Bipolaris sorghicola (isolate BS1) and an unidentified Bipolaris species (isolate BX1) were isolated from johnsongrass in North Carolina. Inoculum of BX1 was mass produced in solid and liquid cultures, whereas inoculum of BS1 could only be produced in solid cultures. When six formulations of inoculum of BX1 were compared, vegetable oil was the best adjuvant. Isolate BX1 displayed some host specificity in pathogenicity tests. In the greenhouse, isolate BS1 was more virulent on johnsongrass than isolate BX1. In growth chambers, increasing conidium concentration and younger plant ages interacted to increase virulence of BX1, as did interactions between inoculation, johnsongrass density, and low soil fertility. In Raleigh, NC, isolate BX1 caused very little damage in the field, with or without pretreatment with metolachlor. In Greenville, MS, isolate BX1 caused significant (52%) mortality to annual johnsongrass with very little damage to corn or grain sorghum. The biocontrol potential of the two organisms is uncertain.

Paraffinic oil applied at 2.3, 4.7, and 9.3 L/ha to the surface of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] leaves spread to provide complete coverage of the leaf surface. Soybean oil applied at the same volumes provided only 30 to 50% coverage of leaf surfaces. Water at 187 L/ha that contained 1.25% paraffinic oil adjuvant provided only about 30% coverage because spray droplets did not spread appreciably. Spread coefficients obtained when five different oil-soluble herbicides were applied to leaf surfaces in paraffinic oil were more than 100 times greater than when applied in water alone. Higher spread coefficients were obtained when paraffinic oil contained herbicides than when paraffinic oil was applied alone. Spread coefficients were also much greater for paraffinic oil alone than for soybean oil with or without herbicides. Stomata on johnsongrass leaves were distorted by paraffinic oil, suggesting that leaf surface wax was dissolved and this might be a mode of entry of herbicide into johnsongrass when applied in paraffinic oil. Stomata were unaffected by soybean oil or by water sprays that contained 1.25% soybean oil adjuvant or paraffinic oil adjuvant.

Investigations showing the effective use of simazine [2-chloro-4,6-bis (ethylamino)-s-triazine] as a selective herbicide in several crops particularly in corn has resulted in a demand for information about its degradation in plants. It is extremely important then to know if toxic residues remain in plants. Evidence to the contrary would be obtained if plants treated with simazine uniformly labeled with carbon-14 in the triazine ring were found to respire radioactive carbon dioxide.

Tubers of sago pondweed (Potamogeton pectinatus L.) were grown at 72 F in a 14-hr photoperiod under 400 ft-c of coolwhite fluorescent illumination. Plants were randomly harvested each day for 30 days, the organs individually weighed, and carbohydrate determinations made on selected tissues. Unsprouted tubers averaged 19.5% dry weight of which 74% was carbohydrate, predominantly in non-extractable form. During growth, the carbohydrate supply in the tubers decreased logarithmically by ½ each 4.93 days. Shoots began to grow logarithmically at 11 days, doubling in dry weight each 4.5 days. After 18 days, the carbohydrate content of the main shoot increased logarithmically, doubling each 7.35 days. Plants produced from average tubers increased 7-fold in dry weight in 30 days. Growth analysis showed that no shoots became self-sufficient before 16 days. Deduced patterns of carbohydrate flow are correlated with reports of herbicidal effectiveness.

This research was conducted near North Platte, NE, over an 18-yr period to determine the feasibility of using herbicides to replace tillage as the weed control method in a winter wheat (Triticum aestivum L.)-sorghum [Sorghum bicolor (L.) Moench.]-fallow rotation. Five tillage treatments [two tillage and three reduced or no-till treatments] were used on the same plots during the duration of this experiment on a Holdrege silt loam (Typic Argiustolls). Herbicides effectively replaced tillage for weed control. The no-till plots treated with atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] after wheat harvest had higher sorghum and winter wheat yields, higher crop residue remaining on the soil surface, and lower weed yields than tilled plots. The most difficult weeds to control were volunteer wheat and barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG]. Soil surface pH decreased over time because of increased use of nitrogen. The pH in nontilled plots was significantly lower than in tilled plots due to lack of soil mixing. Exchangeable calcium was the predominant cation leached from the top 5 cm but showed accumulation between the 5- to 12.5-cm depth. Organic matter content showed little change over time.

In greenhouse tests, the host specificity of Alternaria crassa (Sacc.) Rands, a mycoherbicide for jimsonweed was altered by the addition of water-soluble filtrates of jimsonweed and hemp sesbania or fruit pectin to fungal conidia suspensions. Several crop and weed species that were resistant to the fungus alone exhibited various degrees of susceptibility following these amendments, with 100% mortality occurring to the weeds hemp sesbania, showy crotalaria, and eastern black nightshade when treated with the fungus/pectin mixture. Nonhost plants that were inoculated with conidial mixtures amended with sucrose or cellulose were not affected. Modification of host specificity of this pathogen could have an influence on its bioherbiddal potential

Laboratory experiments were carried out under aseptic conditions to study the effect of nitrogen applied as ammonium nitrate at 0, 20,40,60,80 and 100 ppm (wt per vol) in either distilled H2O or modified Hoagland's solution on germination and radicle length of branched broomrape in association with growing seedlings of different crops. As nitrogen rate increased, seed germination and radicle length of branched broomrape decreased linearly in flax, lentil, pepper, tomato, and wheat in modified Hoagland's solution. Similar responses to nitrogen application were found with distilled water. The parasite's seed germination was considerably lower in the media with wheat than with other crops, and lower still in the absence of crop seedings.

Studies were conducted at East Lansing, MI, in 1994 and 1995 to examine corn yield response to giant foxtail interference and to examine the effect of giant foxtail density on giant foxtail biomass, seed production, and seed germination. Treatments consisted of 0, 10, 30, 60, 84, and 98 giant foxtail plants m−1 of row in 1994 and 0, 10, 27, 30, 60, and 69 plants m−1 of row in 1995. The influence of giant foxtail density on corn yield fit a hyperbolic equation. Corn yields were reduced 13% in 1994 and 14% in 1995 from 10 giant foxtail plants m−1 of row. Corn dry matter at maturity was decreased 24 and 23% from 10 giant foxtail plants m−1 of row in 1994 and 1995, respectively. Giant foxtail seed production increased linearly as inflorescence length increased. The length of a single giant foxtail inflorescence increased as plant density increased and the number of inflorescence produced per plant decreased. Giant foxtail seed production ranged from 518 to 2,544 seeds per plant. Ten giant foxtail plants m−1 of row produced 15,700 seeds m−2. Giant foxtail seed germination was not affected by plant density.

The conditioning and germination processes of witchweed [Striga asiatica (L.) Kuntze] seeds were regulated by synthetic dl-strigol (ST) or natural stimulants (STM) present in a corn (Zea mays L.) root-exudate solution. Seeds conditioned in water for 7 and 14 days required 10−10 and 10−12M ST, respectively, to induce maximum germination (ca. 80%). Surprisingly, conditioning seeds in ST or STM had an adverse effect on the responsiveness of the seeds to the same compounds after conditioning. Compared to seeds conditioned in water, these ST- or STM-conditioned seeds required not only higher concentrations of ST or STM to induce maximum germination, but also longer immersion time to become conditioned. ST or STM inhibits conditioning and thus the regulation of germination by ST or STM depends mainly on the stage of conditioning of seeds when they are exposed to ST or STM. ST or STM stimulates germination only after a pre-germination threshold is reached during conditioning. Exposure of seeds to ST or STM before this critical level is reached apparently inhibits conditioning.

Benghal dayflower (formerly known as tropical spiderwort) is one of the most troublesome weeds in Georgia cotton. Field studies were conducted from 2003 to 2005 to evaluate the relationship between the duration of Benghal dayflower interference and cotton yield to establish optimum weed-control timing. To determine the critical period of weed control (CPWC), Benghal dayflower interference with cotton was allowed or prohibited in 2-wk intervals between 0 to 12 wk after crop planting. Maximum yield loss from Benghal dayflower in May-planted cotton was 21 to 30% in 2004 and 2005, whereas cotton planting delayed until June resulted in maximum yield losses of 40 to 60%. June-planted cotton had a CPWC of 190 to 800 growing degree days (GDD) in 2004 (52-d interval beginning at 16 d after planting [DAP]) and 190 to 910 GDD in 2005 (59-d interval beginning at 18 DAP). In contrast, May-planted cotton in 2005 had a narrower CPWC interval of 396 to 587 GDD (18 d) that occurred 3 wk later in the growing season (initiated at 39 DAP). May-planted cotton in 2004 did not have a critical range of weed-free conditions. Instead, a single weed removal at 490 GDD (44 DAP) averted a yield loss greater than 5%. It is recommended that fields infested with Benghal dayflower be planted with cotton early in the growing season to minimize weed interference with the crop.

Neither herbicides nor Aphthona spp. biological control agents provide satisfactory leafy spurge control in all environments where the weed is found. Open-release and caged field studies were conducted to determine the effect of herbicides used in combination with Aphthona spp. flea beetles on both the leafy spurge control and the biological control agent populations. Leafy spurge density was reduced more rapidly when A. nigriscutis or a mixture of A. czwalinae and A. lacertosa was combined with a fall-applied treatment of picloram plus 2,4-D than when either method was used alone. The combination treatment reduced leafy spurge density 3 to 5 yr earlier than did either the herbicides or the biocontrol agents alone and once reduced, the Aphthona flea beetles maintained acceptable control for at least 7 yr. Spring-applied herbicides eliminated the adult food source and negatively affected the flea beetle establishment, but fall-applied treatments did not reduce the flea beetle establishment or its reproduction. The combination treatment was most successful when used with established Aphthona spp. populations that were not increasing in size or reducing leafy spurge density. Land managers could realize a three- to fivefold cost savings with the combination treatment compared with herbicides alone.

Clomazone dissipation was examined in four soils in field experiments. Field half-lives were 6 to 59 d (average of four field sites was 35 d) for ferrosol (clay loam), kurosol (loamy sand), sodosol (silt loam), and vertosol (light clay). The Hoerl equation provided a better fit to the measured field concentration at all four sites than did a first-order equation. The order of clomazone dissipation rate was ferrosol > sodosol > kurosol > vertosol. Clomazone desorption varied with soil type, with apparent K d values of 3.6, 1.7, 1.8, and 2.4 for ferrosol, sodosol, kurosol, and vertosol, respectively. Clomazone residues became more strongly sorbed with time, as indicated by desorption hysteresis, but detectable concentrations were present in all soils 1 yr after application. The data indicate that the potential for carryover injury to crops is greatest in the kurosol and least in the ferrosol.

Absorption of (2,4-dichlorophenoxy)acetic acid (2,4-D) by honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] was 7.2, 9.3, and 10.9% of the applied herbicide at 1, 4, and 8 days after treatment, respectively. Addition of 1.0% v/v Tween 80 to the treatments increased absorption to 55.8, 71.3, and 78.7% at the same sampling dates. Metabolic alteration of the herbicide occurred only in the aerial portions of the plant, and this was not great enough to be considered as a means of resistance. Translocation of 2,4-D into the roots was more closely related to new root growth than to the amount of top growth. Plants with six leaves and no new root growth did not translocate 2,4-D into the root zone. Plants with the same number of leaves but with an average of five and 20 new roots translocated 2.5 and 7.7%, respectively, of the applied herbicide to the roots.

The effect of soil composition on adsorption of chloridazon by 18 samples of natural soils, with different chemical and textural characteristics, obtained from west-central Spain, was investigated. The effect of removal of organic matter on adsorption and adsorption of the herbicide by the active components of the soils (montmorillonite and humic acid) was also studied. A highly significant correlation was found between the distribution coefficient (Kd) and organic matter content when all the soils or the soils with organic matter content >2% were considered. According to the determination coefficients (r2), organic matter content accounted for 72% of the variance in adsorption in the former case and 92% in the latter. In soils with an organic matter content <2%, there was no correlation between Kd and organic matter content. A significant correlation was observed between Kd and smectite content for soils containing smectite in their clay fraction. Both simple and multiple correlations showed that clay content, excluding the smectite fraction, had a relatively small effect on adsorption of the herbicide. Adsorption of chloridazon by oxidized soils, montmorillonite, and humic acid confirms the effect of organic matter and smectite on adsorption in natural soils.

Absorption and translocation of 14C-mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} in soybeans [Glycine max (L.) Merr. ‘Lee 68’], common cocklebur (Xanthium pensylvanicum Wallr.), and johnsongrass [Sorghum halepense (L.) Pers.] were evaluated under different environmental conditions with and without adjuvants. At a constant level of 40 or 100% relative humidity (RH), an increase in air temperature from 22 to 32 C resulted in a two- to three-fold increase in absorption and a four- to eight-fold increase in translocation of the 14C in soybeans following application to the second trifoliolate. At constant 22 or 32 C an increase from 40 to 100% RH resulted in less than a two-fold increase in absorption or translocation of 14C in soybeans. Autoradiograms indicated that movement of the 14C was primarily into leaves above the treated area. Translocation of 14C was significantly greater following application to the lower stem than to leaves. In common cocklebur, 14C absorption increased about three-fold at both 22 and 32 C with an increase from 40 to 100% RH following application to the second alternate leaf. At both levels of RH, absorption and translocation increased as the temperature was increased from 22 to 32 C. The addition of an adjuvant increased absorption and translocation in common cocklebur under all environmental conditions. When 14C-mefluidide was applied without an adjuvant to johnsongrass, absorption increased five- to six-fold at both 22 and 32 C as RH was increased from 40 to 100%. Translocation in johnsongrass was often affected less by variations in temperature than it was in soybeans or common cocklebur. The adjuvant increased absorption and translocation of the 14C-label of mefluidide in johnsongrass. The 14C-label accumulated primarily in the distal leaf of johnsongrass or in leaves above the treated area.

Seedbed preparation was completed about October 15, just before the fall rains. Four herbicide treatments, 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat), 6,7-dihydrodipyrido(1,2-a:2’,1′-c)pyrazidiinium salt (diquat), isopropyl N-phenylcarbamate (IPC) + butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D), and 3-amino-l,2,4-triazole + ammonium thiocyanate (amitrole-T) were successfully applied before Janaury 15 for control of weeds and volunteer crop plants. Grasses for seed production were sown in March without disturbing the soil. An application of paraquat at seeding greatly increased subsequent seed yields. Little additional germination of contaminating weed grasses occurred after the grasses were planted and they became established rapidly. By the following October most species could be treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) to control winter annual weeds. Where weeds were thus effectively controlled during the establishment period, excellent stands resulted which produced high yields of weed-free seed in the first year of seed production.

The biological effectiveness of any systemic herbicide is vitally dependent upon the absorption of the chemical by the plant. The process of absorption is of particular interest in the use of herbicides and it is only as this process is understood and turned to advantage that maximum effectiveness of applied chemical can be achieved. In foliar absorption, with which this paper is concerned, the cuticle plays a very important role (2). The thickness and general state of the cuticle and the attendant stomata have been shown to vary markedly with growth conditions (10). The submicroscopic structure of cuticles and the accretion of wax deposit on leaf surfaces have been studied (7, 8). These factors are of significance in the consideration of the intimacy of the contact of a particle impinging on the leaf. The chemical nature of the cuticle (6) is undoubtedly of great importance in the partitioning of certain herbicides between a particle of the chemical and the interior of this leaf.

Interest in weed seed predation as an ecological weed management tactic has led to a growing number of investigations of agronomic and environmental effects on predation rates. Whereas the measurements in most of these studies have taken place at very short timescales, from days to weeks, measurements at longer timescales (from several months to a year) have greater relevance to the demographic impact of weed seed predation and potential contributions from this process to ecological weed management. Our aim was to quantify the impact of crop phase, within a corn–soybean–wheat crop sequence, on quarterly and annual seed predation rates of giant foxtail, giant ragweed, and velvetleaf. The study took place in areas of the northern U.S. Corn Belt contrasting in dominant land use: Savoy, IL (2005–2007), where corn and soybean production predominates, and East Lansing, MI (2005–2008), where crop production occurs within an old field/forest landscape matrix. Mean annual rates of weed seed predation by the combined action of invertebrate and vertebrate predators were 31 ± 1.6% for giant ragweed, 37 ± 1.4% for velvetleaf, and 53 ± 1.4% for giant foxtail. Crop phase had negligible effects upon long-term seed predation rates, accounting for less than 2% of observed variation. Weed species and site-year, in contrast, contributed 35% and 40%, respectively, of the variation in cumulative annual seed predation. These results are consistent with the spatial variability in best management practices seen at spatial scales greater than the county level: weed seed predation appears to be an inherently site-specific phenomenon. New developments in managing weed seed predation as an ecosystem service are therefore likely to have local recommendation domains or to be driven by stochastic annual variation related to weather or granivore demography.

Pendimethalin dissipation was studied following annual 1.7 kg ai ha–1 applications to 3-yr-old Kentucky bluegrass turf growing on a Sharpsburg silty clay loam soil and an 85/15 by volume sand/Sharpsburg soil mixture in 150-cm-deep rhizotron containers. Plant tissue, thatch, and soil were sampled periodically between application and 168 days after treatment (DAT). Soil and leachate were collected to monitor pendimethalin movement. Most of the herbicide appeared to remain within the turfgrass system. Pendimethalin concentration was highest in plant tissue and thatch. The 4-hydroxymethyl pendimethalin metabolite was detected in turfgrass tissue up to 42 DAT. No pendimethalin was detected at the 30-, 60-, or 120-cm depths in the rhizotron containers. Traces (≤0.003 mg kg–1) of pendimethalin detected in rhizotron leachate collected between 6 and 14 days after heavy rainfall (88 and 95 DAT, respectively) were attributed to gravitational displacement of soil colloids containing adsorbed herbicide. Pendimethalin application to established turfgrass would not appear to pose a high risk of groundwater contamination.

Florpyrauxifen-benzyl is a new active ingredient that represents an additional tool in rice (Oryza sativa L.) weed control by providing an alternative mechanism of action. Studies were conducted to evaluate soil moisture influences on florpyrauxifen-benzyl absorption, translocation, and metabolism in three problematic weeds. In the absorption/translocation study, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], hemp sesbania [Sesbania herbacea (Mill.) McVaugh], and yellow nutsedge (Cyperus esculentus L.) were treated with [14C]florpyrauxifen-benzyl under two soil moisture regimes (7.5% and 60% field capacity). Greater absorption occurred under moist conditions (60% soil moisture content). More translocation of the herbicide to the area above the treated leaf occurred under moist versus dry soil across all weed species. Sesbania herbacea translocated 25% of the absorbed herbicide above the treated leaf, a result greater than that of the other two weed species at 60% soil moisture. However, no differences in translocation occurred among the weed species at the 7.5% soil moisture regime. In the metabolism study, 95% of the herbicide recovered was in its acid form under the high soil moisture regime for S. herbacea, a species that shows extreme sensitivity to even low doses of this herbicide, and soil moisture influenced the amount of acid form found in all species. While these data provide a limited view into the physiological processes being affected, they do suggest that for E. crus-galli, S. herbacea, and C. esculentus, soil moisture content in the field will likely play a significant role in absorption, translocation, and metabolism of florpyrauxifen-benzyl.