C.O.R.N. Newsletter 2004-03

Dates Covered: 
February 4, 2004 - February 18, 2004
Editor: 
Greg La Barge

Soybean Rust – What are the risks for 2004?

Authors: Anne Dorrance

I have been asked on a number of occasions what the risks will be for soybean rust during this next growing season. I don’t mean to be curt – but this really does depend on which way the winds blow. Let me explain, Soybean rust is a fungus, very similar to the rust fungi that cause wheat leaf rust and corn leaf rust. There are two species of soybean rust, one is a mild strain known as Phakopsora meiombae and the more aggressive strain, Phakopsora pachyrhizi. P. pachyrhizi is the species that as gotten all of the attention. It has quickly moved from its place of origin in southeast China in to Africa then to South America. In South America, it first arrived in Paraguay during 2001 – and from there it has been confirmed in all of the soybean regions in Brazil with reports from northern Argentina. Yield losses in South America ranged all over the board – Speculation on potential yield losses in the US ranged from as high 50% or more. Rust will change the way we produce soybeans – when it gets here.

Four routes have been proposed for soybean rust to reach the US.

Via the Central American land bridge—This rust has a broad host range – so conceivably it could infect and colonize hosts all through central America to reach the US. This would take awhile and is dependent on the fact that there are hosts all the way through central America.

On the winds of a hurricane. Conceivably a storm could pick up lots of rust spores from production fields in northern Brazil and carry these across the Caribbean and drop spores on winter nurseries in Southern Florida or on the Kudzu that grows through out the South. Once the rust is established here, then with spring and summer storms it would track via the rust pathway that we are familiar with for both corn and wheat. There are no reports of this happening (February 2, 2004). Of all of the possible outcomes – this may have the highest probability. This is also the easiest for us to implement management strategies – because we already have recommendations and procedures in place for wheat and corn – they would only need to be tweaked for soybeans.

Spores that survive in debris in shipments of seed or meal. Residue or debris is that is left near production fields were the spores could infect soybean plants. This is questionable. We know from corn and wheat rust fungi that the spores do not survive and serve as inoculum sources in or on seed. The debris is buried with the seed or spores are no longer alive from the time of harvest to planting season. We can take additional precautions here, bury debris from containers away from production fields, and monitor fields that are close to ports or facilities were seed cleaning may take place.

Bioterrisom – this is the big unknown. However, on a practical level, I also think this is unlikely, it is very difficult to get successful infections with many fungi by just spreading them onto plants, there are very specific environmental parameters that have to be met in order for such an attack to be successful.

So what should growers do this year to be ready for soybean rust. Really not much. It is not here yet, when it does arrive, we will manage it, successfully with fungicides. Timing of applications as well as efficacy of material will be very important to this success. Two materials are currently registered for soybean rust in the US. Section 18 requests for 6 additional materials have been applied for. Once approved, we will begin the make application to include Ohio on these labels. After that time, we can make some sound recommendations based on the efficacy trials that USDA is conducting in Brazil and Paraguay. Product costs and projected yields will also play a role in these recommendations.

For 2004, we should be vigilante in scouting and watching our fields for unusual leaf spots or large numbers of leaf spots. I do not think it is wise to stockpile fungicides. Efficacy, cost, and timing are all data that you will want before making a wise decision to managing this pathogen and BEFORE you make that financial investment. But, knowing how much Round-up is sprayed in this state over such a sort period of time, I am highly confident that Ohio producers and custom applicators are up to the task to make fungicide application should they become necessary.

Will the neighbors wheat field planted before fly free day affect my field?

Authors: Patrick Lipps, Bruce Eisley

This question was asked but not answered during the January 15th Crop Profit Game broadcast by Mercer Co. participant. If you missed the Crop Profit Game live on the 15th but want to view the program you can see the program on the web at: http://clickvideo.ag.ohio-state.edu/. Note you will need Windows Media Player 9.0 and a high speed internet connections to best view the program.

Yes, planting wheat before the Hessian fly free date does present a risk to neighboring wheat fields that were planted later. The overall risk level is relative to the presence of insects like Hessian fly and fungal diseases like powdery mildew and leaf rust. The relative date for planting wheat in the fall is based on the Hessian Fly Free date. This is the average date at which the Hessian fly adults are no longer around to lay eggs. Planting after this date generally prevents infestations of Hessian fly.

A field of wheat planted before this date is at risk of the adult Hessian fly laying eggs on the newly emerged wheat. The adults lay eggs on the leaves and the larva migrate down behind the leaf sheaths to the base of the stem. Here larva establish feeding sites causing damage to the wheat. The insect larvae over winter in the crowns of the wheat. In the spring the adults emerge, fly to new areas and again lay eggs on the wheat leaves. Most adults stay in the original infested field and others move to new fields.

The vast majority of farmers plant fields after this date saving themselves and their neighbors losses in yield. The highest risks of damage from Hessian fly will be in locations where growers consistently plant early and the Hessian fly becomes a persistent problem.

The powdery mildew and sometimes leaf rust fungi over winter in fields as infections on the first few leaves produced by the plant in the fall. The earlier wheat is planted, the greater the risk is of being infected. Normal temperatures after the Hessian fly free date are cooler, which are less favorable for fungal disease development. If fall infections occur, the fungi tend to remain dormant over winter on the older leaves and when temperatures become more favorable in the spring they begin to produce new spores. These spores are blown by wind currents to neighboring wheat plants and new fields. Early planting may contribute greatly to the overall level of disease in the field and early spread of disease to new fields depending on the weather conditions in the spring. Regardless the risk of yield losses from disease is increased by early planting and these posses an additional risk to neighboring fields.

Ice In Wheat Fields

Authors: Patrick Lipps, Jim Beuerlein

The weather has provided a variety of winter hazards for wheat. Heavy rain that subsequently froze, freezing rain, snow followed by freezing rain have added to the diversity of situations throughout the state. The ground has been frozen since the first week of January when we had a short thaw period. Reports now indicate that the soil is frozen down to about 18 inches or more. Snow cover is very important for protecting the wheat during the times when we have colder temperatures. Patches of ice in wheat fields during the dead of winter do not damage the wheat crop for the most part because the crop is dormant. This assumes that the wheat plants are well rooted and the base of the crowns of the plants are properly placed at about one inch below the soil surface.

The damage comes when the ice melts, forming pools of standing water that partially or totally covers the plants. If the plants are dormant, standing water may have little or no negative effects. However, for plants no longer dormant, standing water pushes all the air out of the soil and deprives the root systems of the oxygen they must have to survive.

If the standing water drains off the surface before plants come out of dormancy so that oxygen can get to the root system, then the plants should survive. The length of time plants can survive in standing water depends on the rate of metabolic activity, which is a function of temperature. Metabolism slows as the temperature decreases and results in a reduced demand for oxygen. Thus plants can survive flooding longer at low temperatures than at higher temperatures. If the thaw is sufficient to melt the ice and the soil around the wheat plants and low temperatures cause the water to refreeze, the plants may be heaved out of the soil making them vulnerable to cycles of freezing and desiccation (like freeze drying).

No action should be taken at this time or later this spring to eliminate ice problems in wheat fields. Good surface drainage is the key to preventing this problem and is a must for the survival of any crop in the field over winter. Land forming/leveling will eliminate the low spots in a field that collect water leading to crop damage or loss. Where no-till culture is practiced, the effects of land leveling will be effective for many years compared to fields where tillage is used, making leveling more affordable.

Begin to examine wheat fields in early spring as the time for green up approaches. Dig plants from the field, wash off all soil and examine the crowns. Peal the leaf sheaths down to expose the inner parts of the crown. The tissues in healthy plants should be a creamy white color. If the internal tissues are brown or discolored, then these plants are likely dead or will soon be dead. At this time you can also examine plants for soil heaving. Plants heaved out of the ground exposing the lower crown and roots will likely die by mid April. There is no need to assess fields before green up because the weather in February and early March very frequently determines the fate of the field. Any decisions you make now will likely change within the next month or so.

On-Farm Fungicide Seed Treatments

Authors: Dennis Mills, Patrick Lipps, Anne Dorrance

The use of fungicide seed treatments should be an integral part of any crop management system. The potential for loss of plant stands from seed- and soil-borne diseases is greater now than anytime in the past due to modern production systems that favor earlier planting under reduced tillage and limited crop rotations. It is important that agronomic crop producers know what the pathogens are in specific fields to choose the best fungicide or combination of fungicides for that field. Fungicide seed treatments are still the most cost effective way to control seed and seedling diseases to help insure adequate plant stands for maximum return for your production investment. Specific information on seed treatments can be obtained from Extension Bulletin 639 Seed Treatment for Agronomic Cropshttp://ohioline.osu.edu/b639/index.html.

Below is a table listing the on-farm seed treatment products currently labeled for use in Ohio that contains fungicide active ingredients. Although commercially applied fungicide seed treatments offer the best protection against seed- and soil-borne pathogens, acceptable control can be achieved by careful application of products to seeds on farm. Growers should read and follow label directions for both the system and material. Be sure to wear the protective clothing recommended on the label. Most importantly ensure that the seed is thoroughly mixed to provide complete coverage of the seed. Thorough coverage of the seed is necessary for maximum protection of the seed and seedling.

Ohio On-Farm Fungicide Seed Treatments

Product
Active Ingredient(s)
Company
Corn
Soybeans
Wheat
Hopper Box
Agrox Premiere Captan 14.67%
Diazinon 15.52%
Lindane 25%
Metalaxyl 1%
Agriliance
X
X
Allegiance Dry Metalaxyl 12.5%
Trace Chemical
X
X
Apron Maxx RTA Mefenoxam 1.07%
Fludioxonil 0.73%
Syngenta
X
Apron Maxx RTA + Moly Mefenoxam 0.99%
Fludioxonil 0.99%
Molybdenum 4.67%
Syngenta
X
Bean Guard Captan 23.9%
Carboxin 12.5%
Molybdenum 10%
Trace Chemical
X
X
Bean Guard Allegiance Captan 24.4%
Metalaxyl 3.75%
Carboxin 12.5%
Trace Chemical
X
X
Captan Diazinon Captan 36.7%
Diazinon 25%
Trace Chemical
X
X
Dividend XL RTA Difenoconazole 3.21%
Metalaxyl 0.27%
Syngenta
X
Enhance Captan 19.6%
Carboxin 20%
Trace Chemical
X
X
X
Germate Plus Carboxin 14%
Diazinon 15%
Lindane 25%
Trace Chemical
X
X
Grain Guard Mancozeb 50%
Trace Chemical
X
X
Kernel Guard Captan 14.7%
Diazinon 15%
Lindane 25%
Trace Chemical
X
X
Kernel Guard Supreme Carboxin 14%
Permethrin 10.4%
Trace Chemical
X
X
X
Kickstart Lindane 25%
Diazinon 15%
Carboxin 14%
Helena
X
X
X
Latitude Imidacloprid 25%
Carboxin 14%
Metalaxyl 1%
Gustafson
X
X
Penncozeb 80WP Mancozeb 80%
Cerexagi
X
X
Prevail Carboxin 15%
PCNB 15%
Metalaxyl 3.125
Trace Chemical
X
X
X
X
RTU Flowable Fungicide Thiram 12.6%
Thiabendazole 0.34%
Gustafson
X
RTU Vitavax-Thiram Carboxin 10%
Thiram 10%
Gustafson
X
X
X
Stiletto Carboxin 10%
Thiram 10%
Metalaxyl 1.62%
Trace Chemical
X
X
X
SoyGard Metalaxyl 20%
Azoxystrobin 15%
Gustafson
X
X
Vitavax M DC Captan 23.9%
Carboxin 12.5%
Helena
X
X
Vitavax TL Carboxin 10%
Thiram 10%
Trace Chemical
X
X
X
Warden RTA Mefenoxam 2.15%
Fludioxonil 0.72%
Agriliance
X

Source: Ohio Department of Agriculture Pesticide Product Registration Database

Dealing with Dandelions I: Biology Aspects

Authors: Mark Loux, Anthony Dobbels

Dandelions have become much more widespread in Ohio crop production fields over the past 5 years or so. There are aspects of the biology of this weed that are allowing it to be extremely successful in the niche provided by our current crop production and weed management systems.

What are the factors of dandelion’s biology that contribute to this success? Among a number of plants that are really successful in their weediness, dandelion may be one of the most remarkable. It is found virtually everywhere in the world, and it can adapt to many different habitats. Dandelion can be described as having a general-purpose genotype and fairly extreme phenotypic plasticity. In other words, its genetic makeup makes it suitable for a variety of habitats, and a given dandelion population is then able to further modify its expression of these genetics (growth, development, appearance, etc) to fit its circumstances.

For example, dandelion plants growing in the open will adopt a wide leaf, spreading growth habit, while those within a crop canopy will adopt a more narrow leaf upward growth habit to improve their fit where competing with other plants. Recent research at Michigan State University has shown genetic variation within and among dandelion populations. Additional research is being conducted to determine if this variation leads to differences in dandelion response to herbicides. Here are some additional fun facts about dandelion biology:

Roots
Dandelion plants produce a deep taproot, and extensive root branching occurs from this taproot. The root crown (at base of plant) can divide to form numerous branches, and if cut off below the crown (as with shallow tillage), the plant can produce several new shoots and a cluster of new plants. Root pieces can regenerate into new dandelion shoots and roots. At the end of the growing season, the root shortens and draws the crown into the soil to protect it from adverse conditions. Dandelion has allelopathic properties – secretion of chemicals by the roots can reduce the germination and growth of other plant species. Finally, although we have not tried to verify this in practice, the age of a dandelion plant can be determined by counting the annual growth rings in the root. Who would have thought?

Growth and Flowering
Seedling dandelion plants usually produce only leaves in their first season of growth, although they can occasionally bloom during the first year. Seedling plants will bloom in the spring of their second year of growth. Dandelion can flower throughout the year. Most plants will flower in April or May, and they can flower again in the fall. A winter thaw of one week can result in flowering and seed production. For a single plant, the time from first day of blooming until ripe seeds are released averages 9 to 12 days. Flowers can close in high temperatures or other adverse conditions and re-open when favorable conditions occur.

Seeds
Dandelion plants are apomictic – they produce seeds without fertilization of flowers. The seeds are 80 to 90% viable when produced, so they do not need cold weather or other conditions that cause seeds of other weeds to lose dormancy and germinate. Each flower produces hundreds of seeds, and seeds can move with wind a third of a mile or more. The seeds produced and disseminated in spring typically germinate later that same spring, while seeds produced in the fall germinate the following spring. Dandelion seedlings can emerge all year, but major flushes of emergence occur in May and September.

Dealing with Dandelions II: Why is this weed currently such a problem?

Authors: Anthony Dobbels, Mark Loux

A number of aspects of dandelion’s biology allow it to have an excellent fit in Ohio crop production fields with our current tillage and herbicide use patterns. Dandelion seedlings can emerge in tilled and no-tilled fields, but some longer period of no-till conditions are required for the plant to become well established with a deep taproot. One year of no-tillage is adequate for this to occur, and the root just gets bigger the longer it goes uncontrolled.

Much of Ohio is under the “no-till for a year or two” scenario, where we are growing soybeans and often wheat under no-till conditions, but using some type of minimum tillage for corn. While continuous tillage probably prevents dandelion from becoming a real problem, minimum tillage following a period of no-tillage is not effective at removal of established dandelion plants. In fact, minimum tillage may actually stimulate the dandelion to produce multiple shoots and further its spread. Dandelion does extremely well under continuous no-tillage of course. So, our current tillage systems suit dandelion just fine – what else helps it out?

It appears that our current management of herbicides in the spring in many no-tillage soybean fields is resulting in less than effective dandelion control, and is also allowing for further infestation by new seedlings. Specifically, the practice of using only glyphosate in Roundup Ready soybeans and delaying the first glyphosate application until sometime in May is problematic with regard to dandelion control.

Recent research at OSU and Penn State shows that: 1) the combination of glyphosate plus 2,4-D is more effective than glyphosate alone in the spring, especially when applied before May and during periods of cold temperatures; and 2) application of glyphosate too late in May, may not effectively reduce dandelion populations, since the dandelion has already gone to seed and senesced (herbicide cannot move into the roots at this point).

In a study at OARDC Northwest Branch in 2003, control with glyphosate applied alone on April 20 and 30 was only 30 and 7% respectively (as measured on June 23), but control with a combination of glyphosate plus 2,4-D ester was still 100% on April 20 and 70% on April 30. Control with both treatments was near 100% when applied on May 10 or 20. The combination of glyphosate plus 2,4-D was also most effective at Western Branch in April applications.

At OARDC Western Branch, treatments on May 10 and 20 appeared to effectively control dandelion approximately one month later. When we measured dandelion population density at the time of crop harvest, application of glyphosate alone or glyphosate plus 2,4-D on May 10, followed by a postemergence glyphosate application, resulted in almost complete elimination of dandelions. However, application on May 20 resulted in only about a 50% reduction in population density, since the dandelions had already produced mature seeds before May 20. Further north at Northwest Branch, we observed effective reductions in the dandelion population through the May 20 application, since dandelion development was delayed compared to Western Branch.

Another problem with the late May application is that most of the dandelion has gone to seed by this time, providing for an immediate new flush of dandelion seedlings. Which brings us to the other problem with glyphosate-only programs. Residual herbicides applied at or before planting can control seedling dandelions that emerge in May or early June. While we lack data on residual control of dandelions, it has a very small seed that germinates well on the soil surface or at shallow soil depths, and we assume that many broadleaf herbicides have activity on dandelion. So, moving away from herbicide programs consisting of a glyphosate/2,4-D burndown plus a residual herbicide (Canopy, Valor, FirstRate, etc), and toward programs without preplant burndown where glyphosate is the only herbicide used, have helped the success of dandelions.

Dealing with Dandelions III: Management strategies

Authors: Anthony Dobbels, Mark Loux

Tillage can control established dandelions, but only if aggressive, such as a moldboard plow followed by some type of spring seedbed preparation. Less aggressive tillage should control seedling dandelions, but most of these emerge in May after the crop has already been planted. One benefit of tillage is the burial of dandelion seeds, which are not long-lived in soil and do not emerge from deeper soil depths.

Control of a population of established dandelions is likely to require 2 years, and the right combination of application timing and herbicides. It is generally not possible to completely control all established dandelions with one herbicide application, so fall or preplant treatments should ideally be followed by postemergence treatments to control dandelion regrowth.

Herbicide programs need to also take into account the emergence of seedling dandelions in spring and fall, since fields that have become severely infested with dandelions are likely to have an abundance of dandelion seed. Application of herbicides in the fall is probably the most consistently effective treatment to reduce dandelion populations. Previous newsletter articles have contained information on the most effective fall treatments.

In the sections that follow, we discuss dandelion control in corn, soybeans, and wheat, including the all-important follow up to last fall’s treatments and the most effective spring treatments where herbicides were not applied last fall. If at all possible, avoid application of spring herbicide treatments during periods of cold nighttime temperatures (temps approaching freezing), and allow a day or more of warmer weather before resuming application.

Fields where herbicides were applied last fall:

Fields with fall treatments often appear to be free of dandelion into May, but we have typically observed later regrowth of plants that were not completely controlled and emergence of plants from seed. Herbicide applications at the time of corn or soybean planting may therefore be too early to help control later-emerging plants. So, use of effective postemergence treatments is important to achieve maximum reduction of dandelion populations.

Most effective postemergence soybean treatments: Roundup Ready soybeans – glyphosate or a combination of glyphosate with Classic or FirstRate/Amplify; NonGMO soybeans – Classic or Synchrony. A number of postemergence corn herbicides appear to have activity on dandelion, including dicamba, Callisto, Equip, Steadfast, Hornet, etc. We generally suggest use of a combination of corn herbicides where possible, such as Callisto plus atrazine, Steadfast ATZ plus dicamba, Hornet plus dicamba, Lightning plus Distinct, or similar treatments. Among the postemergence herbicides we have tested, Callisto plus atrazine has been among the most effective on dandelion.

Soybean fields without herbicide treatments last fall:

Most effective spring treatments include glyphosate plus 2,4-D ester, or a combination of glyphosate plus 2,4-D ester plus CanopyXL. The addition of Valor to glyphosate plus 2,4-D will not generally improve control, but can occasionally result in more rapid burndown. In OSU research, the addition of Aim to glyphosate/2,4-D has not improved the speed or effectiveness of dandelion control.

Including a residual herbicide with the glyphosate plus 2,4-D will help control later-emerging seedlings. Use a glyphosate rate of at least 0.75 lb ae/A, and a 2,4-D ester rate of 0.5 lb ai/A for applications between 7 and 15 days before soybean planting.

The 2,4-D ester rate can be increased to 1.0 lb ai/A for applications earlier than 15 days before planting for several 2,4-D products, including E-99 (Agriliance) and Weedone 650 (Nufarm). Other 2,4-D ester products specify a waiting period of 30 days for rates between 0.5 and 1.0 lb. Where it is not possible to use 2,4-D ester, glyphosate plus CanopyXL may be the most effective treatment.

Spring treatments should generally be applied after about April 7 for most effective dandelion control. Applications before the dandelions produce seed will be most effective – before about May 10 in central Ohio and possibly earlier the farther south one moves.

Preplant treatments should ideally be followed by an effective postemergence herbicide to achieve greatest reduction in dandelion population (see section 1 for postemergence options). However, it is possible that regrowth of dandelion may not occur by the time of postemergence herbicide application, which reiterates the need for a multi-year program to effectively control established dandelions.

Corn fields without herbicide treatments last fall:

Most effective spring treatments include Lumax, Lumax plus 2,4-D ester, and a combination of glyphosate plus 2,4-D ester plus atrazine or an atrazine premix product (e.g. 2,4-D ester plus FieldMaster or Expert). These treatments should be applied fairly close to the time of planting to maximize residual control, so use a 2,4-D ester rate of no more than 0.5 lb ai/A at least five days before planting.

Other treatments with activity on dandelion, but somewhat less effective for either initial control or reduction in population, include: Balance plus atrazine, Curtail plus atrazine premix, and Hornet plus atrazine premix. Preplant treatments should ideally be followed by an effective postemergence herbicide to achieve greatest reduction in dandelion population (see section 1 for postemergence options). However, it is possible that regrowth of dandelion may not occur by the time of postemergence herbicide application, which reiterates the need for a multi-year program to effectively control established dandelions.

Spring treatments for wheat

Several wheat herbicides have activity on dandelion, but may only suppress established dandelions. Most effective treatments include Express plus 2,4-D, or Curtail (premix of Stinger plus 2,4-D). Use of the highest labeled rates will improve control, but be sure to follow label directions on rate, wheat growth stage, spray carrier, and use of adjuvants to avoid wheat injury. Avoid application during periods when wheat is not actively growing due to overly wet soil conditions.

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance (Plant Pathology), Peter Thomison (Corn Production), Jim Beuerlein (Soybeans & Small Grain), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology);District Specialists: Ed Lentz (Agronomy); Extension Agents: Roger Bender (Shelby), Barry Ward (Champaign), Todd Mangen (Mercer), John Hixson (Union), Greg La Barge (Fulton), Howard Siegrist (Licking), Dusty Sonnenberg (Henry) Mark Keonig (Sandusky), 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.