Category: Corn

Ear and Stalk Rots May be an Issue in Corn

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

stalk and ear rot of corn
Stalk rot (left) and ear rot (right) of corn.

With the dry then wet (then dry again) weather pattern we had this year, corn went through a lot of stress. Stressed corn is much more susceptible to ear rots and stalk rots. The degree of severity is dependent on a variety of factors, so it is wise to scout fields prior to harvesting in order to identify problematic fields and give them harvest priority.

Several different pathogens can cause ear rots in Maryland; the main contenders are listed in the table below. Although they typically do not affect yield, they can cause grain quality issues through the production of mycotoxins. Furthermore, if infected grain is not dried quickly or to a low enough moisture content, infection can spread, even when in the bin. Therefore, it is important to scout and identify fields that are infected with ear rots and harvest those first. It is better to pay a few cents in propane to dry the wet grain than to wait and risk infection levels getting worse, and the potential for elevated mycotoxin concentration in the grain. Quickly dry infected grain to 15% for short-term storage and to below 13% for long term storage and it is not recommended to store infected grain for longer than a year. It is important to note that not all ear rotting fungi produce mycotoxins, so I would recommend working with your Extension agent or crop advisor to get proper identification so that you know the species in question and thus if mycotoxin contamination is a concern.

Table 1. Common ear rots of corn.

Disease Pathogen Symptoms (see next page for pictures) Mycotoxin
Fusarium ear rot Fusarium verticillioides “Starburst” kernels, white kernels, infected kernels may be scattered on ear Fumosin
Gibberella ear rot Fusarium graminearum Ear covered in white mat often with pink hue, infection starts at tip and can progress to butt end of ear Vomitoxin (DON)
Diplodia ear rot Stenocarpella maydis and S. macrospora White fungal mat on ear, may cover the entire ear None
Penicillium ear rot Several Penicillium species Blue-grey spores on kernels developing on damaged ears (hail, deer feeding, insects, birds, etc.), may infect the germ of the kernel Some species may produce mycotoxins
Trichoderma ear rot Trichoderma viride Green spores in between kernels None
Aspergillus ear rot Aspergillus flavus Olive green spores on ear, usually starting at tip, associated with damaged ears (feeding from insects, deer, birds, etc.) Aflatoxin

Stalk rots are also a harvest concern. Like ear rots, stalk rots are also caused by many different pathogens, several of which are listed in Table 2 below. No single factor causes stalk rots; they are rather the end result of a host of factors that contribute to a net deficit in plant carbohydrates needed for grain fill. The grain fill process is a major carbohydrate sink for the plant. As the plant produces carbohydrates through photosynthesis, it allocates almost all of it’s carbohydrate production to filling the kernels. A healthy plant will have sufficient leaf area to maximize photosynthesis and can therefore produce enough carbohydrates to fill the grain. However, when photosynthetic leaf area is compromised, the plant cannot make enough food to fill the kernels. In order to compensate for the deficit, the plant cannibalizes carbohydrates from existing tissues. The first tissues to go are the stalks, which are then easily compromised by stalk-rotting pathogens. Stalk rot is a byproduct of stressed plants during the growing season, particularly during grain fill.

Table 2. Common stalk rots of corn.

Disease Pathogen
Anthracnose stalk rot Colletotrichum graminicola
Diplodia stalk rot Stenocarpella maydis
Charcoal rot Macrophpmina phaseolina
Gibberella stalk rot Fusarium graminearum
Fusarium stalk rot Multiple Fusarium species

Any factor that reduces leaf area or reduces photosynthesis after pollination will predispose plants to stalk rots. These include reduced leaf area through insect feeding, lesions from foliar diseases, or mechanical damage (such as hail). Other factors include inadequate fertility, water stress, and excessive plant populations. Another significant factor is hybrid genetics; both resistance ratings to stalk rotting pathogens as well as ear and kernel size. High-yielding, large kernel hybrids are more susceptible to stalk rots if they are not kept healthy through grain fill.

Scout fields for stalk rots as early as black layer. The “pinch test” is one way to scout for stalk rots. Pinch the stalk in between the nodes at one of the lower two nodes. You should not be able to pinch healthy stalks, but rotted stalks will fairly easily collapse. Do this at several random locations to assess the field. Alternatively, you can do a “push test,” which involves pushing the corn stalks approximately 30 degrees from horizontal (8 inches laterally) at a height of about eye level. Healthy stalks will return to vertical while infected plants will not. If more than 10% of plants tested exhibit stalk rot symptoms, you may want to harvest as soon as possible or risk a not-so-fun harvest of lodged corn.

Maryland Regional Crop Reports: August 2024

Reports are for crop conditions up to August 1, 2024.

Western Maryland

Welcome rains have sporadically arrived in Washington County. This has been the story for much of the summer. It depends on your location and how much rain you receive, out of which storms. Earlier in the spring, the southern part of the county was blessed more than the part that hugs the Mason-Dixon Line. July has seen that trend nearly turned on its head. Wheat is off, and test weights and yields were good. Many acres of optimistic double-crop beans were planted again. Moisture has dictated the success of those plantings. It is too soon to make any predictions on corn yields, but in many places, plants are shorter, but the ears might fill just fine. So we wait. In two weeks, choppers will start running, and corn silage will be our first indicator of yields. Peach harvest started a little early, and they are smaller, and yields are lower, but they are sweet.—Jeff Semler, Washington Co.

Central Maryland 

Corn and soybeans are well into reproductive stages and further along than previous years. Most of the region has experienced drought conditions throughout the growing season. Some growers have begun chopping early corn silage given how far hot dry weather has pushed the crop. Very limited disease pressure throughout the region. Recent rains have been welcomed, where received. Most precipitation events have been sporadically distributed to say the least.—Mark Townsend, Frederick Co.

Northern Maryland

We ended July with around 3” of rain here at the Harford County Extension office. Rains were more periodic in July; however, that is not the case for the entire region—rains continue to be scarce the further west into Baltimore and Carroll County you go and the rain that has fallen across our region has been very scattered and localized. You can find corn that looks very good and you can find corn that looks very poor all in the same county. I do believe that most places are “holding on” in terms of yield—I think we will fare OK and we may have avoided a complete disaster but corn yields will certainly be off of our norm. Soybeans are flowering and look good; if they can fill all the pods they’re initiating then soybean yields should be strong; the next few weeks will make or break them.—Andy Kness, Harford Co.

Upper and Mid Shore

The first couple of weeks in July brought us more of the high temperatures we’ve been experiencing, but unlike June, we were finally blessed with some much-needed rain across the region. While some areas received more rain than others, it was all welcome. The timing couldn’t have been better, as most of the corn was entering the reproductive stages right at the start of the month. Due to this, late-planted corn is likely to yield better than the earlier-planted corn. Both full-season soybeans and corn are now in their reproductive stages. Most of the corn has finished pollination and is moving into kernel development. On the small grains front, yields were either on par with or lower than last year, with not many reports of fields outdoing last year’s yields. The recent rains have also triggered a flush of weeds. If you look out over the soybean canopy, you’ll see those notorious pigweeds, common lambsquarters, morningglories, and annual grasses making an appearance, especially in the lesser-managed fields.—Dwayne Joseph, Kent

Lower Shore

We have had periodic rains the last few weeks and much of the drought damaged corn is greening up. Farmers are optimistic that the corn will pull through and have average yields. The later planted corn the better, in terms of less drought damage. Most corn is now in reproductive stages. Some corn is being aerially sprayed with fungicides. Milo is heading out. Soybean also faced drought damage, but is looking good with the recent rains. Double crop beans are starting to take off with growth. Substantial weed or pest pressure has not been reported..—Sarah Hirsh, Somerset Co.

Southern Maryland

The region is finally getting some relief from the hot dry conditions we have experienced since June. Rain showers have been scattered, so some areas are better off than others. Unfortunately, some of the rains have come a bit late for corn which was past pollination. For the conditions this year, the crop overall looks much better than should be expected. Soybeans follow much of the same story. Many full season beans could never get off the ground with a lack of moisture and constant deer predation. These plants are now trying to canopy and flower but are way behind schedule for this time of year. Weeds, especially annual grasses, marestail, Palmer amaranth and common ragweed have taken advantage of the extra sunlight and lack of canopy closure to germinate. Many fields are speckled with these weeds coming in later in the season.  Double crops beans struggled to germinate in the dry conditions or were planted late. They have made good strides in the last couple of weeks. Vegetable crops are coming off now with a consolidated harvest season due to the hot temperatures as of late squeezing the harvest window.—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

Maryland Regional Crop Reports: July 2024

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

Western Maryland

Dry, dry, dry. The pleasant spring has turned into a dry summer so far. Even when the heat isn’t oppressive, the sun is bright, and the wind blows all wonderful conditions for drying out things. Corn and full-season bean planting is a memory. Wheat harvest is in full swing, and yields and test weights are good. Two cuttings of alfalfa are off, and we are hoping for enough moisture to make a third cutting. Double-crop beans are going in the ground, further proving that farmers are the most optimistic people on the planet. Until next month, keep looking up. One day, those clouds will have rain in them, and we will need it.—Jeff Semler, Washington Co.

Central Maryland 

The wet spring resulted in lots of slugs and replanted soybeans. However, in the last few weeks, the rain has disappeared here in Montgomery County. Temperatures have soared into the upper 90s, resulting in some very dry topsoil, subsoil which is quickly losing moisture, and drought-stressed crops. Some corn fields are starting to tassel, and soybeans are beginning to flower.—Kelly Nichols, Montgomery Co.

Northern Maryland

June was unusually dry and we are in a drought situation. Wheat and barley harvest and straw baling was a breeze to the dry weather, and harvest came about 1-2 weeks earlier than normal due to the dry, windy June. Yields were not near the record-setting numbers we’ve seen the past two years but they were still respectable. Having small grains off early will greatly benefit double-crop soybeans, assuming there’s enough moisture in the ground to germinate them. Earliest planted corn is in tassel by July 4 and we thankfully got a couple of decent storms just as tassels were pushing through and alleviated drought scenarios in many fields; that rain likely saved several bushels. Full season soybeans are also starting to come along nicely now after a slow start that some moisture is back in the soil.—Andy Kness, Harford Co.

Upper and Mid Shore

Center pivots have been working double time, keeping corn and soybean fields in the region irrigated amid the ongoing dry spell. Significant rain events are a distant memory, and the summer solstice has brought record heat, contributing to visible water stress symptoms on non-irrigated fields. All corn acres are planted, and early-planted corn is currently tasseling. Small grain harvest is progressing well, aided by the dry weather, which has extended the harvest window. As the small grain harvest wraps up, double-crop beans will soon be planted. Meanwhile, sprayers are busy applying post-emergence herbicides to fields to manage pre-emergence weed escapes, most likely due to the absence of an activating rain. Hopefully we get some rainfall soon.—Dwayne Joseph, Kent Co.

Lower Shore

We had a very dry couple of weeks. Crops were showing signs of drought stress with stunting and leaf burning in some fields. This was followed by a 2-4” rain event across much of the Lower Shore. Corn is approaching late vegetative stages, but not yet tasseling. Wheat has been harvested and double crop soybean planted.—Sarah Hirsh, Somerset Co.

Southern Maryland

No report.

*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

Considerations For Making “Late” Corn Sidedress Applications

Nicole Fiorellino, Assistant Professor & Extension Agronomist | nfiorell@umd.edu
University of Maryland, College Park

With the recent dry weather, some corn sidedress applications have been delayed past the optimum application window, causing farmers to think about the necessity of a “late” sidedress application. Let’s discuss corn growth stages and nitrogen (N) utilization in the plant and summarize research findings of yield response to “late” sidedress applications. This information can be useful for farmers to decide how to make decisions based on profitability, which sometimes may mean foregoing a late application which may result in decreased yields.

What is the “short stave”?

I often quote Liebig’s Law of Minimum and the visual analogy of a barrel made of wooden staves to represent agronomic management decisions, specifically fertility decisions. The first step to correcting a growth problem, be it fertility or otherwise, is identifying the problem that must be corrected – determining the “short stave” of the barrel limiting its capacity. While the gut reaction to stunted corn that missed a sidedress application may be a N deficiency, the “short stave” could be dry soils. I have seen corn that visually improved this week just due to precipitation. If you have heavier soils, good organic matter, maybe used manure, your corn may improve as the soil is rewetted and some N in the soil makes its way to the plant, eliminating the need for a trip across the field. Further, a rushed N application without precipitation in the forecast is not useful, as the N will not reach the plant roots with water as its vehicle.

Defining a “late” application

Each farmer may have a different definition of “late” sidedress application, so we should clarify this term and translate it to corn growth stages. Corn sidedress application is recommended between V4 and V6, to provide N to the corn as it enters a rapid uptake phase through the rest of the vegetative growth stage, as depicted in Figure 1. As the plant tassels and enters reproductive growth, the plant shifts from soil N uptake to translocation of N stored within plant tissues to the grain [1]. Thus, VT is the “turning point”, where a sidedress application between V6 and VT could be characterized as “late” but one might categorize any application after R1 as “the point of no return.” Confirming the growth stage of your corn is an important point to consider when weighing the possibility of a late sidedress application.

Figure 1. Nitrogen utilization of corn crop by plant tissue across the growing season. Source: Iowa State University Extension.

Risks of a late sidedress

Beyond missing the optimum window of utilization of applied N by the corn plant, there are other risks to consider when weighing a late application. Taller corn with more canopy coverage runs the risk of physical damage to the corn as application equipment moves through the field. There is the risk of leaf burn with foliar product applied, although the use of drop nozzles could help minimize this. Moreover, the delayed application of N may have stressed the corn in the early growth stages, already decreasing your corn’s yield potential. This means that even with perfect conditions and unlimited nutrients moving forward in the growing season, the yield “ceiling” has already been lowered. So, the cost of an additional N application will not be realized in profit (increased yield) and the most profitable decision may to forego applying more nitrogen. Finally, no farmer wants to risk making an N application when there is potential for loss to the atmosphere or to nearby surface water. Including potential off-site losses of applied N not utilized by the crop into the decision-making process may help make a late application decision more clear.

Yield impacts with late sidedress – pre-tassel

Yield benefits with sidedress through late vegetative growth compared to no application has been observed in other areas of the country; with researchers at Purdue University demonstrating sidedress at V15 and even up to R1 showed improved corn yield compared to no sidedress application, but still significantly less than corn sidedressed at V4 or V6 [2,3]. Research performed at Ohio State demonstrated an N application up to V10 minimized yield loss [4] and results from Cornell indicated significantly decreased corn yield with sidedress at V10 compared to sidedress at V4, V6, or V8 but significantly better than corn yield with no sidedress application [5]. In Minnesota, where the growing season is shorter, a sidedress application at V12 did not result in increased corn yield compared to no sidedress or sidedress prior to V8, with the researcher attributing this to compromised yield potential from early season N deficiency [6]. While these data are not local, they illustrate the potential for rescuing a corn crop from total loss with a sidedress application while the corn is still in the vegetative growth stage.

Yield impacts with late sidedress – post-tassel

Limited research findings exist to evaluate corn yield response to N application post-tassel [7]. There is a potential for rescue with a post-tassel sidedress application where severe N deficiency is observed, but this decision should be balanced with the potential return [6]. The lack of research findings of a post-tassel sidedress application should indicate this practice may not be recommended to optimize corn yield, farmer profitability, or environmental benefits.

Conclusions

Multiple factors should be considered when weighing a late sidedress application, first, determining the “short stave” and considering it could be drought, not N deficiency, and second, confirming the growth stage of the corn. While there are risks associated with late sidedress application, namely physical damage to corn with application equipment or increased potential for N loss off-site, data support sidedress application up to the end of vegetative growth can result in corn yield between optimum sidedress application and no sidedress application. There is no research to support yield benefits with sidedress applications post-tassel. Farmers should understand that early season N deficiency may have limited corn’s yield potential and consider this point when making profitable, late season sidedress decisions.

Sources:

[1] https://agcrops.osu.edu/newsletter/corn-newsletter/2015-20/when-it-too-late-fertilize-corn-nitrogen

[2] https://www.agry.purdue.edu/ext/corn/news/timeless/CornRespLateSeasonN.html

[3] https://www.extension.purdue.edu/extmedia/AY/AY-364-W.pdf

[4] https://agcrops.osu.edu/newsletter/corn-newsletter/2014-21/late-applications-nitrogen-corn

[5] https://blogs.cornell.edu/whatscroppingup/2021/07/26/too-late-to-sidedress-nitrogen-%E2%88%92-summary-of-4-years-of-data/

[6] https://blog-crop-news.extension.umn.edu/2020/07/late-season-nitrogen-application-is-it.html

[7] https://agcrops.osu.edu/newsletter/corn-newsletter/2015-20/when-it-too-late-fertilize-corn-nitrogen

Maryland Regional Crop Reports: June 2024

Reports are for crop conditions up to June 6, 2024.

Western Maryland

I have a  good friend who says, “I don’t have forty years of experience farming; I have one year’s experience forty times.” This spring has been just like that. We have had more moisture than last year, but then came the hot days, cool weather, and more moisture. Corn is planted, and the first cutting of hay is in the barn. Soybean planting is winding down, and grain harvest will be here before you know it, starting with barley. With the moisture we will see how much disease took its toll. Fungicide applications weren’t always as timely as we would hope because of the frequent showers. Until next month when harvest is underway it is then the story will be told.—Jeff Semler, Washington Co.

Central Maryland 

Planting is almost complete. Slugs have been an issue; some soybean fields will need replanting. It was getting a bit dry, which did provide a good hay-making window. However, a thunderstorm is rolling in as I write this, giving us some needed moisture. Small grains are looking good. Summer annual weeds like pigweed, crabgrass, and foxtail are starting to take off with this warmer weather.—Kelly Nichols, Montgomery Co.

Northern Maryland

Spring has been a little challenging in our area. A dry spell in mid-late April made herbicide efficacy less than ideal, followed by several weeks of a lot of rain, which activated herbicides but prevented the timely termination of other cover crops. Early planted corn and beans are up and out of the ground, with earliest planted corn around V6 and getting it’s second shot of nitrogen. Rainy weather in late April early May delayed planting the remainder of the crop by about two weeks. These later planted fields are much further behind than usual but are looking good. There has been some slug damage present, it gets worse the further west you go in the region. Barley nearing harvest and wheat is starting to turn. There are symptoms of head scab but it remains to be seen how severe DON levels are in the grain. The wet weather has made it very difficult to make timely dry hay.—Andy Kness, Harford Co.

Upper and Mid Shore

Corn acreage is looking good, with a nice color and uniform growth. Depending on when it was planted, corn is in the V2 to V5 stages right now. Most of our full-season soybeans are already in the ground. As usual, rain across the region has been hit or miss, with some areas getting a lot more than others. These downpours might not be ideal, but they’re certainly better than no rain at all. Barley harvest is just around the corner. Summer annual weeds are popping up and are ready to impact yield potential. If your residual herbicide program hasn’t kept them in check, now’s the time for a POST application. And remember, using multiple modes of action in your tank-mix slows down the evolution of herbicide resistance in weeds.—Dwayne Joseph, Kent Co.

Lower Shore

has been planted and currently in emergence stage to around V4 stage. Corn is looking good, and being sprayed to combat early season weeds. Soybean planting is currently underway. In a few instances, early planted soybean (early April) had to be replanted due to slug damage. Wheat is looking good and drying down. Farmers are gearing up to cut wheat, which is earlier than anticipated.—Sarah Hirsh, Somerset Co.

Southern Maryland

As I write this, a very welcome rain is falling outside my window. As we move into the hotter days of June, the old adage that we are only a week away from a drought at any time is holding true. Two weeks ago it was too wet to get into fields and this week we have corn fields starting to show curling leaves and drought stress. In general corn is off to a good start with most sidedress N applications completed. There have been a lot of catch up full season beans planted in the last 2 weeks. Slug feeding has been minimal this year. Barley is drying down with harvest expected any day. Wheat will not be far behind. Ryegrass continues to be a challenge for producers in both burndown situations in corn and beans, as well as small grains. Many fields may need a harvest aid to kill the ryegrass and allow for timely harvest of wheat. Given the wet conditions following flowering, we are encouraging producers to get the wheat crop off as quick as possible to maintain grain quality.—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

June IPM Insect Scouting Tips

Emily Zobel, Senior Agriculture Agent Associate | ezobel@umd.edu
University of Maryland Extension, Dorchester County

Corn

Continue scouting for cutworms and stink bugs. The threshold for cutworms is 2-5% cut plants up to the V5 stage and with active larvae present. Stinkbugs will move into corn as surrounding small grains are harvested. When scouting for stinkbugs, pay close attention to the thorax of brown color stink bugs as the beneficial spined soldier bug is often mistaken for the invasive brown marmorated stink bug. The spined soldier bug has a prominent spine on each “shoulder.” NCSU’s suggested threshold is 13 stinkbugs per 100 plants for V1-V6, 10 stinkbugs per 100 plants for V14-VT, and 28 stinkbugs per 100 plants for R1-R2. The most critical time to treat if between V14 to VT is just before the primary ear is exposed to avoid banana ear. Stinkbugs will likely be around the primary ear at this point so that should be the target of the application.

Soybean

Early-season defoliator pests that are active right now include bean leaf beetles, green cloverworms, slugs, and grasshoppers. Soybeans can typically withstand a decent amount of defoliation before yield losses occur. If defoliation reaches 30%, and you are finding one grasshopper per sweep or 2-3 bean leaf beetles per plant treatment may be advisable.

Figure 1. Bean leaf beetle with feeding damage on a soybean leaf. Photo by Adam Sisson, Iowa State University, Bugwood.org.

Alfalfa

Begin scouting for potato leafhopper. Ten sets of 10-20 sweeps using a sweep net should be taken in random locations in the field. A detail threshold for alfalfa is based on the plant size and cost of the hay can be found online but a general guideline is  3” or less is 20 leafhoppers per 100 sweeps, 4-6” tall is 50 per 100 sweeps, 7-10” tall is 100 per 100 sweeps, and greater than 11” is 150 per 100 sweeps. If the field is more than 60 percent bud stage or if it has experienced “hopper burn,” the alfalfa should be cut instead of sprayed. Fresh-cut alfalfa should not be sprayed as leafhopper adults tend to move out of the field when it is being cut.

Figure 2. Potato leafhoppers in a sweep net. Photo by Bryan Jensen, University of Wisconsin, Bugwood.org.

Thoughts on Tar Spot Management

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

Tar spot is on the mind of many farmers as we enter the 2024 growing season and I have had many conversations with farmers and consultants about strategies for managing this disease. Here are some things to consider and keep in mind as we get into the peak of the corn growing season.

Tar spot is a disease of corn caused by the fungus Phyllachora maydis. This disease was first reported in limited amounts in Harford and Cecil County in 2022; in 2023 the disease spread to at least 8 counties in Maryland and by harvest ‘23, we found tar spot at a frequency of over 50% of fields scouted here in Harford County.

The tar spot disease cycle starts with old corn crop residue where the fungal spores lay dormant over winter. As conditions become optimal for its development in late spring/summer, spores are released and blown and/or splashed onto corn plants where the spore will germinate and infect the plant. Approximately 12-15 days after infection, symptoms will develop on the corn leaves and/or husks, which include dark, raised, lesions, which are the reproductive structures called stromata (Fig. 1). Inside the stromata are spores (Fig. 2), which are released and will infect new tissue. Tar spot is a polycyclic disease, meaning it has multiple generations or cycles per year. New infections will occur throughout the growing season for as long as green, living corn tissue is present and environmental conditions are favorable.

Figure 1. Tar spot stromata (raised black specks) on corn leaf.
Figure 2. Microscope image of P. maydis ascus containing ascospores, which are blown and splashed to infect new corn tissue. Image: A. Kness, UMD.

Here in Maryland and the Mid-Atlantic, tar spot has not been reported to cause any significant epidemics or yield losses thus far, mostly because it becomes established late in the growing season; but that is not to say that serious epidemics couldn’t happen. In the Midwest, tar spot has been reported to cause upwards of 50 bushel per acre yield loss, and it was ranked the #1 yield-limiting disease for corn in the U.S. in 2021, 2022, and 2023.

Since tar spot was first confirmed in the United States in 2015, we have learned a lot about its epidemiology. Tar spot hails from the cooler mountain areas of Latin America. When tar spot first moved into the U.S., we had initially thought that mild temperatures and moisture were key variables in the development of the disease; however, recent research has found that moisture plays a role, but temperature is far more crucial. Webster et. al. (2023) found that monthly temperature average between 64-73°F were optimal for tar spot development and temperatures exceeding 73°F significantly reduced tar spot progression. What was more interesting is that they found that moisture both promoted and inhibited tar spot disease progression. Moisture early in the disease cycle aids in infection, but prolonged moisture (greater than 90% humidity) actually inhibits disease progression. Tar spot develops when relative humidity is less than 90% for a 2-3 week period, coupled with mild temperatures. This makes sense for many that may have observed tar spot in 2023, which was not a particularly wet year.

With this in mind, we should consider how these weather parameters influence our management of this disease here in Maryland where our summers tend to be hotter and more humid than many areas of the corn belt states.

If you look at the 5-year average monthly temperatures from regional weather stations (Table 1), you can see that the months of July and August for Mid-Atlantic regions are well outside of the 64-73°F window for optimum tar spot development. Compare that with data from Iowa for example, and they consistently run within or very close to the optimal temperature range. While only a few degrees may not seem like much, I believe our hot summers may actually keep tar spot at bay until later in August and September on an average year, which would be consistent with when we have found tar spot in Maryland in 2022 and ‘23. If these trends hold true, the majority of our corn crop is well into later grain fill stages by the time milder temperatures arrive, effectively avoiding tar spot development during the most crucial growth stages. In contrast, 30-day average temperatures are within or near the 64-73°F optimum range during corn’s most vulnerable growth stages in the corn belt.

Table 1. Average Monthly Temperatures (°F), 2019-2023
  Westminster, MD Salisbury, MD Arlington, VA Waterloo, IA
May 63.46 64.08 66.13 60.70
June 72.48 72.95 75.53 72.90
July 79.54 77.99 80.96 75.52
August 77.22 76.25 78.77 72.00
September 69.94 69.99 72.60 66.20

Where tar spot could become problematic here are instances where we have an unusually cool June and July which would put the majority of our corn at risk of tar spot infection during it’s most vulnerable time, which is tasseling through early to mid grain full.

Another situation where tar spot could be a problem is for late planted and late maturing hybrids that are in reproductive phases in August and September. Fields that are corn after corn are also in a higher risk situation.

For 2024, I would highly recommend scouting and paying close attention to the weather conditions just prior to tasseling through grain fill in your corn fields. There is an app that can help you determine your tar spot risk, called Tarspotter, and has been reported to be 90% accurate. The app takes into consideration regional weather data and field management to determine a risk percentage. It’s available for download for free on iPhone and Android.

If you decide to treat your corn with a fungicide to manage tar spot, VT/R1 timing is still found to be the most effective and economical. A fungicide application at this time will also effectively manage other common foliar fungal diseases of corn (which we shouldn’t forget about), such as grey leaf spot and northern corn leaf blight. Most fungicides labeled for tar spot are effective, however there is a better response to products that have 2 and 3-way modes of action.

This year we will continue to conduct research on tar spot in Maryland with funds from the Maryland Grain Producers Utilization Board. If you find tar spot this year, please report your findings to me via email (akness@umd.edu) or phone (410-638-3255) or on corn.ipmpipe.org.

Maryland Regional Crop Reports: May 2024

Reports are for crop conditions up to May 3, 2024.

Western Maryland

April has brought us many showers. The triticale is all in the silos for the most part, and corn planting has begun. The wheat and the barley are looking good. Producers have a keen eye out for FHB, and thus, fungicide is on the docket. Pastures are looking good and first cutting alfalfa is not far off. Warmer temperatures are on the horizon.—Jeff Semler, Washington Co.

Central Maryland 

The wet, cool spring has turned into a hot, dry spring this week. Currently, the highest chance of rain (about 60%) is for this weekend. Planting is in full swing, and the first cutting of orchardgrass will start in a couple weeks. Wheat and barley are heading; if the drier weather keeps up, it will lower the risk for Fusarium.—Kelly Nichols, Montgomery Co.

Northern Maryland

Rain has been hard to come by with only about 1” of accumulated rain in the last 4 weeks. Corn and soybean planting has been in rolling for 2.5 weeks now, with a very large majority of it within the last week to 10 days or so. Small grains generally look very good, pastures and hay fields have also enjoyed the cooler than normal March and April. Wheat is anywhere from boot to head emergence. After a soggy start to April, we could use some rain.—Andy Kness, Harford Co.

Upper and Mid Shore

The rains from early in the month are now just a memory, with clear skies and no significant rainfall since. Dust clouds swirling on the horizon are a clear sign that #Plant2024 is underway. Farmers are terminating their cover crops and tilling the soil, readying it for planting. This year, we’re running a week or two ahead of last year’s schedule, raising hopes for another bumper crop. Small grains are currently heading, with some currently flowering.—Dwayne Joseph, Kent Co.

Lower Shore

After a rainy stretch, we’ve gotten some dry weather this past week. About half or more of cover crop acreage has been terminated. Some ground is being tilled, while the majority will be planted no-till. Corn is currently being planted. Wheat is looking very good. If wheat varieties are susceptible to Fusarium Head Blight and if the wheat is flowering, fungicides should be considered. The first cutting of hay has started.—Sarah Hirsh, Somerset Co.

Southern Maryland

Field conditions are a mixed bag. Areas to the north have turned dry in the last week. Areas to the south received more rain delaying field operations. In drier areas, soil has become hard and compacted, aggravated by wet conditions over the winter. This is a year where big differences in soil conditions can be observed between no-till and tilled fields. Planters have been rolling for the last two weeks with conditions mostly ideal for planting. Corn emergence looks good so far. Slugs were a concern early, but drier weather has helped with that issue. We have many acres of early planted soybeans again this year. Burndown programs have been challenged this year with many escapes of annual ryegrass. Wheat is headed and beginning to flower now. We are observing some yellowing of the flag leaf and leaf below the flag leaf across many fields that showed up in the last 10 days. We are working to determine the exact cause, but believe it related to environmental conditions with perhaps some virus issues like BYDV as well. A lot of good dry hay has been made in the last two weeks. On the fruit and vegetable front, plasticulture strawberries look very good and are ripening now. All of our main season vegetable crops are preparing to go in the ground this week. High tunnel crops are coming off now.—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

Biological Products: To Use or Not To Use (and how to systematically answer this question)

Nicole Fiorellino, Extension Agronomist | nfiorell@umd.edu
University of Maryland, College Park

Have you thought about how you might incorporate newly-available biological products into your operation? Maybe you are interested, but skeptical about the return on investment? I will briefly define “biologicals” then provide my thoughts on how to navigate the old adage, “to use or not to use.” I operationally define biological products as commercially-available amendments that are adding a living organism to your growing system, either to the soil or directly to the plant. Generally, these products are meant to replace a fertilizer application by unlocking nutrients stored in the soil or amplifying natural processes that harness nutrients, namely nitrogen (N), from the atmosphere. While a variety of products from different brands can be broadly categorized as biologicals, it is important to take the time to understand the specific “mode of action” of individual biological products and compare that to your field conditions as a first step towards deciding if you will use a product.

Most biological N products aim to increase the mineralization of organic N stored in your soil to inorganic forms that are plant available. The mineralization step of the N cycle is mediated by microorganisms that spend energy to digest organic N and transform it to inorganic, plant-available N. When there is ample inorganic N present in the soil, like after a fertilizer application, for example, the microorganisms are “signaled” that ample N is present and they conserve energy by slowing down, or even stopping, mineralizing organic N. So biological products aim to “block” the signal to microorganisms that instructs them to cut off mineralization and they signal microorganisms to increase the organic N that is mineralized; hence adding more N to the soil with additional fertilizer application.

The increased availability of the soil storage of organic N or the provision of N to plants without fertilizer is accomplished through the introduction of novel N-fixing bacteria that allow a cereal crop, like corn, to fix N like a legume; by providing a stimulant to native soil bacteria to kick-start mineralization; or by infecting the corn plant with an N-fixing bacteria that fixes N from the atmosphere with no additional available N present in the soil – each of these examples represents the mode of action of a different biological product. While it seems like these products have the potential to supply nearly unlimited amounts of N to your crops, they should be viewed as fertilizer replacements, not necessarily as bonus N on top of your current fertility plan. Moreover, despite some marketing claims that yield benefits would be observed across all acres of a farm, a farmer might be more likely to observe a yield response where fertility is low, maybe on marginal acres where fertilizer applications or field operations are delayed due to logistics and timing. Finally, beyond the cost per acre of the product itself, you may want to consider the ease of use of the product and the cost in time associated with product use, including restrictions on tank mixing, application timing, and extra trips across the field.

Once your head is spinning from those considerations and you think you may want to try a new product, your next step may be to see out local research data on a product’s efficacy or maybe even check with your neighbor to learn about their experience with the product. The specific nature of the individual biological products and their interaction with soil nutrient concentration means that University data or even data from your neighbor may not represent the results you might expect on your farm. Unlike the universally-expected yield response with increased fertilizer application across the spectrum of soil and environmental conditions, the potential yield response to the use of biological products varies greatly with location, soil type, and weather conditions – meaning in the same location across multiple years, there may be a different response to the use of these products.

We recommend performing trials on your farm to aid your decision to use biological products. A first step to determine a yield response will be to understand how efficiently you are using N fertilizer on your field. This can be accomplished with a simple field-length strip plot protocol using multiple N fertilizer rates and up to two biological products of your choice. The Agronomy Program at University of Maryland has launched an On-Farm Trials program, with funding support from the Maryland Grain Producers Utilization Board. We encourage farmers to sign up to participate in the trials, one protocol is a biological product comparison. As we enter our second field season in 2024, more information for how to sign up for the trials and brief results summary from 2023 can be found at https://bit.ly/UMDOnFarmTrials or you can email Dr. Nicole Fiorellino at nfiorell@umd.edu or Mr. Gene Hahn at ghahn@umd.edu for more information. We offer a payment to offset potential yield loss and to compensate you for your time spent working with our team to execute the trials. If you have not planted corn yet, there is still time to sign up! Check back to the November research summary issue of Agronomy News for 2024 Field Trials results.

Planting Green Workshop/Field Day

Farmers and ag service providers are invited to learn about the latest research on planting green techniques and slug control methods.

Activities will include:

  • Planting green demonstration
  • Biomass and root sampling activities
  • Soil pit investigation
  • Slug scouting and control methods
  • Single species and mixes, sandy and clayey soils

When: Thursday, May 9, 2024 9:30 am – 2:30 pm

*Field day will include coffee, light breakfast and lunch

Where: Central Maryland Research and Education Center

12000 Beaver Dam Rd, Glenn Dale, MD 20769

For More information and to register: https://millionacrechallenge.org/planting-green-workshop/