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June 4-11, 2000
C.O.R.N. 2000-16
In This Issue:
A.
To Treat or Not to Treat Replantings
B. It’s Time To
Monitor Potato Leafhopper on Alfalfa
C. Slug Update
D. Guidelines to
Avoid Injury from AIM Herbicide
E. Wheat Diseases
Continue to Develop
F. Harvest Aids
for Wheat
G. Stewart’s
Bacterial Leaf Blight in Corn
H. Estimating
Nitrogen Losses in Corn
I. Hail Damage to
Corn
J. Modified Relay
Intercropping Update
A
number of reports have been received about significant stand losses in corn and
soybeans due to seed maggots or slugs. In
such situations, two questions normally arise.
First, what level of stand loss warrants replanting, and second, should a
seed treatment be applied to prevent the similar damage to the replanting?
Whether
a replanting is required is dependent on an accurate assessment of the stand
loss and an estimate on whether a late planting will produce a yield that will
significantly exceed that of remaining stand and cover the additional costs
linked to the replanting process.
If
a decision is made to replant, then the question of treatment is raised since a
grower does not want a new seeding to experience the same fate that occurred to
the first planting. In part, the field habitat has not changed and the pest
population is likely still present. But,
weather conditions have likely changed and the potential for rapid emergence may
have been altered depending on soil moisture and temperature conditions.
If the initial loss was due to slugs in a no-tillage habitat, the slugs will likely remain active if moist conditions remain under the surface residue. Given the periodic rains of the past week, hot spots of slug activity will likely remain and possibly cause problems for a new seeding. However, a bait treatment can be expensive and selective treatment of hot spots is needed to maximize the benefit of such a treatment.
If
the initial loss was due to seed maggot in a tilled habitat of high organic
content, it is possible that a new seeding may be hit by subsequent generation
of seed maggot. In such a case, the probability that a significant maggot
infestation will occur again at the same location are low but soil conditions
remain that supported the initial infestation.
However, the expense of applying a seed treatment to prevent a seed
maggot is relatively low, and degree of protection may be warranted to prevent a
re-infestation of new seeding.
Second
cutting alfalfa needs to be monitored at this time for potato leafhopper.
A series of ten sweep samples should be taken at least weekly to
determine whether economic infestations of leafhopper warrant rescue treatment.
Given the periodic rains that have recently occurred, alfalfa stands
should be developing rapidly if weevil was successfully controlled during the
first cutting. Where weevil infestations were not effectively controlled during
the first cutting, alfalfa development may be significantly retarded.
The economic threshold for leafhopper is based on the stand height where the collection of leafhoppers per ten sweeps should not exceed the stand height expressed in inches. During the past week, we observed six adult leafhoppers per ten sweeps on our plots which were eight inches in height. Since the leafhopper count per ten sweeps was less than eight and no nymph activity was visible, a rescue treatment was not warranted. Furthermore, since alfalfa growth is vigorous, the threshold for treatment may be increased. However, if leafhopper numbers suddenly increase or vigorous growth begins to decline due to heat stress, rescue treatment in the future may be warranted.
Treatment of second cutting alfalfa for potato leafhopper may or may not be needed depending on the late spring growing conditions and leafhopper abundance. The need for treatment of early third cutting alfalfa will be more likely since peak leafhopper activity often coincides with the harvest of the second cutting. Every alfalfa field is different and leafhopper abundance may differ from one field to another. Optimal leafhopper management depends on periodic monitoring of leafhopper activity applying a pendulum sweep with a standard sweep net.For more information, visit the Fact Sheet on Potato Leaf hopper on Alfalfa.
Slug
injury is continuing throughout Ohio. Farmers
should continue to monitor their corn and soybeans for slug damage and treat if
injury is severe and the crop is not growing out of it.
Reports of large slug populations causing severe damage in 4-5 leaf stage
corn are still being reported. In
situations where plant stand has been greatly reduced by slugs, replanting might
be necessary. Decisions for
replanting should be based on agronomic guidelines.
If replanting is done, it should be remembered that the slugs are still
there. If seeds are planted no-till
into these fields and growing conditions are not conducive to quick seed
emergence and growth, molluscicide treatment might be warranted since the slugs
are still able to cause significant damage.
Tillage prior to the
For more information, visit the Fact Sheets on Slugs on Ohio Field Crops and Slugs and Their Management.
Many
producers are considering postemergence application of AIM for control of
velvetleaf in corn, due to its low price. AIM
is a contact herbicide that is excellent for control of velvetleaf, but it can
cause contact-type injury to corn foliage. In OSU research, corn has always seemed to recover well from
this type of injury, and injury from contact herbicides is generally less of a
concern than injury from systemic herbicides.
In our research over the past 5 years, leaf burn observed 14 days after
postemergence application of Aim has ranged from 0 to 17%, with most of the
injury in the 0 to 5% range. Injury
is usually almost unnoticeable by about 30 days after application.
The most severe injury occurred when we applied on a cool, misty morning
to wet corn foliage. Based on the label and our experience, consider these
recommendations to reduce injury from AIM:
Apply with nonionic surfactant (0.25% v/v). Crop oil concentrate can be used under dry conditions, but may increase injury.
Do not tank-mix with EC formulations of other products, as the solvents in the EC formulations can increase injury.
If tank-mixing with a product that requires the use of a nitrogen fertilizer, use the minimum recommended rate of nitrogen fertilizer.
Avoid applying to wet corn foliage, or under conditions that are unfavorable for evaporation of spray droplets on foliage.
Avoid
application during environmental extremes, such as very hot or very humid
conditions.
Calibrate application equipment and avoid sprayer overlap.
Three
wheat diseases are now developing in the state's wheat that could significantly
impact the yield potential of the crop. Wet
weather and thunderstorms have increased the risk of significant yield losses
from each. It is important for
wheat growers to scout fields for disease soon for disease problems.
Head
Scab
is one of the most serious diseases of wheat.
It significantly reduces yield and affected grain contains a toxin (vomitoxin)
that makes it unfit for milling and baking.
Symptoms of Head Scab are beginning to be evident in southwest Ohio.
We have reports of some fields with up to 10% affected heads.
Based on weather information we have received, it is possible to have
moderate levels of scab in this section of the state.
The northwest section of the state has the greatest risk from head scab
due to high precipitation levels over the past two weeks.
Growers in northwest Ohio should begin to see symptoms of head scab by
the end of this week or early next week.
It is very difficult to predict the overall level of disease that may
occur. The cool night temperatures
(mid 40 F and low 50 F) and cool days (low to mid 60 F) we have experienced will
limit the overall amount of disease that may occur. However, it is possible for some fields to have relatively
high levels of disease. Look for
heads with bleached spikelets that were killed by the scab fungus.
Stagonospora
Leaf and Glume Blotch has been spreading slowly, but steadily from lower
leaves to upper leaves over the past week.
Frequent rain showers and wind will move the spores from infected leaves
up to the heads. Leaf blotch can be
recognized as oval brown to tan spots usually with yellow halos.
As the temperatures rise over the next week, leaf blotch will become more
severe. The Stagonospora fungus attacks the heads of the plants causing brown
lesions on the glumes near the glume tips. Severe
glume blotch may result if the weather turns warm and wet.
Shriveled, light weight kernels will result from affected heads. Yield losses will likely be common in the more susceptible
varieties.
Leaf
Rust is showing up in many fields throughout the state. So far the percentage flag leaf area affected is low.
Warm weather and frequent light rain will favor spread of the disease.
Leaf rust causes small rusty red pustules on the leaf surfaces. Severe infection of flag leaves can cause shriveled grain and
low test weights. Yield loss will
be greatest on susceptible varieties when flag leaves are attacked during the
grain filling process.
We are currently in a phase of wheat growth where herbicides should not be applied, in order to avoid yield loss. However, several harvest aids are available for application later this month when wheat has reached the hard dough stage. Roundup and a number of 2,4-D products are labeled for use as harvest aids. Roundup should be applied at a rate of 1 quart/A after the hard dought stage when grain moisture is 30% or less, and at least 7 days before harvest. The 2,4-D products should be applied after hard dough stage - rate varies with product and type of formulation. Applied at the proper time, Roundup probably has less potential to cause wheat injury than 2,4-D. However, wheat grown for seed should not be treated with a harvest aid. Take precautions to minimize drift, since susceptible corn, soybeans, gardens, etc may be close to the wheat field.
Large numbers of flea beetles have overwintered this year due to the mild winter weather. The higher flea beetle population indicates there is increased risk of Stewart's bacterial leaf blight. Much of the corn in the state is in the V3-V6 stage of growth. Now is the time when symptoms of Stewart's blight can be seen in young corn plants. Affected plants develop long, linear, yellow stripes on the leaves. Heavily diseased plants appear stunted and may begin to develop tillers. Under heavy disease pressure plants may be killed by systemic bacterial infection causing the plants to wilt and die. We have seen several fields with up to 10% of the plants showing the characteristic yellow stripes on the leaves. This disease will continue to spread in the field as long as flea beetles remain active.
For identification of Stewart's Bacterial Leaf Blight on Corn.
In
May some parts of the state received heavy rainfall. Producers in these areas
may have concerns about nitrogen loss, particularly those who applied N in early
spring or last fall. Temperatures have been warm enough that early-applied
anhydrous and other ammonium forms have converted to nitrate-N. In the nitrate
form, nitrogen is susceptible to loss under the right conditions. Most of this
loss potential is from denitrification. Denitrification losses may be
significant when relatively warm soils remain saturated for three days. Standing
water is evidence of saturated soils, but even bare soils that an individual
cannot walk across without sinking into the ground are saturated. There is no
test that can precisely determine how much nitrogen has been lost, but there are
some options available to producers that can assist in making sound N management
decisions.
One
of these options is the pre-sidedress nitrate test (PSNT). For this test a
producer needs to collect 10-15 random soil samples (12-inch depth) from a
sampling area no larger than 20 acres, and send to a reputable lab. The lab will
determine the nitrate concentration of the sample. Any sample that has more than
25-30 ppm nitrate should have adequate N for the rest of the season. If it is
less than 25 ppm the full rate of N needs to be applied. Some states recommend
reduced rates of N between 15 and 25 ppm. Ohio State University research,
however, showed that our soils are too variable for consistent recommendations
between 15 and 25 ppm, and deficiencies may occur later in the season at these
reduced N rates. A producer also needs to be aware that the soil nitrate level
may change by the time they receive the test results. Most labs have results in
several days, but the actual soil nitrate level may be less than the test
results if a heavy rain has fallen between the time the soil samples were
collected and the results received. Also, this test only determines nitrate-N.
If a large amount of ammonium type of nitrogen has recently been applied and has
not converted to nitrate, the test will not include this N in the results.
For
those with Internet access, another tool to estimate N loss is a software
program on Ohioline. This program will ask for inputs on location in the state,
soil type, saturated soil events, type of N fertilizer, time of application, and
so forth. The software uses long term weather averages as defaults in estimating
N events. Selecting 'Nitrogen Transformation and Loss' at
http://ohioline.ag.ohio-state.edu/lines/farm.html#SWARE
will download the program.
If
you do not have Internet access another tool to estimate N loss is a point
system developed at the University of Minnesota.
This system has been modified to fit Ohio conditions. It also asks a
series of questions and assigns a point value depending upon the answer. The
higher the point values, the greater chance of benefiting from additional N.
The questions and point values are given below:
FACTOR
1: What N product was used?
Anhydrous
ammonia with N-Serv 2
points
Anhydrous Ammonia
3 points
Other fertilizer banded
4 points
Other fertilizer broadcasted
5 points
FACTOR
2: When was the fertilizer N applied?
After
April 20
3 points
Before April 20
5 points
FACTOR
3: What has been the predominate soil moisture status in the field this
spring?
Normal
soil conditions
1 point
Wet soils 3
points
Standing water/saturated soils 4
points
FACTOR
4: What is the crop's current condition?
Green
plants/>12" tall
1 point
Green plants/<12" tall
2 points
Chlorotic plants/<12" tall
3 points
Chlorotic plants/>12" tall
5 points
Total
the score for the four factors and use the following guidelines:
Less
than 11 No
supplemental N recommended
11-16
Evaluate again in 4-7 days
17 or more
Add an additional 40-70 lbs. N/acre
The "re-evaluation" option is only viable until you no longer have side-dressing options. Illinois research has found that 50 lb N/acre as a supplemental N rate was satisfactory for a wide range of conditions. While a total score of 17-18 would merit a 40 lb/acre N recommendation. A total score of more than 18 may require a higher N rate.
Keep
in mind that good judgment is still important when using various methods to
estimate N needs. Also, each field
needs to be evaluated individually. The
PSNT, N software and point value system are intended to serve as guides and not
as definitive determination of N needs.
Last week I received several reports that hail storms had caused moderate to severe damage to several corn fields in central Ohio. Given the vegetative stage of corn in these affected fields, the prognosis for recovery is good. Most of this corn had not progressed much beyond V7 (7-collar stage) last week when the injury occurred, and most of the damaged corn was probably at V5-6. Defoliation by hail at this early stage of growth seldom translates into yield loss. A table developed by the crop insurance industry that relates percent defoliation in corn to percent yield loss doesn't "predict" yield loss until the corn plant reaches the V5 stage (or the 7-leaf stage using the hail adjustor's staging system). Moreover, according to hail adjustor table estimates, 100% defoliation at V5 results in a yield loss of less that 10%. For more information on the effects of early season defoliation on corn, consult an article in the May 15-21, 2000 issue of C.O.R.N. (2000-13) "What's the Impact of Early Season Leaf Damage in Corn?"
Modified
Relay Intercropping (MRI), the planting of soybeans into standing wheat, has
begun in north central Ohio. This system of intercropping does not use coated
soybeans and wheat rows are typically 10 or 11 inches in width. Also, MRI
planting occurs in early June as opposed to planting in early to mid May for
other systems of intercropping done in wider rows.
Soybeans
in the MRI system are generally sown into wheat after pollination with a grain
drill or tool bar planter. The wheat into which the soybeans are being planted
is generally in 10 to 15 inch rows with a tramline. One of the most challenging
aspects of MRI is gauging when to plant soybeans. Light or the lack of it, has a
profound effect on the growth of intercropped soybeans. Soybeans planted too
early into well-tillered wheat(as we have in this year) often will become very
tall and spindly and result in weak plants that do not grow or yield well. In
the MRI system, soybeans planted about 15-25 days prior to wheat harvest have
provided the most consistent yields. theoretically, earlier planted soybeans
should yield better, however as was mentioned above, competition with wheat
often produces a poor quality soybean plant, or if soybean growth is vigorous,
wheat growth is diminished. Therefore, MRI attempts to plant the soybeans into
wheat that will soon ripen and allow more light onto the developing soybean
plant. Management in the MRI attempts to balance wheat and soybean plant growth
needs and thus maximize yields.
Thus,
an MRI system adds 14-25 days to the soybean growing season when compared to
soybeans planted in a double crop system. The wheat plant, by virtue of its wide
adaptability, is able to tolerate slightly wider row spacing and the stress of
soybean planting with minimal yield loss. Five years of replicated field trials
on the MRI system have resulted in favorable average soybean and wheat yields
(73 bu/acre for wheat and 28 bu/acre for soybeans). Wheat yields in good years
have exceeded 80 bushels per acre and soybean yields over 40 bushels per acre.
The
MRI system offers producers many benefits. Because two crops with vastly
different growing seasons and cultural requirements are produced in the same
field in the same year, MRI offers producers both a production hedge and a
marketing hedge. All businesses must utilize assets maximally to optimize
profit. Thus farmers in the MRI system utilize their time, equipment, land and
labor during a period (normally early June) to grow a second crop with a good
probability of at least an average soybean yield (28 bu/acre).
The
MRI system is also very favorable from an environmental perspective in that soil
erosion is minimized with the small grain crop and often very little herbicide
is needed to grow soybeans sown into the standing wheat. The potential to
no-till corn into an MRI system is currently being studied.
It
should be noted that soybean yield results in the MRI system are highly
dependent on adequate rainfall in July and August. In 1999, no rain fell on the
MRI plots after August 13 and the soybeans yields were at 5 bu/acre (the lowest
since the beginning of the trials).
In
summary, MRI is a system requiring a high level of management for success. To
learn more about the management of MRI and to review previous trial summaries go
to: http://www.ag.ohio-state.edu/~craw/ag/ag.htm
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Contact your local Ohio State University Extension Office or e-mail
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.
Contributors to C.O.R.N. this week include: State Specialists: Peter Thomison (Corn Production), Pat Lipps (Plant Pathology), Anne Dorrance (Plant Pathology),Erick DeWolf (Plant Pathology), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Hal Willson (Entomology) and Ron Hammond (Entomology); District Specialists: Ed Lentz (Agronomy); Extension Agents: Dave Jones ( Allen), Steve Bartels (Butler), Steve Prochaska (Crawford), Greg LaBarge (Fulton), Howard Siegrist (Licking), Glen Arnold (Putnam), Ray Wells (Ross), Clark Hutson (Seneca) and Roger Bender (Shelby).
Editor: David A. Jones Web Editor: Nathan Watermeier
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.
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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.
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