C.O.R.N. Newsletter 2005-05

Dates Covered: 
March 8, 2005 - March 22, 2005
Harold Watters

Assessing Wheat Stands in Late Winter and Wheat Management During the Spring

Authors: Jim Beuerlein, Robert Mullen, Edwin Lentz, Patrick Lipps

Assessment of wheat stands can only be made after later winter green up when the risk of excessive freezing and thawing is low. This usually occurs by mid to late March, but in some years with extended winter weather this may not occur before the first week of April in northern Ohio. The first inspection of wheat fields should be to look for heaving damage.

Heaving is recognized when the crowns of the plants are pushed up out of the soil as the soil freezes and thaws during late winter. Close examination of the plants indicate that the crowns and upper roots are exposed with only a few roots remaining in the soil. These plants will green up and look normal for a while, but within a few weeks heaved plants will turn brown and die. Growers generally describe this as fields 'going backwards'. Heaving is generally worse in fields with compacted, wet, high clay content soils. Generally, heaving is more important in conventional tilled fields with little surface residue than in no-till fields with residue that protects against wide changes in temperature of the upper inches of the soil. Wheat that is planted too shallow is also more prone to heaving problems than wheat that has been planted at the recommended one and a half inches deep.

Adequate tiller development is essential for high yields, but excessive tillering is unnecessary and may lead to lodging. Fields planted within 10 to 14 days of the Hessian Fly Safe Date using 1.3 to 1.6 million seed per acre (18 to 24 seed per foot of row) with about 20 to 25 lb of actual nitrogen/A applied at planting rarely have problems with low tiller numbers in the spring. In fact they generally have many more tillers than are needed for maximum yield. Our experience from counting heads of wheat in fields prior to harvest indicate that most Ohio fields have from 40 to 60 heads per foot of row. If 20 seed were planted per foot of row then each plant will end up with 2 to 3 head bearing tillers. These are the main tillers that developed during fall growth.

Yield potential is reduced if tiller numbers fall below 25 per square foot after green up. Fifteen tillers per square foot is considered minimum for an economic crop. The number of tillers per square foot is equal to the number of tillers in 20.5 inches of 7 inch wide rows or 14.5 inches of 10 inch wide rows. Obviously, late planted fields should be visited to determine if adequate numbers of tillers are present.

After greenup, wheat plants will continue to develop tillers until the stems begin to elongate at Feekes' growth stage 6. This growth stage generally occurs in early April in Southern Ohio and by mid-April in northern Ohio, but this may vary by as much as two weeks depending on the weather. If nitrogen was applied in the fall at planting, then there is no need to hurry an early spring application. Our research has indicated that you should not count on early applications of nitrogen to stimulate tiller development. Tillers will develop regardless of the amount of nitrogen applied in early spring, especially if some nitrogen was applied in the fall. Wheat plants at over-wintering growth stages (Feekes growth stage 3) do not have a high demand for nitrogen. Remember that these over-wintered plants must develop new root systems before they can take up much nitrogen. This may take several weeks after green up. Tiller development is more a function of temperature and plant density than applied nitrogen amount at this time of year. This is different than what wheat growers observe in more southerly areas, like Virginia or western Kentucky, because the time between spring green up and the end of tiller development is short in Ohio, perhaps only 3 to 4 weeks, whereas in southern states it may be 6 to 8 weeks or more. This is the reason we need to have plants develop adequate tillers in the fall. Tillers will continue to develop until the day length approaches about 14 hours per day in late April, but tiller development may be stopped by high temperatures in mid-April. Nitrogen can be applied anytime between green up and when the first node is visible on the stem (Feekes' growth stage 6) to achieve maximum yield.

Feekes' growth stage 6, or beginning stem elongation, is determined when the first node is visible at the base of the larger tillers on the plants. You can assess growth stage by pulling tillers from the field and stripping the lower leaves and leaf sheaths down to expose the lower stem. The first node will be visible as a hard swelling on the stem about one half inch to an inch and a half above the roots. Determining this growth stage is important for completing nitrogen applications and the timing of applications of certain herbicides with restrictions after this growth stage. It is important to get all the nitrogen on the crop by Feekes' growth stage 6 because over half of the nitrogen that the plant uses to produce yield is taken up over the next 3 to 4 weeks and you want the nitrogen there and available for when the plant needs it.

Predicting Flea Beetle Activity and Stewart's Disease for the 2005 Corn Crop

Authors: Ron Hammond, Bruce Eisley, Dennis Mills, Patrick Lipps

Stewart's bacterial leaf blight has not been of concern in most areas of Ohio over the past two years due to the colder winters that reduced the populations of the corn flea beetle during 2003 and 2004. The occurrence of Stewart's bacterial disease is totally dependent on the level of flea beetle survival over the winter. For many years the winter temperatures have been used to predict the risk of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters. The 'flea beetle index' is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February. Index values less than 90 indicate negligible disease threat, 90-95 indicate low to moderate levels, 95-100 indicate moderate to severe and values over 100 predict severe disease levels.

We checked the average temperature for December, January and February at several locations in Ohio to determine the risk level according to the 'flea beetle index' for 2005. The location and the corresponding index was: Wooster, 83; Hoytville, 80; South Charleston,87; Piketon, 97; and Ashtabula, 81. These numbers indicate that the risk of Stewart's bacterial leaf blight should be low in northern and west central Ohio with the possibility of moderate disease risk in south central Ohio.

Although the 'flea beetle index' has been a relatively good predictor over the years, we still recommend that growers scout their corn fields for the presence of flea beetles, especially if they know they have planted a hybrid that is susceptible to Stewart's disease. For those growers wishing to take preventative action against flea beetle, the newer commercially applied insecticide seed treatments Cruiser and Poncho, or the grower applied products Concur and Latitude, are labeled for flea beetles.

Flea beetle adults become active in the spring when the soil temperatures reach 65 F. Adults are most active on sunny, warm, windless days. They hide in cracks in the soil during windy, cool or cloudy days. After feeding and mating, adult females lay eggs at the base of the corn plants. Larvae feed on corn roots and are full grown in about two weeks. There are at least two generations per year in Ohio. The beetle over-winters as an adult in the soil near corn fields. It prefers bluegrass sod, but may be found in fence rows, roadsides and woods. If the adult fed on diseased corn in the late summer or fall, it may carry the bacterium that causes Stewart's disease of corn in its gut over the winter. In the spring as the corn emerges, the flea beetles feed on the young plants and spread the bacterium which in turn causes seedling wilt and leaf blight. You can get additional information on Stewart's disease of corn on the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/stewarts.htm, or information on the flea beetle from the OSU Extension Fact Sheet CV-1000-94.

Soybean Seed Treatments and Soybean Aphids

Authors: Ron Hammond, Bruce Eisley

There has been considerable interest around the state about using seed treatments in soybean, namely Cruiser, for control of soybean aphid. We do NOT recommend this practice because the time between soybean planting and arrival of soybean aphids in Ohio is probably too far apart for adequate control. While evidence from tests with Cruiser in Ohio and other states does indicate the ability to reduce populations of insects feeding on soybean seedlings, the material does not last long enough to manage mid-to-late season pests. Two factors come into play with soybean and the aphid in Ohio. First, most of our soybeans are planting in May or at latest, early June. Then, soybean aphids, based on past experiences in 2001 and 2003, do not arrive in large numbers until mid-to-late July, approximately 2 months later. It is doubtful that seed treatments will reduce populations at this time. One of few positive field tests came from Wisconsin where soybeans were planted in mid-June and the aphid, because of nearby overwintering, arrived in soybeans by early July. This was only a 3-4 week time interval between planting and aphid arrival. Additionally, laboratory studies from Minnesota suggest that only a month’s worth of protection is offered. Thus, we will continue to recommend traditional IPM management tactics in Ohio: scout and sample weekly, use a threshold of 250 soybean aphids per plant, and treat with foliar insecticide when threshold is reached.

We will continue to examine seed treatments this coming year against soybean aphid, which is expected to be a major problem. We will also be studying seed treatments against other soybean pests, including bean leaf beetle and seed corn maggot. Because of the inability to predict high bean leaf beetle densities in the spring, we do not generally recommend seed treatments for them unless you are in an area with known high populations or perhaps growing soybeans for seed where quality is an important issue. Our experience with seed corn maggot is much better, and we know that when incorporating a living green cover crop such as an old alfalfa field into the soil, the potential for significant stand reduction from maggot feeding is high. Thus, we DO recommend a seed treatment in those cases where a grower is tilling a green cover into the soil. By doing more studies across Ohio and the Midwest this coming year, perhaps our recommendations on the use of seed treatments might change in the future. However, at this time, we still recommend using IPM practices of scouting and using thresholds in most instances!

New Horseweed Management Publication Available

Authors: Mark Loux

Weed scientists from Ohio State, Purdue, and the University of Illinois have co-authored a new publication on horseweed (marestail), titled “Biology and Management of Horseweed”. The publication is available as a pdf file on the OSU Weed Science website – https://agcrops.osu.edu/weeds. OSU Extension weed scientists also have a supply of the printed publication, which we are making available free of charge. Contact Mark Loux (loux.1@osu.edu) or Jeff Stachler (stachler.1@osu.edu) if you would like to have some mailed to you. We appreciate any help you can provide toward getting this publication into retail ag dealerships or other places of business where they would be available to producers. Additional information on horseweed can also be found at the following Purdue University weed science web page - http://www.btny.purdue.edu/weedscience/marestail/index.htm.

Don’t Overlook the Benefits of Crop Rotation

Authors: Robert Mullen, Patrick Lipps, Peter Thomison

The corn-soybean rotation is by far the most common cropping sequence used in Ohio. This crop rotation offers several advantages over growing either crop continuously. Benefits to growing corn in rotation with soybean include less disease and insect build up, more weed control options, fewer difficult weed problems, and less nitrogen fertilizer use. Corn grown following soybeans typically yields about 10 percent more than continuous corn, and requires 12% less nitrogen fertilizer.

No-till cropping systems, which leave most of the prior crop residue on the surface, are more likely to succeed on poorly drained soils if corn follows soybean or meadow rather than corn or a small grain, such as wheat. The influence of crop rotation on corn response to tillage and soil type has been well documented in long-term OSU-OARDC studies. On poorly drained Hotyville silty clay loam soils in NW Ohio, where corn followed soybean or meadow, yield differences between no-till and tilled ground were greatly reduced. Crop rotation with soybeans had much less effect on corn response to tillage on well-drained Wooster silt loam soils in NE Ohio. This yield advantage to growing corn following soybean is usually much more pronounced when drought occurs during the growing season. In studies conducted in Minnesota, the yield advantage to an annual rotation of corn and soybean compared with monoculture was frequently greater than 25% in low yielding environments.

The uncertainty over soybean rust and other soybean stress issues (soybean aphid), along with what some perceive as greater economic returns, has generated greater interest this year in second year corn. Many growers recognize the risks associated with continuous corn but question the degree to which corn yields would be reduced by inserting a second year of corn in their cropping sequence, i.e., alternating two years of corn with a year of soybean. After reviewing past crop rotation studies, I’ve found that some studies show no yield difference between second year corn and continuous corn, whereas other studies show a slight yield advantage for second year corn over continuous corn.

Growers who intend to plant second year corn should consider management practices that will minimize potential yield losses. Dr. Bob Nielson, corn Extension agronomist at Purdue, and some of his colleagues have written an article entitled “Mitigate the Downside Risks of Second Year Corn” (available online at http://www.agry.purdue.edu/ext/corn/news/articles.04/CornCorn-1222.html) that contains a good list of suggestions for corn growers willing to accept the risks associated with second year corn.

The Fight Against Soybean Rust Starts with Calibrating Your Sprayer

Authors: Erdal Ozkan

The months of March and April are the best time to thoroughly check the sprayer and calibrate it properly. To do this now is more important than ever before because of the arrival of Asian Soybean Rust to the U.S. This disease has been detected in 9 southern states, as far north as Missouri. It may arrive in Ohio this year. There are no soybean varieties currently available that have high levels of resistance to soybean rust. This leaves us with only one option: be prepared to do as good a job as possible spraying fungicides registered to control this disease.

Fungicides manufactured to control Soybean Rust work. However, success will largely depend on proper application. Proper application starts with selecting the right equipment, specifically nozzles, and spraying the right amount of fungicide uniformly across the field before the disease is detected.

Pesticide manufacturers have invested heavily to determine the most effective and economical application rate for the fungicides labeled for Soybean Rust. However, it is up to the applicator to make sure the recommended amount is applied.

Why calibrate?
Calibration is the best way to find out if the sprayer is ready to deliver the desired rate. And do it early. The window of opportunity to spray for soybean rust is much narrower than for most pests. You will not want to take time to calibrate after the rust has arrived.

Results of many "Sprayer Calibration Clinics" in Ohio show that only a third of applicators are applying chemicals at a rate within 5 percent (plus or minus) of the intended rate, which is the accuracy level recommended by USDA and EPA. Of the two-thirds who are missing the mark, about half are under spraying and the other half are over spraying. In one extreme case, the applicator would have been over spraying by 75% had he used the nozzles he just purchased and installed on the boom. Other states show similar accuracy levels.

Calibration takes about 30 to 60 minutes and requires only three "tools": a watch, a measuring tape, and a jar graduated in ounces. Several calibration methods are available but the one described below is simple, straightforward, and does not require the memorization of equations.

Calibration method
When the spray tank is clean, fill it at least half full with water since the amount of water in the tank may affect travel speed. Measure the distance between nozzles in inches and then drive a designated distance depending on the nozzle spacing. For a nozzle spacing of 20 inches, drive 204 feet at normal spraying speed. Drive 136 feet for 30-inch spacing; 113 feet for 36-inch spacing; and 102 feet for 40-inch spacing. Then run the parked sprayer at the same pressure level for the same amount of time it took you to drive the designated distance, and collect the output of each nozzle. Calculate the average nozzle output by dividing the total output from all nozzles by the number of nozzles tested. The average nozzle output in ounces equals the gallons per acre applied. For example, if you catch 15 ounces the rate is 15 gallons per acre.

The next step is to minimize the application error. If the difference between your intended application rate and the actual rate is greater than ± 5 percent of your intended rate you should make some adjustments. For example, if your intended application rate is 20 gpa, the calibrated rate should be between 19 and 21. For small changes in the application rate try adjusting the pressure. For larger changes either adjust the travel speed or replace nozzles with the appropriate size. You need to repeat the calibration process until your application error is no greater than ± 5 percent.

This calibration method is explained in detail in Ohio State University Extension (OSUE) Fact Sheet AEX-520, available from your County Extension Office, or from the Ohioline web site: http://ohioline.osu.edu/aex-fact/0520.html.

Just spraying the right amount of fungicide on each acre is not enough to achieve effective control of soybean rust. Uniform deposition on the spray target is as important as the total amount deposited. Each nozzle type produces a unique spray pattern. Some nozzles require precise overlapping of patterns from adjacent nozzles. Check the nozzle catalog to find out the appropriate boom height for your nozzle spacing that will produce uniform spraying across the boom.

Calibrate frequently
Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used may require a new calibration. A Nebraska survey showed that the more often a sprayer was calibrated, the more accurate the application rate. If you hear on the news this summer that Soybean Rust has reached States south and southwest of Ohio, be prepared to spray for soybean rust. Do this after recalibrating your sprayer.

Soybean Rust Update after the Brazil Trip

Authors: Anne Dorrance

Well, it appears that this rust fungus overwintered in Florida. Tests were started late last week to determine if the spores were still viable but from the appearance of the tissue in the picture, I would be surprised if they were not new lesions. It is still not time to panic. I learned a lot in Brazil and at the rust meetings in Arizona last week, and the take home messages at both meetings were:

1. THIS IS MANAGEABLE – we saw humungous fields in Brazil and the only place where we could find active rust lesions were in the check plots and in the skips of the sprayers. US producers will actually have more resources available than the Brazilians to assist in tracking and monitoring soybean rust in the US, and to assist in the best timing of fungicide applications. Production practices differ in Brazil for managing this disease based on latitude as well as disease pressure. One thing the farm managers all said that every year has been different and rainfall plays a key role in how the disease develops.

2. Fungicide timing is key to limiting losses – both strobilurin and triazole fungicide chemistries work best if applied prior to spore arrival. Not 2 weeks before – but just prior. Triazoles have the added benefit that if lesions have started they can stop or arrest development for the length of time the fungicide is in the leaf.

3. Coverage and canopy penetration are critical to the ability of the fungicides to limit development. This is a lower canopy disease. It is still not clear why, we heard conflicting information on this, but the bottom line is that this is where the fungicide needs to go.

4. The critical time to protect plants will be from beginning flowering (R1) to full seed (R6). This is where the greatest yield losses do occur. It is rare that infections can get established in the late V-stages. But this is one of those cases where we will have to monitor.

5. Rust is going to be challenge to diagnose. Early brown spot looks exactly the same as early rust lesions. Once the uredinia and spores are produced on these lesions – it’s a no brainer and then becomes easy to identify.

6. When to begin fungicide applications and what products to use will depend on two things – how much inoculum actually builds-up in the southern US. For example if this rust development is slow and does not spread to Arkansas until late June – this will delay all of our fungicide applications. If the rust develops quickly through the spring and Kentucky is reporting active lesions by mid-June, we should be applying fungicides much earlier.

7. We are still waiting for some final details to be worked out on the monitoring system. At this point, Ohio will have 30 plots (20 courtesy of United Soybean Board via check-off dollars and 10 USDA-APHIS and Ohio Dept. of Agriculture Plots). ALL suspect finds will go through the OSU C.Wayne Ellett Plant and Pest Diagnostic Clinic for verification prior to uploading into the national database. This national database is not launched just yet, but when it is – we will all have access to this map and can all monitor the development of rust.

One final thing – this is going to be a very dynamic situation. Companies are going to “tweak” their labels based on the data from this past year in South America. By soybean flowering time here – some of this should be settled as well as some additional Section 18s. This is the first time this disease will have developed in the US and we will learn the hard way what can be easily transferred from South America and what can not. But I think in the long run, with a little common sense and some cool heads, we can deal with this – even better than they have in South America.

Archive Issue Contributors: 

State Specialists: Erdal Ozkan (Ag Engineering), Mark Loux and Jeff Stachler (Weed Science), Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Ed Lentz (Agronomy), Robert Mullen (Soil Fertility) and Jim Beuerlein (Soybean and Small Grain Production). Extension Agents and Associates: Roger Bender (Shelby), Steve Bartels (Butler), Mark Koenig (Sandusky), Dusty Sonnenberg (Henry), Greg LaBarge (Fulton), Bruce Clevenger (Defiance) and Harold Watters (Miami)

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.