Rasprostranjenost, biološke karakteristike i suzbijanje Asclepias syriaca L. / Distribution, biology, ecology and control of weed species Asclepias syriaca L.

In previous years in the Balkan region, including Serbia, spread of invasive weed species Asclepias syriaca L. was recorded. It supposedly arrived to Serbia from neighbouring Hungary, where it was grown as honey plant. Due to allelopathic properties and strong concurrence, this species does not allow regeneration of old sand fields. It is most common in neglected orchards and vineyards, sandy terrains along roads and railways, embankments, where form pure A. syriaca association, or several additional weed species occur, but with absolute dominance of this weed. From uncultivated areas on which it forms "oasis" its spread was noted especially in wheat, barley, sunflower, soybean, rapeseed crops, in orchards and vineyards. Considering all negative aspects of uncontrolled spread of A. syriaca on ruderal and agricultural areas, the aims of the paper were monitoring of its spread and the study of biological and ecological properties, as well as the establishment of possible ways of its control. On the territory of Vojvodina, common milkweed population has a tendency of spread and colonization, particularly near roads and water flows. It is established on almost all soil types in Vojvodina. It grows on poor to very calcareous soils, as well as on poor to very humic ones. Common milkweed withstands soil with the content of available forms of phosphorous and potassium below the optimum , but also the soils with high to damaging content of these elements. The analysis of the biological spectrum of stands of ass. Asclepiadetum syriacae, Lániková in Chytrý 2009, established that it is hemicryptophyte and therophytein, with a domination of hemicryptophytic character. Annual seed production of A. syriaca seed per m2 is from 1.336,53 to 10.109,61, and with the increase in plant density per unit area, production of fruits is reduced. The share of milkweed seed in soil seed bank is very low, and therefore A. syriaca does not form permanent seed bank. Seed dormancy is stopped by its exposure to lower temperatures for several months, and moisture has an important role in the increase in seed germination. Allelopathic properties of common milkweed were confirmed by examination of root water extract effects on maize , soybean and sunflower seed germination at concentrations of 0.05-0.1g of dry root weight per 1ml of distilled water. Significant susceptibility of cultivated sorghum and Johnson grass to the applied extract was recorded. From common milkweed root extracts prepared by various solvents, the highest inhibiting effect to soybean seed germination had butanol extract, and to germination of seed of cultivated sorghum, ethyl acetate and butanol extract. It was the same with wild sorghum and redroot pigweed while none of the applied extracts had significantly negative effect on maize and soybean germination. In field trials, allelochemicals from A. syriaca root reduced maize and millet yield. Root water extracts at the applied concentration of 0.04g/ml reduced maize yield by 10-15%, of fodder sorghum by 12.5% and broomcorn by 23%. In studies regarding chemical control of A.syriaca in field conditions,the highest efficiency was recorded for herbicides based on glyphosate, 2.4-D and tembotrione, as well as for bentazone and bentazone + dicamba after tree-years long application.Dicamba was recorded as the least efficient. Terbuthylayine and clomazone herbicides in pre-emergence application at higher label rates efficiently control common milkweed from seed, while imazamox and oxasulfuron applied at lable rates efficiently control young plants of common milkweed at the phase of 2-4 leaves.