The role of the growth stage of weeds in their response to reduced herbicide doses

The influence of weed growth stage on the efficacy of selected herbicides applied at reduced doses was investigated under pot experiments at the Institute of Soil Science and Plant Cultivation - State Research Institute in Wrocław. Three weed species were used as tested plants: Anthemis arvensis L., Chenopodium album L. and Stellaria media L., which were sprayed at different growth stages: 2-4, 6-8, and 10-12 leaves. The experiment included the following herbicides: tribenuron-methyl, iodosulfuron methyl sodium + amidosulfuron, and metribuzin + amidosulfuron, used at full doses and reduced by 25 and 50%. Three weeks after treatment, fresh weight of weeds was determined. Weed control was significantly related to weed species, growth stage, type of herbicide and its dose. Among the tested weed species, S. media showed the weakest reaction to the herbicides used and it was only slightly affected by herbicide rate and growth stage. Later herbicide treatments, when the weeds reached the stage of 6-8 and 10-12 leaves, resulted in diversification at the level of herbicide effects and doses

The influence of selected spraying parameters on two formulation of sulfonylurea herbicides effect

The objective of this study was the evaluation of spray volume and nozzle type effect on different formulation (water dispersible granules - WG and oil dispersion - OD) of two sulfonylurea herbicides: the mixture iodosulfuron methyl sodium + amidosulfuron and iodosulfuron methyl sodium + mesosulfuron methyl efficacy. There were investigated three levels of spray volume (125 l*ha-1, 250 l*ha-1 and 350 l*ha-1) and two types of nozzle (extended range flat nozzle TeeJet XR 11003-VS and drift guard flat nozzle TeeJet DG 11003-VS). Each herbicide was used at recommended dose and reduced by half. Spray volume and nozzle type did not affect activity of the mixture iodosulfuron methyl sodium + amidosulfuron, but differentiated the efficacy of OD formulation of iodosulfuron methyl sodium + mesosulfuron methyl, when it was applied at lowered dose. As spray volume rose, herbicide efficacy decreased. Nozzle type influenced OD formulation of the mixture iodosulfuron methyl sodium + mesosulfuron methyl, independently on dose. Significantly weaker efficacy was obtained when drift guard nozzle was used

Influence of environmental conditions and crop competition on morphological and biological diversity of Avena fatua L. and Solanum nigrum L.

This study investigated the effects of climate/soil conditions and crop competition on selected morphological traits, biomass productivity and some other biological aspects of the weedy species Avena fatua L. and Solanum nigrum L. The species examined came from arable fields differing with respect to soil type and crop species according to the following pattern: A. fatua (in maize – brown soil, in spring wheat – podsolic soil), S. nigrum (in maize – brown soil, in potatoes – podsolic soil). The investigations included measurements in their original habitats and in a controlled environment. Plants grown on fields with brown soil reached higher values of the evaluated traits as compared to those recorded for plants grown on a podsolic soil. The height of A. fatua was similar in both habitats because competitive ability of the crop balanced the soil effect. There were no differences in plant morphology and biomass productivity within the two species when plants were grown in the same soil/climate conditions but on different soils S. nigrum exhibited variation in plant height and biomass productivity. Both species similarly responded to reduced light that revealed differences between them in chlorophyll content. Seeds of A. fatua and S. nigrum, regardless of their origin, germinated better in darkness than in the light and seeds of both species were more able to germinate when they were collected from plants grown in the light conditions from above the crop canopy. All seeds of S. nigrum also germinated better under warm conditions (20°C)

Amino acid content and biomass productivity of selected weed species as an indicator of their response to herbicide stress

Biomass reduction and amino acid content in plants of Papaver rhoeas L. and Stellaria media L. were investigated to evaluate response of these species to herbicide stress under various temperature (25/16 and 8/2 oC) and relative humidity (50 and 75%) regimes. Weeds were treated with tribenuron methyl (15 g × ha-1), a mixture of 2.4-D with florasulam (180 + 3.75 g × ha-1), and a mixture of 2.4-D with dicamba (1252.5 + 97.5 g × ha-1). The fresh weight of weeds and the content of free branched-chain amino acids (valine, leucine and isoleucine) in plant tissue were recorded. Tribenuron methyl was the herbicide that most limited biomass productivity, regardless of weed species and climate conditions. S. media was more sensitive to herbicides than P. rhoeas. Weed response to herbicides was dependent on temperature, but not on relative humidity. Tribenuron methyl applied to both weed species under various temperature regimes caused significant amino acid deficiency. The reduction in amino acid content in plants of P. rhoeas was greater at warm temperature compared to the cold regime due to stronger reaction to tribenuron methyl applied under these conditions. In most of cases, the mixture of 2.4-D + dicamba induced overproduction of amino acids

Effect of combined application of herbicides with retardants depending on Triticum aestivum L. growth stage

In 2013–2016 the possibility of combined application of herbicides with retardants in winter wheat was investigated in Institute of Soil Science and Plant Cultivation in Wrocław. Two retardants (1. chloromequate chloride, 2. trinexapac-ethyl) were used in tank mixture with fluroxypyr and florasulam + amino- pyralide. The mixtures were applied on two dates: 1. at the end of tillering, 2. at the stage of 1–2 nodes (florasulam + amino- pyralide) or at the stage of flag leaf (fluroxypyr). Efficacy of weed control was affected only by date of treatment. Irrespective of which herbicide-retardant combination was used, the weed sup- pression was the lowest on plots treated with the mixtures at a later growth stage. It was reflected in the size of grain yield re- ceived from these plots, that was comparable to untreated control. Application of the mixture of fluroxypyr with trinexapac-ethyl in winter wheat tillering and flag leaf growth stages contributed to seed uniformity decrease

The influence of selected spraying parameters on two formulation of sulfonylurea herbicides effect

The objective of this study was the evaluation of spray volume and nozzle type effect on different formulation (water dispersible granules - WG and oil dispersion - OD) of two sulfonylurea herbicides: the mixture iodosulfuron methyl sodium + amidosulfuron and iodosulfuron methyl sodium + mesosulfuron methyl efficacy. There were investigated three levels of spray volume (125 l*ha-1, 250 l*ha-1 and 350 l*ha-1) and two types of nozzle (extended range flat nozzle TeeJet XR 11003-VS and drift guard flat nozzle TeeJet DG 11003-VS). Each herbicide was used at recommended dose and reduced by half. Spray volume and nozzle type did not affect activity of the mixture iodosulfuron methyl sodium + amidosulfuron, but differentiated the efficacy of OD formulation of iodosulfuron methyl sodium + mesosulfuron methyl, when it was applied at lowered dose. As spray volume rose, herbicide efficacy decreased. Nozzle type influenced OD formulation of the mixture iodosulfuron methyl sodium + mesosulfuron methyl, independently on dose. Significantly weaker efficacy was obtained when drift guard nozzle was used

The competitive ability of Chenopodium album and Echinochloa crus-galli in maize crops depending on the time of their occurrence or removal

Small-plot experiments for two levels of infestation (20 and 40 plants per m2) with Chenopodium album L. and Echinochloa crus-galli (L.) P. Beav were conducted in the 2009–2011 seasons. In the first variant, the effect of time of weed removal on maize was investigated. Weeds were removed in the following growth stages of maize: one, three, five, and seven leaves, the beginning of stem elongation, and the stage from the fourth to sixth node. The second variant concerned the effect of time of weed emergence on maize and included the same maize growth stages as mentioned above. In both treatments, weed competition was compared to the control – the plot completely free from weeds, as well as to the plot fully covered with weeds. Echinochloa crus-galli in the amount of 20 plants per m2, which were not removed until the five-leaf stage or which emerged immediately after the seven-leaf stage of maize, did not show any competitive effect on the growth and development of maize. Chenopodium album was characterized by a similar effect at the same level of weed infestation severity and when not removed until the five-leaf stage as well as in the case of plants that emerged after the seven-leaf stage of maize. Both species present in an amount of 40 plants per m2 needed to be removed no later than at the three-leaf stage of maize

Determination of the tolerance of maize cross-breeds and their parent material to bromoxynil – an inhibitor of photosystem II

Herbicides can exert a phytotoxic effect on maize (Zea mays L.) plants. High maize cross-breeds tolerance to herbicides can be obtained by proper selection of parent material. Based on the knowledge of phenotypic signs of damage, it is possible to discard the parents that are the most susceptible to herbicides. The aim of the study wasto compare the response of maize cross-breeds Dumka and Rywal, their parental forms, and lines to bromoxynil – the herbicide belonging to PSII photosynthesis inhibitor group. Herbicide was used at the recommended (400 g ha-1) and double (800 g ha-1) rates. Bromoxynil phytotoxicity was reflected in changes in plant morphological traits,growth inhibition, and green matter reduction of the female parent of cross-breed Dumka and its component S64423- 2. This indication was confirmed in the study of photosynthesis parameters –chlorophyll content and chlorophyll fluorescence in leaves. The cross-breed Rywal and their male parent proved to be tolerant to the bromoxynil.