Corn Fungicides … To Spray or not to Spray

All of the corn fields that I have seen this week look very similar to this one.  I am seeing very little (if any) disease pressure.

SO … Do I spray or not?  This is literally the same decision that we had to make with our wheat crop this year.

A fungicide application will cost will cost in the neighborhood of $20 – $25 per acre.  At the current corn growth stage will this application pay?

Most corn studies have found the greatest yield benefit from a fungicide application to be at the VT (Tasseling)   to R1 (Silking)  growth stages. Intuitively, this makes sense since this is typically a time of high disease pressure, and the tissues we want to protect most are present and active. The ear leaf and those leaves that are younger are the solar panels that generate the sugars that then fill the grain. These later applications take us further into the season with the protection of this foliage.

Continued scouting is needed, especially in fields with susceptible hybrids and a history of foliar diseases. These 3 diseases are the most prevalent this time of year.

Gray leaf spot: symptoms of GLS include tan, rectangular lesions up to 2-4 inches long that first appear on lower leaves. Lesions are bordered by leaf veins and can turn gray later in season. Infection requires dew or foggy conditions and high relative humidity in the canopy.

Tar spot:  this relatively new foliar disease prefers wet weather and moderate temperatures and can progress rapidly under the right conditions. The main signs of tar spot are raised, black spots called stroma that cannot be rubbed off and appear on both upper and lower leaf surfaces.  In general, fungicides with multiple active ingredients (AI) are more effective against tar spot and should be applied between VT and R3 in a high disease environment (>5% severity).

Northern corn leaf blight:  keep an eye out for tan, “cigar-shaped” lesions (Figure 3) that will expand up to six inches in length across leaf veins. NCLB is favored by high relative humidity and wet, but slightly cooler conditions than those that favor the development of GLS.

Corn Fungicide Options for 2023

Field Observations Thru August 4


Corn development continues to vary throughout the county.  After tasseling the next growth stage is R1 – Silking.

R1 – Silking.

  • At least 50% of plants in the field will have 1 or more silks emerged. Look at  only the uppermost ear on the corn plant.
  • Pollen grains will land on silks and if receptive,  fertilization will occur.
  • Silks are viable and receptive to pollen for at least 5 days.
  • The plant  uses the most water per day (0.35 inches) during R1, making it very sensitive to stresses.
    • The largest yield reduction occurs with stress at silking
  • Silks have highest water content among all parts of the corn plant.
  • Drought causes silk  elongation to slow down and pollen shed to speed up.
  • Potential kernel number is determined.
  • Maximum plant height is achieved.
  • Potassium uptake is essentially complete and nitrogen and phosphorus uptake is rapid in the plant.
  • Nutrient content by leaf analysis is highly related to the final grain yield at this time.

See all information on all corn reproductive growth stages here.


R3 Beginning Pod

      • A plant can have all of the following:

developing pods,    withering flowers, new open flowers and flower buds

  • Potassium uptake rates peak shortly
    after R2, ranging between 3.5-5.2 lb K2O /acre/day
  • Last growth stage to treat for white mold
  • Scout for insects and diseases.  Spray foliar insecticide or fungicide, if needed.
  • Identify water stress,
    which affects pod formation.

County Rainfall Update








Corn Water Requirements

Soybean Water Requirements


Field Observations Thru July 21


Corn growth varies greatly throughout the county, but, more fields are beginning to tassel.  As corn begins to tassel, nutrient (K > N > P) and water (0.30 inch per day) demands for the crop are close to maximum. Heat and drought will affect potential number of kernels.  Scout for insects (e.g., corn leaf aphid, western bean cutworm, corn earworm, fall armyworm) and diseases (e.g., gray leaf spot, southern rust, northern leaf
blight). Total leaf defoliation severely affects final yields.

VT (Tasseling) – Stage VT occurs two to three days before silking, when the last branch of the tassel is completely visible but silks have not emerged yet from the ear shoot. The plant has reached full height and the pollen shed begins. The time between VT and R1 can vary with different hybrids and due to environmental conditions.
Pollen shed (pollen drop) normally occurs during the late morning or early evening. Hail damage is more serious at this time than for any other growth period. All leaves have emerged and the complete loss of a pollen source would result in no grain formation.

We are nearing a point in the growing season where it is time to scout your corn fields and make a decision regarding fungicide applications. Click here to view the 2023 corn fungicide ratings.


Postemergence herbicide applications – Don’t forget the preharvest intervals (PHI) for grazing or harvest. Read more here.


Soybean Postemergence Weed Control – Grasses

Soybean Postemergence Weed Control – Broadleaves

Soybean Growth & Development – R2: Full Bloom

  • Open flower at one of two uppermost main-stem nodes
  • About 50% of the total mature node number has been established.
  • Very rapid nitrogen (N), phosphorus (P), potassium (K) and dry-matter accumulation is occurring and will continue through R6.
  • Defoliation of the plant of 50% at this stage will reduce yield by 6%.
  • Approximately 60 days away from beginning of physiological maturity (R7).

County Rainfall Update

Mount Vernon, OH

Corn Water Requirements

Soybean Water Requirements

Field Observations Thru July 14


2nd cutting is well underway.  Potato leafhoppers are very active. If you haven’t cut yet, continue to monitor, where damage is increasing, cut as soon as weather permits.

Click here for alfalfa insect scouting calendar

Click here for more information on Potato Leafhopper


Our corn growth varies greatly throughout the county. Some fields are beginning to tassel and some field are at V8.

V12 to V13 – Six weeks after the plant emerges, V12 begins. Moisture or nutrient deficiencies may reduce the potential number of seeds, as well as the ear size, seriously. These two components of yield have key development during the period from V10 to V17. The length of time for the plant to develop through these stages affects harvestable yield.

Early maturity hybrids normally progress through these stages in less time and have smaller ears than later hybrids. Higher plant populations are needed for earlier hybrids to produce grain yield similar to normal-maturity hybrids in the adapted region. Cultivation of plants at this time will destroy some of the plant roots. Brace roots are developing from the fifth node and the first above-ground node.

V14 to V15 – Seven weeks after the plant emerges, V14 begins. The corn plant at V15 is only 12 to 15 days (around one to five V stages) away from R1 (silking). This vegetative stage is the most critical period of seed yield determination. The number of ovules that develop silks, and thus the number of kernels, is being determined. Any nutrient or moisture deficiency or injury (such as hail or insects) may seriously reduce the number of kernels that develop.

The tassel is near full size but not visible from the top of the leaf sheaths. Silks are just beginning to grow from the upper ears. Upper-ear shoot development has surpassed that of lower ear shoots. A new leaf stage can occur every one to two days.

Brace roots from the sixth leaf node are developing, and the permanent roots have continued to elongate and proliferate, eventually reaching a depth of about 5 to 8 feet and spreading several feet in all directions. In some hybrids, brace roots also will develop from the eighth and ninth leaf nodes or even higher. Some corn plants in North Dakota may only develop 16 leaves.

Critical corn growth stages

Table 5. Postemergence Herbicides in Corn – Grasses

Table 6. Postemergence Herbicides in Corn – Broadleaves


Soybeans are starting to look a little bit better, however, there are still a lot of “yellow” beans throughout the county.  Two possible reasons are Yellow Flash and Soybean Cyst Nematode.  Other possibilities are seedling diseases and water-logged roots, more information on these topics next week.

After planting, the second biggest challenge we face is timely weed control.  If you haven’t already made a postemergence application, it might be time to check your fields.  Most beans (and weeds) are at stage that might warrant an application.  The links below will contain OSU Herbicide rating for postemergence applications.

Soybean Postemergence Weed Control – Grasses

Soybean Postemergence Weed Control – Broadleaves

Soybean Growth & Development – R1: Beginning Bloom


  • Open flower at any node on the main stem
  • Flowering begins at 3rd to 6th node (V6 to V10 stage)
  • Flowering period is 3 to 4 weeks
    –Begins ~6 to 8 weeks after emergence
    – Peaks R2 to R3; ends ~R5
  • Vertical root growth rates increase rapidly
    – As much as 1.3 to 3.2 in/day


Wheat harvest has come to an end and most of the straw is in the barn.  From what I hear, wheat yields were pretty good with little to no disease issues.

If you removed the straw, remember to account for the additional fertilizer removal when planning for fertilizer needs next year.  Read more here.

Double crop beans have been, or are being planted now.  Click here for the Double Crop Soybean Production Guidelines from Dr. Laura Lindsey.

Misc. – Something you don’t see everyday.

I can honestly say that I have never seen one of these before! Click on the picture to see the video. If you know what it is, put your answer in the comment section.  Be sure to check back next week for the answer!

… AND THE ANSWER IS – Horsehair Worm

County Rainfall Update

Corn Water Requirements

Soybean Water Requirements

Pest of the week – Soybean Cyst Nematode

Soybean Cyst Nematode

Click to enlarge

Soybean Cyst Nematode (SCN) is the number one contributor to yield loss in soybean crops nationwide, causing an estimated $1.2 billion dollars in damage annually. This pest has been detected in 71 counties in Ohio, with the highest concentrations located in the northwestern part of the state where soils tend to be sandy in content.

Symptoms: Significant yield reduction may take place with absolutely no above-ground symptoms. This is one of the main reasons you should sample fields for the presence and abundance of SCN.

Symptoms of SCN injury can easily be confused with other problems such as nutrient deficiencies, herbicide injury, disease, poor drainage, etc. The presence of oblong areas of stunted, yellowed plants is suggestive of SCN damage. Symptoms are generally more pronounced when soybean plants are under stress from such conditions as drought, low fertility, or compaction. Infected plants have poorly developed roots and very few Rhizobium nodules.

Click to enlarge

Early in the growing season (6 weeks after planting), close examination of the roots may also reveal small, white to yellow spheres (bodies of female nematodes) attached to the root surface. These females are not much bigger than grains of coarse sugar, and should not be confused with the much larger Rhizobium nodules.

Click to enlarge

Lifecycle: In the early life stages, SCN is a microscopic (1/64 inch long) roundworm that feeds on soybean roots. There are three major life stages of cyst nematodes: egg, juvenile, and adult. In Ohio, the life cycle can be completed in 24 to 30 days under favorable conditions. It is possible to have three to five generations (complete life cycles) each growing season.

Management Options:

Step 1: Collect soil samples to identify the fields that have cysts and monitor egg populations.

Step 2: Rotate crops

Step 3: Use resistant soybean varieties/seed treatments wisely.

Step 4: Use best management practices.

Step 5: Manage other diseases.

Step 6: Prevent introduction.

Click here for OSU SCN Factsheet

Why are my soybeans yellow? Part 2

Soybeans throughout the county just don’t look good right now.  Development has been slowed and many fields have areas (sometimes large areas) with a light green or yellowish tint to the beans.  What is causing this yellowing? One possibility is:

Soybean Cyst Nematode

The soybean cyst nematode (SCN) remains the most devastating and yield-limiting soybean pathogen in Ohio and North America. SCN can cause over 30% yield reduction with no visible symptoms, therefore, early detection of this pathogen relies on testing your fields to know your SCN numbers!

Symptoms of SCN injury include presence of patches of yellow and stunted soybeans, with more pronounced symptoms in plants under stress and in sandy soils. Infected plants have poorly developed fibrous roots and with fewer Rhizobium nodules. Early in the growing season (6 weeks after planting), close examination of the roots may also reveal small, white to yellow spheres (bodies of female nematodes) attached to the root surface. These females are not much bigger than grains of coarse sugar, and should not be confused with the much larger Rhizobium nodules.

Spring is a good time to sample for SCN. A soil test in spring will reveal if SCN is present and if so, at what levels. If you are planning to participate in an on-farm trial that requires soil sampling, a subsample can be used for SCN testing. Additionally, if you planted corn, a soil sample from that field will reveal if you have SCN but most importantly, how much SCN. Knowing your SCN numbers will help you determine the best management strategy.    

With funding from the Ohio Soybean Council and promoting the mission of The SCN Coalition, we will process up to TWO soil samples, per grower, to be tested for SCN, free of charge.

Download and complete this Soil Sample Submission Form and mail your samples to:

OSU Soybean Pathology and Nematology Lab 

Attn: Horacio Lopez-Nicora, Ph.D.

110 Kottman Hall

2021 Coffey Rd.

Columbus, Ohio 43210


Field Observations Thru May 26


Most of our first cutting is complete.  If you have not mowed yet continue to monitor for alfalfa weevil.  As regrowth starts begin to monitor for potato leafhopper.


What a difference a week makes.  Most of our corn is now planted and about 50% has emerged.


Soil Crusting

Soil crusting is still an issue.  Continue to scout for emergence problems.  A few fields saw a return of the rotary hoe to help break the crust and aid in crop emergence.


Like corn, bean planting is coming to an end.  Soil crusting is also an issue in many of our bean fields. Continue to scout these fields for emergence problems.  Read more here.


Slug damage was a problem early in a few fields.  The forecasted warm and dry weather should help to eliminate this problem.



Scout for disease and insects:

Cereal Leaf Beetle Scouting Information

Powdery Mildew Scouting information

Head Scab Scouting Information

Most of our wheat is nearing a time when a decision must be made.  All of the wheat fields that I have looked at are showing no signs of disease pressure.  Here are some factors to consider

  1. No existing disease pressure
  2. The head scab forecast system is showing a very low chance of scab
  3. Fungicide cost can range from $12 – $18/acre plus application charges
  4. New crop wheat price is hovering around $6.20/bushel
  5. The 6 – 10 day precipitation outlook is for below normal rainfall and mild temperatures.