Changes of Weed Flora in Cereal Fields Over the Last 31 Years in Van, Turkey

Abstract

Agricultural activities carried out over time, and accordingly the developments in pest control methods, and climatic changes caused by the global warming affect the composition and density of weeds in agricultural areas. In order to determine and reveal the causes of this change, a survey was conducted on cereal fields in Van in 2017 and compared with the results of a 31 years old survey. A total of 71 weed species belonging to 23 plant families were identified in 2017, while 84 weed species belonging to 24 plant families were identified in 1986. Looking at the weed density in unit area, it was found that the weed averages were 41.8 in a square meter in 2017 and 82.8 in 1986. In both surveys, the number of weed species was almost equal to each other and the coefficient of Similarity Index (SI) for 2 surveys was calculated as 0.58 in terms of weeds. While the roughfruit corn bedstraw (Galium tricornutum Dandy.), tuberous cranesbill (Geranium tuberosum L.) and rye (Secale cereale L.) were detected as the most intensive species in 1986, the narrowleaf knotweed (Polygonum bellardii All.), goatgrass (Aegilops spp.) and summer pheasant's eye (Adonis aestivalis L.) were identified as the densest species in the recent study. When the weed distribution was assessed based on their abundances, the field bindweed (Convolvulus arvensis L.) with 21.3% frequency of occurrence and yellowweed (Boreava orientalisJaub. & Spach) with 19.5% frequency of occurrence were detected as the most common weeds in 2017. The field bindweed (Convolvulus arvensis L.) was the most common weed type in both studies, while the yellowweed was found to be common only in 2017. When both studies were compared, it was seen that the total weed density had decreased at a significant level during the last 31 years, although there had been significant increase in the density of several weeds, such as the yellowweed (Boreava orientalis Jaub. & Spach). It is considered that this decrease was due to the increase in cultivation and pest control techniques.