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Cropping System Diversification Reduces Severity and Incidence of Soybean Sudden Death Syndrome

A research study published in the American Phytopathological Society (APS) Plant Disease journal examined the effects of cropping system diversification on management of soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, that provides some insight into preventing the disease for growers. SDS is a major disease that impacts North and South America. Estimates of annual yield losses in the United States due to SDS have ranged between 0.6 and 1.9 million metric tons during the years from 2006 to 2014, accounting for $200 to 750 million in monetary losses over the same time.

The study included a 2-year, 3-year, and 4-year crop rotation as well as a control. The rotations were as follows:

·      2-year: corn-soybean

·      3-year: corn-soybean-oat (with a red clover cover crop)

·      4-year: corn-soybean-oat-alfalfa

The study also examined differing crop practices, with manure application on the 3 and 4-year rotations and reduced rates of fertilizers, as well as weed management regimens. The study took place between 2010 and 2015.

Analysis shows cropping system diversification can be an effective strategy to manage SDS, especially when incorporating oat, clover and/or alfalfa into an annual crop rotation. Even in years when SDS disease pressure was low, the strategies’ effect was consistent over six years. SDS severity was 17 times higher in two-year cropping system plots, compared with extended and diversified systems, specifically four-year systems. F. virguliforme was isolated at higher frequency from roots from the 2-year system compared with the more diversified systems in 2012 and 2013.

Low levels of SDS in 2011 and 2012 may be explained by the amount of precipitation in those years. Development of SDS is highly dependent on soil moisture, and higher-than-average precipitation, especially during soybean reproductive stages, has been associated with SDS epidemic years. All 4 years of the study when severe SDS symptoms were observed had one or more months during the growing season where rainfall greatly exceeded the monthly average.

When it came to yield results, three and four-year systems showed 40 percent greater yields than in two-year systems. Between 50-87 percent of yield variance was explained by SDS incidence; SDS severity caused 30-70 percent variation in yields.

Extended and diversified cropping systems were correlated with lower F. virguliforme population densities. In both soybean and corn plots sampled in 2012 and 2013, the pathogen’s density in the soil was approximately fivefold greater in the two-year system, as compared to the four-year system. F. virguliforme can survive in soil for years as thick-walled chlamydospores and rotation with corn has been shown to be ineffective for reducing F. virguliforme soil populations or SDS symptoms.

The explanation for higher SDS severity and pathogen presence in the two-year system may be the result of the greater frequency of soybean planting, which creates inoculum build-up in the soil. Corn residue can support survival of the SDS pathogen, which could help explain increased SDS in two year rotations. It is possible alternating corn and soybean is more conducive to SDS than is interruption of that cycle with other crops.

Alfalfa and clover are susceptible to F. virguliforme infection, thus pathogen reduction in the extended rotation may be more closely attributed to the inclusion of oats. In addition, oat used in rotation or as a cover crop has been shown to suppress root rot diseases on certain crops because it produces avenacins, which are active saponin compounds that have antimicrobial activity against several fungal pathogens.

Diversified cropping systems, especially those integrated with livestock production, offer numerous potential environmental and agronomic benefits, including improved soil quality, greater nutrient cycling and retention, greater water-holding capacity, lower rates of soil erosion, and improved control of weeds, diseases, and insect pests. The loss of crop diversity in the Midwestern United States, due especially to reductions in small grain, hay, and pasture production, is linked with significant reductions in livestock production in the region, thus the reduction of manure application to fields. The study asserts that adoption of diversified systems will require growers to learn new practices and adapt to new farming equipment, which could serve to benefit growers financially in the long-run, by limiting yield loss.

Project Type: 
Duration: 
11/05/2018
Category: 

Inoculation Method Impacts Symptom Development Associated with Diaporthe

Soybean (Glycine max) is one of the most important crops in the United States. One production constraint includes the five diseases caused by species of Diaporthe, which can greatly affect yields. During 2014, approximately 1 million metric tons were lost in the U.S. and Canada from Diaporthe-associated diseases.

A research study used many inoculation techniques over five decades to study more than 150 Diaporthe isolates, that can be further separated into five types, from symptomatic soybean stem samples from Iowa and around the region. The researchers’ goal was to examine aggressiveness, disease severity, pathogen recovery and relative treatment effects of each of the five types of isolates to find the more effective ways to research the diseases, and ultimately combat them. Their study suggests different inoculation methods can have a significant impact on the study of symptom development in soybeans, with the toothpick and stem-wound inoculation methods being the most effective techniques on three of the five types to yield research data.

This study was published in 2019. To view the whole study, click here.

Project Type: 
Duration: 
03/04/2019
Category: 

Effect of Tillage and Cultivar on Plant Population, Sudden Death Syndrome, and Yield of Soybean in Iowa

Sudden death syndrome (SDS) affects soybeans around the world and accounts for millions of tons of yield loss in the United States and Canada, ranking it as one of the top 10 yield-reducing diseases of soybean for 16 years. Managing SDS has been difficult with the lack of effective foliar fungicides and completely resistant cultivars, environmental influences and inconsistent management practices.

The researchers in the study aimed to determine the impact conservation tillage had in relation to SDS. Conservation tillage practices have become common practice to preserve soil moisture and prevent erosion, and has shown results in reducing soybean cyst nematode (SCN) populations in the field. Both SCN and SDS have a linked severity, but SDS also has a positive correlation with the soil moisture content.

The field experiments took place in Iowa in a field with a history of SDS and were evaluated for five consecutive years. Data showed there were differences in root rot severity and foliar disease symptoms across the years among different cultivars, but this was not due to tillage. Although yields were different across the years, researchers write that this was not due to tillage and can be explained by seeding rates and sufficient rainfall. The study confirms using resistant cultivars is the best practice to fight SDS, and that seed treatment, SCN management and diversification in cropping systems can aid in disease resistance. In all, incidences of SDS were not dependent on tillage method, as the incidence of disease was consistent throughout the study. SDS resistant cultivars would make the most impact.  

This study was published in 2019. To view the whole study, click here.

Project Type: 
Duration: 
03/04/2019
Category: 

The Effects of ILeVO and VOTiVO on Root Penetration and Behavior of the Soybean Cyst Nematode

Soybean cyst nematode (H. glycines) is the most damaging pathogen of soybean in the United States and Canada. The main management strategy has been to rotate soybean crops with non host crops. However, this strategy has not proved always effective, leaving the need for more study and application of nematode-protectant seed treatments.

The goal of the study was to determine the effectiveness of two different seed treatments on soybeans: ILeVO (fluopyram) and VOTiVO (Bacillus firmus I-1582). These two seed treatments coat the soybean seeds in active ingredients (AI) to help the plants fight different pests and diseases, while also using a less amount of AIs as it’s applied directly to the seed and root area of the plants and not across an entire field.

The researchers grew soybeans and inoculated the roots of the treated and untreated soybeans with H.glycines at various soil depths. The data supports that ILeVO fights against H.Glycines, but gets less effective as the roots grow away from the treated seed. ILeVO also significantly reduced second-stage juvenile (J2) SCNs compared to the untreated soybean seeds. ILeVO treated seeds also significantly reduced the movement of J2 populations compared to the groups of non treated seeds and groups of just the J2 populations. VOTiVO had no effect on the measured parameters in the study.  

This study was published in 2019. For the whole study, click here.

Project Type: 
Duration: 
04/01/2019
Category: 

Identifying Biotypes of Glyphosate-Resistant Horseweed

Since being brought to market in 1974, glyphosate has become the most widely used herbicide in the U.S. From less than 44 million pounds used annually in agriculture in 1995 in the U.S., to over 253 million pounds in 2015, the herbicide has become a heavily relied on weed management tool. This can be explained through the advent of glyphosate-resistant row crops, which allowed growers to commit to using the herbicide on weeds without causing any damage to plants. The conventional usage of glyphosate has resulted in numerous incidences of weed resistance to the herbicide over the last decade.

In order to understand the evolutionary outcomes of weeds subjected to strong, continued selection as a result of prolonged glyphosate use in row crops, researchers from both Iowa and Ohio examined the variations of resistance in self-pollinating Conyza canadensis (horseweed). Their research was published this past summer in the Nature Scientific Reports journal. Researchers chose to focus on horseweed due to the fact that this weed has become prevalent among low-til to no-till crops. Horseweed has become a problem in fields due to the fact that in tillage cropping systems, seeds could not germinate in the low tillage depths. With the availability of glyphosate-tolerant crop breeds, low-till to no-till cropping systems could be implemented, which increased horseweed germination rates. Glyphosate was a widely adopted herbicide used to kill horseweed, which has resulted in high resistance rates. Glyphosate resistant horseweed was first reported in Ohio and Iowa in 2002 and 2010, respectively.

Researchers collected seeds from a single maternal plant from 74 biotypes from six north-central Ohio counties, and 74 biotypes from 32 southern Iowa counties, from agricultural and non-agricultural land (parks and ditches). Researchers targeted counties with large areas of soybean production and known horseweed populations, due to the the weed’s problematic rise in no-till soybean fields.

This procedure was used because maternal seed families are expected to be full-siblings due the fact that horseweed self-pollinates, virtually making copies of itself, to very high representing evolutionary units on which selection for herbicide resistance can act.  These seeds were then germinated and grown, and then sprayed with various rates of glyphosate, and the rates of tolerance to the herbicide were measured.

Results from the study show that nearly all Ohio agricultural biotypes of horseweed (approximately 76 percent) were classified as R4 or extremely resistant (the study ranked tolerant varieties on a scale of 1-4, with R1 being least resistant to glyphosate exposure and R4 being extremely resistant to glyphosate exposure), as were 62 percent of biotypes from the non-agricultural sites. In Iowa, glyphosate resistance levels were more diverse among the seeds collected. R4 biotypes were clustered in south central/southeast parts of the state, where no-till agriculture is more common (R4 biotypes made up only 26 percent of plants). Approximately 45 percent of non-agricultural biotypes were between R1–R4 resistance, with the remainder being susceptible to the herbicide. These results illustrate that horseweed resistance levels to glyphosate can be very high in both states, and that even non-agricultural sites likely serve as a refuge for glyphosate-resistant biotypes.

The study concludes that there are multiple mechanisms through which weeds can be resistant to glyphosate, with those in the R1 biotype having less mechanisms of resistance than those classified as R4, which allows for horseweed to be more tolerant of the herbicide. These mechanisms for horseweed include reduced translocation and vacuolar sequestration, which would be the common injuries that lead to plant death in glyphosate. There have been other studies that show that some horseweed varieties can actually metabolize glyphosate, which is another mechanism of resistance, as well as target site resistance.

Project Type: 
Duration: 
12/05/2018
Category: 

Yard and Garden: Lawn Mowing Tips

April 30, 2014

AMES, Iowa — Proper mowing practices play a vital role in helping to maintain a healthy, sustainable home lawn. Horticulturists with Iowa State University Extension and Outreach answer questions about lawns and lawn mowing. Homeowners and gardeners with lawn questions should contact horticulturists at Hortline by emailing hortline@iastate.edu or calling 515-294-3108.

What is the proper mowing height for a lawn? 

2014 Crop Scouting Competition Open to High School Students

April 28, 2014

AMES, Iowa — The Integrated Pest Management program at Iowa State University is hosting its fourth crop scouting competition on Aug. 5 for teams of Iowa high school students. Organizers announced the 2014 theme, Crop Scouting Innovations, this week along with extending an invitation to participate to teams of high school students (those completing grades 9-12).

Emerald Ash Borer Confirmed in Jasper County

March 28, 2014

DES MOINES – Emerald Ash Borer has been positively identified in a residential tree in Newton in Jasper County from a larva sample collected on March 20, 2014. EAB kills all ash tree species and is considered to be one of the most destructive tree pests ever seen in North America.
 

Emerald ash borer confirmed in Keokuk County

January 30, 2015

Iowa map of emerald ash borer confirmations

DES MOINES – Emerald Ash Borer (EAB) has been positively identified in the Iowa community of Hedrick in Keokuk County. EAB kills all ash tree species and is considered to be one of the most destructive tree pests ever seen in North America.

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