For growers in northern South Dakota and southern North Dakota, this July issue of Walking Your Fields newsletter contains articles about: the role of water in corn development, fungicide applications, soybean aphids and diseases. Articles are written by DuPont Pioneer agronomists in South Dakota and North Dakota and are distributed on behalf of DuPont Pioneer account managers and Pioneer sales reps.

1. As we look at the 2013 growing season to date, we are
tracking well behind 2012 Growing Degree Units (GDUs).
But compared to the 30 year average, we are similar for
the area. Tracking GDU accumulation on your farm will
help estimate management windows and crop growth
stages.
The Pioneer website allows you to calculate GDUs for
your specific location and planting date: https://
www.pioneer.com/home/site/us/agronomy/tools/gdu/
Wade Marzahn was recently hired as the new KM Area
Field Agronomist. Wade’s previous employment was with
MZB Technologies, a precision farming company from
Watertown, SD, where he spent 11 years. In this previ-
ous role, Wade sold, supported and trained participating
retail clients on the value and agronomics behind using
the MZB Precision Farming System, a zone based sys-
tem. Wade has a lot of experience with nutrient variability
within agricultural fields and a great understanding of the
value to be expected from variable rate applications of
fertilizer and seed.
Before joining MZB Technologies Wade worked as an
agronomist for Midwest Ag Services of Jamestown, ND.
Wade and his wife, Renee, have four children: Breanna,
16; Landon, 14; Nicole, 11; and Andrew, 9. The Mar-
zahn’s live in Groton, SD where they enjoy time with fami-
ly, camping, 4-H and watching athletic events.
In South Dakota, annual precipitation varies from 13 to 30
inches per year. This can result in water stress in corn
and drought for many areas, depending on which end of
the spectrum growers find themselves.
Water is essential to corn growth, especially at tasseling
when the corn’s uptake of water increases dramatically.
From now through the dent stage, corn demands an aver-
age of a ¼ inch of water per day. Inability to receive this
amount of water can lead to decreased yields.
Root growth can help compensate for the increased wa-
ter need, as the expansion of the root system reaches
deeper into the soil profile to help the plants extract more
soil moisture. However, air temperatures also greatly in-
fluence water needs. Temperatures in the 90s during
corn growth will double the corn water requirement
WALKING YOUR FIELDS® newsletter is brought to you by your local account manager for DuPont. It is sent to customers several times throughout the growing
season, courtesy of your Pioneer sales professional. The DuPont Oval Logo is a registered trademark of DuPont. PIONEER® brand products are provided subject to
the terms and conditions of purchase which are part of the labeling and purchase documents. ®, TM, SM Trademarks and service marks of Pioneer. © 2013 PHII.
Accumulated Growing Degree Units
GDU Calculator
(May 1 - July 14)
Location
2013 GDUs
Accumulated
2012
30
Year
Avg
+/- 30
Year
Avg
Aberdeen, SD 1104 1295 1102 +2
Brookings, SD 1089 1313 1060 +29
Faulkton, SD 1148 1319 1162 -14
Huron, SD 1196 1406 1207 -11
Lisbon, ND 1158 1311 1073 +85
Oakes, ND 1109 1258 1079 +30
Watertown, SD 1031 1262 1039 -8
Wahpeton, ND 1043 1224 1057 -14
New Field Agronomist
Role of Water in Corn Development
Table 1. Estimated Corn Evapotranspiration and Yield
Loss per Stress Day During Various Growth Stages
Growth Stage
Evapo-
transpiration*
(inches/day)
% yield loss per
day of stress
(min-ave-max)
Seedling to 4 leaf 0.06 ---
4 leaf to 8 leaf 0.10 ---
8 leaf to 12 leaf 0.18 ---
12 leaf to 16 leaf 0.21 2.1 - 3.0 - 3.7
16 leaf to tasseling 0.33 2.5 - 3.2 - 4.0
Pollination (R1) 0.33 3.0 - 6.8 - 8.0
Blister (R2) 0.33 3.0 - 4.2 - 6.0
Milk (R3) 0.26 3.0 - 4.2 - 5.8
Dough (R4) 0.26 3.0 - 4.0 - 5.0
Dent (R5) 0.26 2.5 - 3.0 - 4.0
Maturity (R6) 0.23 0.0
Adapted from Rhoads and Bennett (1990) and Shaw (1988). From: What
Happens Within The Corn Plant When Drought Occurs? Joe Lauer, Uni-
versity of Wisconsin-Extension, 2003.
*Evapotranspiration is the total of the water used by the corn plant
and water lost to evaporation.
WALKING
YOUR FIELDS
®
www.pioneer.com
July 24, 2013 - Issue 4
<<

2. when compared to temperatures in the 60s. Water stress
impacts corn yield the most during pollination, followed by
grainfill and vegetative growth stages.
Irrigation is an option to optimize yields. Checking your
fields using probing methods is important as irrigation
must be started early enough to fully benefit the crop and
increase yield potential. Most irrigation systems cannot
keep up with crop water demands during the later critical
growth periods (VT to R3). The first priority for irrigation
should be a 3-week period starting just before tassel (VT)
and ending just after silking. Corn is less susceptible to
water stress during later grain-development stages (R3).
Soil water levels should be maintained to allow the crop
to reach maturity (R6).
Understanding Water Usage in Corn
Water is acquired, used and lost through evapotranspira-
tion (ET). In this process, water is removed directly from
the soil surface to the
atmosphere by evap-
oration and through
the plant by transpira-
tion. Plant transpira-
tion is the evaporation
of water from leaf and
other plant surfaces.
For corn, evaporation
often accounts for 20
to 30 percent and
transpiration 70 to 80
percent of total ET
over the length of a
growing season.
The amount of water retained for the plant is affected by
the soil texture and organic matter. Soil serves as a res-
ervoir to the plant, even though not all water is accessible
to the plant. Water held by the soil between field capacity
and permanent wilting point is called “plant-available wa-
ter” and varies by soil texture. Ranges of available water
at fine sandy soil are 0.7 to 1 inch, increasing up to clay
which holds 1.8 to 2.4 inches.
As soil dries, water stress can occur at 50 percent or less
of plant-available water. In many cases, irrigation is in-
stalled to compensate for decreased precipitation. Using
irrigation can increase yield up to 30 percent by decreas-
ing ET.
Several areas received crop damage due to the recent
hail storms. Yield losses vary based on crop stage and
severity of the damage. Many growers are wondering if a
foliar fungicide should be applied to protect the injured
plant tissue from potential diseases causing additional
yield losses later in the growing season.
Many diseases favored by wounding or plant damage are
not controlled with foliar fungicides, such as those caused
by bacteria. Bacterial causing diseases include Goss’s
Wilt, common smut and stalk rots in corn. Neither bacteri-
al pustule on soybeans nor bacterial leaf streak in wheat
will be controlled. Bacterial diseases may also be more
prevalent due to the wounds caused by hail.
However, wounds are not required for certain foliar dis-
eases like gray leaf spot in corn and frogeye leaf spot in
soybeans to infect plants. Diseases like these are more
likely to develop as a result of the rain and humidity fol-
lowing a storm or hail event rather than from tissue dam-
age to the crop and can be managed with a foliar fungi-
cide (Jackson, University of Nebraska. 2010).
Fungicide applications on hail damaged plants should
only be recommended if significant fungal diseases are
present. Fungicides are effective tools for protecting yield
potential of plants if significant disease levels are present
but do not improve the yield potential of crops. Other pos-
itive yield responses result from hybrid susceptibility and
previous crop history and tillage practices.
Pioneer®
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web-based subscription service that combines your field
data with real-time agronomic and weather information.
 Track field by field Precipitation and GDUs
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 On-The-Go organized field applied data
Pioneer Field360 Notes pinpoints your field location via
satellite imagery so you can record notes or photos on
the spot.
 Displays field boundaries for Pio-
neer customers
 Easy to use interface; available
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with notes and photos
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Contact your local Pioneer Professional for more Info!
Image 1. Evapotranspiration is the sum
of evaporation from the land’s surface +
transpiration from the plant. Image:
SalinityManagementGuide.org
Foliar Fungicide Applications
on Damaged Crops
Photo: DuPont Pioneer

3. As we approach the end of July, soybean aphid scouting
should be underway. Weekly scouting is a good practice
this time of year as populations have the ability to in-
crease quickly. Even if you planted soybean seeds treat-
ed with a nicotinoid insecticide to delay aphid population
establishment, you will still want to scout your fields for
this pest from V5 through R5.
The soybean aphid overwinters in buckthorn and mi-
grates to legumes (soybeans, alfalfa and clovers) in July.
It’s less than 1 mm in length but when left untreated, eco-
nomic infestations can reduce yields by more than 10
bushels/acre.
Symptoms. Aphid-infested soybean plants may look sim-
ilar to a potassium defi-
ciency: curled leaves,
often yellow on the out-
side. Aphids produce a
sugary excrement, known
as honeydew, on leaves,
which promotes soot
mold growth and can
serve as a feeding ground
for ants. Plants infested
by the soybean aphid will
also appear shorter.
Besides a stunted plant
with noticeable discolora-
tion, you can also detect
these oval-shaped, light green pests with black “tail
pipes” near the end of the abdomen by doing numerous
sweeps through the field.
Take Action. Count the number of aphids on 30 to 50
plants throughout the entire field and calculate the aver-
age number of aphids per plant. If aphid populations
reach 250 per plant and are increasing during the R1 –
R5 growth stages, consider a foliar insecticide to control
the population. Your local Pioneer sales rep can help with
product recom-
mendations.
There are also
several beneficial
insects that feed
on soybean
aphids and can
naturally control
the aphid popula-
tion. They include
Asian lady bee-
tles, damsel
bugs, green lace-
wing larvae, and
insidious flower
bugs.
Bacterial leaf blight – Cool, wet weather are the opti-
mum conditions for disease development. Both brown
spot and bacterial leaf blight can be found on the same
plant. Leaves tend to appear ragged as dead areas on
leaves will fall out as the leaf is retained.
Phytophthora Root Rot – Scout one to two weeks after
excessive rains as phytophthora prefers warm, saturated,
compacted soil. Phy-
tophthora can be
present from VE
through R6 growth
stage, and it displays
seed rot, seedling
blight and root/stem
rot phases. Phy-
tophthora can rot
soybean seeds and
cause damping-off
which can be diag-
nosed by the dark
brown discoloration
of the stem, usually
beginning at the soil
line. Symptoms of the root/stem rot phases include a
smaller than normal root mass and a discolored tap root.
By the time you notice above-ground symptoms like an
uneven, stunted stand, the plant has already been infect-
ed below ground for several weeks. Plants may also be
light-green due to minimal nodulations on the roots. Dur-
ing later growth stages, dark-brown to red-brown lesions
progress up the stem from the roots. Wilting and plant
death may soon follow, especially if the plant is stressed.
White Mold (Sclerotinia Rot) - Sclerotinia white mold is
favored by cooler night temperatures (50-60°F) and moist
conditions in the plant canopy. In addition to cool temper-
atures, the production of white mold mushrooms requires
moist soil and a closed canopy. If surface soil moisture is
low or the soybean canopy is not closed during flowering,
the fungus would not be able to produce mushrooms.
When scouting for this dis-
ease, pay attention to the
fields that had white mold
previously and that have
good soil moisture and a
closed canopy. The first
evidence of white mold is a
chlorotic, girdling lesion
covered with white, fluffy
mycelium at one of the
middle nodes. The evi-
dence of the disease be-
comes conspicuous in Au-
gust when dead tops start
to show up in fields. To
help manage white mold
select tolerant varieties.
Soybean Aphids
Photo: Bruce Carlson
Soybean aphid damage on soy-
bean leaves.
Soybean aphids and an ant on a soybean
leaf. Aphids excrete “honeydew,” a sugary
substance that attracts other insects and also
results in development of sooty mold.
Photo: Marty Lovrien
Soybean Diseases
Plants wilting among healthy plants is
often a symptom of phytophthora.
Photo: DuPont Pioneer
Photo:DuPontPioneer
Soybean plant showing symp-
toms of white mold.

4. WALKINGYOURFIELDS®
KM Nuttall, Marzahn
DuPont Pioneer
Sales & Marketing
PO Box 466
Johnston, IA 50131
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