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Protect and Enhance the Nation's Natural Resource Base and Environment Reducing Weeds in Lemon Orchards with Less Herbicide Issue Weeds covering an orchard floor compete with the trees for water and nutrients, reducing the number and size of fruit at harvest. Growers at different times have tried mowing, disking and cover crops for weed control, but mowing causes a weed shift to grass and nutsedge species that are difficult to control. Disking can prune roots and damage tree branches and trunks, and although leguminious cover crops suppress weeds they also compete with trees for water and may reduce yields. Growers currently either broadcast spray post-emergence herbicides on the entire orchard floor–regardless of where weed patches are located–or spot spray weed patches where they exist and thereby reduce the amount of chemical used to control weeds. Broadcast spraying the orchard floor wastes chemical and increases the herbicide load in the environment. Spot spraying reduces the amount of herbicide wasted but is labor-intensive, slow and costs more than broadcast spraying herbicides despite reducing the amount of herbicide sprayed. What has been done? A comprehensive series of weed-control studies in lemons, conducted by faculty in the University of Arizona College of Agriculture and Life Sciences since 1993, have proven that clean culture, where the orchard floor is kept completely free of weeds using herbicides, still provides the best environment for lemon growth and maximizes yield, both for the first harvest and for the cumulative yield of all harvests in a season. An optical chlorophyll-detecting spray system currently on the market detects weeds on the orchard floor, triggering spot applications of herbicide directly to them, and skips spraying on bare ground. Called the NTech WeedSeeker, this boom-mounted system is used on commercial orchards in California, where it was developed, but it has not caught on in Arizona. By spraying only the weeds, herbicide use in one study was reduced by 60 percent where there was a 20 percent weed cover in the orchard..UA researchers have tested the sprayer in commercial lemon orchards in Yuma and Hyder, Arizona. Impact Study results show that conventional broadcast sprayers and the NTech WeedSeeker automatic spot sprayer system result in comparable weed control in lemon orchards, with both types of systems providing good or commercially acceptable weed control. The NTech Weedseeker spray system reduced the amount of herbicide used 88 percent in an orchard irrigated with microsprinklers, and 56 percent in a flood-irrigated orchard. Assuming a $5 per acre postemergence herbicide cost, this weed control spray system would result in savings for citrus growers amounting to $4.40 per acre per application (there are 8 to 10 applications a year) for microsprinkler irrigated orchards, and $2.80 per acre per application for flood-irrigated orchards. Costs saving increase as the cost of the herbicide increases and there are additional savings due to reductions in the amount of time workers spend mixing and loading herbicide sprayers. Funding Arizona Citrus Research Council Yuma Mesa Pest Abatement District Arizona Department of Agriculture–specialty crop grant program Contact William B. McCloskey, associate specialist Department of Plant Sciences The University of Arizona PO Box 210036 Tucson, AZ 85721-0036 (520) 621-7613 office (520) 621-7186 Email: wmcclosk@ag.arizona.edu Return
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