Distribution and quantitative abundance of weedy sunflower of Helianthus annuus L. in Serbia

Abstract

The Helianthus annuus L. species that appears as a weedy sunflower differs from sunflower crop in height, pronounced branching, fenotipic variability, presence of anthocyan pigment, the numerous small heads, relativly small and morphologically various seeds (shape, color, motlling), dormancy and britlle seeds, etc. Having of mind that weedy sunflover (WS) has been spreading for more than two decades on crop and non-crop land in the area with intensive sunflower crop production in Serbia, and where it causes large yield losses in many crops (row crops and cereals), as well as due to confirmed cases of reduced herbicide efficacy the aim in thase study was to determine the distribution and defined population size of WS in whole teritory of Serbia. During three years, on the region with intensive sunflower crop production (Banat, Bačka, Srem, Stig) we monitored the present WS populations and assessed the quantitative and qualitative traits of populations. A scale  from 1-4 was used to estimate the number of plants in the population (1- species cover up to 5% of the surveyed area, 2- species cover 10-15% of ther surveyed area, 3- species cover 25-50% of ther surveyed area, and 4- species cover over 50%  of ther surveyed area). Over 200 populations of WS have been recorded in the whole territory of Serbia, and this is shown on a UTM rate 10x10 km. The lagest WS populations (5 to 15 ha) with the highest number of plants (> 100,000) and average density (about 5 m^-2 plants) were recorded in the site of Padinska Skela (in crop and non-crop lands), Zbeg (predominantly on non-crop land) and Surčin- Galovica (predominantly in crop land). Based of the traits of phenotipic diverity/discrimination, the population from Stari Žednik was most similar to sunflower crop [with the central head and apical branching, with the lowest number of heads compared with other WS populations (18.5 plants^-1, while some populations had up to 59.4 heads plant^-1) and the lergest size of heads (8.1 cm in diameter)]. These results should be guide for farmers in planning crop plannting, taking the best measures to WS control within the concept of antiresistance strategy, given the confirmed cases of reduced susceptibility of this weed to herbicides, as well as the obligation to eliminate it on non-crop land, given that the main corridors of its expansion are areas along roads and canales, field crop margines, lost crop land etc.