Economics of fungicides in 2014 corn

July 20, 2014 in Corn, Corn Disease Management

Over the course of the week many people have asked if fungicides will be profitable in the 2014 corn crop.  The answer depends on several factors including: 1) potential for disease (hybrid resistance level, environment, presence or history of disease), and 2) economics (grain price, yield potential, and the cost of fungicide application).  I’ll try to keep the discussion as to the point as possible for clarity.

Potential for disease. The first thing you need to do when deciding if/when you should apply a fungicide to corn this year is to determine how much disease there is in the field. The most common disease in Delaware this year is Grey leaf spot. For Grey leaf spot and other residue-borne diseases, if you have greater than 5% severity on any of the three leaves below the ear in 50% or more plants in the field then the level of disease might require intervention. However, other factors will impact future development of disease including hybrid genetics and the environment. A “worst case environmental scenario” for a residue-borne disease such as Grey leaf spot is a no-till, irrigated field of continuous corn with a history of the disease. Table 1 provides some guidelines that may help you determine the risk level of your field based on hybrid resistance rating and irrigation practice.

 Table 1.  Hybrid resistance rating to Grey leaf spot, irrigation, and potential need for fungicide application in Delaware.  In this table disease is assumed to be present on 50% or more of plants at greater than 5% severity on the 3rd leaf below the ear leaf or above. In addition, the worst case scenario is assumed: a field with a history of GLS, no-till, corn after corn, and moderate temperatures. The lack of any of these factors will further reduce the likelihood of a fungicide benefiting the crop.

Hybrid Resistance Rating to GLS Irrigation practice Potential need for fungicide application (VT-R2)
Highly Resistant Irrigated Low-Medium
Unirrigated Very low*
Moderate Irrigated Medium
Unirrigated Low-Medium
Low resistance Irrigated High
Unirrigated Medium-High

*In general, dryland corn that is highly resistant to GLS does not require a fungicide application for management.


Economics.  With corn heading towards $4.00 per bushel, a greater yield benefit is needed to cover application costs. Table 2 provides examples of the bushel returns you would need to cover fungicide treatment (applicator cost + product) at different grain prices.

Table 2. The required bushel / acre yield increases required to pay for various fungicide application costs at 5 different grain prices.

Application Cost (per Acre) Grain Price (bu)
$3.50 $4.00 $4.50 $5.00 $7.00
$20 5.7 5 4.4 4 2.9
$25 7.1 6.3 5.6 5 3.6
$30 8.6 7.5 6.7 6 4.3


The likelihood that a fungicide will pay for itself is greatest in situations where disease potential is high, application costs are low, and grain prices are high. How often does the fungicide pay for itself? A 2011 paper published in the journal Phytopathology examined 187 studies of corn responses to fungicides conducted throughout the corn belt from 2002-2009.   The chances that the application costs of a fungicide would be covered by the yield return were estimated across a range of grain prices ($2-7 / bu) and application costs ($16-40 / acre). In a nutshell, the research showed that in over 85% of the grain / application cost combinations, there was a greater than 50% chance that the application of a fungicide would not pay for itself if there was less than 5% disease severity on the ear leaf between R4 and R6. Conversely, only 33% of the grain / application cost combinations did not pay when there was more than 5% disease severity on the ear leaf between R4 and R6.  Therefore, the greatest chance for a grower to break even or profit from a fungicide is when the potential for disease is high.

In addition, the study showed that although fungicide use in corn can certainly be beneficial, responses are also highly variable from location to location and year to year. For example, fungicide applications reduced corn yields in 26-48% of the studies included in the metaanalysis.

The take home message is that you will need a greater bu/A yield increase this year to cover the application cost. You are more likely to recover this cost in disease favorable environments (no till, irrigated, corn after corn, history of GLS or other common residue-borne diseases) when susceptible hybrids are planted.

Reference: P. A. Paul, L. V. Madden, C. A. Bradley, A. E. Robertson, G. P. Munkvold, G. Shaner, K. A. Wise, D. K. Malvick, T. W. Allen, A. Grybauskas, P. Vincelli, and P. Esker. 2011. Meta-Analysis of Yield Response of Hybrid Field Corn to Foliar Fungicides in the U.S. Corn Belt. Phytopathology 101:1122-1132.


Delaware Potato Disease Advisory # 10

July 18, 2014 in Potatoes, Vegetables

The 10th Delaware Potato Disease Advisory can be found here:  Potato Disease Advisory #10 July 18 2014


Thoughts on Half Rate Fungicide Use in Field Crops

July 12, 2014 in Corn, Corn Disease Management, Soybean, Soybean Disease Management

Research has shown that when applied at labeled rates, fungicides can and do significantly increase crop productivity in disease favorable environments.  Rates provided on labels are determined by chemical companies following years of research and huge financial investments.  Not only are the rates chosen to give the grower adequate control of listed pathogens, but they also reduce fungicide resistance risk.  By applying fungicides at levels lower than the rates listed on the label you not only significantly reduce any benefit in terms of disease suppression, but also increase the chance that pathogens with resistant characters will continue to grow and reproduce.  Once resistant individuals dominate a population disease control with that product and also products with active ingredients belonging to the same group lose efficacy.   In some cases, such as with the strobilurins, efficacy may be completely lost.  This is why products such as Quadris and Headline can no longer be used to control Frogeye Leaf spot in soybeans in many states in the South and Midwest.

I encourage you to follow the labels and ensure that these valuable disease management tools remain effective for years to come.  There are many products available that have excellent efficacy on fungal diseases in Corn and Soybean and these products vary in price.  I suggest selecting a product that fits your budget and can be applied at the labeled rate as opposed to purchasing a more expensive product and cutting the rate to make it fit your budget.       

Soybean Disease Update

July 4, 2014 in Profitible soybean management, Soybean, Soybean Disease Management, Soybean diseases

This last week I surveyed 20 full season soybean fields in Kent County, Delaware.  Most fields were around v5, with a few further along.  The following, fairly obvious diseases or disorders  were present in some fields.


1) Bacterial blight.  This is typically an early season disease that comes in from the residue.  The bacteria causing the disease enters via wounds and natural openings, produces a toxin within leaves.  Often leaves appear ragged, and yellow lesions form at the leaf edge.  The disease is most severe in young tissue so you may see it early in young plants or in the upper portions of the canopy in older plants.  Lesions eventually dry out and may fall from the plant, resulting in a “shredded” appearance.  This is a fairly common disease that does not require control.  It can be confused with other foliar diseases, particularly Brown spot.

bacterial blight close

Soybean showing early symptoms of bacterial blight. Note the bright yellow halo and angular lesions. Lesions may have a water soaked appearance. No fungal structures will be present in or on lesions. Photo by N. Kleczewski

2) Brown spot.  This is disease caused by Septoria glycines,  a fungus that is present in soybean residue.  The pathogen is spread to the foliage by splashing rain, and symptoms are most evident on very young plants or the lower portions of the canopy in older plants.  The fungus produces lesions of leaves that are small, brown, and irregular in shape.  This disease can be confused with bacterial blight.  Unlike bacterial blight, Brown spot hangs out in the lower parts of the canopy and is not often noticed in the upper canopy.  We tend to think that brown spot isn’t an issue, but in cases where defoliation of the lower canopy is severe (>25% of the canopy defoliates early ) you can see reductions in yield and seed quality.  How often this occurs in Delaware is not currently known.

3) Downy mildew.  Downy mildew isn’t caused by a bacterium nor a fungus.  Instead, it is caused by a fungal-like-organism (Pythium spp. and Phytophthora spp. are other members of this group).  Symptoms include yellow lesions on the top of the leaf that eventually turn grey with red margins.  On the underside of the leaf grey to white fuzzy masses can be seen on the opposite side of the lesions.  Sporangia often can be viewed with the aid of a hand lens.  This disease can be seed or residue borne, but also can spread long distances on air currents.  Downy mildew requires extended periods of wet weather or humid conditions, and does not do well above 80F.  This is why we tend to see it in fields with older plants and dense canopies.   Last season downy mildew was widespread in many soybean growing regions and was evident in many soybean fields in Delaware.  This disease has historically not been an issue, so control has not been warranted.  If pods are affected seed quality can be impacted.

DM on soy

A soybean leaf with typical small, yellow lesions that can be indicative of Downy Mildew. Fuzzy grey to white masses are often present on these lesions on the underside of the leaf. Sporangia can be viewed with the aid of a 10-20x hand lens. Photo by N. Kleczewski

4) Sun scald.  No this isn’t a disease, but some people may think they are seeing Cercospora leaf blight, which causes purple seed stain.  Cercospora leaf blight tends to occur later in the season, and symptoms will be more uniform across the leaf.  Leaves turn purple and eventually develop a leathery appearance.  Sunscald occurs when leaves flip over and exposed to strong sunlight.  In the case of sun scald, you will notice that often only the portion exposed to the sun is purple and there is a clear line of unaffected tissue that was shaded from the sun.  Upper tissues are commonly affected.  High temperatures or wind also can contribute to sun scald symptoms.  Sunscald is superficial and not an issue.


Sunscald on soybeans occurs when leaves are flipped and exposed to strong sunlight. Often symptoms are apparent in the upper canopy. Photo by N. Kleczewski



Cucumber Downy Mildew Detected in Maryland

July 3, 2014 in Vegetables

Cucumber Downy Mildew has been detected in Maryland and confirmed by Kate Everts, Vegetable pathologist for UMD and UD.  Growers should begin preventative fungicide programs for CDM and diligently scout for disease symptoms on susceptible crops.  Fungicide recommendations can be found in the 2014 Commercial Vegetable Production guide at this link:  Commercial Vegetable Production Guide 2014.  For more information on the CDM forecast, field identification, and control recommendations, follow this link: CDM information


Characteristic Cucumber Downy Mildew symptoms on a leaf.



Herbicide Drift vs Holcus Spot in Field Corn

June 27, 2014 in Corn, Corn Disease Management

Some growers may notice round tan colored lesions with red margins and yellow halos on some corn. These symptoms can be either herbicide injury (gramoxone in particular) or a minor disease called Holcus spot. Holcus spot is a bacterial disease of corn that can occur on young corn and is rarely damaging.

Lesions start off as dark green, water-soaked spots that turn white to tan to grey with time. Lesions are often surrounded by a reddish boarder and a cream to white colored halo. Lesions are range from 1/8 and ½ inch in diameter. Holcus spot can pop up early in the season after windy, warm, and wet weather (75-85°F). The pathogen resides on residue, where it can be splashed onto the lower parts of the plant. Therefore you may see more of these symptoms under no-till, irrigated corn. The pathogen enters corn leaves through wounds or natural openings, but does not appear to spread from leaf to leaf.

spot on cornholcusgramoxone2014

Herbicide drift of Holcus spot? Photo By N Kleczewski 2014



Separating herbicide drift and Holcus spot

Fields that are impacted by herbicide drift tend to have the following characteristics:  1) The field is located near a field that has recently received a burndown herbicide application.  2) The symptoms tend to be more severe at the edge of the field and decrease as you move away from the field edge.  The affected edge likely is downwind of the suspect source of the herbicide drift.  3) Other plants around the field will show herbicide damage.  If all three of these are present, there’s a good chance you are dealing with herbicide drift.

Regardless of the source, corn showing potential herbicide drift injury or Holcus spot are not at risk. Plants will grow out of herbicide drift and Holcus spot is not known to be yield-limiting.  Within-season management is not available nor is it required.


Late Blight Reported in North Carolina and Long Island

June 23, 2014 in Potatoes, Vegetables

Late blight was found in commercial fields in Long Island and Carteret County, NC over the weekend. Potatoes and tomatoes should be aggressively scouted for symptoms of the disease and preventative fungicides should be applied.


See the 2014 Commercial Vegetable Production Recommendations-Delaware for recommended fungicides: Veg Recs


Information on scouting, symptomology, and management can also be found here: Late Blight Website

lateblightunderFigure 1.  A potato leaf with symptoms of late blight.  Photo by Nancy Gregory, Plant Diagnostician, University of Delaware.

Getting your bins ready for wheat storage

June 20, 2014 in Wheat, Wheat Diseases

Now is the time to be getting your grain bins ready for storing your wheat.  Doug Johnson, UKY, wrote and excellent article on the best practices for preparing storage bins.  Access his article by clicking this link:  Getting bins ready for wheat storage

2014 Wheat Variety Trial Disease Ratings

June 17, 2014 in Wheat, Wheat Diseases

The 2014 Delaware wheat variety trial disease ratings are now available.  To access the writeup click here:  Wheat Variety Trial Writeup 2014

Successful disease management in small grains starts with the selection of varieties with good levels of resistance to common diseases such as powdery mildew, leaf and stripe rust, leaf blotches, viruses, and Fusarium head blight.  The variety trials give growers and consultants an opportunity to compare varieties under our growing conditions.

In Delaware this season, Stagonospora leaf blotch and powdery mildew were prevalent. Due to a cold, penetrating winter and a cool spring, powdery mildew and leaf blotches were not prevalent until after Feekes 8/9 in many fields. Leaf rust was not detected until after flowering and was not an issue in 2014. Stagonospora was moderate to severe in some unsprayed fields in parts of Delaware. Fusarium head blight/scab was prevalent, but low in incidence and severity. Most fields were well below 2% field index, a measure of bleaching at the field level. Tan spot was also present in many fields, but not found at the variety trial in Marydel, Delaware.

Keep an eye out for Basil Downy Mildew

June 14, 2014 in Vegetables

We are seeing basil downy mildew in plants shipped to several big box stores along the eastern shore.  Cornell has an excellent factsheet on BDM which can be found at this link:  Cornell Factsheet on Basil Downy Mildew

Often you will not see the spores, which occur on the underside of the leaves under humid conditions  However, you can see chlorosis of the foliage, leaf drop, and a general unhealthy look to the plant.  If suspect plants are watered and then placed in a plastic trashbag, spores on infected leaves should be visible within 24 hours.



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