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Ohio State University Extension


C.O.R.N. Newsletter 2005-07

Dates Covered: 
April 4, 2005 - April 12, 2005
Steve Prochaska

Fungicide Timing is Key to Manage Soybean Rust

Authors: Anne Dorrance

The drills and planters are most likely primed and calibrated for planting this season. So if this is a normal Ohio spring – it will be raining and you will have time to read this article!! One of the big lessons from South America and South Africa is that timing of fungicides is key to how well they work. Any given fungicide will have so many days that it will protect a plant. This goes for all products on all crops. On soybeans, many of the products for rust have a 14 to 21 day “life”. So if you spray your field and the rust spores do not arrive until day 20, then you’ve just lost some money and will have to immediately spray again – provided it is before the R5 growth stage. The best use of your fungicide dollar, whether you choose a strobilurin or a triazole, is to have it on the plant before the spores arrive, but only by 2 to 3 days. This will be an easier task for some than for others. If you have total control over your sprayer – know how many days it will take to cover your fields. You may not have as many options, if you must rely on a commercial applicator – but they will also be watching the movement of rust – and will have their timing set on the total acreage of their customers.

The next question, you most likely have – is how do I tell that spores are arriving in my area? Routinely, on an annual basis, we track the movement of corn rust and wheat rust. Our wonderful, smart, intuitive colleague from Kentucky (yes, we are buttering him up), calls us and reports that rust has been identified in his state. Annually, we then find rust in southern Ohio and 10 days after that, we find rust in northern Ohio. As many of you know, when you find these first rust lesions, they are very rare and scattered across the region. We expect soybean rust to be the same. The only exception will be, if rust builds up rapidly in the south – with tons and tons of inoculum on kudzu, soybeans, and other hosts. In this case – a more aggressive and conservative approach will be needed.

This year with soybean rust, you will be able to follow the movement on the USDA soybean rust website . Go to this website and you will see a map of the United States with the areas that have been scouted and found to be negative (green) and areas that have been scouted and reported red. In the comments pages will be information on the amount and intensity of the infection. You will then be able to click on the state of Ohio. On this page and in this newsletter, I will be providing updates throughout the season on appropriate fungicide timing and strategies.

Growth stage of the soybean crop is going to be critical to monitor. The most critical time will be from flowering (R1) to full seed (R6). Fungicide applications at R6, will have little effect because the there is little yield loss after this time – but more importantly, there are restrictions on the use of these materials after R5. Many of the preharvest intervals are 21 days or longer.

As of today, April 1, the movement of rust appears to be slow and finds are isolated. But needless to say, this will be an interesting season.

Synchrony XP Receives Federal and Ohio Registration

Authors: Mark Loux

In a previous C.O.R.N. article (12/2004), we discussed Canopy EX, the initial replacement product for Canopy XL. Dupont has introduced Synchrony XP, another chlorimuron-containing herbicide that can be applied preplant, preemergence, or postemergence, without the 45-day period between application and soybean planting that limits the use of Canopy EX. Synchrony XP has the same ratio of chlorimuron (Classic) to thifensulfuron (Harmony GT) that was in Synchrony STS, but a lower percentage active ingredient (so product rates are higher for XP compared to STS). Synchrony XP is labeled at rates of chlorimuron that are comparable to those provided by Canopy XL and EX, and it can aid in burndown and provide significant residual control when applied at those rates. The product rate comparison to provide similar amounts of chlorimuron is as follows:

2.5 oz Canopy XL = 1.1 oz Canopy EX = 1.1 oz Synchrony XP
3.5 oz Canopy XL = 1.5 oz Canopy EX = 1.5 oz Synchrony XP

The benefits of using a chlorimuron-containing product in preplant soybean programs include the following: 1) chlorimuron aids in the burndown (when combined with 2,4-D and/or glyphosate) of a number of broadleaf weeds, including dandelion, marestail and ragweeds (if not ALS-resistant), prickly lettuce, purple deadnettle, henbit, and mustards; 2) chlorimuron provides residual control of many annual broadleaf weeds, allowing for more effective control of tough weeds such as giant ragweed and ultimately resulting in more flexibility in postemergence herbicide application timing (other residual herbicides can provide this same flexibility as well).

Unfortunately, the sulfentrazone (Authority) component of Canopy XL, which is absent in Canopy EX and Synchrony XP, did provide residual control of black nightshade, waterhemp, and ALS-resistant marestail. Canopy EX and Synchrony XP do not provide residual control of these weeds. Consequently, although chlorimuron provides a fairly unique combination of burndown plus residual weed control, other residual herbicides (e.g. Valor, Gangster) may have a better fit in soybean herbicide programs where these weeds have been problematic.

Spring Has Sprung - Current Weed Growth Status!

Early-flowering winter annuals, such as common chickweed, purple deadnettle, henbit, annual bluegrass, whitlowgrass, and speedwell species, are flowering and beginning to produce viable seeds. Burndown treatments should therefore be applied very soon where the goal is to reduce winter annual seed production. Applications within the next two weeks should greatly reduce seed production for these weeds. Later applications will allow plants to produce significant quantities of seeds, which will maintain or increase the weed population for future growing season.

Giant ragweed, spring germinating - marestail/horseweed, Atriplex, and knotweed species have begun to emerge in central Ohio. What does this mean? Non-selective burndown herbicides should be added to residual herbicides to ensure complete control. In some fields, the addition of 2,4-D ester may be adequate, but most will also require glyphosate or Gramoxone.

Reminders on Spring Dandelion Control

Authors: Mark Loux

Dandelion continues to be problematic in many fields in Ohio and surrounding states. Dense, well-established stands of dandelion can interfere with crop establishment and growth, especially when the crop and weeds are competing for limited soil moisture. Getting a well-established dandelion population under control can be a several-year process of implementing the most effective treatments in fall and spring. Fall application of herbicide can be one of the more effective methods of reducing dandelion stands, but rarely is effective enough without follow up treatments the next spring/summer. In fields that have not received a fall treatment, selection and timing of spring herbicide applications can be especially important to get a leg up on the problem. Here’s what we know from several years of research:

- Spring burndown treatments should be applied before dandelion flowers begin to senesce, since herbicide effectiveness decreases in later growth stages. Consequently, treatments should be applied earlier in spring in southern Ohio compared to northern Ohio.
- The combination of 2,4-D ester plus glyphosate has been more effective than glyphosate or 2,4-D alone across a range of application dates and weather conditions, and especially under cold conditions.
- A 2,4-D ester rate of 1.0 lbs active ingredient per acre can be more effective than the 0.5 lb rate. 2,4-D rates should be limited to 0.5 lb when corn or soybeans will be planted within 1 to 2 weeks. This rate should be applied at least 7 days before soybean planting. Several 2,4-D ester products, including Weedone 650 and E-99, allow application of 1.0 lb up to 15 days before soybean planting. For other 2,4-D products, allow 30 days between application of 1.0 lb and planting.
- Increasing the glyphosate rate from 0.75 to 1.1 lbs of acid equivalent per acre can improve control of dandelion, and should be strongly considered when application is less than 7 days before soybean planting and 2,4-D ester can no longer be used.
- We have observed reduced control of dandelion when herbicides are applied during or just after periods of abnormally cold spring weather (temperatures less than about 35 degrees?). Where possible, avoid herbicide application at these times, and delay application until after several days of more normal temperatures.
- Application of chlorimuron-containing herbicides (see related article in this issue of C.O.R.N.) in combination with glyphosate or glyphosate plus 2,4-D ester can improve dandelion control. Such combinations can improve the rate of herbicide activity, but more importantly, they are more effective at preventing mid-season regrowth of dandelion. Mixing Valor with glyphosate or glyphosate plus 2,4-D ester results in more rapid burndown activity, but dandelions have a tendency to regrow in mid-season. Aim has not improved the speed or effectiveness of dandelion control in OSU research. Other preemergence soybean herbicides do not generally contribute much to dandelion control.
- The seed produced by dandelions last fall or this spring will germinate and emerge primarily later this spring. Therefore, use of preemergence herbicides with residual activity on seedling dandelion is essential to prevent further increases in the population. We have limited data on residual control of dandelion, but we assume that atrazine and most broadleaf soybean herbicides provide at least some residual control.
- In OSU research, Lumax and Lexar have provided the most effective control of dandelion in corn, with regard to rate of initial burndown and prevention of regrowth. In at least one study, the addition of 2,4-D to Lumax resulted in more effective reduction of the dandelion population at the end of the growing season. Other options in corn that are not as consistently effective: mixtures of atrazine premix products with glyphosate or glyphosate plus 2,4-D; and mixtures of Balance plus atrazine plus 2,4-D.
- In both corn and soybeans, fields should be scouted within 3 to 6 weeks after planting, and postemergence herbicides applied to control dandelion regrowth. This also applies to fields that received a fall treatment, since dandelion sometimes does not regrow until mid-season in these fields. Failure to implement a follow up postemergence treatment can result in limited impact on the dandelion population (in other words, competition with the crop has been reduced, but the dandelion population has not).

Planting Rates for Optimal Yield in Corn

Authors: Peter Thomison

When corn is produced for grain in Ohio, recommended plant populations at harvest (or final stand) can range from 20,000 to 30,000+ plants/A, depending on the hybrid and production environment. Hybrids differ in their response to high plant population with some exhibiting stalk lodging at the upper end of the plant population range. Populations for corn silage typically exceed those for grain by 2,000 to 4,000 plants/A. Seed companies specify a range in final stands for the various corn hybrids they market, and these seeding rate guidelines should be followed closely to maximize crop performance.

Yield potential of the production environment (i.e. soil productivity, etc.) is the primary factor determining hybrid yield response to increasing plant population. Seeding rate adjustments should be made on a field by field basis using the average yield potential of a site over a 3 to 5 year period as the major criterion for determining the appropriate plant population. When determining the realistic yield potential for site over a 5-year period, it may be appropriate to ignore the highest and lowest yields, which may have occurred during years that were unusually favorable or unfavorable for corn performance.

Higher seeding rates are recommended for sites with high yield potential that have high soil fertility levels and water holding capacity. On very productive soils which may average yields of 175 bu/A or more (such as a drained, Kokomo silty clay loam), final stands of 30,000 plants/A or more may be required to maximize yields. On soils averaging 150 bu/A, final stands of 26-28,000 plants/A may be needed to optimize yield. Lower seeding rates are preferable when droughty soils or late planting (after June 1) limit yield potential. On soils that average 120 bu/A or less, final stands of 22,000 plants/A may be adequate for optimal yields.

If a grower plans to rely extensively on field drying that can delay harvest, there may be little benefit from using high plant populations above 30,000 plants/A. We recently completed a study that evaluated effects of plant population (24,000 to 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. Although the 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. Grain moisture, averaged about 23-25% on the first harvest date, 17-19% on the second harvest, and 16% or less on third harvest date. After the first harvest in early/mid October, stalk lodging increased as much as 80% for certain hybrids - resulting in yield losses of nearly 50%.

Achieving Targeted Plant Populations in Corn

Authors: Peter Thomison

Final stands are always less than the number of seeds planted per acre. Cold, wet soil conditions, insects, diseases, cultivation and other adversities will reduce germination and emergence. Generally, you can expect from 10 to 20 percent fewer plants at harvest than seeds planted. To compensate for these losses, you need to plant more seed than the desired population at harvest. Many seed companies recommend over-planting by 10 to15%.

To calculate your own planting rate, consider the following formula:
Planting rate = Desired Population per Acre / (Germination x Expected Survival)

Germination is the percent seed germination shown on the seed tag (converted to decimal form). Expected survival is the percent of seedlings and plants that you expect to reach harvest maturity under normal conditions (converted to decimal form). Ninety percent survival (or 10% plant mortality) is about average. If you are planting very early when the soil will likely remain cool for several days following planting, you may want to reduce expected survival by 5 percent. A similar approach should be followed when planting no-till especially in heavy residues.

Target stand at harvest - 26,000 plants per acre

Seed tag indicates 95 % seed germination

Assume 90% survival (10% plant mortality)

Planting rate = 26000 / (.95 x .90) = 30,409 seeds per acre

According to the formula, you should consider a planting rate of approx. 30, 400 seeds/A to achieve the final stand of 26,000 plants/A you are shooting for.

Soybean Aphids in Ohio Now

Authors: Bruce Eisley, Ron Hammond

This past week we were able to find newly hatched aphids on buckthorn on the campus of Ohio State University in Columbus and from pictures sent to us, they do appear to be the soybean aphid. Having discussed this find with colleagues from other states, it appears that we probably have our first discovery of soybean aphid in the state since soybean aphid eggs do hatch immediately following bud break on buckthorn. Although we do not believe that our major problems in Ohio will come from soybean aphids that overwinter in the state (we currently think our largest populations come from migrating aphids from more northern states in early to mid summer), these newly discovered aphids suggest that aphids are overwintering successfully, and is the first suggestion that are our predictions for the presence of aphids this summer might be on track. We will be following this buckthorn in Columbus and other locations in the state over the next few months to obtain a better indication as to the potential for future problems this summer. Growers should continue to read this newsletter for future developments on the soybean aphid front.

Spring Soil Testing for the 2005 Growing Season

Authors: Robert Mullen

Knowing the nutrient status of your corn and soybean field soils this spring could save you substantial money in 2005. As most of you know, the costs of buying and applying fertilizers will be considerably greater this year than in the past. Soil testing will provide you with information that will help you make important economic decisions this year. If you were not able to test your soil last fall, it can still be done early this spring.

Soil test results and their interpretation from the Tri-State Recommendation publication (Ohio, Indiana, Michigan) and the Ohio State University computer program , designated as SOIL99A.EXE ) will be useful in helping answer important questions. For example, (1) Is the soil’s phosphorus and potassium status sufficient so that these nutrients will not limit crop yield this year?; (2) If these nutrients are in a low to deficient status, how much should be applied?; and (3) If these nutrients are in the maintenance range, should any fertilizer be applied? The Tri-State Recommendations show that the critical level for plant available soil phosphorus (P) for corn and soybeans is 15 ppm (30 lbs/a), with a maintenance range of 15 ppm (30 lbs/a), Thus, soil P levels of 30 ppm (60 lbs/a) would represent the upper limit of the maintenance range. If your soil P level is already in the midrange of the maintenance range, you may be able to save money by not applying P fertilizer this year. Furthermore, soil P levels greater than the maintenance range would not be expected to contribute to an additional increase in corn or soybean grain yield. The concept for recommendations of potassium (K) for the yield of corn and soybean grain is similar to that of P. However, the critical K level in the soil is dependant up on the cation exchange capacity (CEC) of the soil. Thus, for a CEC of 10, the critical soil K level is 100 ppm (200 lbs/a) and for a CEC of 20 it is 125 ppm (250 lbs/a). The length of the maintenance range is 30 ppm (60 lbs/a). Again, an increase in corn and soybean grain yield would not be expected if the K is above the maintenance range.

The first step in testing your soil this spring is to contact a reputable soil testing laboratory to obtain their sample kit, which usually consists of an information sheet and sample container. The information sheet contains important information about how to take the sample and how to handle it before it is sent to the laboratory. Most laboratories have a standard test package which includes the test parameters of pH, buffer pH, phosphorus, potassium, calcium, magnesium, and CEC. Other tests that may be optional are organic matter and micronutrients.

If the test results are to be useful, it is important to obtain a soil sample that is representative of the area of interest. You may wish to sample level, bottom-land separately from hillsides or the top portion of the hill. For the random sampling approach, usually 15-20 cores for 5 – 10 acres of uniform area should provide useful information about the generally fertility of the area. The more variable the topography or lack of uniformity, the more samples should be taken to get a good indication of the soil’s fertility. For conventional tillage, the sample should be taken to a depth of 8 inches. However, for no-tillage practices, two samples should be taken and tested separately. A shallow sample should be taken to 4 inches and a deep sample taken to a depth of 8 inches. Testing the two samples separately will show any stratification of the nutrient concentrations that may be present as well as provide a measurement of the pH in the upper soil layer. The soil cores from a given area should be mixed thoroughly and a cup-size sub-sample taken for the laboratory analysis. A high-quality soil testing laboratory should be able to provide the test results within two working days.

It is important that soil testing be used to obtain knowledge about the nutrient status of the soils on your farm, not only for economic crop production purposes, but also from an environmental protection standpoint. Nutrients, whether they come from synthetic fertilizers sources or from organic sources, such as animal manures, should not be added to the soil in amounts greater than what the crop will use. Using soil testing as a diagnostic tool to monitor the nutrient status of the soil is an important aspect of best management practices of any farming enterprise.

Tips to Improve Sprayer Performance

Authors: Erdal Ozkan

Paying attention to certain things will help improve the accuracy and performance of your sprayer and save money. Applying chemicals with a sprayer that is not calibrated and operated accurately could cause insufficient weed, insect or disease control which may lead to reduced yields. The following tips will help improve the performance of your sprayer and keep it from failing:

1. Check the gallon per acre application rate of the sprayer. This can only be determined by a thorough calibration of the sprayer.
2. Check your spray nozzles' output periodically for clogging. How the chemical is deposited is as important as the amount applied. Know what kind of nozzles are on your sprayer and whether or not their patterns need to be overlapped for complete coverage.
3. Setting the proper boom height for a given nozzle spacing is extremely important in achieving proper overlapping. Conventional flat-fan nozzles require 30 to 50% overlapping of adjacent spray patterns. Flood-type nozzles require 50% overlapping.
4. Misaligned nozzles, nozzle tips with different fan angles on the boom, clogged nozzles and uneven boom height are the most common causes of non-uniform spray patterns. They can all cause streaks of untreated areas that result in insufficient pest control and economic loss.
5. Use water in your sprayer that looks clean enough to drink. You don't have time to clean plugged nozzles.
6. Never use a pin, knife or any other metal object to unclog nozzles. They will change the spray pattern or flow rate of the nozzle.
7. Know your actual travel speed, and keep it steady as possible. Doubling the speed may let you cover the field twice as fast, but it also cuts the application rate in half.
8. Pay attention to spray pressure. Variations in pressure will cause changes in application rate, droplet size and spray pattern. At very low pressures, the spray angle will be noticeably narrowed.
9. Don't waste your chemical. After all, you have paid for it. Spray drift wastes more chemicals than anything else. Don't spray when the wind speed is likely to cause drift. Don't take the risk of getting sued by your neighbors because of the drift damage on their fields. Keep the spray pressure low if it is practical to do so, or replace conventional nozzles with low-drift nozzles. Use other drift reduction strategies: keep the boom close to the target, use drift retardant adjuvants, and spray in early morning and late afternoon when drift potential is less.
10. Calibrate your sprayer periodically during spraying season to keep it at peak performance. Use clean water while calibrating to reduce the risk of contact with chemicals.
11. Carry extra nozzles, washers, other spare parts, and tools to repair simple problems quickly in the field.
12. Clean your sprayer as often as possible and do a thorough clean-up at the end of the spray season.
13. Be safe. Pesticides are poisons. Read the chemical and equipment instructions and follow them. Wear protective clothing, rubber gloves and respirators when calibrating the sprayer, doing the actual spraying and cleaning the equipment.

Archive Issue Contributors: 

Mark Loux and Jeff Stachler (Weed Science), Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Erdal Ozkan (Agricultural Engineer), Ron Hammond and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Robert Mullen and Maurice Watson (Soil Fertility). Extension Agents and Associates: Roger Bender (Shelby), Gary Wilson (Hancock), Dusty Sonnenberg (Henry), Mark Koenig (Sandusky), Harold Watters (Miami), Greg Labarge (Fulton), Howard Siegrist (Licking), Glenn Arnold (Putnam) and Steve Prochaska (Crawford)

Crop Observation and Recommendation Network

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.