Small vs Large Plot Studies on Fungicides and Yield — Which is Better?

Nathan Kleczewski, Extension Specialist – Plant Pathology;; @Delmarplantdoc

Over the last 10-15 years there has been much discussion in the agricultural realm about the utility of fungicide trials conducted on small plots, vs those on larger plots. Small plots typically are 5-10’wide, and 20-50’ long, depending on the crop and study. Large plots typically consist of strips of varieties or treatments, and therefore are as wide as the width of a sprayer or planter and typically span a cross section of the field. Today I’m going to discuss the advantages and disadvantages of both types of studies and go over some new research on the subject.

Small plot research can be conducted on a relatively small area, easily replicated, and allows for multiple treatments to be tested simultaneously (think nitrogen x spacing x fungicide timing for example). Limitations in plot size can result in larger than typical variability, especially with corn research. This is because a small amount of ear loss at harvest can have a fairly large effect on overall plot yield, and the number of plants in the plot is small. Thus, small differences in the absolute number of plants in the plot and ears harvested can result in more variability in yield from plot to plot. In the past, many also discounted small plot research due to perceived edge effects from and alleys influencing results. Edge effects result from the plants on the outside of plots experiencing a slightly different environment than those on the inside. In large plots, the edge effect relative to the overall treatment area is small. However, in small plot research, the edge effect can be large in some instances. However, at least with fungicide work, research indicates that alleys and edge effects do not influence overall results (Vincelli and Lee 2015).

Contrast this with larger scale studies such as strip trials. These studies do not suffer from as many issues with yield-related variability, at least regarding corn, because plots are much larger and therefore grain samples are less influenced by ear loss and limited population. Edge effects are minimized due to large plots, as mentioned previously. The downside is that due to the plot size, strip trials are often limited to a small number of treatments. Consequently, the same trial needs to be conducted across many sites and years before enough observations are made to draw a meaningful conclusion.

That brings me to my last point. Some people, for whatever reason, completely discount small plot research results. Often, many of the aforementioned claims are mentioned in this argument. In the end, is there really any difference in results? Researchers at Iowa State recently published a study that examined small plot and strip plot fungicide trials conducted in Iowa from 2008-2015 (Kandel et. al, 2015). A total of 230 strip plot trials and 49 small plot trials were included in the analysis. Based on their analysis, the researchers found that the yield responses for the various treatments were similar. However, the data from small plot trials were slightly more variable. For example, to detect a given yield response, a split plot trial would need three treatment replications per field and 12 locations, whereas a small plot trial would need seven replications at each site and 12 locations. Their results show that small plot data show the same results as the large plot data, but might need a little more replication to detect a difference when compared to strip trials. Both small plot and large plot data are useful for agriculture, and both have their advantages and disadvantages. However, neither should be discounted when it comes to providing useful information to growers.

Lastly, I will leave you with a link to a great little article from the University of Nebraska called “Field Studies: What do you mean 5 bushels per acre is not significant?” In this article the authors do a great job of discussing research and terms such as significance and variability. This is a good read heading into meeting season and Crop School. Find the article here:


  1. Vincelli and C. Lee, 2015. Influence of open alleys in field trials assessing yield effects from fungicides in corn. Plant Disease pp 263-266.

Kandel Y.R, C.L Kyveryga, P.M., Mueller, T.A. and Mueller, D.S. 2017. Differences in small plot and on farm trials for yield response to foliar fungicides in soybeans Plant Disease

Foliar Fungicides for Corn – Yes or No?

Nathan Kleczewski, Extension Specialist – Plant Pathology;; @Delmarplantdoc

We are entering that time of year when growers start to think about fungicides for corn. Depending on who you speak to you will hear that they range from being 100% necessary to 100% unneeded. In reality, it’s likely somewhere in between. Before I get too far into what to consider, let’s go over how foliar diseases can impact a corn plant.

Foliar pathogens of corn tend to fall into two groups. One group produces toxins that kill plant tissues and the pathogen feeds off of these decaying or dead tissues to grow and reproduce. An example of such a disease is Gray leaf spot. The second group of foliar pathogens produce “straws” that allow the pathogen to siphon nutrients from living host tissues. These pathogens need the plant to be alive in order to grow and survive. Examples of this type of pathogen include the rusts.

When either type of pathogen affects the plant, particularly the ear leaf after tasseling, it uses carbohydrates that the plant needs for filling the ear. The ear leaf and leaf below provide the majority of carbohydrates for ear fill, and this is why they are the most important tissues to protect and focus on. When carbohydrates are limited, the plant can start to draw nutrients from its reserves in the roots and stalk to support ear fill. Consequently, the roots and stalk may not have sufficient nutrients and energy to survive, and these tissues may weaken. The end result is typically reduced yields, and potentially greater chance of lodging later in the season. In sum: if the ear leaf is significantly impacted by foliar disease before black layer, there is a chance you may see yield loss and standability issues later in the season. Remember- I am saying that there is a chance. I am not saying it is a certainty.

Gray leaf spot.

Northern corn leaf blight.

That being said, foliar fungicides will benefit you and your operation if you are at high risk for commonly occurring foliar diseases. What are the most commonly occurring diseases that you will see in Delaware and Maryland? 1) Gray leaf spot and; 2) Northern corn leaf blight. These are residue-borne diseases that need persistent, wet conditions to infect foliage. Diseases such as common and southern rust can occur very sporadically, typically not until very late in the season, and are not considered significant, yield-limiting diseases in this region.

Now that you know what diseases may impact your corn, how do you go about determining the likelihood that a foliar fungicide can help you? Paul Vincelli, from the University of Kentucky likes to use the idea of a risk ladder. The higher up you are on the ladder, the greater your risk of falling to disease-related problems, and the more likely you will see a benefit from a fungicide application. What are the ways to move up the risk ladder? Here is my list of the major factors influencing foliar fungicide effectiveness, in order of importance.

The higher up you are on the corn disease ladder the greater the risk you are for falling to disease related issues.

1) Hybrid resistance to commonly occurring foliar diseases. Is your hybrid rated good to excellent for Gray leaf spot or Northern corn leaf blight? If yes, then the risk of developing these diseases, regardless of other conditions, is greatly reduced. If your hybrid is rated poor to fair for these diseases, then, if the conditions favoring disease occur, a fungicide application could be beneficial.

2) Residue and rotation. Are you planting into ground that was in corn last season? Are you planting no-till? Increased amounts of corn residue provides more material for the Gray leaf spot and Northern corn leaf blight pathogens to overwinter, grow, and potentially infect your corn under the right conditions. If you rotate to soybean or other crops such as vegetables, or till your ground, the amount of these pathogens available to infect your field is greatly reduced.

3) Irrigation. Are you heavily irrigating your corn? The longer the amount of leaf wetness, the greater opportunity for foliar diseases to infect the plant. Dryland corn only receives water with rain and therefore, risk is related to weather patterns.

4) Standability of your corn. Did you purchase a hybrid with good to excellent stay green or standability ratings? If yes, then the potential for late season lodging, even if facilitated by foliar disease, is greatly reduced.

After going over these factors, where are you on the ladder? If you are high up and at risk of falling, then what can we say about the foliar fungicides? First- when should the fungicide be applied and how many applications are needed? For a fungicide application to be the most effective, applications should occur between VT and R1. If disease is not present at this time the application can be delayed as far as R3. Research on multiple fungicide applications has indicated that growers will see the greatest return for their investment by applying a single fungicide application at this timing. Unless you are growing for the yield contest, multiple applications are not required and are not likely to be economically beneficial.

In addition, there are many products to choose from. For an unbiased rating of the most commonly used foliar fungicides for corn click here. I’m not going to discuss which products are the best, rates, etc. However, I will say that you should be certain that you are seeing a return on your applications. Are you being told that a new product is, “the best”? Are you hearing the word, “guarantee”? Prove it to yourself. After all, it’s your field, right? How can you do this? Leave an untreated section or strip of the field to allow yourself to compare yields and standability at the end of the year. Ensure that the section can be harvested and that it is representative of the field. Do not use field edges. By doing this you will have an idea of if the application had an impact in that field. Simply comparing fields is not appropriate. Why is this? Because each field will differ in conditions that will impact disease and yield. As such, any differences you see are confounded with a multitude of other factors that may impact yield. Untreated areas or strips can be related to a specific field and therefore allow you to make more informed decisions pertaining to treatment effectiveness.

Remember- foliar fungicides are a helpful tool for producing corn, but are not always required. Look at your risk ladder and if you decide you want to make an application, save yourself some guesswork and leave an untreated area of the field to assess later in the season. They say a picture is worth a thousand words, right? The same can be said for conducting a simple, on farm trial.

Seedling Diseases in Soybeans

Nathan Kleczewski, Extension Specialist – Plant Pathology;; @Delmarplantdoc

Soybeans grown in Delaware and Maryland can succumb to various diseases early in the growing season. These diseases typically are favored by conditions that slow soybean emergence and favor pathogen growth, such as wet weather immediately following planting.  There are several pathogens that can kill soybean seedlings, but in our area Fusarium is the most commonly encountered issue, followed by Rhizoctonia. To manage seedling diseases, plant soybeans when the daily soil temperatures at the 4 inch depth average at least 65°F or more. Consider seed treatments for seed lots that have less than 85 percent germination (by the warm germination test). There are many commercial seed treatments available that may help with stand establishment, and can help improve stands in some circumstances. Treat seed with a fungicide if germination is lower than 85 percent. Seed with germination below 75 percent generally should not be treated or used for seed. Many of the newer seed treatments have low use rates and must be applied by certified seed treatment applicators. Remember that seed treatments can help with seedling emergence and provide some additional protection for about 2 weeks after planting. These products will not be effective for managing diseases that can infect roots later in growth (e.g. brown stem rot) or provide any protection against foliar diseases later in the growing season. Below is a table from the mid-Atlantic field crop disease management guide, which Dr. Hillary Mehl and myself help produce through Virginia Tech. The table provides general performance of fungicide active ingredients against some causal agents of seedlings that you may encounter. These are not commercial trade names, and some seed treatments contain multiple fungicide modes of action. The guide can be downloaded from the University of Delaware Commercial Field Crops Webpage under the “Useful Links” heading at

Powdery Mildew in Peas

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Pea powdery mildew is currently widespread on Delmarva. This disease occurs throughout the US. The pathogen can overwinter in debris, on alternate hosts, or (less commonly) be seedborne. Because the pathogen is widespread, high disease severity occurs when conditions are favorable. Powdery mildew is favored by nights with dew, moderate temperatures (68-75F), and low light intensity. These conditions have prevailed in Maryland and Delaware for the last several weeks. Powdery mildew infestations can lead to uneven ripening of the crop, and yield loss (fewer peas per pod, lowered pea weight, etc.). Quality losses also occur. Several pea cultivars that are resistant to powdery mildew are available, and should be used if possible. Fungicides that are registered for management of powdery mildew include sulfur, which needs to be applied at 3 to 10 lbs/A, and Endura and Priaxor. These fungicide treatments can be costly because two applications at a 10 day interval may be needed.

Hail Damage and Fungicide Use in Field Crops

Nathan Kleczewski, Extension Specialist – Plant Pathology;; @Delmarplantdoc

With recent hail in the region, some growers may be wondering about the use of certain fungicides (specifically some containing strobilurin active ingredients (QoI FRAC group 11) for the mitigation of plant stress or to protect the plant against wounded plant tissues. Some people consider fungicides for hail-damaged crops because it is believed that hail can either increase infection of fungal pathogens or increase plant stress and therefore disease. Furthermore it is believed that the potential physiological effects of strobilurins allow for plants to recover from hail damage and limit potential yield losses. It is important to note that the fungi that infect field crops do not require wounds to infect and cause disease. It is also important to note that bacterial diseases, which potentially could increase with wounding of plant tissues, will not be controlled by these fungicides.

What does the research say? Researchers from the University of Illinois conducted a two year field study using simulated hail damage (via string mowers) at the V12 stage followed by foliar fungicides containing either pyraclostrobin or azoxystrobin (both strobilurins). Overall, the study showed that the fungicides did not provide any yield benefit to hail-damaged corn. A link to the study can be found here:

A study at the University of Wisconsin examined different corn hybids and fungicides for their reaction to anthracnose. During the course of the study hail naturally damaged the corn in the trial. Although the hail did reduce yields, fungicides did not improve plant health or result in improved yields. A soybean trial that was conducted at the same time and also damaged by hail showed no differences between fungicide treated plots vs. untreated controls. A write-up of these studies can be found here:

Other research looking at timing of hail damage to corn and soybean and various pesticides was conducted by researchers at Iowa State. Results of their studies indicate that hail damage to soybean at R4 caused less yield loss than hail damage at R1. In corn, hail damage at R2 caused more yield loss than hail damage at VT.  Fungicide application, either immediately following injury or applied several days afterwards, did not have an effect on yield.  These studies were recently published in Plant Health Progress- located when you search under the keyword “hail”

Fungicides are effective at controlling fungal diseases and their benefits are realized when used in situations where fungal diseases are likely to limit crop productivity. They will not help with bacterial diseases, such as Goss’ wilt, bacterial stalk rot, or bacterial leaf streak. The current studies indicate that the application of fungicides for mitigation of hail damage does not appear to significantly improve yields over untreated controls. If you do choose to apply a fungicide to hail damaged crops this year, it would be a good idea to leave an untreated strip in the field to allow for a comparison of treatment effectiveness at the end of the growing season.

Potato Late Blight Update #6 – June 1, 2017

Nathan Kleczewski, Extension Specialist – Plant Pathology;; @Delmarplantdoc

Late blight was reported 5/29 near the North Carolina and Virginia border. Weather has been conducive for disease. A protective fungicide application for late blight protection is recommended. I have included Early Blight P values as well. A P value of 300 is the threshold for early blight fungicide application.

Greenrow – May 1, 2017

Date DSV Total DSV P Value
5/30-6/1 5 22 244
5/25-5/30 3 17 225
5/23-5/25 4 14 179
5/15-5/23 7 10 161
5/4-5/15 3 3 104
5/1-5/4 0 0 30


Notes: Season severity of 18 severity values indicates the need for the first fungicide application. An accumulated severity of 7 after fungicide application identifies the need for a subsequent fungicide application. You can personalize your late blight forecasts for specific fields, sign up for email or text alerts, and enter in management information at

Real time fungicide application timing tables for locations within Delaware can be accessed at

See the 2016 Commercial Vegetable Production Recommendations-Delaware for recommended fungicides:

Any suspect samples can be sent to the Plant Diagnostic Clinic or dropped off at your local Extension office. Dr. Nathan Kleczewski can also be contacted at or 302-300-6962.

The website USABlight tracks tomato and potato late blight across the nation and can be found here: Information on scouting, symptomology, and management can also be found on this website.

MELCAST for 2017

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

We began our yearly dissemination of MelCast for watermelons on Friday, June 2.

MelCast is a weather-based spray advisory program for watermelon developed at Purdue University. The program uses hours of leaf wetness and temperature during leaf wetness periods to determine when a fungicide should be applied. Weather information is used to calculate how favorable weather is to the development of gummy stem blight or anthracnose. The output of the program is an “environmental favorability index unit” (EFI) for each day. The EFI values are added together. Once the threshold of 30 EFI is reached, a fungicide application is recommended. After the fungicide application, begin adding the EFI again from zero. If two weeks elapse and you have not accumulated 30 EFI, spray anyway. Also, add 2 EFI for each overhead irrigation event. We currently run MelCast for three locations in Delaware (Coverdale Crossroads, southeast of Laurel, and southwest of Laurel) and five locations in Maryland (Galestown, Hebron, Salisbury, Waldorf and Woodbine). Use EFI values for the location that is nearest to your farm.

To use MelCast on your farm, please call Karen Adams (302-856-7303) or Sheila Oscar (410-742-8788) and give us your name and e-mail address. More details about how the program works are available at our Disease Forecasting Web page, which is at: In addition, we post the MelCast Advisory online three times a week.

Late Season Fungicide Applications in Wheat

Nathan Kleczewski, Extension Specialist – Plant Pathology;; @Delmarplantdoc

I have had some questions regarding fungicides and application timings in wheat approaching flowering. In particular, the question of efficacy on canopy and head diseases has come up in conversations. The first thing to note is that the fungicides that are recommended for Fusarium Head Blight (FHB) suppression (Caramba, Prosaro, Proline) are effective in controlling foliar diseases. Commonly encountered foliar diseases include Stagonospora leaf blotch, tan spot, powdery mildew, and the rusts. However, it is important to understand that although these products are labeled for FHB, they are only effective if applied at the correct timing. Applying these products before flowering will not result in FHB suppression. This is because the FHB pathogen infects flowering grain heads (Figure 1).

Consequently, application of materials before flowering are not going to be as efficacious for FHB as they will be if you make these applications from the start of flowering (when about 50% of your main tillers are flowering) to 5-6 days after the start of flowering (Figure 2).

Figure 1. The Fusarium Head Blight Disease Cycle. The FHB pathogen grows on crop residue (corn, small grains predominantly). When it rains for 7-10 days prior to flower, the fungus can produce spores. Spores can be rain dispersed or moved long distances on air currents. When grain is flowering, spores that land on the head or anthers colonize these tissues and move into the grain head. Once in the head they can choke off water and nutrient movement, resulting in bleaching. The FHB pathogen can produce vomitoxin (DON) under the right conditions. Applications prior to flowering are not efficacious for FHB suppression.

Figure 2. Wheat heads just starting to flower. Flowering starts at the center and moves to the top and bottom of the heads. Anthers will be yellow for a short period after flowering. This yellow color indicates that they carry pollen. Fungicides should be timed such that roughly 50% of your main tillers are starting to or have recently flowered. Applications at this timing ensures that the glumes and anthers are protected from FHB. These same fungicides are very effective in managing foliar diseases of the canopy. Our research trials since 2013 have shown that in the majority of cases, the flowering timing is just as efficacious if not better for managing our most common foliar diseases (Table 1). This is because in most cases, these diseases do not reach the flag leaf or leaf below the flag leaf until near the flowering stage. This doesn’t mean that earlier applications cannot be profitable and efficacious, in fact in some cases, such as early infection by stripe rust, applications at flag leaf may be warranted, but it does mean that you can expect good to excellent protection of the major tissues contributing to wheat yield in many growing situations in Delaware and Maryland.



Table 1. An example of a wheat fungicide trial we conducted at the Wye, Maryland, in 2016

Product Timing
Leaf Blotch
(% Sev)
Untreated control 7.3 a 45.9 c 56.4 de
Twinline FGS 8/9 9 5.9 ab 48.1 b 58.7 cd
Tilt FGS 5 4 6.9 a 47.2 bc 58.8 cd
Quilt Xcel FGS 5 7 3.9 bc 45.9 c 59.8 bcd
Quilt Xcel FGS 8/9 10.5 3.0 bcd 46.7 bc 61.1 bcd
Quilt Xcel fb Quilt Excel FGS 5 fb 8/9 7 fb 10.5 2.4 cd 47.2 bc 59.9 bcd
Tilt FGS 8/9 4 3.1 bcd 48.0 bc 54.6 e
Prosaro FGS 10.5.1 6.5 0.3 d 51.8 a 63.4 ab
Caramba FGS 10.5.1 13.5 1.4 cd 51.3 a 65.1 a
Quilt Xcel + Prosaro FGS 5 fb 10.5.1 7 fb 6.5 0.3 d 51.3 a 63.4 ab

FB = followed by. FGS = Feekes growth stage where 5 occurs with 2nd shot of N, 8/9 is flag leaf emergence/early boot, and 10.5.1 is flowering. Different letters within a column indicate statistical differences between treatments. In this trial, leaf blotch complex was managed the best when products were applied at flowering. These treatments also resulted in the greatest test weights and yields under these conditions.