Improve Your Odds Against Palmer Amaranth
Palmer amaranth is a troublesome weed. With its rapid growth rate and enormous capacity to produce seed, this weed can go from limited to a severe infestation in one or two seasons.
Several herbicides have activity on Palmer amaranth, but season-long control is tricky.
Effectiveness Of Herbicides On Palmer Amaranth
Cadre is highly effective, but every year brings new reports of Palmer amaranth resistance to Cadre. Without Cadre, producers will need to rely on pre-emergence herbicides, such as Valor and Dual Magnum, or early postemergence contact herbicides, such as Cobra or Ultra Blazer.
Although Cobra and Ultra Blazer are effective options, these herbicides must be applied to Palmer amaranth that is approximately two inches in height for reliable control and have no residual activity.
Prowl H2O and Solicam are least effective on Palmer amaranth with control ranging between just a few days and approximately one week. Dual Magnum may provide control for three to four weeks, while Valor has been shown to provide control for up to two months.
Factors To Improve Pre-Emergence Herbicide Applications:
Incorporation. Pre-emergence herbicides require incorporation into the soil to become activated. Incorporation can be conducted with light tillage, rainfall or irrigation.
Timing. Herbicides that are not incorporated will either turn to a gas and dissipate or be degraded by sunlight. The “yellow herbicides,” like Sonalan, require incorporation as soon as possible, while products like Dual Magnum can persist for five to 10 days.
Depth. Herbicides should be incorporated as shallow as possible. Most weeds, particularly grasses and pigweeds, germinate within the top one-fourth of an inch of soil. Therefore, it is important to concentrate the herbicide in that shallow zone to maximize weed control.
Equipment. If mechanically incorporating, it is best to use a field cultivator. This ensures good mixing and generally will not move the herbicide too deep into the soil. Conversely, a disc harrow commonly slices the herbicide deep into the soil in a streaked pattern, which distributes the herbicide too deep into the soil and fails to achieve good mixing.
Rain or Irrigation. If rainfall is not predicted, irrigating with one-half inch of water will consistently and effectively incorporate the herbicide.