Posts Tagged ‘wheat diseases’

Wheat Disease Scouting

Friday, May 1st, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Be on the lookout for several wheat diseases now. Powdery mildew is appearing in very dense stands and in headrows and on susceptible cultivars. The small white-to-tan spots of fungal growth are getting easy to spot when present. Most of what I have seen has been in the lower canopy and does not require treatment. Keep scouting. The second disease worth looking for is stripe rust (Figure 1). I am seeing some reports of it in the South and there might be low levels in our area that go undetected until some yellowing of the leaves appears. Stripe rust is getting more aggressive so it is important to identify it early and apply a triazole fungicide, such as Tilt or Caramba; a strobilurin, such as Quadris or Headline; or a combination product like Quit or Stratego. If these products are applied from flag leaf fully expanded until head emergence very good to excellent control should be achieved. None of these products labeled for powdery mildew or rust control, except Caramba, will aid in scab control.

Stripe Rust of Wheat

Figure 1. Stripe rust pustules on the underside of the leaf

Scab or Fusarium head blight suppression is achieved with well-timed applications of Prosaro (Proline + Folicur) 6.5 fl oz/A , Caramba 14 fl oz/A, or Proline (alone) 5.7 fl oz/A. None of the other fungicides labeled for wheat will give the same level of suppression as the above three, according to work done by Arv Grybauskas at the University of Maryland. No fungicide provides the level of control that most growers would like to see, but they are the best that we have and can provide suppression of the disease, especially if conditions are favorable. Suppression of scab depends on very precise timing of the application. For the fungicides to work to the best of their ability they need to be applied when the anthers first appear (Figure 2). The fungus infects through the flower parts of the wheat so it is the newly flowering wheat heads that need to be protected. Once pollination takes place the fungus is only susceptible to the fungicides for a very short time.

Wheat is at risk when temperatures are warm and wet during flowering, the risk increases when the wheat crop is planted in no-till corn stubble and there is no rotation. The new risk management tool is located at the Fusarium head blight website http://www.wheatscab.psu.edu. It can be useful once heading begins and the risk of scab increases as flowering approaches. The new version that is running now has the ability to give a 24-72 hour forecast looking at the previous several days as well as the weather forecast for the next several days. Those buttons are at the top left side of the forecast page.

 timing

Figure 2. Correct timing for fungicide application for scab suppression

Risk Assessment Tool for Predicting Fusarium Head Blight or Head Scab on Wheat

Friday, April 17th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

It is not too early to be thinking about scab on wheat. During the winter meetings we talked to some audiences about the relatively new scab prediction model that is available. The following is some information about the model and the site where it can be found.

The goal of this experimental predictive system is to help growers assess the risk of Fusarium head blight in their region. Major outbreaks of Fusarium head blight are associated with specific weather patterns prior to flowering of the wheat crop. Researchers at Penn State University, Ohio State University, Kansas State University, Purdue University, North Dakota State University, and South Dakota State University have worked together to developed models that predict the risk of a major epidemic (greater than 10% field severity) based on observed weather patterns. The website is http://www.wheatscab.psu.edu/. The directions on the website are easy to follow; however, if you are going to use this tool to help predict the occurrence of scab and time any necessary applications for control, it is important that you start using the website several weeks before heading. Arv Grybauskas and I will be writing commentary for our region when the time is closer for potential scab infection. Remember that this predictive system is only a tool and should be used as such. The website has some good information on the limits of the risk assessment tool and how it should be used.

Prosaro and Caramba are two of the new fungicides that are labeled for suppression of Fusarium head blight or scab and should be considered if needed. More information on this prediction tool and control options will be covered in the next several weeks.

Wheat Disease Update

Friday, April 17th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Most foliage diseases are at low levels at this time, except where excessive amounts of fertilizer or manure have produced extremely lush growth that favors powdery mildew.

Scouting for powdery mildew is advised at this time. There have been scattered reports of low disease severity of leaf rust and stripe rust in several states such as LA and GA at this time. Weather has been wetter than normal recently in the South so we will have to wait and see what happens as the season progresses. We had another wheat sample test positive for soilborne wheat mosaic virus this week. As I stated last week, once you have identified it you can implement the only control strategy and that is to plant a resistant wheat variety.

Prevention of Disease in Small Grains

Friday, September 12th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Be sure to plant fungicide treated seed for control of loose smut and common bunt especially if you saved your own seed for planting. Select varieties that are high yielding as well as resistant to powdery mildew, leaf rust and stripe rust.

Agronomic Crop Diseases

Friday, June 13th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat
The wheat crop is made and now drying down. There was a late season disease that popped up that was not seen until now. Sharp eyespot is a disease that is caused by Rhizoctonia cerealis and causes stunting and “whiteheads” when it is severe. It can cause areas in the field that vary in size to be stunted and mature prematurely. As with take-all, the best control for sharp eyespot is rotation of at least one year out of small grains. The disease begins on the outer leaf sheath near the base of the plant. Lesions on the stems are light-brown to straw-colored with a sharply defined dark brown border. This disease could be confused with take-all but there is generally little root rot associated with sharp eyespot. Generally the disease is not severe enough to warrant control measures other than rotation with legumes or other nonhost crops.

Sharp eyespot on stems

Note sharp eyespot symptoms on lower leaf sheath.

Scab or head blight is present at varying levels in some fields and others have none. Fortunately for most growers, scab was not as bad as it could have been this year. There were some fields, mostly in Kent County so far, where scab is severe and growers should check for scab and adjust their combines accordingly. See the last issue for more info on scab.

Corn
Pythium root rot
has been the most common problem we have seen in the lab so far this season. With corn under water earlier in many places these conditions are extremely favorable for Pythium root rot. Seed treatments with metalaxyl or mefanoxam (Apron, Apron MAXX, Apron XL and others) should provide good control. Corn treated with Dynasty alone would not be effective under severe conditions for Pythium and should be combined with an Apron product for optimum disease control.

Seedling anthracnose was also diagnosed this week. Seedling anthracnose often occurs when corn follows corn especially in no-tillage systems. Initially, small watersoaked spots are seen and become tan with red or red brown borders as they age. Eventually the small hairs or setae of the fungus can be seen with a hand lens in the center of the lesions.  Anthracnose rarely causes any loss at this stage of growth and the plants grow out of the initial infections, which can recur later in the season if the weather is favorable for anthracnose leaf blight. Burying crop residues may be helpful in reducing these early season infections but do little or nothing in reducing the late season leaf blight and stalk rot phase of anthracnose.

Wheat Diseases

Friday, June 6th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The wet weather and the warmer temperatures will accelerate the development of scab if it is present and the symptoms will become more evident as the temperatures get warmer this weekend. Some scab is present on Delmarva. The first symptoms of Fusarium head blight include a tan or brown discoloration at the base of a floret within the spikelets of the head. As the infection progresses, the diseased spikelets become light tan or bleached in appearance. The infection may be limited to one spikelet, but if the fungus invades the rachis the entire head may develop symptoms of the disease. The base of the infected spikelets and portions of the rachis often develop a dark brown color. When weather conditions have been favorable for pathogen reproduction, the fungus may produce small orange clusters of spores or black reproductive structures called perithecia on the surface of the glumes. Infected kernels are often shriveled, white, and chalky in appearance. In some cases, the diseased kernels may develop a red or pink discoloration.

 

Fusarium head blight or scab on wheat.

 

Fusarium head blight or scab on wheat head.

 

Grain produced in heads damaged by Fusarium head blight is often shriveled, white, and chalky in appearance.

Fusarium graminearum is known to produce two important mycotoxins, deoxynivalenol (DON) and zearalenone, which can contaminate the diseased grain. The mycotoxin DON can cause reduced feed intake and lower weight gain in animals at levels as low as 1-3 ppm, especially in swine. Vomiting and feed refusal can occur when levels of DON exceed 10 ppm. Humans are also sensitive to DON, and the FDA has recommended that DON levels not exceed 1 ppm in human food. Ruminant animals, including dairy cows and beef cattle, are less sensitive to the toxin. The fungal toxin zearalenone has estrogenic properties and produces many reproductive disorders in animals. Swine are the most sensitive to the toxin, but cattle and sheep may also be affected. Zearalenone concentrations of 1-5 ppm can result in negative effects in animals and humans. Producers concerned about these mycotoxins should have grain tested prior to feeding to animals. Contact the state department of agriculture or local extension office for more information about testing for mycotoxins.

When high levels of Fusarium head blight are present in fields, precautions can be taken to reduce mycotoxin contaminations of the grain. The mycotoxin contamination is often highest in the severely diseased kernels. Adjusting the combine to blow out the small, shriveled kernels can help reduce mycotoxin levels. Harvested grain should be dried to 13.5% moisture as soon as possible to limit continued fungal growth. Grain suspected to have been damaged by Fusarium head blight should be tested for DON and zearalenone. Do not mix contaminated grain with good grain prior to a mycotoxin analysis. The mixing will result in more contaminated grain, which may be difficult to sell. Edited from Penn State fact sheet on Head Blight authored by Eric DeWolf. http://www.wheatscab.psu.edu/PDF/Fusarium_Head_Blight_.pdf

Other wheat diseases that we are seeing are take-all and, just recently, tan spot. Take-all is characterized by patches in the field that can vary in size but the wheat is generally stunted and the heads bleach out prematurely. Infected plants can be easily pulled out of the ground due to the extensive root rot that occurs. The other symptom is the dark streaking at the base of the stem (lowest node under the leaf sheaths). See picture. Take-all can be controlled by rotating out of wheat for a year. However planting wheat followed by double crop soybeans followed by wheat is not an effective rotation for take-all control. Manganese levels also interact with take-all. Be sure that soil levels of manganese are adequate for the crop and check pH so that the managanese is available. High pH makes manganese unavailable.

 

Take-all symptoms on the lower nodes. Note lack of roots as well.

Tan spot was identified in my wheat fungicide trials near Middletown. This foliar disease can look like Septoria (Stagnospora) leaf and glume blotch. It is caused by the fungus Pyrenophora tritici-repentis. It is too late for any control but this disease will be favored by the wet and warm weather. Most of the spots were in the lower canopy and may reach the flag leaf before the plants begin to dry down. Applications of foliar fungicides at heading or earlier should provide pretty good control of this disease. At present most of the infection is in the lower canopy and the effect on yield should be minimal if the disease does not move up to the flag leaf or the leaf below the flag leaf.

 

Tan spot symptoms on wheat.

Wheat Diseases

Friday, May 16th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

After looking at two of the three wheat variety trial plots, disease levels continue to be low. There is some speckled leaf blotch caused by Septoria tritici on lower leaves in both trials in Sussex County. The amount present is low in the canopy and too little to have any affect on plant health at this time. The rain of last Friday may have produced favorable weather for scab if wheat was flowering at that time. The rain forecast for Thursday night and Friday may have little effect on most of the wheat in DE since most has flowered and may not be susceptible. Growers need to remember that the fungicides applied for leaf diseases at heading or earlier will have little or no suppression of scab (head blight). It appears that there is little to no Proline, Caramba, or Folicur available for scab suppression this season.

Small Grain Diseases

Friday, May 9th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

 Wheat
Last week we did identify barley yellow dwarf virus on wheat in two locations in Sussex County. One was identified as BYDV-pav strain and the other tested positive for BYDV-pav as well, but also tested positive for cereal yellow dwarf virus CYDV-RPV. This used to be BYDV-RPV, the most serious strain. Both are transmitted by aphids, and there isn’t much that can be done for management except resistant varieties.

Information from an Illinois bulletin:
BYDV and cereal yellow dwarf virus (CYDV). Aphids spread BYDV and CYDV disease. Aphids carrying the virus transmit it to wheat plants through their saliva when they feed. The most serious yield loss results from fall infection by viruliferous aphids’ feeding on wheat seedlings. Fall infections typically result in stunted plants and fewer tillers when spring growth resumes. Leaf discoloration is usually the most notable early-season symptom. Leaves may be varying shades of red to purple, pinkish-yellow to brown. As the plant continues to grow, older leaves typically begin to die back from the tip and may feel somewhat leathery, while the new leaves begin to discolor. Spring infections occur as well, but they commonly discolor only the flag leaf and typically do not cause significant yield reductions.

There were three strains of BYDV: MAV (mild), PAV (serious), and RPV (more serious). This was probably confusing enough, but for numerous biological reasons the BYDV-RPV strain has been renamed and put in the cereal yellow dwarf group; its acronym is now CYDV-RPV. Testing of plant material for BYDV or CYDV should include tests for both BYDV-PAV and CYDV-RPV (formerly known as BYDV-RPV) to be certain, first, whether a virus is causing the symptoms and, if so, which one it is responsible.

Barley yellow dwarf virus-PAV strain

Proline for scab suppression was featured in an article in WCU Volume 16, Issue 6 (http://agdev.anr.udel.edu/weeklycropupdate/?p=130). Now, Caramba (metconazole) from BASF and Folicur (tebuconazole) from Bayer CropScience have also received section 3 federal registration for use in wheat. In terms of efficacy against head scab and vomitoxin, Proline, Caramba and a tank mix of Proline + Folicur are very comparable. Data from studies conducted across the US show that on average Proline + Folicur, Caramba, and Proline alone, when sprayed at flowering (Feekes 10.5.1), had about 50% reduction in scab and about 42% reduction in DON when compared to the untreated check. Proline is recommended at rates between 4.3 – 5.7 fl oz/acre, Caramba between 14 – 17 fl oz/acre, and the tank mix of Folicur + Proline at 3 fl oz/acre of each product (commonly referred to as Proline 3+3). I am not sure if Folicur and Caramba are available or if state labels have been issued yet for use this season, but if scab control is needed these three products are the products of choice.

For scab suppression, the best results were achieved when these products were: applied at flowering (Feekes 10.5.1), forward and backward mounted nozzles were used to achieve maximum coverage of the heads, and the products were applied to moderately resistant wheat varieties. With the hope of controlling as many diseases as possible with a single fungicide application, producers may be tempted to apply these products as early as boot (Feekes 10). However, for head scab management, treatments applied at Feekes 10 are much less effective than those applied at Feekes 10.5.1. It should be noted that even when applied at the correct growth stage none of these products will provide complete scab control, especially if prolonged periods of wet conditions occur during and after flowering. The term here is SUPPRESSION. What producers can expect is a reduction of head scab and vomitoxin, but NOT total 100% control.

Reprinted in part from “More Fungicides Registered for the Suppression of Head Scab in Wheat” by Pierce Paul and Dennis Mills in the May 5 edition of the Crop Observation and Recommendation Network newsletter from the Ohio State University agronomic crops team.

Small Grain Diseases

Friday, May 2nd, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Barley
Several diseases are present at this time. Powdery mildew, which we had reported earlier, seems to be found primarily on the variety ‘Thoroughbred‘. The spot blotch form of net blotch is also present in some varieties at low levels that should not affect yields. The latest “new” disease that appeared at heading is loose smut. This fungus is present in the seeds at planting and grows with the germinating plant and systemically infects the head and replaces the seed with its dark brown spore masses. Grain harvested from infected fields should not be used for seed unless it is treated with a systemic fungicide such as Baytan, Dividend, and Raxil. Because the spore masses weather and are absent during harvest the fungus does not cause surface contamination of the harvested grain so the feed value is not affected. Plant certified smut free seed and/or treat with a fungicide for loose smut control.

 

Loose smut of barley caused by Ustilago nuda

 Spot blotch and net blotch

Spot blotch on left two leaves, net blotch on right two leaves

 

Barley scald caused by a fungus Rhynchosporium secalis.

The last disease that I am seeing in barley is scald. This disease overwinters in old barley debris or can be seed borne. Look for the water-soaked gray-green spots that appear initially. As the lesion the dries out the center becomes bleached then tan with a brown margin (see photo). Some lesions can be very large and several spots can merge and kill the leaf. Rotation and use of resistant varieties is the best control method.

Wheat
Powdery mildew is still the most prevalent disease present. Continue to scout and remember that the end of flowering is the last opportunity to apply a fungicide for control. We have not confirmed it yet but I believe we have seen barley yellow dwarf mosaic virus (BYDMV) in wheat this week. A late fall infection or early spring infection produces symptoms of off-color wheat, which may be stunted in varying degrees, as well as red-purple flag leaves (the uppermost leaf). Since this virus is aphid transmitted, fields that are early planted or have had high aphid infestations are the most at risk. The later the infection occurs the less the effect on yield. Aphid control, including seed treatments, may prevent BYDMV as well as avoiding early planting.

 

Barley yellow dwarf causing reddened flag leaves

Flowering has begun for many wheat fields due to the warm weather last week. The remainder will be flowering in the next week or two. If you want to check the Scab Forecasting website visit: http://www.wheatscab.psu.edu/ for more info. Right now the risk for scab statewide for the next 48 hours is low.

Fusarium Head Blight and Management Options

Friday, April 25th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

With all the corn that was planted last season much of our wheat crop was planted in corn ground with varying levels of tillage: no-till, minimum-till, and mold board plowed. The one down side of planting into corn residue if it is exposed on the soil suface is that one of the stalk rot fungi, Fusarium graminearum, is also the principal pathogen that causes Fusarium head blight or scab of wheat. Vulnerability of wheat is increased when the fungus is present in the field versus having the fungus blow in from another site.

Fusarium head blight (FHB) or scab of wheat and the accumulation of the mycotoxin deoxynivalenol (DON) in harvested grain, are periodically problems in Delaware. High DON levels will end up in rejection of wheat loads. Fortunately in recent years we have not had a severe outbreak of scab in Delaware.

Strobilurin fungicides (e.g., Quadris, Headline) or fungicide containing a strobilurin (e.g., Quilt, Stratego) are not recommended for scab control because they may result in elevated DON levels compared to untreated wheat. The only class of fungicides that have not had this increase in mycotoxins is the triazole class. The only registered triazoles for wheat and barley in Delaware are Tilt and Proline. There has been a much higher rate of success at suppressing scab with Proline than with Tilt in work conducted by Dr. Arv Grybauskas at the University of Maryland.

Proline Information
The proper use of Proline will help suppress FHB and DON when used with other FHB/DON management tactics. However, Proline is not a “silver bullet” for managing FHB/DON. In other words, do not expect Proline to provide the same level of FHB/DON control as you have come to expect when fungicides are used to control other wheat diseases. The key is to think in terms of disease suppression, not control. Nevertheless, a 40% reduction in FHB and DON can have a significant economic impact locally, state-wide, and regionally if FHB is moderate to severe in 2008. But, be advised that significant losses due to FHB and/or DON can still occur even where Proline is applied if FHB is severe.

For FHB/DON suppression the Proline 480SC label indicates a use rate of 4.3 to 5.7 fl oz/A applied to wheat “within a time period from when at least 75% of the wheat heads on the main stem are fully emerged (~Feekes stage 10.4) to when 50% of the heads on the main stem are in flower (~Feekes stage 10.52)”. Applications cannot be made within 30 days of harvest. Although the Proline label allows for some flexibility in terms of timing of application, most of the efficacy data for Proline in suppressing FHB/DON are based on application at early flowering (Feekes stage 10.51).

Excellent fungicide coverage on wheat heads is crucial to achieve the greatest possible FHB/DON suppression. This is no small challenge since most spray systems used in wheat were developed to deliver pesticides to foliage (horizontal structures). In order to maximize coverage on heads (vertical targets), significant changes may need to be made to the sprayer boom system. Also, discipline must be exercised to ensure that proper sprayer pressure and volumes are used. The Proline label gives some suggestions on how to achieve acceptable spray coverage.

Making Appropriate Fungicide Spray Decisions
One desire we all have is for fungicides to be used only when needed. Regular field scouting for foliar fungal diseases has been successfully used by growers for many years to determine if and when to spray fungicides. However, this is not possible with FHB since once symptoms are present it is TOO LATE to spray. Note: Proline is also effective on glume blotch, rusts, and tan spot.

Go to http://www.cdms.net/ to access the Proline label.

Below are some general guidelines to help you determine if you should spray Proline for FHB/DON suppression.

During period leading up to, during and immediately after head emergence:

*Soil moisture has been good for the past month (relates to spore production, dispersal of Fusarium graminearum spores, and crop infection)

*Crop has good yield potential (relates to economics and crop density, which increases canopy humidity and may increase spore production, facilitate spore dispersal, and encourage crop infection)

*Temperatures 68-86°F (relates to spore production and crop infection)

*Humidity is high (80% day or night) and/or free water (such as dew) is present on the heads during this period (relates to spore production, dispersal, and crop infection)

If most or all of the above conditions exist when the crop is just beginning to flower, consider spraying as soon as possible.

New Web-Based FHB Prediction Tool
In addition to the above general guidelines, an exciting new tool can also be used to help determine the FHB risk and need to spray. This tool is a web-based, disease forecasting model made available by Penn State University, The Ohio State University, Kansas State University, and the U.S. Wheat and Barley Scab Initiative. This forecasting model utilizes real-time weather data from numerous National Weather Service stations within each state. Go to http://www.wheatscab.psu.edu/ and click on “Risk map tool”.

You will be asked if you are growing winter or spring wheat. At this point you will come to a U.S. map and are asked to click on the state of interest. The FHB Risk Management Tool page will have a map that shows where the weather data are being retrieved. To the upper left corner of the page is a calendar section labeled “Assessment Date”. This section needs a bit of explaining. You will note right away that the tool will only let you click on the current date and the preceding 7 days. So, if you estimate your crop will begin to flower (the beginning of FHB susceptibility) on May 7, but it is only May 3, the best you will be able to do is to determine if the weather on May 3 (or the previous 7 days) is favorable for FHB. My advice is to begin determining the FHB risk using this model 1-2 weeks out from crop flowering. Keep checking your wheat and keep checking the model every 1-2 days. By the time your crop reaches early flowering, you should have a good feel for the FHB risk in your area. If the forecast model says the FHB risk is high (medium if you are not a risk taker), and the forecast matches your local weather and crop reality, then you might consider spraying as soon as possible.

Once you actually see it and play around with it, what I have said above will make much more sense. The model does have several practical limitations in predicting final FHB levels; these are clearly discussed within the Prediction Center website. Perhaps the greatest limitation of the model is that it does not account for weather conditions during flowering and grain fill. Specifically, disease-favorable weather occurring during late flowering and grain fill can greatly impact final FHB/DON levels. The bottom line is that final FHB/DON levels may not always be reflected by the model’s risk output. The authors of the model discuss this limitation under “Reality Check” in the “Model Details” section of the Prediction Center.

We all hope that FHB is non-existent this spring. However, if this is not the case, wheat producers now have an additional tool to use to minimize FHB and DON development this spring.

Adapted for Delaware from “FUNGICIDAL CONTROL OF FUSARIUM HEAD BLIGHT (HEAD SCAB) AND DEOXYNIVALENOL (DON) IN WHEAT” By Don Hershman in the April 14 issue of the Kentucky Pest News. http://www.uky.edu/Ag/kpn/kpn_08/pn080414.htm#whefun

If you have read all this you may be wondering what this is all about. In the past we have not had a fungicide for scab control to consider. The added management decision is whether to wait and use a new fungicide at flowering that would give some level of scab suppression and rust and glume blotch control if the weather turns out to be favorable for scab or take your chances that it does not show up and take advantage of the disease protection that the strobilurins or strobilurin/triazole combos provide, when applied at head emergence. Unfortunately we do not have any current data with Proline and its control of other diseases besides scab, since we have not had weather for diseases in the last several years that provided the needed disease control information.