Category: Corn

Tar Spot is Starting to Appear in Maryland

Andrew Kness, Senior Agriculture Agent | akness@umd.edu
University of Maryland Extension, Harford County

Tar spot has started to pop up in corn fields and we have received several reports from Harford, Cecil, Queen Anne’s, and Kent County, Maryland over the past couple of weeks. These reports are about one month earlier than we have first reported tar spot in years past, with the July 23 confirmation of tar spot in Cecil County being the earliest.

Fortunately, all reports and all of the fields I have scouted myself, tar spot is present but at very low levels. The predominant disease I am seeing right now remains gray leaf spot, which makes sense as this is a disease that prefers warmer temperatures and tar spot tends to favor cooler temperatures.

With tar spot being present in our region earlier than usual, growers should be vigilant with scouting and monitoring this disease. Most of the corn crop in Maryland is at or close to R3 or near even near black layer in southern Maryland, which is towards the tail end of major yield concerns associated with disease infection. Furthermore, acres treated with a fungicide between VT-R3 should have sufficient protection to get them through grain fill. If you have corn that is later tasseling you will want to pay special attention to these fields to monitor tar spot levels and other foliar diseases that could potentially reduce yields. These fields may warrant a fungicide pass if you were not planning it already.

As you are scouting your corn fields, be on the lookout for tar spot. With funding from the USDA-NIFA, we are conducting a survey of tar spot’s distribution in Maryland. If you have tar spot, or think you might, please report it to corn.ipmpipe.org or reach out to me at akness@umd.edu or (410) 638-3255. Reports are kept anonymous and individuals and/or farms are not identified in any public reports or publications.

Mid-Summer Insect Scouting Priorities in Row Crops

Hayden Schug, Agriculture Agent | hschug@umd.edu
University of Maryland Extension, Charles County

As we move into July and August, insect pressure tends to ramp up across Maryland row crops, particularly in soybeans and corn. These months are critical for monitoring pest activity and making timely, threshold-based decisions. Several pests are commonly active during this period, including corn earworm, stink bugs, Japanese beetles, other defoliators, and spider mites.

Corn earworm moths typically migrate into Maryland in larger numbers in mid to late July, although some can overwinter here, and early flights have already been reported moving up the coast. In soybeans, larvae can cause significant injury during the R1 to R5 growth stages by feeding on pods and developing seeds. When I ran the numbers, the threshold was approximately 2.5 larvae per 15 sweeps, but thresholds can vary depending on market value and treatment cost. You can use the NCSU dynamic threshold calculator to run your own field-specific estimates: https://go.umd.edu/CEW. It’s important to sample evenly across the field, as female moths may lay eggs in clusters, leading to localized infestations. Many corn earworm populations show resistance to pyrethroids, so growers should consider using alternative insecticide chemistries when treatment is needed.

An image of corn earworm, green cloverworm, and soybean looper on a white background
Figure 1. Common soybean pest caterpillars. Graphic by Hayden Schug, University of Maryland.

Defoliating insects, such as Japanese beetles, bean leaf beetles, grasshoppers, green cloverworms, and soybean loopers, can all be active during July and August. Last year in Southern Maryland, there were soybean fields that reached defoliation thresholds from grasshopper feeding alone. In many cases, damage was more severe in the center of the field, so it’s important to walk the entire field and not rely solely on edge scouting. Defoliation thresholds are based on cumulative injury from all feeding insects. Economic thresholds are 30 percent defoliation before bloom (V1–V6), 15 percent from bloom through pod fill (R1–R6), and 25 percent from full seed to maturity (R7–R8). A helpful visual guide and estimator tool is available through the University of Nebraska (Figure 2).

Diagram of soybean plant and how to determine defoliation percentage
Figure 2. Sampling soybean defoliation. Infographic by Justin McMehan, University of Nebraska.

Stink bugs, including brown and brown marmorated species, are another priority pest in soybeans and corn during mid-summer. They damage pods by piercing and feeding on developing seeds, often resulting in aborted or shriveled beans. Scouting is most important from R3 to R5. The general treatment threshold is five stink bugs per 15 sweeps, but this drops to three per 15 sweeps in fields grown for seed or planted early.

Finally, spider mites may become a problem during periods of hot, dry weather, especially along field edges. These pests cause stippling and bronzing of leaves and can spread quickly under drought stress. Treatment should be considered when active mites are present on the undersides of leaves and bronzing or stippling begins to move into the upper canopy. Threshold estimates follow the 15 percent defoliation threshold, and plants should be treated when that level of injury is reached. 

In corn, Japanese beetles can clip silks and interfere with pollination. The treatment threshold is 3 or more beetles per ear, and pollination is still ongoing. Almost all pollination occurs within the first 4-5 days of silking, so any damage done by silk clipping after that period should not affect yield. It is important to look at ears throughout the field as Japanese beetles tend to congregate on field edges. 

Regular scouting during the next several weeks will be essential to managing pest pressure effectively. Making decisions based on economic thresholds helps protect yield while avoiding unnecessary insecticide applications. If you would like assistance with scouting, pest identification, or choosing control options, contact your local Extension office.

Scouting Smarter: June Insect Pressure and Threshold Tips

Hayden Schug, Agriculture Agent | hschug@umd.edu
University of Maryland Extension, Charles County

As Maryland’s corn and soybean fields move into early vegetative and reproductive stages, June marks a key time for pest scouting. Early detection and threshold-based decisions are the foundation of a strong Integrated Pest Management (IPM) strategy, and this month brings several common threats that row crop producers should be on the lookout for.

Begin scouting for stink bugs in corn, especially along field edges. These pests often move in from neighboring wheat fields during harvest or from forested areas. They tend to show up first along borders and gradually move toward the field interior, so edge-focused scouting is important early on. From V1 to V6, the treatment threshold is 13 stink bugs per 100 plants; this drops to 10 per 100 plants from V14 to VT. Pyrethroids have shown good knockdown efficacy against stink bugs, but keep in mind that they tend to have a short residual period.

Soybean fields are also entering critical scouting windows. VE to V3 soybeans are susceptible to early defoliation from bean leaf beetles, grasshoppers, and other chewing pests. While the damage may look concerning, soybeans can tolerate up to 30 percent defoliation before bloom without experiencing yield loss. Be sure to scout multiple locations across the field, not just the edges, as field borders often exaggerate pest pressure.

Slugs have caused some issues this spring in Southern Maryland. While most fields are planted by June, it’s still worth noting that slugs can remain a concern, especially in no-till systems with heavy residue. Ensuring good furrow closure is key to preventing slugs from accessing germinating seeds. Using row cleaners to clear residue from around the furrow can also help reduce slug habitat and early pressure. If damage is suspected, conducting stand counts can help determine whether replanting is necessary as soybeans can compensate for stand loss. 

Alfalfa should be scouted for potato leafhoppers beginning in late May/early June. Regular scouting is very important, once hopper burn becomes visible in the field, yield loss has already occurred. Unlike alfalfa weevil, where the first harvest often reduces populations enough to avoid further issues, potato leafhoppers have multiple generations each year and can quickly reinfest fields after harvest or treatment, so continued scouting is necessary. For a dynamic threshold calculator and detailed scouting tips, check out this resource from Penn State Extension, https://extension.psu.edu/potato-leafhopper-on-alfalfa.

Hot and dry weather can also accelerate the development of secondary pests, particularly spider mites along field edges. While not typically a major issue in June, early flare-ups can occur during periods of drought stress. It’s worth inspecting leaf undersides in stressed areas to catch hot spots before populations expand.

Effective scouting depends on consistent, thoughtful observation. Early morning or evening visits often reveal pests that remain hidden during the heat of the day. Scouting beyond the field edge helps avoid over- or underestimating pest populations. Most importantly, only apply insecticides when economic thresholds are met. Doing so helps reduce unnecessary costs, preserves beneficial insects, and slows the development of pesticide resistance.

Corn Fungicide ROI Calculator

Andrew Kness, Senior Agriculture Agent | akness@umd.edu
University of Maryland Extension, Harford County

The Crop Protection Network has a new corn fungicide return on investment (ROI) calculator: cropprotectionnetwork.org/fungicide-roi-calculator. This can be used to determine estimated ROI for your corn crop and can be used to select if and which products to use. Pre-populated data is used, but you can customize the inputs for your operation. The following is information on the tool from the Crop Protection Network website:

Information on the Corn Fungicide ROI Calculator

The purpose of this calculator is to share results from university uniform corn fungicide trials conducted in the United States and Canada, and allow farmers and others in the agricultural industry to calculate the potential return on investment (ROI) for corn fungicide application across a variety of user-defined factors, which is based on research data included in this calculator. 

The treatment cost, expected benefits, and breakeven probability values shown in the calculator are estimates based on data and not guaranteed values. Also, values are derived from data collected in trials designed to test specific product comparisons, and data are not available for all labeled fungicides on corn. Data are not comprehensive and represent only the treatments tested in these trials.

How were fungicide products selected for inclusion in the calculator?

The Corn Disease Working Group (CDWG) develops annual uniform testing protocols based on feedback from university extension specialists. Trials typically test between five and 10 fungicide products per year, per trial. Products are selected based on availability and market share, and typically represent products available to and used by a majority of farmers. Focus is also placed on newer products where efficacy data might be lacking across the corn production belt of the United States.

How were treatment costs determined?

The CDWG solicits information on fungicide product pricing and application costs from university extension specialists annually. Methods for collecting these costs vary by state or province and year. Specialists may collect pricing information from surveys or direct feedback from university Extension, industry, farmers, and other agricultural personnel. Product and application costs are averaged, and a national mean and median are determined for each product based on submitted data. The treatment costs for each product listed can be changed to tailor the expected benefit estimates to local pricing.

How are expected net benefits/acre calculated?

The expected net benefit is an estimate of ROI when considering several variable factors that can be measured or estimated. These factors include the proportional yield benefit (yield of the treated plots vs. non-treated) for each fungicide across a range of disease levels. This is then combined with total treatment cost (cost of the fungicide plus application cost) and expected commodity sale price per bushel with both parameters fit to a function that estimates the expected net benefit per acre. This function is only a best estimate based on the available data and reported, real-world treatment costs. Unaccountable error and uncertainty exists in the data and actual ROI may occasionally be significantly different from the estimates reported here.

How are expected breakeven probabilities calculated?

Thousands of simulations were performed to estimate the expected ROI of fungicide usage application across a range of inputs used to calculate expected net benefits. The expected breakeven probabilities represent the proportion of total simulations that had an expected net benefit of zero or greater, given a fungicide and set of crop characteristic inputs.

What does disease severity mean?

“Low” indicates simulations made using a final end-of-season disease severity level of 1%. “High” indicates simulations made using end-of-season disease severity level of 5% or above. The levels were chosen based on previous research demonstrating detectable yield loss from disease at 5% or above. You may also choose to explore a different end-of-season severity by ticking the box next to “I’d like to enter a custom disease severity %.” Disease severity levels should be set at what is expected for a particular hybrid in a particular field at the end of the season.

Important notes about data

Currently data available in the calculator are from university uniform corn fungicide trials conducted across 19 states and Ontario, Canada between 2019 and 2022. Primary diseases in this data set were tar spot and southern rust. Diseases, such as gray leaf spot, northern corn leaf blight, and others, were observed at lower frequencies in this dataset.

Disclaimer

This information is only a guide, but is based on multi-year research across multiple locations. Contributors and data managers assume no liability resulting from the use of these estimates. 

References to products in this resource are not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer. 

Find out More 

The Crop Protection Network (CPN) is a multi-state and international collaboration of university and provincial extension specialists, and public and private professionals who provide unbiased, research-based information to farmers and agricultural personnel. Our goal is to communicate relevant information that will help professionals identify and manage field crop diseases.

Find more crop protection resources at the Crop Protection Network. 

Acknowledgments

Data compilation:

Maria Oros, Isaac Baumann, and Jason Lo, Data Science Institute, University of Wisconsin-Madison

 

Maryland Regional Crop Reports: April 2025

Western Maryland

Weather has been different in 2025 for sure here in Washington County. We had some of the lowest temperatures for some years and the longest sustained cold spell in recent memory. Hopefully this will help break some insect and disease cycles. Additionally, the snow was good ground water recharge although not as much as we would have liked. Then came the dry weather. The later part of winter and early spring has been unseasonably dry if we can even use that phrase anymore. Recent showers and projected precipitation has raised our hopes again for a good crop year, even if the only activity to date has been fertilizer and manure application. Planters are being tuned up and farmers are practicing their patience waiting for soil temperatures to raise.—Jeff Semler, Washington Co.

Central Maryland

Temperatures have been all over the place. It was 80 degrees a few weekends ago, and this morning it was 29 degrees. Temperatures are predicted to be a bit more spring-like over the next week and a half. Recent rains have made small grains and cover crops look better. We are still in a drought. Nitrogen and herbicide applications have gone out on wheat and barley. In eastern Montgomery County, wheat is at Feekes 5 (leaf strongly erected).—Kelly Nichols, Montgomery Co.

Northern Maryland

The theme for this winter has been cold and dry. We did get a few significant snow storms, but we are still very dry—recent rains are contributing to some good topsoil moisture at the moment. Hay and pastures look very good. Small grains did not tiller very much in the fall but have greened up and look decent and the second shot of nitrogen will be going on in the next week or so. Temperatures have dropped back into the 30s and 40s this week and soil temperatures are still running about 5 degrees cooler than normal. In a normal year there would be planters hitting the fields in the next few days for a few early plant fields, but not this year—we are still a couple of weeks from that.—Andy Kness, Harford Co.

Upper & Mid Shore

No report this month.

Lower Eastern Shore

Spring has sprung but the ground is still cold and wet. Farmers have been able to get into the fields to apply manure, and most manure application is done. Some fields are being tilled. The first spray of spring nitrogen is being applied to wheat. Cover crops are still growing on the majority of fields, although termination has begun. Corn and soybean planting has not started due to wet and cold soil conditions.—Sarah Hirsh, Somerset Co.

Southern Maryland

Farmers are preparing for planting. Everyone is busy spreading litter/manure, applying herbicides and completing field operations before planting commences. The region received some much-needed rains over the last two weeks with more anticipated this weekend. Field temperatures are still a little cool for planting with the cold front moving through this week driving temperatures lower. I suspect most planters will hit the field next week when temperatures warm again. Burndown of annual ryegrass continue to be a challenge.  Small grain crops are at jointing stage. Most of the second N applications are being made now. Alfalfa fields are a but earlier than normal with first cutting coming up soon. Alfalfa weevil is active. Hay fields have greened up nicely. We have struggled with fall planted cool season grasses across the region. Stands did not establish due to the dry fall and annual weeds are plentiful without the competition.—Ben Beale, St. Mary’s Co.

*Regions (counties):
Western: Garrett, Allegany, Washington. Central: Frederick, Montgomery, Howard. Northern: Harford, Baltimore, Carroll. Upper & Mid Shore: Cecil, Kent, Caroline, Queen Anne, Talbot. Lower Shore: Dorchester, Somerset, Wicomico. Southern: St. Mary’s, Anne Arundel, Charles, Calvert, Prince George’s

University of Maryland Researchers Encourage Farmers to Participate in TAPS program

Researchers at the University of Maryland are inviting growers across the state to participate in their University of Maryland – Testing Ag Performance Solutions (UMD-TAPS) program this year. The program is supported by the Maryland Soybean Board and will run throughout the summer.

Piloted at the University of Nebraska-Lincoln, the TAPS program provides farmers with a zero-risk opportunity to advance their agricultural management skills and knowledge. It serves as a growing season contest and research framework, designed to uncover how producers’ management decisions drive crop yields, farm profitability, and input-use efficiency.

Growers must make decisions about variety selection, fertility, pest management, and irrigation and their management decisions will be executed in small plots at the Wye Research and Education Center. Decisions made by all participants will be executed in one field, in a true head-to-head competition. The goal is to identify which suite of management decisions will become the most profitable, efficient, and highest yielding.

Researchers at the Maryland Agricultural Experimentation Station (MAES) WYE Research and Education Center will lead the program and gather data on each plot to share with farmers.

When the season ends, growers will participate in an awards dinner where they will gain access to valuable data sets to help them enhance their agricultural operations.

The irrigated corn competition is limited to 20 teams and the irrigated soybean competition is limited to 15 teams. Due to limited availability, researchers urge teams to sign up as soon as possible.

Interested applicants can sign up by following this link: bit.ly/UMDTAPS25. For any questions, please reach out to Dr. Nicole Fiorellino at nfiorell@umd.edu.

2024 Soybean & Corn Pest Management Survey

Farmers and crop consultants are encouraged to complete this survey

This survey is intended to estimate the impact of pests on soybeans and currently used management strategies. Your perspective is valuable in making these estimates as accurate as possible. Your responses will be kept confidential and only aggregated responses for the state will be published. You can find last year’s estimates at https://midsouthentomologist.org.msstate.edu/Volume17/Vol-17-1_TOC.html.

The survey can be completed online at https://delaware.ca1.qualtrics.com/jfe/form/SV_8GnhiHa4rn9ToPP or by following the QR code. If you have any questions, please contact us by email or phone. We look forward to hearing from you.

Local Contact: David Owens, University of Delaware     

Email:            owensd@udel.edu                  bcsam@udel.edu        

Phone:            C: (302) 698-7125        

Local Contact: Kelly Hamby, University of Maryland

Email:       kahamby@umd.edu

Phone:      C: (925) 354 0483

2024 Corn Hybrid Performance Trials Results

Nicole Fiorellino | nfiorell@umd.edu
Assistant Professor & Extension Specialist, Agronomy

The 2024 Maryland Corn Hybrid Trials results can be found at https://psla.umd.edu/extension/md-crops or downloaded at the link below. Many thanks to Louis Thorne, Gene Hahn, and Audrey Sultenfuss for their time spent preparing, establishing, collecting data, and preparing the report. These trials could not be completed without them. I greatly appreciate the Center managers and personnel who assist our team with executing these trials.

We are grateful for the funding provided by Maryland Grain Producers Utilization Board to support these trials. MGPUB provides our program with checkoff funding to support applied agricultural research and so we may generate results that directly benefit Maryland producers.

Download the 2024 Corn Hybrid Trials Report here

Maryland Regional Crop Reports: September 2024

Reports are for crop conditions up to September 5, 2024.

Western Maryland

August brought us more rain than June and July combined. The hay and pasture fields responded, and there is hope for continued grazing and another cutting. The soybeans are probably the greatest beneficiary of the moisture. They are looking great as their pods fill. Modern varieties are a wonder to behold. Corn silage harvest began earlier this year thanks to the heat and drought. Many folks are glad they planted a little extra corn, primarily due to the need for forage and the low grain price forecast. Running it through livestock will add value. Triticale and oats are going in the ground for both fall and spring forage. Cool mornings and mild days have raised our countenance here in Western Maryland.—Jeff Semler, Washington Co.

Central Maryland 

August has finally brought some much needed rain; although amounts have been scattered throughout the region. A storm last week caused crop damage in some areas of the region. While it won’t be a year for record-breaking yields, most of the corn and soybeans are looking fairly good. The majority of corn is in the dent stage and is starting to dry down. Silage chopping has begun. Full season soybeans are in the beginning seed stage (R5).—Kelly Nichols, Montgomery Co.

Northern Maryland

About 6” of rain fell in August, which really woke up soybeans, especially later planted beans and double crops. Unfortunately, the rains have ceased, with the last measurable rainfall coming over two weeks ago. Rain is predicted for this weekend, so fingers crossed for good rainfall to finish out what could be a strong late season bean crop. Corn is rapidly drying down and a few acres have been harvested but the majority of corn is still 25% moisture or better. We are about another 10-14 days before the combines are rolling hard. Tar spot was also confirmed in the region at the end of August, consistent with the two years prior. A lot of good dry hay was put up over the last two weeks.—Andy Kness, Harford Co.

Upper and Mid Shore

July’s much-needed rains tapered off, leaving August with sporadic showers that varied significantly depending on your neck of the woods. This inconsistency has led to some challenging conditions for crops. Signs of water stress have become apparent; soybean leaves are cupping and corn leaves are curling from lack of moisture. In response, center pivots on irrigated fields have been fired up again, helping to maximize yield potential after a brief respite in July. Corn is drying down, with some early-planted fields already harvested. Soybeans are also moving along, with early maturing varieties starting to turn and double crop beans filling out their pods. The dry conditions earlier in the season provided the perfect environment for Palmer amaranth to thrive and compete with the crops. They can clearly be seen towering over the soybean and even corn in both conventional and organic fields. The region has also noticed more spotted lanternfly activity as these pests hit their final growth stage and take to the air. While they’re mostly just a nuisance in agronomic crops, controlling them can really help out your local fruit and vegetable grower, who would surely appreciate the effort.—Dwayne Joseph, Kent Co.

Lower Shore

Corn is drying down, but harvest has not yet begun. Due to low grain prices, farmers are inclined to let corn completely dry in the field, rather than take a moisture price hit at the mills. Drought stress during vegetative and early reproductive phases hurt corn. Yield is anticipated to be poor, and ears look small. Soybean is looking better than corn, especially double-crop soybean planted after wheat. There have not been reports of serious pest or weed damage. Cover crops are being flown into some corn fields via airplane.—Sarah Hirsh, Somerset Co.

Southern Maryland

Conditions remain very dry across the majority of Southern Maryland. Corn harvest is in full swing with reports of average to well below average yields. Yields vary greatly within and between fields depending on soil type and where isolated showers happened to fall. Grain quality is a major concern this year. Growers are encouraged to get corn off as early as possible. Beans continue to put up the good fight. Many full season beans are yellowing and drying down. Double crop beans will need some more help to fill out pods. Farmers have been scouting for pod worms and stink bugs. Thankfully, only a few fields have reached threshold and required a treatment so far. Weeds continue to require attention as fields have taken longer to canopy if at all, allowing greater opportunity for weeds to gain their share of the limelight. We continue to see ragweed, pigweeds of all types, and morning glory present. Deer damage is readily apparent in later planted beans that are failing to re-grow or canopy following deer feeding. Forages have struggled this summer with many fields of cool season grasses requiring replanting this fall or next spring.—Ben Beale, St. Mary’s Co.

*Regions (counties):
Western: Garrett, Allegany, Washington. Central: Frederick, Montgomery, Howard. Northern: Harford, Baltimore, Carroll. Upper & Mid Shore: Cecil, Kent, Caroline, Queen Anne, Talbot. Lower Shore: Dorchester, Somerset, Wicomico. Southern: St. Mary’s, Anne Arundel, Charles, Calvert, Prince George’s

Tar Spot Update: First Reports for 2024

Andrew Kness, Senior Agriculture Agent | akness@umd.edu
University of Maryland Extension, Harford County

Figure 1. Map of tar spot of corn for 2024 growing season as of September 5.

Our first official reports of tar spot have been confirmed in Maryland for 2024; almost exactly on pace for when we first detected tar spot in 2023 and 2022. The first report came from a dent corn field in Baltimore County on August 22 and subsequent reports were made from fields in Harford County on August 27 and September 4. All of these fields are near black layer and yield loss due to tar spot infection is not likely unless infection occurred earlier in grain fill or during pollination. It is not likely that we had tar spot infections occurring in July due to the extreme heat this year. Tar spot infections require lower temperatures than other common fungal diseases of corn such as gray leaf spot.

As average daily temperatures begin to dip into the mid 70s and mid 60s, tar spot symptoms will likely start to flare up in corn. Tar spot can spread as long as there is green tissue on the plant, which means symptoms can worsen even past black layer, making for a field that could look far worse than it actually is. For reference, last fall I did yield checks in two corn fields and one research plot that had fairly moderate levels of tar spot infection (Figure 2) but still yielded very well (220-300 bu/a), with the field with the worst symptoms topping 300 bushels. What likely happened is tar spot infected corn close to R5-R6 and it continued to spread after black layer since the plants stayed green beyond physiological maturity due to the stay green effect of foliar fungicides that were applied to these fields. Even though tar spot spores can blow short distances in the wind, if you are harvesting a field infected with tar spot, it would be a good practice to try to clean as much corn fodder off of equipment prior to moving to a new farm; a blower or air compressor will do the trick.

Figure 2. Tar spot symptoms on a senesced corn leaf.

As you are scouting your corn fields, be on the lookout for tar spot. With funding from the Maryland Grain Producers Utilization Board, we are conducting a survey of the distribution of tar spot in Maryland. If you have tar spot, or think you might, please report it to corn.ipmpipe.org or reach out to me at akness@umd.edu or (410) 638-3255. Reports are kept anonymous and individuals and/or farms are not identified in any reports, publications, or communications.