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7/5/2010 - 7/11/2010

White Mold Mushrooms Show Up

By XB Yang, SS Navi and Linus Li, Department of Plant Pathology

Over the last 10 days the weather was favorable for the production of soybean white mold mushrooms in Iowa. Yesterday we visited fields near Clear Lake in north central Iowa with crop consultant Dan Muff and found abundant white mold mushrooms in a continuous soybean field, which had a closed canopy with wonderful growth. The density of the mushrooms was very high, 3 apothecia/square foot, and soybean plants are likely to be infected.  The early showing in such a large number in this field was due to early planting, good growth and a higher number of sclerotia from last year. According to Dan, this field had very bad white mold and this year it was planted April 29. 

white mold mushroom

  Photo credit: SS Navi and XB Yang

The level of soybean white mold occurrence this year is likely to be less than last year, because last year we had a record cool July. Statistically, the chance to have two years in a row with record cool temperatures is unlikely, although early July in this season has been cool and wet in Iowa. Because white mold can continue to attack soybean in August, the weather conditions in part of August are also factors that impact the outbreak of soybean white mold. The risk of white mold varies from field to field, in addition to flowering weather conditions. The field we visited was planted April 29, had early canopy closure and was loaded with sclerotia, representing a high-risk situation. If white mold risk is high in your field, consider using a fungicide to protect your soybean.  See our previous article on white mold control for chemical information.

white mold mushroom

  Photo credit: SS Navi and XB Yang

We also found many white mold mushrooms in a cornfield. Rotation with corn to promote white mold mushroom production is a good measure to reduce white mold risk for next year’s soybean. However, white mold spores produced in a cornfield can travel up to 45 yards, with most infected plants in areas adjacent to the cornfield, according to a study from our lab in 1995. The study was done in two locations, one in Humboldt and one near Ames. For the field at Ames, spores traveled further. When white mold spores land on soybean plants that are flowering and environmental conditions are right, they can infect soybean plants. The effects on soybean yield by spores from cornfields are yet to be determined. These infected plants, however, produce sclerotia, which are the source of future infections. This presents a challenge: how to balance management practices of using corn rotation to reduce white mold risk.


XB Yang is a professor of plant pathology with research and extension responsibilities in soybean diseases. Yang can be reached at (515) 294-8826 or by emailing xbyang@iastate.edu.

Iowa State University Corn Field Guide Reprints to be Available

By Adam Sisson, Corn and Soybean Initiative

The Iowa State University Extension Corn Field Guide is a valuable in-field reference and popular resource for agribusiness personnel and corn producers. The publication helps with in-field identification of pests, diseases and disorders of corn in the Midwest and is produced in a pocket-size format with weather-safe pages.

Last year, more than 50,000 copies of the Corn Field Guide were printed and distributed. The publication is so popular that they are difficult to keep in stock. Several agribusinesses have asked to reprint the guide.

To make these guides available for reprinting at a reasonable cost, in the near future we will be combining field guide orders from multiple agribusinesses into one larger print run. Agribusinesses can choose the number of field guides they want to print and the guides would display the organization’s logo in a prominent place on the back cover.

Corn Field Guide cover mockup

If you would like more information about reprinting the Corn Field Guide, specific cost estimates, minimum order size, etc., please contact Adam Sisson at 515-294-5899 or ajsisson@iastate.edu.

 

Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at ajsisson@iastate.edu or by calling (515) 294-5899.

ISU Extension Field Agronomist Positions Available in Northeast and West Central Iowa

By Clarke McGrath, Corn and Soybean Initiative

Two Iowa State University Extension field agronomist positions currently are available. One position serves northeast Iowa and is based at the Borlaug Learning Center at the Northeast Research Farm near Nashua, Iowa. The other position serves west central Iowa. Proposed start dates for these fulltime positions are as soon as possible.

Extension field agronomists provide educational leadership, grounded in research-based science, to help Iowa crop producers and agricultural industries prosper. These positions will focus on development, delivery and support for crop production, crop protection and crop systems programming, as well as applied research.

These positions will deliver information and educational programs to Iowa farmers primarily through collaborations with agribusiness partners, including ISU Corn and Soybean Initiative partners. Additional clientele groups and partners who may cooperate with ISU Extension field agronomists include educational institutions, governmental agencies, farm and conservation organizations and the mass media.

In addition to educational program development and delivery, these positions will develop and manage applied research on cooperating private farmers’ fields and at ISU research farms. Research will focus on crops, soils, manure management and pest management.

Applicants for these ISU Extension field agronomist positions must have a bachelor’s degree in agronomy, crop science, soil science, entomology, plant pathology, weed or seed science or related field and three years of experience at a comparable level directly related to the duties of these positions. Additional, preferred qualifications for applicants are listed in the official position announcement posted online.

Applications must be submitted online at https://www.iastatejobs.com/applicants/jsp/shared/position/JobDetails_css.jsp

To ensure consideration, submit applications by July 30, 2010.

For more information regarding these vacancies, please email Clarke McGrath at cmcgrath@iastate.edu or call 712-215-2146.

 

Clarke McGrath is the partner program manager and ISU Extension agronomist with the Corn and Soybean Initiative. McGrath can be contacted by email at cmcgrath@iastate.edu or by calling 712-215-2146.

Summary: Foliar Fungicide on Soybean in Iowa (2006 – 2009)

By Daren Mueller and Alison Robertson, Department of Plant Pathology

We recently collated and summarized data from soybean fungicide small plot trials conducted by Iowa State University faculty and staff, and on-farm trials conducted by the Iowa Soybean Association On-Farm Network, the ISU Corn and Soybean Initiative and the ISU Northwest On-Farm research program.

  • For the total 831 observations, the overall mean yield response was 2.18 bu/A. 
  • Yield response of small plot trials (282 observations) was 1.67 bu/A, compared with 2.44 bu/A for on-farm strip trials (549 observations).  
  • The mean yield response varied among years: 2.11 bu/A (for 8 observations in 2006), 4.42 bu/A (16 observations, 2007), 2.37 bu/A (599 observations, 2008) and 1.46 bu/A (208 observations, 2009).
  • Applications at R2 and R3 resulted in the highest mean yield response (2.32 bu/A and 2.42 bu/A, respectively).  The mean yield response for a fungicide application at R1 was 1.07 bu/A, while the mean yield response at R4 and R5 was <1 bu/A.
  • The mean yield response was greatest for fungicides that contained a strobilurin, either alone (2.52 bu/A) or in a premix (2.13 bu/A).
  • Disease ratings were not taken from all plots. Where noted, brown spot, downy mildew, Cercospora leaf blight and frogeye leaf spot were rated. The predominant disease was brown spot. Mean yield response was greater when disease severity in a field at R5 was >5 percent (1.79 bu/A) compared with disease severity <5 percent (0.68 bu/A).
  • Based on the price of soybean of $9.48 and $24 product + application, the breakeven yield response is 2.53 bu/A

Considerations for 2010
In our research, we have found that foliar disease severity in Iowa seldom reaches high enough levels to impact yield significantly. The warm, wet start to the 2010 growing season, however, has been favorable for brown spot development in the lower canopy. If this weather continues (warm with frequent rains), we could see brown spot move up into the mid-canopy of soybean plants, and impact yield. Thus, a foliar fungicide application at R3 could be a good decision.

Other things to consider before applying a fungicide include economics (e.g., the price of soybean, and price of product plus application). Scout fields to determine disease pressure. Specifically, check on brown spot severity in the mid canopy. Frogeye leaf spot also may occur in the mid-canopy and Cercospora leaf blight in the top canopy. 

Daren Mueller is an extension specialist with responsibilities in the Corn and Soybean Initiative. Mueller can be reached at (515) 460-8000 or by email at dsmuelle@iastate.edu.
dsmuelle

Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be reached at (515) 294-6708 or by email at alisonr@iastate.edu.

Summary: Foliar Fungicide on Corn in Iowa (2007 – 2009)

By Daren Mueller and Alison Robertson, Department of Plant Pathology

Data from corn fungicide small plot trials conducted by Iowa State University faculty and staff, and on-farm trials conducted by the Iowa Soybean Association On-Farm Network, the ISU Corn and Soybean Initiative and the ISU Northwest On-Farm research program were recently collated and summarized:

  • For the total 574 observations, the overall mean yield response was 4.04 bu/A. 
  • Yield response of small plot trials (173 observations) was 4.39bu/A, compared with 3.89 bu/A for on-farm strip trials (401 observations).  
  • The mean yield response in all years was similar: 3.42 bu/A (2007), 3.83 bu/A (2008) and 3.72 bu/A (2009).
  • The mean yield response was higher in corn-following corn trials compared with corn-following soybean trials (4.54 bu/A vs 3.96 bu/A).
  • Applications at VT, R1 or R2 resulted in the highest mean yield response (4.12 bu/A, 4.21 bu/A and 4.17 bu/A, respectively).
  • Greater yield responses occurred with fungicides that contained a strobilurin alone (4.57 bu/A) compared with fungicides that contained a premix of a strobilurin and a triazole (2.85 bu/A).  (Side comment: It will be interesting to see if the trend continues, since the newer premixes contain roughly equivalent amounts of strobilurin active as the strobilurin alone fungicides.)
  • Mean yield response was greatest when disease severity in a field at R5 was high.  If disease severity on the ear leaf at R5 was <5 percent, mean yield response was 4.83 bu/A, however, when disease severity on the ear leaf at R5 was >5 percent, the mean yield response was 9.46 bu/A.
  • Based on the price of corn of $3.72 and $24 product + application, the breakeven yield response is 6.45 bu/A

Considerations for 2010
Before applying a fungicide to corn, do some homework. Consider the price of corn, price of product plus application and drying costs. Consider hybrid susceptibility and the disease history of the field. Scout fields to determine disease pressure. Look on the leaves of the plant below the ear leaf. If you see several spots, and you are growing a susceptible hybrid, you may want to consider spraying a fungicide.

This warm growing season has led to rapid growth and development of corn in Iowa. There are fields of corn across the states that are tasseling. From a disease perspective, nothing is too unusual. Eyespot has again been reported in northwest and north central Iowa, the odd gray leaf spot lesion has been observed on the lower leaves on corn in eastern Iowa and common rust is out there -- you just need to look for it.  In most years in Iowa, leaf diseases of corn start to increase rapidly toward the end of July.  Bearing in mind that the effective period of a foliar fungicide is 14-21 days, this begs the question: should we be fueling the crop dusters now, or should we wait a couple of weeks before applying a fungicide? Unfortunately, we don’t have enough data to answer that question at the moment.  Foliar fungicide trials at Nashua (2007 through 2009) showed that yield response was greatest when a fungicide was applied the last week of July/first week of August. In 2008 and 2009, this corresponded to growth stage R1, but in 2007, the corn tasseled early, and the R2 application resulted in the greatest yield response. 

Daren Mueller is an extension specialist with responsibilities in the Corn and Soybean Initiative. Mueller can be reached at (515) 460-8000 or by email at dsmuelle@iastate.edu.
dsmuelle

Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be reached at (515) 294-6708 or by email at alisonr@iastate.edu.



This article was published originally on 7/12/2010 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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