General Information
Good weed control is important in cotton production. Weed management systems should prevent weed interference, be economical and sustainable, reduce weed seed bank in soil, prevent weed resistance and neither injure cotton, reduce quality, or lint yield. Weeds compete with cotton for moisture, nutrients, and sunlight. Weeds can reduce lint quality due to additional trash and staining of fibers leading to low grades and discounted prices. To be successful, weed management systems require advance planning and timely execution. Any delay in an application may mean reduced control, higher herbicide use rates, and greater herbicide costs.
A successful weed management plan will use multiple methods to keep weed populations low. Tillage and seedbed preparation should eliminate all emerged weeds prior to planting. Components of a weed management plan can include many of the following: 1) Early preplant burndown which may contain a herbicide with residual activity; 2) Burndown application at planting which may include a residual herbicide; 3) Post-emergence applications with or without a residual herbicide; 4) Post directed herbicides which may include a residual herbicide; 5) Layby herbicides; 6) Pre-harvest applications or defoliant and desiccant applications. The use of mechanical cultivation with rotary hoes, rolling cultivators, or sweeps may reduce the need for a herbicide application early in the growing season. Use of specific herbicides depends on the weed spectrum of your field, economic considerations and application system. Consider your situation and tailor a weed control program to your needs. The following sections will guide you in the decision making process.
No-till or Reduced tillage Special care should be taken to apply timely preplant and/or burndown herbicides to provide a weed free seedbed at planting. Concern about glyphosate resistant horseweed will necessitate the addition of other herbicides to the glyphosate tank (see glyphosate resistance management section). When cotton is grown without tillage consider applying Prowl (pendimethalin) pre-emergence and water in if irrigation is available and rainfall is not expected within 5 days. If irrigation is not available consider applying Sequence (glyphosate + S-metolachlor) early post-emergence to provide residual annual grass control.
Glyphosate Resistance Management The development of glyphosate resistant weeds has ended an era of glyphosate only weed control in many cotton-growing regions. It is better to be proactive and implement measures to avoid weed resistance to glyphosate. Some suggestions for avoiding glyphosate resistance are as follows: 1) Use multiple herbicide chemistries each year. Do not rely on glyphosate as your sole means of weed control, 2) consider growing the Liberty Link variety and use glufosinate, 3) add other herbicides to your glyphosate tank, 4) use a soil residual herbicide at planting, 5) rotate to a different crop where other weed control options are available.
