Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) killed nearly 100% of the wild garlic (Allium vineale L.) plants when applied in spring, but was less effective when applied in the fall. Treatment in the spring with paraquat consistently killed more wild garlic plants than treatments at any other date. Eradication of a wild garlic infestation was achieved after applications for three successive springs. Near eradication was achieved with two annual applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Among herbicides evaluated postemergence on wild garlic, mefluidide (N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], asulam (methyl sulfanilylcarbamate), and picloram (4-amino-3,5,6-trichloropicolinic acid) were not effective for controlling wild garlic. Glyphosate [N-(phosphonomethyl)glycine] and a mixture of cyperquat (1-methyl-4-phenylpyridinium) and 2,4-D ester reduced wild garlic populations by over 60%.

Host-specific interactions can maintain genetic and phenotypic diversity in parasites that attack multiple host species. Host diversity, in turn, may promote parasite diversity by selection for genetic divergence or plastic responses to host type. The parasitic weed purple witchweed [Striga hermonthica (Delile) Benth.] causes devastating crop losses in sub-Saharan Africa and is capable of infesting a wide range of grass hosts. Despite some evidence for host adaptation and host-by-Striga genotype interactions, little is known about intraspecific Striga genomic diversity. Here we present a study of transcriptomic diversity in populations of S. hermonthica growing on different hosts (maize [Zea mays L.] vs. grain sorghum [Sorghum bicolor (L.) Moench]). We examined gene expression variation and differences in allelic frequency in expressed genes of aboveground tissues from populations in western Nigeria parasitizing each host. Despite low levels of host-based genome-wide differentiation, we identified a set of parasite transcripts specifically associated with each host. Parasite genes in several different functional categories implicated as important in host–parasite interactions differed in expression level and allele on different hosts, including genes involved in nutrient transport, defense and pathogenesis, and plant hormone response. Overall, we provide a set of candidate transcripts that demonstrate host-specific interactions in vegetative tissues of the emerged parasite S. hermonthica. Our study shows how signals of host-specific processes can be detected aboveground, expanding the focus of host–parasite interactions beyond the haustorial connection.

Blackgrass (Alopecurus myosuroides Huds.) and silky windgrass [Apera spica-venti (L.) P. Beauv.] are becoming a significant problem in Europe. Due to the development of herbicide-resistant biotypes and unwanted side effects of herbicides, there is a need for new integrated weed management strategies to control weeds. Therefore, reducing weed infestations by targeting seed production during crop harvest should be considered. In 2017 and 2018, we estimated the fraction of the total seed production of A. myosuroides and A. spica-venti in a field that potentially could be collected by a grain harvester during winter wheat (Triticum aestivum L.) harvest. Twenty plants of each species were surrounded by a porous net before flowering to trap shed seeds during reproductive development. Seeds were collected and counted weekly up until and immediately before wheat harvest, and the ratio of harvestable seeds to shed seeds during the growing season was determined. Alopecurus myosuroides produced on average 953 seeds plant−1 in 2017 and 3,337 seeds plant−1 in 2018. In 2017 and 2018, 29% and 37% of the total A. myosuroides seeds produced, respectively, were retained on plants at maturity. Apera spica-venti produced on average 1,192 seeds plant−1 in 2017 and 5,678 seeds plant−1 in 2018, and retained 53% and 16% of the seeds at harvest, respectively. If a grain harvester potentially collected approximately 30% of the total seed production of the two grass weeds and removed or killed them, it would reduce seed input to the soil seedbank. However, such methods cannot stand alone to reduce weed pressure.

Common cocklebur root and shoot interferences were investigated as factors causing soybean yield reductions in the field. Significant decreases in soybean yield resulted from common cocklebur shoot interference when the two were grown together with the common cocklebur roots confined in plastic bags. Soybean yield decreased further when common cocklebur roots were not confined, but this decrease resulted, in part, from increased common cocklebur shoot growth. Wire mesh cylinders of varying diameters, placed in gaps in the soybean rows and designed to spatially restrict soybean shoot growth, reduced yield more than did gaps alone. When similar cylinders lined with black plastic were placed next to the soybean rows to restrict both within-canopy light and space for soybean shoot growth, soybean yield was reduced most (44%) with concomitant changes in stem height, stem diameter, lodging, and branches, nodes, and pods/plant. Interference of common cocklebur with soybeans resulted primarily from shoot interference, and competition for light within the soybean canopy implicated as the major factor causing the soybean yield reduction.

We have come together to discuss the way in which weeds and water work together to influence yields in agriculture. In the small allotment of time available to us this morning a review of basic knowledge about this relationship would be so general that it could help no one. I believe it would be more appropriate, and more helpful for a group so large, if I tell you of some of the hard realities which come to bear on food production across the world because of this relationship of weeds with moisture. These stories will have to do with such practical matters as the expansion of the world's most important crop, and the difference between good and bad crops on the two sides of the same river under identical climatic conditions in Middle Asia.

Root and shoot extracts of 3-week-old sudangrass [Sorghum sudanense (Piper) Stapf, var. Piper], grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.) plants degraded 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in order: shoot > root and corn ≫ sorghum = sudangrass. In 3-week-old detopped plants, the rate of atrazine exudation was 14 times greater in sudangrass and sorghum than in corn when grown in Keith sandy loam containing 0.5 ppmw 14C-atrazine. Extraction and analysis of plant shoots revealed that 7 to 8% of the 14C was present as atrazine in sudangrass and sorghum whereas no atrazine was found in corn. In 14C tracer studies, thin-layer chromatography showed that sudangrass and sorghum metabolized atrazine by a pathway which differed from the pathway in corn. Sudangrass and sorghum metabolized atrazine primarily to 2-chloro-4-amino-6-(isopropylamino)-s-triazine and 2-chloro-4-amino-6-(ethylamino)-s-triazine which are only partially detoxified compounds. Corn metabolized atrazine to 2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine (hydroxyatrazine) which is non-phytotoxic.

Isolated plant cells (Zinnia elegans Jacq. leaf tissue) and protoplasts (immature tomato fruit, Lycopersicon esculentum Mill.) were obtained by hydrolysis of pectic substances in the middle lamella and the primary cell wall, respectively. Both types of cells were stabilized in an inorganic salt solution and used to study absorption and distribution of four 14C-herbicides. Intracellular distribution within the protoplast was determined by ultracentrifugation in a discontinuous Ficoll gradient. Marked absorption of p-nitrophenyl-α,α,α-trifluoro-2-nitro-p-tolyl ether (fluorodifen) and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) by the isolated cells was observed; absorption increased with time. Trifluralin was retained within the cell more strongly than fluorodifen. Similar absorption patterns of fluorodifen and trifluralin by protoplasts were observed. Trifluralin was incorporated to a greater extent than fluorodifen by the cells and protoplasts. Trifluralin was distributed evenly between the mitochondrial and the chloroplasts-nuclei fractions; whereas fluorodifen was concentrated in the chloroplast-nuclei fraction. No significant absorption of 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea fluometuron) or 3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea (chlorbromuron) was detected by either the isolated cells or protoplasts.

The transition period to certified organic production can present a significant weed management challenge for growers. Organic certification requires that prohibited fertilizers and pesticides must not have been used for 36 mo before harvest of the first organic crop. Understanding how organic management practices and initial weed seed-bank densities affect weed population dynamics during the transition period may improve weed management efficacy and adoption of organic practices. We examined how tillage systems (full or reduced) and cover crop species planted during the first transition year (rye or a mixture of timothy and red clover) affect the seedling densities of three common annual weed species, common lambsquarters, velvetleaf, and foxtail spp., during the 3-yr transition period. Weed seeds were applied in a one-time pulse at the beginning of the study at three densities, low, medium, and high (60, 460, and 2,100 seeds m−2, respectively), and cumulative seedling densities of each species were assessed annually. Treatment factors had variable and species-specific effects on weed seedling densities. In general, the full-tillage system, with an initial cover crop of timothy and red clover, resulted in the lowest density of weed seedlings following seed-bank augmentation. There was little consistent association between the initial densities of applied weed seeds in the weed seed bank at the start of the transition and weed seedling densities at the end of the transition period. This suggests that when multiple crop and weed cultural management practices are employed during the organic transition period, initial failures in weed management may not necessarily lead to persistent and intractable annual weed species management problems following organic certification.

Knowing the distribution of weed seedlings in farmer-managed fields could help researchers develop reliable distribution maps for site-specific weed management. With a knowledge of the spatial arrangement of a weed population, cost effective sampling programs and management strategies can be designed, so inputs can be selected and applied to specific field areas where management is warranted. In 1997 and 1998, weeds were sampled at 612 to 682 sites in two center pivot irrigated corn fields (71 and 53 ha) in eastern Colorado. Weeds were enumerated when corn reached the two-leaf, four-leaf, and physiological maturity stages in a 76.2- by 76.2-m grid, a random-directed grid where sites were established at intervals of 76.2 m, and a star configuration based on a 7.62- by 7.62-m grid within three 23,225 m2 areas. Directional correlograms were calculated for 0, 30, 60, 90, 120, and 150° from the crop row. Fifteen weed species were observed across fields. Spatial dependence occurred in 7 of the 93 samples (a collection of sampling units for a particular weed species that was detected within a field at a particular sampling time and year) for populations of field sandbur, pigweed species, nightshade species, and common lambsquarters. Correlogram analysis indicated that 18 to 72% of the variation in sample density was a result of spatial dependence over a geographic distance not exceeding 5 to 363 m among the examined data. Because of the lack of spatial correlation for weed seedling distributions in these eastern Colorado corn fields, interpolated density maps should be based on grid sizes (separation distances) less than 7.62 m for weed seedling infestations.

The effects of a gall mite (Aceria malherbae) and sublethal doses of either 2,4-DB or glyphosate on field bindweed growth were evaluated under laboratory conditions. Mite feeding reduced field bindweed shoot biomass 37 to 48% and root biomass 46 to 50%. 2,4-DB at 0.07 to 0.14 kg ae ha−1 or glyphosate at 0.14 to 0.28 kg ai ha−1 reduced field bindweed root biomass 25 to 52%. Combining A. malherbae feeding with either 2,4-DB or glyphosate application reduced root biomass of field bindweed plants more than mites or either herbicide alone. Live A. malherbae were present on field bindweed 3 wk after treatment with either herbicide. Combination of A. malherbae with sublethal herbicide doses may allow for field bindweed suppression while reducing potential herbicide injury to crops and maintaining A. malherbae populations.

Cultivation timings were used in conjunction with postemergence herbicides to determine their effect on sicklepod control in soybean. Treatments using cultivation alone resulted in less than 70% sicklepod control. A postemergence application of chlorimuron following metribuzin applied postemergence was usually more effective in controlling sicklepod with cultivation 7 days after application than with cultivation 3 days before or at application, or with no cultivation. Cultivation at any timing in conjunction with a postemergence application of imazaquin following imazaquin preemergence improved sicklepod control compared to imazaquin without cultivation. Sicklepod control with chlorimuron postemergence followed by cultivation 7 days after application was as good as or better than two sequential applications of chlorimuron with no cultivation. Imazaquin or metribuzin preemergence followed only by cultivation provided less than 80% control in two of three experiments.

Adsorption of l-butyl-3-(3,4-dichlorophenyl)-l-methyl-urea (neburon), determined spectrophotometrically, varied considerably among representative soils of six Hawaiian great soil groups, ranging from 29% in Lualualei soil to 94% in Honouliuli soil. The adsorption of neburon was strongly correlated with organic matter and total soil nitrogen; other soil properties were not related.

Initial and residual neburon phytotoxicity to oats in the greenhouse was dependent on total soil nitrogen, organic matter, and the degree of neburon adsorption. Based on ED50 values, neburon toxicity in soil types decreased in the following order: Lualualei, Wahiawa, Mahana, Paaloa, Waimanalo, Kapaa, and Honouliuli. Complete neburon inactivation was obtained in Honouliuli and Waimanalo soils within the 150-day duration of this experiment, and nearly complete inactivation in Mahana and Kapaa soils.

Herbicide performance was markedly altered by soil incorporation, depth of incorporation, crop seed placement, soil type, and rainfall. Of the 25 herbicides studied, 2-chloro-N,N-diallylacetamide (CDAA) and isopropyl-N-(3-chlorophenyl)carbamate (CIPC) and mixtures of them showed most promise. Herbicide-placement studies showed that the selectivity of these herbicides in cotton largely depends on herbicide placement in relation to the crop seed and on rainfall. Without rainfall, CDAA incorporated in moist soil above the cotton seed provided excellent weed control with minimal injury to cotton. CDAA was readily leached from the zone of germinating weed seed by rain or irrigation on coarse-textured soils. Without rainfall, CIPC was slightly inferior to CDAA in weed control but more stable in performance over a wider range of environmental conditions. Mixtures of CDAA and CIPC were somewhat superior to either alone. Commercial usage of these herbicides in moist soil depends on the development of suitable equipment for application.

Most of the 3-amino-2,5-dichlorobenzoic acid (amiben) absorbed by treated plants was converted to N-glucosyl amiben in the roots. Only small amounts of amiben and N-glucosyl amiben occurred in stems and leaves. The N-glucoside was not metabolized further and remained in vegetative tissue of soybeans for at least 50 days. Soybeans which were depleted of carbohydrate reserves by starvation in the dark absorbed less amiben and produced less N-glucosyl amiben than did plants treated under normal illumination. A similar trend was noted for tomato plants treated in a comparable manner.

A natural product in corn, the 2-glucoside of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, is capable of inactivating triazine herbicides. Two essentially isogenic corn lines, Mississippi selection GT112 (susceptible to atrazine and simazine) and GT112 RfRf (resistant), contained the compound in both roots and shoots. The content of the roots was about equal for the two lines and decreased with age. In shoots of GT112 seedlings 13 to 28 days old, the 2-glucoside content reduced with time to half the original value. In shoots of GT112 RfRf, the 2-glucoside content doubled from 13 to 17 days, then decreased. Shoots of GT112 RfRf contained 1.6, 3.6, and 2.4 times more 2-glucoside at 13, 17, and 28 days, respectively, than GT112. However, 13-day-old homogenized shoots of GT112 converted 1.8 times more atrazine per μM of 2-glucoside than GT112 RfRf. Susceptibility of GT112 to triazine herbicides is not due to absence of the 2-glucoside or its inability to convert atrazine.

Horsenettle (Solanum carolinense) is a drought-resistant, deep-rooted perennial plant that propagates itself from rhizomes and seed, both of which are produced in abundance. In pastures propagation from seed is probably of minor importance as compared to the steady increase in infestation occurring from rhizome growth.

Field dodder (Cuscuta campestris Yunck.) emerged as well in total darkness as in light, but seedlings did not twine about the host. Under the shade of alfalfa, dodder emerged normally, but attachment was reduced more than 90% and delayed 7 to 10 days. Attached dodder shaded by alfalfa did not develop its characteristic golden color, grew very slowly, and was delayed in maturity 3 to 4 weeks.

A weevil, (Rhinocyllus conicus Froelich) was introduced into Missouri in 1975 to aid in reducing populations of musk thistle, (Carduus nutans L.). The weevil was recovered in 1976 from as far as 3.2 km from the release site and 4.8 km in 1977. Infestation levels of flower heads at the release site ranged from 46 to 90%. Native parasites (Bracon mellitor Say) and [Aliolus curculionis (Fitch)] were reared from weevil larvae.

We sprayed yellow nutsedge (Cyperus esculentus L.) with 0.56, 1.12, and 2.24 kg/ha of (2,4-dichlorophenoxy)acetic acid (2,4-D) at the two and four-leaf stages in both field and growth chamber studies. Compared to non-treated plants, these rates significantly reduced shoot weight, rhizome weight, and rhizome number 12 days after application. There were no significant differences in these growth responses among the rates tested, when applied one, two, and three times at consecutive 12-day intervals. We pretreated two and four-leaf plants with 0.56, 1.12, and 2.24 kg/ha of 2,4-D immediately before foliar application of 14C-2,4-D. The increase in pretreatment rates decreased the percentage of the applied radioactivity which was absorbed and translocated. Of the radioactivity absorbed, a rather constant percentage translocated from the treated area in the different treatments. The radioactivity translocated from the application site for at least 288 hr after treatment. Less than 19% of the 14C-2,4-D applied was absorbed into the leaves 24 hr after application. Ninety-eight to 100% of the methanol-soluble radioactivity that translocated to developing leaves, rhizomes, and roots chromatographed identically to 14C-2,4-D.

Phytase activity increased 2 to 3 fold in barley (Hordeum vulgare L.), 6 fold in corn (Zea mays L.), and 12 fold in squash (Cucurbita maxima Duchesne) seedlings 2 days after the initiation of germination in the dark. Most of the phytase was found in the embryo of the seed, presumably in the cotyledon(s). Gibberellic acid and benzyladenine supplied during germination exerted only limited influence on the development of phytase in these seedlings. Of the herbicides studied, only sodium arsenite exerted an influence on phytase activity per se that was of physiological significance. The presence of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-N-isopropylacetanilide (propachlor), 2,6-dichlorobenzonitrile (dichlobenil), or α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine (trifluralin) in the culture solution during germination partially inhibited the development of phytase activity. The herbicidal inhibition was enhanced if potassium phosphate at a non-inhibitory level also was present in the culture solution. The interaction of atrazine and amiben with phosphorus was not due to increased internal concentrations of inorganic phosphorus to a level inhibitory to the development of phytase activity.