Factors Affecting the Activity of Di‐allate and Tri‐allate

Abstract

Summary. Factors investigated included the susceptibility of Avena fatua L. at various stages of growth, the amount of moisture needed to activate di‐allate in Regina heavy clay, the vapour action of di‐allate in soil, the effect of organic matter on the availability of di‐allate, and the persistence of di‐allate and tri‐allate in Regina heavy clay. A. fatua sown at depths of 5–15 cm was killed by di‐allate or tri‐allate. as were seedlings treated at the 15–2‐leaf stage. Seedlings of spring wheat (Triticum aestivum L.) survived rates of 24 oz/ac if the shoots were 1–3 cm long prior to exposure. When di‐allate at 16 oz/ac was mixed with a 5 cm layer of Regina heavy clay (wilting point 19–6%) slightly less than 15% soil moisture was required to give complete control of A.fatua. Further experiments indicated that a large percentage of A. fatua seedlings were killed by the action of di‐allate vapour in the soil. In other tests the activity of di‐allate and tri‐allate was reduced when the percentage of organic matter in the soil was increased by adding peat. This could explain why there is little damage to wheat sown in treated soil of high organic content while similar rates can cause extensive damage in soils of low organic content. Under comparable conditions tri‐allate persisted for a longer period in the soil than di‐allate. Both chemicals exhibited a lag period after which their breakdown appeared to follow a first‐order reaction. Differences in the period of persistence were attributed to a much longer lag period and a slightly slower rate of biological breakdown for tri‐allate as compared to di‐allate. Facteurs affectant l'activité du di‐allate et du tri‐allate

Degradation, Adsorption and Volatility of Di‐allate and Tri‐allate in Prairie Soils

“…After 0, 2, 4, 6 and 8 weeks duplicate samples from the various non-sterile treatments were analysed for di-allate (Smith, 1969b). The results (Table 2) confirm the rapid degradation in Regina heavy clay as previously reported by Banting (1967). A slightly faster breakdown is indicated in Weyburn loam.…”

“…For all soils studied the adsorption of di-allate from solution was considerably less than that of tri-allate, and with both there is a correlation between the degree of adsorption and the organic matter content. A similar correlation has been reported between soil organic matter and the relative phytotoxicities of tri-allate (Banting, 1967) and di-allate (Banting, 1967;Koren, Foy & Ashton, 1968), which is indicative of adsorption of both herbicides to organic matter. Adsorption of herbicides can occur to soil colloids as well as organic matter (Bailey & White, 1964); also other factors, such as clay content and herbicide solubility, are doubtless involved in the adsorption and leaching of di-allate and tri-allate, as has been suggested for other thiolcarbamate herbicides (Gray & Weierich, 1968;Koren, Foy & Ashton, 1969).…”

“…Duplicate tri-allate-treated soils were analysed (Smith, 1969a) after 0, 4, 8 and 12 weeks (Table 3) from which it seems that at all moisture levels degradation is slightly faster in Weyburn loam than in Regina heavy clay. At the clay These experiments confirm that di-ailate is more rapidly degraded in warm moist soils than tri-allate (Banting, 1967), and that the losses appear to be microbial in origin. The breakdown appears to be dependent upon soil type and also upon the degree of moisture.…”

“…Relatively little research has been undertaken to determine the fate of di-allate and tri-allate in soils. Kaufman (1967) has reported breakdown of di-allate in silty clay loam and Banting (1967) observed losses in activity of both herbicides in Regina heavy clay with time, whereas in sterilized clay chemical activity was only slightly reduced after several months. This suggested that tri-allate and di-allate can undergo microbiological degradation under warm moist soil conditions, and more recent experiments (Smith, 1969a) have tended to confirm these observations.…”

“…When correctly incorporated herbicidal activity remains for several months (Molberg et al, 1964). Ofthe two, di-allate is the more volatile and there is evidence that di-allate vapour may account largely for the control of wild oat seedhngs (Banting, 1967).…”