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June 11 - 17, 2002
C.O.R.N. 2002-17
In This Issue:
A) Corn Seedling Disease and Poor Growth
B) Adjuvants for Postemergence Grass Herbicides in Corn
C) Field Corn Insect Update
D) Soybean Aphid Management in Ohio
E) More on "Late" Applications of Nitrogen to Corn
F) Using Growing Degree Days to Predict Corn Leaf Stages
G) Check for Freezing Injury in Wheat
H) Predictions for Wheat Head Scab
I) Using Precision Technology Clinic, June 19
J) Small Grains Day, June 20
K) Combine Yield Monitor Calibration Clinic, June 20
L) OSU Weed Science Field Day, July 10
M) Fact Sheet on Cressleaf Groundsel
We have had many reports of seedling blights and poor growth of corn over the past week. Many growers are also reporting high levels of flea beetle feeding on young corn plants and are wondering if Stewart's wilt is causing much of the problem. Stewart's wilt is present in fields, but you should expect those hybrids with better levels of resistance to this disease to be protected from seedling death. Generally, Stewart's wilt is recognized as faint yellow to white stripes in leaves of affected plants. When the bacterium becomes established in the vascular tissues of the plant the growing point becomes diseased and the plant wilts and dies in a few days. Frequently, plants remain alive and produce secondary tillers that also develop the yellow leaf stripe. These plants usually remain stunted as compared to healthy plants.
If corn plants are not growing normally there are many other causes that have been identified this year. Even though you find flea beetle injury on the leaves, take time to dig up plants and look at the roots. Wash off the roots with water and look for darkened areas on the seminal root system, the mesocotyl (stem between seed and crown) and nodal roots emerged from the crown. The wet soil conditions and cool soil temperatures have provided the conditions for serious seedling root diseases caused by a number of different organisms. We were recently sent diseased seedlings from a field that lost about 75% of the plants to seedling blight. Fusarium was recovered from the mesocotyl and crown tissues. In other samples Pythium has been recovered from seedling roots.
In many situations where seedlings are struggling to grow, root disease is a part of the problem. When insects and slugs are affecting the tops of the plants and fungal rots are affecting the roots, the plants will have a very difficult time growing. There is little the grower can do to help these plants other than control insects and slugs as appropriate. Warmer soil temperatures and less wet soil conditions will help the plants produce new nodal roots so adequate nutrients can be taken up to initiate vigorous growth. These are the same wet soil problems we saw last year. It is likely that this year's crop will develop a poor root system as well, which may lead to stalk quality problems later.
Armyworms - Reports from north central Ohio indicate that armyworms are being detected in no-till corn planted into a rye cover crop. 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, corn planted no-till into old hay fields or no-till plantings into fields with a lot of grasses. 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 leafs and then progress to the new growth - especially when corn approaches the early whorl stage. For additional information see the armyworm 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. Treatment of armyworm larvae reaching maturity will achieve limited results because the period of maximum feeding will have passed.
European Corn Borer - Overwintering European corn borer moths are being caught in pheromone traps throughout Ohio. Even though most of the corn observed while driving around central Ohio remains in early V1 or V2 stages of development and is unlikely to attract or support development of 1st brood, corn fields that were planted early and may be approaching mid-whorl stage should be inspected for possible economic infestations of 1st brood ECB.
If fields are nearing the whorl stage, then signs of early larval activity may be found if one inspects a significant number of plants. Egg masses may be found on the underside of corn foliage if one searches long and hard. If whorl injury (shot holes and window-pane feeding) appear abundant, then about 20 plants should be inspected at 5 locations in the field to determine the proportion of stand exhibiting whorl injury. In the inspection process, a number of whorls should be pulled and opened to determine presence or absence of ECB larvae. When larvae are found, the average number of larvae per plant may be estimated based on the proportion of stand exhibiting whorl injury and the proportion of injured plants actually having larvae present. If the number of larvae found exceeds an average of one or more per plant and the larvae have not yet begun to burrow into the stalks, the infestation may warrant a rescue treatment.
Based on the experiences of numerous researchers, extension agents, and consultants throughout the Midwest, the following guidelines should be used in determining the need for an insecticide application.
Sampling for the soybean aphid should begin in mid-to-late June, and definitely be on-going during the R1 to early R2 (flowering) growth stages. Sample the upper leaves from 4-5 plants from 20 locations in the field, and rate the aphid infestation on a scale of:
0 = none
1 = 1-10 per single leaflet
2 = 10-30 per single leaflet
3 = 30-100 per single leaflet
4 = 100-300 per single leaflet
5 = >300 per single leaflet
An average rating of 3 or higher across the field suggests that soybean aphids are common and abundant, and treatment should be considered. At a rating of 3 or higher, you will probably also find aphids on the petioles and stems that suggest an increasing population. If honeydew is present in the field and noticeable, the aphid population is probably high.
Timing of the insecticide application will be very important in achieving good control. The current thought is that the late vegetative stages prior to flowering will be too early to spray. Other states have seen a rebound in aphid densities when an insecticide is applied this early because of the reproductive capabilities of the remaining aphids. However, detecting an early infestation in late June will alert growers to potential problems.
Most insecticide applications should occur in early to mid July during flowering or immediately thereafter. Observations from other states suggest that the greatest benefit from an insecticide application will come during this time period. The later in the summer an insecticide application is made, the less the benefit from that spray. Spraying late in the season after pods have filled or following dispersal of winged aphids in mid-to-late summer will be too late to prevent economic yield loss. During those times, an insecticide application will fall into the revenge category, and do little good.
Our current thought is that best control will occur using ground equipment. Good coverage is essential and will be best achieved by spraying with higher pressures and higher gallons per acre. The following insecticides are labeled for soybean aphid control, although additional ones might be labeled later. The current insecticides are Asana XL (5.8 to 9.6 fl oz per acre), Furadan (0.25 to 0.5 pt per acre), Lorsban 4E (1 to 2 pts per acre), Mustang (3.4 to 4.3 fl oz per acre), Penncap-M (1-3 pts per acre), and Warrior (1.92 to 3.2 fl oz per acre).
Care should be taken during flowering if bees are actively working a soybean field. Although bees are not usually associated with soybeans, they do forage in soybeans and problems could occur if hives are nearby. Label directions pertaining to most of the insecticides and state regulations state that the insecticide should NOT be applied to blooming or flowering crops if bees are actively working in the target area. Thus, most materials for soybean aphid control should be applied in early morning or late day when bees would not be active in fields. Also, Ohio regulations state in 901:5-11-04 of the Ohio Administrative Code "No pesticide which is required to carry a special warning on its label indicating that it is especially toxic to honey bees, shall be dispensed over an area of one-half acre or more in which the crop plant is in flower unless the owner or caretaker of any registered apiary located within one-half mile of the treatment site shall be notified by the person who applies for himself or engages a pesticide applicator no less than twenty-four hours in advance of such intended treatment; provided, however, that these locations are registered and identified as required by section 909.02 of the Revised Code of Ohio, and that such apiary locations have been posted with the name and telephone number of the owner or a responsible caretaker". The names and addresses of registered apiaries are available at the Ohio Department of Agriculture at 1-800-282-1955. Growers should be advised to follow all label directions and state regulations; it is the soybean grower's responsibility!
Persistent rains this year may force many growers to sidedress
their nitrogen (N) in corn this year much later than what is considered normal.
Other growers may be supplementing their earlier N applications to replace N
lost from denitrification and leaching. The following are some suggestions from
extension soil fertility specialists at Ohio State and Purdue University from
past years that address various questions concerning N applications to corn
after planting.
HOW LATE CAN N BE APPLIED? Corn utilizes large quantities of N during the grand
growth stage. From the 8 leaf stage through tasseling N uptake is 4 to 8 pounds
per day. For most corn hybrids N uptake is complete shortly after pollination.
So, most of the N should be
applied prior to the 10-leaf stage, with any supplemental applications complete
by or shortly after tasseling. Under conditions of severe N deficiency, some
response would be expected to low rates of N (30 to 60 pounds) as late as three
weeks after pollination.
WHAT IS THE BEST N SOURCE TO USE? Ammonia or N solutions knifed in, or ammonium
nitrate over the top are preferred in most situations, especially high residue
fields. Granular urea can also be applied over the top in clean tilled situations.
Both granular urea and ammonium nitrate broadcast in standing corn will cause
some foliar burn when granules fall into the whorl. While it may appear unsightly,
little yield decrease normally occurs if the fertilizer is applied prior to
the 10-leaf stage.
HOW MUCH N SHOULD BE APPLIED? If the corn has gotten too tall to sidedress by
this point (late June and early July), it has probably not been severely stressed
and yield potential is still good. An example would be rotation corn after beans
which had some starter or 28% applied with herbicides with good green color.
Supplemental N rates at this point should probably be in the 0.5 to 0.7 pounds
N per bushel of expected yield.
CAN I BROADCAST UREA AND 28-0-0 SOLUTIONS "OVER THE TOP"? Using broadcast
applications of urea and 28% N solution to sidedress N will cause some burn
to foliar tissue of corn plants. Damage results when urea granules or 28% UAN
solution get inside the leaf whorl of corn plants.
The severity of injury is determined by the plant's stage of growth, the amount
of N used and form of N. If the plant growing point is at or below the soil
surface (or when plant has six collared leaves or less), the extent of foliar
injury caused by burn will usually be negligible if the N rate is kept below
50 lb/acre. Even with higher N rates at later vegetative growth stages the injury
from leaf burn is normally not so severe that it outweighs the potential benefits
received from the N addition. The degree of this plant burning is less with
urea granules than with other N products.
Dribbling 28% solution with drop nozzles as a narrow band on the soil surface
is an alternative approach that can help reduce foliar burning. Dribbling 28%
is also a more efficient use of N than broadcast surface application because
it helps reduce N volatilization.
CAN I APPLY N TO EVERY OTHER ROW? Research in Indiana, Illinois and Iowa has
all shown that farmers can knife ammonia or N solutions in every other row middle
(60 vs. 30 inch spacing) with no reduction in yield. The only caution is that
extra attention must be paid, especially in wet conditions that no knives plug
with soil. A plugged knife in 60 inch spacing gives 4 rows with no N and will
seriously reduce yields.
(The following was adapted from an article in the Purdue
Pest Management & Crop Production Newsletter written by Dr. Bob Nielsen
last year.)
Predicting when a field of corn will reach particular leaf stages is important
for planning post-emergence applications of certain herbicides and sidedress
N fertilizer, especially if your farming operation is so large that regular
field inspections are not feasible. Moreover, while visual evaluation of plants
is the best method for staging corn development, there are occasions when this
approach may be difficult to apply. When extensive early season plant injury
has occurred due to frosts, hail injury, or insects, identification of the first
rounded leaf and subsequent leaf collars may be difficult. This year persistent
rains, and periodic flooding and ponding in some fields have also contributed
to loss of leaves used in staging corn growth.
Dr. Bob Nielsen 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 if you know when
the crop emerged, but if not you can estimate that event also. Corn emergence
typically requires 100 to 150 GDDs.
Research conducted by Dr. Nielsen and graduate student Kirby Wuethrich indicates
that corn leaf developmental rates can be characterized by two phases. From
emergence to leaf stage V10 (ten visible leaf collars), leaf emergence occurs
approximately every 85 GDDs. From leaf stage V10 to tasseling, leaf emergence
occurs more rapidly at approximately one leaf every 50 GDDs. Previously, about
60-65 GDDs were generally associated with the appearance of new leaf collars
during vegetative growth.
Example: 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 125 GDDs, then the estimated leaf stage for the
crop would be between V7 and V8. This estimate stems from first subtracting
125 from 785 to account for emergence, then dividing the result (660) by 85
to equal 7.8.
Dr. Nielsen warns 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 heat
unit method may be useful in timing when plants will reach an approximate stage
of growth.
We estimated that the yield loss in the worse fields at 80% or more, but most affected fields had trace to about 50% loss estimates. It is very difficult to determine what actually happened in many of these fields, but damage must have been associated with a specific growth stage of the plants. Those fields or plants within fields that were affected must have been at a very specific and vulnerable growth stage to develop such variability in damage. From my observations, freezing injury must have taken place right during or after pollination. Thus, the vulnerable time period must have been within only a few days. Growers in the area reported temperatures only as low as 26 to 30 degrees F, but several commented that there was a very visible frost on the fields.
Wheat development pushed ahead rapidly over the past week due to the warmer temperatures. Growers in southern Ohio can now begin to assess fields for head scab development. Heads affected by scab have dead, bleached out florets. Frequently only a few florets are killed on a head, but sometimes the entire head may be killed. Scab risk predictions for southern Ohio have been low, except for late flowering fields in the far southwest corner of the state where the scab risk is moderately higher. Fields in northern Ohio were in flower over the past week during a time when rain showers occurred over a several day period. However, rain showers were scattered so scab risk will likely vary depending on which fields had rain. Based on weather information prior to flowering, fields in northwest and northeast Ohio had conditions favorable for scab development. Of concern are counties in the extreme northwest and northeast areas of the state. We are continuing to monitor the conditions in these areas and will have a more complete picture of the scab risk over time. These predictions do not mean that scab will be severe in these areas, but the predictions mean that weather conditions were conducive for scab development and there is a probability of some scab occurring in these areas.
You can get updated risk predictions from the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease by clicking on Forecasting Fusarium Head Scab of Wheat in Ohio.
"Using Precision Technology to Optimize Crop Diagnostics and Performance" will be the theme of the June 19 East Central Ohio Crop Diagnostic Clinic at the David Miller farm near Millersport.
The program will feature using computerized hand-held GPS systems for crop and field data collection, the application of field sensors for use of information on compaction, moisture and electrical conductivity as well as light bar guidance systems for sprayer efficiency. The program will get underway at 5:30 p.m. with a light supper and run until 9 p.m. The cost per person is $7.00 payable at the door. All segments will be taught and demonstrated in the field by OSU specialists. Certified crop advisor or continuing education credits are available. Free Dermascan skin screening will be available. For additional information contact OSU Extension Licking County by phone at (740) 349-6900 or by e-mail at siegrist.1@osu.edu.
Wheat farmers and suppliers are invited to attend the Small Grains Day on June 20, 2002 starting at 1:30 to 5:00 pm at the O.A.R.D.C. Northwest Branch Research farm on 4240 Range Line road near Hoytville, Ohio. The program will include wheat varietal selection, disease management, wheat nitrogen and sulfur management, seed treatment, milling and identity preserved issues, and a review of wheat best management practices. Presenters include: Dr. Pat Lipps, OSU Extension Pathologist; Dr. Ed Lentz, OSU Extension District Agronomist; Dr. Clay Sneller, OSU wheat breeder, and Ms. Diane Gannon, Nabisco quality control manager. Free and open to the public. CCA credits.
When wheat harvest time approaches it can become time consuming and discouraging to calibrate yield monitors on combines. Improperly calibrated yield monitors can essentially generate useless or difficult to interpret data. Taking the time to calibrate a yield monitor properly can go a long ways when it comes time to make important decisions from your yield data. University and industry specialists will be conducting a combine yield monitor calibration clinic on June 20. The program will cover components and mechanics of a yield monitor, calibration tips and procedures, yield map interpretation and data management, and industries perspective on yield monitors. The Conservation Action Project will sponsor a meal prior to the event at 5:00. The clinic will be from 6-9 pm at the OARDC's Northwest Branch, 4240 Range Line Road, Custar, Ohio. There are 1.5 CEU credits available for crop management. This event follows the small grains field day held at the same location from 1:30-5:00 pm. Visit the OSU precision agriculture web site http://precisionag.osu.edu for more details.
The 2002 OSU Weed Science Field Day will be held at 9
am on July 10 at the OARDC Western Branch near South Charleston. This self-guided
tour of OSU research plots provides the chance to see side-by-side comparisons
of a variety of herbicide programs for corn and soybeans. Western Branch is
on SR 41 approximately 4 miles south of I-70. Contact Mark Loux for more information
(614-292-9081 or
loux.1@osu.edu.
In response to many questions and concerns about Cressleaf Groundsel, we created
a fact sheet with information on identification, toxicity to livestock, and
control. The fact sheet contains color photos and is in PDF format. It will
be on the OSU Weed Workshop web site at some point, but can be emailed now upon
request. Contact Mark Loux (loux.1@osu.edu)
or Jeff Stachler (stachler.1@osu.edu)
to receive it via email.
Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.
Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/
C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
State Specialists: Pat Lipps, Anne Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Loux & Jeff Stachler (Weed Science), Ron Hammond (Entomology), and Bruce Eisley (IPM), Extension Agents: Dave Jones (Allen), Barry Ward (Champaign), Steve Prochaska (Crawford), Bruce Clevenger (Defiance), Greg LaBarge (Fulton), Gary Wilson (Hancock), Alan Sundermeier (Henry), Howard Siegrist (Licking), Ray Wells (Ross), Clark Hutson (Seneca), and Roger Bender (Shelby)Editor: Clark Hutson Web Editor: Tom Rosati
Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
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