C.O.R.N Newsletter 2008-08

Crop Observation and Recommendation Network

April 7, 2008 - April 15, 2008

Nitrogen Concerns in Wheat - Edwin Lentz, Robert Mullen

            Producers still have time to apply their spring topdress of nitrogen. Ohio State University research has shown that yields are not affected by delayed nitrogen until after early stem elongation (generally the end of April). Studies over the last five years have shown that yields were the same or slightly better when a single application occurred at Feekes 6 (first node visible of early stem elongation) compared to initial greenup. Yields dropped 10 ­ 15% when a single application was delayed to early boot stage. At this time, we would recommend producers to apply N as soon as field conditions allow application equipment and that there is no need for more expensive aerial applications. Since we are applying N between initial greenup and early stem elongation, any nitrogen source would be appropriate, so selection should be based on cost and availability.

            Some producers who had applied N in February have asked whether there are any tests they may use to check the N status of their plants at this time (concerns that the N may have been lost). Unfortunately there are no definitive tests. Tissue analysis is a relative test and not a procedure used to make N recommendations. A producer may topdress a wheat strip in a field with extra N now and then later use a chlorophyll meter to compare to the rest of the field at early stem elongation. The meter will qualitatively detect differences and assist in a best guess look. However, even if a significant different green color is observed or detected, a producer will not be able to determine how much more to apply based on research information.

Alfalfa Weevil - Ron Hammond, Andy Michel, Bruce Eisley

            As we enter the spring months where we hope to see some warmer temperatures, we need to remind alfalfa growers that the time for scouting for alfalfa weevil is close. The need for scouting is when heat unit accumulation beginning from January 1 reaches 250- 300 heat units (HU). This time period is when we begin to have weevil egg hatch and start to see feeding. Growers in southern Ohio will see this sooner than those growers in central and northern Ohio. Remember that fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier. As of April 7, southern locations are around 235 HU, central and northern sites are near 125 and 100, respectively. Thus, we would recommend that growers in the southern third of Ohio begin sampling this week, while those in the central and northern thirds begin in the coming weeks. We will update heat unit accumulations in the coming weeks in this C.O.R.N. newsletter.

            Alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. When alfalfa is 16 inches in height and there are more than 4 larvae per stem, early harvest is recommended. See the OSU Alfalfa Weevil FactSheet http://ohioline.osu.edu/ent-fact/0032.html for more on alfalfa weevil scouting and thresholds. For insecticides that are labeled for alfalfa weevil, see http://entomology.osu.edu/ag/545/aiaw.pdf. Remember that it is still too early to scout for potato leafhopper since they do not move into Ohio until May.

Preplant Herbicide Applications - Jeff Stachler

            Spring has sprung! Summer annual weeds such as giant ragweed, lambsquarters, Atriplex, and prostrate knotweed have started to emerge in central Ohio. The emergence of these weeds increases the need for appropriate preplant (burndown) herbicide mixtures in no-tillage crops. With few preplant herbicides applied to date due to cold and wet soil conditions, questions are being asked about the importance of 2,4-D in preplant herbicide applications. Because of the prevalence of dandelion and glyphosate-resistant weeds such as giant ragweed, marestail (horseweed), common ragweed, and lambsquarters in Ohio no-tillage fields, the addition of 2,4-D in preplant herbicide applications is very important in achieving effective weed control prior to planting. At this point in the season, it is more important to include 2,4-D in preplant herbicide applications and to  delay planting of corn and soybean rather than planting the crops and controlling weeds after planting. We will continue to monitor weather conditions and weed populations and recommend appropriate preplant herbicide  mixtures as the season progresses.

Consider Controlled Traffic for 2009 - Randall Reeder

            Farmers who have established a controlled traffic system have a huge advantage this spring. For the majority of farmers who don¹t have controlled traffic, this may be the perfect year to make plans to transition into controlled traffic for 2009.  If a farmer already has, or is planning to invest in, a RTK autosteer system, then controlled traffic is a natural companion that can help maximize the return from the autosteer system.

Advantages include:

            Firm tracks to drive on. The benefits for this spring would include timely N application on wheat and earlier corn planting by at least a day or two. Later in the year, consider the value of timely application of pesticides and harvest. Firm tracks give better traction and minimize the risk of getting stuck.

            Minimized compaction. Driving on permanent lanes keeps heavy wheel traffic off most of the soil where roots are growing, including all corn rows. With compaction under control, continuous no-till will be more economical.

            Reduced input costs. With precise autosteer and permanent lanes, benefits include reduced costs for fuel, labor, seed, pesticides and fertilizer.

Disadvantages:

Are mainly confined to upfront costs of getting all equipment to match the primary width and wheels to line up in the desired tracks. If the change is done immediately, the costs might be substantial. But if carried out over a few years as equipment is traded in, the extra cost will be minimal. Efficiency of small grain and soybean harvest may drop slightly.  Perhaps the most persuasive argument for controlled traffic is in the answer to this question: do you wish you already had it?

Fall Anhydrous Ammonia - Should You Be Concerned? - Robert Mullen, Edwin Lentz

            Some producers are wondering how much, if any, of their fall applied nitrogen has been lost. Fortunately we have a rather cold winter, and if fall application was made to cool soils (<50 F) as anhydrous ammonia, then losses are most likely minimal up to this point. The real question is how much loss potential are we looking at this spring? This is difficult to foresee, but with soils warming and more rainfall in the forecast nitrogen loss may be something producers face.

            If nitrogen was applied after November 1 with an inhibitor, losses are likely to be minimal. However, this inability to predict the potential loss is one of the reasons Ohio State University does not recommend fall applied nitrogen.

            Now the question is how do you identify if additional nitrogen will be needed this spring? Presidedress soil nitrate test (PSNT) is one tool that could be used to assess soil nitrogen supply. Soil samples should be collected in mid to late-May to a depth of one foot. Fields with nitrate levels greater than 25 ppm are unlikely to respond to additional nitrogen, but fields with less than 25 ppm may require additional nitrogen input. The rate of nitrogen applied should not be greater than 70 pounds per acre (if PSNT is less than 25 ppm). Tissue testing can also be used to evaluate the crop during the growing season. The only thing to be cognizant of is the potential influence of the growing environment. If it is a cool and dry, or exceptionally wet spring, tissue testing may reveal a deficiency that is not related to soil nutrient availability. The presence of the deficiency is due to adverse growing conditions.

            An alternative tool that may be useful to evaluate fall N programs is the establishment of a nitrogen rich test strip. Typically 100 pounds of N per acre are applied in a small strip (applicator¹s width) to compare with the rest of the field. This visual comparison may help answer nitrogen availability questions throughout the growing season.  Keep an eye on your corn and be ready to act if necessary.