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6/17/2013 - 6/23/2013

Japanese Beetles Begin Emergence

By Erin Hodgson and Cody Kuntz, Department of Entomology

Japanese beetles have a wide host range that includes many species of fruit and vegetable crops, ornamentals and field crops. Adults are metallic bronze and green with white tufts along the side of the abdomen (Photo 1). This pest is becoming a more common corn and soybean pest in Iowa. Adults started to emerge in late May last year, but the cooler temperatures this year have slowed down development in 2013. 
 

Photo 1. Japanese beetle adults are metallic bronze and green, and have white tufts of hair along the side of the abdomen. Photo by David Cappaert, www.ipmimages.org.

 

Literature shows adults need about 1,030 growing degree days (base 50°F) to complete development. Japanese beetles will continue emergence until around 2,150 degree days. Based on accumulating degree day temperatures in 2013, Japanese beetle adults should be active in some areas of southern Iowa this week (Figure 1). However, a few adults were already collected in pheromone traps in Story County (central Iowa) today, so expect adults to show up in northern Iowa in about seven days if warm temperatures continue. To more accurately predict adult emergence in your area this summer, use this website to generate up-to-date information. Click on the “View Degree Day Map” button in the left corner of the page, and then set the parameters for degree days to create a new map. Make sure to set the start date to January 1 of the current year and the end date to today; set the base temperature to 50°F and the ceiling temperature to 86°F.

Figure 1. Growing degree days accumulated (base 50°F) for Japanese beetle adults in Iowa (Jan. 1 - June 19, 2013). Adults begin emergence around 1,030 degree days. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

 

Damage and Management

Adults prefer to feed between soybean leaf veins, but can ultimately consume most of the leaf (Photo 2). The treatment threshold for Japanese beetles in soybean is 30 percent defoliation before bloom and 20 percent defoliation after bloom. Most people tend to overestimate plant defoliation, but this reference can help with more accurate estimations. In corn, Japanese beetles can feed on leaves, but the most significant damage comes from clipping silks during pollination (Photo 3). Consider a foliar insecticide during tasseling and silking if there are three or more beetles per ear, silks have been clipped to less than ½ inch, and pollination is less than 50 percent complete. 
 

Photo 2. Japanese beetles skeletonize soybean leaves. Photo by Mark Licht, ISU

 

Photo 3. Japanese beetles are strongly attracted to silking corn. Photo by Erin Hodgson, ISU.

 

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

Prevented Planting and Crop Cover Considerations

By  Stephen K. Barnhart, Department of Agronomy

There continue to be questions about cover crops and prevented planting options. With  the ‘no grazing or harvest until after Nov. 1‘  qualifier, here are my initial thoughts.

 

‘Spring cereals’ – oats, spring triticale, barley, spring wheat          

If planted in June, they will mature and likely shatter seed by mid to late summer. Shatter seed may produce some volunteer plants in the fall. If the ‘rules’ permit mid-season management, then disking the mature cereals in late summer would effectively ‘plant them’ for significant fall growth and retain erosion protection.

If planted in late summer, they would provide decent fall growth, but are subject to frost kill.

 

‘Winter cereals’ – rye, winter triticale, winter wheat

Brian Lang, an ISU Extension and Outreach field agronomist in northeast Iowa, planted rye in spring 2012. He clipped some and left some unclipped. The unclipped overwintered with noticeable winterkill. The ‘late summer clipped’ overwintered very well. Winter triticale would probably behave similarly; winter wheat would be more susceptible to winterkill.  If planted in June, all would provide some forage after Nov. 1.

If planted in late summer, these crops should overwinter OK, but would not produce lots of fall harvestable growth. They would provide some grazing. If planted early to mid August, they would produce more fall forage.

 

Ryegrass

Ryegrass planted in June would  probably be OK; there should  be some forage for grazing in November, maybe enough for mechanical harvest.

 

Other questions

I wouldn't recommend planting perennial forage grasses and legumes (including clover) in June for future hay fields unless there is good season-long vegetation/competition control to keep light availability to the establishing forage seedlings.

Perennial forage grasses and legumes (including clover) for future hay fields could be planted in early to mid August. This might be considered a better planting time if there is adequate soil moisture and likelihood of average or better rainfall.     

Annual forage legumes, such as crimson clover, Berseem clover and field peas or cowpeas, may not provide enough useable growth (or die prematurely) before Nov. 1 to justify their cost.  Most of these also require a special rhizobia inoculant for adequate nodulation and nitrogen fixation.

Annual, warm-season, forage species (such as Sudangrass, sorghum x Sudangrass hybrids, millets and teff)  are all frost/freeze sensitive and will likely winterkill and deteriorate by Nov. 1. They will provide cover and  ‘scavenge’ or hold existing soil nutrients, but will not likely provide highly desirable forage by Nov.1.

Buckwheat  will provide summer cover and ‘scavenge’ or hold existing soil nutrients.

Brassicas (turnips, kale, forage rape, ‘radishes’) should be planted from late July into August for best forage  yield and quality by Nov. 1.  If planted in June, most of these will likely ‘bolt’ and produce seed by fall. They can be planted with a cereal grain such as oats, triticale or rye. They are not legumes, but will intercept and hold soil nutrients like grasses. The brassicas will winterkill; however, depending on the cereal grain used, the cereals may regrow the following spring.

In addition to the economic decisions about cost and return alternatives to late planting, prevented planting, failed planting, insurance payments, etc., you also should consider the following:

  • How the field is managed through the summer – weed management, erosion protection, etc.
  • Whether you want the cover to winterkill or persist into the next growing season
  • Seed availability
  • Pre-applied nitrogen
  • Susceptibility of these alternative cover or forage crops to carry-over herbicides
  • Forage quality after Nov. 1; whether it will be grazed or whether there will be a stored forage option ( silage, hay).

 

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management. Barnhart can be contacted at (515) 294-7835 or by email sbarnhar@iastate.edu.

Wanted: Soybean Fields with Seedling Blight

By Alison Robertson, Department of Plant Pathology and Microbiology


This will be our third year surveying soybean fields with seedling blight in an effort to identify what pathogen species contribute to stand loss in Iowa. This survey is part of multi-state projects funded by USDA NIFA and check-off funds from the United Soybean Board and the North Central Soybean Research Project. One goal of the research is to develop diagnostic kits that could be used to identify the causal organisms responsible for seedling blight in a field.

To date, more than 83 oomycete species (Pythium, Phytophthora, Phytopythium and Aphanomyces) have been recovered from soybean seedlings sampled from throughout the North Central Region. Fungal species associated (for example, Fusarium and Rhizoctonia) with diseased soybean seedlings are being identified. Pathogenicity and fungicide sensitivity assays for each species are in progress. 

Do you know of a soybean field with seedling disease? If yes, please contact Alison Robertson, alisonr@iastate.edu or 515-294-6708, so that we can arrange to visit the field and sample seedlings.

Side-hill seeps result in corn emergence problems

By Roger Elmore and Mahdi Al-Kaisi, Department of Agronomy


Iowa’s wet spring and cool temperatures not only slowed planting progress but also slowed Growing Degree Day accumulations. These factors contributed to yellow corn plants across the state as well as within-row variability in plant to plant growth and development. Seedling diseases reduced stands.

We might expect all of those problems to surface considering the conditions the crop has experienced to date. We expect stand losses in low areas of fields in wet years due to prolonged standing water on planted or emerged corn (see link). However, one rarely seen problem has developed: corn stand losses on side hills. 

 

Saturated soils result in reduced corn stands

Saturated soils on sloped areas (Figs. 1 and 2) with corn planted in the second or third week in May resulted in poor germination and damping off and, in some cases, dramatically reduced stands. Soil temperatures at and soon after planting were conducive for rapid germination and emergence. So, we can rule out temperature as a causal agent. In some cases, the seed swelled (imbibed water) but neither the radical nor mesocotyl emerged. In cases where the radical and/or mesocotyl did emerge, they died before much growth occurred (Figure 3). (Colleagues at the Plant and Insect Diagnostic Clinic are examining seedlings for pathogens as we write.)

Figure 1. Field with reduced stands on side hills due to saturated soils (foreground and just below the crest of the hill in the background). the field slopes down in the foreground to the lowest area, which ponded and has no surviving plants (toe slope), and then back up the other side. Boone County, June 11, 2013.

 

Figure 2. A cross-section of sloped field with potential side-hill seepage.

 

 

Figure 3. Seeding that succumbed in saturated soils prior to emergence. Boone County, June 11, 2013.

 

One of the possible reasons for stand losses on side-hill slopes, also known as the mid-slope (Fig. 2), is water seepage leading to continuously saturated conditions and thus a lack of oxygen supply for seedlings to develop.  Areas with water seepage like this are called ‘side-hill seeps.’

 

Side-hill seeps described

One of the main reasons for side-hill seepage is existence of an impermeable layer or pan layer that restricts vertical water movement into the soil profile (Fig. 2). Also, in some cases it can be related to lateral flow where a layer of sand and gravel sandwiched between glacial debris channels water to the side- or mid-slope. This impermeable layer probably lies just below the area where the emergence failure occurred. 

One of the practices to alleviate problems in areas with side-hill seepage is planting deep-rooted perennials. Either alfalfa or perennial grasses will reduce soil moisture and prevent potential saturated conditions in seep areas. Reduced or no-till alleviates the problem as well.

 

Higher pH soils in saturated areas?

The potential for higher pH soils in saturated areas exists in addition to issues with stand establishment. Generally, water associated with side-hill seeps is high in dissolved minerals such as calcium and may create an alkali condition. If highly dissolved salts exist, salinity may result in crop failure in these seep areas. Continuous row cropping in these areas may reduce soil quality and increase soil erosion and water ponding conditions at the lower portion of the slope length - the toe-slope (Figure 2).

 

Summary

Extensive spring 2013 precipitation fostered ideal conditions for side-hill seeps. Soil profiles were saturated and excess water moved laterally due to downward vertical flow restrictions.  This soil saturation occurred during critical stages of germination and early stages of growth. These conditions deprived seedlings of oxygen necessary for growth and/or slowed growth to the point where pathogens were able to overcome the struggling seedlings. Corn stands were compromised.

Evaluate field conditions during wet conditions and document areas with side-hill seepage. Develop a management plan that may include conservation tillage, use of no-till, tiling, and/or planting perennials with deep roots to utilize excess moisture. These practices will help alleviate side-hill seep problems in the future.

This article expands on an Iowa Farmer Today Crop Watch Blog posted on June 13, 2013.

 

Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by e-mail at relmore@iastate.edu or 515-294-6655. 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.

Prevented Planting and Soil Health

By Mahdi Al-Kaisi, Department of Agronomy

The current wet conditions present a significant challenge to farmers in terms of delays in planting corn and soybean. The high percentage of acres under wet conditions can force farmers to entertain the idea of prevented planting by using cover crops or leaving the ground bare. There is a possibility that some of the acreage may be left fallow without any cover crops or annual crops growing due to a shortage of cover crop seed at this time. Leaving soils bare without any active root system can cause significant damage, not only in terms of potential soil erosion, which is a major concern that we are currently facing this season, but also in terms of changes in soil health and productivity in the following season due to problems such as fallow syndrome.

During the period of leaving soil fallow, several chemical and biological changes may take place. When soil is left bare without any active root system or under saturated conditions for an extended period of time, these changes in soil biological properties can be carried into the next season. Some of these potential changes are induced by the absence of active root systems in such areas that is essential in building up the microbial community responsible for nutrient cycling in the root zone. Therefore, planting of any annual crop during prevented planting can have significant value in sustaining such microbial community known as arbuscular mycorhizae (AM), which is essential for nutrient cycling such as P. It was documented through research that corn grown the following season in fallow soils will exhibit P deficiency.

In summary, cover crops are very beneficial in improving soil health, not only through improvement in soil physical structure and water infiltration, but most importantly soil biological community. The existence of active root system of any plant (i.e., cover crops, soybean, etc.) can remediate the potential damage caused by fallow or excessively wet conditions. Cover crops will also serve to retain some of the existing soil nutrients and reduce their loss through leaching and surface runoff.

Figure 1. Wet field in central Iowa, May 29, 2013.

 

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 6/24/2013 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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