A late spring and wet conditions have delayed soybean
planting in some areas. Soybeans are ‘day length sensi-
tive’ plants...
Heavy spring rainfall can cause concerns about nitrogen
(N) loss in corn fields and raises questions about the
need for su...
Glyphosate on Soybeans
Spraying soybeans with glyphosate can occur through R2
stage. Reproductive phases are as follows:
KB Crompton, Fore, O’Leary
DuPont Pioneer
Sales & Marketing
PO Box 466
Johnston, IA 50131
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ND & Northern MN Walking Your Fields newsletter-June


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This June issue of Walking Your Fields newsletter contains articles about: planting date impact, nitrogen loss, glyphosate restrictions and early weed control.

Articles are written by DuPont Pioneer agronomists in North Dakota and Minnesota and are distributed on behalf of DuPont Pioneer account managers and Pioneer sales reps.

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ND & Northern MN Walking Your Fields newsletter-June

  1. 1. A late spring and wet conditions have delayed soybean planting in some areas. Soybeans are ‘day length sensi- tive’ plants. This means flowering and maturity are trig- gered by the length of the night, or dark period. When adapted maturity varieties are planted before the middle of June, flowering is triggered by shorter days (actually longer nights) after June 21. For each three to five day delay in planting, flowering and maturity are delayed only about one day. That means that if you plant the same variety on May 10, and 30 days later on June 10 the maturity of the later planting is delayed about six to ten days. This happens regardless of the maturity of the variety. Soybean Development Flowering usually begins six to eight weeks after seedling emergence, and continues for three to four weeks. How- ever, flowering will occur earlier if soybeans are planted late. Warm temperatures accelerate development, espe- cially flowering. A full season soybean variety will normal- ly flower in the first 10 days of July. If there is a hot period in mid June, it can flower up to two weeks earlier. When this happens, and if there is good weather for the rest of the season, higher yields result because of the extended reproductive period. The soybean plant may flower 10 days earlier, but it won’t necessarily mature 10 days earli- er because of day length controls. Generally, yield poten- tial increases as the length of the flowering to maturity stage increases. Warm weather in August or early September does not hasten maturity much, unless it causes water deficit stress. Sometimes, temperature is blamed for stress, be- cause hot temperatures often accompany drought. A cool fall does not delay maturity much either, although yields may be reduced if the cool weather is accompanied by heavy rain, causing disease. The flowering period is influ- enced more by temperature, but maturity is more strongly influenced by photoperiod. The rapid shortening of days starting in mid August drives the soybean to maturity; temperature has only a small influence on maturity. KEY SUMMARY POINTS  Soybeans are day length sensitive plants that adjust their final maturity to compensate for late planting. De- layed planting will delay the onset of flowering by only a matter of days, even when planting is delayed for weeks. Harvest dates will only be delayed by about one day for each three to five day delay in planting.  Normal maturity soybean varieties should be planted at least until about June 10. Earlier varieties would be induced to flower before sufficient vegetative growth is achieved to produce top yields.  Even normal maturity varieties may be shorter when planted in June. When the normal vegetative period of six to eight weeks is shortened, the effect on the soy- bean plant is usually reduction in height.  Warm temperatures will induce earlier flowering and a longer flowering period, cool temperatures will induce later flowering and a shorter flowering period. A long- er flowering period is associated with higher yields.  Maturity is strongly influenced by photoperiod (day length). Warmer or cooler than normal temperatures do not greatly influence maturity. The rapid shortening of days starting in mid-August drives the soybean to maturity; temperature has a small influence. Derek Crompton Field Agronomist Zach Fore Field Agronomist Mike O’Leary Product Agronomist June 10, 2013 - Issue 3 WALKING YOUR FIELDS® newsletter is brought to you by your local account manager for DuPont Pioneer. It is sent to customers 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. Planting Date Impact on Soybean Development and Maturity Photo: Pat Branick, DuPont Pioneer
  2. 2. Heavy spring rainfall can cause concerns about nitrogen (N) loss in corn fields and raises questions about the need for supplemental N applications. There are two types of N loss: 1) Leaching—movement with water be- low the root zone, and 2) Denitrification—loss to the atmosphere. In general, leaching losses are more likely on sandy soils where water can move through the profile quickly. Denitrification is more likely on medium and fine textured soils that are not well drained. The exact extent of N losses through leaching and/or denitrification follow- ing the heavy rains is difficult to determine. Both of these loss processes occur through the nitrate form of N, so the potential for significant loss is determined by the amount of the N supply that was in the nitrate form when the ex- cess rainfall occurred. Losses depend on many factors such as when the N was applied, the forms of N applied, soil characteristics, and how wet the soil is. Where fertilizer N was applied before planting, the timing of the application and the form of N used are important in determining the risk of loss. Keeping in mind that losses occur through the nitrate form of N, the timing of nitrate formation is an important consideration in evaluating po- tential losses. Fall-applied fertilizer N has a high risk for loss following excess rainfall because most or all of the N would be in the nitrate form by mid-May. For spring pre- plant applications, ammonium forms of N such as anhy- drous ammonia or urea are converted to nitrate-N in about four to six weeks. Urea usually is converted to ni- trate more rapidly than anhydrous ammonia. Nitrogen solutions (28% UAN) contain half of the N as urea and the remainder as ammonium nitrate. Essentially, when this fertilizer is applied, it contains 75 percent of the N as ammonium and 25 percent as nitrate. Denitrification losses can occur within a few days if the soil remains saturated or flooded and nitrate-N is present. Warm temperatures and extended periods of saturated conditions favor high losses. Work in Illinois suggests that four to five percent of the nitrate-N present can be lost each day the soil remains saturated. Table 1 from the University of Nebraska provides some estimates of deni- trification losses at various temperatures and times of saturated soil conditions. Options for applying supplemental N when it is needed include traditional side-dressing with anhydrous ammonia or N solutions. Urea-ammonium nitrate solutions (28%) can also be applied as a surface band or as a broadcast spray over the growing crop. Dry N fertilizers such as urea or ammonium nitrate can also be broadcast applied to the crop. Leaf burning from solution or dry broadcast applications should be expected. Applying the dry materi- als when foliage is dry will help to minimize burning. Basi- cally, broadcast N rates should be limited to 90 lbs. N/ acre for corn with 4 to 5 leaves and to 60 lbs. N/ acre for corn at the 8-leaf stage. Under N deficient conditions, corn will respond to supplemental N applications through the tassel stage of development if the N can be applied. Feel free to contact your local Pioneer Sales Repre- sentative to assist you in assessing your N needs. (Source: Portions of this article are from Dr. Larry G. Bundy, U of WI Extension Service, ‘Evaluating Nitrogen Losses Following Excessive Rainfall.’) To help you assess potential fertilizer N losses, download the simple and reliable Supplemental Fertilizer N Work- sheet from the University of Minnesota. http:// bit.ly/17iNb9A. (Source: Schmitt and Randall, U of MN.) Glyphosate on Corn Corn can be damaged by spraying glyphosate too late in the growing sea- son. Ears appear to have aborted kernels or scat- tered pollination.  Corn may be sprayed broadcast or over the top with glyphosate until it reaches V8 stage or 30 inches in height (whichever comes first).  Corn can be sprayed between 30 and 48 inches with a ground sprayer employing drop nozzles that direct the spray to the base of the corn plants and avoids direct application of spray solution into the whorl of the corn plant. Table 1. Estimated denitrification N losses influ- enced by soil temperature and days saturated. Soil Temp (°F) Days Saturated N Loss (% of applied) 5 10 55-60 10 25 75-80 3 60 5 75 7 85 9 95 Source: Shapiro, University of Nebraska. Restrictions on Spraying Glyphosate Ear on left shows irregular kernel set resulting from a late glyphosate application. Ear on right is from unsprayed plant in same field. Pho- to: Clyde Tiffany, DuPont Pioneer. N Loss Following Excessive Rainfall
  3. 3. Glyphosate on Soybeans Spraying soybeans with glyphosate can occur through R2 stage. Reproductive phases are as follows:  R1--Plants have at least one flower on any node.  R2--Plants have at least one flower open on one of the two uppermost nodes (Four days after R1).  R3--A 3/16 inch pod at one of the four uppermost nodes (Ten days after R2). After you see the first flower, you have approximately two weeks to spray glyphosate to stay on label. This recom- mendation is a clarification of previous definitions of spraying glyphosate on soybeans throughout flowering. Application timing is critical when using glyphosate or other post-emergence herbicides to control weeds in corn. The weeds need to be emerged, but not too large that they compete with corn and reduce yields. Usually this control is accomplished with multiple applications of glyphosate, and/or by using glyphosate in combination with herbicides that provide residual weed control. Critical Weed-Free Period The critical period of weed control is the interval when weed control is required to provide maximum yield. Weed competition before this period will not affect yield, if weeds are controlled by the start of the critical period. In addition, weed competition after the critical period will not affect yield. Figure 1 shows when weeds were removed during the first 4 weeks after planting, corn yield was 100 percent (solid line). When the crop was kept weed-free for at least 7 weeks, corn yield was also 100 percent (dashed line). It is difficult to predict the critical period, because it de- pends upon the weeds (how competitive the different weed species are, their density, when they emerge), and the environment (soil moisture, nitrogen, etc.). Research conducted on weed interference in corn indicates that weeds should be controlled by at least the third week after planting, and weed emergence should subsequent- ly be prevented until about 8 weeks after planting (or more accurately, 14-leaf or V12 corn). If a non-residual herbicide like glyphosate is applied three weeks after planting, a second herbicide application or cultivation will probably be required to keep later germinating weeds controlled, or a residual herbicide will need to be added to prevent further weed germination during this window. Herbicide Systems According to research at University of MN by Dr. Jeffrey Gunsolus, the longer the duration of weed competition, the greater the impact on yield. His research concluded:  The best economic return came from a pre-emergence application of a residual soil herbicide (acetochlor) fol- lowed by a post-emergence application of glyphosate at the 5-inch weed stage.  A one-pass application of a residual a soil herbicide (acetochlor) plus glyphosate at the 1-inch weed stage can maximize yields.  One post-emergence application of glyphosate did not maximize yields or returns in his study (Gunsolus, 2005). Always read and follow label directions and safety pre- cautions. Early Weed Control is Critical in Corn Figure 1. Source: Reprinted with permission by Chris Boerboom, U of WI. ‘Timing Post-emergence Herbicides in Corn and Soybeans.’ For nearly a half century, the National Corn Grower’s Association’s corn yield contest has provided corn grow- ers an opportunity to compete with colleagues to grow the most corn per acre ~ helping feed and fuel the world. This NCGA contest has given participants the recognition they deserve as well as an opportunity to learn from their peers.  June 15: Early entry deadline. Cost per entry $80.  July 12: Final deadline to submit all entries. Cost per entry $110. Entry fees for Pioneer corn hybrids paid by Pioneer. Enter a Pioneer® brand hybrid in the yield contest and all entry fees and membership dues are paid by Pioneer directly to NCGA. Talk to your Pioneer Sales Representative about your entry. On-line entries are available by following this link: https://membership.ncga.com/CornyieldContest/ NCGA National Corn Yield Contest
  4. 4. WALKINGYOURFIELDS® KB Crompton, Fore, O’Leary DuPont Pioneer Sales & Marketing PO Box 466 Johnston, IA 50131 ADDRESS SERVICE REQUESTED PRESORTED FIRST-CLASS MAIL U.S. POSTAGE PAID PHI CUSTOMER INFO Follow your DuPont Pioneer Agronomists @PioneerNDakota or @PioneerMN In this issue:  Planting Date Impact  N Loss Following Rain  Glyphosate Restrictions  Early Weed Control  NCGA Yield Contest This Walking Your Fields® newsletter is brought to you courtesy of your Pioneer Sales Representative and DuPont Pioneer Account Manager. Thomas Frappier Account Manager Jim Kokett Account Manager Kyle Gerner Account Manager Trent Velure Account Manager Tyler Oachs Account Manager Bruce Thomas Account Manager Brett Goodman Account Manager Jeremy Baumgarten Account Manager Marc Cartwright Account Manager Adam Erickson Account Manager Matt Carlson Account Manager