I. Gencsoylu et al. (2003) Phytoparasitica 31 (2): 139-143
Effect of Drip and Furrow Irrigation Methods on Bemisia tabaci Populations in Cotton Fields I. Gencsoylu, *'1 A.R. Horowitz, 2 F. Sezgin a and C. Onciier I Effects of drip and furrow irrigation and their application at three different levels, on Bemisia tabaci populations, were studied during the 1999 and 2000 growing seasons in Aydln, Turkey, with the objective of attaining water rates of 100% (full), 66% (2/3) and 33% (1/3) during irrigation periods. All plots were irrigated during four different phenological periods, viz., blooming, boll setting, boll and 5-10% of boll open stage. The number of whitefly immatures was significantly greater in furrow-irrigated than in drip-irrigated plots in both 1999 and 2000 and there were significant differences found in the effect of the irrigation methods and their application levels as well. In all trials, the number of whitefly nymphs was the highest in the 33% (1/3) water supply with both drip and furrow methods. KEY WORDS: Cotton; Bemisia tabaci; drip irrigation; furrow irrigation; population dynamics. INTRODUCTION The cotton production area in Turkey is approximately 719,000 ha per year. Most of the cotton fields in Turkey are irrigated by the border method. Recently, changing climatic factors have affected water availability in Turkey. Water is becoming expensive, and more difficult to locate. Drip irrigation is used mostly in greenhouses and in some fields that have limited water sources, but it has not yet been used in cotton production. Although this irrigation method provides water use efficiency (1), the cost of installing and maintaining the system is considered to be too expensive for growers. However, as water supplies become more and more limited, farmers must turn to alternative irrigation methods such as furrow and drip irrigation which would provide better water use efficiency than the border method. The whitefly (Bemisia tabaci) population in the Great Menderes Valley has not reached economic injury level and is still at a low level. Recently, cotton growers started using different irrigation methods that affect the population level. In a study by Radin et al. (12), irrigation methods were found to have an effect on water stress. The effect of reduced water stress on B. tabaci has received some attention in studies. Flint et al. (3) reported that up to four times as many whitefly nymphs were found on cotton in furrow-irrigated plots compared with drip-irrigated ones. Mor (10) found that water stress on cotton affected the whitefly nymph population in Israel and suggested that it increased nymphal survival. Although the effects of water stress on cotton pests were studied in the past (2-7,9), the Received April 4, 2002; received in final form Nov. 6, 2002; http://www.phytoparasitica.orgposting Feb. 3, 2003. 1Dept. of Plant Protection, Agricultural Faculty, Adnan Menderes University, Aydm, Turkey. *Corresponding author [e-mail:
[email protected]]. 2Dept. of Entomology, ARO, Gilat Research Center, M.E Negev 85280, Israel. aAgricultural Structure and Irrigation, Agricultural Faculty, Adnan Menderes University, Aydm, Turkey. Phytoparasitica 31:2, 2003
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effect of drip or furrow irrigation on cotton pests has not been studied extensively and little information is available in the literature. In the present study we compared the effects of two different irrigation methods, and three different irrigation levels, on B. tabaci populations at different phenological periods of the cotton crop. MATERIALS AND METHODS Experiments were conducted during the 1999 and 2000 growing seasons in cotton fields at Adnan Menderes University, Research Center of Agricultural Faculty, located in Aydln Province, Turkey. Two irrigation methods, furrow and drip, and their applications at three different levels, were studied each year with the objective of attaining 100% (full), 66% (2/3) and 33% (1/3) of the irrigation rate during irrigation periods. The cotton variety was 'Nazilli-84', which is well adapted to the local environment. Each plot consisted of six 50m-long rows, including edge rows. Surface drippers were placed between every two rows, with 25 cm interrow spacing. All plots were irrigated at four different growth stages, viz., bloom stage, boll setting, boll stage, and 5-10% of boll open stage, as is the usual practice in Turkey. Moisture deficiency in the cotton root zone was measured by the gravimetric method and amount of irrigation water applied was determined for all plots. Irrigation was applied on July 14 and 27, Aug. 17 and Sept. 4 in 1999, and on July 6, 17, Aug. 1 and 22 in 2000. All plots received the same fertilization and cultivation practices during the 2 years of the experiment. No insecticides were applied to control the whitefly population in either year. The randomized complete block design with three replications was used in each year. There were 3-m spaces left between blocks to reduce edge effects. Data were collected weekly and analyzed by using ANOVA of the SAS. Duncan's Multiple Range Test (MRT) was conducted where significant F-values were obtained. Samplings of B. tabaci populations To estimate the levels of 3rd and 4th instar B. tabaci nymph populations, leaves were randomly chosen; they contained pupae and 3rd instars on the four most heavily infested leaves collected from the 5th mainstem node to the plant apex of each plant (11). Twenty leaves were collected from five randomly selected plants near the center of each plot. A total of 60 leaves from 15 plants were checked for each irrigation level in both furrow and drip irrigation plots. Nymphs were counted on the whole leaf, since infestation was very low (4). Weekly whitefly samplings (nine different dates) started on July 21 in 1999 and on July 20 in 2000. Then the leaves were placed in bags and brought to the laboratory for examination under a stereomicroscope. RESULTS This research study attempted to determine the effects of furrow and drip irrigation methods and rates of water supply on populations of B. tabaci in cotton during the growing seasons of 1999 and 2000. In all treatments, the whitefly population level was higher in 1999 than in 2000. In furrow-irrigated plots, whitefly samplings extended from July 21 to Sept. 22 in 1999, and from July 20 to Sept. 21 in 2000. The highest population levels were recorded on Aug. 24-25 in both years. The seasonal average number of nymphs per leaf was greater in 1999 than in 2000, and there were significant differences in the effect of irrigation rates on the 140
I. Gencsoylu et al.
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