How do herbicides affect plants

The growth inhibitor herbicides have no postemergence activity; therefore, the timing of application is critical. Dinitroanilines have various requirements for incorporation into the soil. Consult the individual product label for specific recommendations. The cell membrane disruptor postemergence herbicides control both grasses and broadleaf weeds by destroying cell membranes and causing rapid desiccation of the plant.

There are two types of cell membrane disruptor herbicides: the bipyridylium and the diphenylethers. The bipyridylium herbicides require thorough plant coverage to be effective, and they have no soil activity. The diphenylether herbicides act in a similar way but more slowly. Some of them are more selective between crops and weeds. The herbicides Goal and Reflex have significant soil activity. However, their true mode of action is unknown.

They are used to selectively control wide-leaved grasses such as crabgrass or dallisgrass in narrow-leaved grasses such as bermudagrass lawns. They are also very effective on cocklebur and common ragweed. These herbicides bind tightly to soil clay and organic matter, so they have no residual, preemergence activity. Plants rapidly turn yellow or pale and may look water soaked; then they dry up. The effects of the bipyridylium herbicides are rapid.

Even small droplets that drift to nontarget vegetation cause specks of burned tissue. Roots of perennial weeds are seldom killed because these herbicides do not usually translocate to the roots. The organic arsenicals accumulate in root and leaf tips and symptoms are first seen on leaf tips. They rapidly kill leaf and stem tissue. When applied over cotton to control grasses or cocklebur, they sometimes cause speckled leaf burn and red stems on the cotton plants; however, this has little effect on overall growth.

Be careful to prevent drift during application so that non target plants are not harmed. Applying systemic herbicides shortly after cell membrane disruptors or organic arsenicals is not advised. Paraquat and diquat are generally considered to be nonselective and harmful to both grass and broadleaf vegetation.

In peanuts, however, some selectivity can be achieved by using paraquat at the cracking stage. Lipid synthesis inhibitors are unique because they act only on annual and perennial grasses, not on broadleaf plants. With the exception of diclofop, these herbicides are applied postemergence and have little or no soil activity.

Crop oil concentrate or some other type of adjuvant must be used to increase herbicide uptake into the leaf. To be most effective, these herbicides should be applied to actively growing grass weeds. If grass weeds are stressed and slow growing, these herbicides will be less effective. These herbicides disrupt lipid biosynthesis in grass plants.

All plants contain lipids, which are fatty acids essential for plants to function normally. Plant cells contain lipid membranes. Membranes help the plant cell regulate what moves in, what moves out, and what remains out. Because these herbicides prevent the plant from producing fatty acids, membranes cannot form. Leaves absorb these herbicides quickly and within an hour they can not be removed by rain.

Symptoms develop slowly on grass plants and may not appear for 7 to 14 days. Initial injury is seen where the newest leaves are developing. These regions usually turn pale or yellow and then die. The area at the base of new leaves quickly becomes mushy, has a rotted appearance, and new leaves in the affected area can be pulled easily from the rest of the plant.

This new category of herbicides can be used at extremely low rates, controls both grasses and broadleaf plants, has soil and foliar activity, and is essentially non toxic to mammals and most non vegetative life forms. Amino acid synthesis inhibitors bind to a specific enzyme and prevent the development of amino acids essential to plant life.

When these herbicides are applied preemergence, symptoms do not usually appear until the plants have emerged from the soil. On broadleaf plants, symptoms include red or purple leaf veins, yellowing of new leaf tissue, and sometimes blackened terminals.

Herbicides in this category are very crop specific. The spray tank must be cleaned thoroughly before the sprayer is used on a potentially susceptible crop. In general, symptoms are more severe on young plants or when plants are metabolically active. When misapplication occurs, symptoms of treated plants are usually uniform throughout the treated area. It is likely that plants in the treated area need to be destroyed due to significant injury and illegal herbicide residue on the plants.

Herbicide symptoms may occur when the sprayer is not properly cleaned after a previous herbicide application. Sprayer contamination is problematic in highly diversified cropping systems. This problem can be easily avoided by ensuring that sprayers are properly cleaned between different herbicide tank loads.

Herbicide symptoms from sprayer contamination can occur up to several months after using the uncleaned sprayer, since dry herbicide particles can be redissolved causing symptoms. Just spraying until the sprayer is empty does not mean the sprayer is clean. There are herbicide residues that can be on the side of the spray tank, in the spray lines, sumps, pump, filters, and nozzles. All of these parts can be a potential source of contamination.

Small amounts of herbicide residue in the spray lines or filters can cause significant damage to the next crop to be sprayed. In general, postemergent herbicides sprayed directly on the crop foliage have greater potential injury than soil applications, especially when surfactant or adjuvants are included to enhance pesticide spread or uptake. Injury from sprayer contamination can affect crop growth and development for several weeks after application and in severe cases can reduce crop yields.

The field pattern can provide clues to the sprayer filling routine in the field where the crop damage occurred. Crop injury that is associated with one or two sprayer tank loads would suggest sprayer contamination.

Symptoms from contaminated tanks are usually worse at the beginning of the spray with damage diminishing with spraying and tank reloading.

Always follow the herbicide label for directions and recommendations for the best method and cleaning agent to use when cleaning out the spray equipment. Consult labels for the products that were previously in the tank and for the products that will be used for the next application. Rinsing with just water may not remove the residue and the herbicide may remain tightly adsorbed in the sprayer through several loads.

Further loads that contain other herbicides, oils, fertilizers, or basic pH blend may cause the herbicide to desorb, disperse into the spray solution, and damage susceptible crops.

Herbicide residues may persist in the soil and affect susceptible crops for one or more years following application. Crop sensitivity depends on the crop, soil properties, soil moisture and temperature and herbicide. Crop injury from herbicide residue in the soil, however, is not restricted to persistent residual herbicides applied the previous year. It may happen from herbicide applied to burndown weeds before planting. For example, dicamba and 2,4-D applied to burndown weeds before cotton or soybean planting may severely injure these crops.

Herbicide labels often provide guidelines on intervals between herbicide application and the planting of sensitive crops. Herbicide injury symptoms on sensitive plants can occur from exposure to low soil concentrations. This is not meant to be a comprehensive bibliography of references dealing with herbicides, but rather is meant to highlight a few references that may be especially useful.

This database has toxicity data for pesticides across many species. It provides a good starting point for finding pesticide use, occurrence, and effects data on the web. This publication provides a breakdown of seventy-eight common herbicides organized by translocation mechanism and then mode of action. It further subdivides the information into chemical type and then common and trade names. A brief paragraph describes each mode of action and types of vegetation that the herbicide is often used to control.

This is a recent reference for mechanistic health and environmental toxicity information for pesticides, including herbicides and insecticides. The aquatic life benchmarks for freshwater species provided in this module are based on toxicity values reviewed by U.

EPA and used in the Agency's most recent risk assessments, developed as part of the decision-making process for pesticide including herbicides registration. Acute and chronic benchmarks are provided for fish, invertebrates and aquatic plants.

The table of benchmarks provides links to supporting ecological risk assessments. Each aquatic life benchmark is based on the most sensitive, scientifically acceptable toxicity endpoint available to U. EPA for a given taxon. EPA's goal is to add to these benchmarks annually. Skip to main content. Contact Us. Literature Reviews This section presents an annotated bibliography of references providing information on stressor-response relationships for herbicides, as well as general background on herbicide properties.

Report No. Environmental Toxicology and Chemistry Archives of Environmental Contamination and Toxicology 53 1 Dewey SL Effects of the herbicide atrazine on aquatic insect community structure and emergence. Ecology 67 1 Duke SO Overview of herbicide mechanisms of action. Environmental Health Perspectives Archives of Environmental Contamination and Toxicology Environmental Health Perspectives Supplement 1 Environmental Toxicology and Chemistry 14 9 Physiological Zoology 71 6 Lydy MJ, Linck SL Assessing the impact of triazine herbicides on organophosphate insecticide toxicity to the earthworm Eisenia fetida.

Science of the Total Environment Wildlife Society Bulletin 32 4 Pesticide Science 53 1 Aquatic Toxicology 99 2 CAS Registry No. Geological Survey. Environmental Pollution Ecotoxicology and Environmental Safety Stressor Identification Vol 2. Examples and Applications Vol 4. Data Analysis Vol 5. Causal Databases Glossary.

Contact Us to ask a question, provide feedback, or report a problem. Applied primarily to genetically engineered, glyphosate-resistant varieties of soybeans, corn, canola and cotton. Also applied to control woody plants. Because of its broad spectrum and relatively low toxicity to animals, it is used in horticulture and in the control of aquatic macrophytes.

The plant species were identified at the species level whenever possible, and some species, including Setaria spp. The mean abundance of each plant species was calculated in four repeated plots of the same treatment for each observation. The total number of species was estimated by all the species rooted within each of the quadrats in the plots of the same treatment at each of the four samples taken each year.

For each species, the mean relative frequencies were estimated by recording the presence or absence of all the species rooted in each quadrat of the four repeated plots of the same treatment at the four sample times each year over three years. We combined RLQ and fourth-corner analyses to test the covariation between the herbicide treatment variables R table and plant species traits Q table , constrained by the mean abundance of each plant species L table 36 , Five functional traits of plant ecological performance were chosen on the basis of the potential effect of herbicide type, herbicide dose, and time year and month of the application.

The plants that could not be determined at the species level were excluded from the combined RLQ and the fourth-corner analyses. The five functional traits were life form annual, biennial, and perennial , number of cotyledons monocotyledon and dicotyledon , flowering onset month , seed length cm , and plant height cm. We used 49, permutations in all the randomization procedures and a false discovery rate method to adjust the P values for the multiple tests used in the fourth-corner analysis and the combination of the RLQ and fourth-corner analyses.

An independent t test was used to analyse the difference in the mean frequency of each plant species between each herbicide-treated plot and the blank control. Both atrazine and tribenuron-methyl changed the species composition of the plant community. The total number of plant species in the plots treated with the herbicide was lower than that in the blank control plots Table 1.

Moreover, both herbicides significantly altered the relative frequency of some plants but had no significant effect on the species with relatively high frequencies in the blank control, including Digitaria sanguinalis , Amaranthus retroflexus , Chenopodium album , and Abutilon theophrasti Fig.

The number of plant species whose relative frequency was inhibited by herbicides was higher than the number of plant species whose relative frequency was increased by herbicides Fig. However, based on the fourth-corner analysis, herbicide type had no significant effect on plants with different life forms, different numbers of cotyledons, different initial flowering months, or different plant heights and seed sizes.

Relative frequency of occurrence of 31 plants across the quadrats: a mean frequency of plant sample without herbicide; b — g the frequency of plant sample treated with herbicide compared with mean frequency of plant sample without herbicide. Note: data are the percentage of all quadrat cells in which the species was recorded in June, August, September, and October in , and Here, and in Fig. The horizontal line under a letter indicates that the relative frequency of a species in this treatment did not change that of the blank control.

The effects of atrazine and tribenuron-methyl on plant community composition were not consistent. The relative frequency was significantly changed for more plants by atrazine Fig. Moreover, the upper positive part of the second RLQ axis identifies perennial species i: Metaplexis japonica , s: Lactucaindica , c1: Cirsiumarvense var. However, the lower positive part of the second RLQ axis identifies annual species v: Eleusineindica , z : Cyperus microiria , Fig.

Results of the first two axes of the RLQ analysis: a scores of species, b coefficients for environmental variables, and c traits. The values of d give the grid size. Herbicides reduced the plant community diversity in the fallow field, but there was no significant difference in the effects of atrazine or tribenuron-methyl on the species diversity indices of the plant community Table 2.

However, the effects of the herbicide doses that were less than the RFAC on the plant community composition and community diversity of the fallow field were not lower than the effects of the RFAC of the herbicides. Compared with the blank control, the inhibition by atrazine or tribenuron-methyl on the total number of species in the plots did not increase with the increase in dose Table 1.

However, according to the fourth-corner analysis, herbicide dose had no significant effect on plants with different life forms, different numbers of cotyledons, different initial flowering months, or different plant heights and seed sizes. The plots with relatively high concentrations of atrazine were found in the upper positive part of the second RLQ axis. These plots were characterized by perennial plants with longer seeds Fig. Pots with relatively high concentrations of tribenuron-methyl were found in the lower positive part of the second RLQ axis.

These plots were characterized by annual plants with late flowering onset Fig. As the number of years of herbicide application increased, the number of plant species decreased and the inhibitory effect of the herbicides was enhanced. The variation in the diversity index between the plots treated with the different herbicides and the blank control was not consistent during the different months of the plant growing season throughout the year Fig. The effects of atrazine or tribenuron-methyl on plant community diversity did not change significantly after three years of continuous herbicide application Fig.

However, the observation time had no significant effect on the functional composition of plants. The right part of the first RLQ axis highlights the trait attributes dicotyledonous, longer seeds, and perennial life cycle associated with the increase in observed years Fig. The left negative part of the first RLQ axis highlights the trait attributes monocotyledonous and later flowering onset associated with the later growing season September and October Fig.

The year and month in which observations were recorded had no significant effect on the presence of plants with different life forms, different numbers of cotyledons, different initial flowering months, or different heights or seed sizes based on the fourth-corner analysis.

Plant communities in field edges, fallow fields, and other semi-natural habitats of agricultural landscapes may be at significant ecotoxicological risk from herbicides applied to nearby crop fields In agricultural landscapes, field margins, fallow fields, and other semi-natural habitats are often the only remaining habitat for wild plant species and support diverse plant communities that help sustain pollinators, predators, and beneficial arthropods 21 , Previous studies have indicated that herbicides, even at low concentrations, adversely affect plant communities, causing a decline in forb cover and reduced the flowering of key species 21 and a reduction in the frequencies of certain species Our data on plant species diversity and community composition of a fallow field support these findings.

However, some studies have suggested that herbicides may not reduce the diversity of plant communities in agricultural landscapes 42 , The important result of our study is that atrazine and tribenuron-methyl altered the species composition and reduced the diversity of the plant communities in the fallow field in no more than three years.

Our results were partly due to the species-specific sensitivity of plants to these selective herbicides Atrazine had little effect on perennials, while tribenuron-methyl had little effect on monocotyledons Fig. Herbicide types were one of the important factors affecting the diversity of weed communities 42 , Furthermore, the response of plant communities to herbicides is related to community characteristics 47 , The succession of the vegetation with fallow age also revealed a gradient of plant strategies 1 , In this study, the fallow field was in an early fallow stages immediately following agricultural disturbances.

The communities in early fallow stages are often dominated by opportunistic ruderal species with fast growth and an annual life cycle 1. The herbicides, particularly atrazine, killed or inhibited annuals, which may be one of the reasons for annuals appearing more frequently in the blank control plots and perennials appearing more frequently in the herbicide treated plots.

In aggregate, the herbicides altered the plant species composition and reduced plant community diversity by reducing the number of species in the fallow field. Although species richness is not necessarily the most suitable indicator of healthy non-crop habitats in adjacent farmlands because some species are known to respond positively to disturbances 20 , changes in the number of species will inevitably affect the plant interactions in a plant community. Herbicides may not be an important factor in changing the functional composition of plant communities in the short term, but the long-term cumulative effects of herbicides on the functional composition and structure of plant communities in agricultural ecosystems need to be taken seriously In this study, although atrazine and tribenuron-methyl both reduced the number of plant species, they did not significantly change the functional composition of the plant communities within three years.

Previous studies have shown that fertilizer drift appeared to have a much stronger effect than herbicide drift on the plant trait composition in field margin strips 20 ; however, a significant interaction between herbicides and other agrochemicals shifted the functional structure of communities over the course of 11 years Although plant functional trait analysis could better reveal the value of non-food plant resources to food production and biodiversity in agroecosystems 4 , 51 , studies on the effects of herbicides on plant functional groups in agroecosystems are limited.

It is worth noting that contrary to our assumptions, herbicide doses less than the RFAC had a similar effect to the RFAC of the herbicides on the total number of species Table 1 and their relative frequencies Fig. These results may be explained by the effects of herbicides on the growth of individual plants.

Herbicide doses less than the RFAC could damage plant growth 52 , 53 and reduce seed production 44 , which could directly change the soil seed bank input. From another perspective, we could explain the results by the effects of the herbicides on the plant offspring. Sublethal herbicides have been shown to affect the germination and seedling growth of the F1 generation of plants, although species-specific responses were not consistent The effects of sublethal herbicides on plants could change the development of the plant community; thus, plant community diversity and species composition may be changed.

With this in mind, more attention should be paid to the prevention and control of the ecological risks of low concentrations or sublethal doses of herbicides in agricultural landscapes, which are often caused by herbicide drift and runoff from sprayed fields into adjacent non-target areas 44 , A certain width of herbicide-free isolated areas could be maintained between farmlands and non-target areas to controls ecological risks Herbicides are applied to farmland at least once a year and are used in most fields for many years, so the time factor has often been considered in research on the influence of herbicides on plant diversity in an agricultural landscapes In this study, the effects of herbicides on plant community diversity during different months of the growing season in a year were inconsistent Fig.

This may be because different plants have different growth cycles and different species have different response times to herbicides Thus, observations made during different months of the year should be cautiously compared in studies on the effect of herbicides on plant communities.

On the other hand, previous studies as well as this study have shown that the effects of herbicide application over many years on plant community diversity were irregular The effect of herbicides on the development of species communities was evident over time However, abiotic conditions and other unmeasured deterministic or stochastic processes, which could be driving observed plant patterns, may affect the amount of time it takes for herbicides to alter plant communitiesy These findings must be interpreted with caution for several reasons.

Our experiments only tested two herbicides commonly used in China as well as plant communities in a 3-year field study with a randomized block design; therefore, they represent just one sample of semi-natural habitats in the agricultural landscape of China.

We used only two of the commonly utilized herbicides from a long list of herbicides that are frequently applied to Chinese farmland. Moreover, we did not consider the effects of herbicide application time after three years on the plant community in the agricultural landscape, which may result in an underestimation of the ecological risks arising from herbicides applied to wild plants in fallow fields.