The first of this group was nitrofen, introduced in They are generally used in preemergence or early postemergence weed control. They are primarily contact herbicides and are readily absorbed by leaves and roots. Translocation is limited. They induce chlorosis and necrosis as visible effects of activity.
Their mode of action is thought to be inhibition of electron transport and coupled photophosphorylation. In some instances they induce growth responses, resembling the action of auxins and the phenoxy herbicides.
Some of the more successful herbicides are found in this group. They are foliar applied, do not translocate, and are enhanced by high volume sprays containing surfactants to increase coverage.
They are used to control broadleaf and grass weeds in soybeans, peanuts, and other legumes, postemergence weed control in wheat, barley, soybeans and sugar beets. They include acifluorfen, lactofen, and oxyfluorfen. The imidazolinones are a relatively new class, first appearing in They are meristematic inhibitors which inhibit amino acid branched-chain biosynthesis. They are more effective against broadleaf weeds than grasses, and have both foliar and soil activity. Soil persistence ranges from moderate to long.
Imazapyr has been used the longest, as a nonselective, broad-spectrum herbicide with residual activity in noncrop areas and forestry. Imazaquin is a selective pre- and postemergence herbicide which has enjoyed wide use on soybeans.
Imazamethabenz-methyl is a selective postemergence herbicide against wild oats, mustards and buckwheat in sunflowers, wheat and barley. Imazethapyr is a preemergence, preplant incorporated and postemergence material for control of annual and perennial grass and broadleaf weeds in soybeans and other legumes.
This class, closely related to the imidazolinones, were introduced by Dow AgroSciences in Flumetsulam is a selective preplant, preemergence and postemergence material for tough broadleaf weeds in corn and soybeans, and sold in the U. Metosulam, similar in selectivity, is not registered in the U. Chloransulam and diclosulam are being developed in the U. Their mode of action is similar to that of the sulfonylureas and imidazolinones.
N - 2,6-difluorophenyl methyl[1,2,4]triazolo[1,5- a ]pyrimidinesulfonamide. This recently introduced class of herbicides is a family of postemergents with high activity against all grasses at economical rates. Consequently, they are applied to most broadleaf crops with little risk of crop injury. At higher rates of application some soil activity is observed.
In grasses the compounds are readily translocated from point of uptake to the growing meristem. Weather apparently has little effect on activity. Notably, they are all effective against the arch enemies crabgrass and johnsongrass. Fluazifop-butyl is the most widely used of the group, for postemergence control of both perennial and annual grass weeds, over-the-top in broadleaved crops, especially cotton and soybeans.
Some recent additions to the class include propaquizafop, quizalofop-P, metamifop and pyriftalid. These were highly selective for broadleaf weeds and were translocated throughout the plant. Several compounds belong to this group, of which 2,4-D and 2,4,5-T are the most familiar.
The phenoxy herbicides have complex mechanisms of action resembling those of auxins growth hormones. They affect cellular division, activate phosphate metabolism, and modify nucleic acid metabolism. The latter product, 2,4,5-T, used mainly to control woody perennials, became the subject of extended investigation, particularly because of its use in Vietnam in combination with 2,4-D as Agent Orange.
Certain samples were found to contain small amounts of a highly toxic impurity, 2,3,7,8-tetrachlorodibenzo- p- dioxin, commonly referred to as tetrachlorodioxin, or dioxin. Although alterations in manufacturing procedures reduced the dioxin content to minimal levels, 2,4,5-T registrations were cancelled and the product voluntarily removed by the manufacturers in Agent Orange was replaced with Agent White, a mixture of 2,4-D and picloram, which was longer lasting and more effective.
More than 33 million pounds manufactured in the United States, is used each year in 35 ester and salt forms. In agriculture it is used on cereal, grain crops and sugar cane for the control of broadleaf weeds, and on rights-of-way, turf and lawns, and in forest conservation programs. The manufacturing process for 2,4-D used in the United States does not result in any level of tetrachlorodioxin contamination. Thousands of ureas, also called substituted ureas, have been tested as herbicides and many are in use today.
Fluometuron is illustrated. Others include linuron, diuron and monuron, fenuron-TCA, siduron and tebuthiuron. Most of the ureas are relatively nonselective and are usually applied to the soil as preemergence herbicides; some have postemergence uses, while others are active when foliar applied.
The ureas are strongly absorbed by the soil, then absorbed by roots. Their mechanism of action is to inhibit photosynthesis—the production of plant sugars—and, indirectly, to inhibit the Hill reaction. Despite the number and age of this group new ones continue to make an appearance. Two recent additions include isoproturon and cumyluron, the latter of which though structurally a urea has an unknown mode of action.
Neither is used in the U. There are yet a larger number of ureas not registered for use in the U. These are foliar applied, translocated herbicides that interfere with normal plant amino acid synthesis. They are more effective against grasses than broadleaf weeds, and are considered to be nonselective foliar compounds with no soil activity. They penetrate rather slowly, thus rainfall shortly after application can reduce effectiveness.
Found here are glyphosate, glufosinate, fosamine and glyphosate trimesium. Glyphosate, now the most widely used pesticide in the U.
It is recognized for its effectiveness against perennial, deep-rooted, grass and broadleaf weeds, as well as woody brush problems in crop and noncrop areas. It is a translocated, foliar-applied herbicide that can be applied at any stage of plant growth or at any time of year, with most types of application equipment, including the new wick, roller, and wiper devices. Its mechanism of action appears to be the inhibition of the synthesis of aromatic amino acids, which results in the inhibition of nucleic acid metabolism and protein synthesis.
There are a number of salt forms registered for glyphosate. The growth of glyphosate was dramatically enhanced starting in the mids by the creation and marketing of several crops corn, cotton, soybeans, canola with others planned bioengineered to render them tolerant to applications of glyphosate. This technological advance allows farmers to spray the non-selective herbicide onto these crops to achieve excellent weed control without significant crop damage.
Although similar traits were introduced into certain crops for other herbicides including imadazolinones and glufosinate these have not matched the commercial success enjoyed by glyphosate. Glufosinate is used primarily for grass weeds in orchards and vineyards as a postemergence herbicide. Surprisingly, it is used as a desiccant on potatoes, and for weed control in minimum tillage systems.
Only two compounds of significance fall into this minor class. They are chlorthal DCPA; often sold as the dimethyl ether which is called chlorthal-dimethyl , developed in , and endothall, which appeared in Chlorothal is a quality crabgrass herbicide, but is also highly effective against most grass and broadleaf weeds in vegetables.
Endothall is used in sugar beets for a narrow range of weeds, as an aquatic herbicide, as an algicide, and as a desiccant for cotton, potatoes, alfalfa and clover. Its low toxicity to fish makes it an ideal aquatic herbicide, and an outstanding example of environmental protection through pesticide selectivity.
Because these herbicides inhibit the formation of chlorophyll, the green pigment in plants, the weeds soon lose their color following uptake, and thus appear bleached. They are also referred to as being carotinoid biosynthesis inhibitors. These newer herbicides control grasses and broadleaf weeds, are compatible with the bipyridiliums and a wide range of preplant soil incorporated preemergence herbicides. Pyrazon formerly chloridizon , used almost exclusively on sugar beets, is a selective, pre- and postemergence herbicide for broadleaf weeds and is unusual for the group in being a photosystem II inhibitor.
Norflurazon is used as a preemergence herbicide for control of annual grasses and certain broadleaf weeds in cotton, soybeans, and vine and deciduous fruit crops.
Fluridone is an aquatic herbicide used in ponds, drainage and irrigation canals, lakes and reservoirs, for the control of most aquatic weeds at any stage of growth. Clomazone formerly dimethazone is a pre-emergence or preplant incorporated herbicide for grass and broadleaf weeds in soybeans, cotton and vegetables.
Oxadiazon is used for weed control in dry-seeded rice, and for turf and ornamentals. Among the newest family members are beflubutamid, picolinafen and oxadiargyl.
The first is an experiment being evaluated for use on small grains. Oxadiargyl is not used in the U. The carboxylic acid herbicides like their benzoic acid relatives are identified by the carboxylic acid radical attached to the benzene ring. More specifically, this COOH group is usually referred to as the carboxyl group.
In this group are picloram, triclopyr, fluoroxypyr, clopyralid and quinclorac. These are hormone herbicides that translocate in both the phloem and xylem. They are ideal for control of perennial broadleaf weeds and brush, and have both soil and foliar activity. Picloram is long-lived in soil, while triclopyr and clopyralid are much less persistent. Their mode of action is that of the synthetic auxins, acting like the natural plant hormone indoleacetic acid, and like their kindred phenoxy-, and benzoic-acid herbicides.
Pyridine is a benzene ring with one of the carbons replaced by a nitrogen, as in the illustration. There are several substituted pyridines used as herbicides. Dithiopyr is a selective pre- and postemergence material, used only on turf to control a wide variety of grass weeds.
It is frequently formulated with other herbicides and on fertilizers. Thiazopyr is a selective preemergence compound that works well for practically all grass weeds, on a wide variety of crops, including citrus, cotton, corn, peanuts, soybeans and potatoes. They appear to be microtubule assembly inhibitors.
The quality of seeds produced may be benefited, despite the anticipation of harvest of only 3 days, mainly when there is a risk of occurrence of rainfall before the harvest or attack of pests or microorganisms. The results of all variables considered to evaluate the physiological quality of cowpea seeds from desiccated plants at pre-harvest decreased, relative to the control, when using glufosinate-ammonium.
Table 3. According to McNaughton et al. However, Assis et al. The glyphosate herbicide negatively affected the germination GE , first germination counting FGC , emergence EM , and electrical conductivity EC of cowpea seeds, relative to the control. Zuffo et al. Revista Caatinga. Zhang et al. Evaluation of harvest aid herbicides as desiccants in lentil production. Weed Technology, , reported that the seed water content at the time of application can affect the translocation of glyphosate to the seeds.
The use of the carfentrazone-ethyl, flumioxazin, saflufenacil, diquat, and paraquat resulted in higher GE and EM than the use of glyphosate and glufosinate-ammonium Table 3. The glyphosate and glufosinate-ammonium herbicides may have been absorbed, since they were sprayed directly on the pods, which, in cowpea plants of the cultivar BRS-Tumucuma, are located above the leaves.
Despite glufosinate-ammonium is classified as a contact herbicide, it has better translocation inside the plant than paraquat LACERDA et al. Regarding the vigor of the seeds, the results for FGC showed that the pre-harvest desiccation with carfentrazone-ethyl and paraquat resulted in more vigorous seeds than the other treatments. Intermediate vigor was found for flumioxazin, saflufenacil, and diquat, and low vigor was found for glyphosate and glufosinate-ammonium Table 3.
Lower emergence speed index ESI was found for seeds from plants desiccated with glufosinate-ammonium when compared to the other herbicides, which presented similar results to each other Table 3.
The accelerated aging AA test showed that the desiccation with diquat resulted in the lowest seed vigor, followed by glufosinate-ammonium; the other treatments presented no significant differences from each other Table 3. The EC test showed that glufosinate - ammonium, paraquat, and glyphosate presented higher leaching of exudates. The EC found for the other herbicides varied from According to Botelho et al. Revista Agro mbiente, , The interaction between herbicides and storage environments was not significant.
Glyphosate was the most harmful herbicide to the physiological quality of cowpea seeds after their storage, resulting in lower seed quality relative to the control, except for EC, which showed no differences between herbicides Table 4. Daltro et al. In addition, Botelho et al. The glufosinate-ammonium and saflufenacil herbicides negatively affected the GE, FGC, and AA of the treatments, when compared to the control.
Tavares et al. These herbicides may have been translocated to seeds still in formation, since they were sprayed directly on the pods, which are located above the leaves, negatively affecting their quality. Positive results were found for the use of carfentrazone-ethyl, flumioxazin, and paraquat when compared to the control treatment Table 4.
These herbicides did not affect the physiological potential of the seeds after six months of storage, and some variables showed better results than those of the control. However, Santos et al. Regarding the effect of the herbicides on the physiological potential of the cowpea seeds, the herbicides carfentrazone-ethyl, flumioxazin, and paraquat resulted in higher seed germination and vigor than the other herbicides.
The use of the herbicides saflufenacil, diquat, and glufosinate-ammonium resulted in seeds with intermediate physiological potential. The results of some variables for the glyphosate herbicide were lower than those found for the other herbicides used Table 4.
The storage of seeds in the cold controlled environment room resulted in higher seedling emergence percentages and emergence speed index than the storage in the not-controlled environment room; and a lower release of exudates was found for seeds stored in the not-controlled environment. Marcos Filho and Vieira reported that the results of this test can be affected by several factors and require careful monitoring to assure consistency.
These factors include water content, genotype, size, and physical condition of seeds, water volume and dimensions of containers used for imbibition, water quality, precision of the conductivity meter, sample size, imbibition time, temperature during imbibition, and reading procedures. The use of a pre-harvest desiccant can be a great harvest management tool to speed up harvest and help you make better use of your time.
The use of Reglone allows for a quicker dry down of your crop which helps get the crop in the bin faster. The quicker dry down will also help you to be more efficient by allowing you to combine faster, spread straw better, combine later into the night, and start earlier in the morning. Quicker dry down also helps you protect the grade of the crop and avoid any environmental factors that could delay harvest. Contact herbicides are best suited for desiccation of pulse crops.
This option is also available for canola, but the dense canopy makes the dry down process a little more challenging for a contact herbicide. Systemic herbicides such as glyphosate can be used alone or in conjunction with a contact, such as heat to desiccate a crop. This mode of action offers enhanced control for those trouble fields that have high weed pressure late in the season. It can take days for Glyphosate to show activity on the crop, so the addition of Heat LQ can speed up the rate of dry down.
The downside is, these products do not help the crop mature, which is why a timely application is so critical. Early applications can have detrimental affects on yield and quality. Systemic herbicides are most commonly used for desiccating canola acres. Depending on the marketability, these products may also be used on some pulse and cereal crops.
First off you will want to look at the field as a whole and see if there is a general colour change from green to yellow amongst the entire field. The time to desiccate dry beans ranges from late August to early September when conditions are cool and moisture is high. Dry beans can be harvested by undercutting and windrowing, swathing or straight combining. Cutting and windrowing is more common for row-cropped beans and vine-type varieties that pod low to the ground.
Direct harvest or swathing with lifters prior to combining has been more common for solid-seeded beans and bush-type varieties with higher pods.
Both undercutting and swathing of dry beans have a similar effect as desiccation. This reinforces the fact that desiccants do not bring about seed maturity, but instead help dry down plant material for ease of harvest. The decision to pull the trigger on desiccation or preharvest weed control depends on a combination of factors.
Here are a few questions to run through as you consider whether late-season herbicide is truly needed:. Estimate how much these areas differ in maturity.
If some areas are way behind, consider harvesting in stages. Some of these green spots could stay green for a long time. This means an increased risk of residue concentration in the seed sample if product is applied. If most of your crop is close to harvest, late-season herbicide may not even be an option for you depending on the product and its PHI.
This is especially true for peas that mature in the heat of summer. You may not need a desiccant if the crop is already progressing nicely.
Consider the types of weeds present, their populations, distribution within the field and development stage.
0コメント