By Guy Collins
Management of glyphosate resistance is still one of the greatest challenges in modern cotton production. Weed management can often be expensive and cumbersome. However it is important to note that even when prices are relatively low, there are no corners that can be cut when it comes to managing weeds. See the links below for some of the best performing management strategies in combating glyphosate-resistant pigweed in reduced-tillage systems.
Glyphosate-based Weed Management Programs
Liberty-based Weed Management Programs
These are very general programs that can be, or may need to be, adjusted or modified to address growers’ needs or to adhere to label requirements. See the 2015 Cotton Information Book for additional and complete weed control information. Contact your local county extension agent for a hard copy of this publication. An electronic version can be found on this cotton portal. Copy and paste the following link into your browser: http://content.ces.ncsu.edu/cotton-information/
Growers should consider the following before utilizing these programs:
- Observe label restrictions for all products including restrictions on rates, soil texture, application methods, tankmixing with other products, plant-back restrictions, rotational restrictions, season-long use rates, etc. Note: the grower is liable for any crop injury resulting from applications of Liberty to Widestrike cotton.
- Product selection should be based on other weed species in the system or compatibility with other herbicides, efficacy, rotational restrictions etc. In some cases, other herbicides not listed in the programs above can be added to the system, or can replace some herbicides in the system, in order to address the entire weed spectrum.
- Adjust rates for weed size, soil type, growth stage, etc.
- In some cases, there are generic products available that could be as effective as name brands. If using generics, adjusting rates for equivalency may be necessary for some herbicides. Observe label requirements for each individual product.
Regardless of the weed management program used, the same basic principles apply in order to sustainably achieve the best control possible. These principles include the following:
- Start clean (Use pre-plant residuals and control/eliminate emerged weeds prior to or at planting). If emerged weeds are not controlled properly before planting, rest-assured that the rest of the season will also be challenging.
- Plant cotton into warm soils with appropriate moisture (when weather forecasts following planting are likely to promote rapid emergence, seedling growth and vigor) to avoid or minimize the likelihood of herbicide injury.
- Aggressive use of residuals is essential to managing weeds in modern times. Prevention of pigweed emergence is always the best approach.
- Rotate chemistries and use tank mixes with more than one mode of action. This is one critical way we can combat the development of resistance to additional chemistries.
- Target small weeds with post emergence applications of all herbicides using appropriate rates, application volumes (> 15 GPA), and appropriate application time of day for some post-emergence herbicides (1 hour after sunrise to 1 hour before sunset). For pigweed, “small” is defined as “the largest weeds in the field are less than 3 inches tall”. Keep in mind that pigweed can grow at a rate of one inch per day if conditions are right. Applications of Liberty made to larger weeds is NOT a sustainable approach and we badly need to protect this herbicide for the long-term!!
- Timeliness of post emergence applications will allow for best control possible. Growers are farming more acres, and over a larger area than ever before. Frequent and heavy rains, along with equipment or labor limitations can often present challenges to timeliness. Regardless, timely sequential applications allow for targeting small weeds and for overlapping residuals (to avoid “opening windows” through which pigweed can emerge).
- Handweed surviving weeds. Handweeding is truthfully weed control for the following season. Although no one wants to have to handweed, it is essential in combating glyphosate resistance and effectively reducing the seedbank for the long-term. If appropriate early season programs are utilized (i.e. residuals, timely post applications, etc), then handweeding should be noticeably less expensive. This process should begin in early to mid July, before pigweed seed reach maturity.
Source:ncsu.edu