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5/14/2012 - 5/20/2012

Bean Leaf Beetles are Moving to Soybean

By Erin Hodgson, Department of Entomology

In March, I predicted low overwintering mortality of bean leaf beetles based on our mild winter. You may have noticed adults became active in alfalfa starting in April. They are strongly attracted to soybean and will slowly move as plants emerge this month. The adults fly short distances (less than 167 feet on average) and infestations can be highly aggregated. Some research plots around southern and central Iowa have decent numbers feeding on unifoliates.

Bean leaf beetle is easily disturbed and will drop from plants to seek shelter in soil cracks or under debris. Sampling early in the season requires you to be sneaky to estimate actual densities. In some cases, you may just see leaf defoliation and not the beetles (Photo 1). Although overwintering beetles rarely cause economic damage, their presence may be an indicator of building first and second generations later in the season.

soybean leaf defoliation
 
Photo 1. Soybean can compensate for early-season defoliation by bean leaf beetle. Photo by Erin Hodgson (May 17, 2012 near Ames, Iowa).

Maybe more important than defoliation, bean leaf beetle can vector bean pod mottle virus in soybean. There can be a reduction in yield in bean pod mottle virus-infected plants resulting from reduced seed size and pod set. This effect on soybean yield is most severe when soybeans are infected as seedlings. Bean pod mottle virus can cause a bleeding hilum or seed coat discoloration, and so food grade beans are at a higher risk for grading penalties (Photo 2). Fields with a history of persistent infestations and bean pod mottle virus should consider an insecticidal seed treatment. 
 
seed symptoms

Photo 2. Soybean diseases, such as bean pod mottle virus, can cause seed coat discoloration or a bleeding hilum. Photo by Jeff Bradshaw.

Overwintering beetles should be suppressed by the high adoption rate of insecticidal seed treatments in Iowa. But if first and second generation beetles become an issue, I will provide updated treatment thresholds for higher market values. For more information about bean leaf beetle biology, visit this ISU Soybean Insects Guide website.


Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847.

Seedling Diseases Reported in Corn and Soybean

By Alison Robertson and Gary Munkvold, Department of Plant Pathology and Microbiology

Several reports of losses in corn stand due to seedling disease are being reported from eastern Iowa.  In the May 15 Crop Minute Roger Elmore reminds us that we have had a long corn planting season that began in mid-March and is still going in mid-May. Most of the seedling disease issues that are being reported are from fields that were planted April 23 to 27, just before we had a period of cold wet conditions and soil temperatures dipped back down below 50 F.

What should you be looking for?
Affected seedlings tend to be scattered in the wetter areas of the field. Growth stage ranges from the V1 to V3 growth stage. The seedlings are yellow and wilted, or dead (Figure 1).  When the seedling is dug up, the mesocotyl is rotted (Figure 2) and nodal root growth development may be poor. 

Remember, the mesocotyl is very important in the early growth of a corn seedling.  It acts as a pipeline for water and nutrients between the radicle and seminal root system and the growing point of the developing seedlings. Nodal roots become visible at around V2 but only become the dominant root system at around V6 (Abendroth et al., 2011).


Figure 1. Damped off corn seedling (M.Carlton)

 


Figure 2. Damped off corn seedling showing the rotted mesocotyl (M.Carlton)


What pathogen(s) is responsible?

Samples received by the Iowa State University Plant Disease and Insect Clinic and Robertson Lab have been plated. Thus far the pathogen causing seedling disease appears to be Pythium spp. 

There are numerous species of Pythium that can affect corn, and many of these species also cause disease on soybean. Over the next few months, the Robertson Lab will identify the isolates collected down to the species level. We will also assess the fungicide sensitivity of the isolates we collect from corn since research from Ohio State University (OSU) found a significant variation in sensitivity to commonly used seed treatment fungicides within and amongst species. Thus, a seed treatment might provide adequate protection against seedling disease in one field, but may not be sufficient in another field.

Numerous Fusarium species and a few Rhizoctonia spp. may also cause seedling disease of corn. Similarly, research at OSU has found sensitivity to seed treatments varies within and amongst Fusarium spp.

Soybean damping off
We have just received our first samples of soybean damping off. These were very early planted beans from two fields in northern Iowa. We will be plating these samples to determine the pathogen(s) responsible. Seed quality may have been an issue in these two cases. Information from several sources, including the Iowa State University Seed Testing Laboratory, suggests that soybean seed quality is below average this year, probably due to the overly dry conditions during the harvest season. It is well-known that lower quality soybean seed is more vulnerable to seedling disease, and is more likely to respond to fungicidal seed treatment.

Survey of seedling diseases of corn and soybean
This is a reminder that I am again looking for soybean fields with seedling disease issues for a North Central Region research project on soybean seedling disease that is being funded by USDA-NIFA and the United Soybean Board.  In collaboration with other researches in the North Central region, the Robertson and Munkvold labs are identifying the major species causing seedling disease on soybean in the region, what environmental factors favor infection by each species and subsequent disease development, and assessing the sensitivity of each species to seed treatment fungicides. In our soybean seed treatment studies, which are being funded by the Iowa Soybean Association, we are also collecting seedling pathogens that will be identified and screened for fungicide sensitivity.

In addition to diseased soybean seedlings, we are also interested in collecting samples from cornfields with damping off for similar studies.

If you know of a field with seedling disease issues, please contact me at 515-294-6708 or alisonr@iastate.edu so we can coordinate sampling the field. 

 References
Abendroth et al. 2011. Corn growth and development


 

Alison Robertson is an associate professor in the plant pathology and microbiology department with extension and research responsibilities; contact her at alisonr@iastate.edu or phone 515-294-6708. Gary Munkvold is a professor of plant pathology and seed science endowed chair in the Iowa State University Seed Science Center with research and teaching responsibilities in seed pathology. He can be reached at (515) 294-7560 or by email at munkvold@iastate.edu.

2012 Western Bean Cutworm Cooperators Needed

By Adam Sisson, Integrated Pest Management

Western bean cutworm (WBC) is a pest of corn that has expanded it’s range across Iowa and states east of Iowa. Beginning in 2003, Iowa State University set up a network of pheromone traps to monitor WBC. This provides yearly moth emergence data to enhance scouting efforts.

Cooperators are needed in 2012 to monitor traps and record data to the Iowa State University Western Bean Cutworm Monitoring Network website. Producers interested in becoming part of the monitoring network this year, or those who want more information should email wbcutworm@iastate.edu. To take part in the monitoring, include postal mailing address in the email message.

The trapping program consists of:

  • Building moth traps out of one-gallon milk jugs and pheromone lures supplied by Iowa State University.
  • Monitoring traps every other day for new moth captures (Fig. 1).
  • Reporting trap data to the website.
     


Figure 1. Western bean cutworm adult moth

 

Adam Sisson is an Integrated Pest Management program assistant. Sisson can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899.

Crop Minute - Long Corn Planting Season

The long corn planting season this year – from mid-March through May has the benefit of spreading risk. Roger Elmore, extension corn agronomist, reminds producers to keep in mind the "growth stage" of the field they are scouting  – as they may have fields at three different stages of growth. Decisions on herbicide applications and other management practices are based on growth stage.

Conservation Practices Save Soil and Sustain Agriculture

By Mahdi Al-Kaisi, Department of Agronomy

“The nation that destroys its soil destroys itself”— Theodore Roosevelt

Conservation planning is becoming increasingly necessary, especially with the current weather challenges we are experiencing and the unpredictability, intensity and duration of rain events. Soil erosion is always associated with tillage intensity in the spring when land is most vulnerable. The vulnerability is created by the lack of vegetation cover or residue to protect the soil surface from the intensity of rain. 

Many factors contribute to this problem, but tillage is considered the primary one. Another concern is the conversion of Conservation Reserve Program (CRP) land back to agriculture production. Conversion can significantly setback soil quality and environmental benefits gained by many years in CRP. Land in CRP is generally enrolled for production and environmental reasons: row crop production can be marginal and damaging to both soil and water quality. Thus, enrollment in CRP prevents these highly erodible lands with marginal productivity from further deterioration.

Soil conservation practices can play a significant role in sustaining soil quality as climate change imposes additional stress on natural resources, including soil. Over 80 percent of Iowa's landscape is in agriculture production activities, such as row crops, pasture and forestry. Therefore, in order to sustain soil quality and maintain high agriculture productivity, conservation practices need to be part of the portfolio of our agriculture systems, not only for environmental concerns, but for economic viability. Economic viability comes through the increase in the resiliency of agriculture production systems. Iowa has the largest percentage of active agriculture land in the nation. Coupled with intense management, this raises concerns about the resulting impact on soil and water quality when conservation practices are absent.

Many producers have voluntarily adopted conservation practices that lessen the negative effects of agricultural activities on the environment. The outcome has been significant over the past few decades, with benefits in crop productivity, more efficient use of time and equipment, and a reduction in soil erosion. However, the current soil erosion level stands at approximately five tons per acre and in some areas in the state can exceed that rate by 10 fold or more.

Implement and target conservation practices in sensitive areas

To minimize the impact of soil erosion on soil and water quality we must examine and sustain our efforts of implementing and targeting conservation practices in the most sensitive areas. Current commodity prices, coupled with promotion of tillage technology, present significant challenges to producers who want to integrate conservation practices into their systems. But the reality is conservation practices if treated in a system approach and not as single separated practices can provide high economic and environmental rewards.

In order to promote a conservation ethic and land stewardship, producers should consider adopting conservation plans that are:

• practical,
• site specific,
• achieve the intended objectives,
• and are easily integrated within an overall production system.

These conservation plans can include, but are not limited to, no-till, strip-tillage, cover crop, perennials, grass waterways, terraces, buffer strips, pasture erosion control, manure application plan, soil testing, etc. Conservation planning and implementation of such practices need to be considered carefully as solutions to reduce potential row cropping system effects on soil and water quality. Conservation practices must be an integral and essential component of nutrient reduction and sediment and nutrient loading plans as one of the effective solutions in protecting soil and water quality.

The bottom line is that we must sustain one of the greatest strengths of Iowa agriculture, our soil.


Contour cropping in southwest Iowa.

 


Mahdi Al-Kaisi is a professor in 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.

Conservation System Management Considerations

By Mahdi Al-Kaisi, Department of Agronomy 

Managing conservation systems at the right field moisture is a critical factor to ensure successful outcomes. Plants showing a delay in growth may be explained by improper planting depth, soil surface or side-wall compaction due to planting in wet soil conditions, or nutrient deficiencies such as phosphorus or potassium. Seedbed preparation along with tillage or planting equipment settings, have a combined effect on plant performance.

It is very difficult to isolate the exact cause of poor plant performance when soil conditions and management practices are not at their best. While scouting fields and evaluating soil conditions, producers need to check soil moisture below the soil surface at the seed depth as well as where the nodal root system gets established – at a depth of three-fourths to 1 inch deep under normal conditions. Adequate soil moisture with adequate nutrient availability, friable seedbed without sidewall compaction, can provide a good growth environment for root systems. 

To ensure the successful transition from conventional to no-tillage or minimum tillage systems, nutrient management considerations including starter fertilizer and timing of nutrients application are critical. A proper fertilizer program is necessary. Plant needs for N, P and K are basically the same regardless of the tillage system. Current research shows that the tillage system has little effect on N, P and K crop needs. However, the timing and method of application are vitally important to no-tillage success, especially in cold-wet soil conditions where mineralization of soil nutrients is much slower compared to conventional tillage.

Conservation tillage systems such as no-tillage have a positive impact on soil productivity and profitability, especially under extreme weather events of wet or dry conditions. These systems protect soil, conserve energy, improve soil tilth and soil organic matter, and can reduce the capital costs associated with the tillage equipment used in conventional tillage. Conservation decisions made now can affect soil erosion over the next several years.

Research on soybean production after corn shows no yield or economic return advantages for any conventional tillage system over no-till.  Studies show that no-till economic returns for corn on well-drained soils are much greater than other conventional tillage systems. Even in cold and wet soils with adequate drainage, both no-till and strip-tillage performed very well compared to conventional tillage systems. 

In summary, tilling corn residue for the soybean crop year does not improve soybean yield. There may be some challenges in managing corn residue, but simple modification of the planter to include residue cleaners, heavier down pressure springs, or other residue management attachments are far more cost effective than the expense associated with conventional tillage.


Soybean planted in no-till.


 

Mahdi Al-Kaisi is a professor in 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 5/21/2012 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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