This has been the major seed-marketing gimmick for the past 25 years. The success of this marketing gimmick is apparent in that virtually all new varieties claim a perfect or near perfect disease index. This data is generated by the seed companies themselves without any independent verification. Regardless of disease claims, all new varieties have sufficient resistant since resistance and in most case moderate resistant is sufficient. This is apparent in that Vernal, a variety now over 50 years old, with a disease index of 13 still yield relatively well and improves in yields as stands age relative to new varieties. You can check this out at Wisconsins "compare varieties".

An exception might be on very heavy soils with poor internal drainage in which case HR levels of PRR and Aphanomyces may be useful. I would ask the seed rep for the exact level of resistant to these diseases or which of their varieties have the best resistance.

After 3 years, stands are thinning due to root and crown rots. Varieties with a high or perfect disease index is overkill and for marketing purposes. These varieties may well be lacking in an important agronomic traits. Alfalfa varieties are no different that other crop varieties or animal breeds. If they are strong in some area they are weak in other areas, usually yield.

Solution: All varieties now sold have good major disease resistance. I would tend to stay away from varieties with a perfect or near perfect Disease Index, if nothing else, as a protest against marketing gimmicks.

Click here for an abstract of an excellent analysis of the yield, disease resistance and winter-survival based over 200,000 observations. Because of copy write, I can only link to this site which will go to an abstract.

The entire paper will show up if you copy the following into google. "Physiological Genetics" Purdue