July 1, 2011                          Issue No. 9

Management of Small Grain Diseases

Fungicide Efficacy for Control of Wheat Diseases

The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) has developed the following information on fungicide efficacy for control of certain foliar diseases of wheat for use by the grain production industry in the U.S. Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes most widely marketed products, and is not intended to be a list of all labeled products.

Efficacy of fungicides for wheat disease control based on appropriate application timing

¹ Efficacy categories: NL=Not Labeled and Not Recommended; P=Poor; F=Fair; G=Good; VG=Very Good; E=Excellent. Efficacy designation with a second rating in parenthesis indicates greater efficacy at higher application rates.

² Efficacy may be significantly reduced if solo strobilurin products are applied after stripe rust infection has occurred

³ Insufficient data to make statement about efficacy of this product

⁴ Multiple generic products containing the active ingredients propiconazole and tebuconazole may also be labeled in some states.  Products including tebuconazole incude: Embrace, Monsoon, Muscle 3.6 F, Onset, Orius 3.6 F, Tebucon 3.6 F, Tebustar 3.6 F, Tebuzol 3.6 F, Tegrol , and Toledo.  Products containing propiconazole include: Bumper 41.8 EC, Fitness, Propiconazole E-AG, and PropiMax 3.6 EC. 

This information is provided only as a guide.  It is the responsibility of the pesticide applicator by law to read and follow all current label directions.  No endorsement is intended for products listed, nor is criticism meant for products not listed.  Members or participants in the NCERA-184 committee assume no liability resulting from the use of these products.

Keys to Successful Fusarium Head Blight (Scab) Management

The window for management of head blight extends from flowering to the early milk stage. While in the boot, the head is protected from Fusarium. After mid-milk, it becomes more difficult for the fungus to infect the kernel and damage is less severe. The most severe head blight epidemics have involved multiple infection periods (environment conducive for FHB development) and cultivars susceptible to spread of the fungus throughout the head. Further information on the biology and management of head blight can be found in the NDSU Extension Bulletin PP804.

High humidity, rain, dew, moderate temperatures, and ultra violet radiation affect pathogen survival, spore production, spore spread, infection process, and disease development.  Cold temperatures and dry conditions limit fungal growth and infection. Extended duration of high relative humidity is one of the key factors indicating high risk of infection in the current Fusarium head blight model.  

Fusarium head blight (scab) risk assessment models have been developed by the cooperative efforts of researchers based at multiple Land Grant Universities and involved in the U.S. Wheat and Barley Scab Initiative. The group used the data from wheat head blight epidemics around the country. The collaborative efforts of these university epidemiology groups continue to increase the scab model efficiency and accuracy level. Although the scab model has been developed based on wheat head blight epidemic data, the wheat scab epidemics often translate into quality problems for barley as well. 

Scab Model: The Model gives the percent risk of 10% or more scab severity based on weather conditions (humidity, rain, and temperature) suitable for spore development in the week before flowering and suitable environment for infection and disease development. Final scab level will depend on weather between flowering and early dough stages. The model allows input by the user on the degree of susceptibility of the wheat variety and a 48 hour prediction, as well.  The risk map will change with the degree of variety susceptibility to Fusarium head blight.

Research also is ongoing to develop a risk model for DON (vomitoxin) production in barley.  The current model provides information on Fusarium head blight infection risk to help producers make timely fungicide applications.  Information on currently registered fungicides for North Dakota is provided by the NDSU Extension Service.

NDSU Small Grain Disease Forecasting Home
Web Site:  http://www.ag.ndsu.nodak.edu/cropdisease/

Choose nearest NDAWN site and then flowering stage and variety susceptibility.  National FHB Forecasting Home  Web site:  http://www.wheatscab.psu.edu/     

choose spring wheat and then ND 

Wheat Streak Mosaic Severe in Some Wheat

Some winter wheat plots in the state have been so severely infected with wheat streak mosaic virus, that these plots were destroyed to prevent further movement of the wheat curl mite and virus to neighboring fields. A winter wheat field west of Maddock appeared to have WSM symptoms and tested positive for WSM.

Questions have arisen as to the source of the wheat curl mite for these plots and also for some commercial winter and spring wheat fields with infection. 

Grass hosts most susceptible to the mite and the virus include wheat, corn, sorghum, cheat grass, field sandbur, and jointed goatgrass.  Grass hosts that are susceptible to the virus, but poor hosts for mite increase include oat, barley, rye, barnyard grass, and green foxtail.  Neither the virus or the mite survive in or infect broad leaf crops. 

Although wheat crops or volunteers are the primary source of infection and mites, grassy weeds in fields or along field edges may serve as sources for the virus and mite.  The NDSU Extension Publication PP-646(http://www.ag.ndsu.edu/pubs/plantsci/smgrains/pp646.pdf) and the Univ. of Nebraska Publication (http://elkhorn.unl.edu/epublic/live/ec1871/build/ec1871.pdf) have more information on mite and virus hosts and mite movement. 

Later this growing season, when growers will be considering planting winter wheat again, extreme care must be made on what ground they plant into, and how volunteers or grassy weeds will need to be destroyed prior to planting.  This disease also has implications for cover crop choices, as we don’t want a lot of virus present in cover crops. 

Marcia McMullen – marcia.mcmullen@ndsu.edu

Iron Chlorosis in Soybeans

Dr. Kandel and Dr. Goos submitted a good article on iron deficiency chlorosis (IDC) last week. The problem continues and in many fields has intensified due to the continuous wet weather.

Dr. Goos has shown that any field that shows chlorosis loses about 5 bu/acre right off the top. The yields continue to decrease the longer the soybeans are chlorotic. Fields that never green up until harvest will yield less than 10 bu/acre in my experience. As the fields dry as we hope they will, the problems will become less. Growers outside the Valley are seeing yellowing where they have not seen it before. They had the soil conditions favorable for the condition (soil carbonates), but if the soil is not wet, the symptoms do not express themselves due to the chemistry of carbonates. Sprays of most iron chelates and other products are temporary ‘band-aids’, since iron is not mobile in the plant. Iron is taken up by exposed leaves and may temporarily green-up the plants, but new leaves are just as likely to show deficiency. A spray of Fe-ortho-ortho-EDDHA may be more effective, but based on University of Minnesota work about 15 years ago, the effects are inconsistent. Making a big note to yourself to consult Dr. Goos’s “yellowsoybeans.com” website to choose a more IDC Variety in the future, and perhaps apply a row-placed Fe-ortho-ortho-EDDHA like Soygreen at planting would be a good activity for now.

On another related topic- note how wheel tracks during this wet period are more green (less yellow) than the rest of the field. Later in the season they will be less green than the rest of the field. The reason is most likely due to relative moisture within the track. Wheel tracks dry faster than the rest of the field now, so they are less chlorotic. When the field dries, the wheel tracks will wick water into them and be more moist than the rest of the field and will be more chlorotic. Something to talk about when you get together with friends.

Dave Franzen - David.franzen@ndsu.edu

Leached or Lost Nutrients

Calls continue to come in relating to leached or lost nutrients due to the continuous rainfall this spring. A couple calls this last week were due to very low chloride levels in small grain tissue tests.

Chloride moves in the soil with water, so loam and coarser textured soils on hilltops and slopes are susceptible to chloride leaching in addition nitrate and sulfate. It is unusual to find chloride levels as low as reported in tissue recently and these levels are categorized as deficient. What does this mean to the crop? In one instance, the sample came from winter wheat, which seems to be more susceptible to deficiency symptoms than spring wheat. The field had two varieties of winter wheat; one showed characteristic non-pathological spotting on the leaves and the other did not. The spring wheat showed no symptoms. Deficient chloride reduces grain yield about ten percent. A remedy would be foliar chloride application of about 5 lb/acre chloride from either potassium chloride or calcium chloride. The potassium chloride would need to be soluble potash, and would need to be vigorously agitated to get it into solution.  Some fertilizer retailers have the proper equipment to make this solution, but most do not. Calcium chloride is more soluble and requires less agitation to get into solution, but it is not as accessible to retailers. Calcium chloride is used in tractor tires to increase weight and as a snow melting agent. Yield increase from chloride comes from increased kernel size, so it is possible to regain some yield with an application. Obstacles are physical and logistical. It may not be physically possible to spray the field with chloride due to wet conditions. There may also be more important applications to make, including fungicide applications and perhaps nitrogen and sulfur applications.

Sulfur deficiency is showing up in many areas on a number of crops. All crops are susceptible to sulfur deficiency under wet conditions in loam textured and coarser soils on hilltops and slopes in the state. Field pea S deficiency was recently diagnosed in the southwest and I suspect that many other crops are suffering as well. If the crop is small enough to apply dry fertilizer, either ammonium sulfate or granular gypsum would work. If the crop is large enough that a high-clearance sprayer has to be used, streamed ammonium sulfate solution or ammonium thiosulfate can be used. Rainfall is needed to move the S into the soil, although that has not been a problem this season so far.

The expected leaching of N from hilltops and slopes is beginning to cause N deficiency symptoms to appear. However, in the eastern part of the state in high clay soils another problem is denitrification- the conversion of nitrate to nitrous oxide gases due to saturated soil conditions. The continuous wetness of our clay soils during the past 10 days has almost certainly decreased the available N supply in many fields. These fields need to be monitored closely over the next couple weeks to determine the N status of the crops and to try to apply supplemental N in the areas not drowned out by water.