C.O.R.N. Newsletter 2010-26

Dates Covered: 
August 17, 2010 - August 23, 2010
Editor: 
Andrew Kleinschmidt

Soybean Aphid Update

As summer comes to an end, we are still seeing very low numbers or no aphids in most soybean fields.  This confirms our observations and thoughts from last fall when we saw aphids on buckthorn die before eggs were laid, and we began thinking that 2010 would be a low-aphid year, keeping with Ohio’s two year on-and-off cycle.   At this time, unless you have that one in 500 fields that might have a moderate aphid population or extremely late planted soybeans which still may require sampling to ensure aphid numbers stay below threshold, most growers should be past the time of concern.  Remember that if soybeans have reached the late R5 to R6 growth stage, the threshold can probably be raised higher.   You will probably need well over 1000 aphids at that point to probably cause yield losses.

For the remainder of the summer, we would expect to see aphid populations come up slightly in numbers prior to their move to buckthorn.   This fall we sample known buckthorn in Ohio to see if aphids lay eggs, which will be an indication of what might be in store for us in 2011.  We will report those findings during September and October.  

Corn Closing in on Maturity

Ohio’s corn crop continues to develop rapidly as a result of this season’s early planting and above average temperatures. According to the NASS (www.nass.usda.gov), as of August 15, 82 percent of corn was in dough, compared to 43 percent last year and 59 percent for the five-year average. Thirty-four percent of corn was dented, compared to four percent last year and 10 percent for the five-year average. In many fields, corn in full dent has achieved the half-milk line stage (also referred to as the “starch line”). Thermal time from half-milkline to physiological maturity (“black layer”) is approximately 280 GDDs (http://www.kingcorn.org/news/timeless/GrainFill.html ) which corresponds to about 10 days if we accumulate at least 28 GDD daily. Based on conditions as of August 1, the NASS has forecast Ohio's corn average yield at 176 bushels per acre, up 2 bushels from last year's record yield of 174 bushels per acre. If these estimates for maturity and yield come to pass, we may be looking at a very large, early maturing crop.

In the August 12, 2010 issue of the Illinois Pest Management Bulletin, Dr. Emerson Nafziger provides an interesting perspective on effects of growing conditions, especially temperature and rainfall, on development of the Illinois corn crop this year. The following is an excerpt - complete article online at http://bulletin.ipm.illinois.edu/article.php?id=1402

“Corn to the Finish Line: Racing or Collapsing?”

The 2009 and 2010 growing seasons represent two extremes in terms of temperatures and growing degree-day accumulations since planting. Planting was a full month earlier in 2010 than in 2009, and GDD accumulations since planting are running as much as four to five weeks ahead of accumulations after planting in 2009….

Soil moisture ratings currently show 74% of fields with adequate-to-surplus topsoil moisture. This number was 80% in 2004 and only 43% in 2007. As is usually the case, some parts of the state, especially parts of central, eastern and southeastern Illinois, are dry or very dry, while other parts, mostly in the west and northwest, have had too much rain. Rainfall patterns have been close to ideal in some places. The effects of rainfall during the remainder of the season this year will be less than we would normally estimate during mid-August, only because the crop is so far along that water isn't going to be a serious limitation if it hasn't been limiting up till now. Exceptions to this are in replanted or late-planted fields, where more rainfall will be needed to finish out the crop.

Many people worry that the continued (and continuing) high temperatures have been hard on the crop and that we cannot expect it to yield as much as it might have with average or below-average temperatures in August. I would concur with that concern, not so much because the crop is filling grain poorly this year, but because it tends to continue filling for a longer period when temperatures are lower, in some cases producing the "bonus fill" that results in larger-than-normal kernels in years like 2004 and 2009. We can't accurately forecast final kernel size, but it might be closer to the 85,000 to 90,000 kernels per bushel that we consider normal, and not the 70,000 to 80,000 that we can see under unusually favorable conditions during late grainfill.

Another widely reported issue this year is "tip-back," which refers to abortion of some kernels on the tip of the ear. Conditions during and after pollination were generally favorable this year, and it's not clear that kernel number per ear (or per acre) is lower than normal. But we have a tendency to view aborted tip kernels as lost yield potential. In some cases, when conditions after pollination are unfavorable and we end up with only 300 to 400 kernels per ear, this view may be accurate; the crop can usually fill more kernels than this unless filling conditions deteriorate. But if tip-back takes kernel counts down from 700 to 600 per ear (in fields with around 30,000 ears per acre), it's quite possible that kernel size will increase a little as a result, and there may be little or no loss in yield.

Rapid development and early maturity will be among the more memorable aspects of the 2010 corn crop. In our planting date trial at Urbana, corn planted on April 5, April 21, May 10, and May 28 had by August 10 accumulated about 2,575, 2,400, 2,200, and 1,920 GDD, respectively. At current accumulation rates of about 28 GDD per day, a hybrid that needs 2,750 to mature needs only about 6 more days to reach black layer, and the same hybrid planted on May 10 needs about 20 more days to reach maturity. These projections generally seem to track with what we're seeing in the field.

Many people feel that the high temperatures, which we commonly hear reported as the "heat index" (which dramatizes temperature by combining it with humidity into a "human misery" measurement) have been harmful. In reality, while high night temperatures are a negative factor, daytime temperatures in the 90s have not done much harm in areas where soil moisture has stayed adequate. Corn plants do not suffer from high humidity like we do, except indirectly: high humidity means higher night temperatures, and leaves may stay wet longer in the morning, which can increase disease development. Some insects also like higher humidity…”

Other references:

Nielsen, R.L. 2008. Grain Fill Stages in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at (http://www.kingcorn.org/news/timeless/GrainFill.html ) (URL verified 8-16-10).

 

During the past week, I’ve received several questions about tassel ears in corn. Corn is the only major field crop characterized by separate male and female flowering structures, the tassel and ear, respectively. However, in most corn fields it is not unusual to find a few scattered plants with a combination tassel and ear in the same structure - a "tassel ear." The ear portion of this tassel ear structure usually contains only a limited number of kernels.

Tassel ears often appear on tillers (suckers) arising from plants with normal ears and tassels. These tassel ears are produced at a terminal position on the tiller where a tassel would normally appear. However, tassel ears may also be produced by individual plants. No specific cause of this condition is known but it often occurs in shorter spindly plants associated with delayed emergence and uneven crop development. Some hybrids may also be more prone to tiller under certain environmental conditions and these tillers may give rise to tassel ears. Tassel ears are frequently observed along the edges of fields where early season soil compaction and saturated soil conditions may have contributed to this abnormal growth and development. Tassel ears are a reminder that the male and female parts of the corn plan are structurally very closely related. Wild progenitors of corn-teosinte spp. have complete flowers tassels and silks together. These can be crossed with Zea mays (normal corn).

There has been some speculation that a fungal disease called "crazy top" may be responsible for this abnormal ear condition. Crazy top does affect the appearance of tassels and ears but the symptoms are distinctly different from those of the tassel ear phenomenon. Crazy top causes the tassel and/or the ear to become leaf-like. In severe cases, the whole top of a plant and ears are replaced with a mass of leaf-like structures. Visual symptoms and more details concerning crazy top are available online at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/crazytop.htm

For more information on tillering, check out fact sheet AGF-121-95, "Corn Growth and Development - Does Tillering Affect Hybrid Performance?" It’s available online at http://ohioline.osu.edu/agf-fact/0121.html

Dr. Bob Nielsen, extension corn specialist at Purdue University, has an article with excellent pictures of plants with tassel ears – “Tassel-Ears in Corn”  available online at http://www.agry.purdue.edu/ext/corn/news/timeless/TasselEars.html

Corn Silage Harvest is Imminent

Corn development has been progressing at a rapid pace with the recent warm temperatures. Early planted corn is already being harvested for silage in some parts of Ohio. So it is time to check the whole plant moisture content now, if you haven’t done so already.

Ensiling corn at the proper dry matter content provides high quality preservation resulting in good animal performance and lower feed costs. Harvesting corn too wet (low dry matter content) results in souring and seepage of the silage and reduction in animal intake. Harvesting too dry (high dry matter content) promotes mold development because the silage cannot be adequately packed to exclude oxygen. Harvesting too dry also results in lower energy concentrations and reduced protein digestibility. 

Harvest Moisture Guidelines

Corn silage preserved between 30 and 38% dry matter (62 to 70% moisture) generally provides good silage fermentation and animal performance. The optimal dry matter content varies with type of storage structure (Table 1). 

Table 1. Optimal dry matter contents for different storage structures.

Type of Structure Optimal % Dry Matter
Horizontal bunkers 30 to 35 
Bags 30 to 38
Upright, top unloading 33 to 38 
Upright, bottom unloading 35 to 40* 

*The higher DM concentration for bottom unloading silos is a compromise between forage quality and unloader requirements

Kernel stage not a reliable guide for timing silage harvest

Dry matter content of whole plant corn varies with maturity.  Research has demonstrated that the position of the kernel milk-line is not a reliable indicator for determining harvest timing. Geographic location, planting date, hybrid selection, and weather conditions affect the relationship between kernel milk-line position and whole plant dry matter content. In a Wisconsin study, 82% of the hybrids tested exhibited a poor relationship between kernel milk-line stage and whole-plant % dry matter. In Ohio we have seen considerable variation in plant dry matter content within a given kernel milk-line stage.

Determining Silage Moisture

The only reliable method of determining the optimal time to harvest corn silage is to sample the crop and directly measure the % dry matter of whole plants. This information combined with average whole plant dry-down rates can be used to roughly predict the proper time to harvest corn silage.

How to Sample Fields

Collect about 5  representative plants from the entire field. The plants should be representative from an area with representative plant population and not from edge rows. Collect separate samples from areas that may have different dry down rates, such as swales and knolls. The moisture concentrations of plants can vary within a field (plants will be wetter in low lying area and drier on knolls) and this should be considered when collecting your sample plants.

Put plants in a plastic bag, keep them cool, and chop as quickly as possible. The plants should be uniformly chopped (using a cleaver, machete, chipper shredder, or silage chopper) and then mixed thoroughly to obtain a sample with representative grain to stover ratios for dry matter determination. Some farmers prefer sampling only 2 or 3 plants without any additional sub-sampling to reduce the chances of a non-representative grain to stover ratio that can affect the results. In this case, choosing representative plants is even more critical. 

Determine the dry matter content by drying the plant material using a Koster oven tester, microwave, convection oven, taking to a lab or using a vortex dryer. For more details on these and other methods, see the following links:

http://www.extension.org/pages/Dry_Matter_Determination

http://ohioline.osu.edu/agf-fact/0004.html

http://www.abe.psu.edu/extension/factsheets/i/I101.pdf

Make sure the sample does not dry down and keep it cool until the dry matter determination is performed. The accuracy of the % dry matter value will be largely determined by the care taken in sampling, drying, and weighing the samples. Whole kernels and cob pieces can be difficult to dry completely without burning the leaf tissue.

When to Begin Field Sampling

We know that kernel milk stage is not reliable for determining the actual harvest date, but it is a useful indicator of when to sample fields to measure plant dry matter. Corn in Ohio should be first sampled to measure dry matter at full dent stage (100% milk, no kernel milkline) for conventional tower or bunker silos, and at 1/4 milkline (milkline one-fourth down the kernel, 75% milk remaining) for sealed (oxygen-limited) tower silos. It is important to begin sampling early as a precaution against variation in dry down.

Predicting the Harvest Date

Once whole-plant % dry matter is determined, an average dry down rate of 0.5% unit per day can be used to estimate the number of days until the optimal harvest moisture. For example, if a given field measures 30% dry matter at the early sampling date, and the target harvest dry matter is 35%, then the field must gain an additional 5% units of dry matter, thus requiring an estimated 10 days (5% units divided by 0.5 unit change per day). 

This procedure provides only a rough estimate for the harvest date. Many factors affect dry down rate, including hybrid, planting date, general health of the crop, landscape position, soil type, and weather conditions. Early planted fields and hot and dry conditions like we’ve been experiencing can accelerate dry down rates to 0.8 to 1.0 % unit per day. Fields should be monitored closely and more frequently under these conditions. In general, corn silage that is slightly too dry is worse than corn silage that is slightly too wet.  Therefore, starting harvest a little early is usually better than waiting too long.

Evening Field Day near Continental

The Putnam County Extension office and Putnam Soil and Water Conservation District will host a field day at the farm of Howard and Lois Weller on Thursday, August 19 starting at 6:30 p.m. The Wellers live approximately two miles west of Continental on county road E.
 
The field day is at the same location as the Manure Science Review earlier in the day.
 
The Wellers have a tile control structure installed to control the drainage of the soybean field south of their farmstead. We will view this control structure. Howard will also have a spare tile control structure sitting at the site for farmers to view. Tile control structures can be used to prevent liquid manure from escaping from farm fields. They are also being used to prevent summer rainfall from being lost into ditches and resulting in increased crop yields.
 
Several cover crops were planted in 30 foot by 240 foot strips in mid July at the tillage day site so farmers can see what the more commonly used cover crops look like.  Signs are posted listing the seed variety, seed cost and planting method (some were both drilled and broadcast followed by shallow tillage) of each cover crop. A sample bag of the seed will also be on site. Cover crops include various radish varieties, cereal rye, oats, cow peas, winter peas and AC Greenfix.
 
Local implement dealers will be speaking about and demonstrating shallow tillage equipment on wheat stubble. Shallow tillage can be used to disrupt soil cracks and worm holes to prevent manure from escaping into subsurface drainage tile.
 
Frank Gibbs will be on hand to smoke a field tile. This consists of blowing pressurized smoke into the tile and observing the smoke as it escapes through worm holes, crawdad holes and cracks in the soil.
 
Manure sidedress demonstration of corn using row ready manure tankers and manure incorporation toolbars. Corn was planted in late July for the sidedress demonstration and we expect to have three sidedress toolbars to demonstrate.
 
There is no cost to attend the evening field day and registration in not expected. 

Weather Update

The last two weeks saw temperatures much above normal with rainfall near normal. However, as was discussed two weeks ago, rainfall was highly variable, from less than 0.50 inches to over 5 inches. Normal for the 2 week period is around 1.75 inches.

The outlook for the remainder of August calls for much above normal temperatures to continue. Temperatures this week will start cooler the first half but temperatures 4-10 degrees above the normal (normals are lows 80s and low 60s on average across the state plus or minus 3-4 degrees from north to south) will return thereafter. Rainfall now looks below average the rest of this month. There will still be pockets of heavier rain, but the heaviest rains look north and south of the state. The northeast and far south stand the best chances for rainfall. Average for the rest of the month is near 1.75 inches. Most places will see an inch or less of rain the next 10 days.

 

Archive Issue Contributors: 
Archive Issue Authors: 

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.