Establishing Alfalfa and Weed Management

Mr. Jeff Stachler, Extension Agriculture Educator, Auglaize County, The Ohio State University Extension

Due to excessive rainfall in 2015, many alfalfa stands went downhill and were destroyed or will be destroyed this spring.  Now, new seedings need to be established.  Have you thought about what needs to be done to successfully establish alfalfa?

The first task is to obtain a soil sample or samples. If the field is less than 15 acres, then a single soil sample will suffice. If the field is larger than 15 acres, take multiple samples based upon management zones or based upon a grid pattern.  Management zones can be based upon soil type, topography, soil organic matter, or a combination of these. If a field has been in no-till and the field will remain untilled, obtain two soil samples per field, zone, or grid, one at a 4” depth for pH and another at an 8” depth for fertilizer recommendations.

For good establishment of alfalfa, soil pH needs to be 6.8 for mineral soils having subsoil pH less than 6.0 and 6.5 for mineral soils having subsoil pH greater than 6.0.  Bray P1 soil test phosphorus (P) concentrations should be between 25 and 50 ppm. The Mehlich III soil test P concentrations should be between 40 and 79 ppm.

The recommended rate of potash is based upon the soil test level in ppm, the cation exchange capacity, and yield goal.  If lime is required and the Bray P1 soil test value for phosphorus is below 25 ppm, delay planting until the fall or next spring as stand establishment will likely be poor.  Fertilizer and lime should be incorporated to maximize efficiency. If you are surface applying lime and fertilizer, it is even more important to wait a year before establishing alfalfa. 

Select varieties having the best disease resistance (the best way to fight diseases), good forage quality, best fit to soil types, and high yields. Have seed inoculated with nitrogen-fixing bacteria and treated with fungicides to manage seedling diseases, especially when planting in the spring. 

Prepare a proper seedbed. A smooth firm seedbed allows for good soil to seed contact, leading to improved establishment. Control all weeds prior to establishment.  Control perennial weeds the year before establishment.  For no-tillage seedings, control grass sod with glyphosate at least one month in advance of seeding and manage previous crop residue for good soil to seed contact.

Seed alfalfa as early in spring as possible. For southern Ohio, target March 15th and for northern Ohio, target April 1st.  For fall seedings, plant as close to August 1st as possible. Seed alfalfa to a depth of ¼ to ½ inch in clay and loam soils and ½ to ¾ inch in sandy soils.

Control weeds for best establishment of alfalfa. Alfalfa yields may be improved at least 8% over the life of an alfalfa stand if weeds are controlled in seedling alfalfa. To control the most weed species in non-Roundup Ready alfalfa, apply Raptor at 4 to 6 fluid oz/ acre to 1 to 3 inch weeds. Raptor controls lambsquarters, annual grasses, and ragweed more effectively than Pursuit.  Include ammonium sulfate or urea ammonium nitrate, along with a methylated seed oil at 1 to 1.5 pints/acre. In Roundup Ready alfalfa, apply glyphosate at 0.75 lb/acre of acid equivalent (22 fluid oz of a Roundup product) to 3 to 4 leaf alfalfa.  Include ammonium sulfate at 8.5 lb/100 gal of spray mixture. It is critical to properly manage leafhoppers in seedling alfalfa. Successful establishment ensures the healthiest, longest lasting, and highest yielding alfalfa.