Mississippi County
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University of Missouri Extension Crop Update
5/1/2008
Purple Corn
David Dunn Soil Testing Lab Manager, Delta Center 573-379-5431 (dunnd@missouri.edu)
Compared to Nitrogen and potash, phosphorus does not move much in the soil. Feeding roots must continually grow into new zones. Phosphorus does not move very fast or far with soil water solutions. That is why sometimes corn plants will show a purple color early in the season. Purple corn sometimes develops during a wet cool spring. Let’s take a look at the factors that can lead to purple corn.
If there is adequate available phosphorus in the soil, rapid strong root growth is the key to preventing purple corn. Phosphorus deficiency is more prone to develop on heavier soils. Root growth is slow and shallow, not covering enough area to access the phosphorus it needs. In no till soils the surface layer may be depleted in phosphorus. Heavier soils restrict root growth limiting access to new areas of phosphorus. Soil compaction may also limit root growth. You may not have had an opportunity to work your fields this spring. The extra time and expense of a tillage trip may pay off.
The soil chemistry following flooding may also limit soil phosphorus availably. My studies of in rice soil showed that immediately after the flood was removed phosphorus availability was low and progressively increased during the fall and winter. With all the rains and standing water some fields that tested OK for phosphorus last fall may suffer from low phosphorus availably this spring. Once again tillage could help by increasing soil aeration.
Some corn varieties are more prone to visual symptoms than others. It is a good idea to ask your seed rep if the variety you selected is susceptible.
If you have purple corn this year, what can you do? The first thing to do is determine if there is adequate phosphorus in the soil for your corn crop. My suggestion is to collect a soil sample from both the purple and the green areas of your field for comparison. Have them tested for basic fertility. If there is adequate phosphorus in the purple area the best thing to do is wait. It will probably grow out of it. In a test on purple corn with adequate soil phosphorus we looked at many options, MAP, DAP, chicken litter, and foliar feeding. Some things yielded a bit more but in the end the untreated area produced 200 bu corn. If the soil test shows a need for additional phosphorus, put it on. Use a more readily plant available form such as MAP, DAP, or liquid 11-37-0. This will assure that that plant can access it quickly.
The other soil factor to consider is soil pH. Low soil pH will limit the plants ability to utilize phosphorus. If the soil under your purple corn is low in pH consider liming as soon as possible. My studies have shown that lime applied in the spring can increase yields this fall.
What about foliar feeding purple corn? Generally foliar fertilizers are expensive. But with $6.00 corn what’s expensive? It is difficult to find foliar phosphorus products that contain more than 1 lb phosphorus per gallon. Putting on more than one or two gallons at one time can burn small corn plants. Read the label carefully and do not apply foliar fertilizers at rates higher than recommended.
These are some of the steps you can take to avoid purple corns this spring.
Purple corn from near Sikeston in 2003. Soil tested adequate for P and pH (69 lb P/acre and 6.4). Tissue test on Purple was 0.15% P, green was 0.26% P. At this stage sufficiency is 0.25% P. MAP, DAP, chicken litter, and foliar feeding were compared to untreated check for thew purple corn. In the end the untreated still yielded 200 bu/acre.
4/11/2008
Wheat:
More rain fell over our area on already saturated soils. Fortunately, this last system delivered much less rain compared to previous rains. I have heard the amount to be around 1.5 inches. However, even a sprinkle is too much rain when fields are already saturated. Much has been asked about the outlook for wheat, unfortunately, when dealing with plants and environmental conditions the answer always centers around the word, “depends”. Producers already know that the outlook is much less favorable than at the beginning of green up, however, no one knows the total loss. Continue to check fields, plan on nitrogen loss via leaching on coarser soils or denitrification on clay soils, in some cases expect both. However, how much loss “depends”. Saturated soils also mean an oxygen depleted root zone. Regardless of the amount of nutrients available, uptake is limited until oxygen levels are restored. Therefore, some yellowing (nitrogen deficiency) is a symptom of lack of oxygen, not lack of nitrogen. If you are questioning how much nitrogen is needed for your wheat or the time frame for available nitrate nitrogen from nitrogen sources, I again reference David Dunn and Peter Scharf’s article at: http://extension.missouri.edu/mississippi/nitrogenandfloodwheat.shtml. Keep in mind wheat’s peak nitrogen demand is during internode elongation, Feekes 6 through Feekes 8 (approximately 10 – 12 inches of growth). After that point uptake from the soil begins to slow and demand on the plant itself begins for head development.
Too Late to Lime?
David Dunn
With all the wet weather this spring farmers are behind in field preparations. In the next two weeks corn planting should be well underway, but lime and fertilizers still need to be applied. In order to get everything done producers will have to prioritize field work and budget their time wisely. One of the items I would not skip this year is lime. Anyone who has been to the fertilizer dealership recently knows that N-P-& K are more expensive than ever. Also, as the cost of fuel has gone up, so has the delivered cost of lime. But lime is still a good deal. The lime you apply this year should be active in the soil for the next three years. At $25 per ton and one ton per acre that’s about $8.00 per year. How many bushels of corn does this represent? Of course the amount of lime you need to apply will depend on your soil test. The ideal pH range for corn is 6.0 to 6.5.
One of the questions that I am frequently asked in the soil lab is “Will lime applied this late in the year help this year’s corn crop?” My answer is that when soil pH is below 4.8 conditions toxic to growing plants exist in the soil and lime will increase yields. If the pH is between 4.8 and 6.0 low pH limits the availability of P and K to the growing plants. At this pH level lime will not increase yields if sufficient P and K are in the soil. At pH levels above 7.0 nutrients like phosphorus, zinc, boron, and copper become less plant available. Lime should not be applied in such situations. Soil testing is the key to your liming decisions.
In a study performed at the University of Missouri-Delta Center two types of lime were compared to an untreated check. Red and white lime was applied to a pH 4.8 soil at the recommended rate. The lime was then incorporated with tillage and cotton was planted. The pH was checked at two-week intervals. Within two weeks the white lime had increased soil pH to over 6.0. The red lime achieved this level within three months of application. See figure 1. While both types quickly increased the soil pH out of the toxic level the white lime increased the pH more. Cotton lint yields were increased by over 100 lbs./acre for both types of lime. In this study liming just before planting paid for itself the first year.
What about pelletized lime? It is often sold at a steep premium as a quickly acting lime product. Delta Center studies have shown that when pell lime is used at equivalent effective rates as ag lime the effect on soil pH and yields is the same. However a ton of pell lime costs much more than a ton of ag lime. When the same dollar amounts of pell and ag lime were compared, ag lime won hands down. In 2006 several rates of pell and ag lime were compared as a rescue treatment applied post planting to corn growing in 4.9 pH soil. Given an ag lime cost of $25/ton and a pell lime cost of $125/ton both a ton of ag lime and 400 lb of pell lime will cost $25. Comparing these two rates, the ag lime produced 123 bu while the pell lime produced 103 bu.
This year corn producers will have to make difficult choices. My best advice is to assemble all the information available before making decisions. Lime, if needed, should not be left out of a profitable farming operation.
Figure 1. Soil pH for lime treatments measured at two-week intervals on an acid soil at Portageville, MO.
3/27/2008
Wheat:
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.
3/19/2008
Wheat:
Wet feet! Southeast Missouri has received its fair share of water over the last 24 hours. Winter weather has delayed development of the crop compared to this time last season. This delay may help get through this current stress a little better than if the plant was in peak nitrogen demand, which occurs during internode elongation, between jointing and flowering. Continue to monitor your wheat as we enter this phase of development for nutrient deficiency symptoms. As far as water standing over a wheat plant, level of damage is dependent on stage of development, temperature and length of time. Periods of large rainfall remind us about the importance of selecting well drained fields. Take the opportunity over the next several days, as water recedes, to evaluate the drainage in your fields and make plans to repair those problem areas when the opportunity comes around.
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.
Corn:
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 continous, uninterupted use of the same mode of action over an extended period of time.
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University of Missouri Extension Mississippi County mississippico@missouri.edu Updated 05/24/04 |
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