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Submitted to: American Society of Agronomy
Publication Type: Proceedings Publication Acceptance Date: 12/4/2009 Publication Date: 2/2/2010 Citation: Krugner, R. 2010. Movement of Glassy-Winged Sharpshooters in a Deficit Irrigated Citrus Orchard. In: American Society of Agronomy, California Chapter, California Plant and Soil Confeence, February 2-3, 2010, Tulare, California. p.32. Interpretive Summary: Effect of plant water stress on glassy-winged sharpshooter (GWSS) population density and movement was evaluated in a citrus orchard (‘Valencia’) with three experimental irrigation treatments: 100%, 80%, and 60% of the crop evapotranspiration (ETc). GWSS population density and activity were monitored weekly by visual inspections, beat net sampling, trapping, and a novel mark and capture technique using protein markers (soy milk, whole milk, and egg white). Plant conditions monitored included temperature and humidity in the tree canopy, leaf surface temperature, water potential, and fruit quality and yield. GWSS populations were negatively affected by severe plant water stress (60% ETc) and positively affected by moderate plant water stress (80% ETc). Citrus trees irrigated at 60% ETc had significantly warmer leaves and lower xylem water potential. Fewer GWSS egg masses, nymphs, and adults were found on trees irrigated at 60% ETc than at 80% ETc. The adult GWSS population was reduced, on average, by 50% in trees under severe water stress. However, the total number of fruit and number of fruit across several grade categories was also substantially reduced in the 60% ETc treatment. A more complete understanding of the effect of plant water stress on crop yield and GWSS populations may improve GWSS control and limit spread of Xylella fastidiosa to susceptible crops. Technical Abstract: A two-year study was conducted in a citrus orchard [Citrus sinensis (L.) Osbeck cv. ‘Valencia’] to determine the effects of plant water stress on population density and movement glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar). Experimental treatments included irrigation at 100% of the crop evapotranspiration rate (ETc) and continuous deficit-irrigation regimes at 80 and 60% ETc. Microclimate and plant conditions monitored included temperature and humidity in the tree canopy, leaf surface temperature, water potential, and fruit quality and yield. GWSS population density was monitored weekly by a combination of visual inspection, beat net sampling, and trapping. Movement of GWSS among treatment plots was quantified through a mark and capture technique using protein markers (soy milk, whole milk, and egg white) and yellow sticky traps. GWSS populations were negatively affected by severe plant water stress; however, population density was not linearly related to decreasing water availability in plants. Citrus trees irrigated at 60% ETc had significantly warmer leaves, lower xylem water potential, and consequently hosted fewer GWSS eggs, nymphs, and adults than trees irrigated at 80% ETc. Citrus trees irrigated at 100% ETc hosted similar numbers of GWSS as trees irrigated at 60 and 80% ETc. Although the adult GWSS population was reduced, on average, by 50% in trees under severe water stress, the total number of fruit and number of fruit across several fruit grade categories were significantly lower in the 60% ETc than in the 80 and 100% ETc irrigation treatments. Spatiotemporal distribution and movement H. vitripennis in the orchard will be discussed with emphasis on the development of strategies to focus control efforts, enhance the efficacy of biological control, and effectively limit the spread of Xylella fastidiosa induced diseases to susceptible crops. |
