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Fatoua villosa (mulberry weed) is a new and invasive weed of container nurseries and landscapes in the southeastern United States. Studies were conducted to determine the effects of light, planting depth, mulch depth, and temperature on mulberry weed seed germination and seedling emergence. Light stimulated mulberry weed seed germination, with less than 5% of seeds germinating in the dark compared with 48 to 60% germinating in the light. In all emergence studies, the highest number of seedlings emerged when seeds were placed on the soil surface, with emergence decreasing as planting or mulch depth increased. Planting depths of ≥ 1.8 cm or mulch depths of ≥ 3.7 cm reduced mulberry weed emergence by ≥ 90%. These data suggest that mulch would control mulberry weed effectively. To study the effects of temperature on germination, two seed batches collected locally in October 1998 and August 1999 were used. Maximum germination of seeds collected in 1998 occurred at 25 C, with germination decreasing at higher temperatures and no germination at lower than 15 C or over 40 C. For seeds collected in 1999, maximum germination occurred from 19 to 29 C, with germination decreasing with temperatures above 29 C or below 19 C. At temperatures of 15 and 42 C germination, percentages were 71 and 11%, respectively. Seedlings germinated at 15 C developed slowly but otherwise appeared normal. For both seed lots, seedlings were stunted and chlorotic at ≥ 38 C. That mulberry weed seed germinated over a wide range of temperatures suggests its potential to emerge throughout most of spring, summer, and autumn in the southeastern United States.
Field studies were conducted to evaluate the tolerance of Italian ryegrass and the metribuzin-sensitive winter wheat cultivar Dozier to metribuzin, chlorsulfuron, flufenacet plus metribuzin, chlorsulfuron plus metsulfuron, diclofop, and combinations of these herbicides applied preemergence (PRE) and postemergence (POST) to wheat in the two- to three-leaf (2–3 LF) at Feekes' stage 1 and to one to two tiller wheat (TILL) at Feekes' stage 3. Italian ryegrass control was 80% or greater with diclofop at all rates and application timings; flufenacet plus metribuzin PRE at all rates; metribuzin POST at 2–3 LF at all rates; and chlorsulfuron or chlorsulfuron plus metsulfuron PRE followed by (fb) metribuzin POST at 2–3 LF. Control of 2–3 LF Italian ryegrass was inconsistent with flufenacet plus metribuzin, chlorsulfuron, and chlorsulfuron plus metsulfuron. Italian ryegrass control was poor with flufenacet plus metribuzin TILL, metribuzin PRE, and metribuzin TILL. Metribuzin applied alone and after chlorsulfuron or chlorsulfuron plus metsulfuron injured wheat. Wheat recovered from flufenacet plus metribuzin injury. However, injury from metribuzin at 280 g ai/ha PRE, 2–3 LF, and at 420 g/ha, 2–3 LF, resulted in season-long injury. Yields were significantly reduced because of metribuzin (PRE, 2–3 LF, or TILL) injury and also by chlorsulfuron or chlorsulfuron plus metsulfuron (PRE) fb metribuzin (2–3 LF).
Field studies were conducted in 1995 and 1996 to investigate postemergence tank mixtures of sethoxydim with various acetolactate synthase (ALS)- and non–ALS-inhibitor herbicides for weed control in sethoxydim-resistant (SR) corn. Giant foxtail control with sethoxydim was 96% and was equal to control with tank mixtures of sethoxydim plus bentazon, dicamba, dicamba plus atrazine, bromoxynil, and nicosulfuron plus bromoxynil. Giant foxtail control with sethoxydim plus atrazine, sethoxydim plus bentazon plus atrazine, and sethoxydim plus ALS-inhibiting herbicides plus 2,4-D was reduced to 60 to 89%. Common ragweed control was equal to or above 91% for tank mixtures that included bentazon plus atrazine, dicamba, dicamba plus atrazine, halosulfuron plus 2,4-D, and CGA 152005 plus primisulfuron plus 2,4-D, and the tank mixture of nicosulfuron plus bromoxynil. Common lambsquarters control was equal to or above 91% from all broadleaf herbicide treatments except bentazon and the tank mixture of halosulfuron plus 2,4-D. In these studies, only tank mixtures of sethoxydim plus dicamba or dicamba plus atrazine controlled giant foxtail, common ragweed, and common lambsquarters equal to or greater than 91% in SR corn.
Nomenclature: Atrazine; bentazon; bromoxynil; CGA 152005 (proposed name prosulfuron), 1-(4-methyl-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl] urea; dicamba; 2,4-D; halosulfuron; nicosulfuron; primisulfuron; sethoxydim; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L. ‘Dekalb 592SR’.
Additional index words: Herbicide-resistant corn, herbicide tank mixtures, sethoxydim-resistant corn.
Abbreviations: ACCase, acetylcoenzyme-A carboxylase; ALS, acetolactate synthase (EC 22.214.171.124); COC, crop oil concentrate; DAT, days after treatment; MCB, multiple comparisons with the best; NIS, nonionic surfactant; POST, postemergence; SR, sethoxydim resistant.
Studies were conducted to develop a weed management strategy for common purslane in lettuce based on available cultural and chemical control methods and an understanding of common purslane biology. A wide-band application of bensulide or pronamide reduced common purslane emergence compared with the standard narrow band. Both narrow and wide bands of pronamide as well as a wide band of bensulide reduced the time required to thin and hoe lettuce. The wide-band pronamide treatment reduced thinning time more than did the narrow band. Overall, none of the herbicide weed management expenses were lower for pronamide treatments than for bensulide and the control. Wide-band bensulide reduced weed management expenses compared with the control, whereas narrow bands did not. Common purslane plants uprooted 1 or 2 wk after emergence (WAE) did not produce any viable seed. Plants uprooted 3 WAE produced from 1 to 60 viable seeds, and seed production increased rapidly from 4 to 6 WAE. Flame and 2% (v/v) glyphosate treatments reduced seed production by uprooted common purslane.
Nomenclature: Bensulide; pronamide; common purslane, Portulaca oleracea L. #3 POROL; lettuce, Lactuca sativa L.
Additional index words: Banded herbicide, weed seed production.
Abbreviations: DAT, days after treatment; GDD, growing degree day; WAE, weeks after emergence.
Field studies were conducted in 1996, 1998, 1999, and 2000 to determine the effect of glyphosate (isopropyl amine salt) on rice injury and yield when applied postemergence at 0, 70, 140, and 280 g ai/ha to dry-seeded rice in the three- to four-leaf (3- to 4-L), midtiller (MT), panicle initiation (PI), and boot (BT) growth stages. Glyphosate at 140 and 280 g ai/ha applied at the 3- to 4-L, MT, and PI growth stages resulted in the greatest foliar injury, and 280 g ai/ha was more injurious than 140 g ai/ha at the first rating, with the exception of MT and PI 2000, where they were equal. Glyphosate treatments resulted in the least visible foliar injury when applied at the BT stage. Rough rice yield was reduced by glyphosate applied at 280 g/ha to rice in the MT growth stage three out of four years. Applied to rice at PI, glyphosate at 140 g/ha reduced yields two out of four years, and three out of four years when applied at 280 g/ha. BT-stage applications of glyphosate at 70, 140, and 280 g/ha reduced yields two out of four, three out of four, and four out of four years, respectively.
Field studies were conducted to evaluate corn vigor reduction, weed control, corn yield, and economic returns in a no-till system with various herbicide strategies using full and reduced rates of acetochlor and atrazine with glyphosate, glufosinate, or imazethapyr imazapyr in their respective type of herbicide-resistant, no-tillage corn. Crop vigor reduction due to herbicide injury was 10% or less with all treatments. A burndown plus a full label rate of a residual herbicide applied early preplant (EPP) generally provided less than 80% control of giant foxtail, common waterhemp, and common cocklebur but usually greater than 85% control of common ragweed and common lambsquarters. Two-pass strategies generally provided greater than 85% control of all species evaluated. Early postemergence, mid-postemergence (MPOST), and late postemergence strategies generally provided inconsistent and poor overall weed control. EPP–MPOST strategies generally provided lower weed control than strategies using acetochlor or atrazine EPP followed by a postemergence application. Corn yield and net economic returns followed a similar trend as weed control, with strategies that provided greater than 80% weed control showing minimal crop vigor reduction and high grain yields. Two-pass strategies with residual herbicides generally provided the highest yields, economic returns, and low coefficients of variation (CV) of net income. Although EPP strategies provided similar economic returns as some of the two-pass strategies, they had higher CVs, implying greater risk to economic return.
Nomenclature: Acetochlor; atrazine; glufosinate; glyphosate; imazapyr; imazethapyr; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; common waterhemp, Amaranthus rudis Sauer. # AMATA; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L. ‘Dekalb 626’, ‘Pioneer 3395’, ‘Pioneer 34T14’.
Additional index words: Application strategies, application timing, tank mixes.
Abbreviations: ac/at , acetochlor EPP followed by atrazine plus; ALS, acetolactate synthase; CEC, cation-exchange capacity; CV, coefficients of variation; EPOST, early postemergence; EPP, early preplant; MPOST, mid-postemergence; LPOST, late postemergence; OM, organic matter.
Field studies were conducted from 1998 to 2000 at Belleville, IL, to evaluate tolerance and weed control in glyphosate-resistant soybean with sulfentrazone application. Sulfentrazone alone caused 14 to 16% height reduction 14 d after treatment (DAT), and sulfentrazone plus chlorimuron caused 26% height reduction 14 DAT. Minimal height reduction (0 to 11%) was observed 56 DAT. Sulfentrazone alone controlled giant foxtail 97 to 100%, yellow nutsedge 96 to 98%, common waterhemp 97 to 98%, common cocklebur 91 to 94%, and ivyleaf morningglory 100%. Sulfentrazone alone controlled common ragweed 63 to 89% and giant ragweed 50 to 72%. Sulfentrazone plus chlorimuron or cloransulam increased control of common and giant ragweed to 95% or greater. Sulfentrazone followed by glyphosate increased control of yellow nutsedge, common waterhemp, and ivyleaf morningglory compared with a single application of glyphosate. Sequential applications of glyphosate controlled weeds 93 to 100%. Sulfentrazone plus chlorimuron or cloransulam postponed the application of glyphosate at the 10-cm weed height by 12 d. Despite the injury, sulfentrazone did not reduce grain yield. Inadequate giant ragweed control reduced grain yield by approximately 48%.
Nomenclature: Chlorimuron; cloransulam; glyphosate; sulfentrazone; common cocklebur, Xanthium strumarium L. #3 XANST; common ragweed, Ambrosia artemisiifolia L. AMBEL; common waterhemp, Amaranthus rudis Sauer AMATA; giant foxtail, Setaria faberi Herrm. SETFA; giant ragweed, Ambrosia trifida L. AMBTR; ivyleaf morningglory, Ipomoea hederacea L. Jacq. IPOHE; yellow nutsedge, Cyperus esculentus L. CYPES; soybean, Glycine max L. Merr. ‘Pioneer 94B01 RR’.
Additional index words: Herbicide injury, postemergence, preemergence, stand reduction.
Abbreviations: DAT, days after treatment; fb, followed by; POST, postemergence; PRE, preemergence; WL, weeks later.
Field and greenhouse studies were conducted from 1997 to 2001 to determine cabbage response to posttransplant applications of pendimethalin (0.56 to 2.24 kg ai/ha). Differential variety response was minimal, and applications greater than 0.56 kg caused severe and persistent crop injury and reduced head number and yield in ‘Azan’, ‘Storage 4’, ‘Super Elite’, and ‘Super Red 90’. Pendimethalin (1.7 kg) applied posttransplant reduced cabbage yield weights 23, 30, and 87% with bare root, large, and small transplants, respectively. Application (0.84 kg) to soil, foliage, or soil and foliage caused 0, 81, and 82% dry weight reduction by 21 d after treatment, respectively. Anatomical analysis of two-leaf seedlings collected 3 wk after pendimethalin treatment (1.12 kg ai/ha) showed stunting of the shoot apical meristem and its emerging leaves, disorganization of apical structure with disruption of normal cell division and cell expansion, and abnormal differentiation of the vasculature in leaves and hypocotyls.
Nomenclature: Pendimethalin; cabbage, Brassica oleracea L.
Field experiments were conducted at four locations in Kansas in 1999 and 2000 to evaluate grain sorghum response to simulated drift rates of four herbicides. Imazethapyr, glufosinate, glyphosate, and sethoxydim were applied at 1/3, 1/10, 1/33, and 1/100 of the use rate when plants were 10 to 20 cm tall. Visible crop injury increased as rates of each herbicide increased. Glyphosate and imazethapyr caused the most injury and glufosinate the least. Data show that some plants that were significantly injured 2 wk after treatment (WAT) recovered 8 WAT. However, some plants that received the highest rate of imazethapyr or glyphosate died. Grain sorghum yields were reduced only when injury was severe. This research showed that the potential for sorghum injury from off-target herbicide drift is greater from imazethapyr and glyphosate than from sethoxydim or glufosinate.
Experiments were conducted from 1994 through 1996 to determine the effect timing of malathion applications have on cotton response relative to postemergence applications of pyrithiobac. Treatments were initiated approximately 1 mo after planting (four to six leaves) and included pyrithiobac at 70 g ae/ha applied alone or in combination or with malathion applied at 1 or 3 d before and at 1 or 3 d after pyrithiobac. At 7 d after treatment (DAT), pyrithiobac plus malathion applied in combination caused 34, 28, and 21% cotton injury in 1994, 1995, and 1996, respectively. Malathion applied 1 d before pyrithiobac resulted in 18% injury in 1994, 11% in 1995, and 15% injury in 1996, whereas malathion applied 1 d after pyrithiobac injured cotton 15 and 11% in 1994 and 1996, respectively. Injury of cotton subjected to malathion applied 3 d before pyrithiobac was not different from pyrithiobac applied alone. When malathion was applied 3 d after pyrithiobac, injury occurred only in 1995. At 14 and 21 DAT, the combination of pyrithiobac plus malathion caused the most cotton injury. Seed cotton yield was not adversely affected by any treatment when compared with pyrithiobac applied alone.
Nomenclature: Malathion, O,O-dimethyl phosphorodithioate of diethyl mercaptosuccinate; pyrithiobac; cotton, Gossypium hirsutum L. ‘DES 119’, ‘DPL 50’.
Additional index words: Crop injury, insecticide, interaction, pesticide, timing.
Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence.
Field experiments were conducted in 1996, 1999, and 2000 to evaluate weed control and snap bean response to postemergence applications of fomesafen at registered and reduced rates. S-Metolachlor was applied preemergence to all plots to suppress annual grasses. Snap bean injury generally increased as fomesafen rate increased, but at rates up to 0.28 kg ai/ha, injury by fomesafen was similar to or less than that from bentazon. Fomesafen at rates as low as 0.07 kg/ha provided near-complete control of common ragweed, and rates of 0.14 kg/ha or more of fomesafen controlled ivyleaf and pitted morningglories and 5-cm or smaller common lambsquarters as effectively as did bentazon. Control of all weed species from fomesafen alone at 0.21 kg/ha did not improve with the addition of bentazon at 0.28 kg/ha. Although snap bean injury from fomesafen was as high as 43% 1 wk after treatment, snap bean yield and net returns were similar to those from S-metolachlor alone. In a rate and application timing study, fomesafen at 0.14 kg/ha applied to three-trifoliolate snap bean was the least injurious to the crop, whereas applications at 0.28 kg/ha to one- or two-trifoliolate snap bean provided the best weed control.
Nomenclature: Bentazon; fomesafen; S-metolachlor; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; snap bean, Phaseolus vulgaris L. ‘Bronco’, ‘Gator Green’.
Additional index words: Fomesafen linear effect, snap bean yield, net returns.
Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.
Conidia of Myrothecium verrucaria, sprayed in an aqueous phase–paraffinic crop oil emulsion (1:1 v/v) at 470 L/ha, controlled red, ivyleaf, smallflower, and tall morningglory plants (three- to five-leaf stage) by causing severe necrotic injury to leaves and stems. Conidia were not efficacious if applied in an aqueous carrier without oil. When applied in the field as directed postemergence treatments to sugarcane, a concentration of 4 × 108 conidia/ml generally provided > 90% death of morningglory, comparable with the atrazine standard at 2.2 kg ai/ha, and did not cause significant crop injury. Conidia produced on potato dextrose agar or rice flour slurry were about equally effective. When killed by autoclaving, conidia continued to be efficacious, indicating that the symptoms produced by the fungus were not primarily caused by infection. A high performance liquid chromatography analysis of filtrates from the fungal growth media or of harvested conidia showed the presence of several macrocyclic trichothecenes (MT), some known to be phytotoxins. These included verrucarin A and H, roridin A and H, and isororidin E for filtrates and verrucarin A and roridin A for conidia. However, only trace amounts of MT were detected in leaves of treated morningglory plants at 24 h after treatment and none at 48 and 96 h even though the fungus was isolated from leaves up to 14 d after treatment. Further study is needed to identify the causal agents responsible for the phytotoxicity produced by M. verrucaria and to assess potential of this organism as a mycoherbicide.
Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and crop safety with preemergence (PRE) and postemergence (POST) applications of mesotrione alone and in tank mixtures with acetochlor and atrazine. Corn injury was less than 4% with all mesotrione treatments in 1999 and 2001, but it was 8 to 20% in 2000, when rainfall was 3.1 cm 7 d after PRE applications. Mesotrione PRE at 0.16 and 0.24 kg ai/ha did not adequately control most broadleaf weeds or giant foxtail. Tank mixtures of mesotrione plus acetochlor controlled smooth pigweed and giant foxtail but did not adequately control common ragweed, common lambsquarters, or morningglory species. Control by tank mixtures of mesotrione plus atrazine at 0.56 kg ai/ha was frequently low and varied with rainfall after PRE applications. All weed species were controlled 80% or more by mesotrione plus acetochlor PRE or atrazine plus acetochlor PRE followed by mesotrione POST at 0.11 kg/ha.
Nomenclature: Acetochlor; atrazine; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L.
Additional index words: HPPD-inhibiting herbicides, triketone herbicides.
Abbreviations: COC, crop oil concentrate; DAT, days after treatment; fb, followed by; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate; WAT, weeks after treatment.
Metolachlor, dimethenamid, acetochlor, and a commercial premixture of flufenacet plus metribuzin were applied 60, 45, 30, and 15 d before planting (DBP) and at planting (preemergence [PRE]) at Dekalb and Urbana, IL in 1995 and 1996. The soil types were a Drummer silty clay loam (fine-silty, mixed, superactive, mesic Typic Endoaquoll) with 2.8% organic carbon and a pH of 6.5 at Dekalb and a Flanagan silt loam (Fine, smectitic, mesic Aquic Argiudoll) with 2.0% organic carbon and a pH of 6.2 at Urbana. Herbicide and application timing affected giant foxtail control and densities. Neither herbicide nor application timing affected crop injury or grain yield. Test of the main effects showed that metolachlor and flufenacet plus metribuzin were more effective than acetochlor or dimethenamid in controlling giant foxtail at 30 and 60 d after planting (DAP) and in reducing foxtail density at 60 DAP. Giant foxtail control 60 DAP was greater than 80% for both metolachlor and flufenacet plus metribuzin for all application timings. Dimethenamid and acetochlor applied at 60 and 45 DBP provided less giant foxtail control when compared with metolachlor and flufenacet plus metribuzin applied at the same time. All herbicides provided greater than 90% giant foxtail control at the PRE application timing. Giant foxtail control provided by metolachlor and flufenacet plus metribuzin was insensitive to application timing from 60 DBP to PRE, whereas both dimethenamid and acetochlor efficacy was lowered when applied between 30 and 60 DBP.
Eight hard red spring wheat cultivars were tested for tolerance to five postemergence grass herbicides at two locations in Minnesota in 1999 and 2000 at the labeled, one and one-half, or twice the labeled rate. Fenoxaprop plus safener and ICIA 0604 caused the least injury and did not reduce grain yield for most cultivars. Flucarbazone caused intermediate injury and a slight decrease in grain yield for half the cultivars tested. Difenzoquat caused the most injury, regardless of whether the cultivar was genetically sensitive to difenzoquat. Tank-mixing difenzoquat with imazamethabenz reduced injury, even for cultivars that were not genetically sensitive to difenzoquat. Drought stress before application of the postemergence grass herbicides that contain difenzoquat resulted in more potential for crop injury. Excess precipitation combined with high temperatures after application resulted in more potential for crop injury for the other postemergence grass herbicides included in this experiment.
Nomenclature: Difenzoquat; fenoxaprop; flucarbazone; ICIA 0604 (proposed common name, tralkoxydim; 2-cyclohexen-[1-one,2-]1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-(9CI)); imazamethabenz; wheat, Triticum aestivum L. emend. Thell.
Additional index words: Crop injury, herbicide tolerance.
Velvetleaf plants have diurnal leaf movements, which may result in decreased interception of herbicides when applications are made near sunset. However, it is not known if leaf angle alone accounts for diurnal fluctuations in efficacy. Greenhouse experiments were conducted to determine the effect of time of day (TOD) of application and velvetleaf leaf angle on glufosinate efficacy and spray interception. Glufosinate at 90, 180, and 360 g ai/ha was applied to 10-cm-tall plants at 4:00, 6:00, 7:00, 7:30, and 8:00 p.m., respectively. Leaf angles were either manipulated physically to −90° or the plant's natural 2:00 p.m. leaf angle (approximately −10°) or were allowed to exhibit their natural leaf movements. Plant dry weight 3 wk after treatment revealed that TOD effects were observed for all leaf angle treatments after glufosinate application at 90 g/ha. At 180 g/ha glufosinate, there was no TOD effect for plants with 2 p.m. leaf angles, whereas there was a TOD effect for plants with −90° and natural leaf angles. At 360 g/ha glufosinate, biomass for the −90° leaf angle plants was similar to that for the natural and the 2:00 p.m. leaf angle plants when glufosinate was applied at 4:00 p.m. but was significantly different at or after 6:00 p.m.. This suggests that at least 4 h of light is needed to provide optimum herbicide activity when spray interception is reduced as a result of leaf movements. Leaf angle decreased by as much as 70% from 4:00 to 8:00 p.m., which resulted in approximately 50% less spray interception at 8:00 p.m. than at 4:00 p.m. These data provide evidence that leaf angle plays a pivotal role in reducing glufosinate efficacy when applications are made near sundown. However, leaf angle is not the sole reason for reduced efficacy because TOD effects were observed at different leaf angles with 4 h of light, after an application of 360 g/ha glufosinate.
Nomenclature: Glufosinate; velvetleaf, Abutilon theophrasti Medicus #3 ABUTH.
Additional index words: Application timing, glufosinate, herbicide interception, time of day.
Abbreviations: GS, glutamine synthetase; POST, postemergence; TOD, time of day; WAT, weeks after treatment.
The allelopathic potential of wild radish was evaluated in controlled environments by determining if an aqueous extract from oven-dried wild radish shoots suppressed germination and radicle growth of some crops and weeds common to the southeastern United States. In addition, phytotoxicity from topical applications of the aqueous extract was assessed, along with crop and weed suppression by soil incorporated, air-dried wild radish residues. Germination and radicle growth of all species were reduced by the extract compared with distilled water. However, topical applications of the aqueous extract failed to induce injury on any species by 7 d after treatment. Emergence and shoot fresh weight of the bioassay plants were reduced by wild radish residue incorporated into soil, with the level of suppression dependent on the quantity of residue incorporated. Sicklepod and prickly sida were extremely sensitive to incorporated wild radish residues, with > 95% fresh weight reduction at 0.5% (wt/wt) residue, compared with an untreated control. Conversely, yellow nutsedge showed a high degree of tolerance in all trials. Of the crops evaluated, cotton emergence and growth were most sensitive to incorporated wild radish residues. These data indicate that wild radish aqueous extract or incorporated residues (or both) suppress seed germination, radicle growth, seedling emergence, and seedling growth of certain crops and weeds and these responses are attributed to an allelochemical effect.
Nomenclature: Prickly sida, Sida spinosa L. #3 SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; wild radish, Raphanus raphanistrum L. # RAPRA; yellow nutsedge, Cyperus esculentus L. # CYPES; cotton, Gossypium hirsutum L.
Additional index words: Allelopathy, Brassicaceae, cover crop, integrated weed management.
Field and laboratory studies were conducted from 1993 to 1997 to determine the feasibility of controlling nodding broomrape in sunflower by treating crop seeds with pronamide. Soaking sunflower seeds for 5 min in 50% pronamide solution or coating at the equivalent of 2 kg/ha with pronamide did not impair seed germination or seedling growth, and controlled nodding broomrape 49 to 68% and 51 to 77%, respectively, up to 105 d after planting. Studies of the effect of treated sunflower seeds on germination and seedling growth, at several time intervals after the herbicide application (0, 30, 60, and 90 d after treatment [DAT]), were conducted. Soaking with 50% solution or coating at 2 kg/ha reduced seedling growth by 20 and 24% 60 DAT, respectively, compared with the control.
Field research was conducted to test a method of herbicide application in which chemical is placed directly onto cut surfaces of plants during a mowing operation. Specially designed mowers equipped with a fluid application system allow for low-volume herbicide application from the cutting blades during the mowing process (wet blade). Two prototype wet-blade machines, including a sickle bar cutter and a Burch Wet-Blade rotary mower, were used to apply triclopyr, clopyralid, and 2,4-D at various rates and combinations using a total carrier volume of 25 L/ha. Weed management studies were conducted on dogfennel, annual lespedeza, and clovers during a 2-yr period. Wet-blade herbicide applications were effective and performed as well as or better than comparative rates applied using a foliar spray technique. Triclopyr at 2.24 kg ae/ha controlled dogfennel when applied with either the rotary mower or the sickle bar cutter (94 and 77%, respectively). Rotary mower applications of 0.20 kg ae triclopyr 0.07 kg ae clopyralid per hectare in rough turf achieved 90% control of annual lespedeza and 95% control of red and white clovers.
Nomenclature: Clopyralid; 2,4-D; triclopyr; annual lespedeza, Lespedeza striata (Thunb.) H. & A.; dogfennel, Eupatorium capillifolium (Lam.) Small #3 EUPCP; red clover, Trifolium pratense L. # TRFPR.; white clover, Trifolium repens L. # TRFRE.
Field studies were conducted at Yoakum and Stephenville, TX; Jay, FL; and Midville and Plains, GA, to determine the persistence of imazapic applied to peanuts at 0, 70, 140, and 210 g ai/ha. The following year, cotton, sorghum, and corn were planted in the treated plots in Texas, cotton was planted in Florida, and corn and cotton were planted in Georgia and evaluated for carryover injury. Data collected to determine injury included plant heights and weights. In 1999 in Texas and in Florida and Georgia, there was no significant carryover injury to rotational crops from any of the imazapic rates. Data on cotton and sorghum plant height from Texas in 2000 showed height reductions for the 210-g/ha rate on cotton and the 140- and 210-g/ha rates on sorghum. These data showed no significant carryover effects to rotational crops from the 70-g/ha rate of imazapic applied to peanuts the previous year.
Although water is crucial to the performance of preemergence herbicides, pesticide performance has rarely been related to irrigation management. This 2-yr study investigated the effect that amount of irrigation water applied had on activity of simazine. Three rates of simazine at 0, 1.12, and 2.24 kg/ha were applied to a 3-yr-old nectarine orchard that was irrigated with microsprinklers. The performance of simazine was compared between irrigation treatments initially targeted to provide water at 110 (efficient) and 175% (overwatered) of crop water requirements. Simazine effectiveness was based on the survival of oat and cucumber plants that were seeded at 0, 14, 28, 56, and 84 d after herbicide application. A longer time interval to 50% survival indicated prolonged herbicidal activity. Results were consistent between years in that simazine's performance was consistently greater in efficient irrigation treatments. The greatest increases were measured at the higher simazine application rate (2.24 kg/ha); overall averages for the length of time to reach 50% survival for cucumber were 50 and 23 d and for oats were 55 and 15 d for efficient and overwatered irrigation treatments, respectively. Use of an efficient irrigation management technique could have enhanced simazine's performance through a decreased leaching of residues from the weed root zone or less chemical or biological degradation (or both). Adoption of efficient irrigation management has been identified as a best management practice to mitigate leaching of pesticide residues to groundwater in coarse soils in California. This study indicates that efficient irrigation improves simazine performance and that both factors, pesticide application and irrigation management, should be considered when developing a weed management system.
Adjuvants that increase the pH of the spray mixture and solubilize nicosulfuron can enhance biological activity under specific conditions. These conditions include high nicosulfuron rates, difficult-to-control weeds, low spray volumes, and initially acidic spray conditions. The most effective pH adjusters are tribasic potassium phosphate, sodium carbonate, and triethanolamine. In low spray volumes, these adjusters make the spray mixture alkaline and often enhance the activity of nicosulfuron on common cocklebur and large crabgrass. Alkaline conditions rapidly dissolve the sulfonylurea particles and enhance activity with crop oil concentrate, modified seed oil, and hydrophilic nonionic surfactants. pH adjusters did not enhance activity with lipophilic surfactants. Ammonium sulfate slightly increases the pH of spray mixtures and increases nicosulfuron activity depending on species, adjuvant type, and pH adjuster. These results generally support the concept that herbicide solubilization is necessary to maximize the foliar activity.
Nomenclature: Nicosulfuron; common cocklebur, Xanthium strumarium L. #3 XANST; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA.
Field studies were conducted in 1999 and 2000 at seven locations in south Texas to evaluate flufenacet plus metribuzin for weed control and corn tolerance. Texas panicum control with flufenacet plus metribuzin was variable with less than 70% control in 1999 and greater than 75% control in 2000. Palmer amaranth and pitted morningglory control ranged from 41 to 100%. Corn stunting (4 to 13%) was noted in soils with greater than 75% sand. Corn yields with flufenacet and metribuzin combinations were increased up to 19% over the untreated check where stunting was not observed.
Management of volunteer potato is difficult and requires an integrated approach. Soil fumigation is one tactic known to reduce population densities of certain weeds and may be a method to improve the management of volunteer potato. The effect of 1,3-dichloropropene (1,3-D) and metham sodium on potato tuber viability was tested in sealed glass jars at various doses, incubation temperatures, and times of exposure. Tuber viability data were fitted to a logistic model, and I90 doses (90% suppression) were calculated for each combination of temperature and time of exposure. I90 doses for 1,3-D ranged from 41 to 151 kg/ha and from 96 to over 480 kg/ha metham sodium. Both nondormant and dormant tubers were injured by exposure to metham sodium. Soil fumigation with 1,3-D and metham sodium has the potential to greatly reduce the number of viable potato tubers.
Nomenclature: 1,3-dichloropropene; metham sodium; potato, Solanum tuberosum L. ‘Russet Burbank’.
A perceived limitation to incorporating herbicide application decision support system (HADSS™) into routine peanut weed management decisions is efficient scouting of fields. A total of 52 peanut fields were scouted from 1997 through 2001 in North Carolina to determine the weed density in a 9.3-m2 section for each 0.4-ha grid of the field. These weed populations and their spatial distributions were used to compare theoretical net return (TNR) over herbicide investment for various scouting methods and weed management approaches. HADSS was used to determine the expected net return for each treatment in each 0.4-ha section of every field under differing assumptions of weed size, soil moisture conditions, and pricing structures. The treatment with the highest net return averaged across all 0.4-ha grids was considered to be the optimal whole-field treatment. For all 52 fields, TNR for the best whole-field treatment and for site-specific weed management (applying the most economical recommendation on each 0.4-ha grid) averaged $414 and $435/ha, respectively. Estimated return from the commercial postemergence herbicide program of aciflurofen plus bentazon plus 2,4-DB followed by clethodim (where grass was present) averaged $316/ha across all 52 fields. For fields of 5 ha or more (17 fields) in which 12 or more samples were taken, TNR was $500, $510, and $516/ha for three-sample (one pass through the middle of the field with samples taken on both ends and the center of the field), six-sample (two passes through the field with three stops per pass), and full-sample (one stop for each 0.4 ha) approaches, respectively.
Selective placement studies were conducted under greenhouse conditions to determine the relative importance of root vs. foliar absorption of postemergence-applied CGA-362622 by torpedograss. All application methods were equally effective in reducing torpedograss foliage as measured 4 wk after treatment. However, foliar soil and soil-only were more effective than foliar-only in suppressing regrowth at 10 wk after treatment. Foliar absorption by torpedograss and subsequent translocation was determined with radiotracer techniques. After 72 h, 29% of the applied CGA-362622 had been absorbed, and 2 and 7% of the amount applied had accumulated in developing rhizomes and roots, respectively. CGA-362622 was more readily absorbed and translocated by the root. Hydroponically grown plants were transferred to a hydroponic solution spiked with CGA-362622 at 200 ppb. After 6 h, whole plant concentration was 113.1 ng/plant. Only 56% of amount absorbed remained in the roots, the remainder having been translocated to other tissues. The youngest leaf and the immature rhizomes accumulated 2 and 15%, respectively. CGA-362622 soil adsorption was slightly influenced by CGA-362622 concentration and greatly influenced by soil pH. Average percent recovered in the soil solution (i.e., not absorbed) was 15.3 and 27.4% at pH 5.7 and 6.7, respectively. Soil mobility was also pH dependent. Soil solution and soil mobility data support the observation that soil application followed by root entry is more effective in delivering phytotoxic concentrations to the regenerative tissues of torpedograss than foliar application.
Nomenclature: CGA-362622; torpedograss, Panicum repens L. #3 PANRE.
The effect of CGA-362622 on annual grass control in cotton by clethodim and fluazifop-P and crop response was determined in field studies. CGA-362622 applied postemergence at 5.3 g ai/ha injured cotton up to 34% 1 wk after treatment (WAT). Injury was similar when crop oil concentrate (COC) and nonionic surfactant (NIS) were included. Adding fluazifop-P, but not clethodim, to CGA-362622 increased crop injury. Cotton recovered by 3 WAT. CGA-362622 mixed with fluazifop-P at 210 g ai/ha reduced broadleaf signalgrass and large crabgrass control 60 to 80%. Control was similar with COC or NIS in the mixture. Increasing the fluazifop-P rate to 315 g/ha did not improve control. CGA-362622 mixed with clethodim at 105 g ai/ha reduced control 65 to 80% with NIS and 40 to 65% with COC. Increasing the clethodim rate to 175 g/ha, especially with COC, substantially increased control. However, control was still less than that with clethodim at 105 g/ha. Prometryn plus MSMA postemergence-directed 3 wk after gramincide and CGA-362622 application increased control. Cotton yield was similar with clethodim alone and clethodim at 175 g/ha plus CGA-362622. Yield was reduced 29% by CGA-362622 mixed with fluazifop-P at 350 g/ha. Control was reduced by CGA-362622 applied 1 d before or after clethodim but not 5 d before or after clethodim. Control by fluazifop-P was reduced by CGA-362622 applied 1 or 5 d before or 1 d after the graminicide. Under greenhouse conditions, CGA-362622 and pyrithiobac mixed with clethodim, fluazifop-P, quizalofop-P, or sethoxydim reduced control of large crabgrass. Greater antagonism was noted with CGA-362622 than with pyrithiobac, and with fluazifop-P and quizalofop-P than with clethodim or sethoxydim.
Nomenclature: CGA-362622 (proposed common name trifloxysulfuron), N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamid sodium salt; clethodim; fluazifop-P; MSMA; prometryn; pyrithiobac; quizalofop-P; sethoxydim; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; cotton, Gossypium hirsutum L. ‘Stoneville BXN 47’.
Additional index words: Adjuvants, antagonism, herbicide interactions, herbicide mixtures.
Abbreviations: COC, crop oil concentrate; NIS, nonionic surfactant; POST, postemergence; POST-DIR, postemergence directed; WAT, weeks after treatment.
Persistence of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of alachlor and acetochlor, as well as EC formulations of metolachlor, s-metolachlor, dimethenamid, and flufenacet were studied using a bioassay based on root response of oat Kassandra grown in soil. Flufenacet was the most persistent of the herbicides, but biologically available residues were not detected at 0- to 10-cm soil depth 50 d after any herbicide treatment. All herbicides applied preemergence (PRE) in field trials gave good to excellent control of redroot pigweed, black nightshade, barnyardgrass, and green foxtail but only partial control of jimsonweed. Furthermore, when they were applied postemergence (POST) in mixture with atrazine in the field, the control obtained for black nightshade, common lambsquarters, common purslane, and redroot pigweed was excellent, but good to excellent for bristly foxtail and green foxtail. Their efficacy against yellow foxtail and large crabgrass was fair to good. Generally, the EC-alachlor and EC-acetochlor applied POST in mixture with atrazine gave better control of grasses than did their ME-formulations. None of the herbicide treatments showed any phytotoxic effect on corn, and all of them produced corn yield greater than that of weedy control but slightly lower than that of the weed-free control. Flufenacet, s-metolachlor, and dimethenamid were suitable alternatives to acetochlor, alachlor, and metolachlor.
Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; black nightshade, Solanum nigrum L. # SOLNI; bristly foxtail, Setaria verticillata (L.) Beauv. # SETVE; common lambsquarters, Chenopodium album (L.) # CHEAL; common purslane, Portulaca oleracea L. # POROL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; jimsonweed, Datura stramonium L. # DATST; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; redroot pigweed, Amaranthus retroflexus L. # AMARE; yellow foxtail, Setaria glauca (L.) Beauv. # SETLU; corn, Zea mays L. ‘Pioneer Costanza’, ‘Pioneer Eleonora’, ‘Shell Nikerson’; oat, Avena sativa L. ‘Kassandra’.
Additional index words: Acetochlor, alachlor, dimethenamid, flufenacet, s-metolachlor, microencapsulated formulations.
Abbreviations: DAT, days after treatment; EC, emulsifiable concentrate; ME, microencapsulated; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.
Advances in biotechnology within the last decade have caused dramatic changes in agricultural production systems. In Mississippi, over 60% of the soybean hectarage was planted to glyphosate-resistant soybean in the 2001 production season. One advantage of glyphosate-resistant systems may be that fields with fewer weeds at harvest result in less foreign material and lower seed moisture due to less foreign material. Research was conducted to assess the foreign matter and moisture content of representative glyphosate-resistant and conventional soybean by evaluating elevator receipts collected from soybean producers in the southern and midwestern United States. A survey of growers using glyphosate-resistant and conventional soybean was conducted during the fall and winter of 2000. Copies of elevator receipts were collected to compare the foreign matter percentage and moisture content of soybean in both categories. A total of 16,535 ha were represented, of which 13,903 were from glyphosate-resistant soybean and 2,632 were from conventional soybean. Average foreign matter content from the glyphosate-resistant soybean was 1.9%, compared with 2.5% from the conventional soybean. Thus, the glyphosate-resistant program reduced foreign matter, an indication of reduced weed seed and trash contained in the sample or improved harvest efficiency. No difference was noted in seed moisture content between the two systems.
Interference between weeds and crops is a key topic in undergraduate weed science courses. A laboratory exercise was developed at Iowa State University to actively demonstrate how small-seeded weeds can compete with large-seeded crops despite the initial seedling size disadvantage. Spring wheat and wild mustard were grown in pots in monoculture and in competition with each other. One set of plants was harvested at 1 wk after planting and another at 6 wk after planting. Relative growth rates (RGR) were calculated for the 5-wk period using the classical approach of plant growth analysis. The results from four semesters were analyzed to determine whether the experiment was meeting its intended outcomes. It was successful in this regard. In each of the four semesters, wild mustard had a lower initial dry weight and a greater RGR than did wheat. Students were required to write a scientific paper using the experimental results after completing a series of active-learning exercises. Assessment by students suggested that the experiment, active-learning exercises, and writing assignment were valuable activities.
Nomenclature: Spring wheat, Triticum aestivum L. ‘Sharp’; wild mustard, Brassica kaber (DC.) L. C. Wheeler #3 SINAR.
Additional index words: Education, weed biology, weed ecology.
Crop–weed interactions is an important topic for introductory weed science courses. The effect of the timing of weed emergence and the duration of weed competition on crop yield are two topics usually covered when discussing competition. Students generally gain a better knowledge of these concepts through observation in addition to discussion of the underlying concepts. An additive removal and plant-back experiment was used, in the undergraduate weed science laboratory at Iowa State University, to demonstrate critical period for weed control concepts for cultivated radish. In one series of treatments, weeds were sown at the time of radish planting and removed at 2, 3, and 4 wk after planting. In another series, weeds were sown at 1, 2, and 4 wk after radish planting and allowed to grow in the flats until completion of the experiment. Two controls, one weed free and one unweeded, were also included. The results from four semesters suggested that the critical period for weed control began immediately after planting and lasted 3 wk. The timing and duration of the critical period was consistent across the four semesters evaluated. This activity was successful in demonstrating the critical period for weed control in radish.
Nomenclature: Radish, Raphanus sativus L.
Additional index words: Competition, education, weed ecology, weed-free period.
Row crop weed management decisions can be complex due to the number of available herbicide treatment options, the multispecies nature of weed infestations within fields, and the effect of soil characteristics and soil-moisture conditions on herbicide efficacy. To assist weed managers in evaluating alternative strategies and tactics, three computer programs have been developed for corn, cotton, peanut, and soybean. The programs, called HADSS™ (Herbicide Application Decision Support System), Pocket HERB™, and WebHADSS™, utilize field-specific information to estimate yield loss that may occur if no control methods are used, to eliminate herbicide treatments that are inappropriate for the specified conditions, and to calculate expected yield loss after treatment and expected net return for each available herbicide treatment. Each program has a unique interactive interface that provides recommendations to three distinct kinds of usage: desktop usage (HADSS), internet usage (WebHADSS), and on-site usage (Pocket HERB). Using WeedEd™, an editing program, cooperators in several southern U.S. states have created different versions of HADSS, WebHADSS, and Pocket HERB that are tailored to conditions and weed management systems in their locations.
Nomenclature: Corn, Zea mays L.; cotton, Gossypium hirsutum L.; peanut, Arachis hypogea L; soybean, Glycine max L.
Additional index words: Bioeconomic models, computer decision aids, decision support systems, weed management.
Abbreviations: HADSS, Herbicide Application Decision Support System; PDS, postemergence-directed; POST, postemergence; PPI, preplant-incorporated; PRE, preemergence.