Substantial resources are spent each year on weed control, but in many cases eradication projects are incomplete. Here we used the computer program NEWGARDEN to model whether alternate geometric patterns of incomplete removal (99% removed) of the increasingly invasive Callery pear from an isolated fragment differentially affect the rate of population recovery and genetic diversity retention. Geometric patterns of remaining founders within the fragment (1% of the fragment area) included: (A) a long rectangular strip centered on one edge; (B) a square at one corner; (C) a central square; or (D) scattered randomly throughout the entire fragment. Population re-growth and genetic diversity retention measures for each geometric removal pattern were modeled under two contrasting gene dispersal patterns (via both offspring and pollen): short versus long dispersal (both leptokurtic relative to the pistillate plant). After 14 bouts of mating, the greatest difference in census size among comparative recovery populations amounted to 393% (centered founders, long gene dispersal > scattered founders, short gene dispersal). The best pattern of removal for suppressing population regrowth was to leave founders scattered throughout the fragment when gene dispersal was short, or at one corner if gene dispersal was long. The only removal pattern that differed substantially in population genetics characteristics was when remnant individuals were left scattered throughout the fragment and dispersal was short (alleles continued to be lost; observed heterozygosity dropped 13.3% and was still rapidly declining; and inbreeding and/or subdivision were moderate (Fit = 0.12) and still rapidly increasing). Such comparative modeling can be used to suggest removal patterns that might greatly outperform other removal modalities in terms of suppressing the return of weed populations. The effectiveness of such modeling will be improved by acquisition of accurate life history information of targeted species.

Glyphosate resistance has evolved worldwide. Glyphosate is also the most used herbicide in Spain, and current changes in herbicide usage patterns can increase the risk of glyphosate resistance development. The objective of this study was to assess the glyphosate sensitivity of different selected weed species important in Spanish maize (Zea mays L.) fields. To this end, dose–response experiments were conducted under controlled conditions in a growth chamber to examine variation in glyphosate sensitivity among populations of five grass weed species and eight broadleaf weed species that are commonly found in the maize fields in Castilla y León, the biggest maize-growing region in Spain. The glyphosate doses that caused growth reduction by 50% (GR50) were calculated for each weed population. No populations were resistant to glyphosate. In addition, baseline values of glyphosate sensitivity were determined for each weed species. The GR50 baseline values ranged from 10.25 to 53.23 g ai ha−1 for the dicotyledonous weed species and from 16.05 to 66.34 g ai ha−1 for the monocotyledonous weed species. The ratio between the GR50 values of the least and most sensitive populations was used to determine the SI50 (sensitivity index at 50% growth reduction) for each weed species. The SI50 values showed a 1.4- to 3.3-fold difference in sensitivity for dicotyledonous weed species and 1.4- to 2.4-fold difference for monocotyledonous weed species. The sensitivity index was also calculated as the ratio between the GR50 values of the least sensitive population and the baseline GR50 value estimated for a range of susceptible populations (SI50b). SI50b values showed a 1.2- to 1.6-fold difference in sensitivity for dicotyledonous weed species and 1.1- to 1.2-fold difference for monocotyledonous weed species. The sensitivity data generated in this study provide a reference for determining time-dependent changes in glyphosate sensitivity in the commonly found weeds in the maize fields of Castilla y Léon.

Preliminary investigations were conducted to determine the feasibility of making band applications of solid materials (dust and granules) into the crop row.

This paper reports on the synthesis and properties of 38 new herbicides, amino acid derivatives of 4–(2,4–dichlorophenoxy)– and 4–(2–methyl–4–chlorophenoxy)butyric acids. The biological evaluation of the compounds as selective herbicides is being conducted by other investigators and will be published later.

In experimental work with perennial weeds it is often desirable to apply large gallonages of solution from a boom plot sprayer. Moreover, since tillage is frequently a counterpart of the control procedure the sprayer must be constructed to withstand rough usage on cloddy land. The sprayer illustrated in Figure 1 can deliver from 2 to 100 gallons of solution per acre in proper spray pattern through standard nozzles. Being light and strong, it can be pushed comparatively easily across uneven surfaces.

Overall weight of the sprayer is 150 pounds. Rate of travel is gauged by a speedometer indicating zero to 10 mph. Pressure is supplied by a quickly replaceable air pressure tank and the liquid is held in a 2-gallon pressure container. Dosage rate is determined by speed of travel and size of nozzle orifice tip. Because of the large capacity of the liquid flow system from tank to nozzle, loss of pressure is slight even when heavy gallonages of solution are applied. All parts of the system are of copper or brass except the solution tank which is of galvanized iron. However, since the outlet from tank to tubing is at the center of a dished bottom, drainage is good. Pet-cocks at each end of the boom permit thorough flushing. The boom can be set from a 6-inch to a 60-inch height and the angle of nozzle to the ground, adjusted over 20°. A supporting leg is provided at the rear of the frame to keep the sprayer upright when not in use. Air-pressure and speedometer gauges and the spray control valve are mounted directly in front of the operator. When applying 100 gallons of spray per acre, the 2-gallon solution tank permits coverage of 100 feet. Width of spray pattern is 8.5 feet.

Quantifying the level of ecophysiological, biochemical, and agronomical fitness of herbicide-resistant (R) and herbicide-susceptible (S) weeds is useful for understanding the evolutionary development of herbicide resistance, but also for implementing herbicide-resistance management strategies. Although germination is a key fitness component in the life cycle of weeds, germinability of S and R weeds has rarely been evaluated under stressful conditions. Germinability traits of S and non–target site resistant subpopulations of blackgrass (Alopecurus myosuroides Huds.) sharing closely related genetic background were tested under salinity, drought stress, and accelerated seed-aging (i.e., exposed to 100% relative humidity at 45 C from 0 to 134 h) conditions. In addition, the activity of three antioxidant enzymes and protein concentration of accelerated aged seeds of the subpopulations were studied. There were no differences in maximum seed germination (Gmax) and time to 50% germination between the two subpopulations under optimum conditions. However, under salinity, drought stress, and accelerated aging conditions, there were differences between the subpopulations. The salinity, drought, and accelerated aging treatments reducing Gmax of the S subpopulation by 50% were 18 dS m−1, 0.75 MPa, and 90 h, respectively, while for the R subpopulation the corresponding values were 15 dS m−1, 0.66 MPa, and 67 h. No differences were found in the activity of the antioxidant enzymes and the content of protein between non-aged seeds of the subpopulations. The aging treatments reducing the activity of catalase and superoxide dismutase enzymes by 50% were 118 and 82 h for the S subpopulation, respectively, while they were 54 and 58 h for the R subpopulation. In contrast, there were no differences in the effect of the aging treatments on the peroxidase activity and protein content between subpopulations. The results provided clear evidence that the non–target site resistant loci of blackgrass is associated with fitness costs under environmental stress.

Row-middle weed control in Florida vegetable production is challenging and often necessitates several PRE and POST herbicide applications. Coordinating POST spray applications with emergence timings should increase herbicide efficacy by targeting susceptible growth stages. Most published emergence models were developed in temperate climates, and adapting them to subtropical climates can be complex and requires reductionist insights into seed ecology, particularly germination and dormancy. The study objective was to examine the influence of temperature and osmotic potential on seed germination of carpetweed (Mollugo verticillata L.), Carolina geranium (Geranium carolinianum L.), eclipta [Eclipta prostrata (L.) L.], and goosegrass [Eleusine indica (L.) Gaertn.]. Mollugo verticillata seed germination was positively photoblastic, with increased germination at high temperatures (≥35 C), more so with high fluctuating temperatures (35/20 and 35/25 C), and occurred at osmotic potentials as low as −0.5 MPa. Geranium carolinianum seed germinated between 10 and 20 C in light or darkness and at osmotic potentials as low as −0.4 MPa. Eclipta prostrata seed germination was entirely positively photoblastic, occurring optimally between 15 and 25 C and at osmotic potentials as low as −1 MPa. Eleusine indica seed germination demonstrated some degree of positive photoblasticity, with greater germination in the light, peak germination at 35 C, and germination occurring at osmotic potentials as low as −0.5 MPa. Described germination ecology for selected species will provide insights for building ecology-based growing degree-day accounting restrictions for empirically derived emergence models.

The introduced meadow knapweed (Centaurea × moncktonii C.E. Britton), a hybrid of black (Centaurea nigra L.) and brown (Centaurea jacea L.) knapweeds, is increasingly common in pastures, meadows, and waste areas across many U.S. states, including New York. We evaluated the effects of temperature, light, seed stratification, scarification, and population on percent germination in four experiments over 2 yr. Percent germination ranged from 3% to 100% across treatment combinations. Higher temperatures (30:20, 25:15, and sometimes 20:10 C day:night regimes compared with 15:5 C) promoted germination, especially when combined with the stimulatory effect of light (14:10 h L:D compared with continuous darkness). Under the three lowest temperature treatments, light increased percent germination by 15% to 86%. Cold-wet seed stratification also increased germination rates, especially at lower germination temperatures, but was not a prerequisite for germination. Scarification did not increase percent germination. Differences between C. × moncktonii populations were generally less significant than differences between temperature, light, and stratification treatments. Taken together, these results indicate that C. × moncktonii is capable of germinating under a broad range of environments, which may have facilitated this species’ range expansion in recent decades. However, C. × moncktonii also shows evidence of germination polymorphism: some seeds will germinate under suboptimal conditions, while others may remain dormant until the abiotic environment improves. Subtle differences in dormancy mechanisms and their relative frequencies may affect phenological traits like the timing of seedling emergence and ultimately shape the sizes and ranges of C. × moncktonii populations.

Biennial wormwood has been increasing in Manitoba, Canada, but information is limited on the potential of biennial wormwood to reduce crop yields. Field experiments were conducted over 5 site-yr throughout southern Manitoba in 2010 and 2011 to determine the effect of biennial wormwood density and relative time of biennial wormwood seedling recruitment on sunflower growth, development, yield, and seed quality. Biennial wormwood was broadcast on the soil surface at six densities into sunflowers planted in 75-cm rows, either at the same time the sunflower crop was planted (early weed seedling recruitment) or when the sunflowers were at about the four-leaf stage (late weed seedling recruitment). When biennial wormwood emerged at about the same time as the sunflowers, yield was reduced by up to 46%. Early-recruiting biennial wormwood had minimal effect on sunflower growth and development, but sunflower achene size and individual achene weight were reduced, even when no effect on sunflower yield was observed. Biennial wormwood plants that recruited after the four-leaf stage of the sunflower crop had no effect on sunflower yield or seed quality.

Maize dwarf mosaic (MDM) stunts corn growth, delays development, and is the most prevalent viral disease of sweet corn grown in many regions of North America and Europe. Although some weeds escape control in most sweet corn fields, the extent to which MDM influences the weed suppressive ability of the crop is unknown. Field studies were conducted over a 3-yr period to characterize the influence of variable MDM incidence in sweet corn on growth, fecundity, and germinability of wild-proso millet, a common weed in the crop. Treatments included five levels of MDM incidence (0, 25, 50, 75, and 100% of plants infected) in two MDM-susceptible hybrids differing in weed suppressive ability. Previous research showed that hybrid ‘Legacy’ had greater weed suppressive ability than ‘Sugar Buns’. Wild-proso millet biomass and fecundity depended largely on the hybrid in which the weed was growing. Wild-proso millet growing in Sugar Buns weighed 45 to 117% more than wild-proso millet in Legacy. Incidence of MDM in sweet corn affected wild-proso millet biomass and fecundity, but only under high weed population densities. When wild-proso millet was observed at 122 plants m−2, weed biomass increased 9 g m−2 for each additional 10% incidence of MDM of sweet corn. Weed suppressive ability of the competitive and less competitive hybrids were influenced to the same extent by MDM. Coupled with a lack of resistance to MDM in two-thirds of commercial sweet corn hybrids, the disease could be an additional factor perpetuating weed growth and fecundity in sweet corn, particularly in fields with high population densities of wild-proso millet.

Phenoxy herbicides (2,4-D and MCPA) are widely used to manage broadleaf weeds including Palmer amaranth (Amaranthus palmeri S. Watson), one of the most troublesome weeds in U.S. cropping systems. Previously, we documented resistance to 2,4-D and MCPA in an A. palmeri population (KCTR) from Kansas. Our recent research suggested rapid metabolism of 2,4-D bestows resistance in KCTR A. palmeri; nonetheless, the mechanism of MCPA resistance in this population is still unknown. The objectives of this research were to (1) evaluate the level of resistance to MCPA in KCTR compared with two known susceptible populations of A. palmeri, MSS and KSS; (2) study the absorption and translocation of [14C]MCPA in KCTR and MSS plants: (3) investigate the metabolic profile of [14C]MCPA in KCTR and MSS and compare those with MCPA-tolerant wheat (Triticum aestivum L.) plants; and (4) assess the possible role of cytochrome P450 enzymes (P450s) in MCPA metabolism. Experiments were conducted to assess the level of resistance in KCTR. Using [14C]MCPA, the absorption, translocation, and metabolic profiles were assessed in A. palmeri. Involvement of P450s was confirmed using malathion, a known P450 inhibitor. Regression analyses indicate that KCTR population exhibits an $\sim $3-fold resistance to MCPA. No difference in absorption of [14C]MCPA was found between MSS and KCTR. However, the KCTR plants translocated less [14C]MCPA at 48 h after treatment (HAT) and metabolized MCPA more rapidly than MSS plants at 12 and 24 HAT. MCPA resistance in KCTR was reversed upon treatment with malathion, indicating the involvement of P450s in metabolism of this herbicide. This is the first report of characterization of MCPA resistance in A. palmeri.

The identification of herbicide tolerance is essential for effective chemical weed control. According to whole-plant dose–response assays, none of 29 pond lovegrass [Eragrostis japonica (Thunb.) Trin.] populations were sensitive to penoxsulam. The effective dose values of penoxsulam causing 50% inhibition of fresh weight (GR50: 105.14 to 148.78 g ai ha−1) in E. japonica populations were much higher than the label rate of penoxsulam (15 to 30 g ai ha−1) in the field. This confirmed that E. japonica was tolerant to penoxsulam. Eragrostis japonica populations showed 52.83- to 74.76-fold higher tolerance to penoxsulam than susceptible barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. The mechanisms of tolerance to penoxsulam in E. japonica were also identified. In vitro activity assays revealed that the penoxsulam concentration required to inhibit 50% of the acetolactate synthase (ALS) activity (IC50) was 12.27-fold higher in E. japonica than in E. crus-galli. However, differences in the ALS gene, previously found to endow target-site resistance in weeds, were not detected in the sequences obtained. Additionally, the expression level of genes encoding ALS in E. japonica was approximately 2-fold higher than in E. crus-galli after penoxsulam treatment. Furthermore, penoxsulam tolerance can be significantly reversed by three cytochrome P450 monooxygenase (CytP450) inhibitors (1-aminobenzotriazole, piperonyl butoxide, and malathion), and the activity of NADPH-dependent cytochrome P450 reductase toward penoxsulam in E. japonica increased significantly (approximately 7-fold higher) compared with that of treated E. crus-galli. Taken together, these results indicate that lower ALS sensitivity, relatively higher ALS expression levels, and stronger metabolism of CytP450s combined to bring about penoxsulam tolerance in E. japonica.

Glyphosate resistance is spreading in Spain and Portugal due to excessive herbicide use, in both annual and perennial crops. Compact brome (Bromus madritensis L.) is increasing in frequency in these different cropping systems when under conservation agriculture, particularly when glyphosate fails to control it. Fourteen populations from different areas in the Iberian Peninsula were confirmed as being B. madritensis using simple sequence repeat markers and clearly separated from the closely related species red brome (Bromus rubens L.) and ripgut brome (Bromus diandrus Roth). Six B. madritensis populations were classified as resistant, according to both their shikimic acid accumulation levels and their resistance factors based on LD50 or GR50 (values between 4 and 8). Populations with higher resistance factors also showed lower shikimic acid concentrations. Moreover, these resistant populations were able to survive the minimum registered dose for glyphosate in Spain in perennial crops (1,080 g ae ha−1, five populations) or in arable crops before seeding for annual weeds (540 g ae ha−1, one population), under both greenhouse and field conditions. The trials carried out in a glyphosate-resistant field during 2 consecutive years showed that acceptable control (≥90%) was only consistently achieved 90 d after application for preemergence treatment with flazasulfuron in a tank mix with glyphosate, while control with postemergence treatments, such as propaquizafop plus glyphosate, was below 80%. This research describes the first herbicide-resistance report for the weed species B. madritensis, confirming the presence of glyphosate-resistant populations mainly in perennial cropping systems but also in winter cereals from Spain. Due to the limited chemical tools to manage these populations, there is an urgent need for farmers to implement integrated weed management strategies.

A field study was conducted from 2020 to 2023 at Kansas State University Agricultural Research Center near Hays, KS, to understand the emergence dynamics and periodicity of glyphosate-resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) as influenced by cover crop (CC) residue and residual herbicide in grain sorghum [Sorghum bicolor (L.) Moench]. The study site was under a wheat (Triticum aestivum L.)–sorghum–fallow rotation with a natural seedbank of GR A. palmeri. Treatments included (1) fall-planted CC mixture [winter triticale (×Triticosecale Wittm. ex A. Camus [Secale × Triticum])/winter peas (Pisum sativum L.)/rapeseed (Brassica napus L.)/radish (Raphanus sativus L.)] after wheat harvest and terminated at triticale heading stage (next spring before sorghum planting) with glyphosate alone or (2) glyphosate plus acetochlor/atrazine, (3) chemical fallow (no CC but treated with acetochlor/atrazine and dicamba before sorghum planting), and (4) nontreated control (no CC and no herbicide). Results indicated that CC terminated with glyphosate plus acetochlor/atrazine had a delayed and reduced cumulative emergence of GR A. palmeri as compared with chemical fallow and CC terminated with glyphosate alone across all 3 yr. Compared with chemical fallow, the CC terminated with glyphosate alone and glyphosate plus acetochlor/atrazine required 66 to 643 and 105 to 1,257 more cumulative growing degree days, respectively, to achieve 90% cumulative emergence of GR A. palmeri across all 3 yr. The combined effect of CC residue with glyphosate plus acetochlor/atrazine reduced the total emergence counts of GR A. palmeri by 42% to 56% and 82% to 94% as compared with chemical fallow and nontreated control, respectively. These results suggest that fall-planted CC combined with a residual herbicide at termination can be utilized for GR A. palmeri suppression in grain sorghum.

The Conyza genus includes nearly 150 species, comprising closely related weedy species. Proper identification of Conyza spp. is essential to develop effective strategies for their management. The overlap of traits, species varieties, and the putative occurrence of hybridization hampers the identification of Conyza spp. and its management in agricultural and natural environments. Herein, we assessed five DNA barcodes and 32 morphological traits to classify Conyza spp. and survey their dispersion in soybean fields [Glycine max (L.) Merr.] in Brazil in 2019, 2020, and 2021. The Conyza accessions included two species, hairy fleabane [Conyza bonariensis (L.) Cronquist) and Sumatran fleabane [Conyza sumatrensis (Retz.) E. Walker], and each species comprised two varieties. The ITS and rps16-trnQ gene regions showed the ability to distinguish between the two Conyza species, while the matK, rbcL, and trnF-trnF gene regions were not polymorphic. Out of 32 morphological traits, phyllary color, involucre shape, capitulescence type, and inflorescence type were the most polymorphic and even reliable for taxonomic purposes. The combination of ITS or ITS+rps16-trnQ regions and the four morphological markers was able to discriminate 91% of the plants, except those of C. bonariensis var. angustifolia. These results support the taxonomic resolution between C. bonariensis and C. sumatrensis and are useful for other Conyza spp. and other closely related weedy species worldwide. Conyza sumatrensis was detected in 94% of soybean fields across macroregions and seasons in Brazil, while C. bonariensis was sparsely dispersed, mainly in the southern macroregion (MRS 1).

Benzobicyclon tolerance in rice (Oryza sativa L.) is dependent on the presence of a functional HIS1 gene, but the level of sensitivity might vary among different cultivars. Greenhouse, laboratory, and field experiments were conducted to further explore the role of HIS1 in cultivated rice tolerance and to exploit findings toward optimizing benzobicyclon activity on weedy rice (unwanted rice; Oryza sativa L.). In a heredity experiment, benzobicyclon tolerance was confirmed to be a semidominant trait conferred by HIS1 based on the intermediate response (ED50 values) of HIS1 heterozygous F 1 plants. The spatial–temporal expression of HIS1 was next studied in tissue types (blades, sheaths, and whorls) across tolerant cultivars (‘Roy J’, ‘Diamond’, ‘LaKast’, ‘CLXL745’, and ‘XL753’) and growth stages (2- to 3- compared with 5- to 6-leaf). The relative expression of HIS1 was tissue specific and highest in whorls, followed by blades and then sheaths. Minimal differences in expression across cultivars and growth stages were observed. Furthermore, HIS1 was not largely upregulated at 6 h after benzobicyclon treatment. In the same experiment, cultivar tolerance to benzobicyclon at the label rate of 371 g ha−1 was found to be growth stage dependent. Plant growth was reduced by ∼35% when rice plants were at the 2- to 3- compared with 5- to 6-leaf growth stages. These results show that differences in benzobicyclon tolerance among HIS1 homozygous cultivars is likely not directly correlated with the expression of HIS1. In this research a model was proposed and supported by a field proof of concept study, indicating benzobicyclon efficacy on weedy rice is a function of HIS1 zygosity by growth stage at application. Prior research indicates HIS1 is the dominant allele in weedy rice accessions in Arkansas, and thus, based on our model, benzobicyclon should be applied to weedy rice with ≤2 leaves for suppression.

Almonds [Prunus dulcis (Mill.) D.A. Webb] are grown on nearly 650,000 ha in California and generate nearly $4.9 billion in export revenue annually, primarily to the European Union (EU). To facilitate harvest operations, broad-spectrum herbicides such as glyphosate and/or glufosinate are commonly used to control vegetation before harvest. The current minimum preharvest intervals (PHIs) for glyphosate and glufosinate herbicides registered in the United States are 3 and 14 d, respectively. The maximum residue limit (MRL) for glyphosate and glufosinate in almonds in the EU is 0.1 mg kg−1; however, a recent study recommended the glyphosate MRL be reduced to 0.05 mg kg−1. Laboratory and field experiments were conducted to evaluate herbicide transfer from soil to almonds and the effect of longer PHIs on glyphosate and glufosinate residues in harvested almonds. After harvest operations, almonds were dissected into hulls, shells, and kernels for analysis of glyphosate, glufosinate, and their metabolites using liquid chromatography–tandem mass spectroscopy. In the field experiment, glyphosate and glufosinate were detected at 0.121 to 0.291 mg kg−1 in almond hulls and shells. Glyphosate and primary metabolites were below the limit of detection (LOD) in almond kernels at all PHIs. Glufosinate was below the LOD, but the metabolite 3-(methylphosphinico)propionic acid was detected at 0.03 to 0.075 mg kg−1 in kernels from some replicate plots. There were no significant differences in either herbicide or any metabolite among PHI treatments. The lab experiment showed decreasing residue levels from hull to shell to kernel; furthermore, rinsing kernels resulted in 71% and 46% reduction in [14C]glyphosate and [14C]glufosinate, respectively, which suggests much of the herbicide residue may be associated with dust on the kernel surfaces. The results of these experiments indicate very low levels of herbicide transfer from soil to almonds, and increasing the PHI within the tested range did not reduce the already low amounts of herbicide or metabolites in almonds.

Determining whether and how to manage an introduced species requires basic ecological and biological knowledge. If a decision is made to actively manage an invader, doing so efficiently and effectively is critical. Basic biological or ecological information can be key in designing effective and cost-efficient management approaches. We used a greenhouse experiment and observational field studies of naturalized populations to study the modes of pollination, fecundity in the field, seed ecology, population dynamics, and demography of the introduced and toxic weed, black henbane. We showed that henbane was able to self-pollinate. Furthermore, outcrossing did not increase number or size of seeds. Plants in the sampled populations produced an estimated average of 25,300±4,004 seeds by the middle of the growing season. We found no difference in the viability of field-collected seeds that were 1 to 4 yr old. The number of flowering plants in a population was best predicted by the number of rosettes at that location in July of the previous year. The probability of rosettes surviving over the winter to reach reproductive maturity increased with precipitation and growing degree days. Total population sizes fluctuated dramatically between years. Henbane populations are ephemeral, but with large seed banks, outbreaks are possible if conditions are right. Given that this weed is toxic to livestock and humans, it is important to identify infestations and manage populations.

The recognition of the herbicidal activity in the phenylacetic acids by Pybus et al. is a matter of particular interest to those whose work is concerned with weed control in crops unusually sensitive to 2,4-D (2,4-dichlorophenoxyacetic acid) and its derivatives.

Numerous cations were evaluated as possible substitutes for copper in mixtures with diquat (6,7-dihydrodipyrido[1,2-α:2′,1′-c] pyrazinediium ion) for control of hydrilla [Hydrilla verticillata (L.f.) Royle]. Several cations, including ferrous and ferric iron, when substituted for equal weights of copper in the mixtures, were as effective as copper in enhancing the phytotoxicity of diquat to hydrilla. In most instances, death of the test plants occurred more rapidly when the substitutes were used. Ferric chloride, because of its apparent innocuous behavior in the aquatic environment, is a desirable substitute for the more toxic copper. Bluegill sunfish (Lepomis macrochirus RAf.) were unaffected by week-long exposure to ferric chloride at concentrations as high as 100 ppmw. Since ferric chloride alone exhibited no toxicity to hydrilla in the range of concentrations tested, the greater phytotoxicity of the mixtures probably was due to the increased toxicity of diquat. In evaluations using other species of aquatic weeds, neither the addition of copper nor the addition of other cations increased the phytotoxicity of diquat. In most tests, the mixtures of diquat with other cations reduced the level of activity of diquat on weeds other than hydrilla.