Field Crops Notes Spring 2014

Steve Gibson, Extension Agent, Agriculture Cleveland, Lincoln, Catawba Counties

Last growing season we had sulfur deficiencies in our wheat and later in corn.  Many of you reacted for this season but if not please try your best to take soil samples.  Some private labs do not run sulfur but the NCDA lab does.   Also last growing season we had potash deficiency symptoms show up in soybeans.  Soybean harvest removes from the soil 1 ½ pounds per harvested bushel so two good crop years in a row of 40 bushel beans has removed 120 pounds of potash!   If last year you noticed areas in your fields that had soybeans with the edges of leaves yellowing and even drying up and dying, then very likely your problem was low potash.  I did problem area samples in all 3 of the counties and this situation was verified.  In all cases potash was higher at 0 to 3 inches verses 3 to 6 so leaching was not the main problem.  Potash can leach but for the most part only in our sandiest fields.

Nitrogen management remains an ongoing issue.  As good as our corn yields were, I still noticed many, many fields showing nitrogen deficiency symptoms.  The urea form of nitrogen unfortunately is subject to losses due to nitrogen volatilization.  If you would like more information on how to reduce losses please give me a call (704-487-4228.)  This problem will not go away!  I remember comparing nitrogen sources shortly after I started work in 1979 and the urea forms were not near as efficient since losses were prevalent.

Tuesday I looked at some wheat in SC just south of the state line.  I used a sweep net and sampled for cereal leaf beetle adults.  Normally at this time of the year the net would have many but the most adults I got in 50 sweeps were only 2.  This year our growing degree days have not been sufficient to bring this pest out of the overwintering sites but it should happen soon.

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I know many of you treat about this time of the year but please hold off until you find or observe large numbers of adults in the fields.  Better yet to follow the IPM principles it will be best to sample fields for the damaging form of this pest, the larvae.  I know one chemical company was offering a guarantee that an early treatment prior to larval development would work, but this year a treatment now of even the most residual insecticide will not last long enough.   Prior to the widespread adoption of the early application approach we had several years of very light cereal leaf beetle pressure.  By now the parasites that were released have no doubt become better established and I remember that one of them, a tiny parasitic wasp of the eggs was more prevalent later in mid spring.

This leads into another factor in wheat production; that of fungicide use.  Work done at many of the universities has not shown fungicide use to be consistent and even in years of heavy disease pressure, wise variety selection for disease resistance is the most important management decision.   One factor earlier was the treatment cost.  However, now a generic triazole will very likely cost less than $3 per acre.  Please check the enclosed variety description table and if you have planted a variety that is susceptible or moderately susceptible to staganospora (SNB), powdery mildew or tan spot, be sure to monitor your fields and consider a fungicide application.  The best approach for using fungicides on wheat for these diseases is to protect the flag leaf and one or two of the leaves below them.  Therefore the best time to treat for us is after the stems have started elongating and plants are at least a foot tall.   Please note that the variety description table also lists head scab.  Fungicide use for this disease that results in high vomitoxin levels in grain is very different from the foliar diseases and the application timing is after the crop is in the heading stage.  For me this is frustrating because if I get a disease alert by the time I can send a letter out and you get it, it will be too late for you to respond.  I plan this year to call and spread the word perhaps through our agri-suppliers so please have this on your mind.

This year very likely the best timing for fungicide applications and for insecticide applications for cereal leaf beetle will coincide so this will be a big plus.  If you would like a copy of a fungicide effectiveness table please call the Cleveland County Extension office @704-482-4365.   Again, please check the varieties you planted for susceptibility to the SNB, powdery mildew and tan spot so you can be ready.  As always please give me a call if I can help.

Below is a picture of Potash deficiency symptoms on soybeans.If you noticed areas in your fields similar to this and have not applied additional potash this will be a yield robbing problem for you. Remember soybean harvest removes from your soil 1 and a half pounds of potash per harvested bushel.

Cereal leaf beetle adult and larvae. (shown below)  The adults do essentially no damage but they mate and lay the eggs for the damaging larval stage.  Adults have a characteristic orange thorax and a blue abdomen.  Tests done earlier in this area showed a 10% yield decrease for one larvae per tiller.

Source : ncsu.edu