CORN
Crop Observation and Recommendation Network

April 29 to May 6, 2002
C.O.R.N. 2002-11

In This Issue:

A) Adjusting Corn Management Practices For A Late Start
B) Flea Beetles And Stewart's Leaf Blight And Wilt Of Corn
C) Powdery Mildew Developing In Some Wheat Fields
D) Bean Leaf Beetle And Slug Watch
E) What To Do On A Rainy Day

A) Adjusting Corn Management Practices For A Late Start - Peter Thomison CORN Questions

As prospects for a timely start to spring planting diminish, growers need to reassess their planting strategies and consider adjustments. Since delayed planting reduces the yield potential of corn, the foremost attention should be given to management practices that will expedite crop establishment. The following are some suggestions and guidelines to consider in dealing with a late planting season.

Although the penalty for late planting is important, care should be taken to avoid tillage and planting operations when soil is wet. Yields may be reduced somewhat this year due to delayed planting, but effects of soil compaction can reduce yield for several years to come.

If you originally planned to apply nitrogen and herbicides pre-plant, consider alternatives so that planting is not further delayed when favorable planting conditions occur. Although application of anhydrous N is usually recommended prior to April 15 in order to minimize potential injury to emerging corn, anhydrous N may be applied as close as a week before planting (unless hot, dry weather is predicted). In late planting seasons associated with wet cool soil conditions, growers should consider side-dressing anhydrous N (or UAN liquid solutions) and applying a minimum of 30 lb/N broadcast or banded to stimulate early seedling growth. This latter approach will allow greater time for planting. Similarly, crop requirements for P and K can often be met with starter applications placed in bands two inches to the side and two inches below the seed.

Keep time expended on tillage passes and other preparatory operations to a minimum The above work will provide minimal benefits if it results in further planting delays. No-till offers the best option for planting on time this year. Field seedbed preparation should be limited to leveling ruts left by last year's wet, problem harvest - disk or field cultivate very lightly to level. Most newer planters provide relatively good seed placement in "trashy" or crusted seedbeds. Final tillage passes just before planting can be beneficial in suppressing weeds, but may not be practical this year. In many cases, it will be more profitable to complete planting first and control weeds with post planting applied herbicides. Planting into seed-beds which contain emerged weeds will make post planting weed control critical. Effective burn-down applications will help minimize the potential for major weed problems developing later in the season.

Don't worry about switching hybrid maturities unless planting is delayed to late May. If planting is possible before May 20, plant full season hybrids first to allow them to exploit the growing season more fully. Research in Ohio and other Corn-belt states generally indicates that earlier maturity hybrids lose less yield potential with late plantings than the later maturing, full season hybrids.

With no-tillage or reduced tillage, increase seeding rates 10% over those used with conventional tillage. Consult seed company recommendations for specific hybrid planting rates under reduced tillage. Lower yields in no-till can sometimes be related to sub-optimal plant populations at harvest.

B) Flea Beetles And Stewart's Leaf Blight And Wilt Of Corn - Pat Lipps, Bruce Eisley, & De nnis Mills CORN Questions

We have received several reports of high flea beetle populations in certain early planted corn fields in Ohio. Earlier this spring we had an article in the C.O.R.N. newsletter about the increased probability of higher than normal levels of flea beetles overwintering in Ohio due to the relatively warm winter conditions in December, January and February of this year. It appears that these predictions were correct, at least in certain situations where farmers were able to plant corn in April. In field corn, flea beetles by them selves cause little damage to the corn plant, but when they carry the bacterium that causes Stewart's leaf blight and wilt, damage to the corn can result. In the spring, as corn emerges from the ground, the flea beetles feed on the young plants and spread the bacterium which in turn causes seedling wilt and leaf blight. Continued beetle feeding spreads the bacterium causing leaf blight. Additional information on Stewart's bacterial wilt and leaf blight can be obtained on the Ohio field crop disease web site: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/

The best option now is to scout fields for flea beetles and to get information from your seed dealer about the relative susceptibility of the hybrids you have planted. Hybrids that are susceptible should be monitored more closely for flea beetle populations. It is nearly impossible to predict how many of the overwintered flea beetles carry the Stewart's bacterium so we can not give you exact threshold levels on which to base insecticide applications. Your decision to control flea beetles probably has more to do with the overall condition of the field, the growth stage of the corn and the plant population. Flea beetles are more active at warmer temperatures (above 65 F) and hide in cracks of the soil during windy, cool or cloudy periods. Additionally, the corn plants are susceptible to the wilt phase of the disease only during early stages of growth. The loss of stand due to Stewart's wilt is rarely more than 10% on susceptible field corn hybrids. This reduction in stand generally has little effect on yield especially since affected plants are scattered through the field. If the field suffers from additional problems, and greater loss of stand will affect yield, then flea beetle control may be justified.

C) Powdery Mildew Developing In Some Wheat Fields - Pat Lipps CORN Questions

The wheat crop has developed relatively fast this spring due to warmer weather conditions. Wheat in southern Ohio will be entering the boot stage soon whereas in the north the crop is in the late phases of jointing (jointing to flag leaf emergence). The same conditions that have favored the rapid development of the wheat crop is also favoring the development of powdery mildew. There are many varieties grown in Ohio that are susceptible to powdery mildew, so under mild conditions with temperatures in the 60's and low 70's and high humidity the disease develops rapidly.

Wheat producers are encouraged to scout wheat fields in the flag leaf emergence to boot stage for powdery mildew. Plan to scout those fields planted to susceptible varieties because these are the fields most likely to sustain yield loss. Research has shown that if disease affects the upper two leaves by heading, yield losses can be as high as 25% on susceptible varieties. Scout fields by pulling about 50 individual tillers randomly through the field. Evaluate individual tillers by looking at the top (flag) leaf, then the second leaf. One percent of the leaf area (about 2-3 mildew pustules) on the second leaf is the threshold level for applying a fungicide. By the time the second leaf becomes infected, the lower leaves generally have a lot of mildew on them. Fields that need a fungicide application will have lots of powdery mildew in the lower canopy, but mildew becomes an economic problem only if the disease advances to the upper leaves before flowering.

Tilt fungicide (4.0 fl oz/A) has a 24c special local need label in Ohio for application through Feekes growth stage 10.5 (full head emergence). Of the fungicides available to Ohio growers, this material has better efficacy against powdery mildew. We recommend that only susceptible or moderately susceptible varieties be treated because of their higher potential for yield loss, because resistant varieties have less disease and do not show as great a response to fungicide application. Information on powdery mildew and variety susceptibility can be obtained on the Ohio Field Crop Disease web site: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/ and additional information on scouting wheat and fungicide applications can be obtained from the OSU Extension publication "Improving Wheat Yields in Ohio" on the Ohioline web site : http://ohioline.osu.edu/iwy/

D) Bean Leaf Beetle And Slug Watch - Ron Hammond & Bruce Eisley CORN Questions

Bean leaf beetle adults are starting to emerge, and are being found in Ohio. A few soybean fields were planted the past week between rain showers, but with the forecast for more rain this week, there will probably be little additional planting for a while. As these few early-planted fields emerge, the bean leaf beetles will tend to go to them. This could allow these fields to serve as "trap crops", receiving the majority of adult insects. A similar situation occurred in the late 1980s, and some of those early planting fields that year had very large populations of beetles. Thus, growers should watch their early-planted fields very closely for large populations and heavy feeding by the bean leaf beetle.

With the cool and wet weather, conditions are favorable for slow crop growth but good slug activity. If slugs are hatching in these fields, this could result in a serious situation. Growers are advised to watch their fields as crops emerge for early feeding by slugs.

E) What To Do On A Rainy Day - Anne Dorrance, Pat Lipps and Dennis Mills CORN Questions

Many field crop diseases can be managed successfully with host resistance. However, not all wheat, soybean or corn varieties are resistant to all diseases. In addition, pathogens adapt to resistance genes that are used in varieties that are planted over a wide region for a number of years. The best means to tell if your variety has the right 'resistance package' for your farm is to keep good records.

Take this rainy period to maintain records of the varieties to be planted and their resistance traits. For example, when growing soybeans, record the following:

1. Variety, brand, cultivar designation and relative maturity
   
   
2. Phytophthora resistance gene(s) [ is it Rps1k or Rps1c] as well as the partial resistance score [some companies call this field resistance or tolerance - watch the scales, it is scored differently by different companies]. Record if the variety has high, medium or low partial resistance.
   
   
3. Soybean cyst nematode - which source of resistance is in the variety (ie: none, PI88788, or Peking).
   
   
4. Sclerotinia white mold (Sclerotinia stem rot) - record the score given by the company or its relative level (moderately resistant, susceptible or highly susceptible).

Then through the course of the season, as you are scouting your fields, make notes on what diseases you find in your fields or are prevalent in your region. If soybean cyst nematode is the problem then after harvest, take a soil sample. Record if the counts go up or down after planting the resistant variety. For Phytophthora, if after a wet rainy period in July or August. Record how much stem rot was found. If the weather conditions are conducive to disease or there is no build-up of SCN, then you can continue with your current management plan. However, if the SCN population increased and there was a substantial amount of Phytophthora stem rot, you now have the information to make a better variety selection that will provide more protection for the 2003 or 2004 growing seasons.

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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: Steve Prochaska        Web Editor: Tom Rosati

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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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