The following article was written by and all photos supplied by:

Dr. Erdal Ozkan
Professor and Extension State Specialist
Pesticide Application Technology
The Ohio State University

Once a decision is made that spraying pesticides is a must to protect your crop against weeds, insects and diseases, there are two important things you should do to get the most out of your sprayer during the spraying season. One of these important tasks should be accomplished even before the spraying season starts. It is making sure the sprayer is delivering the gal/acre application rate you expect to get from it at the travel speed you operate the sprayer. Many refer to this as “calibration” of the sprayer. The second important thing to do is to operate the sprayer properly and making appropriate adjustments to the sprayer to not waste pesticides and to make sure the pesticides are applied uniformly on the target. Let’s tackle both of these issues one at a time.

Calibrate your sprayer

A sprayer can only be effective, efficient, and safe if it’s properly checked and calibrated before it’s taken to the field, and if it’s periodically checked and calibrated during the spraying season. The primary goal with calibration is to determine the actual rate of application, and then to make the necessary adjustments if there is a difference between the actual application rate and the “expected” application rate. Under some specific circumstances the expected application rate could be the rate chosen by you, the applicator. However, usually, the “expected” application rate is what is mentioned on the chemical label and sprayer operators must follow what is recommended on the label. This required rate is most often given in “gallons per acre”. Your job as the applicator is to make sure your actual application rate matches the recommended rate on the label. You can find out how close your application rate to the label rate only by calibrating the sprayer. Although your goal should be to achieve a perfect match between the actual and the expected application rates, an error margin of less than 5% between the two rates is acceptable.

How to calibrate a sprayer?

Regardless of the sprayer used, calibration requires measuring the nozzle flow rate (gal/min) and the travel speed (miles/hour), and only three things are needed: a watch or smart phone to record the time when measuring the nozzle flow rate or the travel speed, a measuring tape, and a jar graduated in ounces.

Collecting nozzle flow rate from a boom sprayer is relatively easy because spray is directed vertically towards the ground. However, when using sprayers used in orchards and vineyards have nozzles discharging spray in a wide range of directions from close to ground vertically to horizontal and upward directed toward the crop canopy. Using milk liners to connect nozzles to the hoses inserted in collection cups is a practical way to check flow rates of nozzles without getting wet.

Please look at the Ohio State University Extension publication FABE-520 for an easy method to calibrate a boom-type sprayer.  Here is the URL for this publication:

http://ohioline.osu.edu/factsheet/fabe-520.

If you are calibrating a high pressure airblast sprayer used to apply pesticides on trees in fruit orchards, please look at the Ohio State University Extension publication FABE-537.  Here is the URL for this publication:

http://ohioline.osu.edu/factsheet/fabe-537.

Things to do prior to calibration

Before calibration, run the sprayer, inspect it for leaks, and make sure all vital parts function properly and that the sprayer has a good set of nozzles. Some nozzles or screens may become clogged causing under-application. Clean all clogged nozzles and screens before calibrating the sprayer and after each application (especially when powder sulfur or copper are applied in vineyards). Observe the spray pattern before calibration, and often during spraying to make sure there is no clogging. Nozzle wear from extended use causes over-application and/or non-uniform application. Check the flow rate of each nozzle for at least 30 seconds. Check the nozzle company catalog (website) to see what the flow rate of a new nozzle at the same pressure setting is.  Compare the flow rates of nozzles you measured with the flow rate of the new nozzles Replacing a nozzle is recommended if its measured flow rate is 10% greater than that of the new nozzle at the same spray pressure.

Follow safety rules when calibrating sprayers

For safety reasons, calibration should be done using water in the sprayer tank. A mixture containing pesticides may have a slightly higher density or viscosity than water, which may slightly reduce the flow rates of nozzles. However, usually, the difference in flow rates between water alone and a mixture containing pesticides is not significant unless a high volume of high-dense or viscous adjuvants is mixed in the spray mixture. Conversions for spray solutions with different densities are provided by the nozzle manufacturers in their catalogs or websites. Even when calibrating the sprayer using water, always wear the personal protective equipment used for spraying pesticides, such as gloves and goggles.

Other adjustments needed for effective spraying

Knowing that the actual spray application rate (gal/acre) determined through calibration matches the expected application rate (what is on the chemical label) is the first step to achieve maximum accuracy from a sprayer. However, this is only one aspect of achieving effective pest control. How much of the spray reaches the target canopy, and how uniformly it is distributed within the target canopy are two other factors that play important roles in achieving maximum protection against pests.

The goal in spraying pesticides should be landing as many droplets on the target and as uniformly throughout the canopy as possible. This is especially important when spraying fungicides and insecticides. With boom sprayers used for spraying on vegetables, there are several reasons why the deposition on the target is not uniform across the boom. Some major reasons include having different size and types of nozzles mixed on the boom, clogged nozzles and uneven boom height over the target sprayed.

Non-uniform deposition of pesticides on the target canopy is even a more serious issue to deal with. If you a fruit grower, it is very likely that the sprayer you have is like the ones shown in the following pictures.

Unfortunately, the sprayer shown on the left has two design and/or adjustment issues that significantly reduce the spray deposited on the target: 1) The top two to three nozzles on each side of the sprayer aren’t directing spray toward the targets and should be turned off. 2) There are no deflector plates, neither on the top or the bottom part of the fan, to direct the air plume towards the target. These plates that ensure that the sprayed droplets are deposited on the canopy, are present on the sprayer shown on the right.

When spraying an orchard or vineyard using an airblast sprayer, adjust the angle of the deflector plates to match the canopy’s height of the canopy. This adjustment is necessary each time spraying is conducted because the canopy height may vary from one orchard or vineyard to another, or even within the same orchard or vineyard throughout the growing season. A practical way to determine the correct trajectory of the air discharged from the fan is to tie ribbons around the area where air is exiting the fan. Then turn on the fan, watch the direction the air blows the ribbons, and adjust the angle of the deflectors accordingly.

Adjust the air flow when using airblast orchard sprayers

Air generated by the sprayer fan is what carries droplets from the nozzle to the target. Too little or too much air results in ineffective and inefficient coverage of the target. The goal is to adjust the sprayer fan air-flow rate and volume so that the air being directed into the canopy replaces the air already in the canopy, but dies down significantly as it reaches the other side of the canopy. This adjustment will result in very little spray droplets escaping the canopy. Be aware that too much air flow can force leaves together, creating a surface that blocks the passage of air. When air cannot penetrate the canopy, it moves upward in a vertical trajectory, further exacerbating the off-target movement of droplets. In general, most, if not all of today’s air-assisted or airblast sprayers, generate more air assistance than what is needed. This is especially true for vineyard spraying. So, it is very important to take the time to adjust the air stream characteristics (direction, air speed, and air flow rate) suitable for the tree or vine canopy conditions at the time of the spray applications. As a side benefit, a reduction in the airflow rate also lowers fuel consumption. 

I mentioned in this article the highlights of what you need to do to get the best performance from your sprayer. You can find detailed information on several Ohio State University Extension Fact Sheets which you can find by visiting the website for OSUE publications: https://ohioline.osu.edu. Once you are on this site, do a search using my last name (“ozkan”) as the key word for your search. You will see a listing of publications  on sprayer calibration, selecting the right size of nozzle for the intended application rate, how to achieve efficient penetration and uniform deposition of droplets inside the canopy, and how to assess the quality of spray deposition and coverage on the target.

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SWD larvae in fruit

Spotted-wing Drosophila male (L) and female (R).

If you grow a crop that has been impacted by SWD over the past decade, February 28 is your last chance to report how this insect has affected your operation.

Ohio was first infested with spotted-wing Drosophila (SWD) in the fall of 2011. This pest turned long standing IPM programs on their head and forced growers to adopt new monitoring and management practices for this pest or face losing significant amounts of  blueberries, raspberries, strawberries, blackberries, peaches and grapes to larval infestation. While OSU had an active Extension and outreach program to teach growers about this insect since discovery in Ohio, we relied on research generated by several multi-state grants to keep our growers at the forefront of IPM on susceptible crops. While we have made substantial progress on monitoring and managing this pest, there are still many research and management questions to answer. To help inform the next phase of SWD research and outreach, please consider adding your thoughts about how this pest has impacted your operation over the past decade. All responses are confidential.

**This survey is being shared with multiple mailing lists to ensure that we reach as many impacted growers as possible. We apologize if you receive it more than once!

Dear Berry Growers:

As part of a national team of entomologists studying the management of spotted-wing drosophila (SWD), we are reaching out with a request for assistance to help understand the current impacts of SWD on your farm and how these impacts may have changed in the last 10 years.

If you are willing to share insights from your farm, farms you manage, or growers you work with, please complete this short survey, which will take about 15 minutes or less: https://docs.google.com/forms/d/e/1FAIpQLSeW6rCcyM9vf_sjLJDj0J_6G03jlVbBLZt5rlX7kmzSj0Ypog/viewform

How will this information be used?
This information will be used to develop new research goals as part of a USDA Specialty Crop Research Initiative proposal under development. It will also be compared to information collected in similar surveys in 2013 and 2014 to help us understand where challenges still exist for SWD management and what improvements have been made over the last 10 years and shared in extension and scholarly publications.

Who should I contact for more information?
For more information about this survey, contact Hannah Levenson, hklevens@ncsu.edu, 919.434.7882. For more information about SWD management, contact members of our project team or your local extension expert.

Thank you,

Hannah Burrack
Professor & Chair
Department of Entomology
Michigan State University
burrackh@msu.edu

SWD larvae in fruit

Spotted-wing Drosophila male (L) and female (R).

If you grow a crop that has been impacted by SWD over the past decade, February 28 is your last chance to report how this insect has affected your operation.

Ohio was first infested with spotted-wing Drosophila (SWD) in the fall of 2011. This pest turned long standing IPM programs on their head and forced growers to adopt new monitoring and management practices for this pest or face losing significant amounts of  blueberries, raspberries, strawberries, blackberries, peaches and grapes to larval infestation. While OSU had an active Extension and outreach program to teach growers about this insect since discovery in Ohio, we relied on research generated by several multi-state grants to keep our growers at the forefront of IPM on susceptible crops. While we have made substantial progress on monitoring and managing this pest, there are still many research and management questions to answer. To help inform the next phase of SWD research and outreach, please consider adding your thoughts about how this pest has impacted your operation over the past decade. All responses are confidential.

**This survey is being shared with multiple mailing lists to ensure that we reach as many impacted growers as possible. We apologize if you receive it more than once!

Dear Berry Growers:

As part of a national team of entomologists studying the management of spotted-wing drosophila (SWD), we are reaching out with a request for assistance to help understand the current impacts of SWD on your farm and how these impacts may have changed in the last 10 years.

If you are willing to share insights from your farm, farms you manage, or growers you work with, please complete this short survey, which will take about 15 minutes or less: https://docs.google.com/forms/d/e/1FAIpQLSeW6rCcyM9vf_sjLJDj0J_6G03jlVbBLZt5rlX7kmzSj0Ypog/viewform

How will this information be used?
This information will be used to develop new research goals as part of a USDA Specialty Crop Research Initiative proposal under development. It will also be compared to information collected in similar surveys in 2013 and 2014 to help us understand where challenges still exist for SWD management and what improvements have been made over the last 10 years and shared in extension and scholarly publications.

Who should I contact for more information?
For more information about this survey, contact Hannah Levenson, hklevens@ncsu.edu, 919.434.7882. For more information about SWD management, contact members of our project team or your local extension expert.

Thank you,

Hannah Burrack
Professor & Chair
Department of Entomology
Michigan State University
burrackh@msu.edu

This article was written by Dr. Aaron Wilson, OSU Extension, Ag Weather and Climate Field Specialist

Fig. 1. U.S. Drought Monitor depiction for Ohio as of October 22, 2024.

Dry conditions have plagued Ohioans throughout the growing season this year, with another below average week of precipitation this past week. Since the remnants of Hurricane Helene moved through in late September, ample precipitation has been hard to come by. Several cities are experiencing one of their driest Octobers on record, including Cincinnati and Mansfield (2^nd driest), Dayton (3^rd driest), and Athens and Columbus (4^th driest). Many of these locations have picked up less than three-tenths of an inch. Warmer than average temperatures this week have also notched the drought stress back up, with numerous reports of field fires in west central and northwest Ohio. Certainly, where drought conditions have persisted the longest in southeast Ohio, crop yields are generally below average, pastures have been slow to recover, and producers are still hauling water. As of October 22, 2024, the US Drought Monitor still shows about 8% of the state in D4 – exceptional drought with about 65% of the state still experiencing drought conditions (D1-D4).

If you are continuing to experience drought impacts or to document improvements, you can view and/or submit local reports at the Condition Monitoring Observer Reports page. For a more detailed look at conditions and resources, visit our Drought Response Page or for the latest up-to-date conditions, seasonal outlooks, and monthly climate summaries, please visit the State Climate Office of Ohio.

Fig. 2. Precipitation forecast from the Weather Prediction Center for 8pm Monday October 28 – 7pm Monday November 5, 2024.

Weather Forecast – Again we are expecting a big warming trend early this week, followed by an increasing chance of Halloween rain and a weekend cool down. High pressure will remain in control through Wednesday, with strong southerly wind gusts and high temperatures running in the mid 70s to low 80s. With gusty winds and low humidity, fire risk will be elevated. A few daily record highs are at stake as well. A cold front will push through the region on Thursday. Although much heavier rain is expected across the central states, a solid line of showers and storms will drop 0.25-0.50 inches of rain. After brief drying conditions on Saturday, another system could bring rainn showers back into Ohio for Sunday and Monday. Temperatures will be much colder over the weekend, with highs in the 50s and 60s and lows in the 30s and 40s. The Weather Prediction Center is currently forecasting 0.25-0.75” of rain this week (Figure 2).

The 8-14 day outlook from the Climate Prediction Center and the 16-Day Rainfall Outlook from NOAA/NWS/Ohio River Forecast Center show that temperatures are likely to jump back above average with a robust signal toward wetter than average conditions as well (Figure 3). This is not a pattern we have seen in a while but hopefully represents a step toward long-term drought and soil moisture recovery for the area. Climate averages include a high-temperature range of 56-60°F, a low-temperature range of 38-41°F, and weekly total precipitation of 0.55-0.80”.

Fig. 3. Climate Prediction Center 8-14 Day Outlook valid for November 5 – 11, 2024, for left) temperatures and right) precipitation. Colors represent the probability of below, normal, or above normal conditions.

Cover shot of new pumpkin guide

A new 72-page guide, “A Modern Approach to Crop and Pest Management in Pumpkin – ANR 806”, was published in August 2024 to help both beginner and experienced growers produce a better crop. Thirteen specialists from Ohio State University, Michigan State University and Cornell University worked together to produce this guide which increases awareness of modern IPM practices such as mechanical weed control, cover crops, pollinator protection and negative impacts of certain pesticide mixtures. Basic topics like weed, insect and disease management are also covered, as well as the benefits of natural enemies and a pumpkin enterprise budget to measure overall profitability. In addition to colorful images and layman’s text to explain each topic, QR codes are sprinkled throughout the guide to provide deeper dives on most topics via factsheets, bulletins, websites and videos from specialists around the country. Although the guide was written for growers in the Midwest, most concepts will apply to growers in the Northeast and Southeast regions of the country.

Copies of the guide can be ordered and purchased at your local Extension county office or online at OSU Extension Publishing (https://extensionpubs.osu.edu/a-modern-approach-to-crop-and-pest-management-in-pumpkin/).

Pages of the new pumpkin guide

 Midwest Mechanical Weed Control Field Day Returns!

Last year this event was held in Wooster, OH and it was a great success, with over 150 farmers in attendance. This year the event has rotated to West Lafayette, IN, home of Purdue University if you care to attend. A full day of weeding tool demonstrations, trade show, and cultivation education for both vegetables and row crops will be on display.

Champaign, IL. In partnership with Purdue University, this year’s Midwest Mechanical Weed Control Field Day will take place on Wednesday, September 11 at Purdue University’s Horticulture research station. 

At the morning Expo you can see weeding tools and speak with company reps from manufacturers in the US, Europe, and Japan, and meet the farmers in attendance from all over the region. At the morning education sessions, learn from experienced farmers and university weed scientists from surrounding states. ‘Weed control on the tillage spectrum’ will make the connection between tillage and weed management – with demos and talks on tarping for vegetables and plowing down cover crops with residue management in mind. 

A walk-behind tractor exhibition – ‘Walk-Behind Alley’ – features demonstrations of walk-behind tractors and hand tools. A wide variety of cultivators, hand tools, and the paperpot transplanting system will be shown. You can also visit the trade show exhibit booths to meet other supply companies, like equipment dealers for all manner of machinery, seed, tools, fertilizers, and soils. 

At noon, the field day will break for lunch – an opportunity for farmers to meet and network, or continue looking at trade show equipment and speaking with exhibitors. In the afternoon farmers follow the tractors out to the demonstration field, where corn, beets, and brassicas have been planted especially for the demonstrations. Many 3-point, camera-guided, autonomous, and belly-mounted cultivators and cultivating tractors will be demonstrated in the field and explained by manufacturers. These demonstrations will show how the machines should be mounted and properly adjusted according to crop and soil conditions, and will help farmers visualize how the implements can work on their own farms. 

Row-crop tools in demonstration include precision-controlled tine-weeders and several types of camera-guided cultivators with finger weeders and all manner of other tooling – see all types of knives, hilling discs, etc. Demonstrations will be held in 4’’ corn. 

Vegetable weeding tools include cultivating tractors past and present, a variety of belly-mounted and rear-mounted steerable tools, and cultivators from Japan! 

Registration for this full-day of learning and networking on mechanical weed control is just $75. Registration includes lunch and all the machinery demos you can handle. It is recommended that everyone register early as each year space runs out. 

This event is perfect for farmers and ag advisors who want to: see a particular weeding tool before buying it, learn how to adjust cultivators, see what is new in cultivation, or learn from other farmers. 

Here is the general information for the event: 

When: Wednesday, September 11, 2024 

Where: Purdue University – MEIGS Horticultural Research Farm 9101 S 100 E Lafayette, IN 47909

How Much: $75 (includes lunch) 

Register online at: https://thelandconnection.regfox.com/2024-midwest-mechanical-weed-control-field-day

*Walk-in registration will be available, but lunch and conference amenities are not guaranteed.

Field Day webpage: https://www.thelandconnection.org/event/2024-mmwcfd/

For more info on the event or to register by phone, contact Crystal at crystal@thelandconnection.org or (217) 840-2128. 

Inquiries for interviews on radio, print, and beyond are welcomed – Please reach out to Sam Oschwald Tilton, glacialdrift@protonmail.com, or 414-213-5337

Interested in exhibiting your products and connecting with farmers at the field day? Please contact us

Powdery Mildew Detected – This week marks the first week powdery mildew was detected in the pumpkin plots in South Charleston at the Western Ag Research Station. There have been reports of PM being found a week earlier in Wayne County. At the station, the amount of disease detected in the trial was extremely minor; only three white colonies on ca. 60 leaves, top and bottom leaf surfaces inspected, on July 18. Powdery mildew can multiply in the canopy rapidly given warm and humid conditions so the recommendation is to begin treatment when the first colonies are discovered. Today, nine treatments for the powdery mildew fungicide trial on pumpkins were applied. Major fungicides being tested include Milstop, Cease, Switch, Gatten, Procure and Quintec. Results of the trial will be reported when the trial is completed mid-September.

Striped Cucumber Beetle Update – The summer generation of striped cucumber beetles emerged in South Charleston around two weeks ago and have moved off of the foliage and primarily into flowers at this point in the season. Treatment for beetles in the flowers is not recommended as this will only cause significant harm to pollinators in and around the field, plus cause other issues with pest insects (see below).

Sticky panel with rootworm attractive lure

On a related note, the striped cucumber beetle attractant study being conducted at the Western Ag Research Station is about ¾ done at this point. Of the three attractants being tested for striped or spotted cucumber beetles, none seem to stand out as being hyper attractive to these two beetles. There is one lure that is very effective against the Western corn rootworm beetle, which has also begun to emerge from corn fields in the past few weeks.

Aphid infested pumpkin plant

Green lacewing egg in center of circle

1 black circle around ladybug eggs, 2 circles around golden aphid mummies

Aphids Rising…But Why? – What do you get when you apply a pyrethroid insecticide to a pumpkin field in early July? Answer, most likely a field full of aphid covered plants. Why the surge in aphids? This is attributed to the highly toxic nature of the pyrethroid chemical class to natural enemies in the field that are actively suppressing the aphid population. In the photos, you can see some major aphid predators re-establishing on the aphid infested leaves; ladybug eggs, green lacewing eggs and aphid mummies (evidence of parasitoid wasps). The lesson here is unless you have a known pest to control in a pumpkin field which is over threshold, resist the urge to spray a broad-spectrum insecticide. If a treatment must be made, consider selecting products that are less likely to flair aphids or other secondary pests.

In an IPM context, it is important to protect plants with fungicides from diseases such as powdery or downy mildew when they are detected above threshold. Over the past few years, researchers have begun to understand the importance of not adding both fungicides and insecticides to the same tank mix due to harmful synergies, some that are known and many that are unknown, on pollinators and potentially other insects like natural enemies. For a deeper dive into the negative synergy of mixing fungicides and insecticides, Cornell University recently published this bulletin. https://cornell.app.box.com/v/ProtectionGuide-FieldCrop2023.

Cornell Pollinator Guide

World’s smartest toad?

Amphibian Pest Management? – While scouting for powdery mildew on Thursday, I came across this toad cleverly parked at the edge of a pumpkin flower, no doubt waiting for a juicy opportunity to nab a few beetles or bees. First time I have ever seen this!

The Integrated Pest Management Program along with OSU Extension educators across the state are monitoring five key pests this season. Monitoring sites are set up on farmer’s fields across the state and will be updated weekly.

Brown Marmorated Stink Bug – This insect will not be monitored for until late July. Adults are currently active on a broad range of specialty crops.

Spotted wing Drosophila – A total of eight sites have been set up in Greene, Geauga, Loraine, Adams and Ross counties. SWD has been detected in all counties with individual trap counts ranging from 6 to 184 flies. The threshold for this pest is 1 fly. If this threshold is exceeded and ripe or ripening fruit is present, growers should consider applying insecticides or use other cultural methods to manage the infestation through final harvest. Growers with ripening brambles, blueberries, peaches and other soft skinned fruit should be aware this pest is likely present in all 88 counties at this point in the season. Refer to this factsheet for more information https://bpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2020/11/SWD_Ohio_handout_V20.pdf 

European corn borer – Five monitoring sites are set up in South Charleston (Clark Co.), Fremont (Sandusky Co.), Geauga and Huron Counties. All sites are reporting low moth numbers for the past two weeks, ranging between 0-3 moths per trap per week.

Corn earworm – Eight monitoring sites are set up in Clark, Sandusky, Fayette, Huron, Pike and Crawford counties. Moth counts have fluctuated in the past two weeks between 0-17 moths per trap per week, with the highest moth count in Clark county. As we get later into the season, expect larger migratory flights of CEW to be present in the state, especially around silking sweet corn. If you have a trap that is located near a mature sweet corn field, move it to a soon to be silking field, as CEW moths are preferentially attracted to silking sweet corn over young or mature sweet corn plants.

Squash vine borer – There are 11 counties currently trapping for this pest in Clark, Greene, Montgomery, Fayette, Geauga, Ross, Pike, Seneca, Morrow, Summit and Williams counties. Clark, Greene, Seneca, Williams and Montgomery. Reports for the last two weeks show a general reduction of moths captured per trap per week, ranging between 0 and 5. This insect should continue to decline through the rest of the season. As growers walk and scout fields, be vigilant to identify potential SVB damage on plants to estimate injury.

Growers can access and view the monitoring data directly at this site.
https://docs.google.com/spreadsheets/d/1T4Uk8VKH-fY4qms4FlEwQvz8o1Lxk-t8LLHVz97kxNU/edit?usp=sharing

Initial powdery mildew infestation

Heavy powdery mildew infestation

This article was co-written with Dr. Sally Miller, Emeritus OSU Plant Pathology, updated from 2023 post.

The article is detailed and thorough as OSU has had an active powdery mildew evaluation program for over two decades. Here are the key messages to focus on; greater details of each are further into the text:

1. Mid-July is the time to start scouting for PM; when the first colonies are found, begin treatment.

2. Treat every 7-14 days using hollow cone nozzles at 35-50 GPA with a target of 65 PSI.

3. Alternate FRAC codes (letter/number on top of label) when spraying to reduce PM fungicide resistance. For example spray 1 Quintec (FRAC 13), spray 2 Procure (FRAC 3), spray 3 Quintec, spray 4 Procure, etc. Adding a protectant (FRAC M) like Manzate Pro or Chlorothalonil (Bravo) can be done with every spray and enhances overall PM control; it’s the one exception to the rotation rule.

4. There are many great to good products available for PM control; at least 3 current sources are listed in this article to find products; Sally Miller and Jim Jasinski’s trial results listed below and the Midwest Vegetable Production Guide.

5. Some cost of application data is provided toward the end of the article so growers can pair efficacy with economics to see which suits their production goals best.

General PM Biology
Powdery mildew usually appears on pumpkins and other cucurbits in Ohio beginning in early to mid July. While it has not been seen in South Charleston at the research station yet (Clark County), it has been reported in Wayne County. The pathogen, Psudoperonospora cubensis, does not overwinter in Ohio; infections result from spores blown into the area on the wind.  Powdery mildew is favored by moderate to high temperatures and high humidity. However, unlike most other fungal plant pathogens, it is inhibited by free moisture on the leaf surface.

Signs of infection are small circular powdery growths on either side of the leaf, typically the lower leaf surface first. These spots enlarge and can eventually cover most of the leaf surface and kill the leaves. Stems and leaf petioles are also susceptible, but the disease is not observed on fruit. In pumpkins, powdery mildew may also attack the “handles”, which can be further damaged by secondary pathogens.

Powdery mildew is managed using disease-resistant varieties (powdery mildew tolerant and resistant hybrids) and fungicides. Pumpkin and squash varieties vary in resistance to powdery mildew; in general, the more susceptible the variety, the more fungicide needed. The choice of fungicide is important because insensitivity to overused fungicides is common. It is critical that a fungicide resistance management program is followed. Alternate fungicides in different FRAC (Fungicide Resistance Action Committee) groups, indicating different modes of action against the fungus. Fungicide applications should begin when the disease first appears and incidence is low (rule of thumb: at least one leaf of 50 scouted). Fungicides that are labeled for use against cucurbit powdery mildew can be found in the searchable Midwest Vegetable Production Guide for Commercial Growers. In the Cucurbit chapter, a fungicide table lists recommended products and their efficacy against powdery mildew.

Product Efficacy Trials
Field exposed greenhouse based studies at OSU of efficacy of powdery mildew fungicides in Ohio in 2021 indicated that Aprovia Top, Luna Experience, Inspire Super, Rally, Miravis Prime, Luna Sensation, Microthiol Disperss, Vivando and Procure provided very good control of powdery mildew on pumpkins (see table in color below).  Velum Prime, Cevya, Prolivo and Gatten provided good control of powdery mildew on upper leaf surfaces but poor control on the lower surfaces.

Quintec provided good control in 2021 but in other years and other states has failed due to resistance. Fontelis, Bravo Weather Stik, Merivon Xemium, Pristine, and Torino have been shown to provide poor or variable control in Ohio or other states and are not recommended.

Table 1. Field exposed and greenhouse incubated powdery mildew fungicide results.

Jim Jasinski, OSU Extension, has been running field trials in southwest Ohio at the Western Ag Research Station since 2014 to assess fungicide efficacy against powdery mildew on pumpkins. Yearly results of these trials (2014 – 2023) can be found here toward the middle of the page.

Some effective season long fungicide combinations, based on 2021-2023 data, are shown in the second table below. Some of these fungicides were not effective in the Field/Greenhouse bioassays (table in color), but when paired with a broad spectrum protectant like Manzate, provided more effective control than when applied alone. Most experts suggest adding a broad spectrum protectant fungicide like Manzate to more powdery mildew-targeted fungicides to reduce the risk of fungicide development, boost fungicide efficacy and protect the crop from other diseases. However, programs based solely on protective products such as Manzate or Bravo, do not provide good season long protection so addition of other fungicides is necessary.

Always check the label for the full list of allowed crops, use recommendations and restrictions.

Table 2. Field Based Season Long Effective Fungicide Treatments to Control PM in Pumpkin in Ohio in 2021 – 2023.

*sequential applications for research only, must be rotated per label for grower use.

Spray Costs
While much time and energy is spent determining the most effective fungicides to control powdery mildew, less effort has been focused on the cost of the fungicide program, which is a huge consideration for growers. Below are listed some price estimates for a handful of fungicides. Prices extended to growers hinge on many factors so if the prices at your dealer vary compared to what is shown below, that is normal and to be expected.

Cevya – $5.92/oz (ca. $17.75 per application)

Gatten – $4.03/oz (ca. $24.18 per application)

Procure – $3.75/oz (ca. $30 per application)

SiGuard – $13/qt (ca. $13 per application)

Manzate Pro Stick – $3.60/lb (ca. $9 per application)

Quintec – $3.80/oz (ca. $22.80 per application)

Vacciplant – $1/oz (ca. $14 per application)

Vivando – $2.30/oz (ca. $35.42 per application)

Luna Experience – $5.15/oz (ca. $30.9 per application)

Microthiol Disperss – $1.85/lb (ca. $7.40 per application)