Barley weeds

Diphenyl ethers are both systemic and contact herbicides and are used for the selective control of annual broad-leaved weeds and grasses in a variety of crops (such as soybeans, maize, rice, wheat, barley, peanuts, cotton, onions and ornamental trees) under different application scenarios. This class of herbicides contains a diphenyl ether moiety as the core substructure. Acifluorfen, bifnox, chlomethoxyfen, chlorni-trofen, fluoroglycofen-ethyl and fomesafen, etc., are representative compounds of the diphenyl ether herbicides (Figure 1). 

A sound crop rotational system is of basic importance to the organic farmer. It reduces the risk of diseases and pests associated with monoculture, gives better control of weeds, spreads the labour requirements more evenly over the year, reduces the financial risk if one crop yields or sells badly and provides more interest for the farmer. For instance, take-all is a disease that cannot even be controlled chemically. Winter crops are more susceptible to take-all than spring sown crops and wheat is more susceptible than barley, so the safest position for winter wheat is immediately after a break crop. 

Another approach is the utilization of allelopathic rotational crops or companion plants in annual or perennial cropping systems (19). Living rye (Secale cereale L.) and its residues have been shown to provide nearly complete suppression of a variety of agroecosystem weeds (33). Similarly, residues of sorghums, barley, wheat and oats can provide exceptional suppression of certain weed species Q ). Although some progress has been made on identifying the allelochmicals from these plants, much remains to be accomplished. 

Study 2. The effects of wheat, oats, barley and rye mulches on three broadleaf weed species and crabgrass (Digitaria spp.) are shown in Table VI. Weed control data for the corn test at Kinston are not presented because of poor cover crop kill by the paraquat treatment. 

Islam, A.K.M.R. and S.B. Powles. 1988. Inheritance of resistance to paraquat in barley grass Hordeum glaucum Steud. Weed Res. 28 393-397. 

Lee CW, Kim JC, Chang YH, Youn KB (1991) Allelopathic effect of barley and rice straw on weed growth. Korean J Weed Sci 11 122-127... 

Atrazine, one of the herbicides most widely used in the United States and European countries over the last 30 years, is employed for pre- and post-emergence weed control on corn, wheat, barley, and sorghum fields, and on railway... 

The DuPont Company has commercialized two of these compounds. The first of these is chlorsulfuron (Fig. 1), formerly DPX-W4189, the active ingredient in Glean weed killer. It is being marketed by DuPont for use in small grains such as wheat and barley. 

There are more than 100 patents for plant protection by 1,2,4-oxadiazoles. For instance, the oxime ether (257) is claimed to be more effective than known compounds against Phytophthora infestans when applied protectively to tomatoes <87GEP(0)3528753>. Sprays of 5-trifluoromethyl-1,2,4-oxadiazoles, such as (258), show 90-100% protection against Erysiphe gmminis in barley <89JAP(K)63162680>. Other oxadiazoles, for example (259), show complete control of diverse weeds with no damage to rice crops <91JAP(K)02250873>. 

DDT was not the only synthetic chemical to find a use in private and commercial gardens. Plant physiologists in the 1930s had accidentally discovered a way of selectively killing weeds in cereal crops (the dominant source of food for humans— wheat, barley, maize and rice). The plant physiologists interested in how plants controlled their growth had discovered a plant hormone—auxin (indole-3-acetic acid). Chemists soon found that, not only was it easy to make this compound, but they could also easily make... 

So far, it has been established that there is a very large market for crop protection agents globally and that these markets are dominated with crops such as wheat, barley, maize, soybeans, rice, cotton, grapes, top fruit and total weed control in countries and regions such as the USA,... 

Herbicides. The use of herbicides (qv) based on iodine compounds has its main market in Western Europe. In Canada and the United States these compounds are used only to a small extent. The only significant iodine-containing herbicide is ioxynil [1689-85 4] (4,-hydroxy-3,5,-diiodobenzoic acid). This compound, often used in combination with other herbicides, is formulated for controlling many annual broad-leaved weeds, especially black-bindweed, knotgrass, mayweeds, and com marigold post-emergence in wheat, barley, oats, rye, and triticale (142). Annual consumption of iodine in relation to ioxynils is considered to be about 300—500 t (66). 

G-36393, methoprotryn Methoprotryn was introduced in the fall-sown small grain cereals, such as wheat and barley. Its application was always post-emergence in relation to both crop and weeds. In most cases it was combined with low rates of simazine in order to provide residual control of late germinating annual grasses. This combination made it possible for the first time to control broadleaf weeds and grasses with one application. 

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