Wheat Leaf Diseases Observed in 2020 Season in Maryland

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.

tan spot lesions on wheat
Figure 1. Typical symptoms of tan spot on a wheat leaf (A) and wheat plants (B). Images: N. Rawat, University of Maryland.

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.

stagonospora on wheat leaves and glumes
Figure 2. Stagonospora nodorum blotch on a leaf (A) and glume blotch (B).

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.

septoria lesions on wheat leaf
Figure 3. Septoria Tritici Blotch on a wheat leaf (A). Notice the brown lesions restricted by the leaf veins (A). Black dots (pynidia) in the lesions in the enlarged section (B). Images: N. Rawat, University of Maryland.

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.

symptoms of barley yellow dwarf virus on wheat
Figure 4. Symptoms of Barley Yellow Dwarf Virus on wheat leaves (A). Notice the pattern of disease distribution (B). Images: N. Rawat, University of Maryland.

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.

Wheat leaf tip necrosis
Figure 5. Leaf tip necrosis on a leaf (A) and in a field (B). Picture Credit: B. Beale, University of Maryland.

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.

light flecks on wheat leaf
Figure 6. Physiological flecking on wheat leaves.

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.

  1. Disease prevention by growing resistant varieties is the most economical method of control of fungal foliar diseases. Varieties with a good resistance level may be available for some of these diseases, for others a moderate to low level of resistance may be available.
  2. Good-quality and pathogen-free seed should be used for planting. Planting seed infested with these fungal leaf spot pathogens can result in reduced germination and poor seedling vigor.
  3. Seed treatment fungicides can reduce the risk of seedling infections.
  4. Crop rotations can reduce the initial inoculum load of fungal leaf spots.
  5. Management of volunteer weeds that serve as green-bridge for these diseases from one year to the next is helpful.
  6. Several fungicides are labeled for the management of tan spot and the Septoria complex. Early season fungicide application is not recommended in the absence of disease or in an unfavorable environment. A good source of information is the fungicide efficacy table organized by the North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) and can be found on the UMD Plant Sciences/Extension website.

Fusarium Head Blight Risk: June 1, 2020

Nidhi Rawat, Small Grains Pathologist
University of Maryland, College Park

Fusarium head blight risk to susceptible wheat as of June 1, 2020. Visit www.wheatscab.psu.edu

Flowering is all finished across all counties of Maryland now, except for a few late planted fields in the northern part of MD that may still be flowering. Currently the risk of FHB is high in these areas and so FHB fungicides (Prosaro, Miravis Ace, Caramba) should be applied here. For most parts, wheat is now in the grain filling stage and should be ready for harvesting in the next couple of weeks. We experienced some showers this season, but the temperatures remained low, so symptom development in terms of bleached spikelets will be limited. It is advisable to get the DON content of the harvested grain analyzed before taking it to the market.

This is the last FHB risk commentary of the season, but feel free to contact me (email: nidhirwt@umd.edu) if you have any questions related to wheat diseases any time of the year!

Fusarium Head Blight Risk: May 19, 2020

Nidhi Rawat, Small Grains Pathologist
University of Maryland, College Park

Screenshot of FHB risk as of May 19, 2020. Risk is low across the state
Fusarium head blight risk to susceptible wheat varieties as of May 19, 2020. Image from: wheatscab.psu.edu.

Wheat in the Eastern shore and the Southern part of Western shore of Maryland has finished flowering, except for a few late planted fields. Up in the North-western counties of the state (Frederick, Howard, Carroll, Harford) wheat is flowering currently. Past week’s low temperatures slowed the progress of wheat. Heads emerged but waited for a week or so to flower in several places. The FHB risk for Maryland does not show to be high currently. However, the unusual pattern of weather has caused several other foliar diseases to appear across the state. Fungal diseases such as Stagonospora nodorum blotch, Stagonospora tritici blotch, Tan spot, Powdery mildew and even some viral diseases such as Wheat streak mosaic virus and Soil-borne mosaic virus have been observed in wheat fields this year. It is important to remember that Strobulurin containing fungicides should not be applied at this stage. Fungicides will not be effective against any viral diseases. However, the FHB fungicides (Prosaro/ Caramba/ Miravis Ace) will be able to control the other fungal foliar diseases. These fungicides do not need to be tank mixed with another product for spraying. The fungicide products should be applied at the full rate recommended by the manufacturers. Aerial application at a rate of 5 gallons per acre or ground application at 15 gallons per acre with 300-350 um droplet size is recommended. Spray nozzles should be angled at 30°-45° down from horizontal, toward the grain heads, using forward- and backward mounted nozzles or nozzles with a two directional spray, such as Twinjet nozzles.

May 2020 WADE Summary

Dale Johnson, Farm Management Specialist
University of Maryland

Information from USDA WASDE report

Attached is the summary for the May 11 WASDE published on Tuesday. May is the first month for estimates of the new crop year (2020/21). To put these 2020/21 estimates into historical perspective, I have included the past 16 years in this summary spreadsheet.

Corn
Acres harvested, yield, and associated production are estimated to be at an all time high. Total use is estimated to be above the five year average. However, it is not the same magnitude as increased production so ending stocks are estimated to be an all time high of 3.3 billion bushel with an associated historically high stocks-to-use ratio of 22.4%. The next highest stocks-to-use ratio was the 2004/05 pre-ethanol year at 19.8%. This very bearish WASDE report did not move the futures market since it was anticipated and lower prices were already built into the market. December corn settled at $3.35 per bushel on report day.

Soybeans
Acres harvested, yield, and associated production are estimated to be at a five year average. Total use is estimated to be 250 million bushel above the five year average bringing ending stocks down to 405 million bushel, 80 million bushel below the five year average with a stocks-to-use ratio of 9.4% which is not bearish. However, worries about world soybean supply/demand, COVID-19, and the economy continue to suppress soybean prices and November soybeans settled at $8.55 on report day.

Wheat
Wheat production is estimated to be more than 100 million bushel below the five year average. Use is estimated to be slightly above the five year average bringing the ending stocks down to 909 million bushel, 154 million bushel  below the five year average. The associated stocks-to-use ratio is estimated at 43.8%, lower than any of the past five years. However these improved numbers had little impact on futures prices and July/21 wheat settled at $5.36 per bushel on report day.

Download the report as a pdf file here: 2020 May WASDE summary

May 2020 WASDE spreadsheet
May 2020 report. Click to enlarge.

Cause of Red Barley Heads & Wheat Leaf Tip Necrosis

Andrew Kness, Agriculture Extension Agent
University of Maryland Extension, Harford County

Over the past few weeks I have gotten questions about red/purple discoloration to barley heads (Figure 1). These symptoms are not widespread in the field; maybe 1% of heads exhibit this condition. To the best of our knowledge, these symptoms are not caused by a disease but likely a physiological response to an abiotic stress. This spring went from very mild in March to cool and even freezing in April. These symptoms could be a response to environmental conditions, genetic, or a combination of both. Affected heads appear to be viable and able to produce grain.

Discolored red/purple barley head
Figure 1. Discolored barley heads. Images: J. Semler, University of Maryland.

A second condition appearing this year is leaf burn or tip necrosis (LTN) in wheat (Figure 2). This disorder is often a response to cold injury or wind, but can also manifest as a result of heat and drought stress. These symptoms can be intensified by specific leaf rust and stripe rust resistance genes. In any case, there is nothing you can do to remedy the situation.

Wheat with brown leaf tips
Figure 2. Leaf Tip Necrosis on wheat caused by environmental stresses and/or rust resistance genes.

Leaf tip burn/LTN may be confused with barley yellow dwarf virus (BYDV). LTN tends to cause death of the leaf tip resulting in necrotic brown tissue (Figure 2), whereas BYDV can cause a range of symptoms from yellowing of the leaf, which may or may not be accompanied with bronzing/purpling of the leaf tips (Figure 3). Since BYDV is vectored by aphids, symptoms tend to be localized in hotspots in a field, whereas leaf burn and LTN more uniformly affect the entire field.

Purple wheat leaf tips indicate barley yellow dwarf infection
Figure 3. Barley Yellow Dwarf Virus symptoms on wheat.

Considering an Insecticide For Your Small Grain?

Alan Leslie1, Agriculture Agent; Kelly Hamby2, Extension Specialist; and Galen Dively, Professor Emeritus2
1University of Maryland Extension, Charles County
2University of Maryland, Department of Entomology

This time of year, anyone growing small grains will be planning to apply fungicides to manage Fusarium head blight, and many will consider tank-mixing an insecticide to control any insect pest problems at the same time. These tank mixes are an appealing option to reduce the time, fuel, and damage to the crop from having to make a second pass over the field later on in the season. In addition, with many synthetic pyrethroids now available as cheaper generic versions, the costs associated with adding an insecticide to the tank may seem like cheap insurance against possible pest outbreaks. However, to ensure that this added investment gives you a return with increased yields, you should still follow an integrated pest management approach and base the decision to add an insecticide on scouting and documentation of an existing pest problem. Below, we outline several possible insect pests that could be controlled with an insecticide applied with fungicides over small grains, and summarize situations where that application may be warranted, and when it may not.

Aphids. Aphid populations need to be controlled in the fall to reduce Barley Yellow Dwarf Virus incidence in small grains. Spring insecticide applications will not reduce incidence of the disease. Only a few aphid species tend to feed on grain heads, and can reduce yield from head emergence through milk stage (Fig. 1). After the soft dough stage, no economic losses occur. Aphid populations are generally kept in check by insect predators and parasitoids, and thresholds for chemical control of aphids in the spring require at least 25 aphids per grain head (with 90% of heads infested) or 50 per head (50% heads infested) and low numbers of natural enemies. Applying a broad spectrum insecticide when aphid pressure is not above threshold tends to kill off beneficial predatory and parasitic species, which can allow aphid populations to flare up, as they are no longer being suppressed by their natural enemies.

aphids on wheat head
Figure 1. Aphids feeding on wheat head.

True armyworm and grass sawfly. Both true armyworm (Fig. 2) and grass sawfly (Fig. 3) are sporadic pests of small grains and their pest pressure and feeding damage can vary widely from year to year. Automatically applying an insecticide to target these pests is not likely to be a cost-effective strategy since they are not pests that reliably cause economic injury. When these pests are present in high numbers, they are capable of causing significant yield loss through their behavior of clipping grain heads. Scouting should be done to check for the presence of these two pests and insecticide treatment is only needed if they exceed threshold values of one larva per linear foot for armyworm and 0.4 larvae per linear foot for grass sawflies.

armyworm and sawfly larave
Figure 2. True armyworm larva (top). Figure 3. Grass sawfly larva (bottom).

Hessian fly. Cultural methods are the best way to control Hessian fly in small grain, such as planting after the fly-free date, selecting resistant varieties, and using crop rotation to disrupt their population growth. Spring feeding by the fly larvae can cause stems to break, reducing yields. There are no effective rescue treatments for Hessian fly; insecticides targeting fly larvae are ineffective since they are well protected from sprays by feeding inside of the leaf sheath (Fig. 4). If this year’s crop is damaged, it is imperative that fly-resistant varieties are planted after the fly-free date next year.

Hessian fly larvae feeding inside wheat stem
Figure 4. Hessian fly larvae feeding inside of wheat leaf sheath.

           Cereal leaf beetle. This species is widespread in Maryland and is typically present in small grains, though it only occasionally reaches levels that injure crops. Cereal leaf beetle larvae chew the upper surfaces of leaves, leaving them skeletonized (Fig. 5). Larvae can cause yield loss if the flag leaf is severely skeletonized before grain-fill is completed. Insecticides with good residual activity tank mixed and applied with fungicides can potentially control populations of cereal leaf beetles, protect the flag leaf, and improve the yield of the crop if beetle pressure is high. However, predicting whether populations will reach damaging levels is not straightforward, and scouting should be used to guide spray decisions. If a field has 25 or more larvae plus eggs per 100 tillers, and there are more larvae than eggs, then chemical control is needed. In Maryland, a parasitoid wasp species (Anaphes flavipes) may parasitize 70-98% of cereal leaf beetle eggs, so if a field is dominated by eggs with few larvae, insecticide may not be needed. Additionally, feeding by cereal leaf beetle will not cause economic damage after the hard dough stage. So far, we have received no reports of economic levels of cereal leaf beetle in the region.

Cereal leaf beetle feeding on leaf
Figure 5. Cereal leaf beetle larva and feeding damage.

In conclusion, tank mixing an insecticide with your fungicide application can pay off if you have economically damaging levels of an insect pest, but applying any insecticide without a pest problem will not pay off. If populations are present, seem to be increasing, and you will not be harvesting soon, you could gamble. The risks of that gamble include losing money on an unnecessary input cost, secondary pest outbreaks if natural enemy populations are wiped out, or the target pest outbreaks anyway because the application was poorly timed. Scouting fields regularly to document pest pressure and using IPM thresholds as a guide for using chemical controls is the best way to hedge your bets when deciding whether to add an insecticide to the tank this spring.

For more information on tank-mixing insecticides with small grain fungicide applications, check out current research updates from Dr. Dominic Reisig at North Carolina State University: https://smallgrains.ces.ncsu.edu/2019/03/aphids-in-wheat/

https://entomology.ces.ncsu.edu/2015/04/should-you-spray-cereal-leaf-beetle/

And Dr. David Owens at the University of Delaware:

https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/cereal-leaf-beetle/

 

 

Fusarium Head Blight Risk: May 7, 2020

Nidhi Rawat, Small Grains Pathologist
University of Maryland, College Park

Fusarium head blight risk to susceptible wheat varieties as of May 7, 2020.

With the recent showers in the state, the risk of Fusarium Head Blight appears to be high. In the Eastern Shore and the Southern part of the state wheat is flowering/towards the end of flowering. Growers with their wheat still flowering or are within a window of 4-5 days of flowering are advised to spray head scab fungicides (Prosaro, Caramba, Miravis Ace). These fungicides do not need to be tank mixed with another product for spraying. The fungicide products should be applied at the full rate recommended by the manufacturers. Strobilurin containing fungicides should not be sprayed at this stage. Aerial application at a rate of 5 gallons per acre or ground application at 15 gallons per acre with 300-350 um droplet size is recommended. Spray nozzles should be angled at 30°-45° down from horizontal, toward the grain heads, using forward- and backward mounted nozzles or nozzles with a two directional spray, such as Twinjet nozzles. In the Northern counties, we are still around 7-10 days away from flowering.

Fusarium Head Blight Risk: April 26, 2020

Dr. Nidhi Rawat, Small Grains Pathologist
University of Maryland, College Park

Wheat in the Eastern Shore of Maryland has started booting and should be heading out soon. Barley is already flowering there. Note that barley does not show any yellow anthers at flowering and is prone to FHB as soon as it heads out of the boots. Wheat is considered to be at flowering when at least 50% of the heads of a field are beginning to show yellow anthers. With the recent rains FHB risk has increased to moderate/high level in the lower eastern shore counties. Growers here should keep an eye on the FHB risk in the coming days, as wheat heads and flowers here in coming weeks. Fungicides Prosaro, Caramba and Miravis-Ace should be effective in minimizing damage due to FHB in wheat, when applied at flowering. Strobilurin containing fungicides should not be applied now, as they might increase the chances of DON content in the grains. So far, no major concern from other diseases like powdery mildew or rusts has been seen in wheat in the state. Some low intensity incidences of tan spot were observed, which the FHB fungicides applied at flowering should be able to tackle. Up in the northern part of the state wheat is at second node to flag leaf stage, predictably around 2-3 weeks away from flowering.

FHB map of Maryland showing low to moderate risk of head scab
Figure 1. Fusarium head blight risk to susceptible wheat varieties on April 26, 2020.

 Let me know if you have any questions or concerns (nidhirwt@umd.edu).

Don’t Fall Asleep on Head Scab

Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County

Wheat is progressing rapidly across the state due to our mild winter. In the coming weeks, wheat will begin flowering and entering the most critical management stage for Head Scab or Fusaruim Head Blight (FHB). Scout fields as heads emerge and determine when they start to flower (yellow anthers emerging from the middle of the spike). At this stage you will need to make the call to apply a fungicide or not.

Figure 1. Left: Feekes 10.3. Middle: Feekes 10.5.1 (yellow anthers beginning flowering). Right: 4 days after anthesis (white anthers post flowering). Image: A. Koehler, Univ. of Delaware.

Right now, FHB risk is very low across the region, mostly due to the cool nights we are experiencing (Figure 2). However, conditions can turn favorable for FHB very quickly, so don’t fall asleep on it! FHB can sporulate and infect flowering spikes at temperatures in the 50s as long as adequate moisture and humidity is present.

Scab risk map as of April 21, 2020
Figure 2. Head scab risk to susceptible winter wheat varieties as of April 21, 2020.

If conditions turn wet, humid, and above 50 degrees at flowering, FHB risk will be high and you will have about a 5 day maximum window after Feekes 10.5.1 (start of flowering) to make a fungicide application to suppress DON vomitoxin. Optimal timing for a fungicide application is at Feekes 10.5.1 and up to 5 days after. University research has indicated that earlier applications at heading (Feekes 10.3-10.5) do not consistently reduce DON levels in the grain as compared to applications made at or shortly after flowering.

Even though it may seem a bit early and cool, continue to monitor the Scab Risk Tool (www.wheatscab.psu.edu/) to help you assess the risk of developing FHB in your wheat crop so that you’re not taken by surprise.

For fungicide recommendations and other application recommendations, click here.

MD Grain Marketing Site Updated for 2020: Field Crop Budgets and Custom Rates

Shannon Dill, Principal Agriculture Agent
University of Maryland Extension, Talbot County

The University of Maryland Extension has updated extension.umd.edu/grainmarketing site with new input data and spray programs for the 2020 field crop budgets.  

Crop Budgets

Cost of production is very important when making decisions related to your farm enterprise and grain marketing. Enterprise budgets provide valuable information regarding individual enterprises on the farm. This tool enables farm managers to make decisions regarding enterprises and plan for the coming production year. An enterprise budget uses farm revenue, variable cost, fixed cost and net income to provide a clear picture of the financial health of each farm enterprise.

The 2020 Maryland enterprise budgets were developed using average yields and estimated input cost based upon producer and farm supplier data. The figures presented are averages and vary greatly from one farm and region to the other. It is therefore crucial to input actual farm data when completing enterprise budgets for your farm.

How to Use University Enterprise Budgets: 

The enterprise budgets can be used as a baseline for your operation. Make changes to these budgets to include your production techniques, inputs and overall management. New spray programs were added for herbicide resistant weeds.

The budgets are available electronically in PDF or Excel online at www.extension.umd.edu/grainmarketing. Use this document as a start or reference to create your crop budgets. If you have problems downloading any of these budgets, contact information is located on the website.

Cost Per Acre 2020 
  Corn – No Till Corn – Conventional Soybeans Wheat Wheat/Beans
2020 $537.74 $593.58 $346.51 $424.80 $630.50
Increase -5% -4% -5% -3% -4%