C.O.R.N. Newsletter 2008-31

Assessing the Risk of Frost Injury to Late Maturing Corn

Authors: Allen Geyer, Peter Thomison

According to the Ohio Agricultural Statistics Service (OASS), as of September 7, 63 percent of the state’s corn acreage was in the dent stage compared to 76 percent last year and 70 percent for the five-year average. This year’s delay in overall crop development is not surprising given the significant corn acreage planted late. In a May 27 report, the OASS estimated only 64 percent of the crop planted as of May 25 compared to 85 percent for last year and 78 percent for the past five-year average. Delays might have been greater this year if not for the drought stress that has hastened senescence and contributed to premature plant death in many fields. However, in areas of the state where corn is still green and/or in some stage of grain filling, what's the likelihood of frost damage?
Physiological maturity (when kernels have obtained maximum dry weight and black layer has formed) occurs 7 to 8 weeks after silking. At physiological maturity (kernel moisture approximately 30-35%), frosts have little or no effect on the yield potential of the corn crop.
Table 1 shows the average number of calendar days and growing degree days (GDD) required to reach physiological maturity after silking. With average daily high and low temperatures of 80 and 60 degrees F, 20 GDD accumulate each day. At these temperatures, 65 days from silking to maturity are required (1300 divided by 20). With "cooler" high and low temperatures of 75 and 55 degrees, only 15 GDD accumulate daily, requiring more than 87 days from early August silking to maturity.

Table 1. Relationship Between Kernel Growth Stage and Development.

Stage	Calendar Days to Maturity* (days)	Growing Degree Days To Maturity (GDD)
Silk	65	1300
Blister	52	1040
Late Milk/Early Dough	39	775
Early Dent	25	510
Fully Dented	12	250

* Based on average daily high and low temperatures of 80 and
60 degrees F, respectively, during grain fill.

Source: National Corn Handbook. Chapter 40. Growing Season Characteristics and Requirements in the Corn Belt. R.E. Nield and J.E. Newman, 1986.

How many GDD can be expected from now until an average date of a killing frost? To answer this question (approximately), estimate the expected GDD accumulation from September 16 until the average frost date (50% probability) for different regions of the state (Table 2). These GDD expectations are based on 30-year historical normals reported by the OASS. The growing degree day accumulation was calculated using the 86/50 cutoff, base 50 method.
If you want to determine the "youngest stage of corn development" that can safely reach black layer before the average frost date at a given weather station, use the information in Table 2 on remaining GDD in conjunction with Table 1 which indicates GDD requirement to reach black layer at various stages of grain fill. Compare "GDD remaining" for the site with the GDD required to achieve black layer depending on the corn's developmental stage.

Table 2. Estimated GDDs remaining from Sept. 16 to the first fall frost for
Ohio.

Region	Avg. Frost Dates (50% Probability)	Estimated GDD Remaining From Sept 16 to Frost
Northwest	Oct 10 – Oct 20	204 – 254
North Central	Oct 10 – Oct 25	197 – 282
Northeast	Sept 30 – Oct 25	147 – 293
West Central	Oct 10 – Oct 15	225 – 282
Central	Oct 5 – Oct 15	233 – 294
East Central	Sept 30 – Oct 15	158 – 276
Southwest	Oct 10 – Oct 15	240 – 303
South Central	Oct 15 – Oct 20	315 – 367
Southeast	Oct 5 – Oct 15	164 – 227

If your corn is in the early dent stage as of Sept. 16, will it be safe from frost? Probably not, because it needs about 510 GDD to reach black layer based on the kernel development - GDD accumulation relationships indicated in Table 1. Table 2 indicates that there is no region of the state with that number of GDDs remaining until the 50% frost date.
If your corn is in the fully dented stage as of Sept. 9 will it be safe from frost? Table 1 indicates that it needs about 250 GDD to reach black layer from full dent stage and Table 2 indicates that most regions of the state will accumulate sufficient GDD to escape frost injury. The warm temperatures we've experienced recently are helping with heat unit accumulation. Moreover, late planted corn has shown the ability to adjust its maturity requirements. Corn planted in early June compared to early May requires 200 to 300 fewer GDDs to achieve physiological maturity.
Regions in which corn is at greatest risk to frost damage are those with late September/early October frost dates, especially sites in northeast and east central Ohio.
For more on this topic check out the following:
Nielsen, R.L. (Bob). 2008. Late Planted Corn: Enough Time to Mature? Corny News Network, Purdue Univ. [On-line]. Available at http://www.kingcorn.org/news/articles.08/DaysAfterSilk-0729.html

 

Late Season Soybean Diseases

Authors: Anne Dorrance

While you are out looking at corn to see if it is still standing, also take a look at the soybeans this week. We’ve got just about everything out there this year and some plants have more than one!

1. Late season Phytophthora can be found in most fields. Plants are wilted and the characteristic chocolate brown canker is moving up the stem. Many plants are already dead, wilted with the leaves clinging to the plants.
2. Diaporthe stem canker is also present. Here the upper part of the plant is wilted and there is a canker on the main stem at the third or fourth node. You will also find, tiny, round, raised black structures called perithecia of the fungus on the canker. Keep an eye on these fields as harvest approaches, this is part of a complex and Phomopsis seed decay could develop if wet conditions between now and harvest are prevalent.
3. Sclerotinia stem canker – I thought this one had disappeared from the state, but with our cool, wet July it is also present in some fields. In this case plants with Sclerotinia stem canker, also called white mold, are standing straight and tall above the canopy. They are brown and when you look at the lower portion of the stem, white mold or sclerotia will be present. Sclerotia are irregular in shape, similar to rat turds, black but in the middle it is white to pink in color. This is the survival structure of the fungus which will be distributed back to the fields at harvest.
4. Charcoal rot is another root disease caused by the fungal pathogen, Macrophomina phaseolina. Plants will senesce early, I have found this early dying a bit hard to describe - but it will be in pockets and also be in the low lying areas of the field. Water favors infections, but drought conditions really favor disease development. Dig up the plants and look at the tap root and pull back the outer layer of the epidermis. Often, there will be dark lines but the key is a look like pepper was sprinkled on the tap root. These are predominately microsclerotia that are embedded in the tissue and will help the pathogen survive. This pathogen is favored by higher temperatures but I think with the seasonal droughts we’ve had over the past several summers, inoculum may have begun to build up in some locations. This is one to keep an eye on.

Wheat or corn should be planted in those fields that were affected with any one of this diverse group of pathogens. This will prevent rapid build-up of these pathogens in these locations. After that, choose varieties that have resistance to these pathogens. It is becoming more and more important to focus on the partial resistance portion of the resistance package for Phytophthora rather than the Rps gene. Rps1c, Rps1k and Rps3 all have some effectiveness but they still aren’t perfect.

Prepare Grain Bins and Harvesting Equipment Now for Fall Harvest

Authors: Curtis Young

We are now half way through the month of September, and corn and soybeans are maturing rapidly in the fields. The harvest season will soon be upon us. Now is time to prepare storage facilities and harvest equipment for the coming corn and soybeans, before things get too busy. No one needs the added stress of equipment breakdowns or messes to clean-up once harvest begins. There are several suggested measures one should take to reduce slow-downs during harvest, protect personal safety, and prepare the storage facility to maintain as high a grain quality as possible. These measures include: facility inspection and repair, sanitation, and empty-bin insecticide treatments.

Storage facilities should be inspected closely for signs of deterioration, especially for leaks and holes through which insects, birds or rodents can gain easy access to the stored grain or rain and snow can drip or blow in onto the grain to produce wet spots that can lead to mold growth. While inspecting for physical problems, one should also test aeration fans and driers for functionality. Check belts, bearings and gear boxes for wear and proper lubrication. Check electrical systems for corroded connections and frayed wiring before harvest. Mice like to nest inside electrical boxes where they are safe from predators. They will strip insulation from wires for nesting material and their urine causes corrosion. While inspecting control boxes, be sure to seal any openings where mice could get in. Be sure that guards and safety shields are in place over belts, chains and intakes. Seal all leaks and make repairs to the equipment before you need them to manage the grain.

Sanitation can prove to be a very valuable tool in reducing the potential of new grain coming into contact with grain that may be infested with grain damaging and contaminating insects. Grain that accumulated or got stuck in equipment and stayed there throughout the summer months had a great potential of becoming infested with several species of insects. Pieces of equipment that need to be cleaned thoroughly before they are used again include the combine, truck beds, grain wagons, augers, bucket lifts, and grain dumps. Other sources of grain infesting insects include livestock feeds, old seed bags, spilled grain, old contaminated grain that was not disposed of properly and other cereal products. And the number one rule in grain storage is, NEVER LOAD NEW GRAIN INTO A BIN ON TOP OF OLD GRAIN.

Another area of sanitation that is frequently overlooked is the clearing of all vegetation growing around the bases of storage bins. This vegetation can harbor grain infesting insects and provide concealment for rodents. It is advisable to clear all vegetation within 10 feet of the bases of the bins. It would be even more preferable to have the whole storage area cleared of vegetation and be covered with gravel. Follow up the vegetation removal with a residual herbicide application to the cleared area to prevent regrowth. Removal of unwanted vegetation will also improve visibility of obstructions on the ground that could be trip hazards.

The interiors of the storage bins should be thoroughly cleaned. Walls, ceilings, ledges, rafters, braces, ladder wrongs and handling equipment should be swept, brushed or vacuumed clean of all debris, dust and grain. Fans, aeration ducts, exhausts and when possible, beneath slotted floors should be cleared of debris as well. Dispose of all debris in a lawful manner and away from the storage facility. Once all cleaning has been completed, an empty-bin application of an appropriately labeled insecticide is advisable, especially in bins with difficult to clean areas and/or in bins with a history of insect problems. For empty-bin insecticide treatments that are applied as a liquid, allow a minimum of 24 hours for the sprays to dry before loading grain into the bin. It is preferable to have empty-bin treatments applied a least two weeks prior to harvest.

Registered empty-bin insecticides include: Tempo Ultra SC ™ (cyfluthrin), Storcide II ™ (chlorpyrifos methyl plus deltamethrin), Suspend SC ™, and several pyrethrin products can be used to apply a surface treatment to the inside of the bin and provide a residual. Other products that contain diatomaceous earth and/or silicon dioxide such as Insecto, Protect-It, Perma-Guard and others may be utilized. Refer to the individual product labels for lists of insects controlled and application directions. If a bin is known to be heavily infested with insects, an empty-bin fumigation may be required to knock down insect populations before applying one of the above insecticides. The most readily available product for this purpose is phosphine gas producing materials such as aluminum phosphide and magnesium phosphide sold under a wide variety of trade names. Phosphine is an extremely toxic material and fumigations should be conducted by trained, experienced, licensed applicators.

Another measure one might take to reduce the chance of insect infestation is to apply a perimeter spray around the base and up the outside walls of the bin about 15 feet. This may only be necessary in areas where grain infesting insect movement has been observed on the outsides of the storage bins. There are several synthetic pyrethroids (cyfluthrin, deltamethrin, permethrin, resmethrin, etc.) that can be used for this purpose as long as they do not come in contact with the grain.

Grain storage insecticide labels tend to change frequently. As always, check to make sure you are following the instructions on the product label and using the appropriate product for your situation.

Last but not least, review your safety procedures for working with flowing grain, grain harvesting and handling equipment, and personal protection. Anyone who works around the bins and grain handling equipment should know where to find shut-off switches, fire extinguishers, and emergency phone numbers. Being prepared for harvest will reduce the risk of accidents, and knowing how to react in an emergency can save lives.

Agronomic Crops Team at Farm Science Review

Authors: Wesley Haun

The Farm Science Review presents an excellent opportunity for producers, agribusiness personnel, consultants, and other people involved in various segments of production agriculture to obtain information and/or get questions answered. OSU’s Agronomic Crops Team will have a tent with displays covering topics that include Forages, Nitrogen Management, Nitrogen Seeker Sensor, Corn Production Issues, Sudden Death Syndrome/Soybean Cyst Nematodes, Weeds and Weed Management, Grain Drying, and Farm Safety. Extension Specialists will be present to address your specific issues. We will be located in OSU Central.

Weed Survey

Authors: Wesley Haun

Each year in September Extension Agents conduct a weeds survey of soybean fields in their counties. Data in each county is compiled into a state wide database to evaluate for trends and changes in late season weed populations. Producers interested in conducting a weed survey of their farms may contact Harold Watters for further information at watters.35@osu.edu.