Residual herbicides

After use, herbicides decompose slowly, and so affect cultivated plants for many years. In 1990, investigations in many regions of the USSR detected herbicides phytotoxic effects, especially among the si/m-triazine class, on different cultivars in many varied situations [13]. These sym-triazine herbicides, such as protrazin, simazin, atrazine, metazin, and prometrin, were used in different oblasts of the Ukraine, Kirgizia, Kazakhstan, Russia and Moldavia in previous years, especially on corn. Residual herbicide aftereffects led to the suppression and death of crops such as winter wheat, oats, barley, rye, potatoes, beets and sugar beets, linen, onions, watermelons and other melons, and sunflowers. 

Worked Example 7.1. A sample of soil, thought to be contaminated with a herbicide, was collected and all traces of the residual herbicide were removed by digesting in hot water. A sample of known concentration (10 mol dm = 10 mol cm ) gave a limiting current, /nn, of 3.12 mA. What is the concentration of the herbicide in the soil sample if the limiting current is found to be 0.442 mA ... 

Diuron Phenylurea 330-54-1 1.83 -1951 Herbicide A preemergence residual herbicide for total control of weeds and mosses in noncrop areas and woody crops... 

Since many herbicides are crop-specific, herbicide concentrations in farmer s fields are routinely monitored to determine herbicide carry-over. Residual herbicides from the previous year adversely affect alternate crops grown to be grown during the subsequent season. There has been a limited amount of literature describing the successful SFE of herbicides such as sulfonylureas, diruron, linuron, and s-triazines spiked on various solid matrices with COj and methanol modified C02 (1,8-11). Summarized here are the differences in recovery of atrazine from an actual farmer s soil sample as a function of extraction temperature and pressure using both CO2 and methanol modified COj. Also shown are comparisons of recoveries from real vs. spiked samples and also static vs. dynamic modifier addition techniques. 

Bucsbaum, H. and A. Gottleib (1979). Control of existing weeds with residual herbicides. Proc. Weed Sci. Soc. Israel, p. 1. 

DeBarreda, G.D. and A. DelBusto (1978). Mixtures of residual herbicides with glyphosate. Proc. Mediterranean Herbicide Symp., 2 10-18. Madrid, Spain Ministario de Agricultur. 

Crop acres grown with Simazineb residual herbicides acres... 

For the years 2002-2005, simazine was applied to 26.3% of apple and 19.5% of pear crops grown in the United States (Table 17.3). Simazine was the most frequently used residual herbicide in both apple and pear, being applied to an average 108374 A of apple and 13444 A of pear. 

Karhiniemi, A. (1977). Trials with some residual herbicides in nursery plants. Ann. Agri. Fenniae, 16(1) 37 48. 

Gomez de Barreda, D., E. Lorenzo, M. Gamon, A. Walker, C. Ramos, A. Saez, E.A. Carbonell, J. Garcia de la Cuadra, N. Munoz, A. del Busto, and A.L. Lidon (1996). Persistence and leaching of some residual herbicides in uncropped soils. Bull. Environ. Contam. Toxicol., 56 219-224. 

Triazine herbicides provide cost-effective, broad-spectrum weed control and are key tools in conservation tillage. Although the chemical alternatives to the triazines are more costly and generally less efficacious, they are considerably more reliable as weed control methods and more compatible with current farming operations than available nonchemical weed control methods. Even as more com acreage shifts to herbicide-tolerant com, the need remains for residual herbicides such as the triazines to manage resistant weeds and to avoid the need for multiple tillage passes for weed control. 

However, because values of basic compounds are often below the soil pH, as soils become more acid, adsorption of bases such as s-triazines increases. This means that s-triazine herbicides tend to be inactivated once they come into contact with acid soils. On the other hand, residual herbicidal activity can persist in nonacid soils where adsorption is relatively weak, controlled largely by physical adsorption rather than electrostatic attraction to soil surfaces. 

Use of long residual herbicides with a single site of action should be avoided or minimized. 

Buthidazole is a residual herbicide for pre- and postemergence use. Owing probably to its poor water solubility, it is weakly absorbed in the soil, and thus is... 

The herbicides that penetrate through the roots, called soil-applied herbicides or residual herbicides, arenormally distributedinpre-emergence, i.e. before the crop and weeds have emerged, or in some cases incorporated into the soil at pre-sowing. This group of herbicides is characterised by ... 

Recently, a possible future strategy based on a compromise between the old strategy of pre-emergence treatment and the new post-emergence treatment has been put forward. This is based on a mixture of a residual herbicide, such as terbutylazine, and a sulfonylurea at early post-emergence (maize at two to three leaves). In soils not heavily infested with perennial grass weeds, this solution could be optimal. 

R. L Brooks, A. Zosdike, P. J. Porpiglia, CGA-277476 a short residual herbicide for soybean weed control programs, Proc. BCPC Conference — Weeds 79-85 (1995). 

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