, Solstice, Keystone NXT, Corvus, and Surestart II in Glyphosate-Resistant Irrigated Corn

The best treatments provided excellent green foxtail, crabgrass, or shattercane control. All treatments dramatically increased corn yield compared to the control.

Sequential Treatments of Rimsulfuron, Mesotrione, Thifensulfuron, Balance Flexx, Cinch, Cinch ATZ, and Prowl H2O Mixtures for Weed Control in Irrigated Corn

No treatment with less than 1.5 lb/a atrazine provided commercially acceptable Palmer amaranth control. The best level of Palmer amaranth control was produced by treatments that had good preemergence control augmented by a postemergence application with two or more modes of action that contained 0.5 lb/a atrazine. All treatments provided excellent kochia control. The best Russian thistle treatments provided from 77 to 88% control. The best foxtail or crabgrass treatments provided from 91 to 94% control. Combinations of preemergence treatments followed by a postemergence treatment achieved excellent shattercane control.

The interaction of two potential fungal bioherbicides and a sub-lethal rate of glyphosate for the control of shattercane

Greenhouse and laboratory experiments were conducted with the potential bioherbicides Colletotrichum graminicola (Cg) and Gloeocercospora sorghi (Gs) for control of shattercane weed. Single-spray tank mixture applications containing different ratios of the two fungi resulted in additive percent weed biomass losses. Intraspecific (Cg + Cg or Gs + Gs) and interspecific (Cg + Gs or Gs + Cg) sequential applications 1- or 7-days apart indicated antagonistic interactions in percent biomass loss. Application of either fungus with, or 1–3 days prior to, a sub-lethal concentration of glyphosate resulted in an antagonistic percent biomass loss; while application of glyphosate prior to either potential bioherbicide resulted in a synergistic weed disease response. Conidia germination studies conducted both in vitro on agar plates and with leaf impression peels suggest that antagonistic interactions observed in weed disease severity are probably due to the host–pathogen response following infection.

Control of Acetolactate Synthase–Resistant Shattercane (Sorghum Bicolor) in Field Corn with Kih-485

Experiments were conducted in 2004 and 2005 in Virginia to evaluate KIH-485 for shattercane control. KIH-485 was applied to glyphosate-resistant corn at three rates (166, 209, and 250 g ai/ha) and two timings (preemergence [PRE] and postemergence [POST]) and compared to standard rates of S-metolachlor, acetochlor, and pendimethalin. PRE treatments were applied alone, while POST treatments were combined with 1,121 g ai/ha of glyphosate. A single POST application of glyphosate, a nontreated weedy control (WC), and a weed-free control (WFC) were also evaluated. In 2004, at 1 mo after planting (MAP), shattercane was controlled 73, 86, and 93% with the three PRE treatments of KIH-485 compared to only 50, 49, and 48% control with S-metolachlor, acetochlor, and pendimethalin, respectively. Similar levels of shattercane control were also observed with these treatments at 1 MAP in 2005. In both years at 4 MAP, KIH-485 combined with glyphosate applied POST controlled shattercane 96% or greater. However, when glyphosate was combined with S-metolachlor, acetochlor, or pendimethalin, shattercane control was less than 88% in either year. Corn yields with POST applications of KIH-485 plus glyphosate were equivalent to yield from the WFC and greater than yield from any PRE treatment. Early-season shattercane control was promising with KIH-485; however, season-long control only occurred when KIH-485 was applied POST in combination with glyphosate.Nomenclature: Acetochlor, glyphosate, KIH-485, 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)methylsufonyl]-4,5-dihydro-5,5-dimethylisoxazole, S-metolachlor, pendimethalin, shattercane, Sorghum bicolor (L.) Moench SORVU, corn, Zea mays L. ZEAMX

Herbicide Programs for the Control of ALS-Resistant Shattercane (Sorghum bicolor) in Corn (Zea mays)

Growers from three counties in Virginia have recently experienced difficulty controlling shattercane in corn with acetolactate synthase (ALS)–inhibiting herbicides. Seed was collected from these locations and from a susceptible biotype and tested for resistance to imazethapyr, imazapyr, and nicosulfuron in greenhouse trials. Seedlings from these locations were also treated with glufosinate and glyphosate. Greenhouse experiments indicated that one of the four shattercane biotypes was resistant to ALS-inhibiting herbicides. Effective control of the resistant biotype was possible with glufosinate or glyphosate. Field experiments were conducted in 2003 and 2004 to determine the most effective herbicide program utilizing herbicide-tolerant/-resistant corn hybrids for the control of shattercane. Early postemergence (EP) and late postemergence (LP) applications of imazethapyr plus imazapyr or EP nicosulfuron did not control shattercane, and yield from the imidazolinone-tolerant (IT) hybrid was equivalent between these treatments and was equivalent to yield from the weedy control (WC). At 23 wk after planting (WAP), EP applications of glyphosate controlled shattercane 71 and 75% compared to only 21 and 66% with EP applications of glufosinate in 2003 and 2004, respectively. In both years, LP applications of glufosinate or glyphosate controlled shattercane better than did EP applications of glufosinate or glyphosate. Treatment timing with respect to corn yield within either the glufosinate-resistant (LL) or glyphosate-resistant (RR) corn hybrid was critical. EP treatments of glufosinate or glyphosate resulted in yields that were equivalent to yield from the weed-free control (WFC) of each hybrid. LP treatments of glufosinate or glyphosate, however, resulted in yields that were equivalent to only 90 and 91% of yield from the WFC of each hybrid, respectively.

Postemergence Shattercane (Sorghum bicolor) Control in Corn (Zea mays) in Northern Tamaulipas, Mexico

Field studies were conducted in northern Tamaulipas, Mexico in 1991 and 1992 to determine the effectiveness of POST applications of primisulfuron and nicosulfuron on shattercane control in corn. Primisulfuron at 15 g/ha and nicosulfuron at 30 g/ha were the minimal doses required for shattercane control. Both herbicides applied on 5- to 9-leaf shattercane provided excellent (> 90%) control 35 d after application. No corn injury was evident with any herbicide and rates evaluated. Untreated check plots sustained 30 to 56% of yield reduction as compared to herbicide treatment plots.

Shattercane (Sorghum bicolor) Control in Soybeans (Glycine max) with Preplant and Postemergence Herbicides

Field studies were established to evaluate several new herbicides for preplant incorporated and postemergence shattercane control in soybeans. Imazethapyr applied postemergence controlled shattercane most consistently. The type of adjuvant tank mixed with sethoxydim did not influence shattercane control, panicle production, or soybean yields. Preplant incorporated applications of imazethapyr, imazaquin, or clomazone either alone or tank mixed with trifluralin or pendimethalin gave inconsistent shattercane control and soybean yields compared to handweeded plots.

Shattercane (Sorghum bicolor) Control with Alachlor where EPTC Failed

A location in east Central Kansas with a history of continuous corn (Zea maysL.), EPTC (S-ethyl dipropyl carbamothioate) plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) plus dietholate (O,O-diethylO-phenylphosphorothioate) application, and shattercane [Sorghum bicolor(L.) Moench. #3SORVU] was selected for herbicide efficacy investigations. Thiocarbamate herbicides applied before planting corn failed to control shattercane in 1 of 2 years. Adding dietholate did not improve EPTC efficacy in either year. Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] applied preplant failed to control shattercane both years. Treatments which included applications of alachlor at 2.2 kg ai/ha 7 or 10 days after preplant herbicide applications were made provided significantly better shattercane control than did preplant treatments.

Effect of Herbicide Incorporation Methods on Shattercane (Sorghum bicolor) Control in Corn (Zea mays)

Field experiments were conducted at Lincoln, NE, in 1983 and 1984 to determine the effectiveness of subsurface jet injection of herbicides on a simulated shattercane [Sorghum bicolor(L.) Moench # SORVU] infestation in corn (Zea maysL.). Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and EPTC (S-ethyl dipropyl carbamothioate) plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide), incorporated with a disc or applied from the subsurface and surface with a jet injector attached to a sweep plow, generally produced higher corn yields and shattercane control than herbicides applied with the sweep to the subsurface only. EPTC plus dichlormid controlled shattercane better than alachlor. Cultivation improved shattercane control by at least 10% in conjunction with most jet injection and disc-incorporated alachlor treatments. Cultivation increased corn yields by about 10 to 20% when averaged over all herbicides and application patterns. A subsurface plus surface herbicide injection system supplemented with cultivation would be a possible method of incorporating herbicides in reduced tillage to selectively control shattercane in corn.

Slot Injection of Herbicides

INJECTION of thiocarbamate herbicides into a slot created by a coulter was evaluated during a 3-year study in southeastern Nebraska. Control of shattercane, the dominant weed, with the slot injector was similar to conventional double disk incorporation. In both tilled and untilled surface conditions, the slot injector placed the herbicide into the soil with minimal disturbance of the soil and residue. Herbicides which are normally broadcast applied were band applied, reducing chemical costs by two-thirds.

Roller Applicator for Shattercane (Sorghum bicolor) Control in Row Crops

Greenhouse and field experiments were conducted with a roller applicator at Lincoln, Nebraska, during 1979 and 1980. Glyphosate [N-(phosphonomethyl)glycine] concentrations of 5, 10, and 20% and carpet saturations of 50 and 75% controlled shattercane [Sorghum bicolor(L.) Moench] when applied to the top 30 cm of the plant in greenhouse research. In the field, glyphosate concentrations of 5 to 20% with a carpet saturation of 50% controlled shattercane acceptably in soybeans [Glycine max(L.) Merr.], but a concentration of 2.5% with 25% carpet saturation did not. Weed control was comparable whether speed of application was 3.2, 6.4, or 9.6 km/h. Shattercane control in grain sorghum [Sorghum bicolor(L.) Moench.] was excellent at glyphosate concentrations of 5, 10, and 20% and at carpet saturations of 50 and 75%, and sorghum injury was minimal at 25 and 50% carpet saturations. The roller applicator was compared to a ropewick applicator for shattercane control in sorghum. Excellent weed control (90% or greater) with minimal crop injury was obtained with the roller applicator at glyphosate concentrations of 10 and 20% at application speeds of 3.2 and 6.4 km/h and with the ropewick applicator with glyphosate concentrations of 35 and 50% applied at 3.2, 6.4, and 9.6 km/h.

Herbicide Protectants and Antidotes — A Review

Abstract Herbicide protectants can be used to allow increased herbicide doses without injury to the crop or the use of more potent herbicides to obtain a wider spectrum weed control, longer weed control or greater reliability. They may also allow cheap herbicides to replace more expensive ones. The possible uses of activated charcoal are reviewed and the more specific new chemical antidotes R 25788 (N,N-diallyl 2,2-dichloroacetamide) and NA (1,8-naphthalic anhydride) are described. R 25788 is commercially available in mixture with EPTC and with butylate. The mixture with EPTC is used particularly for the control of shattercane (Sorghum bicolor) in maize. NA can be used as a seed dressing to protect a slightly wider range of crops including sorghum, rice and oats and has made it possible to control wild oats (Avena fatua) in oats and wild rice (Oryza punctata) in rice. Other possible uses are indicated and modes of action discussed.