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Disease Management Minnesota’s Fusarium Head Blight (Scab) Epidemic Risk Forecasting System Until recently, the Minnesota small grain crops production community relied exclusively on traditional tools to manage losses caused by FHB. Producers understand that management of FHB includes an integrated approach such as growing cultivars with resistance, applying fungicide at the early flowering growth stage, and managing infested crop residue with rotation and/or tillage. Epidemic risk predictions are used as decision-making tools prior to the time when an application of fungicide should be made to manage disease. A statewide FHB epidemic risk forecasting system has been operational for producers in Minnesota at http://mawg.cropdisease.com since 2004. Agricultural professionals, producers, and others can access either system free of charge to assist in determining whether the risk of crop loss from disease is likely and would warrant incurring additional input costs associated with fungicide application. Operation and maintenance of the Minnesota FHB epidemic risk forecasting system website is funded by the Minnesota Wheat Research and Promotion Council. The site is maintained by a private company, Meridian Environmental Technology, Inc. (Meridian) in cooperation with the University of Minnesota. This Grand Forks, ND company maintains a comprehensive weather database that integrates data collected from surface-observed stations and remotely-sensed information from weather radars and satellites. Observed weather throughout Minnesota is recorded by federal and state agencies such as the National Weather Service and the Federal Aviation Administration (>82 stations), the Minnesota Department of Transportation, Road Weather Information System (93 stations), and the North Dakota Agricultural Weather Network (NDAWN; 10 stations). Remotely-sensed information originates from six NEXt Generation Weather RADar (NEXRAD) weather radars. The outcome is a 4-km resolution composite of hourly precipitation, temperature, and humidity data which is used to update the forecasting system every three hours, for a total of eight times a day. During 2004, five on-farm disease management experiments were conducted within commercial production fields located from north to south in the Red River Valley (near Kittson, Strathcona, Oklee, Perley, and Fergus Falls). During 2005, experiments were again planted at similar locations (near Kittson, Strathcona, Oklee, Perley, and Rothsay). Unfortunately, stand losses due to severe weather and flooding resulted in tests at the Kittson and Strathcona locations being discontinued. During 2006 and 2007, tests were planted near Oklee and Fergus Falls. In total, from 2004 to 2007, 19 environments (location + cultivar flowering period) with ground-truthing data were collected from replicated, small-plot experiments consisting of data from five to 13 varieties. Data from non-fungicide treated control plots were used to support a ground-truthing effort for the FHB epidemic forecasting system. During 2004, the risk forecasting model predicted an elevated (moderate to high) risk that an FHB epidemic would occur in two of five (40%) environments, and a low risk that an epidemic would occur in three of five (60%) environments. No epidemics were observed. Single year model prediction accuracy was 60% for non-epidemics and 0% for epidemics. During 2005, it predicted an elevated risk that an epidemic would occur in one of six (17%) environments, and a low risk that an epidemic would occur in five of six (83%) environments. Two epidemics were observed. Single year model prediction accuracy was 80% for non-epidemics and 50% for epidemics. During 2006, the model predicted a low risk that an epidemic would occur in four of four environments (100%), and no epidemics were observed. Single year model prediction accuracy was 100% for non-epidemics. Again during 2007, the model predicted a low risk that an epidemic would occur in four of four environments (100%), and no epidemics were observed. Single year model prediction accuracy was 100% for non-epidemics. From 2004 to 2007, non-epidemics were predicted accurately 94% of the time and epidemics were predicted accurately 66% of the time. Conversely, the model under-predicted non-epidemics in 6% of the environments and over-predicted epidemics in 33% of the environments. Model modifications made after the 2005 growing season are meant to increase the accuracy of predicting epidemics. Benefits from these changes have not yet been identified because FHB epidemics have not yet occurred since then. National System -- Deployed since 2004, the national FHB epidemic risk forecasting system website located at www.wheatscab.psu.edu is supported by the U.S. Wheat and Barley Scab Initiative. The system services the central and eastern U.S. wheat community located in 24 states, including Minnesota. A number of weather data sources are used by the national model system, with the most substantial data contributions provided by federal agencies. The national epidemic risk forecasting system relies primarily on remote-sensed weather data devices (e.g.: radar, satellites), whereas the Minnesota relies primarily on observed station data. A disease forecasting component based on 24 hour and 48 hour weather forecasts was added to the national model in during 2006. Minnesota will also incorporate weather forecasts into its FHB epidemic risk forecasting website during 2008. Submitted by Charla Hollingsworth, UM Extension Plant Pathologist NDSU’s Wheat Disease Forecasting Web Site NDSU’s disease forecasting web sites will have a new portal this year.
Links to small grain disease forecasting, Sclerotinia disease forecasting, and potato disease forecasting will be available at one site: A person seeking information specifically on wheat disease risk, including Fusarium head blight (scab) may go directly to the following web site: www.ndsu.edu/scabforecast. This scabforecast web site is being reformatted for easier use. It will provide information on the risk of Fusarium head blight (scab), as well as risk of the wheat leaf diseases, tan spot, Septoria blotch, and leaf rust. The risk of these four diseases is based on environmental conditions as recorded by the North Dakota Agricultural Weather Network (NDAWN) stations. This network consists of 67 stations distributed across North Dakota, the Red River Valley, and border regions of surrounding states. The risk map for Fusarium head blight is based on a model developed by plant pathologists at Penn State University, a model which incorporated considerable ND disease and weather data for verification of the model. The scab model also has the opportunity for the producer to indicate whether the variety grown is very susceptible, susceptible, moderately susceptible or moderately resistant to Fusarium head blight. Risk information is available in a chart format and state map format for Fusarium head blight. The information in the models for the leaf diseases was developed at ND, and provides information in a chart format indicating risk of the three leaf diseases over the past 12 days. Such information is another tool that producers may use to determine the need for fungicide application at critical growth stages to control leaf and head diseases in wheat. Statistics on use of the small grain disease forecasting site indicates that June and July are the heaviest use period for this information. Submitted by Marcia McMullen, NDSU Extension Plant Pathologist Diagnosing Leaf Diseases in Wheat Tan spot and Septoria/Stagonospora leaf spotting diseases produce similar leaf symptoms. Tan spot produces oval-shaped, tan lesions that enlarge with age. Lesions are surrounded by a yellow halo, while dark areas eventually form on tissues that were initially infected. Severe disease development causes spots to expand until most, if not all, plant leaf tissues are killed. Yield and kernel weights are reduced if the seed-filling ability of diseased plants is limited early enough. Wet years tend to favor tan spot epidemics, with the result often being yield loss. Planting wheat into fields with infected small grain stubble is especially risky, since it increases the likelihood for seedling infection early in the growing season. If the disease is established prior to flag leaf emergence and extended wet weather is forecast, fungicide application provides a viable control alternative. Some spring wheat varieties have differing levels of resistance to the disease. Septoria/Stagonospora Leaf Spot Complex
Bacterial Stripe Plant leaf symptoms appear initially as thin, light bro Infection of heads produces black streaks on glumes and can result in a range of symptoms from complete head sterility to kernel discoloration/contaminati on with bacteria. Symptom severity depends on when the infection takes place. If flag leaf tissue is killed early on, more yield loss will result. Yield reductions are generally 10% or less. Crop rotation may help manage this disease, as would tillage, since bacterial populations are known to drop when infected stubble is incorporated into the soil. Infected seed provide the primary means of inoculum. Spraying the crop with fungicides won’t help; the chemistry isn’t effective against bacteria. Rust Diseases in Wheat
Infections of leaf rust appear as small powdery pustules on the lower and upper leaves of wheat plants (see leaf rust photo on page 51). The rust spores that are produced in the pustules are reddish in color, which gives heavily infected leaves a brown-red appearance, hence the name of rust for these diseases. A single large rust pustule can produce hundreds of spores every day. The spores are wind blown into the atmosphere and carried by the prevailing winds for hundreds of miles and are deposited on wheat crops in rain. Each of these spores has the potential to infect wheat. Since leaf rust needs only 7-9 days from initial infection to production of spores, there can be up to four generations of rust increase in a crop in a single growing season, which results in an exponential increase of leaf rust infections. Rust infections are highest in years with good temperature and moisture conditions for the wheat crop. The red pustules of wheat leaf rust are usually first observed on winter wheat in Minnesota and the Dakotas in mid-to-late May. In some years leaf rust infects winter wheat in the fall, survives the winter on wheat, and begins to increase very rapidly in the spring when daytime temperatures increase to 70-75 degrees. Leaf rust infections on spring wheat are usually first seen in the Red River Valley in mid-June. Initial infections on spring wheat are caused by spores that have been carried in the winds from the leaf rust infected winter wheats in the southern Great Plains. Leaf rust infections in spring wheat reach maximum levels in mid-to-late July. Yield losses in wheat caused by leaf rust occur annually in the winter and spring wheats grown in Minnesota and the Dakotas. The spring wheats vary greatly for genetic resistance to leaf rust. Some cultivars are highly resistant. On these cultivars very few leaf rust pustules can be found, and the flag leaves stay green for a longer period, thus increasing kernel size and weight. On susceptible cultivars, the flag leaves are covered by thousands of pustules. Heavily infected flag leaves dry down prematurely, reducing kernel size and weight. Planting resistant cultivars is critical to reducing losses due to leaf rust. Losses caused by leaf rust in spring wheats can be as high as 40% in susceptible cultivars. In recent years many growers have also sprayed fungicides on wheat in order to reduce losses due to Fusarium head blight, leaf spots, and leaf rust. Many different races of leaf rust are found every year in the U.S. These races differ their ability to attack different resistance genes in wheat. As a result, wheat cultivars that are highly resistant when first released, often become susceptible within a few years of cultivation due to the increase of races that can overcome its resistance genes. New cultivars with new and effective resistance genes are essential to maintain leaf rust resistance and reduce yield losses. In recent years stripe rust has also occurred in Minnesota and the Dakotas. Stripe rust is a disease that is most common in areas where wheat develops and matures in cool environments. Stripe rust is characterized by strips of very small yellow pustules that grow between the leaf veins. In most years stripe rust may not occur at all in this region. However years with cool and wet weather in the spring and summer (such as 2003 and 2004) may be conducive for the onset and development of this disease. In years when stripe rust does occur, the infections on winter wheat can be seen in early-mid May in southern Minnesota and South Dakota. In recent years stripe infections have reached damaging levels in winter wheats in western and central South Dakota. Stripe rust infections on spring wheats are most common and evident in early July. Many winter and spring wheats have good resistance to stripe rust. This resistance combined with the normal hot weather in July limits development of stripe rust infections in years when the rust is present in the upper Midwest. From 1900-1950s stem rust was a major disease of spring and winter wheat. Infections of stem rust are now rarely seen in the U.S. because most wheat varieties are highly resistant to prevalent races of this fungus. However, most U.S. wheat cultivars are susceptible to a fast-evolving race of stem rust designated Ug99. This race is currently confined to parts of Africa and southwest Asia, but breeders and pathologists are preparing for its possible spread to North America. Stem rust pustules are dark red and are found on stems and occasionally on leaves. The alternate host for wheat stem rust, the common barberry, has largely been eradicated in the spring wheat region. Elimination of the barberry plants removed the sexual cycle of the fungus, which has greatly reduced the number of stem rust races that occur in the U.S. Information on the spread of wheat rusts in the current crop year can be found at the USDA-ARS Cereal Disease Laboratory website (www.ars .usda.gov/mwa/cdl) in the cereal rust bulletins section. Information on the rust resistance in wheat cultivars can be found in varietal trial guides published online by the Minnesota Agricultural Experiment Station (www.maes.umn.edu) and the North Dakota Agricultural Experiment Station (www.ag.ndsu.edu). Models to Help Fungicide Decisions On Small Grains To help producers with “should I or shouldn’t I” spray questions, extension plant pathologists Marcia McMullen of NDSU and Roger Jones,
UM, developed a point-based fungicide decision aid for wheat fungal leaf diseases a number of years ago. It can be found online at SDSU has developed a Small Grain Fungicide Decision Guide as well, in the form of a Microsoft Excel spreadsheet. Go online to http://plantsci .sdstate.edu/planthealth. Click on “Small Grains” then “Small Grain Fungicide Use Decision Guide.” Managing Disease in Winter Wheat Control of volunteer winter wheat is critical following the winter wheat crop to prevent the spread of wheat streak mosaic and other green-bridge diseases. Following winter wheat with a broadleaf crop can also reduce the risk of wheat streak mosaic. Wheat streak mosaic virus is a disease spread by a tiny mite that thrives on grassy weeds and volunteer grass crops, including corn and wheat. Typical symptoms are stunted plants, yellow streaking and green/yellow mosaic discoloration of leaves. Severe outbreaks are almost always associated with volunteer wheat in which mites and virus have survived and multiplied. The mite has a quick life cycle (egg to adult takes only 7 to 10 days) and needs green plants for feeding and reproduction. If no green food hosts are available after hatching, the mite does not survive. Thus, a glyphosate burndown about two to three weeks prior to planting winter wheat will destroy grassy weeds and greatly reduce the threat of wheat streak. More background on the wheat streak mosaic virus can be found on the NDSU extension web site, www.ag.ndsu.edu/pubs/smgrains.html. See the link “wheat streak mosaic.” Also go to http://prairie.ducks.org – click on ‘Agronomy News’ (direct link to DU HRWW management info: http://prairie.ducks.org/ag_news/winterwheat2.pdf) Foliar Fungicides, Liquid N May Not Tank Mix Well NDSU studies show Puma or Discover plus Bronate Advanced applied with the strobilurin fungicides (Quadris, Quilt, Headline) caused severe leaf burn on wheat plants. New tissue that emerged was unaffected. Bronate, and generic formulations plus strobiluron fungicides may also cause similar injury. Tank mixing of mancozeb fungicide and 28-0-0 was tested at NDSU in the past, with results indicating that leaf burn was severe if a surfactant was added to this tank mix. Leaf burning also was compounded if temperatures at spraying were greater than 90° F. The Carrington study and the Crookston study indicated leaf burn was less using 20-0-0-3 than with 28 -0 -0. Innovations such as liquid N stream bars, specialized streamer nozzles, and air spreaders for applying dry urea are essential tools to maximize the potential of foliar N while minimizing leaf burn. The purpose of applying fungicides is to protect the leaf from diseases, and any practice that burns the leaves negates the purpose of adding the fungicide. Product labels usually give possible registered herbicide/fungicide combinations and application practices to follow or avoid. Tips for Better FHB Suppression with Fungicides
FHB, Disease Management Online NDSU: www.ag.ndsu.edu/pubs/plntdise.html and www.ag.ndsu.nodak .edu/extplantpath NDSU Small Grain Disease Forecasting web site: www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm . Recorded updates and information by phone: 1-888-248-7382, 231-6601 in Fargo area. SDSU: http://plantsci.sdstate.edu/planthealth and http://plantsci.sdstate .edu/smallgrainspath UM (NWROC- Crookston): www.nwroc.umn.edu – Click on “Research Areas” then “Plant pathology” or http://mawg.cropdisease.com DON (Vomitoxin) in Wheat – Basic Questions and Answers Testing for DON Sclerotinia Risk Map for Canola Online Scab Epidemic Risk Forecasting System In Action Plant pathologist commentary. This is a new upgrade to the site and is meant to help with map interpretation by adding on-the-ground information from a plant pathologist’s perspective. Found just below the colored map of Minnesota (Fig. A), commentary contains reported and observed disease information and additional tidbits to consider when making the decision of when and how to manage diseases. The text is updated periodically during the growing season. Glenn ≠? Oxen. Since 2006, the spring wheat epidemic risk forecasting model has included an additional equation term representing FHB resistance levels of cultivars. Users have the option of selecting either a specific variety of interest, or a generic FHB resistance level (very susceptible, susceptible, moderately susceptible, moderately resistant). This model modification allows for a more precise prediction since specific variables such as location-specific weather and variety response to FHB are known. It is likely that incorporating FHB resistance levels of varieties into the model may be one of the most beneficial modifications made in recent years. To obtain a specific disease risk figure for a variety, click on the state map at the approximate site where the field of interest is located and select a flowering date. This estimate is based on actual, observed weather conditions, so a date into the future is not available. However, users can use past and current dates in succession to determine if the risk level in the area is increasing or decreasing as the flowering date approaches. Again select an approximate location of the field by clicking on secondary, zoomed-in map. A window with a drop-down menu will appear where you can select your variety, or its FHB resistance level, for an approximated percent risk of disease (Fig. B). Risk of an epidemic is substantially reduced with varieties such as Alsen or Glenn compared with susceptible varieties such as Oxen or Reeder. Access to this information will likely change before the 2008 growing season. Homepage access will reduce the screens needed to retrieve this information. Growth Stage Estimator. To estimate the growth progress of your crop, select the “Wheat Growth Model” and a different state map will be displayed. Click on an approximated location for the field of interest and type in the needed information (variety, date planted, seeding depth), then select the “GO” button. An estimate of the crop growth stages will be displayed. This estimate is based on growing degree days for wheat and is calculated using observed weather conditions. As the number of weather data increase, the estimate will be more and more accurate. For example, an estimate of the early flowering date made at the 2-leaf stage is less accurate than when it is made at the sixth leaf stage. This estimator has proven to be reliably accurate. Additional features. Leaf disease severity estimators for tan spot, Septoria, and leaf rust. Weather conditions can also be accessed from the left side of the home page. Figure A.
Figure B.
Spraying for FHB Suppression: Timing is Everything Fungicide application timing in barley is earlier—at Stage 10.5, when the head has fully emerged. That is because flowering in barley usually occurs in the boot. The barley head on the left is in what is called the half-head stage, which is slightly early for optimum fungicide efficacy. The middle spike is fully headed. This is the optimum stage for spraying Folicur to control scab on barley. Note that the head has just emerged (fully) from the boot. The spike on the right is too old for effective spraying. Note the extension of the peduncle beyond the flag leaf. Also there are no visible anthers. There are about 3 to 4 days difference between these 3 growth stages. Photos: Joel Ransom, North Dakota State University Wheat
Barley
Key Online Crop Production Links & Resources NDSU Crop Production Page: www.ag.ndsu.nodak.edu/cropprod.htm University of Minnesota Extension Service: www.extension.umn.edu - Click on the Farm link. SDSU Extension Service: http://sdces.sdstate.edu – see ‘crops’ link NW Research and Outreach Center Crookston: http://nwroc.umn.edu (on home page, see link to ‘Cropping Issues of NW Minnesota’ for newsletter updated weekly during the growing season) SW Research and Outreach Center Lamberton: http://swroc.coafes.umn.edu NDSU Crop & Pest Report: Updated weekly during the growing season -- www.ag.ndsu.nodak.edu/aginfo/entomology/ndsucpr/index.htm NDSU IPM Crop Survey web pages: Updated at the beginning of each week during the growing season -- www.ag.ndsu.nodak.edu/aginfo/ndipm N.D. Ag Weather Network (NDAWN): http://ndawn.ndsu.nodak.edu/index.html MN Dept Ag Pest Reports: www.mda.state.mn.us/pestsurvey/pestreports Asian Soybean Rust Information Online NDSU: www.ag.ndsu.nodak.edu/extplantpath/programs.html (click on “Soybean Rust update and maps”) SDSU: http://plantsci.sdstate.edu/planthealth (Click on “Soybean Rust”) UM: www.soybeans.umn.edu/crop/diseases/soybeanrust.htm Ohio: www.oardc.ohio-state.edu/soyrust (excellent info on using foliar fungicides to manage soybean rust) USDA Rust Tracking & Alerts: www.sbrusa.net and www.usda.gov/soybeanrust DTN: www.dtnsoybeanrustcenter.com North American Plant Disease Forecast Center: www.ces.ncsu.edu/depts/pp/soybeanrust Project of AgProfessional, Successful Farming, Greenbook, United Soybean Board: www.stopsoybeanrust.com |
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ver a wide range of temperatures as long as adequate moisture is present on leaves for an
extended period (12-24 hours).
Septoria/Stagonospora leaf spot diseases look
much like tan spot early on. Young lesions appear oval-shaped and have yellow halos. As lesions mature, either tiny black fungal fruiting bodies (black flecks) form, or lesions develop grey centers as light
-colored spores are produced. Specific plant symptoms are dependent on which fungi are responsible for causing the disease. Fungicides may be necessary if wet weather is forecast and the disease is present.
wn to golden stripes that appear water-soaked. The bacteria follow plant veins, eventually expanding lengthwise from sheath to tip. 
