No-Till: Making It Work - Weed Control

Table of Contents

1. Weed Control Strategies
2. Available in Published Version of No-till

One of the biggest obstacles to the adoption of no-till is the perception that you grow weeds - not crops. Weeds aren't necessarily worse or more difficult, but the situation is different.

Understanding change in the soil seed bank, weed spectrum, and weed control practices is the key to effective weed control in a no-till system.

The no-till seedbed and weed bank differ from the conventional situation in these ways:

• weed seeds stay on or near the surface where they are subject to predation, extreme cold, desiccation and decomposition
• over time and with management, the number of annual weed seeds in the germination zone is reduced
• the minimal soil disturbance favours the local spreading of deep-rooted perennials and winter annuals, making them easier to control.

Weeds are different in no-till. Generally, the weed spectrum will change in these ways:

• in the first year of no-till, annuals and perennials can be a problem
• in Year 2, the number of annual weed seeds is reduced by natural and cultural means
• in Year 3, the perennials, biennials and winter annuals peak. But with burndown control, their numbers are also reduced.

Weed Control Strategies

In no-till you lose two tools: the use of tillage and pre-plant incorporated herbicides. However, you are not spreading weeds with tillage.

Other weed management tools remain, but the strategy changes.

Preventative Measures

Use weed-free seed sources. Well-cleaned or certified seed is best. Control weed sources at field perimeters, but be careful not to kill sod borders or wildlife habitat in fencerows.

Scout fields and keep records: help prevent local problems from spreading.

Cultural Methods

Rotate crops - changing crops each year will prevent many weeds from getting established, provide more competition, and allow herbicide rotation.

Manage residue - even distribution of residues at harvest will create an even cover over the field, reducing weed seedling establishment.

Plant cover crops - cover crops that are planted or grow (i.e., red clover) after harvest will crowd out weeds.

Mechanical Methods

Cultivation - inter-row cultivation can be combined with sidedress nitrogen applications and chemical controls.

Chemical Methods

Pre- and post-emergence are still useful herbicide application techniques in no-till systems. Residual pre-emergence herbicides can be combined with burndown herbicides. Post-emergence treatments can target the weeds that are present. Refer to OMAFRA Publication 75 and the label for proper timing of post-emergent herbicides. Remember: in no-till, almost all herbicide is applied post-emergent for some weeds, regardless of the crop stage.

Burndowns are the single most important chemical control method. They can be applied to emerged weeds before, during or after planting.

Problem Weed Control in No-Till

Sample only - actual chart depicts over 20 common weed species.

Dandelion (Perennial)

Weed Germinating From Seed

Key characteristic is:

• reproduces only by seed

To control in corn:

• Marksman
• Atrazine

To control in soybeans:

• Sencor, Lexone
• Afolan, Linuron, Lorox
• Pursuit.

Figure 1. Dandelion germinating from seed.

Farmer experience says that Roundup + Pursuit or Roundup followed by a post application of Pursuit + Basagran is effective.

Emerged Seedlings to Mature Plants

Key characteristics are:

• bright yellow flowers
• white seed heads

To control in corn:

• Kil-Mor
• Ultim
• Marksman
• Roundup, Touchdown, Amitrol-T (burndown late fall or before crop emergence in spring)

To control in soybeans:

• Amitrol-T (burndown or post-harvest)
• Roundup (burndown late fall or before crop emergence in spring, post-harvest or pre-harvest)
• Touchdown (burndown in fall, or before planting or post-harvest)

To control in wheat:

• Amitrol-T (burndown before planting or post-harvest)
• Roundup (burndown before crop emergence, pre- or post-harvest)
• Touchdown (burndown before planting or post-harvest)
• Kil-Mor (spring-suppression)
• Spring (suppression) - Caliber, Cobutox, Embutox, Tropotox Plus
• 2,4-D (spring-suppression or post-harvest)

Fall applications are generally more reliable than spring applications. The control of this weed in the spring is dependent on a burndown followed by a residual herbicide that has some activity on the weed.

Prickly Lettuce (Annual, Winter Annual or Biennial)

Weed Germinating From Seed

Key characteristics are:

• reproduces from seed only
• variable-shaped leaves have deep lobes that curve backwards and have spiny midribs

To control in corn:

• choose from many soil-active pre-emergence broadleaf herbicides

To control in soybeans:

• choose from many soil-active pre-emergence broadleaf herbicides

Note: A large percentage of the population is naturally resistant to Pursuit.

Emerged Seedlings to Mature Plants

Key characteristics are:

• stems are erect and tall 1.5 m (5')
• fine tufty yellow flowers from June to late fall

To control in corn:

• Roundup (burndown before crop emergence)
• Touchdown (burndown before planting)
• Marksman (post)
• post - Atrazine, Laddock
• post - 2,4-D, Banvel, Kil-Mor

To control in soybeans:

• Roundup (burndown before crop emergence)
• Touchdown (burndown before planting)
• Blazer + Basagran (post)
  

Available in Published Version of No-till

• Weed Control Strategies
  • Principles and Advantages of Burndown Treatments
  • Perennial Weed Control
• Problem Weed Control in No-till - sample only provided here
• Tips
  • Crop Competition
  • Residue Management & Weed Control
  • Crop Rotation & Weed Control
  • Nutrient Management & Weed Control
  • Mechanical Control
  • Chemical Control
  • Sprayer Adjustments
  • Row-crop Cultivators