Nidhi Rawat and Vijay Tiwari
University of Maryland, College Park
Data from the 2024 University of Maryland small grain variety trials is now posted. Please follow the links below to download the reports. For detailed information on how to interpret variety trial data, please see this factsheet.
Nidhi Rawat, Small Grains Pathologist
University of Maryland, College Park
Wheat in Maryland has either already flowered or is finishing-up flowering. The FHB prediction maps for today and up to the next 6 days predict high FHB risk. If your wheat is still in the window for FHB fungicide application (from flowering up to the following 4-7 days) you should consider the application of FHB fungicides: Miravis-Ace, Prosaro, Prosaro-Pro, or Sphaerex. These fungicides are also effective against other fungal foliar diseases such as stripe rust, powdery mildew, and tan-spot etc. Strobilurin-containing fungicides are not recommended for application at this stage.
Andrew Kness, Senior Agriculture Agent | akness@umd.edu
University of Maryland Extension, Harford County
Tar spot of corn has been confirmed in Maryland for the 2023 growing season. The first report came from a field in Cecil county on August 22, followed by several additional reports in Harford and Carroll county (Figure 1).
Tar spot is a relatively new fugal disease of corn in the United States and it was confirmed for the first time in Maryland in August of 2022. As daytime and nighttime temperatures begin to decline, now is a good time to look for symptoms in your corn fields. Tar spot is favored by cooler temperatures (60-70s), as well as prolonged periods (7+ hours) of leaf wetness from rainfall, dew, or humidity. Tar spot can cause infected plants to senesce prematurely, which can adversely affect yield, especially if infection occurs early in the reproductive stages. Yield losses are not as severe if infection occurs later in the reproductive stages.
Tar spot spores overwinter in old corn crop residue and are deposited onto corn leaves via splashing rain or wind (spores are only wind-blown for very short distances). Once a spore lands on corn tissue, it will germinate and infect the plant as long as the environmental conditions remain conducive. After an incubation period of about 14-21 days, black reproductive structures, called stroma, are visible on the leaf surface (Figure 2). These structures resemble black paint or tar, hence the name “tar spot.”
If you find tar spot in your field, you may want to take precautions to try to prevent its spread during harvest, as you could potentially inoculate new fields by bringing infected residue into the next harvested field. If you’re harvesting an infested field, it would be a good idea to try to remove as much corn fodder off of the equipment before moving to the next field.
Preparations for managing tar spot in 2024 should start in the winter with good seed selection. If possible, choose hybrids with good tar spot resistance (there is no complete resistance); seed companies are starting to rate hybrids for their tar spot resistance/tolerance.
If you find tar spot in your field, I would be interested in knowing about it. We have a grant from the Maryland Grain Producer’s Utilization Board and one objective of the study is to determine the distribution of tar spot in Maryland. Call (410-638-3255) or email me (akness@umd.edu); or submit a report at corn.ipmpipe.org.
Results from the University of Maryland Small Grain Variety Trials are in the tables below. To download a pdf copy of the report, click here.
University of Maryland also rates the relative susceptibility of select varieties of wheat and barley to Fusarium head blight. The results from this trial can be found here.
For questions regarding the small grain trials, contact Dr. Vijay Tiwari (vktiwari@umd.edu) or Dr. Nidhi Rawat (nidhirwt@umd.edu).
If you’d like to learn more about how to interpret variety trial data, view our fact sheet by clicking here.
Alyssa Koehler, Extension Field Crop Pathologist | akoehler@udel.edu
University of Delaware
Seedling diseases are common across many crops, including soybeans. The most common seedling pathogens Pythium spp., Phytophthora sojae, Fusarium spp., and Rhizoctonia solani are often naturally present in the field, but certain environments, like compacted, wet, or poorly-drained soils and cool weather that slows emergence can favor disease development. Infected seedlings may fail to emerge before coming out of the ground (pre-emergence damping off) or die after coming out of the ground (post-emergence damping off), surviving plants may appear stunted with other symptoms visible on the seedling.
Pythium spp. can cause pre- and post-emergence damping off. Development of Pythium is favored by wet soils and we have species in the area that favor both cool and warm weather. Tissue will be brown in color and appear soft and rotting. This can look very similar to Phytophthora in seedlings, but can be confirmed by submitting a sample to the diagnostic lab. Surviving plants may be stunted and have less vigor.
Phytophthora is also able to cause pre-and post-emergence damping off. Tissue will be soft and tan-brown in color. Stems may look bruised and with rotten roots, plants will usually wilt and die. It is also possible to see Phytophthora symptoms develop mid to end of season. Later in the season, dark brown discoloration of the stem will extend from just below the soil line up into the plant (Figure 2).
Rhizoctonia can cause damage pre- or post-emergence. Often rust-brown lesions will be present on the roots or lower stems. In some cases this may girdle the stem stunting or killing the plant.
Fusarium spp. can infect the seed or seedling. There will often be brown lesions on the roots and the root system may appear shrunken. Numerous Fusarium species can be associated with root rot of soybean. Another soybean disease, Soybean Sudden Death (SDS), is caused by Fusarium virguliforme. While F. virguliforme will infect early in the season, symptom of SDS do not become present until the plant reaches reproduction stages.
Seed and seedling diseases can be difficult to manage. Waiting for fields to be relatively dry and delaying planting until soils are warmer than 55°F can favor quicker emergence and growth, which can be beneficial. Genetic resistance is available for managing Phytophthora. Fungicide seed treatments may reduce seed and seedling diseases. In our work over the past three seasons, we have observed faster emergence and improved stand when using seed treatments in April planted soybeans. Although collectively called fungicides, not all fungicide products are effective against all pathogens. Pythium and Phytophthora are fungal-like organisms called oomycetes. Active ingredients, mefenoxam and metalaxyl, have activity on oomycetes, while strobilurins (azoxystrobin, trifloxystrobin, pyraclostrobin, etc.) have activity on Fusarium and Rhizoctonia. For this reason, seed treatments typically have two or more active ingredients. Each year the Crop Protection Network releases a “Fungicide Efficacy for Control of Soybean Seedling Diseases” publication to aid in decision making for seed treatments. The full publication can be found at https://cropprotectionnetwork.org/publications/fungicide-efficacy-for-control-of-soybean-seedling-diseases.
The Crop Protection Network (cropprotectionnetwork.com) is a national working group comprised of Extension agents and specialists from across North America that provide data through publications regarding pest management in agronomic crops. The website and publications can be a great resource to your operation. The following are the most recent fungicide efficacy tables for foliar diseases of corn and soybean.
Andrew Kness, Agriculture Agent | akness@umd.edu
University of Maryland Extension, Harford County
Spring is a busy time on the farm that demands a lot of different tasks; one of the tasks that can be overlooked is scouting your small grains now for the presence of diseases, especially this year considering many areas of the state are off to a wet start. For a few select diseases, scouting now could pay off later in the season.
Most of the wheat in Maryland is somewhere between Feekes 5 (green up) and Feekes 6 (jointing), and most has received its first shot of nitrogen. This is the perfect time to scout your fields for foliar diseases like powdery mildew and the leaf blotch complex diseases.
Powdery mildew (Figure 1) is one of the more common diseases of wheat in our region, although it is typically a non-issue unless it gets out of hand. The fungus that causes powdery typically colonizes wheat in the fall when the plants are small, then goes dormant inside the plant over the winter. Green up is the perfect time to scout for powdery mildew because you will be able to see the powdery white tufts of fungus growing on your wheat plants (Figure 1). These signs are typically observed close to the crown deeper in the canopy and/or on plants that are in double-planted pinch rows or headlands. The disease is often more severe on over-fertilized fields, too. It is good to scout for the presence of powdery mildew now, but do not treat until the wheat begins to joint. Powdery mildew will not begin actively growing until the wheat plant comes out of its winter slumber and begins rapid growth (jointing, Feekes 6), and fungicides have little-to-no activity on dormant fungi. Instead, hold off on a fungicide application until your second nitrogen application at jointing. If you only notice a few sporadic instances of powdery mildew now, you may not even need to treat at jointing, especially if weather conditions become warm and dry. If you decide to hold of on a Feekes 6 application, you’ll still want to keep an eye on it, especially as the flag leaf emerges. The top three leaves, especially the flag leaf, contributes to nearly all of your yield.
Also, know your wheat variety because there are significant differences in resistance and tolerance. Data from University of Maryland, University of Delaware, and Virginia Tech can help you determine your wheat’s susceptibility. In addition, varieties containing the pm6 resistance gene have broken down and are no longer providing adequate resistance here in the mid-Atlantic region, so consider those varieties susceptible.
Similar management should be taken against the leaf blotch complex diseases. If you find them now, hold off on a fungicide application (if at all) until at least Feekes 6. And again, protecting the flag leaf is your main priority, so if the disease is slow to progress due to inadequate weather conditions or host tolerance and the disease is present at low levels, then a fungicide application at Feekes 6 may not be warranted at all. Also, the fungicides we commonly use to manage Fusarium head blight/head scab will also work on powdery mildew and the leaf blotch complex; so our fungicide applications at early flowering typically do a good job at keeping these diseases from progressing to the flag leaf.
For help with identifying diseases on wheat, you can send samples to the University of Maryland Plant Diagnostic Lab, or call your local Extension agent.
Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County
As corn and soybeans begin to enter reproductive growth stages, foliar fungal diseases can have a serious impact on yield if growing conditions favor their development. However, with the hot and dry weather, disease pressure is low and will remain low if these weather patterns persist. Weather patterns in the Mid-Atlantic can switch rapidly and in general, fungicides need to be applied as a protectant, so spray decisions need to be made before the onset of disease. Coupled with the fact that many new fungicides on the market today are promoted to help plants cope with stresses, such as drought and heat, can complicate the decision.
I like to remind folks that fungicides are designed to do one thing—and that is to manage fungal diseases; they do this job very well. Hundreds of university trials have demonstrated that the most likely yield response and economic return occurs when fungicides are applied at the correct time and used when disease pressure is high. When disease pressure is low, yield responses sometimes occur, but are far more inconsistent than when disease is present.
There is also limited university data regarding fungicide utility to help plants manage drought stress. In the lab, strobilurin and triazole fungicides have been shown to regulate stomatal conductance and photosynthesis intensity in some corn hybrids, which improves the plants response to drought. However, when conducted at the field level, results are inconsistent and do not occur predictably. More research is needed to determine if fungicides can improve yields in drought conditions, and if so, when the application should be made. Existing studies indicate that the fungicide needs to be applied before drought stress occurs in order to stimulate the appropriate response in the plant; which again, makes spray decisions difficult without a crystal ball in hand to see into the future.
Another consideration, and perhaps the most important, is economics. While a fungicide application may provide some measurable differences in appearance and/or yield, is it enough to cover the application cost? Again, this is a tricky question to answer, but the body of research indicates that a single fungicide application in corn around VT-R1 and R1-R3 in soybean is the most likely to provide an economic return on investment when disease is present. In the absence of disease, the probability of an economic return is very low. Here are some additional factors that you should account for when considering a fungicide:
The take-home message is to realize that you have the greatest chance for an economic return on your investment with a fungicide application when disease actually develops. Applying a fungicide to help plants cope with drought stress will likely not help to a degree that covers the cost of the application; as replicated field trials have yielded inconsistent and unpredictable results.
Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County
As we get into the swing of the 2020 growing season, it can be helpful to have access to a quick reference for fungicide recommendations for if/when diseases become a problem on your farm. As you are aware, there are several products available for disease management and it can be difficult and confusing to select the appropriate product. Also remember that just because a pesticide is labeled for use on a particular crop to manage a specific pest, does not necessarily mean or guarantee that the pesticide will work to manage it. Pest populations are constantly evolving and therefore develop resistance to products over time. A good example of this is the fungicide, propiconazole; once very effective for managing head scab of wheat, is now ineffective against the pathogen.
To help aid your fungicide selections, the Crop Protection Network has some great resources on fungicide efficacy that they update each year (and soon to come, insecticides and herbicides). The Crop Protection Network is a multi-state and international partnership of university and provincial Extension specialists and public and private professionals that provides unbiased, research-based information.
These publications list the relative fungicide efficacy for the major diseases of corn, soybeans, and small grains and are linked below. If you have trouble accessing or interpreting the information, feel free to contact me.
Nidhi Rawat, Small Grains Pathologist
University of Maryland, College Park
With low temperatures and intermittent showers, this wheat season has been unusual in Maryland. The cool wet season was conducive to the growth of several foliar fungal pathogens. At the same time, several physiological issues caused by the unusual weather conditions manifested themselves on leaves of the plants. The conditions were not too supportive for extensive symptom development for Fusarium Head Blight so far, although DON contents should be analyzed before declaring it a FHB-free year. The major diseases/ physiological disorders observed in the state this year so far are described below to help in identification of the underlying factors.
Leaf Diseases
Tan Spot
The fungal pathogen, Pyrenophora tritici-repentis, produces host-selective toxins that causes yellowing and death of leaf tissue. Symptoms of tan spot early in the season include diamond-shaped or oval spots with a yellow halo mostly on the lower leaves. These spots turn brown and progressively enlarge and coalesce damaging large areas of leaf tissue. These tan colored spots have a small dark brown center resembling an “eye-spot” that is particularly distinctive when holding the leaf up to the sunlight (Fig 1). Tan spot may develop any time during the growing season, but well-developed lesions are frequently observed later in the season. After the season is over, the fungus overwinters in straw and stubble as black fruiting bodies called pseudothecia.
Septoria/Stagonospora nodorum Blotch (SNB)
The causal agent of SNB is the fungus Parastagonospora nodorum. Symptoms usually appear after head emergence and are mostly found on the upper leaves, although all leaves are susceptible. SNB starts as small, water soaked dark brown flecks, which later expand to make larger irregular dark brown lesions (Fig 2). As the disease progresses, the lesions develop an ash gray-brown center containing brown-black pepper grains (pycnidia), which are sometimes difficult to see in brown lesions. Glume blotch, which refers to the SNB on glumes of wheat heads, is caused by the same pathogen (Fig 2). Pycnidia, which are brownish-black pepper grain-like dots, are the asexual reproductive structure of the fungus and are diagnostic of this disease.
Septoria tritici blotch (STB)
STB is caused by fungus Zymoseptoria tritici (previously named Septoria tritici). Symptoms of STB are usually detected on lower leaves in the fall and early spring as yellowish or chlorotic flecks on leaves. Symptoms start as yellowish flecks, especially on the lower leaves, which are in contact with the soil. These flecks enlarge and develop into brown to reddish brown lesions, which are initially restricted to the leaf veins, giving the appearance of parallel sides. More importantly, lesions are associated with the presence of visible pycnidia that are sphere or ball-shaped, gelatinous and gray-brown. These small black pycnidia in lesions are the most reliable in-field characteristic for identifying SNB. Differentiating STB from SNB can be difficult and often requires microscopic observations.
Barley Yellow Dwarf (BYDV)
BYDV is a viral disease caused by a Luteovirus transmitted by aphids. The typical symptom of BYDV, as the name suggests, is yellowing of leaves that starts from the tip and progresses towards the base (Fig 4). The yellow color changes to purple and red as disease develops. Severe infection leads to stunting of plants. Oftentimes the flag leaves of infected plant stand out prominently as a reddish flags. The symptoms of BYDV may often be confused with nutrient deficiency or leaf streak mosaic virus. The disease occurs in patches in the field indicating the area of infestation by aphids, as compared to mineral deficiency, which is present more or less uniformly in the field. Aphid vectors may be visible on the plants infected with BYDV. Unlike leaf streak mosaic virus, BYDV does not have a distinct mosaic pattern on the leaves. Definitive confirmation of BYDV can be done by lab tests.
Physiological Disorders
Leaf Tip Necrosis
Leaf tip necrosis (LTN) is a physiological disorder and can be caused by several factors namely: hot dry air, contact fungicides, foliar fertilizer burn, soil salinity, cool evening temperatures. Even some genetic factors such as leaf rust resistance gene Lr34 or stripe rust resistance gene Yr18 are known to cause leaf tip necrosis. LTN normally progresses from the margins of the flag leaf tip and lower leaves should show some signs of it as well (Fig 5). The severity of the leaf tip necrosis is dependent on both the variety and the growing conditions during flag leaf emergence and early grain-fill and thus some varieties have a tendency to show a lot more leaf tip necrosis than others.
Physiological Leaf Spotting (PLS)
Physiological leaf spotting (PLS) is another issue that we observed this season. There are majorly two factors/ triggers that may cause PLS, namely: chloride deficiency and tissue oxidation due to sun damage. PLS is bit of a black box when it comes to diagnosing or predicting when it will appear. Chloride is an essential micronutrient for plants, and is generally not tested for in tissues or soils. In case of sun damage, spotting occurs after a period of prolonged cloudy weather that is then followed by sunny weather. Such symptoms appear first, and more uniformly, on upper leaves exposed to direct sunlight and little is seen further down in the canopy; but in severe cases lower canopy leaves can express symptoms as well. PLS may be mistaken for spotting caused by the previously described diseases. However, the pattern of distribution of symptoms is more uniform and spread over to a larger geographical area than the diseases. Unfortunately, there is no ‘test’ that can be done to confirm this type of PLS; only the elimination of all other possible causes.
Management of Wheat Foliar Fungal Diseases
It is important to diagnose the correct underlying disease/physiological factor of a disorder in order to make productive management decisions. Following are some of the management strategies that are helpful in the cases of the diseases described above.