White clover is a weed in apple orchards that competes with the crop; also, flowers of this weed are unwanted attractants of honey bees at times when insecticides, which are harmful to these pollinators, are being applied. In 1997 and 1998, white clover flower head and plant control by clopyralid alone and with 2,4-D and apple tolerance to these herbicides were determined. Treatments consisted of clopyralid at 0.10 and 0.21 kg ae/ha, 2,4-D at 1.1 kg ae/ha, and 2,4-D at 1.1 kg ae/ha plus 0.03 or 0.05 kg ae/ha clopyralid, which were applied 2 wk before full apple bloom and 2 wk after full apple bloom, and a nontreated check. No crop injury occurred with any treatment. All herbicide treatments provided some white clover control and flower head suppression. No differences in white clover bloom reduction were observed through May among treatments containing clopyralid. As summer progressed, the effect of clopyralid rate became more apparent. Clopyralid at 0.21, regardless of application time, provided 99% vegetative control and 100% flower head reduction through July. Clopyralid plus 2,4-D controlled white clover better than 2,4-D alone. However, vegetative control and flower head reduction with clopyralid at reduced rates (0.03 or 0.05 kg ae/ha) plus 2,4-D were not acceptable (76% or less and 78% or less, respectively). Thus, clopyralid at 0.10 and 0.21 kg ae/ha will be necessary for acceptable white clover vegetation control and flower head reduction.

Tropical spiderwort (more appropriately called Benghal dayflower) poses a serious threat to crop production in the southern United States. Although tropical spiderwort has been present in the United States for more than seven decades, only recently has it become a pest in agricultural fields. Identified as an isolated weed problem in 1999, tropical spiderwort became the most troublesome weed in Georgia cotton by 2003. Contributing to the significance of tropical spiderwort as a troublesome weed is the lack of control afforded by most commonly used herbicides, especially glyphosate. Vegetative growth and flower production of tropical spiderwort were optimized between 30 and 35 C, but growth was sustained over a range of 20 to 40 C. These temperatures are common throughout much of the United States during summer months. At the very least, it appears that tropical spiderwort may be able to co-occur with cotton throughout the southeastern United States. The environmental limits of tropical spiderwort have not yet been determined. However, the rapid spread through Georgia and naturalization in North Carolina, coupled with its tolerance to current management strategies and aggressive growth habit, make tropical spiderwort a significant threat to agroecosystems in the southern United States.

Experiments were conducted to determine tobacco tolerance to CGA-362622 applied pretransplant (PRE-T) and postemergence (POST) to tobacco and applied the previous year preemergence (PRE) and POST to cotton. CGA-362622 applied at 3.75 or 7.5 g ai/ha PRE-T injured ‘K326’ flue-cured tobacco 1%, whereas POST treatments resulted in 4 to 5% injury. Tobacco injury was transient with no mid- or late-season injury noted. Tobacco yields from all CGA-362622 POST treatments were not different from the nontreated weed-free check. Tobacco treated with 7.5 g/ha CGA-362622 PRE-T yielded greater than nontreated weed-free tobacco or tobacco treated with CGA-362622 POST. When grown in rotation, tobacco was not injured, and yields were not influenced by CGA-362622 applied PRE or POST to cotton the previous year.

Many herbicides that control broadleaf weeds in wheat can antagonize grass herbicide efficacy, resulting in less grain yield due to competition. Also, the broadleaf herbicide carfentrazone-ethyl can injure wheat, leading to less grain yield because of physiological response. Experiments were conducted to evaluate carfentrazone-ethyl antagonism of fenoxaprop-ethyl, tralkoxydim, clodinafop-propargyl, imazamethabenz, and flucarbazone-sodium and injury to wheat with tank mixes of carfentrazone-ethyl plus each grass herbicide or thifensulfuron, tribenuron, metsulfuron, or imazamox. Carfentrazone-ethyl did not adversely affect control of wild oat or yellow foxtail by grass herbicides in wheat. Carfentrazone-ethyl alone caused 21% wheat injury 3 d after treatment. Adding flucarbazone-sodium to carfentrazone-ethyl resulted in the least wheat injury among treatments that included carfentrazone-ethyl. Fenoxaprop-P-ethyl or clodinafop-propargyl with carfentrazone-ethyl also resulted in less wheat injury compared with carfentrazone-ethyl alone, which was attributed to formulation safeners. Sulfonylurea herbicides provided safening of carfentrazone-ethyl similar to flucarbazone-sodium, while imidazolinones did not alleviate injury. Tralkoxydim plus carfentrazone-ethyl gave 28% wheat injury compared with 21% from carfentrazone-ethyl alone. Wheat injury was no longer visible by 20 d after treatment, and wheat yield was not affected by carfentrazone-ethyl injury when wild oat and yellow foxtail were present or controlled with herbicide.

Spatial patterns of the exotic riverine knotgrass (Paspalum distichum L.) were examined in Mediterranean river basins in Southwestern Iberia. The major goals of this study were to assess the degree of invasibility of riparian habitats by this species and to determine the influence of environmental factors and human-induced disturbances that this knotgrass has on both the landscape and the habitat scales. The present study demonstrates the ability of knotgrass to invade riparian habitats in Portuguese freshwater ecosystems. However, most of the spatial variation of the knotgrass cover seemed to be driven by local factors, such as fine sediment enrichment and the fragmentation of riparian woods, and by other anthropogenic interferences in relation to both the fluvial system and the surrounding landscape.

Composted manure produced in deep-bedded hoop structures constitutes a source of nutrients and organic materials that can influence crop and weed emergence, growth, competitive interactions, and soil physical properties. The impact of composted swine manure on corn, soybean, winter wheat, velvetleaf, giant foxtail, and common waterhemp emergence and early growth were compared at compost rates of 0, 8, 16, or 24 Mg C/ha. Compost amendment had no effect on crop emergence but did reduce weed emergence. Inhibition of seedling emergence ranged between 15 and 57% for giant foxtail, 0 and 23% for velvetleaf, and 16 and 76% for common waterhemp. Soil amendment enhanced weed growth but not crop growth. A response surface regression analysis indicated that, while large-seeded crops have constant relative growth rates, small-seeded weed species increase their relative growth rates with compost amendment (P < 0.0001, r2 = 0.5252).

The persistence and efficacy of acetamide herbicides at application timings from fall to preemergence (PRE) were studied in 1998 and 1999 on mollisols (1.1 to 2.8% organic carbon). Metolachlor, s-metolachlor, acetochlor (as an emulsifiable concentrate [EC] formulation and two encapsulated formulations, capsule suspension [CS] and microencapsulated [ME]), and the combination of flufenacet + metribuzin were evaluated at five application times including late fall, 60 and 30 d early preplant (EPP), preplant incorporated, and PRE. Soil bioassays 180 d after application indicated flufenacet + metribuzin, metolachlor, s-metolachlor, and the acetochlor CS had 62 to 74% giant foxtail control, whereas acetochlor EC and ME had 43 to 46% control. Applications at 60 EPP of metolachlor, s-metolachlor, and acetochlor CS provided 70 to 75% giant foxtail control in greenhouse bioassays, whereas flufenacet + metribuzin, acetochlor ME, and acetochlor EC provided 38 to 57% control. At the 30 EPP timing, metolachlor and acetochlor CS had 80 to 82% control, whereas acetochlor EC provided 46% control, and acetochlor ME, flufenacet + metribuzin, and s-metolachlor had 65 to 74% control. Quantitative soil analysis (0 to 6 cm) 10 d after planting (DAP) indicated metolachlor, s-metolachlor, and acetochlor CS concentrations ranged from 12 to 16% and 32 to 47% of applied herbicide for the fall and PRE application timings, respectively, whereas acetochlor (ME and EC) were from 1 to 3% and 16 to 21% of applied for the fall and PRE application timings, respectively. Bioassay reduction was correlated (R2 = 0.68) with soil-herbicide concentrations at 10 DAP.

The limited window of opportunity for glyphosate postemergence (POST) over-the-top applications in glyphosate-resistant cotton poses a problem for growers where a midseason salvage weed control remedy is necessary. The objectives of these experiments were to compare glyphosate and MSMA for midseason weed control and their subsequent effect on cotton fruiting characteristics and yield. Glyphosate at 0.85 kg ai/ha was more effective than MSMA at 1.7 kg ai/ha for POST control of sicklepod, redweed, and pitted morningglory. Single glyphosate treatments applied at the 8-, 10-, or 12-leaf cotton stage resulted in less-effective weed control than when applied at the four-leaf cotton stage. Glyphosate applied at the four-leaf cotton stage followed by a sequential POST-directed application at 6-, 8-, 10-, or 12-leaf cotton stage increased season-long weed control and yield compared with a single application at the four-leaf stage. Both glyphosate and MSMA controlled Florida beggarweed, regardless of POST application timing. Generally, cotton was more tolerant to glyphosate than MSMA when applied over-the-top. Glyphosate applied POST over-the-top to weed-free 12-leaf cotton resulted in a 19 and 14% yield loss compared with the weed-free nontreated cotton in 1997 and 1999. MSMA reduced yield by 58 and 36% in 1997 and 1999, respectively. Glyphosate did not affect weed-free cotton fruit development or yield when applied over-the-top to four-leaf cotton or when a POST-directed application was followed at the 12-leaf stage.

Studies were conducted from 2001 through 2003 to determine the extent of resistance to acetolactate synthase (ALS) inhibitors and glyphosate in Ohio horseweed biotypes. The response of 66 horseweed biotypes to cloransulam-methyl and glyphosate was determined in the greenhouse. Application of 0.07 kg ai cloransulam/ha reduced plant biomass by less than 60% for 38 of the 66 biotypes. Application of 3.4 kg ae glyphosate/ha reduced biomass by at least 80% for the 51 biotypes collected in 2001, but biomass was similar to that of nontreated plants for 11 of the 15 populations collected in 2002. A dose–response study was conducted with selected biotypes, and a nonlinear, logistic dose–response curve was fit to the data to calculate the herbicide dose required to reduce fresh weight 50% (GR50). On the basis of GR50 values, the resistance ratio (R/S) for two ALS-resistant biotypes was 34 and 943 for chlorimuron-ethyl and 32 and 168 for cloransulam, respectively. The R/S ratio for two glyphosate-resistant biotypes was 33 and 39. Results of these studies indicate that, in 2002, ALS-resistant horseweed was widespread throughout Ohio, whereas resistance to glyphosate occurred primarily in several counties in southwestern Ohio.

Wild oat is the most serious grass weed in Argentine barley crops and its control has concentrated on herbicide strategies. Increasing crop density could be an effective strategy to reduce the effect of wild oat on barley yield. However, limited research has been conducted to evaluate the effect of crop density on the competitive balance between barley and spontaneous populations of wild oat. A field experiment was conducted in 1992, 1993, and 1999, to study the effect of spontaneous populations of wild oat on barley sown at densities of 160, 220, and 280 plants/m2. Wild oat density averaged 84 plants/m2. Wild oat biomass increased linearly with weed density in all treatments but was reduced by increasing barley seeding rates. Barley biomass and yield were not affected by wild oat at high crop sowing densities, but for the low and medium barley densities, yield loss was almost 25% when 70 wild oat plants/m2 were established. Barley yield loss was mostly related to competition from the early emerged wild oat. The relationship between yield losses and wild oat density was equally significant when the whole population or only early emerged individuals of the weed were considered.

Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when peas experienced moisture stress.

Junipers (Juniperus spp.) are native woody shrubs that have expanded beyond their normal historical ranges in the western and southwestern United States since the late 1800s. Most ecologists and resource managers agree that juniper has become a deleterious native invasive plant that threatens other vegetation ecosystems, such as grasslands, through a steady encroachment and ultimate domination. The use of fire in managing junipers is based on a management goal to increase the disturbance return interval and thereby reduce the abundance and/or competitive impact of juniper in an ecosystem. In this paper, we discuss rates of juniper encroachment in relation to presettlement fire regimes, juniper encroachment and soil health, postfire vegetation responses, and long-term potential of different juniper treatment scenarios that involve prescribed fire.

Based on field surveys and evaluations in the greenhouse, two fungal pathogens, Bipolaris sacchari and Drechslera gigantea, were identified as promising biological control agents for cogongrass. In greenhouse trials, the application of spore suspensions of these fungi containing 105 spores/ ml in a 1% aqueous gelatin solution to cogongrass plants and their incubation in a dew chamber for 24 h resulted in disease symptoms that ranged from discrete lesions to complete blighting of leaves. Disease severity (DS), based on a rating scale for southern corn leaf blight with 50% as the maximum DS rating, ranged from 42 to 49%. In greenhouse experiments, the application of spores formulated in an oil emulsion composed of 4% horticultural oil, 10% light mineral oil, and 86% water resulted in higher levels of foliar blight with no dew exposure or shorter periods of dew exposure (4, 8, or 12 h) as compared with the application of spores formulated in 1% gelatin. Field trials demonstrated that under natural conditions, the application of a spore and an oil emulsion mixture containing 105 spores/ml of either fungus could cause foliar injury from disease and phytotoxic damage from the oil emulsion. Depending on the application rate (100 or 200 ml/plot), the level of foliar injury ranged from 40 to 86% (based on a field assessment scale of 0 to 100% foliar injury) with B. sacchari as the test fungus. However, with D. gigantea as the test fungus, foliar injury ranged from 9 to 70% depending on the application volume and the oil concentration used. Although B. sacchari and D. gigantea were capable of causing foliar blight on cogongrass, the regenerative ability of the rhizomes allowed cogongrass to recover from the damage caused by these fungi. However, the level of injury caused by these fungi is sufficient to support their use as components for integrated management of cogongrass.

Wide-spread planting of glyphosate-resistant (GR) crops in the United States and glyphosate patent expiration has led to a proliferation of glyphosate products. Growers have questioned their advisors on efficacy and crop tolerance of the many products available. Field experiments were conducted to evaluate eight glyphosate products in 2002 and ten in 2003, representing isopropylamine, diammonium, and potassium salts, applied POST and postemergence-directed (PDIR) at 630 and 1,680 g ae/ha for GR corn and GR cotton tolerance and weed control. There were no differences among products for control of six annual grass and 10 annual broadleaf weed species. No injury to corn from any glyphosate product at 630 or 1,680 g/ha or to cotton from 630 g/ha was noted at any of seven locations. ClearOut 41 Plus™, an isopropylamine salt of glyphosate, and Roundup WEATHERMAX™, a potassium salt of glyphosate, applied POST at 1,680 g/ha injured cotton 27 to 30% and 10 to 17%, respectively, at 3 of 7 locations. No cotton injury was noted with Glyfos®, Glyfos® X-TRA, Glyphomax™, Gly Star™ Original, Roundup Original™, Roundup UltraMAX®, Touchdown®, or Touchdown Total™. No differences were noted among glyphosate products or between rates for corn or cotton yield or cotton fiber properties.

Invasive alien species (IAS) are a major threat to biological diversity on a global scale, necessitating international cooperation to address the problem. This paper gives the context in which action against IAS needs to take place, explains the need for international cooperation, and provides examples of key international instruments, strategies, and programs to deal with IAS.

Perennial pepperweed, found throughout the western United States, reduces biodiversity and causes economic losses in the form of control costs as well as decreased quantity and quality of agricultural yields. The future stream of net benefits of weed management and the future point in time at which they will have accumulated enough to equal total management costs were estimated under different land-use and expansion rate scenarios. Benefits and costs were calculated in present value terms by applying a rate of discount to future values. On land used solely for grazing, the total economic returns from management did not equal total costs until 15 yr after initial treatment. However, on land used for grazing plus hay harvest, cumulative benefits equaled and began to exceed cumulative costs after 4 to 5 yr. The costs and benefits of management efforts were also estimated for a landowner, who controls an adjacent infestation before it spreads. This landowner benefited economically from weed management in as little as 5 to 6 yr, highlighting the importance of cooperative efforts to control nearby weed infestations.

Michigan soybean producers have observed that glyphosate efficacy is sometimes reduced in tank mixtures with foliar manganese (Mn) fertilizers. The objectives of this study were to evaluate the effects of Mn formulation, Mn application timing, tank mixture adjuvants, and Mn rate on glyphosate efficacy. Three Mn formulations, manganese sulfate and ethylaminoacetate chelate (Mn-EAA), manganese sulfate and lignin sulfonate chelate (Mn-LS), and manganese sulfate monohydrate (MnSO4) reduced glyphosate efficacy in greenhouse and field bioassays, but Mn ethylenediaminetetraacetate (Mn-EDTA) did not. Mn-EAA applied less than 3 d before glyphosate reduced glyphosate efficacy on velvetleaf but not giant foxtail or common lambsquarters. The antagonism increased as the interval between treatment applications was shortened but did not appear when Mn was applied to velvetleaf 1 d or more after glyphosate. Including the adjuvants ammonium sulfate (AMS), EDTA, or citric acid in the glyphosate–Mn tank mixture increased control of giant foxtail and velvetleaf but only matched the efficacy of the glyphosate plus AMS control in three combinations: AMS with Mn-LS on velvetleaf, citric acid with MnSO4 on giant foxtail, and EDTA with Mn-EAA on giant foxtail. AMS increased the glyphosate efficacy in Mn tank mixtures as much as, or more than, citric acid and EDTA, with two exceptions: EDTA with Mn-EAA on giant foxtail and citric acid with MnSO4 on velvetleaf. Control of velvetleaf declined as the amount of Mn from Mn-EAA, Mn-LS, and MnSO4 in the tank mixture increased.

CGA-362622 has been registered for postemergence (POST) over-the-top or POST-directed application in cotton. Research was conducted during 1998 in Texas to determine potential cotton phytotoxicity after POST application of CGA-362622 alone and with the insecticides acephate, dicrotophos, azinphos methyl, oxamyl, thiamethoxam, dimethoate, and malathion and to determine the response of four cotton cultivars to CGA-362622 applied alone. CGA-362622 applied with malathion injured cotton more than either pesticide applied alone, and yield was reduced in one of four locations when the pesticides were applied in mixture compared with nontreated cotton. Pyrithiobac or CGA-362622 mixed with malathion injured cotton similarly. The other insecticides tank mixed with CGA-362622 generally did not adversely affect cotton. The cotton cultivars ‘Delta and Pine Land 50’, ‘Paymaster 1220’, ‘Paymaster 1220RR’, and ‘Stoneville 474’ responded similarly to CGA-362622 applied alone or with insecticides.

Experiments were conducted in North Carolina during 2002 and 2003 to evaluate entireleaf morningglory control by 2,4-DB applied alone or with seven fungicides. In a separate group of experiments, tall morningglory control by 2,4-DB was evaluated when applied in four-way mixtures with the following: the fungicides azoxystrobin, chlorothalonil, pyraclostrobin, or tebuconazole; the insecticide lambda-cyhalothrin; and the foliar fertilizer disodium octaborate or the plant growth regulator (PGR) prohexadione calcium plus urea ammonium nitrate. Pyraclostrobin, but not azoxystrobin, boscalid, chlorothalonil, fluazinam, propiconazole plus trifloxystrobin, or tebuconazole, reduced entireleaf morningglory control by 2,4-DB. Mixtures of fungicides, insecticides, and foliar fertilizer/ PGR did not affect tall morningglory control by 2,4-DB. Placing artificial morningglory in the peanut canopy when fungicides were applied did not intercept enough fungicide to increase peanut defoliation by early leaf spot and web blotch or reduce pod yield compared with fungicide applied without artificial morningglory.

The response of rice and barnyardgrass to clomazone rates (0.22, 0.45, 0.67, 0.9, and 1.12 kg ai/ha) and application timings of preplant incorporated, preemergence (PRE), and delayed PRE (DPRE) were evaluated from 1997 to 1999. Rice bleaching at 14 d after planting (DAP) increased from 5 to 35% as the clomazone rate increased. At 14 and 49 DAP, barnyardgrass control decreased with clomazone at 0.22 kg/ha compared with control at higher rates. Clomazone at 0.22 kg/ha resulted in lower grain yield. Clomazone PRE caused less rice bleaching and lower grain yield compared with DPRE timings. These results indicate that initial bleaching by high clomazone rates may not translate into yield loss. Higher clomazone rates may increase rice yield by improving weed control.