C.O.R.N. Newsletter 2011-07

Dates Covered: 
April 4, 2011 - April 12, 2011
Editor: 
Steve Prochaska

Now Is the Time to Fine Tune Your Sprayer

Higher pesticide costs and new chemicals designed to be used in lower doses make accurate application more important than ever. There is no better time than early spring to take a closer look at your sprayer. Here are some of the things I would check on a sprayer to achieve efficient and effective application of pesticides:

•Double-check your sprayer for mechanical problems before you start using it.  You won’t have time to do this when planting is in full swing.

•Clean the sprayer tank thoroughly and make sure nozzle filters are clean.

•Clean spray nozzles, check their flow rates, and replace the ones that are spraying more than 10 percent of the original output.

•Check the agitator in the tank to make sure it’s working properly.

•Run water through the spray system to make sure everything is working properly

•Find out if the sprayer is delivering the proper application rate (gallons per acre).  

One can determine if the chemicals are applied at the proper rate only by carefully calibrating the sprayer. Calibration, perhaps more than anything else, will have a direct impact on achieving effective pest control and the cost of crop production. While applying too little pesticide may result in ineffective pest control, too much pesticide wastes money, may damage the crop and increases the potential risk of contaminating ground water and environment. Results of "Sprayer Calibration Clinics" I participated in Ohio, and data from several other States show that only one out of three to four applicators are applying chemicals at a rate that is within 5 % (plus or minus) of their intended rate (an accuracy level recommended by USDA and EPA). Of those two-thirds of the applicators missing the mark, about half is under spraying while the other half is over spraying. In one particular case, the applicator would be over spraying by as much as 75% had he used the nozzles that he just purchased and installed on the boom. Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used require a new calibration. Frequent calibration is even more important with liquid application because nozzles wear out with use, increasing the flow rate. Over a decade ago, my colleagues at University of Nebraska conducted an interesting survey. The survey results revealed that there is a direct positive correlation between application accuracy and the frequency of calibration. Approximately 67 percent of the operators who calibrated before every spray operation had application errors below 5 percent. Only 5 percent of the applicators who calibrated their equipment less than once a year (once every two, three, four years) achieved the same degree of application accuracy.            

There are several ways to calibrate a sprayer. Regardless of which method you choose, it usually doesn’t take more than 30 minutes to calibrate a sprayer, and only three things are needed: a watch with a second hand, a measuring tape, and a jar graduated in ounces. I will go over an easy way to calibrate a sprayer in the next issue of the newsletter. In the mean time, you can check the OSU Extension publication on boom sprayer calibration. Here is the URL for this publication:

http://ohioline.osu.edu/aex-fact/0520.html

 

- Planting Soybeans into Cold Ground, Think Again and What Are Those Seed Treatments Actually Doing?

- Planting Soybeans into Cold Ground, Think Again and What Are Those Seed Treatments Actually Doing?

One of these weeks it will actually warm up and we will get to plant the 2011 crop!  If you start getting anxious and want to put soybeans into cold soil, you may want to rethink this option.  A very nice study was just published by Iowa State Researcher, Dr. Leonor Leandro, which compared inoculations of soybean seed with the sudden death syndrome pathogen, Fusarium virguliforme.  Seeds which were inoculated at the day of planting developed symptoms at all of the temperatures tested.  Seedlings that were 3 and 7 days old developed more root rot and greater severity of foliar symptoms at cooler temperatures (62 and 73) than those inoculated at warmer temperatures (82).  Their conclusions were that soybean seeds are more vulnerable to infection than seedlings, but seedlings grown in cold soils are also vulnerable.  For Ohio producers that must manage Sudden death syndrome, this study indicates that it may be best to wait until the soils are warmer and plant at optimum conditions for seed germination.

Lots of products are going onto soybeans to provide protection from many soil borne pathogens as well as insects.  This link separates the insecticides from those that are fungicides as well as which soil borne pathogen they actually work against. http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/seed%20treatments%202011.pdf.

Replanting is one of the major reasons to consider using a seed treatment fungicide.  In addition to fields that have a history of poor stands, those that are in continuous soybeans and no-till may also benefit from a seed treatment.  All of these conditions favor the build-up of inoculum for soil borne pathogens.  Replanting of both soybean and corn have become issues in Ohio over the past eight production seasons. Based on surveys from problem fields in the state over the past decade, the spectrum is quite diverse, and includes several water molds (Phytophthora and Pythium) as well as Fusarium graminearum (same fungus that causes head scab, corn ear and stalk rot), Rhizoctonia, and charcoal rot.  Seed treatments can be very effective for protecting seedlings when environmental conditions are very conducive to seedling infection.  However, not all seed treatment products protect against all of the different seedling pathogens.  Product active ingredients and rates of application are all key components for protecting seedlings when the correct environmental conditions occur for seedling diseases to develop.

Phytophthora sojae is limiting factor for soybean on poorly drained soils.  This is managed primarily by resistance genes but In Ohio, Rps1a is no longer effective in any field; while Rps1c and Rps1k may provide protection in approximately 40% of the fields.  Partial resistance for P. sojae is now more important as a management tool in which under high disease pressure, some roots do become infected but that infection is limited and the plants produce good yields.  This is also known in the industry as field resistance or tolerance.  Seed should be treated with either  metalaxyl  or  mefenoxam, but the rates of both of these fungicides are different due to the amount of the primary active ingredient.  In addition, for both products, at the low labeled rates, substantial infection occurs.  However, at the mid-rate, some disease does develop but at the high rates, not any infection occurred in greenhouse inoculations.  We have also shown that in very high disease situations, the highest rate of both products protects stand and yield of highly susceptible and moderately susceptible varieties. 

There are now a a number of strobilurin compounds labeled for seed treatments.  These fungicides impact P. sojae by reducing the size of the colony growth on agar assays and there is also some protection against root infection but it is not a complete control.  Thus, these compounds provide limited efficacy towards P. sojae.

Pythium spp. are becoming more and more prevalent as seedling pathogens of both corn and soybeans.  Numerous species have been identified that contribute to stand loss and many of these can cause seed rot of both corn and soybeans. Planting date is no longer an option to avoid these pathogens as for each planting temperature, there is a Pythium spp. that is a seed pathogen.  The Seed treatments for Pythium are longer and include:  Captan, mefenoxam, metalaxyl, azoxystrobin, pyraclostrobin, and trifloxystrobin all provide control for Pythium, but not for all species.  Based on our surveys there are isolates of several Pythium spp. that are resistant to mefenoxam/metalaxyl, or strobilurins, or mefenoxam/metalaxyl and strobilurin.  Fields with a long history of replant issues may see the most benefit from using treatments that have both metalaxyl or mefenoxam combined with a strobilurin in the mix.

Fusarium graminearum association with soybean seed and seedling decay has only recently been recognized.  For this, how many spores (inoculum) is present can make a big difference.   The more residue (corn with Gibberella stalk rot or scabby wheat) the greater the potential for infection.   Seed Treatment compounds include:  Captan and fludioxonil are very effective in controlling seed infections caused by F. graminearum in both corn and soybean.  The strobilurins have limited efficacy towards this pathogen based on seed assays.  There is concern for both fludioxonil and strobilurin compounds that isolates will become resistant to these chemistries. 

Rhizoctonia solani is another soil borne pathogen that can infect both corn and soybeans. R. solani causes a brick red lesion to form on the roots and hypocotyls.  Seed Treatments include the following:  Previously, Rival fungicide (a combination of PCNB, TBZ, and captan) was very effective as a seed treatment for Rhizoctonia solani, but it is no longer available.  There are several products which are currently labeled:  fludioxonil, ipconazole, carboxin + PCNB, and strobilurin compounds.  There is limited data from Ohio on these compounds as the tests are quite severe and in greenhouse studies none of the fungicides provide complete control.  Rhizoctonia can infect throughout the season, thus combinations of host resistance and seed treatment are needed where this pathogen is a consistent problem.

Phomopsis seed rot is caused by several different fungi that are part of a complex.  This is a seed pathogen, and severely infected seed is chalky white in color and does not germinate. Fludioxonil is one of the primary treatments.  In our lab, the strobilurin fungicides were compared in a rolled towel assay and pyraclostrobin treated seed also provided protection in seed lots with 35% level of Phompsis infection.

Overall use high quality, healthy seed, plant into soil that is optimum for seed germination and growth as well as plant to optimum depth and moisture levels.  Remember, don’t beat the rain and have one of  those 3 and 4 inch dumpers that will saturate the field for days.  If your seed is not protected you will most likely have to replant that field. 

Alfalfa Weevil Update

Although we have experienced cold weather the past few weeks, we are reaching the time when alfalfa growers in southern Ohio should begin monitoring for alfalfa weevil.  As suggested for many years, scouting should begin when heat unit accumulations, beginning from January 1, reach between 250- 300 heat units (HU). This time period is when we begin to have weevil egg hatch and we start to see feeding. These levels have being reached in southern Ohio, with Piketon currently coming in at 200 HU and Jackson at 240 HU at the time of writing this article.  With the projected temperatures for southern OH the next 5 days, scouting should begin.  In central Ohio near South Charleston where the OARDC Station of the OARDC is located, we are only at about 135 heat units. Remember that fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier.  We will update heat unit accumulations in the coming weeks in this C.O.R.N. newsletter.

As a reminder, alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. When alfalfa is 16 inches in height and there are more than 4 larvae per stem, early harvest is recommended. See the OSU alfalfa weevil Fact Sheet at http://ohioline.osu.edu/ent-fact/pdf/0032.pdf for more information on the insect.  For insecticides that are labeled for alfalfa weevil, see http://entomology.osu.edu/ag/images/Alfalfa_Weevil%281%29.pdf .

April Weather Outlook

The weather outlook remains unchanged into April with temperatures near to slightly colder than normal overall and rainfall generally above normal. A series of storm systems will bring rain chances about every 2-3 days for the next 1-2 weeks.  A turn to warmer and drier conditions will likely occur sometime in May.

Weed Control in Wheat

Herbicides should be applied soon to minimize the impact of winter annual weeds on wheat growth and development. The most prevalent weed problems in wheat fields at this time are usually chickweed, purple deadnettle, henbit, marestail, field pennycress, and other winter annuals, along with dandelion.  Giant ragweed and Canada thistle are also starting to emerge.  Several herbicides are available for control of winter annuals in wheat, but one of the following should be used where chickweed is present:  Huskie; tribenuron (Express, Nuance, Victory); or a tribenuron/thifensulfuron premix product (Harmony Extra, Nimble, TNT Broadleaf, etc).  Huskie will control ragweeds and marestail, but 2,4-D should be added to tribenuron or tribenuron/thifensulfuron for control of these weeds.

Most effective control of dandelions will occur when they have resumed active growth, and it is still too early for control of Canada thistle and early-season summer annual weeds.  Control of dandelion is generally variable in spring.  We have had the best results with combinations of tribenuron and 2,4-D, but this may not result in more than about 70% control.  Fields treated at this time for winter annual control should be scouted again later in April to determine if later-emerging populations of summer annual weeds, Canada thistle, wild garlic, or other weeds require another herbicide treatment. In fields without many winter annuals or dandelions, the best advice may be to delay herbicide application until later in spring, and select herbicides based on scouting.

Be sure to follow label guidelines to minimize risk of crop injury and yield loss. Labels for some products specify the number of tillers or leaves that wheat should have before treatment is allowed.  All labeled wheat herbicides can be applied prior to jointing, but the number of herbicide options decreases as wheat progresses through jointing and more advanced growth stages.  Wheat should be dissected to determine growth stage, because size is not a good indicator of stage.  Weather and soil conditions can affect the risk of crop injury from certain herbicides.  Injury from ALS inhibitors (Harmony Extra, Express, etc) is more likely when wet soils and cold temperatures are inhibiting wheat growth.

Most herbicides can be applied using 28% UAN as the spray carrier, although some labels do not provide much guidance on this.  Results of OSU research indicate that wheat should tolerate application of herbicide in 28% UAN well into April, as long as the restrictions on herbicide labels relative to wheat growth stage are followed. For products that are applied with surfactant, consult labels about the surfactant rate when applying in water vs 28%, since surfactant rates may be reduced to minimize the risk of injury when applying in 28%.  Guidelines and effectiveness ratings for wheat herbicides can be found in the 2009 Weed Control Guide for Ohio and Indiana.

Options for Burndown of Marestail in No-Till Soybeans

Effective marestail management programs include appropriate burndown herbicides and also residual herbicides, to control marestail that emerge between soybean planting and early to mid-June (see next article for residual herbicide suggestions).  The information in these two articles can also be found in the OSU/Purdue fact sheet, “Control of marestail in no-till soybeans”, which can be downloaded from our website – https://agcrops.osu.edu/specialists/weeds.  Some assumptions we make about marestail at this point based on our knowledge of resistance and herbicide activity:

- the marestail populations in many Ohio soybean fields are resistant to glyphosate.  Do not plan on trying to control emerged plants with glyphosate alone in burndown or POST applications.  If you are fortunate enough not to have glyphosate-resistant marestail yet, following the guidelines here will reduce the risk of developing resistance.

- many populations are resistant to both glyphosate and ALS inhibitors (chlorimuron. cloransulam, etc).  The ramifications of this include the following:  POST application of Classic, Synchrony, or FirstRate will not control marestail; in burndown applications, the chlorimuron and cloransulam components of premix products (Canopy, Valor XLT, Authority First, etc) will not help control emerged marestail, and will not provide any residual control.  So the other component of the premix (Valor, Authority, or metribuzin) has to carry the load for residual control.  

- With the exception of very small marestail plants, it’s not usually possible to adequately control emerged plants with 2,4-D alone or combinations of 2,4-D with residual herbicides such as Canopy, Sonic, Envive, Authority First, etc.  Even in glyphosate-resistant populations, the addition of glyphosate to 2,4-D is essential to obtain effective control.

- While Valor and Authority cause contact herbicide symptoms on marestail leaves, these herbicides do not actually provide any control of emerged plants.  Because of the contact burn on leaves, some antagonism between Valor and Authority and glyphosate/2,4-D is possible.  

Effective burndown options are shown in the list that follows.  These should all be effective for control of plants up to 4 to 6 inches tall, although we have controlled larger plants.  Where it’s not possible to use 2,4-D ester due to lack of time between application and soybean planting, the cost of an alternative burndown may be twice that of glyphosate+2,4-D.  This is money well spent, since marestail plants not controlled by burndown herbicides are not likely to be controlled this season.  Note – I have taken a few comments from a recent article by Jim Martin from the Kentucky Pest News (fairly magnanimous I think, given that UK ended our bid for an NCAA championship, but Jim is an OSU grad).

1. Glyphosate + 2,4-D + AMS.  Use glyphosate product rates that provide the equivalent to 1.1 to 1.5 lbs ae/A.  Increasing the 2,4-D rate from 0.5 to 1.0 lb ae/A may improve control, but also increases the delay between application and soybean planting from 7 days to 15 to 30 days, depending upon the product.  Some 2,4-D ester products, such as Weedone 650, E-99, Salvo, or Rage D-Tech (a premix of 2,4-D ester plus carfentrazone) can be applied 15 days before planting at the rate of 0.5 to 1 lb ae/A.  Weather conditions need to be favorable for plant growth.  Cold temperatures before, during, or after application may reduce control.  Some grower/dealers have reported increasing variability with the effectiveness of this treatment, especially on larger plants.  Apply to marestail plants that are less than 4 inches tall for optimum results.

2.  Safulfenacil + glyphosate + MSO + AMS.  Saflufenacil product/rates for soybeans:  Sharpen (1 oz – before soybean emergence; 1.5 oz – at least 14 days before planting); Verdict (5 oz); Optill (2 oz).  Sharpen is the least expensive option among these.  An MSO-based adjuvant is a required additive, and it must contain at least 60% methylated seed oil.  Do not substitute nonionic surfactant or petroleum oil concentrate for MSO.  Thorough spray coverage is important. A spray volume of 15 to 20 GPA is normally recommended, especially for such situations as dense stands of weeds and variable plant sizes, as well as plants that emerged in the fall and overwintered.  Do not use saflufenacil as a tank mix partner or sequential application within 30 days of other PPO (Protoporpyrinogen Oxidase) inhibitor herbicides such as Spartan (sulfentrazone), Valor (flumioxazin), etc.

3.  Ignite 280 (29 to 36 oz/A) + AMS (3 lb /A).  Ignite 280 (glufosinate) may be applied as a broadcast burndown treatment before emergence of any conventional or transgenic variety of soybean.  Thorough spray coverage is important. Apply in a minimum of 15 gpa, and increase to 20 gpa in a dense canopy of weeds.  Avoid nozzles that produce primarily coarse droplets.  Weather conditions need to be favorable for plant growth. Warm temperatures, high humidity, and bright sunlight enhance the performance of Ignite 280. Weed control may be reduced when weeds under stress due to cool temperatures, drought, or extended periods of cloudiness.  The addition of metribuzin (4 to 6 oz of 75DF) can improve control and compensate somewhat for large plant size or adverse environmental conditions.  Unlike saflufenacil, Ignite can be mixed with any PRE soybean herbicide, making it a good option where the intention is to use a PRE product that contains Valor or Authority.

 

Residual Control of Marestail in No-Till Soybeans

Residual soybean herbicides should be included in marestail management programs to control plants that emerge between planting (or burndown herbicide application) and soybean canopy closure.  The soybeans can adequately suppress plants that emerge after canopy closure.  Even the most effective residual herbicides may not completely control marestail during this period, especially when they are applied several weeks before soybean planting.  Some considerations in residual herbicide selection:

- It is important to know whether the marestail population is ALS-resistant.  One indicator of this is whether POST application of FirstRate or Classic retains any activity on marestail in the field.  If you are unsure about this, assume that the population is ALS-resistant for the purposes of residual herbicide selection.  Reminder - the PRE soybean herbicide effectiveness table in the “Weed Control Guide for Ohio and Indiana” has ratings on both ALS-sensitive and ALS-resistant marestail.

- The most effective residual herbicides contain active rates of two components – an ALS inhibitor (chlorimuron or cloransulam) and a non-ALS inhibitor such as Valor, Authority or metribuzin.  Premix products included here:  Valor XLT, Envive, Sonic, Authority First, Authority XL, Gangster.  Canopy/Cloak DF actually also falls into this category, but the rate of metribuzin is fairly low at typical product use rates.

- The “Roundup Ready” rates recommended on the labels of these premix products will often be adequate where the population is not ALS-resistant since both components of the premix are contributing to the control.  However, in ALS-resistant populations that non-ALS component of the premix is providing all of the residual marestail control, and the rate of that component becomes more important.  Another way to look at this – Valor will be just as effective as Valor XLT or Envive for control of ALS-resistant marestail, although control of other tough broadleaf weeds may decrease. 

- The “Roundup Ready” rates of the premixes can supply a relatively low rate of the non-ALS component (flumioxazin, sulfentrazone, or metribuzin), and should be increased or supplemented with additional herbicide to obtain enough residual control of ALS-resistant marestail.  We suggest aiming for the following rates:  metribuzin - 8 to 10 oz/A of 75DF; flumioxazin – 2.5 oz of Valor; and sulfentrazone – 0.2 to 0.25 lb ai/A.  Some examples based on this:  the 4 oz rate of Canopy/Cloak DF contains the equivalent of 3.4 oz of metribuzin 75DF so an additional 5 to 6 oz/A of metribuzin should be added; 4.3 oz of Valor XLT are required to apply the equivalent of 2.5 oz of Valor, or additional Valor can be added to lower rates of Valor XLT.  This approach is more problematic with Authority products, where the “Roundup Ready” rates can provide much less than 0.2 to 0.25 lb ai/A, because adding sulfentrazone (Spartan) to get to the higher rate is not necessarily cost-effective.

- In our research, residual control from saflufenacil (Sharpen) is often in the range of 40 to 70%, which is not usually adequate, and it should be supplemented with additional residual herbicide.  Since saflufenacil cannot be applied with products that contain flumioxazin or sulfentrazone, what is the most appropriate partner to mix with Sharpen to improve residual marestail control?  Scepter and Pursuit are somewhat variable for residual marestail control, and do not control ALS-resistant marestail (Optill is a premix of saflufenacil and Pursuit).  We suggest that Canopy/Cloak DF and/or metribuzin are probably the most appropriate tank-mix partners where glyphosate + Sharpen is used as the burndown.  As indicated above, whether using metribuzin alone or mixing with Canopy/Cloak DF, aim for a total of 8 to 10 oz/A of metribuzin 75DF.  The other approach here is to use Ignite for burndown of marestail instead of glyphosate + Sharpen (the cost is about the same), which allows use of any residual herbicide.

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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.