Getting Out of Alfalfa With Herbicides

Many producers are using forages in their crop rotations to improve nitrogen levels in the soil, as a method of weed control, and to improve soil tilth and percolation. The most commonly used forage is alfalfa, although alfalfa/grass mixtures are also used. Alfalfa provides an alternative source of income while protecting the land from soil erosion.

Normally, alfalfa is left in the crop rotation for three to five years before being removed. Currently, tillage is the most common method of removing forages from the rotation. About 30 percent of farmers use a combination of herbicides and tillage.

Removing Alfalfa with Tillage can Create Problems

Tillage is expensive. As many as six tillage passes may be required to effectively remove the alfalfa and leave the field in good condition for seeding the new crop. This requires large amounts of energy and operator time. Costs for removing alfalfa by tillage can range from $20 to $30 per acre.

It eliminates many of the benefits of including forage in the rotation in the first place. Tillage brings dormant weed seeds to the soil surface, giving them a new lease on life. Cultivation also destroys soil aggregation.

Tillage exposes the soil to the elements by burying surface mulch, allowing the soil to dry and creating the possibility of erosion. It also reduces the snow-catching benefits of trash.

Tillage increases the risk of nitrate leaching. Nitrogen released from forage residue may leach below the root zone, making it unavailable for most annual crops.

Four Reasons to Choose Herbicides Over Tillage

1. Soil and water conservation
   Tillage exposes the soil to erosion and allows moisture to escape.
2. Quackgrass control
   Quackgrass is often present when the time comes to remove alfalfa from the rotation. Tillage will eliminate the opportunity for effective treatment with Roundup. In fact, tillage may also encourage the spread of quackgrass.
3. Spring seedbed
   Tillage leaves alfalfa crown carcasses scattered throughout the field. These can result in poor seed placement because of equipment plugging and a rough surface. A no-till seedbed is also more firm, allowing for better seed-to-soil contact.
4. Annual weed control
   Populations of annual weeds such as green foxtail and wild mustard decline in fields that have been in forages for a time. Cultivation will disturb dormant weed seeds, encouraging a flush of annual weeds in the spring.

It's A Fact

If an alfalfa field must be leveled because of pocket gopher damage, a combination of tillage and herbicides will be necessary. In this case, consult with your local forage specialist for herbicide use recommendations.

Alfalfa Removal with Herbicides - Effectiveness & Costs  

Points to Consider

Here are some areas that will affect the manner in which you approach the operation. Give some thought to:

• What weeds you will have to control. Quackgrass by itself can be managed with Roundup. But, if there are other weeds present, such as thistles and dandelions, Banvel may be needed as well.
• What crop will follow alfalfa in the rotation? Banvel and Lontrel leave soil residues that may be harmful to some crops. Always consult product labels for recropping and other information.
• Alfalfa land is often drier, so be prepared to seed early in the spring to take advantage of available moisture from the snow melt.
• As with most treatments, some alfalfa regrowth will likely occur in early summer. Be prepared for an in-crop broadleaf treatment.

General Recommendations

• The best time to spray is after the second cut once plants have begun to grow again. Best results are achieved after the plants have reached eight inches high and are actively growing. September spraying is not too late provided there is adequate time for the product to move down into the plant roots prior to a killing frost (one to two weeks).
• In drier areas of the province, or during dry years when regrowth after the second cut is likely to be inadequate, consider spraying after the first cut. However, regrowth may still occur before fall and cultivation will be necessary.
• Roundup/Banvel mixes generally provide the best results, if there is a mixture of grasses and broadleaf weeds.
• When using Roundup alone, don't drop it below the 1L/acre application rate. If there is a lot of quackgrass present, consult the Manitoba Agriculture Guide to Crop Protection for control recommendations.
• Sow the field early. Alfalfa land is drier than other cropland. If possible, use a seeder that minimizes soil disturbance. Less disturbance means fewer annual weed problems.
• Using a zero till drill is the preferred method of seeding. But, if soil moisture conditions are favourable, lighter seeding equipment can also produce good results.