Leafhoppers, Grasshoppers, and Beetles, Oh My!

Source: Kelley Tilmon, Andy Michel, OSU

As the summer progresses we are receiving reports of insect problems often encouraged by hot, dry weather.  Last week we reported on spider mites and especially if you are in an area of continued dry weather we recommend scouting your soybeans and corn  https://agcrops.osu.edu/newsletter/corn-newsletter/2020-22/watch-spider-mites-dry-areas .

Some areas are also reporting increases in young grasshoppers in soybeans, another insect favored by dry weather.  Grasshoppers of often start on field edges so early scouting may allow for an edge treatment.  Japanese beetles are another common defoliator of soybean that are starting to appear.  Both of these pests fall into a general defoliation measurement, and we recommend treatment if defoliation is approaching 20% on the majority of plants in post-flowering beans.  Download our guide to estimating defoliation in soybean at https://aginsects.osu.edu/sites/aginsects/files/imce/Leaf%20Defoliators%20PDF_0.pdf

A weird problem being reported not just in Ohio but in parts of the Midwest as far-flung as Minnesota is the red headed flea beetle, which is being found in corn and soybean.  This is a small, narrow, shiny black beetle with a red head which springs like a flea when disturbed.  Feeding in soybean creates small round holes and in corn longer narrow strips of damage.  This feeding is seldom economic.  In soybean follow the general defoliation threshold of 20%.  Leaf feeding in corn is almost never economic, but be on the watch for silk-clipping, which is rare but possible.  There are no thresholds in corn, but our Minnesota colleague Bruce Potter suggest this guideline: “flea beetles are very numerous (it is likely more than 5-10/plant), pollination is less than 50% complete, and numerous plants have silks clipped to within 1/2 inch, you might consider an insecticide.”

Finally, earlier in the season we reported higher than usual numbers of potato leafhopper in alfalfa and encouraged stepping up scouting.  In some fields third-cut alfalfa is being heavily impacted by this insect.  You can review our scouting advice for this insect at https://agcrops.osu.edu/newsletter/corn-newsletter/2020-17/time-start-scouting-potato-leafhoppers-alfalfa

Mid-Season Weed Management in Soybeans – Hot, Dry Edition

Source: Mark Loux, OSU

A few weed-related observations while we try to stay cool and hope for a day of rain or at least popup thunderstorms.

 

  • One of the frequent questions during extended dry weather is – do I wait for rain before applying POST herbicides, or just go ahead and apply before the weeds get any larger and tougher to control.  Our experience has been that it’s best to go ahead and apply when weeds are still small, even if it’s dry, and herbicides will usually do what they are supposed to.  Letting them get larger without any sure forecast for rain can make for a tough situation that requires higher rates or a more injurious mix.  On the other hand, waiting to apply can be fine if there is a good chance of rain within the next few days.  It’s not always an easy decision.
  • The deadline for applying dicamba to Xtend soybeans was June 30.  Tavium can still be applied where the soybeans were planted less than 45 days ago and have not exceeded V4, an alternative to dicamba will have to be used.  We should point out that very hot days and warm nights are not appropriate conditions for applying dicamba anyway.
  • The replacement for dicamba on Xtend soybeans is usually going to be glyphosate or a mix of glyphosate with either fomesafen (Flexstar, etc), Cobra/Phoenix, or Ultra Blazer.  Will they cause soybean injury?  Yes.  Will the injury be worse under hot conditions?  Probably.  Do you want weed control?  We assume yes.  Using a less aggressive adjuvant approach can reduce the injury.  Example – applying fomesafen with MSO + AMS will be less injurious than COC + UAN.  Be sure to use adjuvants appropriate for the weed species and size though.
  • Applying POST herbicides early or late in the day may have some potential to reduce injury.  Keep in mind however that the activity of most POST herbicides on weeds is reduced during overnight hours.  In previous OSU research where we applied herbicides at 3-hour intervals from 6 am to 9 pm, activity was substantially reduced from 9 pm through 6 am.  So activity was decreasing after 6 pm and ramping back up after 6 am.  Our studies included fomesafen, glyphosate, Firstrate, 2,4-D, and glufosinate.  Of these herbicides, 2,4-D was the only one not affected by time of day.   Giant ragweed was the only broadleaf weed in the 2,4-D study, which occurred in wheat stubble.

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Drought Projections Do Not Go Well With Fungicide Applications

Source: Anne Dorrance, Pierce Paul, OSU

Several calls this past week for fungicide applications on corn and soybean at all different growth stages.  So let’s review what might be at stake here.

Soybeans.  Frogeye leaf spot and white mold on susceptible varieties when the environment is favorable for disease easily pay the cost of application plus save yield losses.  Let’s dig a bit deeper.  Both of these diseases are caused by fungi but frogeye leaf spot is a polycyclic disease, meaning that multiple infections occur on new leaves through the season while white mold is monocyclic and the plant is really only susceptible during the flowering stage.  Both of these diseases are also limited geographically in the state.  White mold is favored in North East Ohio and down through the central region where fields are smaller and air flow can be an issue.  Frogeye has been found on highly susceptible varieties south of 70, but it is moving a bit north so it is one that I am watching.

White mold is also favored by closed canopy, cool nights and high relative humidity.  So farmers in these areas should double check their variety ratings first.  If it is moderate to low score for resistance (read the fine print) then this year a spray may be warranted.  We have gotten consistent control of white mold with Endura at R1.  Herbicides that are labeled for white mold suppression have also knocked back this disease, but if a drought occurs or no disease develops, losses of 10% or greater can occur due to the spray alone.  For these purposes R1 is a flower on the bottom of 1/3 of the plants in the field.

Frogeye leaf spot –There also must be some inoculum or low level of disease present in the field for this disease to cause substantial and measurable yield losses.   This disease will only move in the canopy when there is regular rainfall.  And again only on susceptible varieties. With dry weather, this will sit and hold. Time to scout for this will be at the end of flowering if it can be found in the field.  With drought conditions, the disease will not impact the crop.

The story is very similar from a corn pathology standpoint. Most of our major diseases (gray leaf spot, northern corn leaf blight, eye spot) are driven by wet, humid conditions, consequently, the dry weather we have experienced over the last several days will keep most diseases in check. Fungicides are not warranted under these conditions; it just does not pay. Although some product labels may mention yield responses under drought-like condition, our data do not support such a benefit. We see the highest yield responses when fungicides are applied to susceptible hybrids at VT-R1 under disease-favorable conditions. These conditions would include extended periods of dew and high relative humidity, especially during the early- to mid-morning hours.

For a disease like southern rust that usually blows up from the south, and tar spot, an emerging disease of increasing concern in the state, fields should be scouted before making an application. Both diseases develop well under warm conditions, but they also need moisture and high relative humidity to spread. In the case of tar spot, based on what we have seen in 2018 and 2019, it usually develops well into grain fill (R4-R5), and as such, may have little effect on grain yield. Data from some states in the western half of the corn belt show that when tar spot develops early, yield loss may be substantial. The same is true for early southern rust development. So, scout fields to see what is out there and at what level before investing in fungicide application.

Soybean Vegetative Growth Stages- VC vs V1

By: Laura Lindsay, OSU

Across the state, soybean growth and development is variable, ranging from early vegetative stages to flowering. However, there has been some confusion regarding the identification of the VC and V1 growth stages. This confusion is mostly due to two definitions of V1…that actually mean the same thing. The Fehr and Caviness Method (1977) is based on the number of nodes that have a fully developed leaf, whereas Pederson (2009) focuses more on leaf unrolling so that the leaf edges are no longer touching. The VC definition for both methods is the same, but the differences start to appear between the methods at V1. Fehr and Caviness define V1 as “fully developed leaves at unifoliolate nodes,” which also means that there is “one set of unfolded trifoliolate leaves unrolled sufficiently, so the leaf edges are not touching.” This second definition is common in extension publications (Pedersen, 2009).

Soybean growth stages are described in the OSU Corn, Soybean, Wheat, and Forages Field Guide (available for purchase here: https://extensionpubs.osu.edu/corn-soybean-wheat-and-forages-field-guide-pdf/). A visual guide to soybean staging is available as a pdf from Dr. Shawn Conley at the University of Wisconsin-Madison (https://coolbean.info/library/documents/2017_Soybean_GrowthDev_Guide_FINAL.pdf).

Changes in status of dicamba product labels for Xtend soybeans – a recap

DSource: Dr. Mark Loux, OSU

 

Ohio Department of Agriculture: Dicamba use in Ohio ends June 30, 2020

 

On June 3, the US 9th Circuit Court of Appeals issued a decision in a case concerning the use of dicamba on Xtend soybeans.  This decision voided the labels for XtendiMax, Engenia, and FeXapan that allows use on Xtend soybeans.  Tavium was not included in this decision, because it was not approved for use when the case was initially filed.  Several excellent articles covering this decision can be found here on the OSU Ag Law blog (https://farmoffice.osu.edu/blog).  EPA stated on June 8, providing further guidance about what this decision means for the use of dicamba for the rest of this season.  The gist of this decision was the following:

“EPA’s order addresses sale, distribution, and use of existing stocks of the three affected dicamba products – XtendiMax with vapor grip technology, Engenia, and FeXapan.

  1. Distribution or sale by any person is generally prohibited except for ensuring proper disposal or return to the registrant.
  2. Growers and commercial applicators may use existing stocks that were in their possession on June 3, 2020, the effective date of the Court decision. Such use must be consistent with the product’s previously-approved label, and may not continue after July 31, 2020.”

ODA subsequently issued a statement regarding the registration and use of these products in Ohio, stating that any application must happen before July 1, 2020.  Partial text from this statement:

“The registration of these products (XtendiMax, FeXapan, and Engenia) in Ohio expires on June 30, 2020. After careful evaluation of the court’s ruling, US EPA’s Final Cancellation Order, and the Ohio Revised Code and Administrative Code, as of July 1, 2020, these products will no longer be registered or available for use in Ohio unless otherwise ordered by the courts.

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True Armyworm Infestations

Source: Andy Michel, Curtis Young, CCA, Kelley Tilmon, OSU

 

As you scout your fields this week be on the lookout for this pest!

 

We received many reports of true armyworm infestations in wheat, barley, and corn. These are black or green caterpillars with stripes along the side and orange heads.  In the spring, true armyworm moths migrate from the south and lay eggs in grasses such as forage and weed grasses, winter wheat and barley, and rye cover crops.  When the eggs hatch, the larvae can significantly damage wheat and barley before then moving to young corn. Usually, moth flights occur in April, but we may have had a second peak the first or second week of May—it’s likely the caterpillars feeding now are from this later flight. Right now, wheat, barley, and corn should be inspected for true armyworm populations. Armyworms like to hide during the day and feed at night, so scouting should occur at dusk or dawn, and/or on cloudy days.

Corn: True armyworm in corn cause the most damage when planted in no-till grassy fields, such as a rye cover crop.  In this case, after feeding on the cover crop, the caterpillars shift onto the emerging corn.  The name armyworm comes from the caterpillars’ behavior of migrating en masse from one location to another. Thus, one should pay particular attention to cornfields adjacent to wheat fields that may have supported a high armyworm population, especially the first several rows into the cornfield. As the wheat matures and dries down, it could stimulate the caterpillars to move.

One may only need to treat the edge of the field closest to the wheat field from which the caterpillars are marching. If armyworms are found in a cornfield, check for the percentage of plants damaged in 5 sets of 20 plants.  If more than 10% of the stand has feeding damage, it may indicate a large infestation, and the field should be re-checked in a few days to see if defoliation is increasing. If defoliation has increased and plants have two or more caterpillars per corn seedling, an insecticide application may be necessary. However, if most larvae are longer than 1 inch, then much of the feeding is complete as the caterpillars will begin to pupate. Also, look for the presence of diseased (black and shriveled) or parasitized caterpillars (having a few or several small, white egg cases on their body)—if found, do not include them in your counting.

If defoliation exceeds 50%, even a rescue treatment may not recover the field without a significant impact on yield.  According to the Handy Bt Trait Table (https://agrilife.org/lubbock/files/2020/02/BtTraitTable_FEB_2020.pdf), only the Vip3A (e.g., Viptera) Bt trait is effective against true armyworm.  Insecticidal seed treatments may offer some control but can be overwhelmed with high populations. Plus, insecticidal seed treatments last only about 4-6 weeks after planting.

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ODA Statement on Dicamba – Official Statement Regarding the Use of Over-the-Top Dicamba Products

Source: C.O.R.N. Newsletter

Official Statement Regarding the Use of Over-the-Top Dicamba Products

 

 

On June 3, 2020, the U.S. Court of Appeals for the Ninth Circuit rendered a decision which vacated the federal registrations of three of the four dicamba products that had previously been approved for use on dicamba-tolerant (DT) soybeans. This decision has caused tremendous uncertainty for soybean producers and pesticide dealers during an agronomically critical time of year.  It is estimated that around 40 to 50 percent of the soybean crop planted in Ohio are dicamba tolerant varieties. The specific products impacted are:  XtendiMax with VaporGrip Technology, Engenia Herbicide, and DuPont FeXapan with VaporGrip Technology. Tavium plus VaporGrip Technology for use on DT soybeans was not covered by this ruling.

In response to the decision, on June 8, 2020, the United States Environmental Protection Agency (US EPA) issued a Final Cancellation Order that outlines specific circumstances under which existing stocks of the three affected dicamba products can be used. The registration of these products in Ohio expires on June 30, 2020.  After careful evaluation of the court’s ruling, US EPA’s Final Cancellation Order, and the Ohio Revised Code and Administrative Code, as of July 1, 2020 these products will no longer be registered or available for use in Ohio unless otherwise ordered by the courts.

While use of already purchased product is permitted in Ohio until June 30, 2020, the Court’s decision and US EPA’s order makes further distribution or sale illegal, except for ensuring proper disposal or return to the registrant. Application of existing stocks inconsistent with the previously approved labeling accompanying the product is prohibited.  If you have questions about returning unused products, please reach out to your pesticide dealer’s representative.

For additional questions, please email pesticides@agri.ohio.gov or call 614-728-6394, and visit ODA’s website for updates.

Corn and Soybean Seedling Blights

Source: Dr. Anne Dorrance, OSU

Low stands or poor development of plants is, unfortunately, a common occurrence for fields that were planted in many regions of Ohio with heavy soil or are poorly drained soil.  Symptoms include skips, missing plants, or dried up and brown seedlings.  There may also be, wilting plants with and rotten, brown, decaying spots or lesions on the roots. Now is an excellent time to scout stands and check to be sure that the fields are not just crusted over – and that the seeds and seedlings that are there are still healthy.

While there, dig up a few of the affected plants, if the roots are brown and soft, the seedling will die eventually or be very weak.  So don’t count them as part of your total stand.  On soybeans check to see if there are nodules, the corky looking knobs on the roots that help legumes fix nitrogen.  The cold, wet weather does not favor nodulation, so this may take a bit longer, for now, native Rhizobium spp. to get a foothold in the plants.  Once the plants have nodules, they will recover and grow.  On corn, the root (mesocotyl) between the young seedling and the seed, should be white.  If it is dark brown or soft, this will also be a weakened plant.  Some pathogens, if the environment is right, will continue to multiply and grow to kill the seedling.

For management, improving soil drainage, and having at least two ingredients in the seed treatment mixture targeting water molds (Pythium and Phytophthora) are necessary for the challenging areas in Ohio that have a history of replanting.  If you do have to replant, take a look at what the seed treatment package is and note what is in the mix.  The one caution, though, is if the field was submerged for more than 24-48 hours (Ponding), this is flood injury, and there are no seed treatments for this.

Recommendations for Soybeans Planted in June

Source: Laura Lindsey, The Ohio State University

While progress is way ahead of last year, soybean planting is spilling into June. (According to USDA NASS, 53% of soybean acreage was planted by May 24, 2020. Last year, at the same time, only 11% of soybean acreage was planted.) As planting continues into June, farmers may want to consider adjusting their cultural practices:

Row spacing. Soybean planted in narrow rows (7.5 or 15-inch row width) generally yields higher than soybean planted in wide rows (30-inch). The row spacing for June-planted soybeans should be 7.5 to 15 inches, if possible. Row width should be narrow enough for the soybean canopy to completely cover the interrow space by the time the soybean plants begin to flower. The later in the growing season soybeans are planted, the higher the yield increase due to narrow rows.

Seeding rate. Higher seeding rates are recommended for June planting dates. The final (harvest) population for soybean planted in June should be 130,000 to 150,000 plants/acre. (For May planting dates, a final stand of 100,000 to 120,000 plants/acre is generally adequate.)

Relative maturity. Plant the latest maturity variety that will reach physiological maturity before the first killing frost. This is to allow the plants to grow vegetatively as long as possible to produce nodes where pods can form before vegetative growth is slowed due to flowering and pod formation. The recommended relative maturity ranges are shown in the table below.