Extension Update by Gary Zoubek [May 17, 2012]

Coming Events

Cropping Update/Nebraska Weather

Planters have continued to make great progress getting the corn and soybeans planted.  A couple of the corn fields that I’m monitoring are in the 3-4 leaf stage and the RoundUp Ready plot that we planted May 4^th is up with the set of first true leaves! Did not receive much rain, but crops are not using a lot of moisture yet!

For the past week March 7^th-March 13^th, the ETgages located East and South of York dropped an average of 2.00” for the week!  Last Thursday with temperatures in the low 90’s and considerable wind, I’m sure was the big ET or evapotranspiration day for the week, but with the corn in the 3-4 leaf stage, the actual crop water use for corn was much less that 2”.  The crop Coefficient for 4 leaf corn is .18 while for 6 leaf corn it is .35.  We don’t count all the leaves when can see when we are staging the crop, we don’t count it as a leaf unless we can see the exposed collar or that area where the leave attaches to the stalk!  The first leaf has a rounded tip!  As I mentioned the two fields I’m monitoring year the ETgages are in the 3-4 leaf stage, so we multiple the ETgage change for the week times the crop coefficient of .18 for 4 leaf corn and the crop has used about .36” for the week or .05”/day!  If the crop was in the 6 leaf stage the crop water use for the week would have been .35 x 2.0 or .7”/day or .10”/day!

The earliest planted soybeans would have been using about the same amount of water as 4 leaf corn, but unless it’s extremely dry we don’t recommend irrigating soybeans in our area until the R-3 stage.  That’s because in our area we have great silt loam soils that hold an average of 2.0” to 2.2” of water per foot of profile and we can typically use water from the top three feet of the soil profile.  We generally say that we can us about half of the soil water with no effect on crop yields so that is about 3 to 3.3” of water that we’re starting the season with!

This past week I also put out an ETgage that has a #30 or grass cover rather than the alfalfa cover that we use for estimating crop water use.  In addition to sharing corn and soybean crop water use estimates I’m hoping to share estimates for well watered grass.  I set it out Thursday morning, so I don’t have a complete week of data, but my estimate is that it dropped between 1.3” and 1.4” for the week or about .20”/day.  Grass water use will be about the amount the ETgage drops each week!

Since I shared info about ETgages last week, this week I want to share information about soil water monitoring and Watemark Sensors.  With an ETgage we can estimate crop water use, while the Watermark Sensors estimate the amount of reserve you have in your soil profile.  When it hot and dry, the wind is blowing and the soil surface is dry we often get the urge to not stress the crop and irrigate, but we may have plenty of moisture at the 6” or 1’ or 2’ depth.  There are several different types of soil water monitoring equipment, but the two most common types are resistance and capacitance probes.  The Watermark sensors measure the energy required to remove the water from the soil.  The drier the soil, the more resistance or energy is required.  We’ve developed charts to estimate what those readings exactly mean!

We generally recommend that we install the sensors in the filed early in the season before the crop is too tall.  We install them at 1’, 2’, 3’ and in some case 4’ depths!  We’ve glued the sensors to plastic pvc so that we can remove them at the end of the season and use them for several years.

Before we install them for the first time we soak them in water, let them dry 24 hours, soak and dry them again twice.  We then install the sensors wet; which improves the response time for the sensors.  By installing them early in the season in a representative part of the field, you will have another tool to make irrigation management decisions with!  Many NRD’s and now the NRCS has excellent programs to encourage the uses of these tools!

Contact Dan at the Upper Big Blue NRD or me if you’d like more information about either ETgages or Watermark Sensors!  We’ll be out and around installing them in new cooperators fields the next couple of weeks!

For more info about ETgages and Watermark sensors, check out the NAWMN website: http://water.unl.edu/web/cropswater/nawmdn.  Check out the Extension Circular “Watermark Granular Matrix Sensor for Measuring Soil Matric Potential for Irrigation Management” and NebGuide  “Using Modified Atmometer (ET) for Irrigation Management”.  We also have videos on how to install and use these tools along with growth charts for estimating the various crops stage of growth and water use as well as charts that estimated the soil water depletions for various Watermark Sensor readings for various soil types.  We’ve ran may soil water retention curves for our soils and have prepared charts that can help you know how much water we have remaining in the soil profile depending upon the soil type.  It’s important that you know your soil type since a given reading for one soil type will indicate adequate soil water, however if it’s a different soil type you may be out of wate!

Finally another good website to estimate your soil water status for soybeans is SoyWater:  http://soywater.unl.edu.  At this website you can provide the legal description for your field, planting date or better yet emergence date and soybean maturity class and SoyWater will estimate your crops various stages of growth and water uses using weather data from the nears automatic weather station.  I’ve been using it the past couple of years and it does a great job!   and other information and it will tell you your soil type as well as estimate your soybean crops stage of maturity and water use.  It will do a great job of estimating when your crop will be at R3 and estimating what the soil water status is.  It may not be as good as and ETgage of Watermark sensors in the field, but the next best thing!  Check it out this season with a field or two and see how you like it?  Let me know if you have any questions!

Yard and Garden

I’ve received a few questions about powdery mildew in lawns and in fact have it in some areas of my lawn that don’t have good air movement or are on the north side of the my house and a spruce tree!  Typically it does not do major damage to turf and is a relatively minor disease in shaded turf and is seldom seen in areas of full sun.  This disease rarely causes more than a cosmetic whitening of the grass blades. Eliminating shade and improving airflow are most effective control methods, but are typically hard to accomplish.  Another option would be to introduce shade tolerant varieties of Kentucky bluegrass or tall fescue would this fall in those areas troubled by the disease.  The powdery mildew on turf will not harm children or pets playing in the yard and will not threaten other land-scape plants — the pathogen that causes powdery mildew in turf cannot infect other plants.

We typically don’t recommend fungicide applications for this disease, but if the appearance of mildew-infected turf is absolutely intolerable, fungicides may be applied for effective control.  DMI class fungicides (metconazole, myclobutanil, propiconazole, tebuconazole, triadimefon, and triticonazole) are most effective in controlling powdery mildew.

More information about Powdery Mildew on turf can be found in our NebGuide: http://www.ianrpubs.unl.edu/epublic/live/g1911/build/g1911.pdf or in the following Purdue publication:

http://www.ces.purdue.edu/extmedia/BP/BP‐111‐W.pdf.

I’ve also received a couple of questions about a disease known as Ascochyta leaf blight.  Typically this is a disease seen in Colorado, but not much in Nebraska, but I’ve seen it here in York several times.  It shows up as small or larger areas of grass that turn straw-colored from the tips down.  Some time it appears as if the mower damaged the tips!  The symptoms may appear anytime, but its more common during hot, droughty periods that were preceded by cool, rainy conditions.  What causes the condition is not well understood, but frequent mowing and dull mower blades may contribute to disease severity by creating more infection sites (wounds).

Some management tips will include following good cultural practice that minimize stress to the turf.  Maintaining grass between 2.5 – 3.5”, maintaining sharp mower blades, avoid mowing during wet weather, maintaining a balanced fertilizer program and maintaining uniform soil moisture.  Since Ascochyta blight is primarily a leaf and not a root or crown disease, it rarely causes plants to die.  The turf will typically recover after a few weeks.  For information about this disease, check out the Colorado State publication: http://www.ext.colostate.edu/pubs/garden/02901.html.

Finally for the latest horticulture information, check out the Back Yard Farmer webpages: http://byf.unl.edu/.  At this site you can view many different videos, as well as check out the latest horticulture updates as well as acreage information!  It’s loaded with lots of research based information!