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June 2012 Archives

Small Grains Disease Update

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While a 11-plus inch deluge made for national headlines in Duluth, much smaller but timely rains have helped stave a worsening of the drought stress in parts of northwest Minnesota. Drought stress is pretty evident is many fields as evidenced by differences in plant height across the field. On June 19, the majority of northwest Minnesota is still rated to be in a moderate drought while a large portion of west central Minnesota is still considered abnormally dry. Timely rains will be needed to allow grainfill not to be impacted by drought as the crop needs nearly a 0.25 inch of water daily at the beginning of grainfill.

Most spring wheat is passed anthesis and in to the grainfill period. Reports indicate that many of you applied a fungicide to protect against foliar diseases and protect against Fusarium Head Blight. The University of Minnesota scouts continue to report that BYDV, stripe rust, tan spot and Septoria spot blotch are the most commonly found diseases. Severe BYDV is being reported from the west and central areas of the state, with yellowing and sever stunting in many cases due to the early season infection this year. Cool wet conditions have seen the increase of Septoria spot blotch in the north west of the state becoming prevalent on the lower canopy. With low humidity and little rain forecast the disease is likely to be slow moving into the upper canopy. Stripe rust is present throughout the state to varying degrees. Faller being one of the most affected varieties with infection reaching mid to upper canopy in some fields, but some stripe rust has also been found on Vantage.

The risk of FHB as predicted by the disease forecast models indicated relatively low risk for most of Minnesota for much of the past 7 days. The exception being much of Kittson county in the extreme northwest corner of the State. The weather outlook for the next 3 to 5 days suggests that the risk is likely waning.

A few calls have come in about powdery mildew having been detected in the lower canopy despite an application of a fungicide at anthesis. Understand that most if not all of the spray volume was deposited on the head and the upper canopy. Consequently it will not give good control of powdery mildew despite the fact that tebuconazole and Prosaro give good control of powdery mildew. The warmer daytime temperatures should really slow down these infections. Powdery mildew will turn from gray white to a tan color when it gets too hot for it to flourish.

The first case of crown rust has been reported on oats in Renville County.

Update on Goss's Wilt in Minnesota

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By Dean Malvick, Department of Plant Pathology

The fact that Goss's wilt is was a widespread corn disease in Minnesota in 2011 is broadly known.  The question of how much Goss's wilt will develop in 2012 is dependent in part on field and weather conditions.  As of June 13, 2012, Goss's wilt had been confirmed over the previous week in several counties in Iowa and Nebraska. Thus it could also start to appear soon in Minnesota.  This article summarizes key points about this disease, including where it has been confirmed in Minnesota, factors that favor its development, and how to recognize it.

Small Grains Disease Update

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The spring wheat in many parts of the state is now fully headed or pretty close to it. The drought stress has been partially abetted with some timely rains over the weekend. Yield potential, however, of the most drought stricken fields has been greatly reduced as tillers and lower leaves were aborted. This is very visible as the canopy opened up. Some of the worst field will likely not yield much over 35 to 40 bushels.

As far as diseases are concerned, these are some of our own observations and those of the scouts that are paid for through a grant of the Minnesota Wheat Research & Promotion Council. Tan spot is still the most prevalent disease, closely followed by stripe rust. Both diseases have progressed to the middle of the canopy, particularly on more susceptible varieties, as is the case for Faller and stripe rust

BYDV like symptomology can be readily found in barley, particular in the southern half of the state. Disconcerting in these cases is the high incidence and the severity; very seldom, if ever, have we seen such a widespread infection across fields, and the severe stunting. Fields have actually been abandoned and replanted with soybeans in the past week.

Now is the time to scout the fields to assess yield potential and the presence of any foliar diseases such as tan spot and leaf or stripe rust. With the increase in precipitation, disease risk models have, and will likely continue to trend higher, especially for the foliar diseases such as tan spot and stripe rust.

The decision to apply a fungicide at Feekes 10.51 will not be easy this year. Given the weather forecast for the next 5 to 7 days, we don't expect the risk models for FHB to increase dramatically. The decision therefore will hinge as much on the presence of foliar diseases as on the risk for FHB. The lower yield potential further complicates the matter.

Small Grains Disease Update

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The Minnesota Wheat Research and Promotion Council funded a disease survey in small grains in 2012. This is a summary of what the scouts have found in the past few days:

The winter wheat is mostly at or just past anthesis is looking very good overall. The spring wheat is not far behind and is more variable. Drought stress is evident in the central and northern portions of the Red River Valley with the area around Crookston being the hardest hit by drought. Available soil moisture at the NWROC is between ~ 2.7 to 3.3 inches in the top 5 ft of three soils series that were sampled last week (or less than 25% of field capacity), with less than 0.5 inch in the top two feet of two of the three samples.

As far as diseases is concerned:

1) Scattered incidence of powdery mildew in winter wheat throughout the state. Incidence and severity generally pretty low except for one particular field where is was quite high.

2) Tan spot can pretty readily found in the middle and lower portions of the canopy of winter wheat and initial infections are starting to show in spring wheat. Incidence in spring wheat is very low. This is likely a function of the fact that most growers now routinely use half a labeled rate of a fungicide at F5 in a tank mix combination with the weed control program. Likewise initial infections of net blotch in barley and Septoria spot blotch in spring wheat can be found.

3) BYDV like symptomology can be readily found in oat and winter wheat across the state. Foci tend to be small (couple of plants) to medium sized (several feet in diameter) circular patches throughout the field. Aphids (bird cherry oat and English grain) can be found but are generally not at threshold. Some stunting evident, something we rarely see.

4) No confirmed cases of aster yellows to date, but the first few cases have been submitted for diagnosis.

5) Stripe rust is now common in the southern portion of the state with incidence nearing 100% in 'Faller' spring wheat (Faller is readily identified because of the rather distinct purple auricles - click here for more details). Severity is approaching 10% on the penultimate and/or flag leaf is some fields.

6) Leaf rust has been confirmed is a spring wheat field near Barrett, MN (west central MN). The variety was unknown but the incidence was low. The reaction type, however, was S.

There is a fair amount of herbicide injury also showing up in spring wheat that may be mistaken for disease symptoms. The drought stress and a couple of cool nights following the herbicide application is causing this increase in the incidence and severity of the herbicide injury.

For high yields, small grains need 14 to 17 inches of water depending on weather conditions and length of growing season. The water used for optimum growth is a combination of stored soil moisture, rain and irrigation. Small grains require about six inches of water as a threshold for grain yield. Each additional inch of water will provide four to five bushels per acre. In deep well-drained soils, the roots of small grains will extract water to a depth of three feet. Small grains are most sensitive to water stress in the boot to flowering stage of growth.

While many parts of Minnesota have come out of the drought, northwest Minnesota is still very dry. As of May 29th, the US Drought Monitor classified this area of the state as either abnormally dry or in a moderate drought. Last week's available soil moisture was less than one inch in the top 3 ft of two soils cores that were taken at the NWROC and less than two inches in the top 3 ft of a third core.

During the peak water use period, small grains can use up to 0.30 inches per day depending on air temperature and cloud cover. Daily crop water use - often called evapotranspiration or ET - depends on plant development and local weather conditions. Small grain water use will generally peak between heading and early dough stage. Daily ET estimates in the tables are based on long term average solar radiation and cloud cover. Daily ET estimates in northwestern Minnesota may be 5 to 10 percent greater than estimates found in Table 1 for central Minnesota because there is a greater chance for clearer and cloud free sky.

Real-time daily crop ET estimations during the growing season can be obtained from the Internet: For North Dakota go to here and for Minnesota go to here.

Small grains are susceptible to fungal infections. Most small grains are irrigated with center pivots; therefore it is better to apply at least an inch of water per irrigation rather than more frequent small applications. Wheat and barley are particularly susceptible to Fusarium head blight (FHB) prior to and during flowering. Irrigation during this period should be avoided if possible thus root zone water should be brought to a high level prior to flowering.

For detailed instructions on how to apply the daily crop water use estimations from these tables within an irrigation scheduling program review the Irrigation Scheduling Checkbook Method from the University of Minnesota Extension.

Table 1.jpg

By Dean Malvick

With most of the soybean and corn crop emerged and growing across Minnesota - it is a good time to assess fields for seedling disease problems and the potential benefits or failures of seed treatments.  The recent fluctuating temperatures and abundant rainfall that resulted in surplus topsoil moisture in about 21% of the state last week (USDA-NASS data) have created good conditions for seedling diseases and root infection by a complex mix of pathogens in many fields.  Scattered problems with seedling diseases have been reported.
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