The phytotoxicity of barban (4-chloro-2-butynylm-chlorocarbanilate) applied 14 days after emergence to wheat(Triticum aestivumL. ‘Waldron’) and wild oat(Avena fatuaL.), at constant, fluctuating or alternating day-night temperatures was determined in controlled environmental chambers. Wheat and wild oat susceptibility to barban increased as post-treatment temperature decreased. Maximum barban selectivity for wild oat in wheat occurred with a constant 18 C or an alternating 18 C day and 10 C night post-treatment temperature. At least three days of 10 C immediately following barban application were necessary to cause wheat injury. However, two days at 29 C immediately after barban application in an otherwise 10 C post-treatment regime reduced wheat injury. Further, a night temperature lower than the day temperature after barban application increased wild oat control but did not correspondingly increase wheat injury compared to the constant temperature treatments.
The herbicides Treflan EC 2 (24% trifluralin) and Devrinol 50 (50% napropamid) applied separately decreased efficiently the incidence of club-root on cabbage seedlings in pot experiments. If these herbicides were applied together with the fungicide Bavistin {50% carbendazim) the control of the disease was in some cases more efficient, as compared with Bavistin used alone. The higher the organic matter content in the soil, the lower the phytotoxicity and dub-root controlling activity of herbicides. Thus, on peat soil the 'herbicides could be applied in much higher rates than on pseudopodsolic soil.
The environmental conditions and ecological niches for weed survival and development in cereals crops are diversified. They are conditioned by biotic and abiotic factors of the environment and natural factors including quantitative rations between species of agrophytocenosis. The object of the studies carried out in 2009-2012 was to determine the weed species composition and infestation in crops of spring cereal species. Two cultivars were taken into consideration for each cereal species. The observations were done on the control (untreated) plots of a field experiment on evaluation of herbicide biological efficacy. The obtained results revealed that regardless of cereal species and cultivar, the weed species composition was similar, however the number of weeds and their biomass were different. The smaller weed biomass and their number were correlated with a higher competitiveness of cultivated cereal plants in relation to weeds. The rye cultivar Bojko showed the highest competitivenes, while the wheat cultivar Tybalt was the least competitive. The highest weed infestation was recorder for wheat in contrast to the lowest one in barley and rye crops. A proper selection of cereal species and cultivars with high competitive abilities should be taken into consideration by organic farms.
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