By now, most post-emergence and/or layby herbicides have been applied and cotton is beginning to lap the middles. Later planted fields may still have time for layby applications depending on planting date and plant size. This generally marks the end of effective weed control measures for the current season, however this also marks the beginning of weed management for next year in our holistic approach to reducing the seedbank of Palmer amaranth (pigweed).
Hopefully, growers employed an aggressive burndown and pre-emergence residual herbicide program to minimize hand-weeding costs, but it is utterly CRITICAL that all surviving Palmer amaranth be physically removed soon.
We have to think long-term with Palmer amaranth. If we are going to sustain cotton production, we must reduce the Palmer amaranth seedbank. As we all know by now, a single female Palmer amaranth plant can produce anywhere between 300,000 seed in dry conditions to nearly 1,000,000 seed in well-watered environments. With that kind of seed production, we are going backwards anytime we allow a few plants to go to seed.
We may have spent a lot of money and obtained good control to this point in the year, but a few escapes can undo the progress we have made.
By this point in the year, we are finished with herbicide applications; we don’t have suitable “salvage” treatments. Our only option to remove escaped Palmer now is hand-removal. A key consideration is removing the weeds before they produce seed.
Well, it is just July, and surely they haven’t produced seed yet, right? Wrong! Within a week after the female seedhead emerges, viable seed are present. The longer the plant grows, the greater the number of seed produced. But, some viable seed are there within a week of head emergence. And there are plenty of emerged heads out there right now.
Below are a few key points to consider when hand-weeding:
- Hand-weeding should be done before viable seed are produced (i.e. before seedhead emergence or as soon as possible thereafter) and continued for several weeks if new flushes emerge or if any weeds are missed the first time through.
- Palmer amaranth has the capacity to develop a very robust root system making large plants difficult to remove. Therefore, hand-weeding is much easier to do before plants become too large.
- Chopping off only the above-ground portions may expose some stalk tissue near the soil surface to sunlight. It has been often observed that this tissue can produce suckers and survive. Therefore, it is important to remove the entire plant (roots included). This is generally much easier to do following a rain.
- Removal of weeds from the field may be necessary if seed production is well under way.
- Removing weeds along ditch-banks or field edges may be as important as removing weeds in the crop. Do not neglect weeds present on field edges.
- Palmer amaranth possesses strong survival characteristics. Even if roots are removed, simply laying removed plants on the ground can allow the plants to re-root and survive, especially if rain occurs within a day or two following hand-weeding. Therefore, effective hand-weeding requires removal of the entire plant (including roots), shaking off any soil from the roots, and turning the plants upside down so that roots do not contact the soil.