Alfalfa Pests Under Gun At Lancaster Crops Day
ANDY ANDREWS
Lancaster Farming Staff
LANCASTER (Lancaster Co.)
Last year, Pennsylvania alfalfa
growers witnessed the heaviest
potato leafhopper pressure in the
past 10-15 years, according to Dr.
Dennis Calvin, Penn State
entomologist.
Calvin spoke to about 65 pro
ducers and agri-industry represen
tatives last week at the Lancaster
County Crops and Soils Day at the
Farm and Home Center.
For the most part, the potato
leafhopper was the insect in alfal
fa. But even with improved resis
tant plant breeds, the pest is
becoming more difficult to control
in alfalfa fields, Calvin noted.
The leafhopper migrates up
from the Gulf of Mexico and east
ern Atlantic seaboard. It doesn’t
overwinter in Pennsylvania, but
can overwinter as fir north as
southern Maryland. It’s a big prob
lem on second or third cuttings and
on established stands.
The tiny insect does mechanical
damage to the phloem cells of the
plant The phloem cells provide
minerals and food to the plant As
the leafhopper saps this, a yellow
color forms on the leaves. This
leads to reductions in dry matter
and especially the alfalfa plant’s
overall crude protein levels. Yield
losses can exceed 1,500 pounds
per acre in established stands.
The leafhopper’s feeding results in a stunted
appearance to the alfalfa plant and V-shaped yel
low areas on the tips of leaves.
There is some hope for the alfalfa grower,
however. There are several varieties that can
fight the leafhopper
• A glandular hair (GH) variety offers true
resistance. The hairs on the plants prevent feed
ing and also release a chemical exudate that can
kill the bugs.
• Non-yellowing varieties. This is not a true
form of resistance, Calvin noted. These varieties
still can see damage, it’s just that they don’t
yellow.
Calvin related the results of Penn State studies
in 1996 that looked at the relative yields of the
two different varieties. The non-yellowing var
ieties yielded about 1.71 tons of alfalfa per acre.
But the GH varieties showed promise, at 1.99
tons per acre.
Sweeps of the plants provided further evi
dence that GH varieties can be the way to go. In
tests of sweeps in 1997, the GH variety registered
only 1.5 leafhoppers per sweep, compared to
15-16 for other varieties.
“There is some economic advantage to using
the material,” Calvin noted, showing that the
resultant improved tons per acre harvest can ben
efit growers.
But overall yield as a result of using the new
varieties depends a lot on the insect pressure at
the site, weather conditions, and other matters, if
growers want to calculate the economic advan
tages of using the new varieties. The material
looks good, Calvin noted, in years with heavy
leafhopper pressure. But there is no yield
improvement in years when leafhopper pressure
is low. But those who use the GH varieties can
benefit from additional chemical treatment for
leafhopper when the insect pressure is higher.
Questions remain, however, do GH varieties
extend the life of a stand? What percent of the
Helds have high leafhopper pressure? How do
the GH varieties compare with traditional variet
ies? And how will they perform after the estab
lishment year? He suggested that growers start
small, experiment a little bit with variety selec
tion, to determine what they think about it.
Calvin also reviewed other pests on Helds,
inrlnding the alfalfa weevil and other pests.
Dr. O. Elwood Hatley, Penn State agronomist,
reviewed the use of alterative forage crops at the
Crops Day. They include spring oats, spring bar
ley, winter rye, triticale, wheat, and others. They
work as a good source of continues year-round
feed, as a hedge against drought, as a tetter, more
efficient use of cover crops for feed (particularly
rye), provide to growers a “window” for manure
applications, and as nitrate retention sources.
PCX' seeding, growers need to
follow a planned program.
Depending on how the material
will be harvested seeding rate
for silage should be 25 percent
above the grain rate and growers
should increase the application an
additional 10 percent when broad
casting. Fertility programs should
be in place.
Dr. Greg Roth, Penn State com
specialist, provided a summary of
the growing year and making use
of yield monitors in the field.
O. Elwood Hatley spoke about
the use of soybeans in the field as a
forage crop. The soybeans are
grown for their vegetative aspects,
not grain.
He examined a Beltsville, Md.
breeding program looking at three
different varieties of silage soy
beans: Donegal (for the Mid-
Atlantic region), Tyrone, and Der
ry. They are named after towns
near Beltsville.
Using soybeans for silage
depends what the grower’s objec
tive is and what previous crop was
grown at the site. Using the right
(Turn to Pag* A 43)
Speakers at the Lancaster County Crops and Soils Day included, from left, Dennis
Calvin, 0. Elwood Hatley, and Greg Roth.
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