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Enhancing extension recommendations to maximize efficacy of spray programs for the Georgia DOT : final report.
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2015-12-23
[PDF-2.19 MB]
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Edition:Final report
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Abstract:Research was conducted to evaluate equipment, adjuvants, and water quality used by the
Georgia DOT on herbicide efficacy for roadside management. From 19 DOT stations, 68% had alkaline
(7.1 to 7.9) water, 32% had hard water (>120 ppm), and 10% had a concentration of more than 5 ppm of
suspended solids. Johnsongrass control was reduced from 50 to 75% when glyphosate was sprayed in water
containing various levels of calcium, magnesium, and iron, compared to soft water. Weed control from
Accord (glyphosate) and Garlon (triclopyr) was reduced by about half when applied with hard water, but
control from Milestone (aminopyralid) in one experiment was similar to treatments made in soft water.
The efficacy of the standard DOT drift retardant adjuvant, Ground Zero, did not reduce the efficacy of
glyphosate in bioassay experiments. The DOT trucks equipped with Boombuster nozzles and Northstar
sprayers delivered the targeted calibration volumes. However, applications showed substantial differences
in uniformity from visual, volumetric, and whole plant bioassays. From incremental distances from the
truck, the total spray volume varied from about 80 to 120% of the targeted application rate. Trucks
equipped with Boombuster and Northstar sprayers controlled broomsedge and vaseygrass 89% or greater
for plants placed from 0 to 20 feet from the truck. However, control ranged 56 to 69% for plants spaced at
25 and 30 feet from trucks, suggesting the DOT sprayers provide insufficient coverage beyond 20 feet. It is
recommend that the DOT sample water several times throughout the year at stations with reported issues in
this research. If fresh water sources cannot be used for applications, it is recommended that ammonium
sulfate, EDTA, or other amendments be used with water sources containing alkaline pH or hardness levels
greater than 100 PPM. Selecting herbicides that have less potential for antagonism is recommend for
controlling broadleaf weeds over 2,4-D, glyphosate, or triclopyr when water quality is compromised. It is
recommended that the DOT request inspections from the manufacturers of the sprayer equipment to
improve consistencies of applications or use alternative sprayers for roadside management.
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