Page 18>-Com Talk, Lancaster Farming, Saturday, April 17,1993 pennSTATE
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Considerations for
selecting com hybrids
in Pennsylvania
Selecting the best com hybrids can be a significant factor in
the profitability of a com production enterprise. The
differences in performance among commercially available
com hybrids of the same maturity generally exceed 15
bushels per acre and frequently reach 50 bushels per acre.
As a result, improving com yields by an average of 5 to 10
bushels per acre through careful attention to hybrid
selection is not unrealistic.
CHARACTERISTICS TO CONSIDER
An effective hybrid selection strategy involves considering!
a number of hybrid characteristics that are important for
performance under your system and then using various
sources of information to choose the most appropriate
hybrids.
Maturity is of primary importance in the hybrid selection
process because it is critical to choose hybrids that can use
as much of the available growing season and still have a
minimal risk of being frosted before maturity. Hybrids that
are too early will have a reduced yield potential and those
that are too late may result in poor quality grain or silage.
Com hybrids are rated in one of two systems; the relative
maturity system and/or the growing degree day system.
Of the two systems, the relative maturity system is
more popular In the relative maturity (RM) system.
hybrids are assigned a days-to-matunty rating based on the
grain moisture at harvest compared to other hybrids As a
result, a hybrid with a lower RM rating should have lower
grain moisture levels at time of harvest than one with a
higher RM rating. The rating is not a measure of the actual
days required for maturity, since it is not uncommon for a
105-day hybrid to require 150 days from the dale it is
planted to reach maturity The ratings also vary somewhat
among companies, this makes comparisons of maturity
more difficult One way to overcome the differences amonj
the companies is to compare moisture contents of specific
hybrids in perfoimance trials where they appeared to-
gether—lower moisture contents translate into an earlier
rating
The second system is the growing degree day system
In this system, the number of growing degree days is
calculated between dates of planting and black layer or
maturity The advantage of the growing degree day system
is that n provides a link between hybrid maturity and local
weather information Disadvantages of this system are 1)
ODD ratings are not necessarily indicative of differences
in gram moisture, because hybrids may differ in dry-down
rates after black layer, and 2) growing degree day require
ments of hybrids may change somewhat with location and
season Hybrids in Pennsylvania frequently do not require
as many growing degiee days as they will use in the
Midwest states Also, growing degree day requirements of
specific hybrids may be lower in cool seasons and late
plantings
A good rule of thumb is that com for grain should
reach maturity one to two weeks before the first killing
frost in the fall Other factors, such as harvest method,
marketing plans, and timeliness considerations may also
have a bearing on maturity selection The need for a field
dry-down period with ear com and dry shelled corn means
that maturity should not be pushed with these systems
Where high-moisture corn harvest is planned, slightly
longer season hybrids can be used Even longer season
f 5 to 10 days) hybrids can be utilized for silage production
provided wet soils will not interfere with harvest Earlier
hybrids may provide some advantages for early com
markets or more timely harvesting If you consider this
approach, be sure to monitor yields of these earlier
maturing hybrids to make sure this strategy is economical
for your system
A key to managing maturities in an area as diverse as
Pennsylvania is to monitor crop development each year
and use this information in selecting hybrid maturities for
future years
Appropriate maturities for gram production in
Pennsylvania are shown in Figure 1 and Table 1
Figure 1. Pennsylvania corn maturity zones.
MATURITY
Hybrid selection is the main avenue for control of the the
most predominant com diseases in Pennsylvania. Stalk rot,
one of the most serious and common com diseases, is
favored by environments where stress occurs during
August. If stalk rot appears to be a persistent problem in
your system, consider placing more importance on
standability and stalk rot resistance in your hybrid selec
tion. Gray leaf spot, northern leaf spot, and northern leaf
blight are also common in Pennsylvania. (
Gray leaf spot is most severe in those fields of continu
ous, no-till com where air drainage is poor. Fields that are
along creeks and rivers are particularly vulnerable to gray
leaf spot because of the extended periods of dew. The
symptoms of the disease resemble a paper match—gray,
rectangular shaped lesions that are restricted by the leaf
veins. Where this disease is serious, gray leaf spot resis-
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AGRONOMY CENTER
Thompsontown, PA
717-535-5151
BEDFORD FARM BUREAU
Bedford, PA
814-623-6194
LARRY BOWER
Linden, PA
717-323-3546
BROOKLAND MILLS, INC.
Me Veytown, PA
717-899-6772
BRUCE B. GAMBLE
& SONS
Concord, PA
717-349-2670
HAKES FARM &
SEED SERVICE
Rod Lion, PA
717-244-2754
ELWOOD HARER
Montgomery, PA
717-547-6133
EDWARD HESSONG
Greencastlo, PA
717-597-9534
HORRACE HEINDEL & SON
York, PA
717-244-3780
HYDRO/KIRBY
AGRI-SERVICES
Lancaster, PA
717-299-2541
GORDON ISENBERG
Alexandria, PA
814-669-9323
College of Agricultural Sciences • Cooperative Extension
DISEASE RESISTANCE
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Participating Northrup
JOHN D. CASSEL & SONS HERBERT MYERS
Hummelstown, PA Lewisberry, PA
717-566-8022 717-697-8903
LYN-LEE FARMS
State College, PA
814-238-1233
SCOTT MELLOTT RHOADS MILLS INC.
Lancaster. PA Selmsgrove, PA
717-295-3470 717-374-8141
MENSINCER BROS.
Nescopeck, PA
717-379-3388
GENE MILLER
Calawissa, PA
717-799-5760
RALPH MILLER
Womelsdorl, PA
215-589-2642
MIKE WASCOK
Dunbar, PA
412-628-3993
NORTHRUP KING
Both northern leaf spot and northern leaf blight occur
most frequently in valley areas where heavy dews and early
morning fog or mist are common. Northern leaf spot (race
3) symptoms are tan to brownish, linear, chain-like lesions.
The northern leaf blight symptoms are elliptical, grayish
green streaks that develop on the leaves and may extend the
length of the leaves. Under severe infection, all leaves may
die. Both diseases can cause early plant death. Resistant
hybrids are the best means of control.
Learn to identify the major com diseases in your area
and select hybrids with specific resistance to these diseases.
Be wary of hybrids advertised as having “good disease
resistance”—instead ask your dealer about specific
resistance to diseases that you know are common on
your farm.
OBERHOLTZER
DAIRY FARM
East Earl, PA
717-354-0832
RICHARD H. KAUFFMAN
Columbia, PA
717-684-2683
RONALD SHAFFER
& SONS
Dalmatia, PA
717-758-6345
SCOn SHIPMAN SOMERSET MILLING CO.
Turbotville, PA Somerset. PA
717-649-6133 814-445-7504
STEVE SHIPMAN
District Sales Manager
717-726-6958
tance should be a primary consideration in your hybrid
selection.
(Turn to Page 19)
Your
King Dealer
HYDRO-KIRBY
AGRI SERVICE
Richland. PA
717-866-5701
MASTER FARMER
FERTILIZER
Lancaster, PA
717-397-5152
PHILLIP PITZER
Aspers, PA
717-677-7716
JOHN SNOOK
Milllmburg, PA
717-966-0957
STEPHEN SNYDER
Mdlersburg, PA
717-362-8735
RICHARD STONER
Alverton. PA
412-887-8854
TWIN FIR FARM
Centre Hall. PA
814-364-9270
WALNUT BARN &
DAIRY EQUIP.
Port Royal. PA
717-436-9429
WARRIORS MARK
FEED CENTER
Warriors Mark, PA
614-632-5490
WAYNE FEED SUPPLY
Dillsburg, PA
717-432-9623
WAYNE FEED SUPPLY
Chambersburg, PA
717-263-4121
KENNETH ZURIN
Mt. Joy, PA
717-898-8736
ERTH-RITE, INC.
Gap. PA
717-442-4171
ALAN HEFLIN
Keymar, MO
301-898-7942
JACK HEFLIN
Woodsboro, MD
301-898-5255
GORDON FLICKINGER
Union Bridge, MO
410-775-7394