When potato leafhopper (PLH) resistant alfalfa varieties forged
onto the market in 1997 they received the same hype as the Cincinnati Reds
are currently enjoying with the addition of Ken Griffey Jr. to their ball
club. How the Reds will do in
2000 remains to be seen but it’s no secret that the first PLH resistant
varieties didn’t meet the expectations of most producers who seeded
these so-called “1st generation” varieties in 1997 and
1998. Early glandular haired
varieties exhibited significant “yield drag” compared to the top
conventional varieties when PLH pressure was low to moderate and still
suffered from some PLH damage when insect infestations were high.
Dr. Mark McCaslin, alfalfa breeder with Forage Genetics in West
Salem, Wisconsin, recently reported that current alfalfa breeding efforts
for PLH resistance has focused on both developing a higher level of
resistance to PLH and improving agronomic performance (i.e. obtaining
higher yields). Some of the
new “3rd generation” glandular haired varieties appear to
confirm progress in these two areas.
Whereas the early PLH resistant varieties had resistance ratings in
the 20 to 30 percent range, some of the most recent offerings are rated at
50 to 80 percent resistance. Improvements
in agronomic performance are verified in the table.
This is 1999 yield data from a 1998 seeding made at four Midwest
locations (Lafayette, IN, Ames, IA, Madison, WI, and West Salem, WI).
At the Iowa and Wisconsin locations, the best PLH varieties (EXP #1
and #2) had higher yields than the commercial checks at each of four
cuttings, including the first-cut when PLH numbers were very low. McCaslin suggests that past PLH resistant varieties were best suited for areas south of Wisconsin where PLH pressure is consistently high and no attempt is made to keep insect populations under control. However, he feels that the new alfalfa varieties (those that are yield competitive in the absence of PLH and with greater than 50% PLH resistance) will be of greater benefit to Wisconsin alfalfa growers. To identify these varieties will take some homework on the part of the producer.
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