C.O.R.N. Newsletter 2004-14

Dates Covered: 
May 18, 2004 - May 24, 2004
Editor: 
Tammy Dobbels

The Yellow Weed Returns!

The yellow flowering weed with an aster type flower and a purplish and hollow stem that is about 20 to 36 inches tall is cressleaf groundsel. It is commonly confused with yellow rocket, a mustard species having four petals and sepals and reaching a maximum height of about 24 inches. The cressleaf groundsel is quite prevalent right now in many fields south of U.S. Rt. 30. It is a winter annual, meaning it germinated last fall. The best way to control it for next year is to get it killed immediately, because it is in the full flowering stage. By the end of this week or next, mature seeds will begin blowing in the wind to cause problems in other fields for next year! Stopping seed production of any winter annual is the key to a successful control program. Applying fall herbicides and/or residual herbicides in early burndown applications will also assist in controlling this species.

To control cressleaf groundsel in no-tillage fields that have not had a burndown herbicide applied, use glyphosate at 1.125 pounds acid equivalent (lbs ae)/A plus 2,4-D ester at 1.0 pint/A. Soybean planting must be delayed for 7 days with this program. Glyphosate alone at 1.5 lbs ae/A should adequately control the cressleaf groundsel if soybean planting cannot be delayed or if no burndown herbicides have been applied to emerged Roundup Ready soybeans.

Timing of Postemergence Herbicides in Corn

Authors: Mark Loux

Due to the early planting and last week’s warm weather, the corn and weeds have grown quite quickly. Below are some considerations for postemergence weed control in corn:

Assuming a weed-free start at planting, apply postemergence treatments in corn before most of the weeds, and especially grasses, exceed 4 inches in height. Delaying application past this point can result in corn yield loss due to prolonged weed interference. Where a preemergence herbicide was applied and the weed population has been reduced, timing of postemergence herbicides should not be as critical with regard to weed interference.
Grass control is generally more difficult in corn than broadleaf control, so grass size should be a primary indicator for the timing of postemergence applications in corn! Postemergence grass herbicides should be applied before grasses exceed 3 to 4 inches in height depending upon the product.

With the rapid corn growth, be aware of limitations on corn height with postemergence corn herbicides. Treatments containing 2,4-D should be applied broadcast before corn exceeds 8 inches in height unless drop nozzles are used. Products containing dicamba (Banvel, Clarity, Distinct, NorthStar, Yukon, Celebrity Plus, etc) vary in their labeling with regard to corn size. As a general rule, treatments containing dicamba will be least injurious when applied to corn that is less than about 8 inches tall and prior to the five leaf stage. However, most of these products allow application to considerably larger corn, although they sometimes specify lower rates. Drop nozzles can be used on larger corn to minimize the risk of injury with these products. In addition, make sure the spray boom is high enough above the corn to allow the proper spray overlap and nozzle pattern. Where the spray boom is too low, excess herbicide may be directed into the corn whorl, increasing the risk of injury.

Products containing ALS inhibitors also vary in their labeling with regard to corn size, depending upon the ALS inhibitor and the premix or tank-mix partners. Restrictions for these products can be found on the label and on pages 75-76 of the 2004 OSU Weed Control Guide. Basis must be applied BEFORE 3-collar (V3) corn. Equip can only be applied broadcast up to 4-collar (V4) corn, but can be applied with drop nozzles up to 8-collar corn. As a general rule, the risk of injury from ALS inhibitors increases when corn development is past the 5- to 6-collar (V5-V6) stage (most critical), or when corn is more than 16 to 20 inches tall. Growth stage is the more critical variable with regard to risk of injury; in some years corn can be fairly short and still be at the 5- or 6-collar stage.

Common Lambsquarters Control, No-Tillage Roundup Ready Soybeans

In fields that have no burndown herbicides applied at this point in time, the common lambsquarters is approaching six inches tall. This is important to know, because glyphosate at 0.75 pounds acid equivalent (lbs ae)/A should be applied to lambsquarters that are LESS than six inches tall for effective control. There are lambsquarters populations in Ohio that are DIFFICULT to control with glyphosate alone. When lambsquarters are between 6 and 10 inches tall, use 1.125 lbs ae/A of glyphosate. When the lambsquarters is larger than 10 inches tall, use 1.5 lbs ae/A of glyphosate.

For no-tillage soybean fields that have not been planted, use 2,4-D ester with glyphosate to improve common lambsquarters control. The addition of 2,4-D ester will delay soybean planting for 7 days. Adding nearly any residual herbicide in the mixture, except for alachlor, metolachlor, Define, or Sencor (ONLY if triazine-resistant lambsquarters is present), can provide season long common lambsquarters control as long as enough rainfall is received.

If Roundup Ready soybeans were planted and they have emerged with no burndown herbicides applied, then Harmony GT or Raptor could be tank-mixed with the glyphosate to improve common lambsquarters control. However, severe injury can occur depending upon what rate these herbicides are applied and upon the weather conditions around the time of application. If an ALS/Roundup Ready stacked trait soybean was planted, then the mixture of Harmony GT with glyphosate will not cause soybean injury.

Sidedressing Corn -What should my rate be? Should I inject or dribble? Do I need an N stabilizer?

Authors: Robert Mullen

What should my rate be?
This is a very subjective question that can have extremely varying answers, depending upon the source of the recommendation. Obviously, within the university system we use the term yield goal to make a recommendation. Yield goal is a term that describes the average potential yield based on previous experience within a specific field. If a field has supported on average 160 bu/A of corn in previous years, that should be the yield goal (on average, obviously the true potential yield is a combination of hybrid, other nutrient levels, and more importantly environmental conditions). Even if one out the past six corn crops on that field yielded 200 bu/A, consider the average yield removed from the field rather than the exceptional year. More than likely, N application rates for the year that yielded 200 bu/A were similar to N rates for the average yield of 160 bu/A. Research reveals that even if the crop can yield 200 bu/A, the soil has the ability to buffer the demand for N. So if you are betting on another bumper crop, the demands for N are still not excessively high, relative to current N application rates. In other words, make your yield goal realistic, and do not apply excessive N in hopes of high yields.

Presidedress soil nitrate test can reveal if the sidedress N rate should be adjusted. This is of particular importance on fields that have historically received manure application. Soil samples can be collected in corn that is between growth stages V4 to V6, and submitted to a reputable lab. To see recommendations for sidedress adjustments based on presidedress nitrate test, see the following webpage: http://www.agry.purdue.edu/hua/issupsnt.htm

Should I Inject or Dribble?
Sidedress N should be injected below the surface soil to minimize N losses by volatilization. If N cannot be injected, dribble applications of liquid N are the next best method of application. Broadcast applications of urea or UAN should be used if the other two options are not available. Obviously broadcast applications can burn the crop, so if this methodology is used expect some burned leaves (especially if it gets warm and dry after application).

Do I need an N stabilizer?
Some propose the use of an N stabilizer with sidedressed N to minimize loss of N and maximize efficiency. The purpose of applying N as a sidedress is to improve the timing of N application to coincide with crop N demand. Thus, N applied as a sidedress should not need an N stabilizer. This is especially true of injected N. Some research shows that inclusion of a urease inhibitor may be advantageous when UAN is applied as a dribble. If rain follows application (within about three days), the advantage of the inhibitor is lost.

Current Risk Of Head Scab In Ohio

Authors: Dennis Mills, Patrick Lipps

Wheat is rapidly advancing through its growth stages due to the warmer weather this past week. Wheat in southern Ohio began to head about 5 days ago and is now flowering. Wheat in northern Ohio is in boot stage or beginning heading and will likely be in flower over the next week end. Wheat is in flower when the anthers are exposed on the heads. Anthers are usually exposed three to five days after heading. Relatively warm temperatures and wet weather during the flowering period increases the risk of head scab. We have been monitoring the predictions for head scab on the Wheat Fusarium Head Blight Prediction Center. This web site provides predictions of the risk of head scab on a daily basis.

Predictions are based on the flowering date of the crop and if the crop was planted after corn or not. So far, for fields in southern Ohio that were flowering over the past week, there is low risk of head scab for fields planted after soybeans (not after corn). However for those fields planted into corn residue the risk of head scab is greater. The prediction models indicate that for fields planted after corn and in flower over the past weekend, the risk of scab was high in Fairfield, Licking, Muskingum, Pickaway, Fayette and Ross Counties.

Wheat growers can obtain daily scab risk predictions by accessing the Wheat Fusarium Head Blight Prediction Center at http://www.wheatscab.psu.edu/.

Powdery Mildew On Wheat, Northwest Ohio

Authors: Dennis Mills, Patrick Lipps

We have received reports of powdery mildew becoming prevalent in fields in northwest Ohio over the past three weeks. Wheat is now growing very rapidly moving from the boot stage to heading in the next couple of days. Powdery mildew appears to be confined to fields planted to susceptible varieties with the more problematic fields having high seeding rates and high nitrogen rates applied. At this time reports indicate that the white powdery mildew pustules can be detected on the leaf below the flag leaf. Our research indicates that if the mildew reaches the leaf below the flag leaf by heading growth stage, susceptible varieties can suffer a 10 to 20% yield loss.

Fungicide application recommendations are based on scouting the field. First and foremost, check to see if the wheat variety planted is susceptible to powdery mildew. If you do not know then contact your seed dealer. If the variety is susceptible, then scout the field. Walk diagonally across the field and pull from 30 to 50 tillers. Examine each leaf on the tiller from the flag leaf down. The threshold for powdery mildew is 2 to 3 white mildew pustules on the leaf below the flag leaf. If the majority of the tillers have mildew on the second leaf then a fungicide application would be appropriate. The purpose of applying a fungicide is to protect the flag leaf and the leaf below the flag leaf from severe disease through flowering and early seed set.

The potential for powdery mildew to continue increasing is relatively high over the next week due to the predicted mild temperatures (50 to 75 degree F range) and the high probability of rain showers that will maintain high relative humidity. The products with the best efficacy against powdery mildew have propiconazole as the active ingredient. Tilt, PropiMax, Stratego and Quilt contain propiconazole. To get maximum effect in controlling powdery mildew apply 4.0 fl oz/A of Tilt or PropiMax or 14 fl oz/A of Quilt. Stratego can be applied at 10 fl oz/A but according to tests across the U. S., it is not as effective against powdery mildew as the other products. Applications at these rates will provide about 3 weeks of disease control and should also protect against Stagonospora leaf blotch and tan spot that generally show up in late May and early June.

You can avoid the issue of powdery mildew altogether by planting resistant or moderately resistant varieties. Variety selection is the most important management decision. Planting high numbers of seed (more than 1.5 million/A) and applying high levels of nitrogen (more than 100 lb N/A per year), will increase the problem of powdery mildew in the field, especially on susceptible varieties.

More information on scouting wheat for diseases can be obtained at http://ohioline.osu.edu/b785/b785_11.html

Soybean Stand Assessment

Authors: Anne Dorrance

This has been a different year already for planting. Parts of the state were extremely dry, others have had near perfect planting conditions and in North East Ohio – it has rained at least twice a week for over 6 weeks. Many fields have not been planted or have been “mudded-in”. Soybean seedlings all need moisture, usually excessive levels, to begin to infect and colonize seeds and seedlings. Rhizoctonia, interestingly, can infect soybeans across a wide range of moisture conditions, from around 25% to fully saturated. Rhizoctonia is a fungus that can cause a range of symptoms, from totally rotted seeds, brown lesions on roots and totally colonized roots. The symptom that is attributed the most to this fungal pathogen is a brick-red colored lesion on the soybean hypocotyls. The hypocotyl is the region on the soybean at the beginning of the stem above the root and below the cotyledon. When Rhizoctonia causes stand losses, use seed treatments that have the following active ingredients: PCNB, fludioxonil, azoxystrobin, TBZ or thiram. Allegiance and Apron XL are not effective against Rhizoctonia. T-22 has had limited efficacy in trials that I have evaluated here in Wooster. http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/seedtreatmentefficacy.htm

Phytophthora sojae and Pythium both require saturated soil conditions. We routinely wet, dry and wet soils again to promote disease in greenhouse studies. These two soybean pathogens can also attack seeds, seedlings and roots at these early growth stages. Phytophthora is favored by somewhat warmer soils compared to Pythiums – where some Pythium spp. will infect plants below 50F. Symptoms caused by these two pathogens are very similar, soft brown rotted roots. Flooding injury can also occur in these same fields, as a result of a build-up of CO2. Roots are injured, soils will smell like something died, algae may be on the surface and the when the roots are dug up – the outer cortical tissue can easily be pulled away but the center of the root – the root stele will be white. Plants can recover from flooding injury. Soybeans will develop new roots above the flooding injury and continue to grow. The only seed treatments currently labeled for Pythophthora and Pythium are Allegiance and Apron XL. For Phytophthora the highest rates on the label are necessary. Phytophthora sojae is also managed by resistance genes (Rps1a, Rps1c, Rps1k and Rps3a. Many fields in Ohio all have P. sojae populations that can kill plants with one or more of these resistance genes. Partial resistance to P. sojae is not effective in the early growth stages before the first set of true leaves begins to form. Seed treatments are a must for fields that have a history of stand establishment problems and require replanting. It was not uncommon for some parts of the state to replant 3 and 4 times before an adequate stand was established. With today’s seed costs, this is no longer an option.

OSU extension agronomist, Jim Beuerlein and several county extension agents have evaluated soybean populations and impact on yield. A minimum of 100,000 soybean plants per acre is all that is required to obtain the potential maximum yield. Soybeans have this great ability to bush out and compensate for their neighbors.

Scout for Armyworm Now

Authors: Ron Hammond, Bruce Eisley

Field corn planted no-till into grassy habitats should be monitored closely at this point in time for armyworm activity. Fields that may be at risk for significant armyworm infestations include corn planted no-till in rye cover crops and corn planted no-till into old hay fields. A severe infestation of armyworm can reduce stand when an infestation occurs in the pre-whorl stage and cause significant defoliation when corn is hit in the whorl stage. Total destruction of a field of no-till corn can occur if a severe infestation is allowed to develop without application of a rescue treatment.

Detection of foliar feeding injury by armyworm on 15 to 20% of a stand should be regarded as an indicator of a potential problem, and the field should be rechecked within a few days to determine whether the impact of defoliation is increasing and a rescue treatment may be warranted. In general, a severe infestation will impact almost 100% of a stand and defoliation of the plants will exceed 50%, stand height is being reduced, and some plants being eaten down to ground level. If defoliation remains less than 50% and the new growth exhibits minimal feeding injury, the stand will likely recover with minimal impact on yield. Rescue treatment in corn may be needed if stand infestation is greater than 50% and larvae are not mature.

Since armyworms are foliar feeders, they are relatively easy to control with most foliar treatments. During the day, armyworm larvae will most likely be found seeking shelter in the whorl or possibly in the ground cover. In general, armyworm larvae will feed first on the lower leaves and then progress to the new growth - especially when corn approaches the early whorl stage. For additional information see the fact sheet at: http://ohioline.osu.edu/ent-fact/0012.html.

Wheat fields should also be checked at this time for armyworm. Check several places in the field and determine the number and size of the worms present. Rescue treatment is recommended in wheat if counts average 6 or more worms per row foot and larva are in the early stages of development or if head cutting is occurring. Treatment of armyworm larvae reaching maturity will achieve limited results because the period of maximum feeding will have passed.

Cutworm Moths Continue to Fly

Authors: Ron Hammond, Bruce Eisley

Cutworm moths continue to fly in Ohio and after the intense capture in central Ohio in late April we would expect to see cutting begin to occur in the next few days. If cutting is above ground, cut plants will likely recover if a timely rescue treatment is applied. In contrast, below ground feeding is generally characterized by wilting plants that have been cut below the growing point, or plants cut off before emergence.

Early detection of cutworm infestations and timely application of rescue treatments are the keys to achieving effective stand protection where preventive treatments have not been applied. Where visible cutworm injury is observed on 3% or more of a stand, application of a timely rescue treatment is warranted, will arrest cutworm feeding, and prevent additional stand losses. If a significant cutworm infestation is detected too late, cutting has occurred below ground and below the growing point, then a rescue treatment may achieve marginal results.

Alfalfa Harvest Underway

Authors: Ron Hammond, Bruce Eisley

Get the sweep nets ready. We normally start finding potato leafhopper (PLH) in alfalfa about the middle of May in central Ohio and so as first cutting alfalfa is made, the second cutting needs to be checked for PLH within a week. Also, if there were a lot of alfalfa weevil in the field when the first cutting was made, the stubble should be checked to make sure the larvae do not damage the new growth as it begins to grow.

Corn Replanting Considerations

Authors: Peter Thomison

By most accounts, corn stands are excellent this year in many Ohio fields. However, there are localized reports of emergence problems (e.g. soil crusting) that may lead to questions about the need to replant. Don't make a final assessment on the extent of damage and stand loss too quickly. Replant decisions should be based on strong evidence that the returns to replanting will not only cover replant costs but also net enough to make it worth the effort. The following are some guidelines to consider when making a replant decision.

If the crop damage assessment indicates that a replant decision is called for, some specific information will be needed, including:

Original target plant population/Intended plant stand
Plant stand after damage
Uniformity of plant stand after damage
Original planting date
Possible replanting date
Likely replanting pest control and seed costs

To estimate after damage plant population per acre, count the number of viable plants in a length of row that equals 1/1000 of an acre and multiply by 1000. (Table 1 shows row length needed for various row widths.) Make several counts in different rows in different parts of the field. Six to eight counts per 20 acres should be sufficient.

TABLE 1

RowWidth
1/1000acre
inches
feet
20
26.1
28
18.7
30
17.4
36
14.5
38
13.8
40
13.1



A major consideration in making a replant decision is the potential yield at the new planting date and possibly different planting rate; this can vary depending on the hybrid used, soil fertility and moisture availability. Tables 2 and 3 show effects of planting date and plant population on final grain yield for the central Corn Belt. Table 2 is a newer chart developed by Dr. Emerson Nafziger at the University of Illinois that includes earlier planting dates and higher optimum plant populations. Table 3 is based on older data from the 1970's, but it still provides a reasonable assessment of potential yield losses, especially for planting dates in June. Grain yields for varying dates and populations in both tables are expressed as a percentage of the yield obtained at the optimum planting date and population.
University of Illinois replant chart developed under high yielding conditions (adapted from Nafziger, 1995-96)

Table 2


Plants per acre at harvest (X1000)
Planting
Date
10
15
20
25
30
35

% of optimum yield
April 10
62
76
86
92
94
93
April 20
67
81
91
97
99
97
April 30
68
82
92
98
100
98
May 9
65
79
89
95
97
96
May 19
59
73
84
89
91
89
May 29
49
63
73
79
81
79


Central Corn Belt grain yields for corn planted at various dates and population rates, expressed as a percent of optimum planting date and population yield (uniformly spaced within row).

Table 3

Planting
Date  
  
 Plants per acre atharvest

12,000
14,000
16,000
18,000
20,000
22,500
25,000
4/20
72
78
83
87
90
93
95
4/25
75
81
86
90
93
96
98
5/1
77
83
88
92
95
98
100
5/6
78
83
88
92
95
98
100
5/11
77
83
88
92
95
98
99
5/16
75
81
86
90
93
96
98
5/21
73
78
83
87
91
94
95
5/26
69
75
80
84
87
90
92
5/31
64
70
75
79
82
85
87
6/5
59
64
69
73
77
80
81
6/10
52
58
63
67
70
73
75
*Adaptedfrom NCH-30"Guideline for Making Corn Replant Decisions."


Here's how these tables might be used to arrive at a replant decision (Table 2 will be used in this example). Let's assume that a farmer planted on May 9 at a seeding rate sufficient to attain a harvest population of 30,000 plants per acre. The farmer determined on May 28 that his stand was reduced to 15,000 plants per acre as a result of saturated soil conditions and ponding. According to Table 2, the expected yield for the existing stand would be 79% of the optimum. If the corn crop was planted the next day on May 29, and produced a full stand of 30,000 plants per acre, the expected yield would be 81% of the optimum. The difference expected from replanting is 81 minus 79, or 2 percentage points. At a yield level of 150 bushels per acre, this increase would amount to three bushels per acre which would probably not justify replanting costs.

It’s also important to note plant distribution within the row. Remember that the values in Tables 2 and 3 are based on a uniform distribution of plants within the row! Add a 5% yield loss penalty if the field assessment reveals several gaps of 4 6 feet within rows and a 2% penalty for gaps of 1 3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. The more numerous and longer the gaps between plants within the row, the greater the yield reduction.

When making the replant decision, seed and pest control costs must not be overlooked. Depending on the seed company and the cause of stand loss, expense for seed can range from none to full cost. As for the correct hybrid maturity to use in a late planting situation, continue to use adapted hybrids switching to early/mid maturities, if necessary, depending on your location in Ohio.

You also need to review herbicide and insecticide programs under late planting conditions. For instance, it may be necessary to reapply herbicides, especially if deep tillage is used. However, try to avoid such tillage depending instead on postemergence chemicals or cultivation for weed control. Concerning insect control, if soil insecticides were applied in the row at initial planting, check insecticide label restrictions before re application. Also remember that later planting dates generally increase the possibility of damage from European corn borer (ECB) and may warrant selection of ECB Bt hybrids (if suitable maturities are available). Understand that replanting itself does not guarantee the expected harvest population. Corn replant decisions early in the growing season will be based mainly on plant stand and plant distribution. Later in the season as yields begin to decline rapidly because of delayed planting, calendar date assumes increased importance.

The cost of replanting will differ depending on the need for tillage and chemical application. The cost and availability of acceptable seed will also be considerations. These factors must be weighed against expected replanting yield gains. If after considering all the factors there is still doubt as to whether or not a field should be replanted, you will perhaps be correct more often if the field is left as is.

The following are some additional on-line sources of information on making replant decisions.
Nielsen, Bob. 2003. Estimating Yield and Dollar Returns From Corn Replanting. Purdue Univ. Cooperative Extension Service publication AY-264-W. Online at http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf.

Nielsen, Bob and Peter Thomison. 2002. Delayed Planting & Hybrid Maturity Decisions. Purdue Univ. Cooperative Extension Service publication AY-312-W. Online at http://www.agry.purdue.edu/ext/pubs/AY-312-W.pdf.

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance, Dennis Mills (Plant Pathology), Robert Mullen (Soil Science), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Peter Thomison (Crop Science � Corn), Bruce Eisley (IPM), and Ron Hammond (Entomology), Ed Lense (Agronomy); Extension Agents: Roger Bender (Shelby), Ray Wells (Ross), Barry Ward (Champaign), Steve Foster (Darke), Howard Siegrist (Licking), Alan Sundermeier (Wood), Gary Wilson (Hancock), Steve Bartels (Hamilton), Tammy Dobbels, (Logan), Glen Arnold (Putnam) Mark Keonig (Sandusky), Harold Watters (Miami), Dusty Sonnenberg (Henry),and Steve Prochaska (Crawford)

About the C.O.R.N. Newsletter

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.