By Darren Hefty
Alfalfa weevil larvae were so thick in many fields this spring that growers were forced to spray for bugs before the first cutting came off. Other growers chose to accept the loss since harvest was right around the corner and wait until in between cuttings to deal with the problem. This is often the question in alfalfa. Since the field is going to be harvested multiple times during the season, when is the best time to make applications of fertilizer or crop protection products? Since it’s impossible to be timely for everyone who may be reading this alfalfa article, I’ll focus on the “between cutting” applications. Here’s a brief list of what you could do between cuttings (or shortly thereafter) to help your alfalfa crop.
Take a soil sample each year in alfalfa production. Proper fertilization can increase tonnage and longevity of your stand. It can also improve the speed of re-growth between cuttings, which helps with weed control. Nutrient deficiencies in alfalfa (and other crops) weaken the plant, allowing disease to come in. Excessively high rates of fertilizer will not provide a short-term economic benefit, so it’s important to apply fertilizer using a balanced approach. Phosphorus and Sulfur have been the most common nutrient deficiencies we’ve seen in alfalfa. Liming is another thing you need to consider as the ideal soil pH for alfalfa production is 6.5 or higher. Soil pH levels down in the 5’s take away nearly all of your yield potential, and we find many alfalfa fields (or at least areas of fields) testing below 6.0 pH. Also keep in mind that per ton of hay, alfalfa removes approximately 60 pounds of K2O potassium, 15 pounds of phosphate, 5 pounds of sulfur, and a small amount of zinc, boron, and other nutrients. Again, that’s per ton of hay!
Insecticides for alfalfa often have between 7 and 21 days they must be on before harvest. Between cuttings is a great time for insecticide applications to eliminate the bugs that can slow re-growth and limit your yield. 1 pint of Lorsban is highly effective on nearly all insect pests of alfalfa. If you’re tankmixing other things like weed control or fertilizer with an insecticide application we’d recommend a pyrethroid like Silencer at 3.2 – 3.84 ounces per acre rather than Lorsban to avoid potential leaf burn from the combination of products. Pyrethroids will typically give a little longer residual control, as well.
Shortly after cuttings can be an excellent time to apply herbicides. Make sure there is adequate re-growth of the weeds so they take in the herbicide and move it to the growing points. There aren’t many choices for broadleaf weed control. Pursuit or Raptor offer the most broad-spectrum control of broadleaf weeds. Buctril is a better choice for lambsquarters and wild buckwheat control. Annual grass control is a little easier with many inexpensive and highly effective herbicides including Select Max. If fields are weedy, especially with tough weeds like quackgrass and dandelions, it’s time to take the alfalfa out and plant a different crop.
Farmers who have been applying fungicides, like Headline at 6 ounces per acre, have seen decent gains in tonnage and quality by improving disease control/prevention in alfalfa. Depending on where your farm is and the amount of disease pressure, you may use fungicides once or twice on each cutting. Some of the best gains have come from keeping the lower leaves healthy and attached to the stem. For that reason, growers have targeted their applications when the alfalfa has about 6 to 8 inches of re-growth.