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2/17/2014 - 2/23/2014

Efficacy Tests of Foliar Fungicides on Soybean Diseases and Yield during 2012 and 2013 Growing Seasons in Northeast Iowa

By Shrishail S. Navi, Department of Plant Pathology and Microbiology

The foliar, stem and root diseases of soybean are significant components of yield loss for crop producers. Use of fungicides is one of the options in management of soybean diseases.  Fungicide use in soybean has increased from <1 percent in 2002 to 11 percent of soybean planted acres in 2012 in 20 soybean-producing states (Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, North Carolina, North Dakota, Ohio, South Dakota, Tennessee, Virginia and Wisconsin) (USDA-NASS). The objective of these trials was to test the efficacy of various foliar fungicides on disease control and yield during 2012 and 2013 growing seasons.

 

Materials and methods

Two trials were conducted in each growing season, 2012 and 2013. Trials were set up in a randomized complete block design with four replications each with 10-ft-wide (four 30-inch rows) × 45.5-ft-long plots at the Northeast Research and Demonstration Farm, Nashua, IA. Trial-1 assessed the efficacy of various fungicides for disease control and yield (Tables 1 and 2) and Trial-2 assessed the efficacy of several fungicides and application timings for control of soybean diseases during 2012 and 2013 cropping seasons (Tables 3 and 4).

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Field operations: Trial-1 in 2012 was no-till planted with Asgrow Brand AG24-31 and in 2013 was planted in a convention tillage system (fall chisel plow, spring field cultivate) with NK Brand S20-Y2 at 188.8k PPA in 30 in. row spacing with a Kinze 3000 planter on May 17 and June 17, respectively (previous crops were corn). Trial-2 in 2012 was no-till planted with NK Brand S25-R3 (previous crop was oats) and, in 2013, no-till planted to NK Brand S25-T8 (previous crop was corn) at 188.8k PPA in 30 in. row spacing with a Kinze 3000 planter on May 20 and June 17, respectively.  In all trials, fungicides were applied using CO2 backpack (10 ft hand boom/ XR8003 tips) as per the treatment details and protocols provided by the companies (Tables 1 to 4). To maintain weed free (including glyphosate-resistant water hemp) plots, pre- or post-emergence herbicides (Outlook, Zidua, Roundup WeatherMax and Fusion) were sprayed at recommended rates. To control spider mites, Lorsban insecticide (1.5 pint/Ac) was used in 2012 and in 2013 soybean aphids were controlled with Warrior II insecticide (1.96 oz/Ac).  Plots were harvested using a John Deere 4420 combine with Shivvers grain moisture meter and Avery-Weigh Tronix weigh scale indicator and yields were adjusted to 13% grain moisture (Tables 1-4).

Fungicides: Four Triazole products (Domark, Proline, Tilt and Topguard), three Strobilurin (Gem, Headline and Quadris) and three mixtures of active ingredients of Strobilurin and Triazole (QuiltXcel, Stratego YLD and Priaxor) were tested (Tables 1-4).

Evaluation for diseases: Pre- and post-fungicide spray diseases ratings were recorded weekly from one week before application through one week before the harvest however, only mean final percent disease severity and incidence are presented in Tables 1 to 4.

Data analysis: Data was analyzed using SAS.

 

Results and discussion

The following diseases were observed in Trial-1 during the 2012 growing season: bacterial leaf blight (trace), frogeye leaf spot (trace), sudden death syndrome, white mold (trace) and Soybean vein necrosis (Table 1). Soybean vein necrosis (Fig 1) is a new disease (Smith et al., 2013). There was no evidence of an effect (P<0.05) of fungicide on disease incidence and severity, but some fungicides reduced (P<0.05) defoliation compared to the unsprayed control (Table 1). Although most fungicide treatments yielded greater than the unsprayed control, no significant (P<0.05) yield differences were noted when comparing sprayed versus the unsprayed control treatment (Table 1). The mean response to fungicides was 2 bu/ac (range -3.26 to 6.32 bu/ac) advantage over unsprayed control (Table 1). In Trial-1 during 2013, white mold was observed. There was no effect of treatment on yield (P<0.05) although mean yield response across all the fungicide treatments was 2.2 bu/ac yield advantage (range 0.86 to 3.82 bu/ac) compared to the unsprayed control (Table 2).

Fig 1. Symptoms of Soybean Vein Necrosis.

 

Diseases observed in Trial-2 during the 2012-growing season were downy mildew and Soybean vein necrosis (Table 3) and, in 2013, white mold and sudden death syndrome (Table 4). Downy mildew incidence and severities in all the treatments was 10-15 percent and that of Soybean vein necrosis 5-10 percent incidence with 1-5 percent severity.  In both 2012 and 2013, no effect (P<0.05) of fungicide application timing on yield was evident (Table 3 and 4). Variation in yields may be due to various factors like weather conditions, crop rotation, disease pressure, variety planted and efficacy of the products.

Remarks: The 2012 (June – September) and 2013 (July – September) growing seasons in Iowa were very dry with below normal rainfall.  Consequently, white mold, sudden death syndrome and foliar disease incidence and severity were low, and it was difficult to detect evidence of an effect of fungicide on disease (Tables 1 to 4). Similarly, no effect of application timing or multiple application timings were detected (Tables 3 and 4). Although, some treatments have shown higher yield advantage of 4 to 6 bu/ac, on average, the mean yield of soybean to fungicide applications was approximately 2 bu/ac, which agrees with similar reports of Mueller, et al., (2014). Products tested in these studies do not imply endorsement of one company over another, nor did discrimination intended against any similar products.

 

Acknowledgements

Thanks to Ken Pecinovsky, Farm superintendent, Northeast Research and Demonstration Farm, Nashua for his assistance.

 

References

Smith, D.L., Fritz, C., Watson, Q., Willis, D.K., German, T.L., Phibbs, A., Mueller, D., Dittman, J.D., Saalau-Rojas, E., and Whitham, S.A. 2013. First report of soybean vein necrosis disease caused by soybean vein necrosis-associated virus in Wisconsin and Iowa. Pl Dis. 97:693.

Mueller, D., Pierson, W., and Wiggs, S. 2014. Evaluation of foliar fungicides and insecticides on soybean in 2013. ICM news Jan 8, 2014.

 

Shrishail S. Navi is an associate scientist working on soybean diseases.

Pesticide Record Keeping App Now Available For Android

By Kristine Schaefer, Department of Entomology

The Iowa State University (ISU) Extension and Outreach  Pesticide and Field Records app is now available to Android operating system phone and tablet users. The app, previously only available for iPads, was developed to help producers and agriculture businesses record and maintain pesticide application information. The free app allows users to link information to specific field locations using satellite mapping and document pesticide application information needed to comply with state and federal record keeping requirements. The app also features a product search option that lists Environmental Protection Agency (EPA) product registration numbers and identifies restricted use products.

Development of the app was funded by the ISU Extension and Outreach Pest Management and the Environment program and a grant from the EPA under assistance of the Iowa Department of Agriculture and Land Stewardship Pesticide Bureau. The app can be downloaded from Google Play for android operating systems and from iTunes for iPads.


Kristine Schaefer is a program manager in the Department of Entomology. She can be reached at 515-294-4286 or schaefer@iastate.edu.

New ‘Focus on Soybean’ Talk Offers Knowledge, Management Tactics for Battling Soybean Root and Stem Rots

By Alison Robertson, Department of Plant Pathology and Microbiology
 
If you attended any Iowa State University Extension and Outreach events in the past two years, you’ll have heard the word "Oomycetes” come up, particularly with reference to seedling diseases of soybean (and also corn). Phytophthora sojae and Pythium species are oomycetes, and they can result in stand loss early on in the season if conditions are particularly wet.
 
While resistant varieties are the main defense against seedling blight and root and stem rot caused by P. sojae, management of Pythium requires use of a combination of management practices that include seed treatments, tillage and soil moisture management.
 
To help growers, crop consultants and extension educators improve their knowledge, understanding and, most importantly, management of oomycetes, Dr. Jim Kurle, assistant professor of plant pathology at the University of Minnesota, produced a webcast presentation, “Oomycete Diseases of Soybean and Current Management.”
 
This webcast, published in the Plant Management Network’s Focus on Soybean resource, discusses the biology of Phytophthora and Pythium pathogens, as well as the environmental factors that influence disease development and their unique aggressive characteristics. Management of diseases caused by oomycetes are also discussed, emphasizing the integration of resistance, chemical controls and cultural practices.
 
The research in this presentation was funded through a USDA Agriculture and Food Research Initiative (AFRI) grant on oomycete diseases (www.oscap.org). Through links and attachments embedded in the webcast player, this presentation leads viewers to other important resources funded through this grant from various universities and programs.
 
This 20-minute presentation is fully open access thanks to funding associated with this grant.
 
This talk and other Focus on Soybean presentations can be viewed at www.plantmanagementnetwork.org/fos. Webcasts on a variety of other crops can be found in PMN’s Education Center.

Focus on Soybean is a publication of the Plant Management Network, (www.plantmanagementnetwork.org), a nonprofit online publisher whose mission is to enhance the health, management and production of agricultural and horticultural crops. PMN achieves this mission by publishing applied, science-based resources for growers, consultants and applied researchers.

Alison Robertson is an associate 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.

Palmer Amaranth in Iowa Update

By Bob Hartzler, Department of Agronomy

Palmer amaranth is native to the Southwest United States, but has been expanding its range for at least 50 years. Most recently it has moved into the Midwest and has been reported in all Cornbelt states except for Minnesota and the Dakotas. This article will provide information on known infestations in Iowa; it is likely there are additional infestations that have not been brought to our attention.

The first confirmed finding of Palmer amaranth in Iowa was near Modale in Harrison County in August 2013. It appearedthe  Palmer amaranth was introduced in two fields where sludge has been repeatedly applied due to the soils being unsuitable for crop production. The sludge was imported from Nebraska, but it does not appear to be a likely source of weed seed. We suspect the seed came as a hitchhiker on trucks bringing the sludge into Iowa. It is likely the Palmer has been present at this site for several years, and it has spread to several adjacent fields. A second, much smaller infestation was later found approximately 40 miles from the initial site. While it probably is too late to eradicate the Palmer at the Modale site, significant efforts are being made to contain the infestation.

Muscatine County was the next confirmed Palmer amaranth infestation. The field is on a sandy soil in the flood plain of the Cedar River. The likely source for Palmer amaranth at this site was swine feed. The infestation appears to be limited to a single field and the adjacent ground. The farmer is taking the problem seriously and there is a good likelihood of eradicating the weed from this location. 

Two counties in the southwest corner of Iowa (Fremont and Page) were the next findings, both adjacent to commercial grain elevators.  The likely source of Palmer amaranth at these sites is grain trucks that have been to areas in Nebraska or Missouri with Palmer amaranth. 

The final report of Palmer amaranth in Iowa was received late in 2013 from a farmer in Davis County. He reported that the operation brings in cotton seed as a feed supplement for a cattle operation and believes this is where the Palmer amaranth originated.

I have not been to the last three infestations; therefore, I am not aware of the extent of the infestations or the efforts being made to eradicate/contain the Palmer amaranth.

Due to long-distance movement of equipment, grain and other agricultural materials, it is inevitable that new infestations of Palmer amaranth will be discovered. Knowing how to identify Palmer amaranth and keeping an eye out for ‘odd pigweeds’ is the best tool to limit the rate of spread of Palmer amaranth. We appreciate being made aware of any new findings of Palmer amaranth in the state.


Known infestations of Palmer amaranth.  Feb. 2014.

 

Bob Hartzler is a professor of agronomy and weed science extension specialist with responsibilities in weed management and herbicide use. He can be reached at hartzler@iastate.edu or 515-294-1923.

 


What is soil health and how can we improve it?

By Mahdi Al-Kaisi, Department of Agronomy

The term soil health  is used interchangeably with soil quality, but in this article, I prefer the use of soil health because it is a more appropriate term in defining soil functions as a living and dynamic natural system. Soil health is a condition, or status, of the soil at a certain place and in a specific environment as compared to a certain reference or benchmark condition. However, the concept of soil health can vary in use based on the priorities placed on different soil functions. Therefore, the concept of soil health should be understood within the context and intention of the users of the soil health term, their goal and the boundaries in which they are working.

In general, soil health, as a measure of soil functions, can be defined as the optimum status of the soil’s biological, physical and chemical functions. This means healthy soils can sustain plant and animal productivity and soil biodiversity (Fig. 1), maintain or enhance water and air quality, and support human health and wildlife habitat.  The underlining principle for a healthy soil is not just a medium to grow plants, but rather a living, dynamic and changing environment that is influenced by what we do and the practices we adopt as human activities. If we agree that the soil is a dynamic and living organism, then we need to apply the human health principles as its metaphor. We, as humans, strive for healthy bodies to perform our tasks most efficiently, and so do soils. 

Fig. 1. Soil food web (source: NRCS-USDA).

 

To understand soil health and how different human activities (i.e., cultivation, land use, etc.) impact it, we need to understand the soil. The soil is a heterogeneous natural body, which basically consists of solid particles (mineral particles), organic matter, water and air. The soil also contains micro and macro organisms that support plant, animal and human life. Its functions as a heterogeneous natural body consist of providing support as the medium for plant growth, the storage and supply of water and nutrients, the purification of pollutants, and wildlife habitat. Organic matter is one of the smallest components of the soil system, but plays an essential role in maintaining soil health/functions. Soil organic matter is derived from living organisms, such as plants and animals, and their byproducts in the soil environment. When organic matter breaks down, it is transformed into different pools as sources of plant nutrients at various degrees of availability and eventually forms the final product called humus. This product becomes the central building block of healthy soil. Therefore, the maintenance of soil organic matter is critical to the health and productivity of the soil; providing a stable soil physical structure for water storage, nutrient exchange with plant roots, aeration and a healthy microbial community will enhance soil health for healthy plant growth.

In agricultural systems, such as row cropping systems, significant stress is exerted on soil functions through management practices such as soil tillage, chemical application and continuous mono-cropping systems. However, management practices, such as soil conservation systems, including no-tillage and extended crop rotations can mitigate negative effects on soil health/functions. A no-till system can restore soil health over time by improving, for example, soil infiltration, organic matter, water storage, soil structure, etc., which are indicators of soil health. The extended crop rotations that include small grains, legumes and cover crops will increase soil biodiversity and protect the soil surface physically during the off season and provide organic carbon input. The introduction of perennials on marginal land can increase wildlife habitat and improve the biological and physical components of soil health. These practices are measures to build healthy soil, which can improve both productivity and the environment.

When the soil is managed as a natural heterogeneous ecosystem by diversifying the input of plants, animals and wildlife, we incorporate the natural order of soil generation principles that led to the forming of the soil. The challenges we face in many parts of the world nowadays are the outcomes of human activities that affect soils by accelerating soil degradation and soil erosion and decreasing water quality and quantity, which are future food security challenges. These challenges can be mitigated through thoughtful and balanced management practices that enhance soil health sustainably as the first step in establishing potential solutions for these problems.


Mahdi Al-Kaisi is a professor of agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at malkaisi@iastate.edu or 515-294-8304.



This article was published originally on 2/24/2014 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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