http://www.ag.ohio-state.edu/~corn/ |
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For June 1 to 6, 1999
C.O.R.N. 99-11
In This Issue:
A) Comments about Postemergence Herbicide Applications
B) Reports of Purple Corn Problems
C) Ohio Wheat Still in Excellent Condition
D) Some Early Season Soybean Diseases Present
E) Stand Losses by Cutworm Under Dry Conditions
F) Bt-Corn and the Monarch Butterfly
G) Modified Relay Intercropping Update
H) The 1999 OSU Weed Science Field Day
Scout all corn and soybean fields for weeds that had a preemergence herbicide applied and begin scouting total postemergence fields. Now that we have gotten to June, most of our weeds have emerged for the season. There may still be additional flushes of weeds if we get an extended wet period, but if we stay dry then we should see very little additional weed emergence. Weeds that can still continue to germinate for another month are giant ragweed, waterhemp, eastern black nightshade, burcucumber, fall panicum, shattercane, and maybe foxtail.
For those individuals that still have dry conditions, be sure to spray corn this week if grasses are present. The grasses are growing and getting more stressed. Switch to a Methylated Seed Oil (MSO) when using Accent and be sure to include 28% Nitrogen or Ammonium sulfate (AMS). The use of MSO with any ALS herbicide will improve weed control. There is a greater risk of injury with these products when using a MSO, but the corn is still small enough in most cases to not be a problem and uncontrolled grasses will cause greater yield reductions than any potential injury at this time.
Any normal (non-herbicide tolerant) soybean fields that have lambsquarters present should be sprayed very soon, especially fields planted before May 1st. Lambsquarters over 4-6 inches tall and stressed are very difficult to control. Pinnacle and Raptor are the only herbicides that will consistently control lambsquarters that are not too tall or temperature or moisture stressed. Spray lambsquarters before they are 4 inches tall if possible. Tank mixing Resource with Pinnacle or Raptor may increase lambsquarters control if they are less than 4 inches tall. Reducing the rate of Pinnacle to be safer to the soybeans is a good idea, however less than full rates of Pinnacle on lambsquarters over 4 inches may cause poor control. Reduced rates of Pinnacle also provide poor control of other lambsquarters species and certain biotypes of common lambsquarters. If Pinnacle is sprayed very soon the long term effects of significant injury now will be less than the yield reduction due to poor control of lambsquarters. Soybeans have a long time to recover from any herbicide injury that may occur in the next 7 to 10 days.
Hemp dogbane is very common in corn and soybean fields this season. Roundup Ultra applied to Roundup Ready corn or soybeans when the hemp dogbane is in the bud to flower stage will provide the greatest control. With this application apply at least 1.0 quart per acre. Higher rates can be more effective, especially if the hemp dogbane is not in the bud to flower stage. Some hemp dogbane is already at the bud stage, which is earlier than normal. Apply Beacon at 0.76 ounces per acre plus 2,4-D Amine at 1.0 pint/A or Banvel/Clarity at least at 0.5 pint per acre or Accent at 0.67 ounces per acre plus Banvel/Clarity at least at 0.5 pint/A for control of hemp dogbane in normal corn. Exceed or Spirit can be used in the place of Beacon. Be sure the corn is at the proper stage to allow 2,4-D and Banvel/Clarity to be applied safely. In normal soybeans Flexstar and Cobra plus or minus Basagran may burn off the leaves of the hemp dogbane, but it will regrow. Make sure the spray boom is set high enough to get good coverage of the hemp dogbane. Consult page 118 in the 1999 Weed Control Guide for Field Crops for additional comments.
During the past week I have received a several calls concerning leaf purpling in corn. Weather conditions are probably responsible for much of this abnormal leaf purpling. While leaf purpling is often associated with phosphorus deficiencies, any stress that inhibits root growth and development can lead to purpling of the leaves. Root growth can be hindered by factors such as cool soil temperatures, crop injury, soil compaction, drought stress, nutrient deficiency, soil-borne diseases, root-feeding insects, current year's herbicide, or herbicide carryover. Development of the permanent (crown or secondary) root system is more sensitive to temperatures than is that of leaves and is more likely to be adversely affected by temperature swings (which have been common in recent weeks) than leaf tissue.
If utilization of sugars (produced by photosynthesis in leaf tissue) is reduced by a restricted, slowly growing root system, then large amounts of sugar build up in the leaves. Such an "overload" of sugars in above ground tissue triggers production of anthocyanin, a purple pigment, and results in purple plants.
Leaf purpling may also be influenced by hybrid genetics - or more specifically, differences in hybrid sensitivity to varying environmental conditions. During early vegetative growth some corn hybrids are more likely to show purpling following periods of cool, cloudy weather or hot, dry conditions. Certain hybrids may show more purpling than others if they contain more anthocyanin producing genes. Genetic purpling itself will usually have no effect on grain yield. Leaf purpling should slowly disappear as temperatures return to normal levels.
The cause of the leaf purpling, not the purpling itself, will determine whether yield loss will occur by harvest this fall. If the cause of the root restriction is temporary (e.g., cool temperatures), then the purpling should disappear as the plants further develop and yield losses should be minimal if any. Much of the purpling we've seen recently should disappear as the rains we're currently experiencing reduce moisture stress. If the cause of the root restriction continues to affect plant growth all season (e.g., soil compaction), then the purpling may continue for some time and some yield loss may result.
Wheat is through the flowering growth stages throughout most of the state and little to no disease increase. The dry weather during flowering has allowed the crop to escape infection most leaf diseases. Some fields of susceptible varieties are still showing development of powdery mildew, but it is too late to do any spraying for leaf diseases. Wheat should not be sprayed for diseases after flowering is complete. Research has shown that there is less than a 50% chance of recovering money spent on fungicide applications made one week post flowering. Very little Stagonospora leaf blotch or leaf rust have been detected in the state as well. We could now use some rain to help grain filling to meet full yield potential.
Reports from the southern part of the state indicate that wheat fields are showing no signs of Fusarium head scab. We will be able to see how the rest of the state has done for scab by next week. Usually, symptoms of head scab show up around 10 to 14 days past flowering if infections occurred. All indications are that we will have very little or no scab in Ohio this year.
Wheat harvest will probably be early this year. How early is difficult to predict, depending on how high the day and night temperatures get over the next three weeks. Daytime temperatures in the upper 80's and low 90's tend to quicken senescence, so several days in a row with hot weather will reduce grain fill and hasten premature death of the plants. As of now it would be a good idea to get your combines in shape for harvest a week earlier than normal (or about the same time as last year).
Soybean stands across the state look good in general. There are a few isolated locations where we are getting some reports of problems.
Rhizoctonia seedling blight has been reported to cause substantial losses in years when there is reduced amount of rainfall and warm soil temperatures. Rhizoctonia is a fungus that survives in the soil and can be found in all of our fields in Ohio. Rhizoctonia infections occur after the seed has germinated and the fungus begins to colonize the root which results in a preemergent damping off. Infections can also occur after emergence and appear as sunken lesions on the lower stem which are a characteristic brick-red color. Typically these lesions occur at the soil surface. There are several seed treatments on the market that can be used to manage this early season disease.
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Rhizoctonia seedling blight |
Fusarium seedling blight can also be a problem on soybeans that have been under stress. Soybeans with Fusarium will have a black color and the stem will be thin and wiry. There are a number of species of Fusarium that can infect soybean seedlings and again this is a pathogen that can be found in many of our fields in Ohio.
Phytophthora sojae - there are reports from some limited areas of the state where soils have been saturated for several days. These conditions are conducive to the development of Phytophthora seed and seedling blight. This pathogen is especially prevalent in our heavier clay soils, under saturated soil conditions the survival structure, oospore will germinate and form sporangia. Inside the sporangia, zoospores will form which can then swim to germinating seeds and seedlings. Symptoms of Phytophthora infections are a pale brown color on the root and hypocotyl. Seed treatments and use of resistance varieties have been the main disease management strategies.
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Phytophthora seedling blight |
A week ago, the rains hit some areas hard and other areas very lightly. Thereafter cool and windy weather followed, and now the temperatures are above normal. In summary, some plantings of corn are under stress and growing very slowly. Where cutworms are present in slow growing corn, stand losses may be severe since the cutworms are growing and can destroy a significant number of corn plants, especially when the corn remains in the early stages of development.
At the Western Branch Station, we are observing above normal cutworm activity in all of our experiments. A number of our experiments already exhibit stand losses of 10% or more in the untreated check plots, and in some experiments average stand loss in the untreated check plots has already reached 30%. Since most of the corn in our plots is still in the 1-2 leaf stage and conditions are very dry, cutworm injury is accumulating rapidly - especially in the dry and lighter soils. Two weeks ago, we applied a series of rescue treatments to a cutworm management trial. The rescue treatments arrested cutworm injury while injury in the untreated check plots continued to increase.
It is important to recognize that under the current conditions, missing stand combined with 3% or more visible cutworm stand injury is an indicator of significant cutworm activity. Given the small size of most corn plants, plus dry and windy field conditions, the ratio of missing stand to visible cutworm injury is very high this season. In brief, areas of a field assumed to represent slow emergence may actually represent areas of intense cutworm injury. Where plants are small and cutworms are present, the potential for additional cutworm injury is high and rescue treatments may be warranted until corn development begins to accelerate.
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Black cutworm larva in base of corn plant. |
During the past couple weeks, the press has focused on a recently published study suggesting that Bt-corn may have a negative impact on Monarch butterfly populations in the corn belt. The source of the story is a laboratory study conducted at Cornell University in which milkweed treated with pollen of Bt-corn was documented to cause a negative effect on Monarch butterfly larvae fed on the Bt-corn pollen treated milkweed compared to milkweed treated with pollen of non-Bt corn pollen. Since the study was published in Nature and promoted by a news release from the Cornell University News Service, the news media quickly picked up the story and linked it to comments from various environmental groups that question the general use of transgenic crops in American agriculture. In brief, the results of a basic study on the effects of Bt-corn on non-target populations was picked up by the popular media which focused on potential ramifications that will take years to evaluate in real life field studies.
The issue on the effect of Bt-corn pollen on Monarch butterflies is nothing new. In March, a graduate student from Iowa State presented a poster on a similar study at the North Central ESA Branch meetings and some studies of the subject date back to 1986. However, since the Iowa State graduate student's study has not to date been published in a prestigious journal or promoted by Iowa State public relations, the issue was not exploited by the popular press.
Over time, the issue of Bt-corn and Monarch butterflies will be reviewed by various panels evaluating the use of Bt-corn. Reductions in pesticide use for corn borer associated with the use of Bt-corn will be cited as an attribute to adoption of Bt-corn. Experts will debate the timing of Monarch butterfly development in relation to corn pollination. Statistics on habitats of milkweed and other flora supporting non-target populations that may be impacted by transgenic crop technology will be reviewed. As field data emerges on Bt-corn and Monarch butterflies, the press will likely ignore the issue since the gradual accumulation of real world field data tends to limit speculation on either side of an issue with no clear cut answers.
In summary, the current press coverage on the potential impact of Bt-corn on Monarch butterflies is another classic example of excessive speculation based on a laboratory study that may or may not be representative of the actual field situation.
Modified Relay Intercropping (MRI), the planting of soybeans into standing wheat, has begun in north central Ohio. Soybeans 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. Normally soybeans are planted from 15-30 days prior to wheat harvest. Light or the lack of it, has a profound effect on the growth of intercropped soybeans. Soybeans planted too early into well-tillered wheat 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.
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Modified Relay Intercropping |
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. Replicated field trials on the MRI system have resulted in favorable soybean and wheat yield results over four years. For a summary of soybean and wheat field trial results go to: www2.ag.ohio-state.edu/~craw/ag/reas98.htm.
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.
In summary, MRI planting is occurring in a very timely fashion, however soybeans are very dependent on timely rainfall in July and August to yield well.
The 1999 OSU Weed Science Field Day will be held on July 7, 1999. This is a self-guided tour of the OSU weed management research plots, including evaluations of new herbicides, herbicide-tolerant crops, and research on narrow rows and weed interference. We will start at 9:00 at the OARDC Western Branch, break for lunch at noon, and resume the tour in the afternoon at Farm Science Review. A lunch will be available at Western Branch at a cost of approximately $10 per person. Reservations are not required, but we would appreciate a phone call to let us know how many in your organization are attending so we can plan for lunch.
The OARDC Western Branch is located about 5 miles south of I-70 on SR 41. Our plot area at Farm Science Review is located north of I-70 on SR 38, directly across SR 38 from the large red storage shed (about 1 mile north of the I-70 overpass, and after the road makes two sweeping turns). There is no exit from I-70 for SR 38 - you must exit I-70 at SR 29 and go west to SR 38, or you can exit at SR 42 or 56 and take SR 40 to SR 38. We look forward to seeing you on July 7.
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
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: Pat Lipps (Plant Pathology), Anne Dorrance (Plant Pathology), Jeff Stachler (Weed Science), Hal Willson (Entomology) and Peter Thomison (Corn Production); DISTRICT SPECIALIST: Ed Lentz (Agronomy, Northwest); EXTENSION AGENTS: Barry Ward (Champaign), Steve Prochaska (Crawford), Dennis Baker (Darke), John Barker (Knox), Howard Siegrist (Licking), Glen Arnold (Putnam) Ray Wells (Ross), Clark Hutson (Seneca) and Roger Bender (Shelby)
Editor: Clark Hutson Web Editor: Steve Lichtensteiger
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
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: Pat Lipps & Anne
Dorrance (Plant Pathology), Hal Willson (Entomology), Peter Thomison (Corn Specialist),
Jeff Stachler (Weed Science), and Jim Beuerlein (Soybean & Sm Grain Specialist);
DISTRICT SPECIALIST: Ed Lentz (Agronomy, Northwest); EXTENSION AGENTS: Dennis Baker
(Darke), Clark Hutson (Seneca), Dave Jones (Allen), Woody Joslin P.A. (Shelby), Greg
Labarge (Fulton), Howard Siegrist
(Licking), and Barry Ward (Champaign).
Editor: David A. Jones Web Editor: Steve
Lichtensteiger
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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