Testing for Nitrogen in the Soil
Delta Regional Soils Testing Lab can give you an answer as to how much Nitrogen
the soil contains. This special soil test can determine how much nitrogen is
still available in both the nitrate (NO3 ) and ammonia (NH4)
form and the results compared to the pounds of Nitrogen applied.
From each field, a pint to a quart of soil is needed and the sampling depth should be from the top 12 inches. The cost is $7 per sample and the turn around time is 2 – 4 days. (cost and turn around time will vary with each extension office). Contact the Scott County Extension office for more information, 545-3516.
Flooded Wheat Fields:
Questions have been coming in about flooded wheat fields. Wheat, like most plants, can tolerate water to a point. In general, damage depends on stage of crop, how long water stays, and temperature. In many cases, 48 hours is a bench mark for crop injury potential. Plants with water over the top for less than 48 hours will usually recover. Water that has been over a plant for more than 48 hours may or may not cause damage. In the short term, continue to check plants in a field for a healthy growing point by finding the node, splitting the stem at the node, and looking at the small wheat head with a hand lens. The small wheat head should appear healthy with a light greenish-yellow color. Like any stressful event, it takes time for a plant to show signs of recovery or complete loss.
Low spots in fields are displaying some yellowing. This is due to oxygen depletion in the root zone and/or nitrogen loss. David Dunn and Peter Scharf provided some information on nitrogen’s behavior in soils after a large rain event. Their information can be found at the following link: http://extension.missouri.edu/mississippi/nitrogenandfloodwheat.shtml.
In summary of
their report, the biggest factor in nitrogen loss is how much of the soil
nitrogen was in the nitrate form compared to the ammonium form. Nitrate is
mobile and ammonium, until converted to nitrate, does not move through the
soil. For example, urea is vulnerable for the first 3 days following
application, and then it is safe for 10 days (ammonium form), and then after 14
days is vulnerable again (nitrate form). Producers can check nitrogen levels in
the soil by sending soil samples to the Delta Center Soils Lab. Sampling is
outlined in the above link. Tissue testing at this early stage would not
provide a complete picture since most wheat is just beginning to joint which
means that rapid uptake of nitrate is just beginning.
The wheat I have looked at is from Feekes 5 (leaves and leaf sheaths erect) to Feekes 6 (first node of at base of stem visible). Some wheat in areas south may be further along than this. Feekes 6 is the cut off for herbicides with hormone imitating modes of action, such as 2,4-D and dicamba. Feekes 6 or later applications of these chemicals may result in crop injury. Harmony Extra is still a choice for later stage applications, check label for rates and weed control spectrum.
Cool, wet conditions also increase the potential for stripe rust which can occur earlier in the season compared to other rusts. As the name implies, the yellow to yellowish red pustule stripes of this disease run parallel with the leaf. Southeast Arkansas has reported some stripe rust near the border of Louisiana. Keep in mind, as a general rule, rust fungi do not survive our winters, so must move up from the south each season. Therefore, carefully scout for these diseases prior to making early season fungicide decisions based solely on weather. Consider the disease tolerance of your variety, also.
As we await good planting weather, evaluate your field history of seedling disease and insects. When making decisions on seed treatment fungicides, consider the fact that individual fungicides have strengths and weaknesses. I ran across an article by Dr. Paul Vincelli, University of Kentucky Plant Pathologist, on some research out of Ohio State University on Pythium. Pythium species are the primary cause of seed rot and damping off in corn, especially in cool, wet soils. Researchers evaluated six different Pythium species found in soil which all feed on corn at some level. The research indicated that the Pythium species responded differently to the various chemistry available. This suggests that soils may possess different species and selecting one chemistry may only provide partial protection. Therefore, consider your field’s history as related to soil borne organisms, soil conditions at planting and seed treatments available. The following is a link to the article: http://www.uky.edu/Ag/kpn/kpn_08/pn080225.htm
Some growers have experienced some loss due to corn rootworm larvae in Southeast Missouri. The Northern Corn Rootworm and Western Corn Rootworm beetles have been primary pests of the corn belt for years. Gradually we have seen these corn belt pests move into Southeast Missouri. However, the dominate rootworm beetle present in Southeast Missouri is the Southern Corn Rootworm (a.k.a. Cucumber) beetle. The Southern Corn Rootworm beetle has a much wider host range and is not considered a primary corn pest. Traditionally, rootworm damage from Western and Northern is identified in continous corn fields due to the host specific feeding of these insects. Crop rotation is still a very good cultural control practice for these pests. There are variants to the Western and Northern beetles that have adapted to overcome crop rotations. The Western variant females will lay eggs in soybean fields in order to have food available for larvae when corn comes into rotaton. The Northern variant has developed an extented diapause where the eggs hatch the second year in order to stay in line with corn/soybean rotations. I do not know of either variant identified, currently, in Southeast Missouri. If you are targeting rootworm larvae this season consider your control source and rates. If you are going with a Rootworm Bt, keep the fields free of grass weeds, especially in no-till or if planting is delayed since larvae could potentially feed on an alternative host and grow past the susceptible size when corn roots become available. Also, pay special attention to refugia requirements since rootworm Bt requirements vary in some respects to that of corn borer Bt.
Johnsongrass added to glyphosate resistant list.
If you have attended a winter meeting within the past 5 years, you have heard some talk on resistance management. Recently, in the U.S. we as extension specialists and researchers have focused concerns over glyphosate resistance. The first weed failure to touch producers in Southeast Missouri was horseweed (a.k.a. marestail). Other weeds identified in Missouri and/or surrounding states include: waterhemp and Palmer amaranth (pigweeds); giant ragweed; and common ragweed. The newest addition to this list is johnsongrass. Johnsongrass has been identified in both southeast Arkansas and Clarksdale, Mississippi as resistant to glyphosate. The news release can be read at the following site: http://monsanto.mediaroom.com/index.php?s=43&item=580
As with almost all cases of resistance throughout the short history of herbicide weed control the number one common factor is continuous, uninterrupted use of the same mode of action over an extended period of time.
Anthony Ohmes, Mississippi County Extension agronomist, provided the agronomy information. Anthony can be reach at 683-6129.
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