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For Week of August 31 to September 7
C.O.R.N. 98-25
In This Issue:
A) Watch for Lodged Corn
B) Flooded Alfalfa-what to Expect
C) Bean Leaf Beetle on Soybeans
Thunderstorms last week accompanied by strong winds and, in some areas, tornados, caused widespread root and stalk lodging in corn. The magnitude of the damage varies considerably - in some localized areas I received reports of corn flattened by the winds and heavy rains. Since most of the affected corn was in the late dent stage of development, nearing black layer, direct yield losses (due to reduced grain fill) may be limited; where lodging was severe grain drydown may be affected. However storm damage will probably have its greatest impact on the harvest operation. Growers need to assess the extent of the damage to determine if harvesting adjustments are required, e.g. use of a reel pickup for severely lodged corn. Growers should identify fields exhibiting lodging and standability problem and consider prioritizing the harvest of these fields to minimize further grain yield losses.
Last weeks heavy rains in northwest Ohio fell on newly emerged alfalfa fields. The wet, saturated soil conditions for several days can promote the development of three alfalfa diseases, Phytophthora, Aphanomyces and Pythium root rot. This Phytophthora is a different species than the Phytophthora that attacks soybeans, however, conditions for infection are very similar. Alfalfa plants that have these diseases will appear stunted, yellow to reddish. Roots of alfalfa with Phytophthora root rot will have black or brownish lesions. Pythium root rot will attack the tap root of young seedlings and cause the tap root to be forked, thereby plants will be shallow rooted and will have problems surviving the winter. Alfalfa plants with Aphanomyces will have light to dark brown roots and hypocotyls.
The good news is that many of the modern varieties have resistance to Phytophthora and Aphanomyces. It is an excellent opportunity to monitor fields to see how these varieties perform under a worst-case scenario. If problems do occur, have the plants diagnosed to determine which pathogen was active. At this time it is too late to replant before winter but growers may be able to replant next spring.
Soybeans are currently in various stages of maturation ranging from early pod fill to the point of harvest. Many fields are at a point where pod fill is complete and foliage is beginning to discolor. Thus, we are at the point where feeding of bean leaf beetles (BLB) may cause significant pod injury, especially if they occur in abundance when the pods may be more succulent than the foliage.
To date, BLB adults activity has been very low. First generation adult activity occurred relatively late and in low numbers. Second generation should be appearing soon in the field and may cause of pod feeding injury. In general, we assume that if adult beetles are in abundance and the proportion of pods exhibiting feeding scars begins to exceed 8%, then a rescue treatment may be warranted to prevent the occurrence of damaged seeds. However, it must also be emphasized that seed damage resulting from BLB pod feeding is primarily due to disease infections, which require favorable wetting periods. Thus, seed damage may be absent despite significant pod injury by BLB if dry conditions prevail in the field. Given the levels of BLB activity observed this year, it is unlikely that a late flush of second generation BLB will cause a significant problem. Furthermore, dry field conditions in many regions of the state should minimize development of moldy seeds if some pod injury did occur. However, exceptions may occur and now is the time to be monitoring soybeans for pod injury where significant second generation BLB activity develops.
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Bean leaf beetle feeding on soybean pod. |
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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 & Anne Dorrance (Plant Pathology), Hal Willson (Entomology) and Peter Thomison (Corn Production); EXTENSION AGENTS: Mike Estadt (Pickaway), Roger Bender (Shelby), Ray Wells (Ross), Clark Hutson (Seneca), Barry Ward (Marion), Gary Wilson (Hancock), Greg La Barge (Fulton) and Steve Prochaska (Crawford).
Editor: Clark Hutson Web Editor: David Etzkorn
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.
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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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