Cockleburs are noxious weeds in Hungary, where they are widespread in row crops, especially in maize, sunflower and sugarbeet. A low density population of these weeds may be harmful because of their large competitive ability, fast growth in early phenological stages, allelopathy, and persistant sprouting.
Allelopathy of Xanthium italicum Mor. was examined during the growing season in 2004. Root and shoot samples were collected at 4 or 5 leaves stage (in the end of May and in the beginning of June) and before flowering (in the beginning of July) before and after rain. Extracts were made in tap water. The test plant was Beta vulgaris L.; its germination, root and shoot growth were evaluated at the 6th and 10th days after treatment.
Most of extracts inhibited the germination of sugar beet. In these experiments the phenological stage of the donor plant determined slightly the effectiveness of the extracts on sugar beet. Generally, significant differences existed between treatments only in cases of concentrated extracts.
Rainfall can modify the inhibitory effect of extracts (especially shoot extracts). Shoot extracts of young plants inhibited stronger germination and growth after rain than before rain. Density of cockleburs influenced the effect of extracts, as well. Generally, differences between the efficacy of extracts was larger after rain.
The results supported the hypothesis that the phenological stage and some environmental factors can modify allelopathy of cockleburs.
In Hungary, the cocklebur species significantly endanger row crops (i.e. corn, sunflower, sugar beet). Their fast spreading is caused by many reasons: long-lasting emergence, reduced sensitivity to many kinds of herbicides, vigorous competitional ability, allelopathy, fast initial growth and changes in climate. The means of allelopathy is used by many species of plants in the competition with one another, as well as by the cockleburs. But the efficiency of this is influenced by many factors. Species with allelopathical effect could show different behaviour under different conditions: they can produce compounds with retarding and stimulating effects in different quantities or compositions. The actual condition of the acceptor plant and the mediator agent (i.e. soil) influence the final effect.
In this experiment influence of phenology and rainfall was studied on allelopathy of cockleburs in May, July and September. A stronger inhibition was observed on growth of cress before rain in July than in May, but this retarding effect disappeared after rainfall. However, the samples collected in September have significant inhibitory effect after rain. Inhibition of sugarbeet’s germination was stronger in May than in July, and the difference increased after rain.
In Hungary, the woolly cupgrass (Eriochloa villosa [Thunb.] Kunth) endanger row crops (i.e. corn, sunflower). Its fast spreading based on some reason viz. long-lasting emergence, reduced sensitivity to many kinds of herbicides, vigorous competitional ability and fast initial growth. Allelopathy, ability of many plant species to produce one or more biochemicals wgich is used tocompete with each others. In this experiment we examined, whether the woolly cupgrass possesses allelopathy, and if so, how influences on the development of cultured crops like maize, sunflower and lettuce.
Experiences has been gained in the last 25 years with plant extracts, fermented juices, infusions and brews of plant origin presented in present paper. Interactions among vegetables growing in mixed cultures have been also summarized with special regard to insect repellent plants and to those interaction when the target plant’s odour is covered and the pest cannot find it. These methods – after the ecological balance of the garden has been returned – can help the growers to keep the pest density under the economic threshold. The allelopathy can be the basis of the presented results.
The research presents the results of the allelophatic effect upon the germination and growth of plants, immediately after springing, viewed as the interaction between the species of Tanacetum vulgare sin Chrysanthemum vulgare and three other crops: wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rape (Brassica napus ssp. oleifera L.). The experiments that were performed consisted in applying treatments with aqueous extracts obtained from the roots, leaves, stems and flowers harvested from T. vulgare plants upon the seeds of the three agricultural crops mentioned before. In all aqueous extracts, the results indicate the presence of some chemical compounds that have inhibiting allelophatic effect. The plants upon which tests were made showed great sensitivity, the results on their germination and growth being significantly negative and highly significantly negative.
The conclusions of this research sustain the idea of setting new research objectives in order to discover the chemical compounds from T. vulgare extracts that have such a stong effect and the possibilities they offer.
Velvetleaf (Abutilon theophrasti Medic.) and Cocklebur species (Xanthium spp.) are more and more dangerous and „difficult to control” weeds in several cultivated plants. The ground cover of these species have became larger in Hungary like other warm-philous species. There are several causes of danger of them, for example: large capability for competition, allelopathic effect, keeping on of emergence.
The allelopathic effect of these weeds were examined on sugarbeet (Beta vulgaris L.). Extracts of plants grown under different conditions have several effect on this species.
Abutilon theophrasti plants were grown in perlite to examine the effect of supplying with nutritive materials on production of inhibitors. The water soluble exudates of the shoots grown with no artificial fertilisers inhibit stronger than grown with them. Acid soluble exudates have contrary effect. The exudates made of roots inhibited the sugarbeet less than shoots.
Effect of drought stress on production of inhibitors was examined on Abutilon theophrasti and on Xanthium italicum. The species responded to missing of water different, and the water, acid and basic soluble exudates had different effect, as well.