This document discusses water usage and needs in corn crops. It notes that annual precipitation in South Dakota varies greatly from 13 to 30 inches, which can cause water stress or drought for corn depending on rainfall. Water is especially important during tasseling and from that stage through dent stage when corn demands 0.25 inches of water per day. Insufficient water can lower yields. While root growth can access more water, high temperatures also increase water needs, potentially doubling requirements in 90 degree weather. Water stress most impacts yields during pollination and grainfill. Maintaining soil moisture through irrigation can increase yields up to 30% by reducing evapotranspiration. The document provides details on corn water usage and loss through evapotranspiration and

1. 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 when
compared to temperatures in the 60s. Water stress im-
pacts corn yield the most during pollination, followed by
grainfill and vegetative growth stages.
Irrigation is an
option to opti-
mize 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 af-
ter 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 evaporation and
through the plant by transpiration. Plant transpiration is
the evaporation of water from leaf and other plant surfac-
es. For corn, evaporation often accounts for 20 to 30 per-
cent 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.
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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.
Photo: DuPont Pioneer
WALKING
YOUR FIELDS
®
www.pioneer.com
July 24, 2013 - Issue 4

2. Goss‟s wilt is beginning to show up in corn fields around
the central U.S. again this year. In 2012, the disease was
found throughout much of the area despite the dry condi-
tions in late summer and fall.
This season, high winds along with sand/soil blasting that
has occurred throughout June have likely created the
kinds of injury necessary for Goss‟s wilt bacteria to enter
corn plants. The prolonged wet weather this spring is
conducive to bacterial diseases in many crops, and corn
has been no exception. Goss‟s wilt is caused by a bacte-
rial pathogen and doesn‟t respond to treatment with fun-
gicides. It is best managed with resistant hybrids and
sound cultural practices.
Typical signs and symptoms of Goss’s wilt
 Long, water-soaked, grayish-green patches or streaks
that turn to large dead streaks with wavy margins
 Dark „freckles‟ appear within or just outside of leaf le-
sions
 Lesions appear to spread along leaf veins
(characteristic of bacterial disease)
 Yellow-orange bacterial ooze (or dried ooze appearing
as shiny flecks)
 Stems may become plugged with bacteria, vascular
bundles appearing orange to brown
The disease generally starts from inoculum surviving on
previous (corn) crop residues, found at or near the soil
surface. Early-season rainfall, especially when heavy or
associated with high winds can lead to infection of the
young corn crop. Early infection can produce the most
devastating symptoms, including wilting and early plant
death. Later infections typically affect leaves primarily,
but may lead to early maturity, or reduced ear size and
lower yields depending on the area affected and time of
symptom onset.
Risk factors to consider when planning for Goss’s
wilt management:
 History of the disease in a field in last year or two indi-
cates presence of inoculum
 Continuous corn raises the risk of inoculum build-up
 Reduced tillage tends to lead to slower residue break-
down and greater risk that inoculum will remain in af-
fected fields
 Irrigated fields tend
to have higher levels
of disease incidence
and severity
As in-season manage-
ment of Goss‟s wilt is
difficult or impossible,
be sure to select hy-
brids with the highest
resistance level availa-
ble for areas that have
multiple risk factors
mentioned above.
Goss’s Bacterial Wilt & Blight
Positive Goss‟s Wilt sampling sites in ND, SD, MN and WI
in 2012.
Goss‟s wilt symptoms on corn leaf. Photo: DuPont Pioneer
Dried bacterial ooze (black arrows) and freckles (white
arrows) are diagnostic of Goss‟s Wilt.
Photo: DuPont Pioneer
A stem cross-section showing vascu-
lar bundles discolored orange to
brown.
Photo:T.Jackson,Univ.ofNebraska

3. Soybean aphids are right on
schedule. Even if you planted
soybean seeds treated with a
nicotinoid insecticide to delay
aphid population establish-
ment, you will still want to
scout your fields for this pest
from V5 through R5.
The soybean aphid overwin-
ters in buckthorn and migrates
to legumes (soybeans, alfalfa
and clovers) in July. It‟s less
than 1 mm in length but when left untreated, economic
infestations can reduce yields by more than 10 bushels/
acre.
Symptoms Aphid-infested soybean plants may look simi-
lar to a potassium deficiency: curled leaves, often yellow
on the outside. 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 soy-
bean aphid will also appear
shorter.
Besides a stunted plant with
noticeable discoloration, 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 con-
trol the population. Your
local Pioneer sales rep can
help with product recom-
mendations. There are
also several beneficial in-
sects that feed on soybean
aphids and can naturally
control the aphid popula-
tion. They include Asian
lady beetles, damsel bugs,
green lacewing larvae, and
insidious flower bugs.
Pioneer®
Field360™
Select software is an
interactive, web-based
subscription service
that combines your
field data with real-
time agronomic and
weather information
 Track field by field
Precipitation and
GDUs using Field 360 Select
 Scouting 101 with GPS located as-planted Products
 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 DuPont Pioneer custom-
ers
 Easy to use interface; available for iOS and Android
Systems
 Instantly map and organize data with notes and photos
 Share your data from the field via email
Contact your local Pioneer professional for more Info!
Pioneer has seen continued growth in sales in the Dako-
tas in recent years. In response to this growth. many tal-
ented people have been hired to be part of this expanding
geography. Also, many employees have taken on new
roles and responsibilities in different areas.
Troy Boomsma is the new Account manager in the Yank-
ton Area. He replaces Myles Konopasek who has been
promoted to Area Manager. Greg Kleinhans is the new
Account Manager south of Sioux Falls, replacing Kyle
Kayser. Kyle has taken on a new role as Field Agrono-
mist for Southern SD. Kyle Christensen is the Product
Agronomist for the same geography. Jim Ruhland was
named Field Agronomist a few months earlier. Taking
over for him in the Mitchell area is Pat VanLith. Jon Fer-
ris is the new Account Manager in the area south of Hu-
ron and west of Brookings. These changes are reflected
on the back page of this issue.
We appreciate your continued support and business! And
as always, we are here to help you succeed.
The Continued Growth of DuPont Pioneer
Soybean Aphids
Aphids found on soybean
leaves. Photo: Josh Shofner
and Brian Buck 7/5/13
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
Photo: Bruce Carlson
Soybean aphid damage on
soybean leaves.

4. WALKINGYOURFIELDS®
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DuPont Pioneer
Sales & Marketing
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