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4/15/2013 - 4/21/2013

Spring rain: The good and the ugly

By Mahdi Al-Kaisi, Department of Agronomy

The current wet conditions are a mixed bag providing moisture to recharge the soil profile and potentially mitigating the residual effect of last season’s drought.  The amount of moisture we received over the past two weeks can significantly improve soil moisture conditions for early-season growth and for the rest of the season.  According to Iowa Environmental Mesonet, since April 17 the daily estimated precipitation statewide average was 1.93 inches, the highest on any individual day since September 13, 1961. 

 

Immediate impacts on soil

Soil erosion: Fields with intensive fall tillage are experiencing significant amounts of soil erosion. The destruction of soil structure during tillage operations reduced water infiltration causing the surface soil to seal and resulting in great amounts of surface runoff and sediment losses to rivers and streams. The lack of residue cover on the soil surface is a main factor in accelerating soil erosion. The reduction in water infiltration of intensively tilled soils means that they may not benefit greatly in terms of subsoil recharge because the majority of the water runs off the soil surface into streams and ditches. In contrast, no-till fields with good residue cover or fields with cover crop will experience much better water penetration and recharge to the soil profile. This, of course, is needed in many areas to mitigate last season's drought conditions. The efficiency of a tillage system in capturing rain and storing it in subsoil is highly affected by residue cover level , how residues were managed (shredded or intact) and the existence of water ways and buffer strips that  slow  water movement and provide more opportunity for water to penetrate into the soil profile.

Soil compaction: The other concern we need to think about this spring is the potential for soil compaction. Wet soil condition presents a challenge with field operations such as applying fertilizers, planting and other daily farm management operations. Avoid entering fields when soil moisture is at or above field capacity, when greatest soil surface compaction or side wall compaction can occur. Soil compactions occurring during planting causes root deformation and subsequently yield reduction. It is worth waiting until field condition is dry enough by monitoring the top 6 inches of soil moisture by preforming field moisture tests. Other problems associated with soil compaction are the potential of early nutrient deficiencies such as potassium (K) during early growth stages when compaction affects root growth.

In summary, the recent rains may help to bring soil moisture to appropriate levels in the top soil that may ensure a good planting season. But it may also create challenges we need to factor in to minimize some potential impacts on crop performance. Tillage intensity and residue management dramatically affects rain harvest and subsoil recharge and the degree of soil erosion we experience.  Practice caution when entering the field this spring to avoid potential soil compaction.


Soil erosion in central Iowa. (Source: Drake Larson)

 

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.

Corn Planting FAQs

By Roger Elmore, Department of Agronomy


Winter ISU Extension and Outreach meetings provided premium-grade fodder for reflection and thought. The January 2013 U.S. drought monitor maps showed drought still persisted across Iowa to a greater extent than in 2012. Thankfully, March and now April rains and snow helped reduce drought severity in many parts of Iowa. This week’s U.S. Drought Monitor reflects significant improvement. Topsoil moisture conditions have subsequently improved, but subsoils in many areas remain short or very short in moisture (NASS). As we ramp up for the 2013 growing season, let’s address some frequently asked questions and concerns discussed over the long 2012-2013 winter.

 

Tillage

Every tillage pass results in soil moisture loss through evaporation. If dry conditions persist at planting in your area, excessive tillage may evaporate precious soil moisture. Keep tillage to a minimum if climatologists forecast dry weather for the rest of the growing season.  No-till operators will likely not have a problem finding good soil moisture conditions at normal seeding depths; however, those with some degree of tillage may need to consider deeper seeding depths to reach moisture (see the discussion below) unless their topsoil has been replenished with recent rain and or snow.

 

Hybrid

As discussed in an earlier ICM News article, producers in more southern Corn Belt locations often plant very early maturities to avoid heat and drought normally experienced in August. If dry conditions persist at planting in your part of Iowa, stick with adapted, high-yielding hybrids that show some yield stability over locations and years. Planting much earlier hybrids will likely result in reduced yields.

 

Row spacing

Responses to corn row spacing are related to light interception. What I understand about this is that yield is optimized if corn canopies intercept 95 percent of sunlight at silking. Interestingly, modern Iowa corn hybrids in 30-inch rows at normal plant populations intercept 95 percent of the light at silking. That explains why we rarely see row spacings narrower than 30 inches improving corn yields over those of 30 inches. That means that row spacings of 20 inches, 15 inches, 12 inches and/or twin rows rarely improve Iowa corn yields. On the other hand, yields are rarely reduced with row spacings narrower than 30 inches. Remember though, yields are likely reduced in rows wider than 30 inches. However, if early-season stress of some kind reduces canopy closure of corn in 30-inch rows, narrow rows may out-yield those of 30-inch rows. Dry conditions during vegetative development could do this.

 

Planting date

Optimum corn planting dates vary across Iowa, depending on soil moisture and temperature, from April 11 to May 13 in southern Iowa; April 15 to May 2 in central and northwest Iowa; and April 12 to May 2 in northeast Iowa. Although corn kernels absorb soil moisture when soil temperatures are less than 50°F, they will not begin germination until soil temperatures reach almost 50°F or higher.

If the sun is shining and the calendar date for your part of Iowa lies on the early side of the range listed above, and if soil temperatures are in the high forties or higher and climbing, checkout the 5 to 7 day forecast. Plant corn if the forecast calls for more of the same. If, on the other hand, the 5 to 7 day forecast calls for a good chance of cold wet weather settling back in for a while, keep the seed in the bag.

 

Soil conditions

Mahdi Al-Kaisi addressed soil conditions for planting in  ICM News a few weeks ago. Field-capacity soils at planting depth are ideal for corn germination and early seedling growth. Beware of soils that are too wet. Side-wall compaction stymies early seedling growth both below and above ground and reduces yield potential. Deeper compaction from planting, spraying and harvesting equipment reduces yields for years. Ensure that soil conditions are optimum at planting.

 

Seeding rates

Optimum plant populations for normal Iowa conditions range between 34,500 and 37,000 plants per acre. Make sure to add in your normal attrition rate - failure to germinate and/or produce a plant - to compute your seeding rate. Attrition rates in our studies range from three to seven percent. If your attrition rate is much greater than that, investigate the causes carefully!

One more note on seeding rates: if conditions are dry at planting and you expect them to persist, this is the year to be conservative when adjusting the planter. On your higher-yielding fields, plant on the average or high end of what you’ve done before - or up to the range suggested in the last paragraph. On fields with less yield potential, I’d back off a bit on seeding rates. Remember though, modern hybrids are more able to tolerate stress than older hybrids.

 

Seeding depth

Standard corn seeding depth recommendations for Iowa are 1.5 to 2 inches. As we mentioned in the early March ICM News, this seeding depth allows for quick emergence and maximum emergence rates as well as proper root system development. As discussed above, soils with moisture levels at field capacity provide the moisture level adequate to germinate seeds.

If soils at 1.5 to 2 inches are drier than field capacity, you could: plant deeper, adjust planter down pressure differently, or plant at 1.5 to 2-inch depths and hope for rain (see Mark Hanna’s ICM New article for more information). The first two options are most reasonable unless you are certain of timely rain, then the third option may be best.

Corn can emerge from fairly deep planting depths depending on soil texture. For example, if necessary to reach adequate moisture, plant corn as deep as 3 to 3.5 inches on clay soils, 4 to 4.5 inches on loam soils, and 5 to 6 inches on sandy soils. Remember though, if soil moisture is adequate at shallower planting depths, there is no reason to plant that deep. An array of problems accompanies unnecessarily deep planting: slower and more variable emergence, increased vulnerability to soil crusting and seedling diseases and insects. All of these reduce yield potential…and the crop is hardly out of the starting blocks!

Allow me to add one more thing on seeding depth. Seeding depth that varies among plants, especially in the same row, reduces yield through uneven emergence and thus uneven competition. This sets up a pecking order that chips away at yields all season long. In my experience, planting too fast is a major contributor to this. Time spent carefully adjusting your planter and speed for conditions specific to each of your fields will pay!

 

Summary

Spring soil and environmental conditions in mid- to late-April and early May usually get corn off to a great start toward maximum yield potential. Full-capacity soil profiles are like a savings account that pays high interest and provides through tough economic times.  That is a ‘textbook’ Iowa spring: our full soil profiles at planting carry us through the vegetative period even during a drought. However, if soil profiles are short of moisture at planting – and it still looks like that in some parts of Iowa - be prepared for conditions we don’t normally experience…and thus for situations for which we can only guess at recommendations.

 

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.

New Changes in Insurance Requirements for Commercial Pesticide Applicator Businesses

By Kristine Schaefer, Department of Entomology, and Gretchen Paluch, Iowa Department of Agriculture and Land Stewardship

On July 1, 2012, the Iowa Legislature passed changes to the Iowa Code that affected the evidence of financial responsibility for commercial pesticide applicator businesses. In order to be issued a license, commercial pesticide applicator licensees (businesses) were required to provide proof of financial responsibility for a minimum amount of $250,000 for property damage and $250,000 for public liability, each separately. On March 28, 2013, the Iowa Code was amended again. The amount of the evidence of financial responsibility was changed to $100,000 for property damage and $100,000 for public liability, each separately, or liability insurance with limits of $100,000 per occurrence and $300,000 annual aggregate. Certificates of insurance meeting the new minimum requirements will be required to renew commercial pesticide applicator licenses for 2013.

For additional information refer to the IDALS Pesticide Bureau website or call 515 281-5601 for commercial pesticide applicator information.

 

Kristine Schaefer is a program specialist in the Department of Entomology. She can be reached at 515-294-4286 or schaefer@iastate.edu. Gretchen Paluch is pesticide bureau chief for the Iowa Department of Agriculture and Land Stewardship.  She can be reached at 515 281-8590 or gretchen.paluch@iowaAgriculture.gov.

Evaluation of Fungicide and Insecticide Seed Treatments on Soybean at Three Locations in Iowa in 2012

By Alison Robertson, Daren Mueller and Stith Wiggs, Department of Plant Pathology and Microbiology, and Erin Hodgson. Department of  Entomology 


With funding from check-off dollars from the Iowa Soybean Association, we have evaluated the effect of commercially available fungicide and insecticide seed treatments. We evaluated seedling diseases, insects, and yield of soybean in Iowa in 2012.  This field study was done at three locations in Iowa: ISU Northeast Research and Demonstration Farm (NERF), Nashua; ISU Southeast Research and Demonstration Farm (SERF) near Crawfordsville; and a farmer’s field in Nevada (two planting dates).  Soybean variety varied by location. Seed treatments were professionally applied by the respective companies.  Varieties are commercially available, but their information will not be disclosed.

 

Materials and methods

The experimental design at each location was a randomized complete block with four replications.  Plot sizes were 10 ft-wide (four rows) by 17.5 ft. Planting and harvesting dates are listed in Table 1, and the seed treatments included are listed in Table 2.  In addition, the effect of a seed treatment plus a foliar application of Headline® (6 oz/A) + Leverage 360® (3.8 oz/A) applied at beginning pod set (R3) on yield was compared.  Seedling disease and insect damage were assessed at 14 days after planting (dap) and 28 dap.  One-meter stand counts were taken 14 and 28 dap, and vigor (plant height) was assessed 28 dap.  Foliar and stem disease was assessed at growth stage R5/R6.  Only diseases that were greater than one percent severity were recorded.  Soybean aphid populations were assessed at growth stage R1 and R3 to R4.5.  Plots were harvested with a plot combine.  Grain moisture at harvest was determined and yields were converted to bu/A at 13 percent moisture.

Table 1. Planting and harvest dates for soybean seed treatment trials in Iowa in 2012.

Location

Planting

Harvest

SERF (Crawfordsville)

May 14

Oct 8

 

Nevada (early)

May 9

Oct 3

 

Nevada (late)

May 23

Oct 3

 

NERF (Nashua)

April 26

Sept 18

 

 

Table 2. Seed treatments products evaluated and yield of soybean in Iowa in 2012.

Treatment

Yield (bu/A)

SERFa

Nevada (early)

Nevada (late)

NERFb

Untreated

67.1

74.9

58.1

54.6

Untreated with foliar sprayc

70.2*

71.3

53.6

59.5*

Poncho  + VOTiVO

69.3

70.8

57.1

56.3

CruiserMaxx Plus with Avicta

71.7*

72.3

55.3

58.7*

CruiserMaxx Plus

70.6*

74.9

61.0

56.8

CruiserMaxx Plus with foliar sprayc

72.2*

68.6*

55.5

59.7*

Pioneer Premium

69.1

73.4

58.0

60.9*

Inovate System

70.1*

77.8

58.0

56.8

Inovate + Metastar

69.7

69.5*

57.3

58.9*

Inovate + Metastar with foliar sprayc

70.0

75.8

58.1

60.2*

Overall LSD (0.1)

2.9

5.0

4.9

3.2

CV (%)

3.5

5.8

7.1

4.6

 

Results

The 2012 growing season was extremely hot and dry.  No seedling disease or insect (bean leaf beetle, soybean aphid) damage occurred in any of the four trials. Similarly no foliar or stem diseases were observed.

No differences in stand counts were detected at either 14 dap or 28 dap in three of the four trials. At the early planting date at Nevada, stand counts at 28 dap for the Poncho + VOTiVO, Pioneer premium and Inovate + Metastar treatments greater than the control (untreated seed) (P<0.1).

Yield varied across locations and ranged from 54.6 to 74.9 bu/A in the untreated control (Table 2). There was evidence of an effect of seed treatment on yield at three of the four sites (P<0.1).  At SERF (Crawfordsville), the yield of soybean treated with either CruiserMaxx + Avicta, CruiserMaxx Plus or Inovate were greater than the untreated control (71.7 bu/A, 70.6 bu/A and 70.1 bu/A, respectively versus 67.1 bu/A).  In the early planting date trial at Nevada, the Inovate + Metastar yielded less than the untreated control (69.6 bu/A versus 74.9 bu/A).  At NERF (Nashua), Cruiser Maxx + Avicta (58.7), Pioneer Premium (60.9 bu/A) and Inovate + Metastar (58.9 bu/A) yielded greater than the untreated control (54.6 bu/A). At three of the four locations, application of Headline® + Leverage® at R3/R4 resulted in higher yields for some treatments (P<0.1; Table 2).

 

Summary

The benefit of a seed treatment on soybean stand establishment was not evident in our 2012 field trials.  Much of the research across the Midwest has shown that seed treatments only protect soybean stand when cold (<55F), wet conditions occur within a few days of planting. In addition, we do not expect to see yield protection in the absence of significant pest pressure.  We did, however, detect evidence of an effect of seed treatment on yield at three of our four sites, although no one product stood out above the rest.  A tremendous amount of research on the biology of soybean seedling diseases in the Midwest is currently being done with funding from USDA-NIFA, the United Soybean Board, and the North Central Soybean Research Program.  The Iowa Soybean Association is also funding research in Iowa.  The goal of this research is to improve our understanding of the pathogens that are causing seedling disease and the conditions that favor infection and disease development both early in the growing season and as the season progresses. The sensitivity of these pathogens to fungicides used in seed treatment products is also being evaluated. These data may help to explain why one seed treatment benefits yield at one location and not necessarily at another.


Acknowledgements

Funding for this study was provided by Iowa Soybean Association.  We thank Bayer CropScience, Syngenta and Valent for treating seed for the study.

 

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. Daren Mueller is an extension specialist with responsibilities in the Iowa State University Integrated Pest Management program. Mueller can be reached at 515- 460-8000 or by email at dsmuelle@iastate.edu. Stith Wiggs is a research associate in the plant pathology and microbiology department. He can be reached at (515) 294-1741 or stithw@iastate.edu. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847.

Nine Species of Pythium Associated with Corn Seeding Blight in Southeastern Iowa

By Alison Robertson, Rashelle Matthiesen and Azeem Ahmad, Department of Plant Pathology and Microbiology

During the 2012 growing season, several thousands of acres of corn in southern Iowa were replanted in late May because of poor stands caused by seedling disease. Many of the fields affected were planted between April 23 and 27.  From April 28 through May 8, 2 to 6 inches of rain fell across southern Iowa and southeastern Iowa, respectively, and soil temperatures dropped below 55°F for four to five days. Approximately, one week later, damped off seedlings were reported in the area.

We received funding from the Iowa Corn Promotion Board, Valent, and BASF to investigate this seedling disease epidemic. We visited 25 affected fields, collected symptomatic seedlings and recovered nine species of Pythium. The most prevalent species recovered was P. torulosum, a known pathogen of corn (Figure 1).  Pathogenicity tests done in the lab and growth chamber established that cool (55°F) soil temperatures favor both seed and root rot caused by P. torulosum.

Figure 1. Species of Pythium recovered from diseased corn seedlings in southeastern Iowa in May 2012. Bars indicate number of isolates recovered from tissue samples from approximately 280 symptomatic seedlings.

 

Fungicide seed treatments protect germinating seed from pathogens. Metalaxyl (e.g., Allegience®) and mefenoxam (e.g., Apron®) have excellent activity against Pythium species. Strobilurins, e.g. azoxystrobin (Dynasty®), trifloxystrobin (Trilex®) and pyraclostrobin (included Acceleron), also have some activity against this group of  pathogens.  A few years ago, researchers in Ohio reported resistance to all these fungicides among Pythium species that they had recovered from diseased corn and soybean seedlings in Ohio (Broders et al, 2007). We tested the Pythium species we recovered in 2012 and also found that they differed in sensitivity to metalaxyl, azoxystrobin, trifloxystrobin and pyraclostrobin; some isolates continued to grow in the presence of the fungicide (Figure 2). Resistance to metalaxyl (and mefenoxam) and also the strobilurins has been reported for numerous pathogens. 

Figure 2.  Range in sensitivity of Pythium isolates recovered from diseased corn seedlings in southeastern Iowa in May 2012 to metalaxyl. Each isolate was grown on media amended with 100pm of metalaxyl. After 72 hours, mycelial growth was measured and compared to mycelial growth on non-amended media (control). Bars indicate percent inhibition of mycelial growth. For most isolates, metalaxyl reduced mycelial growth by more than 80 percent; however, four isolates appeared relatively insensitive to metalaxyl.

 

Valent is expecting registration of a new fungicide, ethaboxam, in 2013, which will be combined with metalaxyl (or mefenoxam) and marketed as the AP3 Fungicide System. Ethaboxam is highly effective against Pythium and Phytophthora sojae, and belongs to a different chemical group than metalaxyl (and mefenoxam). We evaluated ethaboxam and metalaxyl alone and in combination in controlled environment trials using soil collected from four fields in southeast Iowa in which stand loss occurred during May 2012. All treatments reduced root and mesocotyl rot and improved emergence (P<0.05) (data not shown).  In collaboration with Valent and BASF, we will be testing ethaboxam and other experimental compounds on famer’s fields in Washington County, southeast Iowa, this growing season.

Acknowledgements: We thank the Iowa Corn Promotion Board, Valent and BASF for funds to support this work.  We also thank Mark Carlton and Virgil Schmitt with ISU Extension and Outreach, and John Grandin, Growmark, who located and traveled with us to affected fields and helped sample seedlings.

 

Alison Robertson is an associate professor in the Department of Plant Pathology and Microbiology with extension and research responsibilities; contact her at alisonr@iastate.edu or phone 515-294-6708. Rashelle Matthiesen is a research associate; contact her at 515- 294-0581, rashelle@iastate.edu. Azeem Ahmad is an assistant scientist; contact him at 515-294-3639, aaahmad@iastate.edu.

  



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