Glyphosate (Roundup UltraMax, Touchdown, and other generic formulations) is widely used for postemergence weed control in peach orchards. It's broadspectrum, non-selective, economic control makes it an attractive herbicide. Like with any good tool, misuse can be harmful. Improper use or application inconsistent with label directions can cause severe peach tree injury or death. If you use glyphosate in your peach orchard there are five "sins" you should not commit.
1. Applying glyphosate under trees with low hanging limbs and suckers
Low hanging limbs and suckers increase the potential for glyphosate contact with the tree. They are usually in the application area for the herbicide boom or nozzles. At least 10 days prior to glyphosate use, low hanging limbs and suckers need to be removed.
2. Failing to use hooded spray booms
Hooded or shielded spray booms minimize the likelihood glyphosate contact with trees. They also minimize drift potential.
3. Glyphosate application more than 90 days after bloom
Peach trees are sensitive to glyphosate, however the degree of sensitivity varies with the time of year. Peach trees are least likely to be injured when dormant. Once bud swell occurs and trees leaf out injury potential increases. Peach trees, like woody perennial weeds, are most sensitive to glyphosate in mid summer through fall. The label does not allow glyphosate use more than 90 days past bloom because of increasing sensitivity in mid-summer and fall. Peach tree exposure to traces of glyphosate in mid summer through early fall will cause severe damage and probably tree death. One concern during mid-summer is the potential for off-target glyphosate movement into orchards from adjacent fields planted in glyphosate tolerant crops like "Roundup Ready" soybeans and cotton.
4. Spray solution contact with tree
Every effort should be made to apply glyphosate precisely on target weeds. Using spray tips that produce large droplets, operating spray boom at minimum height, using low spray pressure are several ways growers can reduce the potential for off target movement and contact with trees.
5. Using glyphosate in orchards established less than 2 years
Glyphosate can be applied in orchards established 2 years. Therefore orchards must be in their third leaf. Young trees (1st an 2nd leaf trees) are at greater risk of injury and that use is not registered.