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For Week of June 8-14, 1998
C.O.R.N. 98-13
In This Issue:
A) Dry Seedbeds and Poor Corn Emergence Could Result in Yield
B) Lodged Corn Already?! - "Rootless Corn Syndrome"
C) A Few Weed Control Situations
D) Time to Scout First Brood Corn Borer
E) Request for Some Weeds
Dry seedbed conditions in NW Ohio have delayed emergence in some corn fields and caused uneven emergence in others. In many cases, seeds planted in dry soils have not germinated so emergence will not occur until fields receive adequate rainfall. Uneven soil moisture levels in the seed zone are responsible for the uneven emergence. Most of this corn will eventually emerge. In 1993 we experienced similar dry soil conditions in parts of Ohio and it took some fields 3-4 weeks before emergence was complete. As a result of uneven emergence, fields can have a mixture of taller and shorter plants, with plant size differences depending on time from planting to receiving adequate moisture for seed germination and seedling growth. Emergence times may vary between parts of fields, from one row to the next, or from one plant to the next. Due to direct competition of plants at two different stages of growth next to one another, uneven stands typically yield less than even stands. Wisconsin and Illinois research indicates that mixed early and delayed emergence (of about 1 1/2 weeks) within a row can decrease yields 6 to 8%. However a 3-week difference in emergence of 1/2 or 3/4 of the plants within the row can decrease yields by 20 to 22%.
As soil conditions in many parts of Ohio remain dry, it's likely that some corn fields will experience root development problems. "Rootless corn syndrome" (or rootless corn) has been one of the more common root related problems reported in recent years. When corn plants emerge from cloddy seedbeds (or furrows in which there is poor soil seed contact) and are subject to hot, dry windy weather, rootless corn problems may occur. Relatively cool conditions this past week have slowed corn growth and probably limited the appearance of some rootless corn problems.
Under favorable growing conditions, the nodal roots (crown or secondary roots) develop above the seed and comprise the permanent root system of corn. The nodal roots, not the seminal roots (associated with the seed), are important in providing the water and the mineral nutrients that the corn plant needs for normal growth and development.
Plants exhibiting rootless corn symptoms are often leaning or appear ready to lodge. Affected corn plants may only be anchored in the soil by seminal roots or by a single nodal root. This condition is generally observed in plants from about the three leaf stage to the eight leaf stage of development. Before the problem is evident, corn plants may appear vigorous and healthy, but after a storm with strong winds, plants will fall over because there is a limited number or no nodal roots supporting them. Leaning and lodged plants (sometimes referred to as floppy corn) may also be wilted. When affected plants are examined they are found to lack all or most nodal roots. The nodal roots present appear stubby, blunt, and unanchored to the soil.
Rootless corn problems are usually caused by weather related conditions that coincide with development of the permanent root system and environmental factors. These include shallow plantings, hot, dry surface soils, compacted soils, and loose or cloddy soil conditions. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn. Nodal root development is inhibited by hot, dry compacted soils. The force of strong winds can break off secondary roots and inhibit establishment of a permanent root system.
Although certain types of herbicide injury (e.g. 2,4-D, Banvel) and insect feeding (e.g. corn rootworm) may cause lodging to occur in corn plants during vegetative development, there is generally little evidence of their involvement in these rootless corn problems. Nevertheless, there may be situations where insect feeding and/or herbicides may be a contributing factor to the problem.
Poor root development may also occur in no-till fields that were planted when soils were too wet. In addition to likely compaction-induced root problems, abnormal root development may also occur because the furrow walls may have been smeared during the planting operation, preventing good seed-soil contact. If conditions turn dry, the walls of the furrow become hard and act as a barrier to root development. Roots growing in such an environment often appear flattened and under extreme conditions may result in plants' breaking and falling over during wind storms.
Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery. Of course, this is difficult to do in a no-till situation or when the soil is hard and dry. Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as soon as grain moisture conditions permit.
We have observed a few situations that bear addressing this week. In the northern part of the state where conditions are extremely dry, weeds have escaped pre-emergence treatments that received inadequate rainfall for "activation." Annual grasses in corn are reaching the 4 inch stage, and there is some question as to whether herbicide should be applied now to control these. The main option for grass of this size in corn is Accent. If the grasses are not more than 3 inches tall, Basis Gold or Accent Gold may also be used. Our recommendation is to control grasses before they exceed 4 inches in height. Accent becomes inconsistent when grasses exceed 4 inches, and the dry weather also has some potential to reduce Accent activity. Even if significant amounts of rain occur, do not expect "reachback" of earlier pre-emergence treatments containing atrazine. This may occur for very small grasses, but is not likely when grasses are more than an inch tall. OSU research has shown that grasses that are less than 2 inches tall and actively growing can be controlled with less than labeled rates of Accent. However, we advise against reducing rate when conditions are dry and grasses are more than 2 inches tall. Our research has also shown the benefit of using methylated seed oil (Priority MSO, Meth Oil, SunIT, etc) with Accent under dry conditions, especially when tank-mixing with broadleaf herbicides.
In the central and southern part of the state where soybeans were planted fairly early, the weeds may be growing faster than the soybeans. Weed size may warrant post-emergence herbicide application, but it may be quite a while before the soybeans canopy and help with weed control. In this situation, consider use of herbicides that provide some residual control, such as Pursuit or FirstRate. Another alternative is the use of a split post-emergence program, applying a half rate now, and a second half rate in a few weeks.
Regarding application strategies in dry weather, we have come to the following conclusions: 1) if rainfall is in the immediate forecast, post-emergence herbicide activity will be maximized by waiting until after rain to apply, but 2) large drought-stressed weeds can be extremely difficult to control, so 3) where there appears to be no rain coming, apply when weeds are small for best activity. This may result in the need for a later application if late rain stimulates a new flush of weeds, but is a more effective strategy than trying to kill large tough weeds with herbicide mixes that are excessively injurious to the crop.
The spring flight of adult European corn borers has peaked and is now on the decline. Early whorl infestations of first brood corn borer should be evident at this time in the field especially in early planted fields which are in the early or mid-whorl stages of development. In general, development of most corn fields has been delayed by the weather and survival of 1st brood corn borer on corn in the pre-whorl stages will not likely be significant. However, rains have been light (when they have occurred) and corn borer survival may benefit from not having been drowned by heavy rains which often are responsible for reducing 1st brood infestations.
At this point in time, scouting activities for corn borer should emphasize detection of foliar feeding by the early corn borer instars. The earliest signs of feeding activity will be window pane type injury, since the young larvae cannot penetrate through a leaf. The next type of feeding injury detected will be the early shot hole feeding caused by a young larvae boring through the center whorl.
If 75% or more of the stand exhibits whorl feeding injury, potential economic injury may result if the borers complete their development in the stalks. However, since larval mortality may occur at any time, it is important to determine the number of borers present per plant, and determine their predominant stage of growth. If a rescue treatment is considered, it is important to recognize that a treatment will have to prevent the final development of one or more borers per stalk to justify the treatment.
Given current conditions, it appears that the potential for significant 1st brood corn borer injury this season is unlikely. However, one should periodically walk the fields to prevent any surprises.
Additional reading information is available through the Field Crops Pest Management Circular #15, European Corn Borer, Ohio Pest Management and Survey Program.
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European corn borer egg mass. |
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European corn borer "windowpane" leaf feeding. |
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European corn borer "shot-hole" leaf feeding. |
If anyone has some atriplex that is 2-6 inches tall in soybeans please call Jeff Stachler at (614) 292-1393 or e-mail (stachler.1@osu.edu). We would like to conduct research on controlling atriplex with post-emergence herbicides. We need a 170 feet by 295 feet area with a good population of atriplex.
We are also looking for people interested in leaving 3 or 4, 5 feet by 5 feet areas in a field totally untreated if you have a good population of lambsquarters and/or atriplex. We are wanting to determine how many different lambsquarters and atriplex species are in fields. The areas will be scouted during mid-summer and then the seeds harvested in the fall. Please call or e-mail me if you are interested.
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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 and Anne Dorrance (Plant Pathology), Hal Willson (Entomology), Peter Thomison (Corn Production), and Mark Loux and Jeff Stachler (Weed Science); District Specialist: Curtis Young (IPMP); Extension Agents: Roger Bender (Shelby), Clark Hutson (Seneca), Dave Jones (Allen), Greg La Barge (Fulton), Max Mohler (Lima Branch), Mike Estadt (Pickaway) and Ray Wells (Ross).
Editor: Curtis Young Web Editor: Nathan Watermeier
Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination 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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