AgWatch

Specialist Gives Wheat Management Update

DR. ANTHONY OHMES

JACKSON, MO.
   Know Your Growth Stages. Wheat yield like any crop is most influenced by weather. Following weather, fall yield components include variety selection, planting date, seeding rate and placement, and phosphorus availability. Spring yield components include number of viable heads per acre, head size, kernels per head, and kernel weight. To achieve enough viable heads, we rely on tillering. Tillering is from Feekes 2 to 3 which begins in the fall and usually completes in the spring. Tillers formed after Feekes 5 (green upright growth) will not contribute to yield. The head (spike) size (spikelets/head) is determined by Feekes 4-5.  Kernels per spike or number of viable florets are determined by Feekes 6 (jointing). Kernel weight is determined from flag leaf (Feekes 8) through early grain fill.  Wheat maturity is driven primarily by variety response to temperature and photoperiod and not specific dates on the calendar. Therefore, it is important to evaluate a crop by growth stage to help make nutrient and pest management decisions. A good guide for following wheat development is Purdue University’s guide: “Managing Wheat by Growth Stage” at https://www.extension.purdue.edu/extmedia/ID/ID-422.pdf.
   Do You Need a Pre-Green-up N Application?
   Fields with less than 60 tillers per square foot in the early spring between Feekes 2 and 3, apply 30 to 50 pounds of nitrogen to increase tillering. For fields with 60-80 tillers per square foot apply 20 to 30 pounds. In many cases this is where we see split applications boosting yield. However, if plants are healthy and tiller numbers are greater than 80/square foot then holding off until Feekes 5 may be more economical and provide the biggest results.  This is because the time of greatest nitrogen uptake is between jointing (Feekes 6) and head emergence (Feekes 10.5). Therefore pre-jointing applications would supply this upcoming demand and reduce plant damage from ground applications. Consider using urease inhibitors containing the active ingredient NBPT when applying urea based fertilizer.  Tissue tests just before jointing can help determine nitrogen needs at jointing.
   Should nitrogen be applied during snow cover?
The short answer is no. This is especially important when speaking of fields on any slope because of runoff potential from melting snow while the ground is still frozen.
   Does Your Wheat Need Sulfur?
   Remember that low organic matter (<3%), low CEC (<10) soils of southeast Missouri are also prone to low sulfur conditions and sulfur fertilizers should be applied early. A soil test is the best guide for determining the need for sulfur. However, if your soil is prone to low sulfur then 10 to 15 pounds per acre of sulfur would be beneficial. Spring sulfur should come in the form of sulfate sulfur found in products such as ammonium sulfate. This application has a larger impact with an early application.  Sulfur deficient wheat symptoms will begin to be apparent after stem elongation and by second node (Feekes 7) a rescue treatment would not be feasible. Sulfur deficiency symptoms can be found in the MU IPM Guide 1016: http://ipm.missouri.edu/ipm_pubs/ipm1016.pdf
   BYDV and Aphids?
   With cold temperatures (and snow cover) as we begin to move into late February, scouting for aphids should begin as soon as conditions permit for stand evaluation. However, scouting is the best way to determine which fields need an insecticide application to help reduce aphid build up and spread of spring barley yellow dwarf virus (BYDV). When scouting, stop in a number of locations in the field and carry a small trowel in order to dig up individual crowns to check up close for aphids. Even with low numbers, research in Mississippi and Tennessee has shown consistent yield improvement with late winter pyrethroid applications. One suspected reason is removing the initial population of aphids before they have a chance to increase in mid to late March and possibly reducing the infection potential of BYDV.   Scout throughout the field before aphid populations exceed 6 per foot of row. More information is in a recent article from Scott Stewart at University of Tennessee and Angus Catchot at Mississippi State at the following links:
 http://news.utcrops.com/2015/01/spraying-aphid  s-in-wheat-the-next-several-weeks/?utm_source=Tennessee&utm_campaign=8744b32b9d-UTcrops_News_Updates&utm_medium=email&utm_term=0_1708063e0d-8744b32b9d-173413945 and http://www.mississippi-crops.com/2015/01/30/pyrethroids-on-wheat-in-mississippi-does-it-pay/
   For more information on wheat management during green-up contact your local MU Extension office and ask for IPM 1022 “Management of Soft Winter Wheat” or find it on the web at http://extension.missouri.edu/
   DR. ANTHONY OHMES: Regional Agronomy Specialist, University of Missouri


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