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Extension > Minnesota Crop News > Small Grains Disease Update 06/27/13

Small Grains Disease Update 06/27/13

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It may have taken some time to get in to the fields this year, but the small grains crops are now roaring away in the warmer weather. The earliest seeded fields are rapidly approaching heading and with that decisions about whether to use fungicide at anthesis are now front and center.

Tan spot still appears to be the most prevalent disease with incidence up to 74% in scouted fields. If fields were sprayed earlier for this disease, new growth should be assessed to check that it remains free and clear of lesions. Research has shown that, if a fungicide was used at the time of weed control, a fungicide application to suppress Fusarium head blight or scab at anthesis (Feekes 10.51) will generally provide adequate control of tan spot for the remainder of the season. Nonetheless, scout the crop when the flag leaf is fully extended (Feekes 9) to see how aggressively tan spot has moved up through the canopy as about half the days these past two weeks have being favorable for tan spot infections. This is especially important for later seeded fields. If the disease progress is keeping pace with the crop development and lesions can be found on the penultimate leaf at Feekes 9, it is probably warranted to spray a fungicide at Feekes 9 and protect he flag leaf. Fungicide options for the Feekes 9 and Feekes 10.51 timing can be found here.

Cereal aphids continue their march from the southern part of the state steadily northwards. There are now reports of Barley Yellow Dwarf virus (BYDV) in the southern part of the state and so it is very important to scout for these aphids. There is no control method for BYDV other than controlling aphid populations. For a discussion on how to scout for, and control these aphids, please refer this article put together by the State Extension Entomologists Ian MacRae (Uof M) and Janet Knodel (NDSU).

The symptoms of BYDV can be variable depending on growth stage, crop, and variety. Look for stunting of plants (more common in early infections) and yellowing of leaves starting from the tip of the leaf and working down either edge. There may also be red to purple discolorations which are particularly common in oats. Because of our late planted crop, it is at more risk this year from early infection of BYDV which will have a greater impact on yield. Remember there will be about a 1 to 2 week delay before you are to see BYDV symptoms after infected aphids have fed on the plant.

There have also been a few reports of leaf rust in the southern part of the state. At the moment these cases remain isolated but it is important to scout now for these rust diseases. Infection by leaf rust typically occurs at about 64°F with the best development occurring at 68-77°F. The risk models point to slightly less favorable conditions for leaf rust development compared to tan spot to date, but recent rains and next week's weather forecast point to more favorable conditions for leaf rust development.

As we move towards anthesis we need to be thinking about control of FHB. For this, products such as Prosaro, generic Folicur and Caramba need to be applied at anthesis (Feekes 10.51). Unlike for the other fungal diseases, the decision to spray a fungicide at anthesis to suppress FHB is driven by weather-based risk assessment models. The scab diseases forecast tool can be found at http://mawg.cropdisease.com, http://www.ag.ndsu.edu/cropdisease/, and http://www.wheatscab.psu.edu/. Currently the risk models have been trending at low risk for infection for all but the HRSW varieties that are rated very susceptible to FHB. The warm weather and high dew points increased the risk for these varieties to a moderate risk for infection these past few days.

Madeleine Smith and Jochum Wiersma

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