C.O.R.N. Newsletter 2004-29

Dates Covered: 
August 31, 2004 - September 8, 2004
Editor: 
Harold Watters

Now is the Time to Evaluate Corn Hybrids for Leaf Diseases

Authors: Patrick Lipps

Corn growers should take the opportunity to examine the hybrids they have growing this year to decide if they should continue with these hybrids or to choose different ones for planting next year. Additionally, by scouting fields now corn producers can determine the causes of lower yields or harvest problems they may have later. Several important and destructive diseases are now obvious in fields. Pay particular attention to diseases that are severe, with high percentage of leaf area affected and causing death of leaves above the ear leaf. Growers should especially identify diseases that are causing premature plant death. Premature death may also lead to lodging problems and lost ears in the field at harvest. Be sure to visit those fields that appear to be ripening early to identify problems.

Northern corn leaf blight has been particularly severe in fields of a few susceptible hybrids. It is likely that yield losses will result from death of the upper leaves of the plants before or soon after dent stage. This disease can be recognized by its 4 to 8-inch long cigar-shaped, tan lesions on leaves. Because of their large size, having as few as a half dozen lesions on a leaf can kill the leaf. Hybrids with these large lesions, especially those that have lesions on most leaves of a plant are considered to be susceptible and likely do not have specific resistance genes (Ht genes) or a high enough level of partial resistance to prevent or restrict lesion development. In Ohio, the fungus that causes northern corn leaf blight exists primarily as two races (there are other races known); race 0 which is controlled by the Ht1 gene and race 1 which can cause susceptible lesions on hybrids with the Ht1 gene. Additionally, hybrids may have a partial resistance that is effective against all races of the fungus. Most hybrids have a good level of partial resistance to northern corn leaf bight and many have the Ht1 gene. However, occasionally a hybrid is grown that is susceptible. The objective is to avoid planting any hybrid that is susceptible.

We are also seeing a relatively high level of Diplodia ear rot in some fields. This disease is favored by rainfall and wet conditions during the late whorl to tasseling growth stages. Diplodia enters the ears, usually through the base. The first indication of Diplodia is the premature death of the husks surrounding affected ears. When you peel the husks back the obvious thick, grayish-white mold is usually evident on the base of the ear. Generally the kernels on the ears are brown and shriveled or covered with the thick mold growth. Some hybrids are particularly susceptible to this disease. Some fields have been found with 20% to 30% of the ears being diseased which will obviously result in substantial yield loss. Most hybrids have a reasonable level of resistance to Diplodia ear rot and growers are encouraged to avoid hybrids that are susceptible.

Both fungi that cause northern corn leaf blight and Diplodia ear rot survive from year to year on old corn residues. Crop rotation is extremely important in controlling these diseases. Additionally, tillage which buries the infested corn residue will enhance decomposition of the residue and death of these fungi. Regardless, planting resistant hybrids is the first line of defense for Ohio corn producers. Good levels of resistance are also available for gray leaf spot, anthracnose, common rust, and Stewart's bacterial leaf blight as well as other diseases. Talk to your seed dealer about disease resistant hybrids!

Access the Ohio Field Crop Disease web site for additional information and photos of NCLB (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/nclb.htm) and Diplodia ear rot (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/diplodia.htm).

Soybeans - Late Season and Unusual Diseases are Showing Up

Authors: Anne Dorrance

The rains have provided a perfect environment for a number of soybean pathogens this year. We are identifying diseases that have not occurred for some time and others that are rare for some areas of the state.

1. Powdery Mildew - this is a fungus that infects and colonizes the tops of leaves, and gives the leaves a powdery appearance. Early infections are white but over time will turn a dusty gray. Very unusual to have this disease and it is only occurring in isolated fields, this has been managed with resistance. We are also noting that this is worse in fields where winds are blocked by trees. Take note of the variety and don't plant this in fields with reduced air movement.
2. Sclerotinia stem rot is showing up again in isolated fields, these tend to be those where the canopy did develop just prior to or during flowering this year. Take note of these fields, because inoculum is now an issue in these fields, plant varieties which have increased resistance to Sclerotinia. Studies from the North Central Soybean Research Program on Sclerotinia have also shown planting at reduced population densities has also reduced the amount of disease.
3. Diaporthe stem canker. This is a fungus disease which girdles the stem at the third or fourth internode. The top of the plant will be dead above the brown canker. The bottom of the plant from the canker to the soil will be green and the roots will be healthy. Usually, this is an isolated plant here and there, varieties have different levels of susceptibility to this so keep good notes.
4. Those yellow spots - I was in Southern Ohio last week, and came into an area that is not well known for Phytophthora. But when we scouted the area where plants were short and dying early, there were a few dead plants, most were yellow, but low and behold, there were a few with the classic symptoms of Phytophthora stem rot. This pathogen is showing up this year in just about all areas of the state due to the excessive rains. Varieties with high levels of partial resistance will not develop the classic stem rot phase, so take note of what the resistance package is in these areas. This disease is favored in areas of the field where compaction and poor drainage keep these soils saturated for long periods of time. Compounding this is the flooding injury that can also occur in these spots, which kills the roots. These injured roots, are then colonized by a number of soil pathogens, Pythium, Rhizoctonia, Macrophomina, etc. making it very difficult for the plants to form new roots quickly and recover.
5. Soybean cyst nematode - the one everyone likes to deny is here in Ohio. But unfortunately, the areas of fields where this is inhabiting and the number of fields continues to increase. Planting a SCN resistant variety (PI88788) is not always the right or best thing to do for some of our SCN populations. Watch the yield monitors on these fields and make some notes if they are dropping in areas where you have seen high cyst levels in the past. Crop rotation and rotating varieties with different sources of resistance are two major keys to managing this nuisance pest. In fields with High SCN levels we are seeing the white females on the roots, so now is a good time to scout. Focus on those areas of the fields where the height drops substantially and you are getting some of this early maturing. You can also find SCN females in fields with no above ground symptoms.
6. Have fun scouting!

Sweeps in Soybeans for Western Corn Rootworm Adults (WCRW)

Authors: Ron Hammond, Bruce Eisley

We swept soybeans again this year to monitor WCRW adult populations. One hundred sweeps in each of three fields in 10 west central and northwestern Ohio counties were made during the first week in August. The contents of the sweeps were bagged, brought to the lab and the adults counted when time allowed. This is the second year that we have swept soybeans and results show higher WCRW adult populations this year as compared with 2003. This coincides with reports coming from those counties that are monitoring WCRW adults with sticky traps in soybeans. The results, by county, from sweep samples taken in 2003 and 2004 are shown in the following table.







County
2003

2004


Number of WCRW 1

number of WCRW 1


site 1
site 2
site 3
site 1
site 2
site 3
Auglaize
6
2
11
2
7
5
Defiance
8
2
8
5
15
24
Fulton
*
*
*
28
5
51
Henry
*
*
*
10
20
3
Mercer
2
2
7
9
5
3
Paulding
0
2
2
4
6
14
Putnam
*
*
*
1
11
18
Shelby
*
*
*
0
1
26
Williams
2
5
6
7
25
12





* Sweeps were not taken from these counties in 2003.
1 WCRW adults per 100 sweeps per field

Even though sweep counts are up this year they are still not as high as counts being reported by states west of Ohio. Additional information concerning WCRW adult populations in soybeans will be reported in future newsletters.

Herbicides for Summer-Seeded Alfalfa

The time is approaching to begin scouting newly planted alfalfa fields for weed activity. Early competition of weeds in new alfalfa seedings can drastically reduce the stand, especially thick common chickweed. Most of the state has had ideal conditions for large numbers of winter annual weeds to emerge in these fields.

Pursuit and Raptor are the most broad-spectrum herbicides available. Pursuit will provide longer residual control, but Raptor will provide better common lambsquarters and ragweed control. The alfalfa must have a minimum of two trifoliate leaves before applying Pursuit or Raptor. For control of grasses only, Poast, Poast Plus and Select are available. Select will control the most grass species. For control of certain broadleaf weed species, Buctril/Moxy and 2,4-DB are available. The alfalfa must have a minimum of four trifoliate leaves before Buctril can be applied and must have two to four trifoliate leaves before 2,4-DB can be applied. All products mentioned above can only be used on pure stands of alfalfa.

Cooler Weather and Growing Degree Days, How Does This Year Compare to Normal?

Authors: Robert Mullen

In agriculture we are obsessed with “normal,” despite the fact that it is seldom observed during a growing season. There is always something occurring climatically that deviates from the norm, whether (no pun intended) it be excess rainfall, warmer temperatures, cooler temperature, etc. This year has been no different (so maybe this is average?). As mentioned in previous C.O.R.N. articles, excess early season moisture has been problematic delaying planting in some areas and forcing replanting in others. Many also consider this year to cooler than most and are concerned about maturity dates; so are those concerns warranted?

The OARDC has weather stations located at sixteen locations across the state that record hourly weather information. Many of the stations have been in place since 1982. This time period gives a good amount of information to evaluate to determine what is normal, and how far we are deviating from it this year. Compared to the 21-year average, crops that were planted around mid-April have experienced roughly the same amount of growing degree days (GDD) as observed on average. As mentioned earlier, wet conditions early in the year forced some to delay planting or replant crops. Compared to the 21-year average, crops that were planted around Memorial Day (end of May) have accumulated 200 less GDD than normal. Late-April and May temperatures were considerably warmer than normal and account for the difference in GDD between the two planting periods. Thus, there should be more concern about soybeans than corn.

So what, what is a GDD? We use GDD (or GDU - growing degree units) to describe the amount of heat, which drives plant metabolic activity. Higher average air temperatures result in higher metabolic activity (to a point - for corn and soybeans we say that 86 degrees F is the max). When GDDs are low, plant activity is low. If the weather persists, delayed maturity and decreased yield may be observed.

Unfortunately, it appears as if there is little opportunity for our crops to recoup some of the GDD lost this summer. Short range forecasts show that average daily temperatures will be near normal. Thus late planted crops (specifically longer-season soybeans) may have maturity delayed significantly.

Incomplete Ear fill and “Tip Dieback”

Authors: Peter Thomison

During the past week I have received questions about ears of corn with unfilled tips. In some cases, no kernels are evident on the last two or more inches of the ear tip. There are several factors that may cause this problem. The ovules at the tip of the ear are the last to be pollinated, and under certain conditions only a limited amount of pollen may be available to germinate late emerging silks. Pollen shed may be complete before the silks associated with the tip ovules emerge. As a result, no kernels form at the ear tip. Severe drought stress may result in slow growth of the silks that prevents them from emerging in time to receive pollen. Pollen feeding and silk clipping by corn rootworm beetles and Japanese beetles can also contribute to pollination problems resulting in poorly filled tips.

Incomplete ear fill may also be related to kernel abortion. If plant nutrients (sugars and proteins) are limited during the early stages of kernel development, then kernels at the tip of the ear may abort. Kernels at the tip of the ear are the last to be pollinated and cannot compete as effectively for nutrients as kernels formed earlier. Stress conditions, such as heat and moisture stress, nitrogen deficiency, hail, and foliar disease damage, may cause a shortage of nutrients that lead to kernel abortion. Periods of cloudy weather following pollination, or the mutual shading from very high plant populations can also contribute to kernel abortion. Some agronomists characterize the kernel abortion that occurs at the end of the ear as “tip dieback”. Kernel abortion may be distinguished from poor pollination of tip kernels by color. Aborted kernels and ovules not fertilized will both appear dried up and shrunken; however aborted kernels often have a slight yellowish color.

Is the presence of barren tips a major cause for concern? Not necessarily. In many cornfields this year, the favorable growing conditions may have resulted in a larger number of potential kernels per row than normal. So even if corn ear tips are not filled completely, due to poor pollination or kernel abortion, yield potential may not be affected significantly, if at all, because the numbers of kernels per row may still be above normal. The presence of ears consistently filled to the tip may actually indicate that a higher plant population is needed to optimize yields.

Diesel Prices and Fall Tillage

Authors: Randall Reeder

Diesel fuel for bulk delivery to the farm is around $1.50 per gallon. A year ago the price was $1.00. If you're filling storage tanks this price hike can make you wallet seem a whole lot thinner.

If your question is, “How can we save on fuel costs for fall tillage?”, the simple answer is: the less tillage done, the more you save. No-till uses no fuel in the fall, except for running a sprayer once for weed control, or perhaps planting a cover crop.

For a farmer who plans to do about the same tillage in 2004 as in 2003, figure on a 50% increase in fuel costs. Even at our fairly high current cost for fuel, it is still not a major factor in the total cost of tillage. It may seem major because it is an out-of-pocket cost, whereas the cost of the tractor and tillage implement, and labor to run it, is often hidden from immediate view.

Think of the cost of operating the family car. The total cost per mile is around $0.40. Adding a dollar per gallon to the price of gasoline only adds about 4 cents to this cost, but we react more to gasoline prices because we fill up every few days.

Back to tillage, the draft required (and therefore fuel used) for various tillage operations varies widely. Soil type and moisture, tillage depth, speed, spacing of shanks, and sharpness of cutting edges are all important factors. The draft for plowing “heavy” soils is almost double the draft for “medium” soils. Tilling twice as deep approximately doubles the draft.

The following numbers, kind of a composite drawn from several sources, can be used for comparing different tillage tools. Don't think of the “diesel fuel per acre” numbers as precise, but rather as the middle of a fairly wide range.




table 1


Implement
Diesel,gal/acre
Diesel/ac
($1.00/gal)
Diesel/ac
($1.50/gal)
Moldboard Plow 2.2
2.20
3.30
Disk (stalks)
0.8
0.80
1.20
Disk (after plowing)
1.2
1.20
1.80
Chisel Plow
1.6
1.60
2.40
Subsoiler
3.8
3.80
5.70
light harrow*
0.4
0.40
0.60





*light harrow could include implements such as the Phoenix harrow and AerWay.

These numbers show the relatively low cost of fuel, even today. Fuel for chisel plowing followed by disking, for example, will cost just over $4/acre compared to a little under $3 in 2003. The real numbers to consider are TOTAL cost per acre. Tractor and implement overhead plus labor will increase the true cost to around $15 to $20 for chisel plow and disking.

Fuel use for subsoiling will vary greatly based on shank spacing and design. If you forego subsoiling this fall and instead use a light surface tillage tool, the difference in fuel cost could be $3 to $4 per acre. The total cost difference per acre might top $20.

Total costs count. If you put an extra 300 hours on a tractor for “recreational tillage” each year, that is a major cost even if it doesn't show up until you trade tractors. The labor cost, even if it is your own or other family member, is important because it represents time not available for other work, management or leisure. Higher diesel prices can take a lot of the “fun” out of recreational tillage, and if that gives you a reason to switch to less tillage or no-till, that ain't all bad.

For more information on conservation tillage, the best source is the MidWest Plan Service book and/or CD-ROM on Conservation Tillage. Call 800-562-3618 to order.
Archive Issue Contributors: 

State Specialists: Anne Dorrance, Pat Lipps and Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility), Jeff Stachler (Weed Science), Ron Hammond & Bruce Eisley (Entomology) and Randall Reeder (Ag Engineering). Extension Agents and Associates: Bruce Clevenger (Defiance), Andy Kleinschmidt (Van Wert), Barry Ward (Champaign), Gary Wilson (Hancock), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Greg Labarge (Fulton), Harold Watters (Miami), Dusty Sonnenberg (Henry), Howard Siegrist (Licking) and Steve Prochaska (Crawford).

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.