Spider Mites in Soybean

Spider mites often show up when it’s hot and dry outside. Given our current weather (and the promise of more heat to come), it’s a good time to review our scouting and management recommendations. Spider mites feed on a wide variety of plants, and usually enter soybean fields from grassy edges – especially right after the edges have been mowed, which causes the mites to seek out a new food source. (If you have the option, consider holding off on mowing those roadsides and grass margins when it’s hot and dry). When scouting for spider mites, look for areas of the field with a yellow-brown or bronze coloration, especially near the edges. Spider mites feed on cellular fluid, which leads to a characteristic stipled or “sandblasted” appearance on the leaves. If you look closely at an infested leaf, you will likely see the tiny mites moving around, and if you examine the leaf with a hand lens you will see their small, globe-shaped eggs.

Spider mite damage within a soybean field

Isolated spider mite damage within a soybean field. Worth keeping an eye on, but not a reason to spray.

Close-up of spider mite damage to soybean

Close-up of spider mite damage to a soybean leaf. Note the stipled or “sandblasted” appearance.

Application decisions for spider mites can be tricky. Use an economic threshold of approximately 20-25% of foliage discolored before pod set, and 10-15% of foliage discolored from pod set until pods are filled (mid-R6). Consider the extent of the damage and whether it is expanding, the growth stage of the crop (R4-R5 are especially critical), and the likelihood of continued hot, dry conditions. While spider mites are not insects, several insecticides will provide control, including the organophosphates chlorpyrifos and dimethoate, and the pyrethroid bifenthrin. Revisit the field 5 days after an application to determine if eggs or small mites are still present; these materials do not kill the eggs and have short periods of residual activity, so a follow-up application might be necessary. (If a follow-up application is necessary, switch the mode of action).  Newer miticides, including products containing abamectin, are more effective and have a longer period of residual activity, but are usually more expensive.

Using the wrong insecticide when spider mites are in the field (whether the mites were your target or not) can be costly in more ways than one. Most pyrethroid insecticides will not provide control, and can actually make the problem worse by removing predators that normally keep mite populations in check. Remember, if an application is not going to make you any money, it’s best to keep it in the jug.

Contact: Dr. Nick Seiter, Field Crop Entomologist | nseiter@illinois.edu


General information on plant disease management

We have posted some new materials (along with cool visual aids) on basics of integrated disease management.  Hopefully this information will be useful to you during this busy meeting season.  Click here to view this post.

 

Remember you can sign up for updates to the Illinois Field Crop Disease Hub

Dr. Nathan Kleczewski Extension Field Crop Pathologist UIUC


Efficacy vs management trials

With meeting season going full blast, you will be seeing a slew of data pertaining to disease management and the efficacy of various disease management products.  We posted some general tips to keep in mind at the Illinois Field Crop Disease Hub that can be viewed HERE.

Remember that you can sign up for Hub updates (Hubdates?) by entering your email information on the main page.

Nathan Kleczewski- Field Crop Plant Pathologist and Extension Specialist-UIUC


2019 Applied Research Results, Field Crop Disease and Insect Management now available

The 2019 edition of our annual report on applied research in field crop disease and insect management can be downloaded at the following link: https://uofi.box.com/v/2019PestPathogenARB

 

Each year, University of Illinois plant pathologists and entomologists produce a summary of the applied research we have conducted to inform disease and insect management practices in Illinois. This information provides a non-biased, third-party evaluation of control tactics such as pesticides and resistant varieties for use in corn, soybean, and wheat.

The 2019 report includes information on the following topics:

  • Surveys of insect pests and soybean cyst nematodes
  • Control evaluations for diseases of corn, soybean, and wheat (including southern rust, tar spot, fusarium head blight, and more)
  • Evaluations of Bt trait packages and soil insecticides in corn and foliar insecticides in soybean (including western corn rootworm, bean leaf beetle, dectes stem borer, and others)

image of the cover of the 2019 applied research report

For questions about the guide, please contact:

Nick Seiter, Field Crop Entomologist | nseiter@illinois.edu

Nathan Kleczewski, Field Crop Plant Pathologist | nathank@illinois.edu


UIUC Field Crop Extension Conferences- Sign up today!

What do you need to know for the 2020 growing season? The University of Illinois will address several key topics at four regional conferences around the state in January and February. The meetings will provide a forum for discussion and interaction between participants, University of Illinois researchers, and Extension educators.

Conference dates and locations are:
Jan. 22 DoubleTree by Hilton, Mount Vernon
Jan. 29 Brookens Auditorium at University of Illinois, Springfield
Feb. 4   I-Hotel, Champaign
Feb. 12 Kishwaukee College, Malta

2020 topics and presenters include:

“It’s Tough Out There: Supporting Farmers and Promoting Mental Health” by Josephine Rudolphi, U of I Department of Agricultural & Biological Engineering

“Illinois Weather Review: A Look Back at 2019 & Expectations for 2020 and Beyond” by Trent Ford, Illinois State Water Survey, State Climatologist

“How Should We Manage Today’s Corn Hybrids?” by Emerson Nafziger, U of I Department of Crop Sciences, Professor Emeritus

“Updates in Field Crop Disease Management” by Nathan Kleczewski, U of I Department of Crop Sciences

“The New Era of Herbicide Resistance… and You Thought the Last Era was Difficult” by Aaron Hager, U of I Department of Crop Sciences

“What’s the Real Deal with Cover Crops & Soybean Cyst Nematode?” by Chelsea Harbach, U of I Extension

Insect Management in Corn and Soybeans” by Nick Seiter, U of I Department of Crop Sciences

Hemp, What Have We Learned in 2019?” by Talon Becker (Mt. Vernon), Jessica Soule (Springfield), and Phillip Alberti (Malta, Champaign), U of I Extension

Certified crop advisers can earn up to eight hours of continuing education credit. Advance registration, no later than one week before each conference, is $100 per person. Late and on-site registration is $120. Register for the conferences online at https://go.aces.illinois.edu/IL2020CMC.

#illinois   #corn  #soybean  #wheat 

 

— University of Illinois Extension


Harvest time is not the time to determine if a disease affected your crop

It happens every year.

A field is about to be harvested and something is awry.  Perhaps the plants are lodged, ears are poorly filled, or pods shrunken.  What happened to my crop?

From a plant disease perspective, it is nearly impossible to provide any useful information to the producer.  Many pathogens that can cause crop diseases are also excellent saprophytes.  That means they utilize dead or dying plant tissues for nourishment.  Consequently, when plants prematurely senesce, these organisms see these plants the same way as I viewed Golden Corral in college- it’s chow time!  As a result, it is common to observe senesced plants in fields with multiple “pathogenic” organisms present in or on tissues.  For example, I recently read a report form the diagnostic clinic where four pathogenic organisms were detected in soybean stems.  Was it organism 1,2,3, or 4 that caused the disease?  All of them?  Was it something else related to the environment that killed the plant and all 4 moved in afterwards?  Therein lies the problem- when plants are dead there is no way to know what killed it.    The most important thing needed to properly manage a disease is a confidant identification of the pathogen and knowledge that it was the cause of reduced plant performance.

This is why it is so important to be checking fields throughout the season.  Assessing the health of the crop while most plants are still green allows you to understand if the issue is related to environment, disease, insects, or some other factor.  During the season, make a point to assess your fields at least 4-5 times throughout the season, from planting through maturity.  Look for plants that exhibit abnormal growth or symptoms.  Send samples to your state diagnostic clinic for assessment.  By doing this, you arm yourself with the information you will need to defend yourself from potential yield limiting diseases in subsequent years.

Don’t be that guy.  Don’t wait until it is dry.


Avoid the cosmic freakout

Today colleagues in Indiana reported tar spot presence in some of their research plots located in North West IN.  They found an extremely low number of stroma (less than 10) when assessing approximately 500 feet of plots.  When you see or read about the report keep a few things to keep in mind:

1) The amount detected was exceptionally low, and not close to the widespread severity we saw early last year.  For example, on  July 5th, 2018, we detected tar spot in DeKalb at 100% incidence (every plant had some) with an average of 6% severity at the ear leaf at VT.  Those were wet fields, closed canopies, and a history of moderate tar spot.

2) It will be hot and dry for the foreseeable future.  Tar spot likes moderate temperatures and persistent humid conditions.  In corn that is still in the early vegetative stages, the persistent levels of humidity the pathogen likely needs to sporulate, then transfer those spores to plants, germinate, and infect, might not be met.  Last year at this time our fields in DeKalb and Monmouth were at or approaching VT around this time.  This season we are at V6 and V7, respectfully.  There is not much canopy to retain moisture, especially when conditions 3 weeks ago were favorable for disease onset.

3) Continue to scout, but be aware that the majority of the chatter out there about tar spot being detected in the Midwest is based on misdiagnoses of insect frass.  Spraying poop with fungicide is not going to benefit your crop.  Click here for more information on that particular issue.  If you have any suspect samples, send them to the UI plant diagnostic clinic, send me images, and let us know the approximate location of the putative detection.  We are collecting samples as we did last season.

4) We have observed tar spot in Illinois every year since it was first detected.  This disease overwinters in the region, just like grey leaf spot, white mold in soybeans, and Fusarium head blight in small grains.  Last year was the first time that the disease was severe enough to cause yield loss.  Detecting it is not uncommon.  When it arrives and the amount of symptoms expressed during critical periods of grain fill is what is most important.  Last year was the perfect storm of susceptible crop, environment conducive to disease for a prolonged period of time, and infection during a period critical for yield.  We will observe it this season, the question is when, and how severe and widespread it will be.

5) Fields at highest risk for tar spot will be no till, corn after corn fields experiencing moderate temperatures and persistent humid conditions, and had tar spot last season.  Our collaborative research team has preliminary data indicating that any infested residue on the surface of fields can produce viable spores.  Tillage may potentially reduce the overall number of spores available for local infection of a particular field by reducing the amount of surface residue on the field, but there is no reason to expect the act of tillage alone to impact survival and viability of spores produced on the residue remaining on the field surface.  Planting into fields that were soybean last year may reduce initial disease onset.  This disease isn’t a rust.  Keep in mind, until we have hard data these are simply assumptions based on experience and similar pathosystems.

6) It is evident that there is a lot that is not understood about this pathosystem and in particular, pathogen biology and ecology.  Our tar spot coalition, which consists of a group of pathologists and breeders from the Midwest and Florida, is working on coordinated trials and collaborative projects to learn as much as possible about this disease in an effective, efficient manner.  We are working hard to help our producers minimize potential losses due to this disease.

In sum, keep scouting, don’t freak out, and stay hydrated- it’s going to get hot out there!

On a side note, I’d be more concerned about the recent report or Southern rust from Southeast Missouri, especially for our #corn growers in the southern portion of the state.  That disease blows around, and with hot temperatures and a predicted hurricane remnant moving in, it could move a bit, especially in some of these late plated corn fields.


Japanese Beetle Management Guidelines

Japanese beetles (Fig. 1) have been arriving throughout Illinois over the last couple of weeks, and are becoming pretty conspicuous in some areas. Our crops are well behind their usual progress when Japanese beetle emergence occurs, which could impact scouting and management decision making. Several of my colleagues recently wrote an in-depth article on the history, distribution and management of this pest1; you can read the full open-access article here. Some notes on management follow by crop:

Japanese beetle adult

Fig. 1. A Japanese beetle adult hanging out on a corn leaf

Corn: Silk clipping is the primary concern with Japanese beetle infestations in corn. While the beetles will nibble on the leaves also, this does not amount to much. Many fields this season are likely to begin silking when Japanese beetles are at their peak, so scouting will be especially important. Silk clipping by Japanese beetles (as well as corn rootworms) can interfere with pollination. The effect of this feeding can be compounded by heat and drought stress2, which could be an issue in many fields this year given the late timing of pollination. Feeding tends to be concentrated on field edges, so thorough scouting within the field is necessary to determine if a treatment is justified. A rescue treatment with an insecticide is recommended if the following additions are observed:

  • Silks are being clipped to within ½ inch throughout the field
  • There are 3 or more beetles per ear (consider reducing this number if silk clipping is occuring under drought and heat-stress conditions)
  • Pollination is ongoing/less than 50% complete (especially during the first 5 days of silking).

Soybean: Control of Japanese beetles in soybean is rarely justified in Illinois, even though the damage is often conspicuous. Soybeans are fairly tolerant of defoliation in general. The only “wild card” this year is that, like corn, our soybeans are well behind their normal level of development when Japanese beetles (and other defoliators) become active. Making a rescue treatment decision for defoliators is a three-step process:

  • Determine the overall level of defoliation in the field. The recommended economic threshold is 30% defoliation prior to bloom, and 20% defoliation after bloom. Train your eye to accurately measure defoliation, and be careful not to over-estimate the extent of the damage (Fig. 2)
  • If a field is above the economic threshold, sample using a sweep net, shake sheet, or other sampling method to identify the insect responsible and verify that it is still present in the field. (Avoid “revenge” applications, which will not provide an economic return).
  • Choose an insecticide and rate that will provide effective control of the target insect. (Efficacy results from 2018 can be found in the 2018 Applied Research Results on Field Crop Pest and Disease Control report here. Results from trials conducted previously at the University of Illinois can be found in the “On Target” summaries of field crop insect management trials here.
Soybean defoliation levels

Fig. 2. Soybean leaves with differing levels of defoliation. Most observers tend to over-estimate the actual level of defoliation in the field

Most insecticides that control Japanese beetles have a relatively short period of residual control. This is no big deal in corn, as the critical period to protect silks is short anyway. In soybean, the short period of residual activity is another great reason to abide by the economic thresholds for defoliating insects; yield-reducing numbers of Japanese beetles in soybean are rare, and multiple applications for this insect are usually a wasted expense.

1 Shanovich et al. 2019. Journal of Integrated Pest Management 10: 9

2 Steckel et al. 2013. Journal of Economic Entomology 106: 2048-2054

Author contact: Nick Seiter | nseiter@illinois.edu | 217.300.7199