ISSUE 3   May 28, 2009

TAN SPOT SHOWING UP IN WINTER WHEAT, SPRING WHEAT MAY SOON FOLLOW

Reports of tan spot in winter wheat this past week have occurred across the state, and recent rains will favor continued development of the fungus, both in winter wheat and spring wheat. The causal fungus, Pyreonphora tritici-repentis, survives in wheat residue, and when conditions are wet and rainy, the fungus’s fruiting bodies on the straw swell and release spores that can infect the leaves. The early infections appear as small tan to brown spots with yellow halos (see figure of symptoms).

Dave Franzen, NDSU Extension Soil Fertility specialist, says that "yellow areas in winter wheat may be a combination of tan spot and nitrogen deficiency. Nitrogen deficiency does not automatically cause tan spot, but tan spot is usually more severe when N is deficient. Some growers applied N in the fall, and if these areas are present, this might be an indication that a spring application of N might be better in the future. Fall rains were generally high, and the soils have been very wet this spring. The frost came out of the southeast part of the state the first week in April, so there has been a long time that N has been susceptible for both leaching and denitrification. For this year, these areas could be supplemented with stream-bar 28-0-0 (UAN) before jointing stage to bring them out of deficiency. A rain following application will be needed for greatest efficiency".

To control the tan spot fungus, an early season fungicide may be applied, generally when the crop is in the 4-5 leaf stage. The fungicide often is applied or tank mixed with a herbicide application.

A spreader/sticker addition is NOT recommended for the fungicide, if applied in combination with a herbicide. And if soil fertility is an issue, and additional nitrogen needs to be applied, we do NOT recommend applying the early season fungicide in combination with 28-0-0. I cringe when too many things are applied together, and fungicide plus nitrogen may burn the crop. The N application should be a separate operation.

A number of fungicides are available for control of early season leaf spot diseases in wheat. These products generally are also registered for barley, if early net blotch or spot blotch should occur.

The following table indicates products that have registration in North Dakota for early season use:

Product

Active ingredient

Early season use rate

Tilt, Bumper, Propimax, Propiconazole E-AG

Propiconazole

2 fl oz

Stratego

Propiconazole + Trifloxystrobin

4-5 fl oz

Quadris

Azoxystrobin

6.2 fl oz

Headline

Pyraclostrobin

3 fl oz

Quilt

Propiconazole + Azoxystrobin

7 fl oz

Penncozeb, Manzate, Dithane Manex II

Mancozeb

1-1/2 lb

All of the products have good activity against leaf spot diseases at the 4-5 leaf stage. The mancozebs are protectants and generally are less rain fast than the other products.

Although early season fungicide use for leaf spot control is fairly common across the state, growers will get the greatest economic response from early season fungicide use under the following conditions:

  • susceptible cultivar
  • wheat planted into wheat ground
  • rainy weather during early leaf stages
  • Producers who had wheat in a field two years ago may have enough remaining wheat stubble to see some tan spot infection.

     

    NDSU WHEAT DISEASE FORECASTING UP AND RUNNING FOR THE YEAR

    NDSU’s wheat disease forecasting site is now open for the season. It is found at:

    http://www.ag.ndsu.nodak.edu/cropdisease/

    This site provides prediction risks for infection by the tan spot fungus, leaf rust, Septoria blotch and Fusarium head blight, for over 60 NDAWN weather stations. Predictions of disease risk are based on environmental factors only, not on the susceptibility of variety, previous crop, etc.

     

    WHEAT STREAK MOSAIC VIRUS (WSMV)

    I haven’t heard of or seen any wheat streak mosaic virus symptoms, but if present in winter wheat fields, they may become apparent as the weather warms up. The WSMV virus is transmitted by wheat curl mites, which become more active in movement, replication and feeding when temperatures are warm. WSMV can be distinguished from nutrient deficiency because with WSMV, the yellow or pale greening is streaked, or mottled, rather than a more uniform paling of the leaf tissue associated with nitrogen deficiency.

           

    Any plants suspected of having wheat streak mosaic may be sent to the NDSU Plant Diagnostic Lab for testing and confirmation. The address is:

    NDSU Plant Diagnostic Lab
    NDSU Dept. 7660, Box 6050
    Fargo, ND 58105-6050.

    If the sample is sent by FedEx, then the address is:

    NDSU Plant Diagnostic Lab
    306 Walster Hall, NDSU
    Fargo, ND 58102

    The whole plant should be sent, with the root ball encased in a plastic bag, to prevent drying out and prevent soil from covering the leaves.

    Marcia McMullen
    Extension Plant Pathologist
    marcia.mcmullen@ndsu.edu

     

    DISEASE MANAGEMENT WITH FOLIAR FUNGICIDES IN 2009

    In an effort to help plan for disease management in 2009, we have compiled a very brief discussion of scenario’s when fungicide applications may be most beneficial. More information will be given in the future if timing and conditions for disease are optimum, and/or economic diseases are being reported that can be managed with a fungicide application. All information is general, and growers must consider their specific conditions and other management strategies they are employing (for example, resistant varieties or long rotations).

    Wheat and Barley. In general, wet weather provides a favorable environment for leaf diseases. An early season (Feekes 2) application may be beneficial when residue borne leaf-diseases appear. A flag-leaf (Feekes 10) application can be beneficial to protect the plant from fast-moving diseases like leaf rust. For barley, a full head emergence (Feekes 10.5), and for wheat, an early-flower application (Feekes 10.51) is frequently needed to protect against fusarium head blight (scab) when warm and humid conditions persist during flowering. Forecasting models to aid in decision making for wheat are available at:

    http://www.ag.ndsu.nodak.edu/cropdisease/

    Canola. Some research shows a fungicide application at the 2-4 leaf stage can help manage blackleg. However, planting a resistant variety and using good rotation was found to be more cost effective. A fungicide application for white mold may be beneficial when 1-2 inches of rain fall within a week or two of flowering, and humid conditions persist through bloom. A forecasting model to aid in decision making is available at

    http://www.ag.ndsu.edu/sclerotinia/.

    Chickpeas. Growers of chickpeas know fungicides are the key to making a crop. Depending on type grown and environmental conditions, as many as four or more applications may be made. The key to managing the disease, now and in the future, is managing fungicide resistance. The ascochyta pathogen infecting chickpeas (not lentils or peas) is resistant to FRAC 11 fungicides (strobilurins: Headline® and Quadris® ) so those chemicals should no be used. To prevent the loss of other chemicals, rotation of FRAC groups is essential.

    Corn. The primary corn diseases managed by fungicides in the United States are rare or have not been reported in North Dakota. Gray leaf spot has not been found in North Dakota yet, although we will have it at some point. Common rust of corn has been found in ND before, and can be economically damaging. Like other rusts, the earlier it occurs, the more likely it is to cause yield loss. If common rust is reported early, it is possible a fungicide application may be warranted, but again, this has been rare in North Dakota.

    Dry Beans. Fungicide applications may be beneficial for the management of white mold and common bean rust. White mold can be damaging to dry beans, and when when 1-2 inches of rain fall within a week or two of flowering, and humid conditions persisting during flowering, a fungicide application may pay off. The identification of a new rust race in 2008 means that fungicides may be needed to manage the disease in 2009. The earlier rust occurs, the more yield loss a crop may suffer. Onset of rust at striping (pintos) or later is not considered economic.

    Flax. A fungicide trial at Langdon Research Extenison Center has shown a significant yield response to a fungicide application when conditions were favorable for pasmo. Trials are being conducted at three locations in 2009 to further examine fungicide useage for pasmo on flax.

    Lentils. Ascochyta is an important disease that can be managed with fungicides. Like the pea diseases, early onset and high humidity make this disease economic significant, and fungicide trials have shown an economic response under these conditions.

    Peas. Ascochyta is the most important folicar disease of peas, and when it occurs early and humid conditions persist, a fungicide application may be economic. Fungicide trials conducted at the NDSU research extension centers have indicated that an early bloom application was economic under high disease pressure. Although less common than ascochyta, gray mold, white mold, and powdery mildew may also be managed by foliar fungicides.

    Soybeans. The occurrence of economically-damaging diseases of soybean that can be managed with a foliar fungicide are rare in North Dakota. In the absence of soybean rust, it is unlikely a fungicide application will be needed.

    Sunflower. Although sunflower has many diseases, sunflower rust is the most important disease that can be managed with a fungicide. The occurrence of rust, particular on the upper leaves and before ray flower emergence may warrant a fungicide application.

    Sam Markell
    Extension Plant Pathologist
    samuel.markell@ndsu.edu

    Marcia Mcmullen
    Extension Plant Pathologist
    marcia.mcmullen@ndsu.edu


    NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button