CORN
Crop Observation and Recommendation Network

April 28 - May 5, 2003
C.O.R.N. 2003-11

In This Issue:

A) Monitor Planting Depths in Corn for Optimal Stands
B) Plant Full-Season Corn Hybrids First
C) Early Season Insect Problems
D) First Year Corn Rootworm in Ohio
E) Weed Control in Wheat
F) Wheat Growth Stage: Time to Begin to Scout Wheat for Disease
G) Fungicides Currently Labeled on Wheat in Ohio
H) The Effect of Lack of Rainfall on Pre-emergence Herbicides

A) Monitor Planting Depths in Corn for Optimal Stands - Thomison CORN Questions

Several factors need to be taken into consideration when determining a proper planting depth for corn. These include soil moisture and temperature, planting date, soil type, and tillage. Temperatures will be higher at 1 to 2 inches than at 3 inches or deeper. Soils are generally cooler and wetter in mid to late April than in early to mid May. A planting depth of 11/2 to 2 inches is often recommended for corn. In April, when soil is usually moist and evaporation rate is low, the seeding depth should be in the shallower end of this range (not much deeper than 1 1/2 inches). This is particularly important in no-till plantings (especially under heavy corn residue) where soil temperature and moisture will be cooler and wetter than in conventionally tilled soils. However, if you try to plant less than 1 1/2 inches deep, some of the seed may end up much shallower due to variation in the seedbed. These shallow plantings often result in poor nodal root development (this probably contributed to many of the rootless corn problems we encountered in 2002), expose seed more to surface applied herbicides, and should be avoided in all tillage systems. As soils warm up and evaporation rates increase, consider deeper planting - up to 2 1/2 inches on non-crusting soils - to reach moist soil.

Remember, when conditions vary from the norm, planting depths should be adjusted accordingly to optimize emergence. Don't automatically use the depth setting you finished with last year!

B) Plant Full-Season Corn Hybrids First - Thomison CORN Questions

Plant full season hybrids first to allow them to exploit the growing season more fully. Full-season hybrids generally show a greater yield reduction when planting is delayed compared with short- to mid-season hybrids. Once the full-season hybrids are planted, alternately plant early-season and mid-season hybrids, to take full advantage of maturity ranges and to give the later-maturing hybrids the benefit of maximum heat-unit accumulation. In areas with longer growing seasons, consider planting some acreage to early hybrids to have new corn for the early market (which usually commands a premium price and thus partially offsets the income effect of the lower yield associated with early hybrids). Planting early hybrids first, followed by mid-season, and lastly the full-season hybrids also spreads the pollination interval for all the corn acres over a longer time period and may be a good strategy for some drought-prone areas.

C) Early Season Insect Problems - Hammond and Eisley CORN Questions

A significant amount of corn and soybeans has been already planted, and many more acres will go in this week. Over the next few weeks, growers are advised to begin monitoring insect pest populations in their fields. Although problems with specific pests are not being reported just yet, the situation could change quickly. Scouting should include monitoring for cutworms and flea beetles in corn, alfalfa weevil in alfalfa, bean leaf beetle in soybean, along with slug problems in numerous crops, to name just a few. Watch this CORN newsletter throughout the month of May for updates on these and other early season pests!

D) First Year Corn Rootworm in Ohio - Eisley and Hammond CORN Questions

There continues to be a lot of interest about the possibility of problems with first year corn rootworm in Ohio. Based on monitoring by Ohio State University Extension personnel in 2002, beetle numbers did not suggest a large likelihood of significant or widespread problems. There were numerous reports of lodged and goose-necked corn were received last summer, but we believe that this was most likely due to poor root development because of the miserable growing conditions during the spring rather than rootworm feeding. See the CORN newsletter from February 3-17, 2003, C.O.R.N. 2003-3, for a complete article related to the issue.

We are aware that many growers are taking action against this insect in first year corn. For those growers choosing to make an insecticide application, whether a soil insecticide or a seed treatment, we recommend that they leave check strips to determine if the treatment was warranted or not. Extension personnel intend to follow treated fields this coming summer to determine the value of these insecticide applications. We will also further monitor the first year corn rootworm population to determine how widespread the problem is.

E) Weed Control in Wheat - Stachler and Loux CORN Questions

The cold soil temperatures have caused wheat to be shorter than normal. Thus, allowing winter annual and perennial weeds to be more competitive with the wheat and allowing more summer annual weeds to germinate than normal. All wheat in the state is at or past the jointing stage, therefore dicamba should no long be used. Wheat in southern Ohio is near flag leaf emergence, wheat in central Ohio will most likely be at flag leaf emergence by the end of this week, and wheat in northern Ohio is beyond the jointing stage. Therefore it is very important to check the stage of wheat before applying herbicides. Below are some comments about the remaining herbicides:

• We conducted a quick search of 2,4-D and MCPA labels and found the majority to allow application anytime before boot stage. A few labels specify application only until joints are formed in the stem. To reduce the risk of injury after jointing, use water as the carrier and do not apply more than ½ pint/A of ester or 1 pint/A of amine. Most broadleaf, summer annual weeds and mustard species will be controlled by 2,4-D. 2,4-D should reduce the competition of Canada thistle. A tank-mix with Harmony Extra will control most weed species.
  
• Curtail can be applied at rates up to 1.5 pints/A anytime before boot stage, and may be the most effective option on dandelions and Canada thistle. Curtail will also control giant and common ragweed and common lambsquarters.
  
• Harmony Extra, Harmony GT, and Express can be applied until the flag leaf is visible. Harmony Extra is the most effective wheat herbicide for control of winter annuals, but will not control ragweeds and often does not completely kill purple deadnettle. The addition of 2,4-D with Harmony Extra will increase control of summer annual broadleaf weeds, dandelion, and Canada thistle. When tank-mixing with 2,4-D, follow the most restrictive label with regard to wheat stage.
  
• Buctril should be applied before the boot stage. Buctril will control most of the summer annual broadleaf weeds and reduce the competition of Canada thistle and most winter annual weeds.
  

F) Wheat Growth Stage: Time to Begin to Scout Wheat For Disease - Lipps CORN Questions

The cold night temperatures over the past week has dropped soil temperatures back to levels that occurred earlier this month. Cooler soil temperatures generally limit growth and development of the crop. Although, wheat growth appears slow, the crop development is about normal based on the long term average. However, the plants may be shorter than expected for their reported growth stage. Wheat fields in southern Ohio are in flag leaf emergence growth stage (Feekes growth stage 8) or they will be in this stage later this week. In northern Ohio the earlier planted fields are at jointing growth stage (Feekes growth stage 6) and the later planted fields are still at late tillering growth stages. With warmer weather this week most northern counties should report wheat at growth stage 6 by the end of the week. In most areas wheat is rated good with some counties reporting excellent stands in the west central part of the state. In north central and north west Ohio some fields appear to not be growing as quickly, however warmer days should enhance root development and nitrogen uptake to improve their condition. Yield potential for the state looks good to excellent so far.

Feekes growth stage 8 is early flag leaf emergence. A mature wheat tiller has four nodes on the stem that correspond to the presence of four main leaves. The top leaf is the flag leaf. Flag leaf emergence occurs in Ohio in late April or early May depending on location and planting date. To determine growth stage pull some of the larger tillers from various locations in a field. Strip the lower leaves off the stem to expose the lower portion of the stem. The first node is usually from a half inch to three inches from the stem base. Locate this first node and then count the number of leaves above this node. At Growth Stage 8 the flag leaf is just emerging at the top and there will be three leaves between the flag leaf and the first node. If only three leaves are counted on the stem then the wheat is at an earlier growth stage, probably at Growth Stage 6 with one node detectable or Growth Stage 7 with two nodes detectable. Regardless, at this time of year the time between growth stages can be only a few days when the soil temperature is above 55 F and the air temperature is in the 60 F to 70 F range.

Although no significant disease problems have been reported in the state so far, it would be wise to begin to visit fields at flag leaf emergence to check for the presence of diseases like powdery mildew. Powdery mildew is first detected on the lower leaves and causes economic damage when it spreads to the upper leaves of the plants. Take a few notes on the level of disease and return to the field in the next week or so to see if disease is progressing. If disease continues to progress up the plants a fungicide application may be warranted. This is extremely important if you are growing one of the more susceptible varieties currently available.

G) Fungicides Currently Labeled on Wheat in Ohio - P. Lipps and D. Mills CORN Questions

Ohio wheat producers have several fungicide products to choose from to help manage foliar diseases like powdery mildew, Stagonospora leaf and glume blotch and leaf rust. Fungicides are recommended when an economic level of disease occurs in the field and the variety grown is susceptible to disease. Over the years fungicides have been most valuable to wheat seed producers, growers producing Identity Preserved (IP) varieties and to commercial wheat producers during years when weather conditions favor epidemic development of foliar diseases. To date there are five different products available for use by wheat growers. Tilt (Syngenta) and PropiMax (Dow AgroSciences) contain the sterol inhibitor propiconazole . The products, Headline (BASF) and Quadris (Syngenta) contain strobilurin type chemistry. The active ingredient in Headline is pyraclostrobin and azoxystrobin is the active ingredient in Quadris. Stratego (Bayer) contains a combination of the sterol inhibitor propiconazole and the strobilurin trifloxystrobin. Currently, all of these materials are labeled for application through Feekes Growth Stage 10.5 (full head emergence). Tilt, PropiMax, Headline and Stratego have 24(c) special labeling in Ohio for the Feekes Growth State 10.5 application.

The decision to use a fungicide should be based on economics. Growers should take into account the value of the crop, the level of susceptibility of the variety grown and the amount of disease present in the field. Thus, scouting fields is very important because fungicides have to be applied before serious leaf damage has occurred. Generally, fungicides provide greater economic returns when applied to fields before the top two leaves become diseased before full head emergence. All five of these fungicides are very good materials, however each has a little different activity against the various diseases in Ohio wheat fields. Tilt and PropiMax at 4.0 fl oz/A have excellent activity against powdery mildew, Stagonospora blotch and leaf rust. Headline (9 fl oz/A), Quadris (6.2 to 10.8 fl oz/A) and Stratego (10 fl oz/A) are less effective on powdery mildew, but are usually more effective against leaf rust. Therefore, if you are targeting powdery mildew then choose Tilt or PropiMax. Any of these fungicides would be adequate for the other diseases or disease combinations when applied at the appropriate time. Depending on the rate used, the cost of the various fungicides will range from around $9 to over $20 per acre. Cost should be one of your selection criteria. For more information on wheat diseases, scouting and fungicide use, visit the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease and click on wheat, then on the disease of concern.

H) The Effect of Lack of Rainfall on Preemergence Herbicides - Stachler CORN Questions

Corn has been planted for greater than 10 days in many parts of the state with little or no rainfall. For preemergence herbicides to be effective, rainfall is needed to incorporate and activate the herbicides. For most herbicides at least one inch of rainfall, but preferably 1.5 inches of rainfall is needed for proper incorporation and activation. Balance, Harness, and Surpass only need about 0.5 to 0.75 inch of rainfall for proper incorporation and activation.

In conventional tillage fields where rainfall has been inadequate to incorporate and activate herbicides, consider rotary hoeing. The rotary hoeing will incorporate some of the herbicide and control weeds before they emerge. The best time to rotary hoe is when the weeds are in the "white stage". The "white stage" means that weed seeds have germinated, but have not emerged and that they are not green in color. Once a weed has emerged, rotary hoeing will most likely not control that plant. Rotary hoeing usually should be done 7-14 days after planting.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

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: Nathan Watermeier

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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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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