Mississippi County

There are four key components to wheat yield and three of them were determined by late jointing: head size (Feekes 3), tiller and head number (Feekes 5-6) and kernel number/head (Feekes 6).  Conditions were favorable for these three components.  Protecting the flag leaf will help with component four.

The nights never got cold enough to affect the wheat during jointing (Feekes 6).  The dry conditions did prompt some application of water in some sandy regions of the county.  Wheat in general can withstand relatively dry soil conditions.  Remember it is the primary crop of the Plains States, which get considerably less rainfall than the Mid-South.  There is nothing wrong with irrigating the sand wheat but those who do not have irrigation should not get too concerned for the time.  Water holding capacity of the soil has a lot to do with need for irrigation or not.  Sand has less water holding capacity than loam or clay, so if we fail to get rain between now and milk stage then kernel size or weight could be affected.

The University of Nebraska has some good information on water management of winter wheat.  Their research indicates that wheat has two peak water use periods fall and late spring.  Once spring green-up occurs, water use gradually increases until late May or early June.  Through these stages, wheat requires approximately 20 inches of accumulated spring rainfall to reach full yield potential. Water usage is highest after flag leaf emergence through flowering because this is when the plant has the greatest leaf area therefore is transpiring more water, which is lost to the atmosphere, and is preparing for grain fill.  So making sure there is adequate soil moisture for this stage is critical.

In general, to avoid stress only 60% of the water held by a particular soil should be used.  Recharge should occur if less than 40% of available soil water is left.  University of Colorado has developed a guide that can help determine approximately how much soil water is available.  For a coarse, sandy loam soil 25 to 50 percent water is remaining when the soil appears dry and will not form a ball no matter how much pressure is used.  For silt loams this would be crumbly but holds together under pressure.  For clay soils this would be somewhat pliable. At these stages it would be good idea to monitor your crop and prepare to water if rain is not in the forecast.  Generally silt loam and clay soils do not need to be irrigated because they have a high enough water holding capacity.  Adequate moisture would be when soils hold together making a ball under pressure.

Warm, wet or humid conditions are favorable for disease development and spread.  Septoria leaf blotch and tan spot will start on lower leaves and move up the canopy under favorable conditions.  Arkansas has had rust outbreaks but no reports in the Bootheel.  Check your wheat regularly for diseases.  If they are present and conditions are favorable for spread you may want to consider a fungicide application.  If an application is planned remember that various products have wheat stage restrictions.  Some of products are labeled up to Feekes 10.5 or flower emergence.  Waiting too late under favorable disease conditions could reduce flag leaf efficiency.

Corn Replant Decisions

Cool and/or dry conditions could have slowed some corn emergence or has caused sporadic emergence.  With the warm temperatures experienced this weekend and hopefully a good rain shower by the time this article appears the corn planted will be emerging and greening up.  I received a call about a plant stand.  If you are questioning a stand then MU Guide 4091 may help.  The Replant Decision guide is based on research of yield of various stands and planting dates.  Determine plant population/acre by counting plants in 17’5” of row for 30”rows then multiple by 1000.  Plant populations of 20,000, under normal conditions, can lose 6% of normal yield.  Below 18,000 have shown to lose more than 10% of normal.  Uniform stand loss versus sporadic stand loss should also be considered since corn can compensate for neighboring rows.  There are several other factors to consider when making these decisions such as replanting date, cost of replanting, and revenue from sparse stand versus revenue using listed factors of replant.

Soybean Planting

Soybeans were going into the ground in early April in Arkansas and Mississippi.  This was a concern due to the physiology of the soybean plant which is affected by photoperiod.  I talked with Dr. Grover Shannon about early planting and the risks.  

In general, early planting reduces plant height because of the shorter days which can induce flowering and reduce height.  Also plants do not grow quite as well because of cooler nights and days which reduce height.  Early planting of early varieties can increase photosynthesis during the reproductive phase because they are flowering and filling pods during the longest daylight hours during the summer June and July.  Usually Group IV and earlier are indeterminate.  Group III and IV only attain about a third of their height when flowering begins unless they are planted very late in which they will grow a lot less.  Group Vs are usually determinate because they usually flower later in the season which allows them to get good growth.  Determinates usually have attained 50% or more of their growth when they begin to flower.  Flowering in soybeans is controlled by day length.  Group III varieties will flower during our long days or shorter nights, but group Vs need a longer night (usually late July to August when nights get longer) to induce flowering.

Planting date affects harvest date. Late group IVs and Vs can be planted anytime, given there is enough time for development before a killing frost. A cut off date for IIIs and Early IVs should be up to about June 1 and no later.   

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		University of Missouri Extension Mississippi County mississippico@missouri.edu Updated 05/24/04