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May 20 - 28, 2002
C.O.R.N. 2002-14
In This Issue:
A) Addendum To Last Week's Article On Corn Herbicides
B) Switching From Corn To Soybeans - Be Aware Of Herbicie Rotation
Restrictions
C) Herbicide Applications To Stressed Corn
D) What Is That Yellow Weed?
E) Corn Yellowing Should Be Temporary
F) Assessing Frost & Low Temperature Injury To Corn
G) Early Season Flooding And Ponding Injury In Corn
H) Cold Nights And Freezing Injury To Wheat
I) Wheat Foliar Disease And Fungicide Applications
J) Wheat Head Scab Risk Predictions
K) Field Crop Insect Pest Update
L) Sprayer Calibration Pays Dividends
It was pointed out to us that, in last week's newsletter, we had not addressed whether Fultime could be applied to emerged corn using 28% UAN as the spray carrier. The current Fultime label does not address this issue. Dow informed us that they neither recommend nor prohibit application of Fultime to emerged corn in 28% UAN. It is therefore legal to do so, but Dow accepts no liability for resultant injury to corn. Be aware that the current OSU Weed Control Guide states that Fultime can be applied in 28% to emerged corn as long as it is not mixed with other herbicides. This statement, apparently from an earlier Fultime label, is incorrect given the current label and Dow's position at this time.
Any product containing atrazine or simazine- do not plant soybeans until next
year
Axiom, Define, Dual II Magnum, alachlor products, Outlook, Python - plant soybeans
anytime
Balance, Epic - do not plant soybeans until next year
Basis - soybeans can be planted 15 days after application
Callisto - do not plant soybeans until next year
Harness, Degree - do not plant soybeans until next year
Hornet - do not plant soybeans until next year
Surpass, TopNotch - do not plant soybeans until next year
Atrazine, simazine, and Hornet are probably the most problematic among all of the corn herbicides, when the field absolutely has to be replanted to soybeans. The residual life of acetochlor (Degree, Harness, TopNotch, Surpass) in soil is relatively short, and it is likely that soybeans planted 30 days or more after application could survive. Similarly, Aventis sources informed us that soybeans planted 45 days after Balance or Epic application probably could survive. However, manufacturers assume no liability for injury to soybeans when label restrictions are not followed.
Atrazine and simazine are considered to be persistent herbicides. Soybeans can survive atrazine concentrations in soil of approximately 0.17 to 0.35 ppm (an atrazine rate of 1 lb/A corresponds roughly to 1 ppm). The concentration that soybeans can survive varies with soil type, because atrazine will be more active on soybeans in low organic matter, coarse-textured soils compared to high organic matter, finer-textured soils. Atrazine is less persistent in the lower organic matter, coarse-textured soils, though, so it is really impossible to say with any certainty whether soybeans will survive in a given situation, regardless of the amount of rain. The most effective method for determining the risk of injury to soybeans is to sample the soil and send it to a laboratory to determine the atrazine concentration. This can be accomplished fairly rapidly, but can be somewhat costly. We suggest soil samples be taken from the upper two or three inches of soil, and shipped to the laboratory as soon as possible after sampling.
We suggest delaying herbicide application to emerged corn until warmer conditions have improved the vigor of the corn if at all possible. Corn is many fields is very stressed, and will be unable to metabolize herbicide, increasing the risk of corn injury. Some specific suggestions and comments:
The weed is most likely cressleaf groundsel, Senecio glabellus. It has many alias names, such as yellowtop, butterweed, golden ragwort, and yellow ragwort. Cressleaf groundsel is a member of the Asteraceae (Composite) Family and has a winter annual life cycle. That means this critter was in the fields late last fall. The plant grows two to three feet tall, has a hollow stem, little or no hair on the plant, the flowers have yellow ray and disk petals (outside petals are yellow and center petals are yellow), the stem and leaves are often (not always) purple to red in color, and there are many flowers (heads) on the plant including several of the branches.
This species was believed to be quite poisonous and therefore is on the Ohio Noxious Weed List. However, the cressleaf groundsel appears to be only slightly poisonous. Several other Senecio species such as tansy ragwort, Senecio jacobaea, and golden ragwort, Senecio aureus are quite poisonous and common groundsel, Senecio vulgaris, is somewhat toxic. The golden ragwort and common groundsel are fairly common in Ohio, with the cressleaf groundsel rapidly expanding to other areas of Ohio. As of 1988, cressleaf groundsel was found in only 4 Ohio Counties, according to herbarium records. Those four Counties were Butler, Preble, Ottawa, and Erie. Today, we can find this species in every county in Southwest, South Central, Central, and West Central Ohio.
This species continues to spread for several reasons. One, being a winter annual, it can easily get established in no-tillage fields. The seeds can be wind blown like dandelion seeds, so it spreads to many new fields quickly. The shift to postemergence herbicides that have limited or no residual control, especially glyphosate, has helped this species spread. The weather has been warmer than normal in late Fall for the last several years. Lastly, early planting in the Spring allows for early Fall harvests, thus allowing cressleaf groundsel more time to get established.
There is little information on how to control this species at this time. It appears to have some tolerance to 2,4-D. High rates of glyphosate plus or minus 2,4-D may be necessary to control cressleaf groundsel.
Recent cloudy, cool, wet weather has slowed growth of early planted corn. Corn seedlings often turn yellow (due to low nitrogen uptake and/or limited chlorophyll synthesis) or purple (reduced root development) under cool, wet conditions. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool. Yellowing or purpling of corn plants at this stage of development generally has little or no effect on later crop performance or yield potential. If it's induced by environmental conditions, the yellow or purple appearance should change to a healthy green after a few sunny days with temperatures above 70 degrees F. If plants remain yellow then closer inspection and assessment is needed to determine if yellowing is caused by nutrient deficiency or some other factor. Given our weather conditions this year a nitrogen deficiency is most likely responsible for leaf yellowing.
The growing point of a corn plant is located deep inside the seedling where all the remaining leaves originate, as does the tassel. You can observe the growing point by digging up a seedling and splitting the stem from top to bottom. The growing point will be located at the top of the pyramid-shaped whitish stalk tissue near the base of the seedling. In corn seedlings that have just emerged, the growing point is located about 1/2 to 3/4 inch below the soil surface, just above the crown area. The growing point remains at or below the soil surface until the six leaf collar stage (V6), after which its position is elevated as the stalk enters a more rapid elongation phase.
While the growing point is at or below ground, the corn plant is relatively safe from above-ground damage to the leaves and stem. Severe damage from late frosts, hail, anhydrous burn, insect feeding above ground, etc., will usually not kill corn plants younger than the V6 as long as the growing point is not damaged. On the other hand, while the growing point is below the ground, the plant is more sensitive to below-ground insect feeding, flooding or saturated soils.
To determine the viability of young corn plants damaged by frost, the simplest advice is to wait for several days after frost injury for signs of re-growth. Generally 2 to 4 days of 70 degree or warmer temperatures are sufficient to stimulate new leaf growth on an affected plant. New leaf tissue should be emerging from the whorl. If temperatures have been cooler than normal, re-growth may not be readily evident. In that event, you can determine plant viability by splitting the stem lengthwise and observing the condition of the growing point. If the plant is "healthy" the growing point will be firm and white or cream colored. A darkening or softening of the growing point usually precedes plant death.
Subsequent rainy weather can cause problems to freeze damaged corn. Bacterial soft rots can destroy the corn growing point and this often occurs when rains splash bacteria into frost damaged leaf whorls. If growing conditions are favorable, i.e. warm and dry after the freezing event, the plants typically outgrow bacterial damage, but if weather remains cold, wet and cloudy following the freezing event, the potential for this bacterial damage increases.
Injury from freezing can also prevent new leaf growth from unfurling normally resulting in tied leaf whorls - this frost damage sometimes resembles the "buggy whipping" and tight leaf rolling associated with certain herbicide injury. Generally plants exhibiting such symptoms resume normal growth when growing conditions improve. Mowing fields to cut off the tied leaf whorls, and thereby allow normal expansion of undamaged leaf tissue is usually of limited benefit.
The persistent rains that have plagued parts of Ohio during the past 1-2 weeks have resulted in localized flooding in some corn fields, and ponding in others. The following are some tips to consider when evaluating possible damage from ponding and flooding.
The extent to which flooding injures corn is determined by several factors including: (1) plant stage of development when flooding occurs, (2) duration of flooding and (3) air/soil temperatures. Prior to the 6-leaf collar stage (as measured by visible leaf collars) or when the growing point is at or below the soil surface, corn can usually survive only 2 to 4 days of flooded conditions. The oxygen supply in the soil is depleted after about 48 hours in a flooded soil. Without oxygen, the plant cannot perform critical life sustaining functions; e.g. nutrient and water uptake is impaired, root growth is inhibited, etc. If temperatures are warm during flooding (greater than 77 degrees F) plants may not survive 24-hours. Cooler temperatures prolong survival. Once the growing point is above the water level the likelihood for survival improves greatly.
Even if flooding doesn't kill plants outright, it may have a long term negative impact on crop performance. Excess moisture during the early vegetative stages retards corn root development. As a result, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water. Flooding and ponding can also result in losses of nitrogen through denitrification and leaching.
If flooding in corn lasts less than 48 hours, crop injury should be limited. To confirm plant survival, check the color of the growing point. It should be white to cream colored, while a darkening and/or softening usually precedes plant death. Also look for new leaf growth 3 to 5 days after water drains from the field. Sometimes the growing point is killed by bacterial infections during and after flooding, but plant growth continues in the form of non-productive tillers (suckers).
Additional disease problems that become greater risks due to flooding and cool temperatures are corn smut and crazy top. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage is difficult until later in the growing season.
Several locations in the state reported freezing temperatures and the presence of frost over the weekend. Wheat in southern Ohio is flowering and in central Ohio the crop is now in the heading growth stages. Most of the wheat in the north is still in the boot stage of development. Whenever temperatures drop to 30 F at this time of year wheat is vulnerable to freezing injury. Wheat fields that are in the boot stage can take colder temperatures than when the heads have emerged. At the boot stage, the head is covered by the leaf sheath of the flag leaf which gives some protection, but some damage may occur when the temperature drops to 28 F or lower for more than two hours. The type of injury varies with exposure time, but floret sterility could result or the heads could be trapped in the boot. Heads may be distorted as they attempt to emerge as the stems elongate. Newly emerged heads are quite vulnerable to freezing injury when the temperatures drop to 30 F or below. Signs of freezing injury can be seen within a few days after freezing. Injury can occur to the entire head or only a portion of the head. Most frequently the head tip is injured. Damaged florets will turn white and the tissues will shrivel. Yield loss will be minimal if only the top florets of the head are injured, otherwise if entire heads are affected, the loss may be proportional to the number of heads killed. A photo of heads with frost injury can be seen on the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/frost.htm
We have had many questions about applying fungicides at this time. The fungicides (Tilt, Quatris and Stratego) are labeled for application up until full head emergence (Feekes growth stage 10.5). Most fields in southern Ohio are now past this growth stage. There is still time to apply fungicides to wheat in Northern Ohio, but in the vast majority of fields disease levels are not at threshold. We recommend that growers scout only those fields planted to susceptible varieties when fields begin head emergence. If they do not find powdery mildew or Septoria leaf blotch on the leaf below the flag leaf then do not spray. Cooler weather in combination with the clear weather forecast for the next week should slow disease spread. Fields planted to resistant or moderately resistant varieties should have little disease, where disease will likely be confined to the lower most leaves.
Over the next couple of weeks we will attempt to update
growers concerning the risk of wheat head scab. We have been collecting weather
data from a number of locations in the state and have been using our Wheat Head
Scab Risk models to make predictions for those areas of the state that have
fields flowering. We update our Scab Risk forecasts on a regular basis and these
can be viewed at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/Scab%20forecasting%20webpage02.htm.
Weather conditions have been quite variable over the state, but most regions
have received sufficient rainfall during the pre-flowering period to be of concern.
The recent cooler temperatures and the predicted drier weather over the next
week should limit the conditions required for infection. So we expect the wheat
fields that were in flower over the weekend and those to go into flower over
the next few days to have lower risk for head scab. Because of the lag time
for weather stations to post data and the areas of the state with fields in
the critical flowering growth stage, we can make predictions for only a few
locations in southern Ohio based on our pre-flowering weather model (Model I).
This model has fairly high accuracy for predicting when there will not be an
epidemic. Risk predictions are made for early, mid and late flowering fields
at each location. Estimate the flowering time for each of your fields then check
the risk prediction at the weather station location nearest your fields. Another
risk prediction will be made for each of these locations in about 10 days when
the post flowering data can be evaluated.
Get the sweep nets ready. We normally start finding potato leafhopper (PLH) in alfalfa about the middle of May in central Ohio. This year is not any different. The first adult potato leafhopper was found in first cutting alfalfa last week in central Ohio. As first cutting alfalfa is made, the second cutting needs to be checked for PLH within a week.
Emerged corn should be checked starting this week for cutworm damage. Checks
in one to two leaf corn in central Ohio last week found early cutworm leaf feeding
with a few plants cut. Worms were not found in any of the fields checked.
Chemicals labeled for rescue treatment of cutworms are:
Ambush* 6.4 to 12.8 fl oz/A
Asana* XL 5.8 to 9.6 fl oz/A
Capture* 2EC 2.1 to 6.4 fl oz/A
Lorsban* 4E 2 to 3 pints/A
Mustang* 1.4 to 3.0 fl oz/A
Penncap-M* 4 pints/A
Pounce* 3.2EC 4 to 8 fl oz/A
Pounce* 25WP 6.4 to 12.8 fl oz/A
Sevin XLR PLUS 2 to 3 quarts/A
Sevin 4F 2 to 3 quarts/A
Warrior* 1CS 1.92 to 3.20 fl oz/A
Large numbers of millipeds were found last week in an emerging no-till soybean
field in central Ohio. The millipeds were about ¼ to 3/8 inch in length
and found mainly under the debris in the field and in the slit made by the planter.
The millipeds were curled and at first looked like small grubs. They were not
damaging the soybean plants but were probably feeding on decaying organic matter
in the field.
Results of many "Sprayer Calibration Clinics" I participated in Ohio shows that only one out of three applicators are applying chemicals at a rate that is within + 5 % of their intended rate (an accuracy level recommended by USDA and EPA). Of those two-thirds of the applicators missing the mark, about half is under spraying while the other half is over spraying. In one case, the applicator would be over spraying by as much as 75% had he used the nozzles that he just purchased and installed on the boom. The situation is not much different in other Sates. A survey of 152 private and commercial applicators in Nebraska revealed that only one out of four farmers were applying pesticides within 5% of their intended application rate. A survey conducted in South Carolina indicated that nearly 85% of applicators applied pesticides with errors greater than 10% when compared to intended rates. Extension Engineers in North Dakota reported that only 11 of the 60 sprayers they calibrated were applying chemicals as the operator predicted.
Sprayers should be calibrated several times a year. Changes in operating conditions
and the type of chemical used require a new calibration. Frequent calibration
is even more important with liquid application because nozzles wear out with
use, increasing the flow rate. The results of the survey conducted in Nebraska
indicated a positive correlation between application accuracy and the frequency
of calibration. Approximately 67 percent of the operators who calibrated before
every spray operation had application errors below 5 percent while only 5 percent
of those operators who calibrated their equipment less than once a year (once
every two, three, four years) achieved the same degree of application accuracy.
Tere are several ways to calibrate a sprayer. One easy method is explained in
OSUE Fact Sheet AEX-421. This publication can be obtained by either contacting
County Extension Offices in Ohio, or from OSUE web site on Ohioline. (http://www.ag.ohio-state.edu/~ohioline/aex-fact/0520.html)
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.
Ohio State University Specialists and Associates: Pat Lipps , Anne Dorrance and Dennis Mills, (Plant Pathology), , Mark Loux & Jeff Stachler (Weed Science), Ron Hammond (Entomology), Bruce Eisley (IPM), Peter Thomison (Horticulture and Crop Science), Erdal Ozkan ( Agricultural Engineering) and Ed Lentz (Northwest District Specialist) Ohio State University Extension Agents: Steve Bartels (Butler), John Barker (Knox), Bruce Clevenger (Defiance), Mark Koenig (Sandusky), Andy Kleinschmidt (Van Wert), Glen Arnold (Putnam), Roger Bender (Shelby), Clark Hutson (Seneca), Greg La Barge (Fulton), Howard Siegrist (Licking), Dennis Baker (Darke), Barry Ward (Champaign), Alan Sundermeier (Henry), Ray Wells (Ross), and Steve Prochaska (Crawford).Editor: Steve Prochaska 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.
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