Brush and tree control helps prevent pivot irrigator damage
Early autumn is an excellent time to control brush and trees that may interfere with center pivot irrigation.
One of the greatest potential economic losses from center pivot irrigation comes from trees collapsing or rolling the spans. When irrigation equipment is installed near field edges, tree lines are usually trimmed back so they do not interfere with the equipment. Tree limbs as small as 2 inches in diameter can cause a pivot tower to flip or tear off the pivot end boom if branches catch the span V bracing or end gun. Tree branches can also act like a chain anchored to the ground and cause the pivot span to roll causing the structure to collapse.
Herbicides used for brush control have excellent activity on brush and small tree species if applied in the last few days of summer and early fall. Hand sprayers or tractor/ATV mounted sprayers with gun applicators can be used to spray the foliage. Wetting most of the foliage to almost the point of runoff is necessary for most situations.
Brush and tree control herbicides are more effective in early fall as the plants translocate the pesticide to the roots better than in spring. Spray additives are important especially in trees and brush with a waxy or oily leaf cover. If producers make applications in early in September, a follow-up application two to three weeks later can be beneficial in areas where full coverage wasn't achieved and is obvious by leaf color. Foliage sprays need to be used at least few day prior to frost and before significant leaf yellowing.
Trees that are more than 5 inches in diameter at the trunk or at heights above where the sprayer can reach will require cutting or girdling to the trunk to allow for a cut-stump treatment herbicide to be applied to alleviate regrowth. Regrowth is especially a challenge with young wild cherry and mulberry trees.
There are also several dry herbicide products that are designed to be applied around the base of the brush or tree for control. An excellent set of references for woody brush control is available from Ohio State University. These bulletin contains information on additives that are necessary, safety precautions and a comparison chart for products and species coverage effectiveness http://ohioline.osu.edu/for-fact/0051.html http://ohioline.osu.edu/for-fact/0045s.html
Fall is the best season for chemical brush control and is far less expensive than cutting or excavating problem areas. The important thing is to control brush and trees that are growing in the pivots travel area since it is far less expensive to manage these obstacles than to repair a crashed pivot.