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Ohio State University Extension

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C.O.R.N. Newsletter 2010-14

Dates Covered: 
May 24, 2010 - June 1, 2010
Editor: 
Glen Arnold

Wheat scab update: May 24 - Moderate risk

Wheat continues to flower in Ohio, and with frequent rainfall and increased temperatures over the last 7 to 10 days, moderate-high risk predictions cover many areas of the state today (see map below).  Today’s moderate-high risk predictions follow moderate risk for fields flowering over the weekend.

Southern Ohio – Wheat in the southern regions flowered well before this wave of moderate to high risk came through, and as such should have low scab intensity. In spite of the frequent rainfall during the early part of our flowering season, conditions were cool, so fields in southern Ohio likely escaped major scab concerns because of cool temperatures.
 
Central Ohio – Most wheat in central Ohio flowered late last week and during the weekend. This wheat likely escaped this moderate risk of scab. However, late-planted fields in central Ohio may flower by mid-week. If your wheat was late-planted, it is still important to scout fields to determine flowering date. For wheat flowering today, May 24, the risk of scab is moderate for most of the central region. The risk is high for parts of Clark, Coshocton, Delaware, Knox, Licking, Union and a few neighboring counties. 
 
Northern Ohio – In the northern third of the state, wheat began flowering over the weekend and will continue throughout the early part of this week. For wheat flowering today, May 24, the risk is moderate-low for most areas in this region.  The fields in northernmost counties will likely reach flowering by mid week.  Fields flowering later this week in northern Ohio will likely escape scab because of dry conditions, even though temperature are predicted to be in the 80s for most of the next 5 days.
 
Bottom line - Wheat that flowered between Friday May 21 and Monday May 24 and received frequent rainfall and warm temperatures during the seven days leading up to flowering would be at greatest risk for scab. Some of those fields were predicted to be at least at moderate risk during all four days.
 
For those considering applying fungicides for scab management, please remember that these products are most effective when applied at flowering. Some level of scab suppression will occur with applications done two to three days before or after flowering, but efficacy drops considerably as you move away from the actual day the crop flowers. Of the available fungicides, Proline, Prosaro and Caramba are the most effective. Folicur provides some suppression, but is not as effective as the other three products. A tank mix of Folicur and Proline (3+3), provides control comparable to that provided by Prosaro. Strobilurin-based fungicides are not recommended for scab management, since they may lead to vomitoxin contamination of the grain. For the efficacy rating of foliar fungicides http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/OFCDwheatfungicides.pdf
Cereal Leaf Beetlecereal leaf beetle larvae

Cereal Leaf Beetle

The cereal leaf beetle is becoming the threat to wheat yields that we had expected based on high populations of adults.  Reports have come in from many areas of the state, including southern and central Ohio, of larval populations reaching the threshold of 1-2 larvae per stem or flag leaf, and significant feeding occurring. We expect to begin seeing these populations in northern Ohio.  The question that is being asked is how long the flag leaf needs protection, and whether treatment is still warranted based on the growth of the wheat. Cereal leaf beetle, the larvae in particular, damages the plants by feeding on the upper surface of the flag leaf, leaving elongated, grayish scars. Both grain yield and quality are affected by the integrity of the upper two leaves, especially the flag leaf, and the spike. So, the longer these plant parts remain healthy, the better.

cereal leaf beetle damage

Wheat in most of the affected areas is between full head emergence (Feekes 10.5) and flowering (Feekes 10.5.1). These are critical growth stages, since they mark the beginning of pollination and grain fill. Substantial damage to the upper leaves at this stage will reduce the amount of sugars available for grain fill, leading to significant yield loss. Damage to the leaves during mid- to late-grain fill will also affect grain quality, leading to lower test weight. Hence, it is very important to keep the flag leaf healthy throughout the grain fill period to minimize yield and quality loss.       

If treatment is required, see the following for a list of insecticides labeled for cereal leaf beetle on wheat, http://entomology.osu.edu/ag/images/Small_Grains_CLB.pdf .  Pay close attention to the pre-harvest intervals, which range from mainly 21 to 30 days, although a few insecticides are 7 or 14 days.

 

Grass Sawfly on Wheat

As growers are sampling their wheat for the cereal leaf beetle, we also getting reports about a green-yellowish caterpillar.  The concern is that these larvae are armyworms.  Based on pictures we have received, these appear to be one of the grass sawflies which are fairly common in Ohio.  They frequently are found on the orchard grasses and other grasses along road sides.  Every few years, we see more of them showing up in wheat and causing grower concern.   The grass sawfly is actually not a caterpillar, which is the larva of either moths or butterflies.  Sawflies belong to the order Hymenoptera, and are actually related to bees and wasps.  The predominant characteristic that separates them from most caterpillars is that there are more than five prolegs on the abdomen.

sawfly on wheat

Will they cause injury to the wheat?  There is the possibility that they could chew up some leaves and also the possibility that they could clip wheat heads, but as with armyworm it would take quite a few of them to cause significant damage.  Sawflies generally are not considered a significant economic problem in wheat in Ohio.  As a side note, we have been seeing a fair number of adult armyworm moths flying around in the past week, and thus, growers should be keeping an eye out for armyworm caterpillars in the near future.

 

Leaf Rust in Wheat in Southern Ohio

Leaf rust is being reported in parts of southern Ohio, with high severity on the flag leaf. Most of the wheat in that part of the state is at early-mid grain fill, and as such, substantial damage to the flag leaf will result in yield and quality reduction. The weather has been, and will continue to be, favorable for leaf rust over the next few days. Given that we have had adequate moisture and temperatures, rust spores will germinate and infect leaves within 6 to 8 hours, with a new generation of spores being produced every 7 to 14 days. Frequent heavy dew, light rain, or high humidity and temperatures of 59 to 77 degrees F are ideal for rust development. If not managed, the disease will continue to spread, causing yield and quality reduction, especially if the variety is susceptible.

Both Strobilurin- and Triazole-based fungicides are effective against leaf rust (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/OFCDwheatfungicides.pdf), but the Strobilurins may lead to vomitoxin problems, especially since the wheat is just past flowering and conditions have been moderately favorable for scab and vomitoxin. Follow the label carefully before making applications.           

 

Wheat Heads Trapped in the Boot

Fields planted with varieties that are more sensitive to cold temperatures were the ones most affected. However, this does not necessarily mean that these varieties with automatically suffer a yield reduction. Once the heads remain green and healthy and water and nutrients still travel up the stem to the spikelets, these plants will produce grain. Yield will only be affected if the heads are distorted to the point of blocking or stopping the flow of water and nutrients to the spikelets.

 

Wet Weather, Should You Be Concerned About Nitrogen Loss?

For fields that may have received dry urea fertilizer, we would be a little more concerned, but only if the field was waterlogged for at least a day.  Those few fields that may have received a sizable amount of urea-ammonium nitrate (UAN – liquid 28) would be at a little more risk of loss due to the application of nitrate especially if waterlogged for a day or more. 

Our recommendation is evaluate your crops over the next couple of weeks as soil and air temperatures increase and look for any visual symptoms of nitrogen deficiency (general chlorosis or yellowing).  If you are still concerned, you can use the tool we developed a few years ago for evaluating the risk of nitrogen loss (see below).

1) What N source was utilized?
1 point - Anhydrous ammonia with nitrification inhibitor
2 points - Anhydrous ammonia
3 points - Other fertilizer banded
4 points - Other fertilizer broadcast

2) When was the N applied?
2 points - After April 20
5 points - Before April 20

3) How much N has been applied?
1 point - >200 lbs/A
2 points - 150-200 lbs/A
3 points - 100-150 lbs/A
6 points - <100 lbs/A

4) What has been the predominant soil moisture status in the field this spring?
1 point - Normal
2 points - Wet
4 points - Excessively wet (saturated – standing water)

5) What is crop’s condition?
1 point - Green plants > 12” tall
2 points - Green plants < 12” tall
3 points - Chlorotic plants < 12” tall
5 points - Chlorotic plants > 12” tall

Total the score and use the following guidelines:
Less than 13 - Additional fertilizer not recommended
13-16 - Evaluate again in 4-7 days
17 or greater - Add an additional 40-70 lbs N/A

Some producers may consider the use of the presidedress soil nitrate test (PSNT) to determine if additional N fertilizer is warranted. To attain a representative soil sample, collect 15, 1-ft deep random cores from a field and mix them thoroughly. Submit a grab sample from the composite to a reputable lab (a list of labs is available at the following web address: https://agcrops.osu.edu/specialists/fertility/resources/of-interest/testlabs.pdf). You may want to contact the lab and find out the turn-around time (some may be able to complete analysis in a couple of days). If the nitrate level in the soil is between 25-30 ppm then additional N is probably not warranted. Nitrate levels lower than 25 ppm have an increased likelihood of response, but the rates should not be greater than 70 lbs N/A. Work out of Illinois reveals that application of only 50 lbs N/A results in maximum yield over a wide variety of growing conditions.

 

Staging Vegetative Growth in Corn

Several systems are currently used to stage vegetative growth in corn. The "leaf collar" system is probably the method most widely used by university and seed company agronomists in the Corn Belt. With this method, each leaf stage is defined according to the uppermost leaf whose leaf collar is visible. The first part of the collar that is visible is the back, which appears as a discolored line between the leaf blade and the leaf sheath. The oval shaped first leaf is a reference point for counting upward to the top visible leaf collar. This oval shaped leaf is counted as the number 1 leaf when staging. If a plant has 4 visible leaf collars, then it is defined as being at V4. Normally a plant at the V4 stage will have parts of the 5th and 6th leaves visible, but only four leaves with distinct collars. A field is defined as being at a given growth stage when at least 50% of the plants show collars.

Another widely used staging method is the "hail adjustor's horizontal leaf method" developed by the crop insurance industry. Rather than using the uppermost leaf collar, hail adjustors identify the uppermost leaf that is 40 to 50% exposed and whose tip points below the horizontal. Typically a given "horizontal leaf" growth stage based on the hail adjustor's method will be 1 to 2 leaf stages greater than the collar method. From growth stage V1 through about V5 there is typically one additional leaf (above that leaf with the last visible collar) whose leaf tip is pointing below the horizontal. Beyond growth stage V5, two or more additional leaves with 'droopy' leaf tips will usually be evident above the leaf with the last visible collar (so a V6 plant according to the leaf collar method will typically be an 8-leaf plant according to the hail adjustor's horizontal leaf method). One problem with the horizontal leaf method is that it is often difficult to identify the uppermost horizontal leaves in fields that have recently experienced severe leaf damage. Hail adjustors get around this problem because they generally assess hail damage 5 to 10 days after the storm, by which time one or more leaves have emerged from the whorl.

Corn leaf stage is a more reliable indicator of corn development than plant height. This is especially true when we experience wet, cool growing conditions like those of recent weeks. Under these conditions, corn grows more slowly from a height standpoint. Differences in tillage and soil type often have a pronounced effect on plant height but relatively little effect on the stage of vegetative development. For example, within a field, corn may be taller in those areas characterized by darker soil (with higher organic matter) than in areas with lighter soil, especially the clay knolls, yet plants in both areas of the field may be at nearly the same stage when counting leaf collars.

At about V6 stage, or 8-leaf stage of the hail adjustor's method, increasing stalk and nodal growth combine to tear the smallest lower leaves from the plant. This results in degeneration and eventual loss of lower leaves. Hail damage, insect feeding, and fertilizer/herbicide burning promote this process.There may also be occasions when the lower leaves are hard to identify prior to the V6 stage. When extensive early season leaf damage has occurred, identification of the first rounded leaf and subsequent leaf collars may be difficult. What do you then?

Dr. Bob Nielsen at Purdue has described a method for predicting leaf stage development using accumulated heat unit or growing degree day (GDD) information. Given an understanding of corn leaf stage development and heat unit calculation, a grower can predict what leaf stage of development a particular field is at given its planting date and temperatures since planting. It is useful to know when the crop emerged, but if you do not you can estimate that event also. Corn emergence typically requires 100 to 150 GDDs.

Dr. Nielsen proposes that corn leaf developmental rates may be characterized by two phases. From emergence to V10 (ten visible leaf collars), leaf emergence occurs approximately every 82 GDDs. From V10 to tasseling, leaf collar emergence occurs more rapidly at approximately one leaf every 50 GDDs.  Previously, about 60 to 65 GDDs were associated with the appearance of new leaf collars during vegetative growth.

Example (from reference noted below): A field was planted on April 28, but you do not know exactly when it emerged. Since planting, approximately 785 GDDs have accumulated. If you assume that the crop emerged in about 120 GDDs, then the estimated leaf stage for the crop would be about V8. This estimate is calculated by first subtracting 120 from 785 to account for the estimated thermal time to emergence, then dividing the result (665) by 82 (equal to 8.1). 

Dr. Nielsen cautions that these predictions of leaf stage development are only estimates. One of the factors that most influences the accuracy of these estimates is the existence of other growth-limiting stresses and conditions (nutrient deficiencies, compaction, etc.). Despite these potential drawbacks, this method may be useful in timing when plants will reach an approximate stage of growth.

Fore more on this thermal time method for staging corn development, check out the following:

Reference

Nielsen, R.L. (Bob). 2008. Use Thermal Time to Predict Leaf Stage Development in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/VStagePrediction.html.  [URL accessed 24 May 2010].  

Modified Relay Intercropping

Long-term research at The Ohio State University's Ohio Agricultural Research and Development Center (OARDC), in Crawford County Ohio and at other locations in Indiana has shown that Modified Relay Intercropping (MRI) or Relay intercropped wheat (used polymer coated soybeans) will yield about 90 percent of conventional wheat.

A reduction in wheat yield occurred to wheat grown in 15 inch rows over 5 years of study. 

Table 1, Effect of Row Width on Wheat Yield

 

7.5” Rows

15” Rows

LSD (0.05)

Year and Variety

Bu/A

Bu/A

Bu/A

2000 I9824

72.3

70.8

NS

2001 AGRA  GR962

86.7

79.2

4.4

2002 AGRA  GR962

85.1

76.8

3.5

2003 INW0301

66.8

58.6

4.3

2004 INW0301

86.5

84.7

NS

5-Year Average

79.5

74.0

NS

Table 2, Comparison of Wheat yields in a MRI and Conventional Production System, 1999 (bushels/acre)

Variety

MRI

Conventional

Hopewell

80

94

X15

80

93

Agra 962

88

95

Average

83

94

F value: 17.3

significant

LSD 7.6

Interseeding of wheat resulted in reduced yield compared to conventional wheat. For wheat that was not interseeded, a 7 percent yield reduction for wheat grown in 15 inch rows versus wheat grown in 10 inch rows was observed over the 3 soft red winter wheat varieties and 5 years of study (Table 1).  When wheat was interseeded in 15 inch rows, there was a 7% decrease in yield from wheat not interseeded (Table 2). 

Conclusions

In the MRI system, wheat and soybeans have averaged 74 and 30 bushels per acre respectively in 10 years of replicated trials on various production factors (Table 3).  

Table 3, 10 Year Average Yields in a MRI System (bushels/acre)

Year of Trial

Soft Red Wheat Yields

Soybean Yields

1994

65

41

1995

72

27

1997

70

28

1998

73

41

1999

83

5

2000

76

37

2003

67

29

2004

65

47

2007

84

0

2008

82

37

Grand Mean over all plots

74

30

A more complete summary of this Modified Relay Intercropping research is available at http://crawford.osu.edu/topics/agriculture-and-natural-resources/crop-production/mri

 

 

Archive Issue Contributors: 
Archive Issue Authors: 
Topics: 
Small Grain Production
Corn Growth and Development
Modified Relay Intercropping

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.