Eradicating Alfalfa For Direct Seeding

By Garry Mayerle, P.Ag.

SSCA Conservation Agrologist

In the early 70's, northeastern Saskatchewan grain producers who were looking for alternatives to growing wheat started a dehydrated alfalfa industry. Although it is facing "hard times" right now, it has occupied a substantial land base (150,000 acres). One of the most costly aspects of growing alfalfa is getting the land back into annual crop production. With the introduction of direct seeding practices, producers are becoming more interested in taking the alfalfa out of production with less or no tillage.

Lyle Cowell, an agronomist with Sask. Wheat Pool out of Tisdale, initiated a demonstration project to evaluate the ability of various herbicides to take out alfalfa and the common weeds that often get started in alfalfa fields. There have been several projects conducted during the 90's which rated alfalfa control with a number of these products. Lyle used several herbicides that had not been on the market in these previous projects. However, the most unique aspect of Lyle's project was that he set up the demonstration to visually compare alfalfa and dandelion control with these products at three different times during the growing season.

Lyle set up the project in 2 different alfalfa fields close to Star City. One of the sites was heavily infested with dandelions and the other with a fair amount of quack grass. The products that he sprayed are listed in Table 1. He sprayed each of these products May 28, 2000 at the two sites with a plot sprayer at a water vol. of 10 gal/ac. These same treatments were applied again on July 19 and Sept. 28 on adjacent plots.

TABLE 1 - Control Rating of Various Herbicides to Eradicate Alfalfa Stand - Lyle Cowell SWP agronomist

In summary these plots visually showed that the best time to spray out alfalfa for crop production the following year was late in Sept. Many perennial plants need several "kicks" before they can be eradicated. Alfalfa and dandelions are not exceptions. The treatments that were sprayed earlier in the season had varying degrees of control but given time, some of the alfalfa plants and perennial weeds did recover. To successfully produce an annual crop the following year, another "kick" would have to be supplied to continue the eradication process. For the treatments sprayed later in the fall, that "kick" could come with a burn-off and or during the in-crop herbicide application. It would be quite important to plan the rotation so that the in-crop herbicide would provide this good "kick" at the alfalfa and perennial weeds. Final control could be achieved with pre-harvest Round-up.

One of the benefits of a later spraying in dehy alfalfa is that you do get the revenue from 2 cuts of alfalfa. However, dehy alfalfa does deplete soil moisture reserves. To produce a decent yield on alfalfa "breaking", you need good growing season moisture. Taking out the alfalfa earlier may help to build up that reserve of soil moisture. A good compromise may be to pre-harvest the second cut of alfalfa with 1.0 -2.0 L/ac Round-up. This starts to build up moisture reserves shortly after spraying. Also, many alfalfa fields have a lot of quack grass to get rid of. Using this pre-harvest method should go a long ways to reducing quack grass. When the alfalfa and weeds re-grow, you will probably need to take another "kick" at them. An application of 2,4-D ester might be a very economical choice. Of course, one of the difficulties of using this method is getting the dehy plant to approve the pre-harvest. Usually the difficulty for the dehy company is coordinating cutting times to be there on the right day after pre-harvesting. Leaf browning and drop can happen quickly with hot summer days and cutting should probably take place the 3^rd day after the pre-harvest application. Some producers have overcome this hurdle by making an agreement with the dehy company that they will cut and bale the pre-harvested field themselves and it will be processed as a sun cured product. That way the producer can be more responsive to cutting times depending on how the weather is affecting the pre-harvested alfalfa.

Roy Button, a former Soils and Crops Specialist with Sask Ag and Food, did some alfalfa take out trials in the early 90's and found that frost could really affect herbicide control of alfalfa. Before Lyle Cowell sprayed the Sept. 28 replicate, there had been about 4° of frost. He suggests that especially with alfalfa, you would want less than 5° of frost. The latest date you should think about doing the spraying is the end of Sept. You will want at least 6 inches of regrowth to get good uptake of the herbicide. Spraying it later in the fall like this seems to take some advantage of our harsh winters to kill some of the alfalfa and dandelions.

Another issue to be aware of is the herbicide residue left by higher applications of some of these products. Lyle found evidence of herbicide residue after winter in the Amitrol, 2-4,D, and Curtail M treatments. These residues can usually be handled if you keep the right crops in rotation.

Wheat has been sown into one of Lyle's sites. The project will continue with final control ratings and wheat yields taken in 2001. Feel free to call early next winter for these final numbers.