Specific Herbicides Research Articles

Developmental expression of glutathione-S-transferase in maize and its possible connection with herbicide tolerance

Crop improvement for tolerance to specific herbicides is an important breeding target, since molecules performing well with regard to environmental safety are frequently not completely selective for crops. The glutathione (GSH)/glutathione-S-transferase (GST) system is a general mechanism of detoxification that in higher plants may confer tolerance to some herbicides. GSH level and GST activity were measured in different maize inbred lines, in the absence or in the presence of EPTC (a thiocarbamate) and of Alachlor (a chloroacetanilide); a wide genetic variability was observed for these parameters, which appear to be involved in plant tolerance to herbicides. Isozyme analysis was performed on roots, leaves, scutellum, pollen, coleoptile, mesocotyl of the same inbreds: it revealed the presence of many GST forms in maize, showing high polymorphism; they are controlled by at least five genes, the expression of which is developmentally regulated in the different tissues analyzed.

History of Herbicide-Tolerant Crops, Methods of Development and Current State of the Art – Emphasis on Glyphosate Tolerance

Weed management is an integral part of agriculture; weeds lower both productivity and quality of agricultural products. A combination of mechanical, chemical, biological, and cultural methods is expected to deliver a sustainable weed management program for the next two decades. While chemical methods offer the most cost effective means of weed management, crop selectivity has hampered the use of the best chemicals for weed management. Recent progress in gene technology has facilitated the introduction and expression of genes to confer a wide range of traits to crop plants. Application of this technology has resulted in the development of crop plant genotypes that are resistant to a specific herbicide. This article describes the progress that has been made by our group toward the introduction of glyphosate tolerance to crop plants. Glyphosate [N-(phosphonomethyl)glycine] kills plants due to inhibition of the biosynthesis of aromatic compounds via the shikimate pathway. Our approach for introduction of glyphosate tolerance is based on insertion and expression in plants of a gene encoding a glyphosate-tolerant 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, a key enzyme of the shikimate pathway. The wild type enzyme present in plants is susceptible to inhibition glyphosate; variants of EPSP synthase have been produced that are less susceptible to inhibition by glyphosate. Expression of genes encoding these variants has been shown to confer glyphosate tolerance to plants. The degree of glyphosate tolerance is related to the tolerance characteristics of the EPSP synthase variant, its substrate activity, targeting to the plastid, and the level of expression of the variant gene. The tissue specificity of expression of the variant EPSP synthase has also been shown to be critical since glyphosate is a systemic herbicide and is translocated to many growing points within the plant. Our studies on glyphosate tolerance have substantially enhanced our understanding of the mode-of-action of glyphosate, the shikimate pathway, and protein sorting within plant cells, as well as developmental and tissue specific expression of genes in plants. Commercial use of glyphosate tolerance technology is expected to affect positively, the weed management arsenal available to the farmers, the sustainability of farm land and groundwater, and promote the use of a “soft” herbicide.

Herbicides and Chemophobia

Data support the use of chemicals as herbipides as a low-risk procedure when compared to the human health risks caused by other every-day activities. Because of their use as defoliants, specific herbicides, such as 2,4-D and 2,4,5- T, have come to the public's attention. These chemicals have a relatively low toxicity and high biodegradability and their overall effectiveness has helped the world overcome pestilence and poverty in many areas. Contrary to the myths that surround them, herbicides do not cause cancer when applied properly.

Weed Control In Field-Grown Holly

Abstract Two separate experiments were conducted over a 3-year growing period to examine control of grass and broadleaf weeds in three cultivars of Ilex. The effect of application timing and number of applications of a tank mixture of Surflan (oryzalin) + Princep (simazine) [2.2 + 0.9 kg ai/ha (2.0 + 0.75 lb ai/A)] were examined in the first study. Maximum season-long control was obtained with any treatment that contained a minimum of two herbicide applications, with the first applied in March and the second in July. The performance of various 2-way combinations of Surflan, Princep and Goal was examined in the second experiment. Acceptable weed control was obtained with any combination that contained broadleaf and grass-active herbicides. Inspection of data across both studies indicates that timing of application is of greater importance than the specific herbicides used.

FLOWMETERS FOR LIQUID HERBICIDE FORMULATIONS

ABSTRACT An experimental thermal flowmeter was developed and tested along with turbine and piston flowmeters. A solution and an emulsion herbicide formulation were used with the three flowmeters but none of the flowmeters successfully measured flow rates of a suspension formulation. The linearities of the thermal, turbine and piston flowmeters were ±77%, ±45%, and ±8.7%, respectively, for measurement of a solution and an emulsion herbicide formulation. To avoid exceeding a 5% error criterion, each flowmeter needs to be calibrated for the specific herbicide and temperature used.

PLANT GROWTH AND DEVELOPMENT IN MOLECULAR PERSPECTIVE

PLANT GROWTH AND DEVELOPMENT IN MOLECULAR PERSPECTIVE

The Impact of Adjuvants on Herbicide Antagonism

Adjuvants are used to improve spray delivery, to increase spray retention on weed foliage, and to enhance foliar penetration by postemergence herbicides for increased herbicide efficacy. Numerous factors govern adjuvant efficacy, including the specific herbicide, plant species, and environmental conditions. Adding superior surfactants as adjuvants to a sethoxydim tank mix with Na-bentazon may overcome the Na-bentazon antagonsim of sethoxydim activity by facilitating increased sethoxydim absorption and by masking the antagonism similar to increasing the sethoxydim rate. Herbicides such as Na-bentazon contribute alkaline or alkaline earth cations that can form salts of a weakly acidic herbicide such as sethoxydim that are not absorbed readily by the plant. Adding abundant ammonium from ammonium sulfate or other sources may prevent and/or may overcome this antagonism.

Behavior of Dinitroaniline Herbicides in Plants

Dinitroaniline herbicides are absorbed readily by roots and emerging shoots, but shoot exposure is more phytotoxic. Translocation within the plant varies by specific herbicide but commonly is minor. Dinitroaniline herbicides injure plants by binding to tubulin, a dimer protein in the ceil that polymerizes to form microtubules (MTs). MTs form the major part of the mitotic apparatus, including spindle fibers, which enable chromosomes to separate during cell division. Dinitroaniline herbicides prevent tubulin from polymerizing into MTs, thus arresting mitosis. This leads to abnormal cells with more than the normal complement of chromosomes and, frequently, lobed nuclei. MTs also are responsible for orienting cell wall microfibrils in such a way that they prevent lateral enlargement of cells. Treatment with dinitroaniline herbicides leads to disorientation of the microfibrils, leading to one of the common symptoms—spherical cells instead of rectangular ones. Studies on the metabolism of trifluralin in plants have shown that amination, dealkylation, and cyclization all can occur. However, metabolites often amount to a small percentage of the original herbicide. In general, trifluralin seems quite stable within the plant.

Sporophytic-gametophytic herbicide tolerance in sugarbeet

In vitro selection procedures for herbicide tolerance were initially developed in the sporophytic generation of sugarbeet (Beta vulgaris L.), and then tested in the gametophytic generation. The primary objective of our study was to develop and evaluate in vitro techniques for identifying genotypes within heterogeneous seedling populations tolerant to specific herbicides, and to use meristematic cloning procedures to synthesize clones genetically tolerant to the herbicide. Seed from cloned selections tolerant to the herbicide ethofumesate were obtained and compared to plants from seed of the original population (using germination, central bud development, and root dry weight). Verification for in vitro selection accuracy was accomplished by pollen germination studies in the gametophyte. The results indicate that in vitro selection of germinated seedlings in the presence of the proper concentration of challenging agent can be effective in identifying genotypes tolerant to ethofumesate. Such identification was accomplished in fully differentiated tissue, but without the necessity of mature plants. Gametophytic studies, via pollen germination, indicated an association between genes operating in the sprophyte and those in the gametophyte. Cloning the seedlings identified as tolerant genotypes, and subsequent intercrossing of these clones provided a convenient method of synthesizing populations with gene frequencies shifted in the direction desired.

Molecular biology of herbicides

AbstractOne of the most dynamic areas of plant molecular biology is the investigation of the actions of three classes of herbicides: s‐triazines (atrazine, simazine), glyphosate, and sulfonylureas (chlorsulfuron, sulfometuron methyl) (Figure 1). The results of this work are expected to provide the first significant applications of plant biotechnology: directly, in the genetic engineering of crop plants resistant to specific herbicides and, indirectly, in providing a molecular basis for the rational design of new herbicides for specific biological targets.s‐Triazines affect photosynthesis by inhibiting the binding of quinones to the chloroplast membrane QB protein. An s‐triazine resistant QB protein isolated from weeds in fields consistently treated with the herbicide has a serine in place of a glycine in this highly conserved protein. Glyphosate inhibits 5‐enolpyruvyl‐shikimate‐3‐phosphate synthase (EPSP synthase), an enzyme in the aromatic amino acid biosynthetic pathway. Mutagenized bacteria produce a resistant EPSP synthase with a substitution of serine for proline. Sulfonylureas inhibit the acetolactate synthase (ALS) of bacteria, yeast, and higher plants; this enzyme catalyzes the first step in the synthesis of branched chain amino acids. Resistant ALS has been found in bacteria, yeast and tobacco with a proline substituted by serine in yeast ALS. These findings provide a strong basis for developing projected plant biotechnology applications.

EFFECTS OF ANNUAL REPEAT APPLICATIONS OF SIMAZINE, DIURON, TERBACIL, AND DICHLOBENIL IN A MATURE APPLE ORCHARD

Annual tree growth and yields of mature Bancroft apple trees was higher when simazine (2-chloro-4,6 bis(ethylamino)-s-triazine), terbacil (3-tert-butyl-5-chloro-6-methyluracil) and dichlobenil (2-6-dichlorobenzonitrile) were applied annually for 6 yr to control weeds compared to trees that were regularly mowed. Fruit maturity was slightly delayed with herbicide treatment. While acceptable weed control was afforded by all herbicide treatments, repeat applications of terbacil annually gave the highest level of weed control. There was an indication after a number of years of simazine use that common vetch (Vicia cracca L.) would become a major problem. In these trials all herbicides accumulated in the 0- to 15-cm surface layer of the soil profile. Continued use of specific herbicides would have some effect on both potassium and magnesium in foliage collected in mid-July. Nitrogen levels in the leaves were not increased significantly during the study.

Postemergent Herbicides and the Biology of Drechslera sorokiniana: Effects on Conidial Germination, Vegetative Growth, and Reproduction

SUMMARYThe synthetic auxinlike postemergent herbicides 2,4-D, 2,4,5-T, 2,4,5-TP, dicamba, and MCPP were examined for their influence on conidial germination, germ-tube growth, primary branching of germ tubes, and conidial production of Drechslera sorokiniana at molar concentrations of 10-12 to 10-3. All herbicides of the 10-3 M concentration prohibited conidial germination and caused visible plasmolysis of conidium cells. Germination of conidia was not affected by any herbicides at concentrations of 10-12 to 10-4 M. Germ-tube growth and primary branching of germ tubes were stimulated by most herbicides at concentrations of 10-12 to 10-4 M; some nonsignificant inhibition of these structures occurred in response to 2,4,5-TP and MCPP. Mycelial growth was stimulated by most herbicides at concentrations of 10-12 to 10-4 M; significant increases within this concentration range, however, differed with specific herbicides. Conidial production was inhibited by 2,4,5-T and MCPP at all concentrations; 2,4,5-TP and dicamba caused significant increases in conidial production at lower concentrations and a significant decrease at higher concentrations. Only 2,4-D increased conidial production at higher concentrations. The results of the investigation indicate that germ-tube growth is most dramatically stimulated by the herbicides examined and that vegetative growth (germ tubes, branching, mycelium) of D. sorokiniana shows a greater stimulatory response to very low concentrations of the herbicides. The study shows also that the herbicides at their various concentrations may have opposite effects on growth of D. sorokiniana, depending on the stage of growth of the organism.

Postemergent Herbicides and the Biology of Drechslera Sorokiniana: Effects on Conidial Germination, Vegetative Growth, and Reproduction

The synthetic auxinlike postemergent herbicides 2,4-D, 2,4,5-T, 2,4,5-TP, dicamba, and MCPP were examined for their influence on conidial germination, germ-tube growth, primary branching of germ tubes, and conidial production of Drechslera sorokiniana at molar concentrations of 10-1 to 10-3. All herbicides of the 10-3 M concentration prohibited conidial germination and caused visible plasmolysis of conidium cells. Germination of conidia was not affected by any herbicides at concentrations of 10-~1 to 10-4 M. Germ-tube growth and primary branching of germ tubes were stimulated by most herbicides at concentrations of 10-12 to 10-4 M; some nonsignificant inhibition of these structures occurred in response to 2,4,5-TP and MCPP. Mycelial growth was stimulated by most herbicides at concentrations of 10-12 to 10-4 M; significant increases within this concentration range, however, differed with specific herbicides. Conidial production was inhibited by 2,4,5-T and MCPP at all concentrations; 2,4,5-TP and dicamba caused significant increases in conidial production at lower concentrations and a significant decrease at higher concentrations. Only 2,4-D increased conidial production at higher concentrations. The results of the investigation indicate that germ-tube growth is most dramatically stimulated by the herbicides examined and that vegetative growth

Interaction between herbicides, time of application and genotype of wild oats (Avena fatua L.)

A glasshouse experiment was conducted on three groups of genotypes of Avena fatua L. representing those from the north, central and southern regions of the temperate area of Western Australia with a winter growing season. The interaction between genotype groups, three herbicides (barban, difenzoquat and flamprop-methyl) and six times of application was investigated. The results showed that all genotypes did not react similarly to the herbicides tested. Barban, in particular, was very susceptible to the genotype x time of application interaction. Reasons for this are suggested. These include the effect of climatic parameters on the evolution of predominant genotypes in various areas, together with micromorphological variability developed in response to environmental pressure. It is also suggested that the number of days after seedling emergence is as reliable a guide as leaf number for optimum application of barban and that mature wild oat seed-head counts may not adequately reflect important competitive attributes such as dry matter production. The possible erroneous extrapolation to subspecies level from data collected on a species basis is emphasized, as is the possibility of differentially specific herbicides contributing to population shifts towards greater herbicide resistance, and not only in wild oats. Lines of future research are indicated.

Herbicidal Weed Control in Stubble No-Till Planted Corn

Several dozen herbicide systems were evaluated over a 4-yr period for weed control in stubble no-till planted corn (Zea maysL.). Crop tolerance and corn yield data also were obtained. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) and glyphosate [N-(phosphonomethyl)glycine] afforded excellent desiccation of all emerged vegetation each year. The oil-soluble formulation of dinoseb (2-sec-butyl-4,6-dinitrophenol) also afforded complete contact control of emerged vegetation in 1975, the only year it was evaluated. A herbicide system consisting of an acetanilide plus a triazine afforded the most consistent residual weed control. The specific herbicides affording satisfactory control largely depended on the weed spectrum. Fall panicum (Panicum dichotomiflorumMichx.), large crabgrass [Digitaria sanguinalis(L.) Scop.], and yellow nutsedge (Cyperus esculentusL.) were the weeds most difficult to control with the herbicide systems used in these studies. Corn yields were influenced primarily by the degree of weed control achieved, and in several instances by secondary effects of stand reduction or injury.

Chemical weed control in lupins

The response of weeds and narrow-leaved lupins (Lupinus angustifolius) to a number of pre-planting, pre-emergence and post-emergence applied herbicides was evaluated in six field trials between 1970 and 1973. Applied six weeks post-emergence, fluometuron and propazine at 0.75, 1.5 and 3.0 kg, carbetamide at 1.5, 2.0 and 3.0 kg, simazine at 1.5 and 3.0 kg, and chlortoluron at 3.0 kg a.i. ha-1 gave good control of annual weeds present. Only carbetamide 1.5, 2.0 and 3.0 kg, propazine 0.75 and 1.5 kg and simazine 1.5 kg a.i. ha-1 increased grain yield. Decreasing yield with increasing dose rate in the case of fluometuron and propazine in this situation suggested some crop toxicity. Applied pre-planting and incorporated, alachlor 1.0 and 2.0 kg, di-allate 0.84 kg, nitralin 0.6 and 1.2 kg and trifluralin 0.56 kg a.i. ha-1 gave good grass control and, in general, increased yield. They had no effect on the majority of broadleaf species present. Applied pre-emergence, alachlor, propazine and simazine at 1.0 and 2.0 kg, fluometuron at 1.0 to 4.0 kg and pronamide at 0.8 and 1.6 kg a.i. ha-1 in general gave good weed control and increased grain yield. All except alachlor affected both grasses and broadleaf species. The results, however, were seriously affected by rainfall incidence. The results are discussed in terms of the response to incorporation, rainfall incidence and temperature on the activity of specific herbicides.

Results of Breeding for Tolerance to 2,4‐D in Birdsfoot Trefoil1

To develop a weed control system for birdsfoot trefoil (Lotus corniculatus L.) utilizing an effective, inexpensive, and relatively safe herbicide, 2,4‐D, a recurrent selection program was undertaken to breed a strain of trefoil tolerant to this herbicide. We believe that this is the first report of the successful use of recurrent selection to develop herbicide tolerance.A series of tests established that five cycles of field selection had been effective in developing a strain substantially more tolerant to 2,4‐D than commonly used trefoil cultivars. After 2,4‐D treatment, green weight of the lowest yielding progeny line of the tolerant strain was five times that of ‘Viking.’ Survival percentage of the resistant strain was significantly higher than Viking, ‘Empire,’ ‘Mansfield,’ ‘Granger,’ and ‘Tana.’ Fresh and dry weight, plant N composition, and surface wax accumulation were significantly less affected by 2,4‐D in the tolerant strain. Evidence is presented that the 2,4‐D tolerant strain is resistant to the 2,4‐D homologs as well as the parent compound. It was suggested that evaluation of early seedling growth during exposure to herbicides in petri dish culture may prove to be both an effective and efficient screening device in breeding programs to develop tolerance to specific herbicides.

Pesticides and Environmental Quality in Illinois

Covers use of pesticides, monitoring, and reports test results for specific herbicides, insecticides, and fungicides in a model ecosystem. Discuses biological effects, degrative products, and environmental impacts.

Economic Impact of Restricting Herbicide Use

AbstractThe economic impact of restricting herbicide use is directly related to their real benefits. Farmer and consumer benefits from using herbicides are associated with the differences between a production function in which herbicides are used to control weeds and a similar but lower function for combinations of alternative weed control practices—not including herbicides. The lower function shows production without herbicides for the same dollar value of alternative resources—primarily land and labor. It also shows the additional dollar value of the alternative resources needed to get the same production when herbicides are not used. The latter is implicit in evaluating costs of restricting specific herbicides while maintaining production. In one study, it was estimated that banning the use of 2,4,5‐T on 8 million acres of farm and nonfarm land in 1969 would have increased costs to farmers about $32 million, assuming current levels of production were maintained. However, if substitutes for 2,4,5‐T could not include the related phenoxy herbicides, it was estimated that additional costs to farmers as a result of replacing 2,4,5‐T would have been $44 million. In a related study it was determined that restricting the use of all phenoxy herbicides would increase United States farmers production costs about $290 million. In addition about 20 million more hours of family labor would be used and about 6 million more crop acres would be required.