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8/1/2011 - 8/7/2011

Will Goss’s Wilt be the “Disease of the Year” in 2011

By Alison Robertson, Department of Plant Pathology and Microbiology

Reports of Goss’s wilt have been coming in hard and fast this past week. The disease appears to be widespread north of I-80. Despite the hot, dry weather, the disease has progressed rapidly in the field. 

We have been visiting a field near Gilbert and collecting data on the disease. The photos below show the severity of the disease when we first visited the field on July 21 (Fig 1), and on a return visit on Aug. 2 (Fig 2). They were taken in approximately the same place in the field. Across the majority of the field (approximately 95 percent), every plant shows characteristic leaf blight symptoms of the disease (Fig 3). In the headlands, which are bordered by trees, incidence of the disease (percent of plants with symptoms) is as low as 10 percent. Scattered throughout the field are isolated wilted dead plants (less than 1 percent incidence; Fig 4).  We will be monitoring disease progress in this field collecting data to calculate yield loss estimates.

With grain prices so high, it’s difficult to watch a disease come in and rob yield. Not surprisingly, growers are looking for anything to protect yield potential. I am aware of three products that grower’s are trying, and have had questions regarding their efficacy against Goss’s wilt.

Procidic is advertized as a broad spectrum fungicide and bactericide. The active ingredient is citric acid. There is no published data that I am aware for Procidic. Plant Disease Management Reports contains reports on the effect of citric acid on fungal pathogens of horticultural crops, but has no reports of results against bacterial diseases, and no reports on corn. Procidic is labeled for use in Iowa to control Goss’s wilt. The field we are monitoring in Gilbert has had an application of Procidic, as well as an earlier application of Stratego YLD®. We plan to monitor the effect of both products on Goss’s disease development and general plant health.

Another product that has been suggested for use to manage Goss’s wilt is Kocide®. Since this product is not labeled for use on corn to manage Goss’s, it should not be used. Korus et al. (2010) evaluated Kocide® 3000 and Headline® for Goss’s wilt control on two hybrids (one susceptible and one resistant) in Nebraska in 2009. The trial was inoculated with the Goss’s wilt bacterium at growth stage V6/V7. Treatments were applied six days before inoculation, four hours after inoculation or 24 hours after inoculation. Goss’s wilt disease was slightly reduced on a susceptible hybrid with an application of Kocide 24 hours after inoculation, but no differences in yield were detected between this treatment and the untreated, inoculated control. On the resistant hybrid, no treatment differences were detected.

A third product I have heard about that some growers are trying is also a copper-based product called Intercept. There is very little information available on this product. Apparently it has been used successfully to control citrus canker in Florida. Citrus canker is also caused by a bacterium. There were also some fields in Iowa that were sprayed with this product in 2010. There is no published information available on the efficacy of Intercept against Goss’s wilt or citrus canker. I am aware of a couple of fields that have been sprayed in Iowa, and I will be evaluating those fields for the product’s efficacy.

I encourage anyone who tries either of these products to leave one, preferably more, unsprayed strips in the field and meticulously monitor disease development and collect yield data. The check strips should be left in areas of the field that are representative of the entire field.

Management of Goss’s in 2012

The bacterium that causes Goss’s wilt, Clavibacter michiganensis subsp. nebraskensis, survives in infested crop residue. Therefore recommended management practices include growing resistant hybrids, crop rotation and residue management. Continuous corn production together with minimum tillage practices have in part contributed to the epidemic of Goss’s wilt we are witnessing in 2011. Other factors include susceptible germplasm and stormy weather.


goss's wilt
Figure 1:  Goss’s wilt when we first visited the field 21 July, 2011.

goss's wilt august
Figure 2:  Goss’s wilt severity had greatly increased by 2 August, 2011.

leaf blight symptoms of goss's wilt
Figure 3:  Typical leaf blight symptoms of Goss’s  wilt

Goss's wilt symptoms
Figure 4:  A wilted plant surrounded by plant’s with Goss’s leaf blight symtoms


Korus, K.A., Jackson, T.A., Behn, J.L. and Schleicher, C. 2010. Evaluation of foliar treatments and application timings for management of Goss’s bacterial wilt and blight of field corn in Nebraska, 2009. Plant Disease Management Reports 4:FC083

Alison Robertson is an associate professor in the Department of Plant Pathology and Microbiology with extension and research responsibilities; contact her at or phone 515-294-6708.

Flood Damaged Crops, Crop Insurance Payments and Lease Contracts

By William Edwards, Department of Economics

Some Iowa corn and soybean producers are facing substantial if not complete crop losses due to flooding. In particular, many acres of crops in the Missouri River Valley have been under water for a month or more this year. Fortunately, nearly 90 percent of Iowa’s corn and soybean acres are protected by multiple peril crop insurance.

Crop Insurance

Most Iowa producers purchase crop insurance policies with a 75 or 80 percent level of coverage. This means that if crops are a total loss, the producer must stand the first 20 to 25 percent of the loss. However, in 2011 nearly 90 percent of the crop acres insured in Iowa were covered under Revenue Protection policies, which offer an increasing guarantee if prices increase between February and October. So far, this has added over a dollar per bushel to corn guarantees and about $0.25 per bushel to soybean guarantees. Moreover, since Revenue Protection policies are settled at the average nearby futures price during the month of October, rather than local cash prices, farmers will receive a bonus equal to the fall grain basis in their area.

Producers with crops that have been totally destroyed by flooding will not have to incur the variable costs of harvesting. This could save around $20 per acre for soybeans and perhaps $70 per acre for corn, depending on potential yields and drying costs. Nevertheless, even producers who carried insurance at an 80 percent coverage level could be looking at net revenues of at least $100 per acre below those obtained from normal yields this year.

Potential Losses

For example, assume an insured tract has an expected corn yield of 160 bushels per acre and an insurance proven yield of 150 bushels per acre. A normal crop marketed at $6.50 per bushel would bring $1,040 per acre. The insurance indemnity payment for an 80 percent RP guarantee, zero yield, and an October futures price of $7.00 would equal 150 bu. x $7.00 x 80% = $840. Saving $70 in harvest costs would give an equivalent of $910 per acre, or $130 below the value of a normal crop.

For soybeans, assume both the expected yield and the proven yield are 50 bushels per acre, and the crop could be marketed at $13 per bushel. Gross income for a normal crop would be $650 per acre. The insurance payment for a complete crop failure and a $13.75 October futures price would be 50 bu. x $13.75 x 80% = $550. Savings of $20 in harvesting costs brings the equivalent of $570 per acre, or $80 below the value of a normal crop.
In many cases, of course, flooded acres will make up only a portion of the insured unit, so production from non-flooded acres will be averaged in with the zero yields from the flooded acres.

The real question is how much will it cost to clean up fields and bring them back into production next year? Iowa farmers have not had prior experience with fields being under water for extended periods of time, so effects are difficult to estimate. Problems will range from physically removing debris to leveling eroded areas to restoring fertility.

Rental Contracts

What do these questions imply for rental contracts? A great deal of uncertainty, for one thing. Lease agreements in Iowa continue in effect for another year under the same terms if they are not terminated on or before September 1. Either an owner or a tenant can terminate a lease. Operators who rented flood covered land this year may want to think seriously about whether they want to rent those acres next year, especially at the same level of cash rent. Leases can be terminated by delivering a notice in person to the other party, sending it by certified mail, or (rarely) publishing it.

Landowners will have to bear the burden of mitigating flood damages—that goes with owning property. But, a better solution may be for renters and owners to work together to repair the damage and bring the land back into production. Farm operators may have access to machinery that can help accomplish the job that owners do not. In return, tenants should be compensated for their efforts, either directly, through a significant discount on the 2012 rent, or with a long-term lease.

Next Year

In some cases there may be doubt as to whether land flooded this year can even be planted next year. Risk Management Agency rules state that land must be physically available for planting to be insurable. Land that cannot be planted due to weather events that occurred before the sales closing date (March 15 in Iowa) is not eligible for prevented planting payments. When operators report their 2011 production, they can request that their 2011 yield histories reflect a value equal to 60 percent of the county “T-yield” rather than a zero or very low yield.

Close communication and cooperation between owners, crop insuracne agents and renters can be a “win-win” strategy in the long run, but recovery will likely take several years. Additional information about managing flood damaged cropland will be available on the ISU Extension and Outreach flooding website as the waters recede and the situation is assessed.


William Edwards is an Iowa State University professor of economics with extension responsibilities in farm business management. Edwards can be contacted at (515) 294-6161 or by emailing

ISU Extension Offers Ag Drainage School

By Brent Pringnitz, Department of Agronomy; Matt Helmers, Department of  Agricultural Engineering and Biosystems Engineering; and Greg Brenneman and Kapil Arora, Agricultural Engineering specialists

Agricultural drainage is becoming increasingly important due to the critical role it plays for Iowa's bio-economy. Drainage systems that are properly designed and operating are essential to achieving maximum agricultural production capability. These issues will be addressed at the Iowa Drainage School Aug. 23-25 at the Borlaug Learning Center on the Northeast Research and Demonstration Farm near Nashua, Iowa.

People planning to install a new drainage system or retrofit an existing system will want to attend this school. The workshop will focus on drainage design, economics of drainage, water management and legal issues related to drainage.

The intent of the Iowa Drainage School is to provide training about

  • Agricultural drainage concepts
  • Planning and laying out drainage systems, including surveying a profile
  • Calculating tile line sizes and spacing using actual field data
  • Making connections and setting up drainage control structures
  • NRCS and IDDA regulatory considerations
  • Fixing common drainage system issues

Drainage contractors, landowners, professional engineers and consultants, NRCS professionals, county administrators, and others who are involved in making drainage design decisions within their respective businesses and organizations are invited to attend.

This is a three-day school with each day including a combination of hands-on training, lecture and discussion, and problem solving using examples. By attending this school, participants will be able to plan and layout subsurface drainage systems and work out project costs.

Registration fees for this three-day school are $300 per person if registered by midnight, Aug 12. Late registration is $350 and must be received by Aug 19. Class size is limited to 40 participants and pre-registration is required. Registration fees include meals indicated on the agenda, refreshments and handouts.

Additional information, a detailed agenda, and online registration are available at


Brent Pringnitz is an ISU Extension program specialist. He can be reached at the Field Extension Education Laboratory, (515) 432-9548 or Matt Helmers is an associate professor in the Department of Agricultural and Biosystems Engineering with research and extension responsibilities. Helmers can be reached at 515-294-6717 or Kapil Arora and Greg Brenneman are ISU Extension Agricultural Engineering specialists. Arora can be reached at 515-382-6551 or; Brenneman can be reached at 319-337-2145 or

This article was published originally on 8/8/2011 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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