C.O.R.N. Newsletter 2005-34

Dates Covered: 
October 10, 2005 - October 18, 2005
Curtis E. Young

Corn Ear Rot Problems in Ohio

Authors: Pierce Paul, Peter Thomison, Dennis Mills

In a year when stalk quality has been badly affected by poor weather conditions (drought) and stalk rots, lodging of up to 90% is being reported in some cornfields. In addition to not being able to mechanically harvest ears on lodged corn plants, yield loss associated with lodging is further compounded by the fact that ears in contact with the ground often become moldy and develop ear rots, resulting in poor grain quality. While ear rots may be caused by several fungi, the most important ear rot problems in Ohio, Gibberella, Diplodia, and Fusarium ear rots, are caused by some of the same fungi associated with stalk rots, Gibberella zeae, Stenocarpella maydis and several Fusarium species. Hence, the most important sources of spores for infection of the ears are corn stalk and ear pieces left on the ground from a previous crop. Some ear rot-causing fungi also reside in the soil. Under wet conditions, spores are produced on debris on the soil surface and are usually wind-blown or rain-splashed to the ears. When lodging occurs, infection is greatly facilitated by the fact the ears are closer to or come into direct contact with the fungi on infected debris. In addition, infection is further favored by the fact that ears in contact with the grounds often remain moist. Moisture favors the development of ear rots.

Ear rots also occur on plants that are not lodged. During silking and early grain development when the ears are most susceptible to infection, the ear rot fungi usually penetrate the ear via the silk channel. Later in the season, however, infection mostly occurs at the base of the ear where the fungi penetrate the husk. Late season ear rot development is favored by rainfall prior to harvest, especially when the ears do not turn down and water collects at the base of the ear between the husks and the kernel. Poor growth conditions during the early part of this season may have prevented kernels from developing fully in some fields. Poorly developed ears (“beer can” ears) are more likely to remain upright than fully developed ears, and as a result, are more likely to develop ear rots. In addition, whether the ears turn down or remain upright varies from one hybrid to another. Given the rains we have had in some areas over the past few days, fields with poorly developed ears that do no turn down, hybrids with ears that dry in an upright position, and severe lodging may experience the greatest ear rot problems. For more information on ear rots consult the OSU Plant Pathology web site "Ohio Field Crop Diseases" at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/.

With ear rot come the additional concerns of kernel rot and mycotoxin accumulation in storage. In addition to the physical damage caused by ear rots, some ear rot fungi produce mycotoxins that reduce the quality and value of the grain. Storage temperatures above 40F and kernel moisture content of 22% and above are favorable for the growth of toxin-producing ear rot fungi (Fusarium species). Growers are advised to follow certain harvest and storage guidelines to minimize problems associated with kernel rots and mycotoxin contamination:
1. Harvest fields with stalk rot problems early to minimize lodging, and consequently, ear rot development.
2. Harvest at the correct moisture and adjust harvest equipment to minimize damage to kernels. Mold and mycotoxins tend to be higher in (machine or insect) damaged kernels.
3. Dry harvested grain to 15% moisture and below to prevent further mold development in storage.
4. Store dried grain at cool temperatures (36 to 44 F) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.
5. Periodically check grain for mold, insects, and temperature.
6. If mold is found, send a grain sample for a mycotoxin analysis to determine if toxins are present and at what level. Toxins are harmful to humans and livestock.
For more on moldy grain, mycotoxins, and mycotoxins sampling and analysis visit the following websites:

Effects of Harvest Delays on Yield, Grain Moisture and Stalk Lodging in Corn

Authors: Peter Thomison

The growing conditions we experienced this past summer, including drought in many areas, have resulted in major stalk lodging problems across Ohio. As corn harvest finally gets under way in earnest, severe lodging is being reported - in some cases, corn has been nearly flattened by recent storms. The good news is that the warm, dry weather this fall has been very favorable for grain drying, and many fields, even mid-May replant fields, have corn with grain moisture levels below 20%. Therefore there is little need to field dry corn further given these low moisture levels.

Harvest delays expose the crop to less favorable weather conditions, as well as wildlife damage. Additional losses may occur when ears on lodged plants come in contact with wet soils and surface residues resulting in development of ear rots. Ear rots reduce grain quality and lead to significant dockage when the grain is marketed. Some ear rots produce mycotoxins, which may cause major health problems if fed to livestock.

We recently completed a study that evaluated effects of plant population (24,000, 30,000, 36,000, and 42,000 plants/A) and harvest dates (early-mid Oct., Nov. and Dec.) on the agronomic performance of four hybrids differing in maturity and stalk quality. The research was supported by a Pioneer Crop Management Award and the Ohio Top Farmers. Although the four hybrids exhibited similar yield potential when harvested early (early/mid Oct.), differences in yield became evident with harvest delays, which could be attributed to differences in stalk quality. Yield differences among plant population were generally small on the first harvest date, but with harvest delays, major yield losses occurred at the higher plant populations, especially 42,000 plants/A, due to increased stalk lodging. After the first harvest in early/mid October, stalk lodging increased as much as 80% - resulting in yield losses of nearly 50% for certain hybrids. Most of the yield loss occurred following the second harvest date in early November. Grain moisture, averaged about 24% on the first harvest date, 18% on the second harvest, and 17% on third harvest date.

Changes in grain moisture with harvest delays.
Grain moisture content showed a decrease from early-mid Oct. to early-mid Nov. but little or no change between early-mid Nov. and early-mid Dec. (Table 1). Grain moisture, averaged across locations, years, hybrids, and plant populations, decreased 6.3% points between early-mid Oct. and early-mid Dec., with most of the decrease occurring between early-mid Oct. and early-mid Nov. (5.8 % points); only a 0.5 % point decrease occurred after early-mid November. At five of the eight test locations, grain moisture content in early-mid Nov., averaged less than 18% points. At the other three sites, grain moisture levels in early-mid Nov. ranged from 20 to 21% points. Population effects on grain moisture content were not consistent. Differences in grain moisture were also evident among hybrids in early-mid Oct. but generally negligible on the later dates.

Table 1. Grain Moisture (%)

Plant Population HD1 HD2 HD3
24,000 24.9 18.2 17.4
30,000 24.0 17.9 17.3
36,000 22.4 18.0 17.6
42,000 23.7 17.9 17.7
Average 23.8 18.0 17.5

HD1 = early/mid-Oct., HD2 = early/mid-Nov., HD3 = on or after mid-Dec.

Changes in stalk quality with harvest delays.
Harvest delays resulted in greater stalk rot and lodging (Tables 2 and 3). The greatest increase in stalk rot occurred between early/mid-Oct and early/mid-Nov, whereas most of the increase in stalk lodging occurred after early/mid-Nov. Averaged across locations, years, populations and hybrids, stalk rot increased from 44% in early/mid-Oct to 83% in early/mid-Nov and 91% in/or after mid-Dec.; stalk lodging increased from 4% in early/mid-Oct to 24% in early/mid-Nov and 47% in/or after mid-Dec.
The major reduction in grain yield associated with harvest delay can be attributed to the increase in stalk lodging between the early/mid-Nov and mid-Dec harvest dates.

Table 2. Stalk Rot (%)

 Plant Population HD1 HD2 HD3
 24,000  21  72  83
 30,000  42  80  89
 36,000  53  87  95
 42,000  58  93  96
 Average  43  83  90

HD1 = early/mid-Oct., HD2 = early/mid-Nov., HD3 = on or after mid-Dec.

Table 3. Stalk Lodging (%)

 Plant Population HD1 HD2 HD3
 24,000   3  17  33
 30,000   4  20  41
 36,000   4  27  52
 42,000   4  33  59
 Average   4  24  46

HD1 = early/mid-Oct., HD2 = early/mid-Nov., HD3 = on or after mid-Dec.

The 2003 and 2004 growing seasons during which most of this research was conducted were extremely favorable for corn growth and yield. Record corn yields were achieved statewide. Due to stress conditions in 2005, stalk quality is inferior to that of the past two years. In some severely stressed fields, corn died prematurely in August and September and significant stalk deterioration has already occurred. Given the poor quality of corn stalks in many corn fields in 2005, it’s likely that we could expect greater stalk lodging with shorter harvest delays than the research above would indicate.

New Transgenic for Rootworm

Authors: Ron Hammond

Another transgenic corn has been approved for use against corn rootworm larvae. The new corn, known as Herculex RW, is from Pioneer Hi-Bred and Dow Agro-Sciences. As with Herculex I which is for corn borer control, Herculex RW also contains the LibertyLink trait. Herculex RW joins YieldGard Rootworm as transgenic alternatives to soil insecticides for control of corn rootworms. Both will do a good job in controlling rootworm in Ohio.

However, we believe that there are only two conditions in Ohio corn production that might benefit from this new technology: (1) corn following corn or (2) first year corn following soybean ONLY if the western corn rootworm variant is a potential problem based on sampling or other observations. See the article in the C.O.R.N. newsletter, volume 30, on September 12, 2005, for a discussion on the use of all Bt hybrids for corn pests.

For control of both European corn borer and corn rootworm using transgenic technology, there is only one material currently available, YieldGard Plus. Herculex Xtra, which has events for both borers and rootworms and is pending registration and awaiting EPA approval, will be available in the future.

Harvest Dry Grain on Green Soybean Plants!

Authors: Jim Beuerlein

Throughout the state there are areas that experienced drought through some part of the growing season and even throughout most of the season. This stress has resulted in very poor yields in addition to some strange soybean plants in many fields. There are a number of causes for the green stem situation with virus diseases, and poor pod set being the most common. Remember, the reason soybean leaves turn yellow and fall from the plant is that they are absorbed and deposited in the grain which can account for about 5% to 10% of the final yield. However, if pod set is poor but the weather is good during the pod filling process, then it may not be necessary for the plant to digest the leaves to finish pod fill and in this event the leaves remain green and attached to the stem. Occasionally you can find a branch with no pods who's stem and leaves remain green even though the main stem and its pods turn brown and dry naturally. I have also seen plants with three adjacent barren nodes where the attending leaves stayed green while the main stem and its grain dried naturally. Following are some observations and recommendations for the unusual areas and fields we will find.

- High yield fields where plants have green stems and leaves along with dry grain. Those stems and leaves will stay green for some time, so forget the green and get the grain, ASAP. In most instances this condition is variety specific.

-Areas of fields with green leaves at the top of the plant and some green stems with dry grain. The leaves and stems will eventually dry but don't delay harvest. Harvesting these areas will not add moisture to the grain although the damp straw will likely move through the machine more slowly.

- Some fields having really poor pod set, added pods at the top of the plant in early September that will not reach physiological maturity for a couple of weeks. Waiting for that grain to mature will result in lower a test weight of the grain that is already dry and ready for harvest. If the new grain will not account for at least ten percent of the total yield, don't risk loosing the ninety percent already there.

Summary: Most combines can thrash green stem plants with ease. If the grain is dry and threshes from the pods easily with no harvest loss, then harvest ASAP. Pod shatter and loss of test weight are real losses while green stems are only an inconvenience.

Archive Issue Contributors: 

State Specialists: Peter Thomison (Corn Production), Ron Hammond and Bruce Eisley (Entomology), Pierce Paul and Dennis Mills (Plant Pathology), and Jeff Stachler (Weed Science). Extension Educators: Howard Seigrist (Licking), Roger Bender (Shelby), Dusty Sonnenberg (Henry), Curtis Young (Allen), Ed Lentz (Seneca), Harold Watters (Champaign), Glen Arnold (Putnam), Greg La Barge (Fulton), and Mark Koenig (Sandusky).

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.