C.O.R.N. to go....


A Supplement to the OSU Extension Agronomic Crops Team Online C.O.R.N. Newsletter ~ This version for Ohio’s Country Journal is by Harold Watters Harold Watters can be reached in the Logan County Extension office, at watters.35@osu.edu or by phone 937-599-4227.


Ahead of the game this year I looked over the Ohio Crop


Weather Highlights from the National Ag Statistics Service in mid-April and it says we are already 10 days ahead of last year for days available for field-


work. Personally I have the field tile I planned to install this summer already in, but that was almost taken off the table because I did not get any wheat planted last fall. There has


been more tillage than I expected, but then with the string of dry days since March, maybe not as much as could have been done certain- ly, so I congratulate you all on showing


some restraint. Concerns for early May come


from three areas — the cold soils after planting, wheat, and nutrient management.


Impact of low temperatures on corn survival from OSU Extension Corn Expert, Peter Thomison


It’s time to determine how early plant-


ed corn fields responded to recent cool weather, the effects of the low tempera- tures on corn survival will probably be negligible for the most part. In past years, we have observed that early plant- ed corn that was in the process of germi- nating or as far along as the V1 stage (one leaf collar visible) survived freezing soil temperatures in April with little impact on crop performance or plant stand. Agronomists generally downplay the impact of low temperature injury in corn because the growing point is at or below the soil surface until V6 (six leaf collars visible), and thereby relatively safe from freezing air temperatures.


Moreover, the cell contents of corn plants can sometimes act as an "antifreeze" to allow temperatures to drop below 32 degrees before tissue freezes, but injury to corn is often fatal when temperatures drop to 28 degrees or lower for even a few minutes. Effects of low temperatures on germina-


tion are far more serious when combined with snow and freezing rain as in 2005. When dry corn seed absorbs cold water as a result of a cold rain or melting snow, “imbibitional chilling injury” may result. Cold water can cause similar injury to seedling structures as they emerge during germination. Such injury in corn seed rup- tures cell membranes and results in abort-


ed radicles, proliferation of seminal roots, and delayed seedling growth. When tem- peratures remain at or below 50 degree after planting, damage to germinating seed is particularly severe. When this physiolog- ical damage is combined with surface soil crusting, saturated soil conditions, com- pacted soils, deep seed placement, and seedling blights, you have a recipe for widespread emergence problems. To assess the impact of freezing temper-


atures on emerged corn, check plants about 5 days after the freezing injury occurred (and preferably when growing conditions conducive for regrowth have occurred). New leaf tissue should be emerging from the whorl. You can also


observe the condition of the growing point (usually located a half-inch to three-quar- ters of an inch below the soil surface) by splitting seedlings lengthwise. If the grow- ing point appears white to light yellow and firm several days after the frost, prognosis for recovery is good. For some pictures of low tempera-


ture injury to corn check out the fol- lowing article by Dr. Bob Nielsen at Purdue University Nielsen, RL (Bob). 2001. Symptoms of


Low Temperature Injury to Corn and Soybean. Corny News Network, Purdue Univ. online at http://www.kingcorn.org/news/arti- cles.01/Frost_Corn_Soy-0418_Gallery.html


Wheat disease monitoring from OSU Extension Wheat Specialist, Pierce Paul We follow growth stages of wheat to


know when to apply herbicides safely but also to know when, or if, we should apply fungicides. Growers who rely on the height of the crop as an indicator of crop development may miss Feekes Growth Stage 6, a critical growth stage for herbi- cide application, and Feekes GS 8, a critical stage for managing foliar diseases with fungicides. Do not rely on the height of the plants or calendar dates alone to make your management decisions. Walk fields, pull tillers from multiple places, remove the lower leaves, and examine these tillers for the presence of nodes and the emer- gence of the flag leaf. At Feekes GS 8 the tip of the flag leaf, the fourth leaf above the first node, is visible. Plants of different heights and sizes may all be at the same growth stage. Feekes 8 marks the begin-


ning of the period during which we recom- mend that field be scouted to determine which disease is present and at what level. Septoria blotch is usually one of the first


to show up, and it already has been report- ed in some fields. This disease is favored by cool (50-68 degrees), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete. Like many other foliar diseases such as Stagonospora, Septoria reduces grain fill and the size of the grain. It usually does not affect the number of spikelets per spike, an impor- tant yield component that is defined very early in the development of the plant (before Feekes 6). As a result, a foliar fungi- cide application at green-up or jointing is less likely to be as beneficial for Septoria


Nutrient management Determining rates of phosphorus fertil-


izer for corn and soybean is fairly simple. Most of us have soil test P levels in the maintenance range or higher (74% of Ohio). That means we may apply fertilizer rates based on crop removal. The critical soil test level P for corn and soybean in the tri-state area is 15 parts per million (ppm). The top end of the maintenance range is 30 ppm. Meaning that if your soil test P results are between those two limits, then you need only apply maintenance levels. Above 30 ppm, you can reduce or elimi-


nate P2O5 applications for a while — and judging from calls I have received since last month’s column “a while” may mean 10 years or more. From the Tri-State Fertilizer


Recommendations for Corn, Soybeans, Wheat and Alfalfa (on-line at http://ohio- line.osu.edu/e2567/), maintenance appli- cations are determined by the equation: • Pounds of P2O5 to apply = YP (yield


potential) times CR (crop removal). For corn grain crop removal is 0.37


pound per bushel 14 Ohio’s Country Journal • ocj.com • May 2012


and Stagonospiora control as an applica- tion made at or after flag leaf emergence. An early application will certainly control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, but the residual effects of the fungicide will not adequately protect the flag leaf. If the weather conditions con- tinue to be rainy and favorable for foliar disease development, spores will continue to be produced or blown in from other areas, and new infections will occur, even after early applications have been made. In addition, frequent rainfall may also reduce the residual effects of the early fungicide applications, making them even less effec- tive against mid- and late-season foliar dis- ease development. Results from university studies have


shown that the greatest benefits from foliar For soybean crop removal is 0.80


pound per bushel So for the average Ohio corn yield of


160 bushels per acre: • Crop removal is 160 x 0.37 = 59


pounds of P2O5 per acre For an average soybean yield of 50


bushels per acre • Crop removal is 50 x 0.8 = 40


pounds of P2O5 per acre With a two crop rotation, we could


apply 100 pounds of P2O5 every other year to meet the needs of both corn and


fungicide applications were obtained when applications were made between Feekes 8 and 10. This is largely because most of our major foliar diseases usually develop and reach the flag leaf after Feekes 8-9. There are several different fungicides


available for use on wheat. If powdery mildew is the target disease then Tilt or PropiMax should be applied. Tilt, PropiMax, Quadris, Quilt, Stratego, and Headline have good efficacy against Stagonospora leaf blotch, other leaf blotch diseases and leaf rust. Obtain cur- rent pricing of fungicides to determine the most economical control option. Use 20 gal water/A with ground equipment and 5 gal water per acre if applying by airplane. Using less water will lower effectiveness. Check labels for applica- tion timing restrictions.


soybeans. Of course, we continue to soil test on a regular basis to make sure that our calculations hold true. Harold Watters, Extension Field


Agronomist, works out of the Logan County Extension office and can be reached at watters.35@osu.edu or by phone at 937 599-4227. Further informa- tion can be found on our Agronomic Crops Team webpage: http://agcrops.osu.edu. To find an Ohio State University Extension office: http://extension.osu.edu/locate-an-office.


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