CAN GROWERS SUCCESSFULLY THICKEN-UP 
OLD ALFALFA STANDS?  
** AN OLD QUESTION **

Recent reports have suggested that interseeding alfalfa into thin stands can return old alfalfa fields to high production levels. For years, researchers have reported that the practice of "thickening-up" old stands is not effective. In fact, very few of the new alfalfa seedlings really contribute to hay production.   

In Oklahoma we have found that very few plants become established within 1 foot of an old plant. Even in spring following poor stand establishment of fall-sown alfalfa (7 months old), new seedlings seldom get tall enough to be cut by the sickle bar. Dozens of seed per square foot may germinate, but few become a productive part of the stand under good conditions.   

There have been recent news articles suggesting that thickening up old stands can be successful. What new information has brought about this change in alfalfa establishment recommendations? There is no new research to suggest that interseeding alfalfa into old, thin alfalfa stands will be successful.   

Where this practice has worked, several key factors were present which are not common in most alfalfa meadows: light, well-drained soils with low disease levels; the availability of irrigation to quickly bring up new seedlings; and a weed complex which allows burn-back type herbicides to work effectively (Try these with bermudagrass!). The odds are firmly against successfully thickening-up old alfalfa stands. The odds are not much better when trying to thicken up a new stand with too few plants to leave.   

What Kills New Seedlings in Established Alfalfa Stands?   

Environments surrounding germinating alfalfa seeds in an established alfalfa stand is as hostile as possible. Diseases, insects, and nematodes specific to alfalfa have had years to build up in the soil and in the root and crown tissue of older plants. As soon as young, fresh tissue is available (the germinating alfalfa seedling), these pests attack, and this is why many researchers have reported that seedlings emerge but seem to "melt away" in old alfalfa stands.   

One response to this seedling disease problem has been a recommendation to increase the amount of fungicide (e.g. Apron) placed on the seed. It has been suggested that farmers take Apron-treated commercial seed and retreat the seed with a second application of the fungicide before sowing. This load of Apron could injure the seedling and is probably illegal. The label recommendations for Apron fungicide are closely adhered to by seed companies; an additional treatment provides greater than the recommended rate of fungicide on the seed. Abusing label recommendations today insures that pesticide options will be even more limited in the future.   

Other reasons why young alfalfa seedlings seem to "melt away" after interseeding include autotoxicity and competition from older alfalfa plants. Competition is for light, water, and nutrients. Even very thin old stands provide stiff competition for light and water as new seedlings attempt to establish. In addition, the old plants excrete compounds from their roots and top growth which are toxic to the germination and growth of new alfalfa seedlings.   

What Should a Grower Do? For producers with thin alfalfa stands, the best advice is to destroy the stand and rotate to a different crop for at least one year (preferably several years). This allows the pest pressures and autotoxic compounds in the soil to dissipate completely before new alfalfa seedlings are established. Another benefit is the control of troublesome weeds. What if the grower does not have a full year available before new alfalfa acres must be planted? If an old stand is moldboard plowed, a new stand can be established in approximately 4-6 weeks (assuming good rains). However, waiting less than one full year before establishing a new stand is risky.   

Conclusions -- Stop and think before you consider "non-stop" alfalfa. Unless your farm is unique (light soils, irrigation, disease-free, low weed pressures, etc.), attempting to successfully thicken-up old alfalfa stands will usually fail. Even though this practice looks attractive due to lower seedbed preparation costs and lower seed costs (8-10 lb./acre vs. 15-20 lb./acre), it usually is not cost effective. 
 
Additional Information:   

• Alfalfa Stand Establishment Questions and Answers. OSU Extension Circular E-949  
• Alfalfa Stand Establishment. OSU Extension Facts F-2089