|
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
 |
|
|
|
 |
|||
|
Disease Management Wheat Leaf Disease, FHB Forecasts The NDSU Small Grain Disease Forecasting web site -- www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm -- tracks small grain diseases based on weather information provided by dozens of NDAWN weather stations, including sites in western Minnesota and northeast S.D. A grower or consultant may access the nearest NDAWN weather station, choose the growth stage of the crop, and determine risk of these four diseases for that date. At this same site, a summary of weather conditions for the past 12 days also is provided. Current forecasts are also available by phone. Call toll free for a recorded update from any touch-tone phone in Minnesota or North Dakota, 1-888-248-7382, or 231-6601 in the Fargo area. A similar forecasting system for Minnesota can be found online at http://mawg.cropdisease.com and South Dakota (http://plantsci.sdstate.edu/smallgrainspath) – Click on “SD Scab Advisory.” Level of genetic resistance should factor into treatment decisions. See NDSU disease ratings of HRS varieties online at www.ag.ndsu.edu/pubs/plantsci/smgrains/a574.pdf (page 3). UM HRS disease ratings can be found at www.maes.umn.edu/07VarietalTrials/springwheat.pdf (table 3). The forecasting systems are based on locally available weather information such as relative humidity, temperature, and hours of rainfall. The forecasting information attempts to alert producers to the potential for an environment that promotes disease. Growers are encouraged to use the models as another management tool, but cautioned against considering predictions as absolute, as weather conditions and disease levels can change daily. Diagnosing Leaf Diseases in Wheat Tan spot and Septoria/Stagonospora leaf spotting diseases produce similar leaf symptoms. Tan spot produces oval-shaped, tan lesio 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
Leaf Rust The fungus that causes leaf rust on wheat needs warm days and cool nights with six to eight hours of leaf moisture. Plant leaves in the lower canopy are generally the first to become infected since they stay wet longer. Under the right environmental conditions, masses of spores that are capable of spreading disease can be produced about one week after plants become infected.
Yield losses from susceptible varieties can occur if infection takes place before flowering. Disease development is greatest when spores are plentiful and weather conditions are optimum for the fungus. Timely disease management is important since spore populations can build quickly. Fields should be scouted at regular intervals so timely application of fungicides can be made to protect the crop. The USDA Cereal Disease Lab in St. Paul monitors and reports rust development in the southern and central Plains, which in turn can help us keep on top of rust potential in our region. You can find the CDL’s rust bulletins online at www.cdl.umn.edu. Click on the link “Cereal Rust Bulletins.” Susceptible varieties in growth stages up through flowering may benefit from fungicide use, as long as the flag leaf still has relatively few to no pustules of infection. Bacterial Stripe Plant leaf symptoms appear initially as thin, light brown to golden stripes that appear water-soaked. The bacteria follow plant veins, eventually expanding lengthwise from sheath to tip. Infection of heads produces black streaks on glumes and can result in a range of symptoms from complete head sterility to kernel discoloration/contamination 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. Proline Fungicide New for ‘07 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 www.smallgrains.org/Springwh/jun98/wiersma.htm or under “Production and Research Info” at www.smallgrains.org. 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. 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 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 Bayer CropScience Folicur: www.haltscab.com DON (Vomitoxin) in Wheat – Basic Questions and Answers Testing for DON Sclerotinia Risk Map for Canola Online Field Days and Summer Events Asian Soybean Rust Information Online NDSU: www.ag.ndsu.nodak.edu/extplantpath (click on “Soybean Rust Informaton”) 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
Melvin Newman, U Tenn Extension plant pathologist, photographed these Asian soybean rust pustules on leaf samples from Florida.
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 -- 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 |
|||
ns 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.
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.
Plant symptoms differ depending on their
disease resistance levels. Bright orange to reddish spots, called pustules, tear leaf tissues as spores multiply within the leaves of plants and push outward. Moderately resistant plants have smaller erupting
pustules than those that are susceptible, and have a narrow band of yellow plant tissues, called a halo, surrounding the pustule. Resistant plants can be identified
by small off-white to yellow spots, called flecks, on the leaf where infections have been stopped.
fected wheat seed (bacteria have been found in the seed coat).
Bacteria are also suspected to overwinter on aboveground crop stubble in the field. 
