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.

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.

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.

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%.

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.

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.

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.

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.

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.

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.

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.

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.

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.