Palmer Amaranth Control
A comparison of pre-emergence control options.
University of Florida’s Institute of Food and Agricultural Sciences
Several herbicides have activity on Palmer amaranth, but season-long control can still be tricky. The millions of seeds produced will germinate throughout the entire growing season. It has been observed that, “a new flush of seedlings will come after every rainfall.”
Effectiveness Of Pre-Emergence Herbicides
The herbicides listed below (Table 1) were all applied the day after peanut planting. After the applications were made, we visited the treated areas weekly and counted how many weeds were present in each plot. We considered that each herbicide had lost its effectiveness when the Palmer amaranth population reached one plant per three feet of peanut row. This threshold was set because that is when we considered that a post-emergence herbicide application would be necessary.
Control Can Vary Greatly
We also found that the rye cover crop at this
Prowl H2O is highly effective on annual grasses,
For all pre-emergence herbicides, it is important to remember that rainfall or irrigation within seven to 10 days after application is essential to activate the herbicide. We had excellent incorporation at this location, but prolonged drought will likely result in each of these products failing to control Palmer amaranth.
Research funded by the Southern Peanut Research Initiative.
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.