CORN
Crop Observation and Recommendation Network

September 22-28, 2003
C.O.R.N. 2003-32

In This Issue:

A) Status of First Year Corn Rootworm in Ohio
B) Potential Exists For Serious Stalk Lodging Problems in Corn
C) Say No To Planting Wheat After Wheat
D) Soil Compaction Concerns from Grain Harvest

A) Status of First Year Corn Rootworm in Ohio - Bruce Eisley and Ron Hammond CORN Questions

Personnel from Ohio State University Extension sampled for western corn rootworm adults (WCRA) in soybeans fields for the seventh year in a row. The sampling was done using Pherocon AM yellow sticky traps placed in more than 90 fields in 22 counties. Six traps were placed in the soybeans on metal posts at canopy height and located at least 100 feet from the field edge and evenly spaced in the field. The traps were placed in the field at the end of July and changed weekly for six weeks until the early part of September. Each week the old traps were removed from the posts, the WCRA were counted and recorded and new traps placed on the posts. After each trapping week, the number of beetles collected were summed and divided by the number of days the traps were in the field resulting in the average number of beetles collected per trap per day. Research from Purdue indicates that catches in soybean of 5 or more beetles/trap/day during any trapping week indicates a potential problem with rootworm in the field the following year.

At this time we have data from 11 counties and 55 fields that were sampled in 2003. The data that we have so far indicates that the average number of WCR beetles/trap/day ranges from a low of 0 during a weekly trapping period to a high of 2.72. Only eleven of the fields had an average of over 1 WCR/trap/day during one of the weeks that the traps were in the field.

So What Does This Mean

Based on these data, if any of these fields are planted to corn in 2004, a treatment (either insecticide or plant resistance) should not be needed for rootworm. These data do not mean that other fields in a county that were not sampled do not need treatment but it does give good information about the fields that were sampled and about the abundance of the beetles this year.

In addition to sampling with the sticky traps, we sampled soybeans in 8 counties along the Ohio-Indiana border for WCRA the 2nd week of August. Twenty sweeps in 5 places in 3 fields per county were taken and contents of the nets bagged and later counted in the lab. Sweep net samples do not tell us if a field has a high enough WCRA population to warrant treatment the next year, but they do tell us the relative abundance of the beetle population. The number of WCRA per 100 sweeps ranged from 0 to 25. This is the first year that we have swept for beetles so we cannot compare data from this year with prior years data but if we compare these sweep counts with data from Indiana and Illinois where they may sweep several hundred beetles in some of their problem counties, it does indicate how low our beetle populations in soybeans are this year.

The final tally of all of the fields sampled with sticky traps will be included in a later newsletter and also on our web site (http://ipm.osu.edu/).

B) Potential Exists For Serious Stalk Lodging Problems in Corn - Peter Thomison and Patrick Lipps CORN Questions

Conditions exist this year for major stalk lodging problems in corn across the state. Extraordinarily wet soil conditions that limited root development and enhanced significant root rot injury combined with widespread foliar disease damage late in the season have increased the likelihood of serious stalk rot problems. Given these "prospects", growers could experience some significant grain losses if they delay field harvest to allow for natural drydown.

For a corn plant to remain healthy and free of stalk rot, the plant must produce enough carbohydrates by photosynthesis to keep root cells and pith cells in the stalk alive and enough to meet demands of grain fill. When corn is subjected to stress such as that caused by late season leaf blights such as northern leaf blight or gray leaf spot, photosynthetic activity may be sharply reduced and carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by remobilizing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear under stress conditions, the removal of carbohydrates results in premature senescence and death of the pith cells in the stalk and root tissues which predisposes plants to root infection by stalk rot fungi. As plants near maturity, this remobilization of carbohydrates from the stalk to the developing ear can result in a rapid deterioration of the lower portion of corn plants with lower leaves appearing to be nitrogen stressed, brown, and/or dead.

In addition to leaf diseases, stresses which increase the likelihood of stalk rot problems include loss of leaf tissue due to hail; injury to the root system by insects or chemicals; saturated soils restricting normal root growth; root rot diseases; and high plant populations. In some locales European corn borer has caused stalk injury which may also contribute to lodging problems.

Most hybrids do not begin to show stalk rot symptoms until shortly before black layer (physiological maturity). It is usually difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved. Although a number of different fungal pathogens cause stalk rots, the most important in Ohio are Gibberella, Collectotrichum (anthracnose), Fusarium and sometimes Diplodia. A symptom common to all stalk rots is the deterioration of inner stalk tissues so that one or more of the inner nodes can be compressed when squeezing the stalk between thumb and finger. Using this squeeze test it is possible to assess potential lodging (if harvesting is not done promptly). To minimize stalk rot damage, avoid harvest delays. Identify fields which are at greatest risk and harvest these fields first. This year fields which are showing extensive northern leaf blight or gray leaf spot would be prime candidates for early harvest. This is not the year to allow corn to dry in the field to the low 20's or high teens before harvest so as to save on drying costs!

C) Say No To Planting Wheat After Wheat - Patrick Lipps and Dennis Mills CORN Questions

Ohio wheat growers are looking at their calendars and noting that the Hessian Fly Safe date for planting wheat in northern Ohio is this week and their soybeans are not yet ready to harvest. Some are considering planting wheat into the wheat fields they harvested in July. The potential disease risks of planting wheat after wheat in Ohio are too high to even think about it! Every year we receive plant samples from wheat fields that were planted back-to-back wheat. Probably a few people have been successful in planting continuous wheat, but our experience is that most are not. It is almost guaranteed that you will not get top yields in these fields. Why? Because Hessian Fly can cause lodging and low yields but also because disease organisms that survive in the old wheat residues will be in the field ready to attack that new crop as soon as the seed germinates. Do not underestimate the significance of wheat diseases in Ohio, the root rot and a few leaf blight diseases are most problematic when wheat follows wheat in a field.

Take-all root rot is the biggest threat. The fungus lives on old wheat roots and lower stems and also on grassy weeds in old wheat fields. When the new wheat crop is planted the fungus moves to the new plants by specialized fungal strands (runner hyphae) when wheat roots contact old residues. Plants infected in the fall will be weaker and often discolored in the spring and generally die before the seed can mature. Cephalosporium stripe is a second problem that occurs when wheat is planted after wheat. This fungus also resides in the old wheat residues and grassy weeds in the field. Infection generally occurs during late winter when the fungus produces spores in cold wet soils. Damage to wheat roots by freezing and thawing provides avenues for the fungus to enter injured roots. Infected plants develop distinctive yellow and brown stripes on the leaves in the spring as plants attempt to grow and produce heads. Most of these plants die prematurely and produce no seed or only small shriveled seed.

There are several foliar diseases that are generally more important in continuous wheat fields. These include Stagonospora leaf blotch, Septroia leaf blotch and tan spot. Infection can occur in the fall or spring, but survival of these fungi on wheat residues within the wheat field make it easy for the fungus to spread to plants whenever rain splashes the spores from residues onto leaf surfaces.

All of these potential problems suggest that you should not plant wheat after wheat. Wheat planting date studies in Ohio have indicated that the highest yields are obtained when wheat is planted from 5 to 10 days after the Hessian Fly Safe date. Attempt to harvest those soybean fields that you plan to plant wheat into as soon as possible and do a good job of planting wheat no-till. The recommendations outlined in last week's CORN newsletter (Sept. 15 - 21, CORN 2003-31) will ensure a high yielding crop. Please review that article for many helpful wheat production recommendations.

D) Soil Compaction Concerns from Grain Harvest - Randall Reeder CORN Questions

A couple of weeks of sunshine have done wonders in drying out corn and soybean fields. But wet soil below the surface may still be easy to compact and lead to problems next spring, or for wheat planted this fall. Subsoiler demonstrations at Farm Science Review last week revealed fairly high soil moisture. More rain could keep fields wet throughout harvest.

Here are some tips to help reduce compaction, ranging from quick and cheap, to things that work long term.

• Run tires at the correct pressure for the load. Many farm tires are overinflated which reduces the tire footprint, increasing compaction. Over inflation also reduces traction.
• Remove excess weights. For a tractor used to pull gravity bed wagons, remove weights that are only necessary for tillage operations.
• Don't fill the grain cart to capacity. On wet soil, plan to empty the grain cart when it's half to three-quarters full. The grain cart is usually the heaviest piece of equipment in the field, followed by the combine and tractors.
• Try to empty the combine before the grain tank is full. Of course this may reduce field efficiency a bit during harvest, but could pay off in less compaction.
• When you make several trips across a field, try to run in the same path, rather than making a new track with each pass.
• Add more tires, or switch to bigger tires or rubber tracks. More rubber in contact with the ground for the same total axle load means tire inflation pressure can be lower, reducing pressure on the soil.
• Practice controlled traffic. This fall will show the value of this system, whereby all farm equipment is the same width and traffic is confined to specific paths year after year. The opportunities for controlled traffic with big equipment are much greater than a few years ago. Controlled traffic uses relatively narrow tires at high pressures, or rubber tracks.
• Use permanent no-till, perhaps with strip-till for corn. Soil that is tilled every two or three years does not develop a good structure that can support heavy loads as well as long term no-till.
  

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: Andy Kleinschmidt        Web Editor: Nathan Watermeier

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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