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

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July 24, 2013 - Issue 4

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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® 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

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 Pio-neer customers

Easy to use interface; available for iOS and Android™

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!

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

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

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Soybean plant showing symp-toms of white mold.

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