When herbicides are combined under natural conditions or applied in stress conditions (drought, for instance), the efficiency of their action may decrease which results in considerable yield losses. The reason thereto is that another herbicide or stressor can trigger the adaptation mechanism in weed plants, and they survive, resulting in weed infestation. In particular, it applies to such herbicides as acetyl-CoA-carboxylase inhibitors or so- called graminicides, which are effective only for grass weeds control. The efficiency of this groups of herbi- cides is heavily dependent on the environment and often decreases when combined with herbicides, efficient against dicotyledon weeds. It turns out that this occurs due to the fact their final phytotoxicity is not determined at the level of the site of action (herbicide target) but depends on the stage of herbicide-induced pathogenesis – processes, occurring due to the interaction between the herbicide and its site of action. The stress response of the weeds may make its contribution into herbicide-induced pathogenesis. Plants are known to respond to the action of various abiotic stressors in the form of non-specific stress response and depending on the intensity and duration of the stressor’s action, a plant either adapts or dies. At present there are sufficient data, demonstrating that programmed cell death (PCD) is involved in the herbicide-induced pathogenesis. Reactive oxygen species (ROS) induce PCD in specific classes of herbicides. The participation of ROS and PCD in herbicide-induced pathogenesis allows for targeted effects on the phytotoxic action of herbicides, for instance, via combined application of herbicides with possible PCD inducers and prooxidants. The confirmation of the role of non- specific response in the development of phytotoxic action of herbicides is found in the phenomena of cross- adaptation (activation of antioxidant defense) and cross-synergism (activation of oxidative stress) under the application of herbicides. Based on our own research and literature data, the importance of cross-adaptation and cross-synergism in applying herbicides in drought conditions and to determine the nature of the interac- tion in herbicide complexes is discussed. In particular, the review discusses the reduction of phytotoxicity of the ACCase herbicides due to the phenomenon of cross-adaptation in drought conditions and in combination with herbicides, which are acetolactate synthase inhibitors. The results of investigations were presented about the reduction of antagonism in the mixtures of herbicides, which are ACCase and ALS inhibitors, because of the use of substances with prooxidant properties, as well as the inhibitor of the antioxidant enzyme superoxide dismutase. On the other hand, we analyzed the possibility of increasing the phytotoxic effect of herbicides, ACCase inhibitors, in combination with herbicides with prooxidant properties – inhibitors of electron transport in Photosystem 2 (FS 2) chloroplasts and protoporphyrinogen oxidase (PROTOX) inhibitors. It became the foundation for the elaboration of efficient herbicide compositions for wheat and onion fields. While combining herbicides, the issue of synergism is becoming relevant due to the problem of the spread of target-site resis- tance, since, to prevent this type of resistance, it is necessary to combine herbicides with different mechanisms of phytotoxicity. The presented data demonstrate that the increased activity of antioxidant defense systems, which is the result of a long process of evolutionary adaptation of weeds to the action of abiotic stressors, is an element of non-target-site-based resistance to herbicides. Possible ways to prevent the negative impact of non-specific stress response on the efficiency of herbicides, as well as the prospects of the chemical method of weeds control are discussed.

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The problem of using alternative energy sources from renewable feedstock is becoming more and more of great current interest for modern society due to energy crisis and ecological situation which is getting worse. Among many high-yielding plants, perennial cereal miscanthus is an appreciable one for producing biofuel in the form of fuel granules. Cultivating phytoenergetic cultures it is important to apply fertilizers as an important component of the technology, which is aimed at raising yielding capacity of vegetative mass. Unlike other cereals, culm of miscanthus is partially or fully filled with white soft pith. Joints at the bottom of the culm are quite short, and on the top part of the culm they can be of a large length due to the division of intercalary meristem. Thus, during the growing season the largest amount of joints on the culm was in the variant N60 – 7.1 pieces which is more comparing with the control on 1.3 pieces and with N30 - on 0.9 pieces. At the end of the growing season the amount of joints raised slightly. Thus, in the control variant the amount of joints was 6.4 pieces, N30 – 7.3 pieces and N60 – 8.0 which is more comparing with the growing season on 0.6 – 0.9 pieces on the culm. As the result of the estimated indices we defined the greatest amount of leaves in the growing season by the variant N60 – 9.5 pieces per culm, and the least amount was on the control 7.8 pieces per culm, in the variant N30 – 8.7 pieces per culm. The same tendency was at the end of the growing season. Thus, the largest amount of leaves on the culm was in the variant N60 – 10.5 pieces, on the control – 8.5 pieces, N30 – 9.8. The difference in leaves amount on the culm between growing seasons varied from 0.7 to 1.0 pieces. At the end of vegetation the weight of plants was 48.5–77.0 g. The least weight of plants was on the control – 48.5 g which is more on 20.5 g than in the variant N30, and on 28.5 g of the variant N60. So the maximal weight was 77.0 gr in the variant N60. The weight of dry plant on the control was 25.1 g, N30 – 32.5 g, N60 – 37.1 g. The maximal weight of dry plant was in the variant N60 – 37.1 g, that is more on 4.6 g in the variant N30 and 12 g on the control. Pre-harvest density of miskanthus plants by apllying different dozes of fertilizers varied. Thus, the greatest density was in the variant N60 – 42 pieces per m2. The less density was got in the variant N30 – 38 pieces per m2 and the least density was on the control – 37.0 pieces per m2. According to the analysis of yield capacity indices of miscanthus during the years of research and different variants we pointed out that the maximal yielding capacity as for fertilizer dozes was in the variant N60 – 15.58 tons per ha, that is more on 20.7 % than in the variant N30 (12.35 tons per ha) and on 40.4 % that in the control variant (9.29 tons per ha).

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