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In This Issue:
A) They're Back, Bean Leaf Beetles
B) Drought Increases Potential for Stalk Rot and Lodging in Corn
C) Symptom of Sudden Death Syndrome in Soybean
D) Results, On-Farm Wheat Management
E) Drought Information on the Web
F) Symposium on Biotechnology and Specialty Crops
Second generation of bean leaf beetle (BLB) will soon feed on soybeans and may cause significant levels of pod injury. Assessment of a soybean field for potential pod and seed injury must be done on a field by field basis, since each field will likely exhibit a different combination of BLB activity and soybean development. The key factors that must be considered in an assessment include the following:
1. Pod injury level. The percent pod injury should be determined by random sampling about ten plants and counting on each plant, the number of pods with feeding injury and the total number of pods.
2. BLB population level. Adult BLB population should be estimated by taking 10 sweeps with a sweep net at three to four locations in a field. Less than five BLB per sweep are unlikely to cause significant injury. Five to ten BLB per sweep indicates a potential problem possibly warranting rescue treatment. More than ten BLB per sweep will result in significant injury especially if two or more weeks remain until leaf drop.
3. Number of weeks until leaf drop. When the foliage dries and drops, beetles exit the field. Thus, the time remaining for BLB feeding is a key factor in the occurrence of pod injury. If 8 BLB per sweep are found in a field one week away from leaf drop, an additional 10% pod injury will likely occur. But, if 8 BLB per sweep are found in a field three weeks from leaf drop, then the additional pod injury may be 20% or more.
4. Amount of moldy seed. Finally, it is very important to note whether pod injury caused by BLB feeding results in damaged and moldy seeds. Yield losses due to BLB are primarily due to the development of moldy seeds, which adhere to the pod and are lost during harvest. However, under dry conditions it is possible to have minimal development of moldy seeds and minimal impact on yield, despite heavy pod injury. In 1995, we studied two sites on which pod injury had been reduced 10 to 15% by aerial treatment, but no yield impact could be detected since dry weather reduced mold activity.
In summary, assessment of potential pod injury due to BLB feeding is not a simple process. One needs to know how much damage exists and then attempt to predict how much additional damage will occur for given BLB activity in the time remaining before leaf drop. And then one needs to estimate how much seed injury will likely occur and whether a rescue treatment can be economically justified.
In addition to severely reducing corn yields, drought conditions this year may also increase the potential for lodging and stalk rot problems. When stalk rot occurs late in the season as it usually does, it has little or no direct effect on yield. However, the lodging of early diseased corn plants has such an impact on harvest losses that many plant pathologists consider stalk rots to be the most significant yield-limiting disease of corn.
For a corn plant to remain healthy and free of stalk rot, the plant must produce enough carbohydrates by photosynthesis to keep root cells and pith cells in the stalk alive and enough to meet demands for grain fill. When corn is subjected to severe weather stress, photosynthetic activity is sharply reduced as leaves roll tightly and plant growth slows. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and stalk infection by fungi. Even mild, early-season water stress during the pre-tassel stage of development can significantly increase root infection by stalk rot fungi and result in greater stalk rot at maturity. As plants near maturity, this removal of nutrients from the stalk to the developing grain results in a rapid deterioration of the lower portion of corn plants in drought-stressed fields with lower leaves appearing to be nitrogen stressed, brown, and/or dead. Other plant stresses which increase the likelihood of stalk rot problems include: loss of leaf tissue due to diseases, insects, or hail; injury to the root system by insects or chemicals; high levels of nitrogen in relation to potassium; compacted or saturated soils restricting root growth; and high plant populations.
Most hybrids do not begin to show stalk rot symptoms until shortly before physiological maturity. It is difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved. Similarly, certain insects such as European corn borer often act in concert with fungal pathogens to cause stalk rot. Although a number of different fungal pathogens cause stalk rots, the three most important in Ohio are Gibberella, Collectotrichum (anthracnose), and Fusarium. A symptom common to all stalk rots is the deterioration of the inner stalk tissues so that one or more of the inner nodes can easily be compressed when squeezing the stalk between thumb and finger. It is possible by using this "squeeze test" to assess potential lodging if harvesting is not done promptly. The "push" test is another way to predict lodging. Push the stalks at the ear level, 6 to 8 inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present.
To minimize stalk rot damage, harvest promptly after physiological maturity (about 30% grain moisture). Harvest delays will increase stalk rot and result in more lodging. For more information on stalk rot in corn consult Corn Disease Control in Ohio (1989), OCES Bulletin 802, as well as other Plant Pathology Fact Sheets on specific stalk rot diseases.
Several fields were visited last week in which soybeans displayed symptoms of Sudden Death Syndrome (SDS) and/or Brown Stem Rot (BSR). The leaves on the plants had bright yellow spots, which in more advanced stages were turning to dead (necrotic) tissue. Other symptoms for SDS (few roots, discolored crown) and BSR (chocolate- brown intact pith) were not as obvious; thus, we are in the process of isolating the pathogens from these plants. All plants, however, had cyst nematodes. It has been reported that the onset and severity of SDS foliar symptoms is greater in the presence of Soybean Cyst Nematode. Others have noted that areas in fields with a high nematode population density are likely to show SDS foliar symptoms before those with a low cyst nematode population. The nematodes are NOT causing the yellow and necrotic spots on the leaves. In Mississippi, the fungus that causes SDS has been isolated from the nematode cysts, in 46 out of 56 fields. To date in Ohio, all of the SDS affected fields have had high populations of cyst nematode. Since SDS is a relatively new disease for Ohio, more information is needed to make concrete management recommendations. However, severity of SDS may be reduced by crop rotation, resistant varieties, and managing soybean cyst nematodes.
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Symptoms of Sudden Death Syndrome in Soybeans. |
Research plots were established at five different farm locations in four counties (Darke, Fairfield, Hardin, and Henry) to evaluate the influence of fall (0 lb N/A and 30 lb N/A) and spring nitrogen applications (one time 60 lb N/A, one time 100 lb N/A, and 50 lb N/ 50 lb N split application) on wheat production. Plots were planted between September 29 and October 7, 1998. Cooperators selected the variety. Plots were established following soybeans using no-tillage production practices. Seeding depth was 1.0 inches. Nitrogen was applied as a 28% solution, except at several locations where dry fertilizer was broadcast prior to planting. Phosphorus and potash were applied as needed based on a soil test. The data from the locations were combined for statistical analysis with locations serving as replicate blocks.
There was considerable variability in the fall tiller and spring tiller counts across locations, such that fall and spring nitrogen treatments appeared to have little effect on tiller numbers or on the number of heads that developed in late spring. Fall tiller counts for 0 lb N and 30 lb N/A were 55.7 and 65 tillers/2 ft of row, respectively, (not significant, P= 0.21). Spring tiller counts for 0 lb N and 30 lb N/A were 157.5 and 172.6 tillers per 2 ft of row, respectively (not significant, P=0.13). Head numbers and yield also showed some variability across locations, but yield of the treatments with low nitrogen applications had consistently lower yields. Head numbers for the spring nitrogen treatments of one time 60 lb N, one time 100 lb N, and the 50 lb N/50 lb N split were 108, 111, and 106 heads per 2 ft row, respectively (not significant, P=0.09). The only stable factor affecting yield was spring nitrogen application. Treatments that had 100 lb of N applied at one time (89.4 bu/A) or were split into 50 lb N early /50 lb N later in the spring (88.3 bu/A) had significantly higher yield than the one time 60 lb N spring application (80.9 bu/A)(LSD = 2.9 bu/A at P = 0.05).
Results indicated that a nitrogen application in the fall did not increase the number of tillers in the fall or in the early spring in 1998-1999. Splitting the spring nitrogen application to provide 50 lb N/A at green up and 50 lb prior to stem elongation did not increase the yield over a one-time application of 100 lb N at green up. However, treatments that received 100 lb of N in the spring, split or not split, yielded more than treatments where only 60 lb N was applied at green up. The relatively warm winter temperatures and moderate overwinter rainfall was highly favorable for tiller development and survival. Additionally, the weather conditions probably did not restrict nitrogen availability to wheat in 1999. We suspect tiller number results may be quite different in a more normal year with a more severe winter and a cold, wet spring. More studies are planned for the 1999-2000 season.
An easy to reach index of management information for Ohio farmers facing drought conditions is located at www.ag.ohio-state.edu/~corn/drought99. Information on production, marketing and farm families can be found at this site
A symposium on biotechnology and specialty crops will be held September. 2-3 in Reynoldsburg, Ohio. The "Agricultural Biotechnology and Specialty Crop Contracting Symposium" will feature topics of interest to crop producers and those involved in the grain processing industry.
"This symposium is particularly timely with current low commodity prices," said Robert Fleming, Ohio State University Extension District Specialist. "The topics discussed will provide ideas for those interested in increasing their income and spreading their risk through value-added crops. "The results of an external study by Sparks Commodities, Inc., on trends in biotechnology and itsprojected impact on agriculture will also be discussed. "This is the first time a symposium which combines topics on biotechnology and specialty crops with strong support from industry has been offered anywhere in the country," Fleming said.
The registration fee which covers program materials and meals is $80 and must be received by August 27. Registration materials are also available at your local Extension office. For more information, please contact Pam Brown at (614) 292-0315. The Agricultural Biotechnology and Specialty Crop Contracting Symposium is co-sponsored by The Ohio State University Farm Income Enhancement Program, The Ohio Farm Bureau Federation and The Ohio Department of Agriculture with support from the Ohio Corn Growers and Ohio Soybean Associations.
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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: Jim Bueurlein (Hort and Crop Science), Anne Dorrance (Plant Pathology), Pat Lipps (Plant Pathology), Mac Reidel (Plant Pathology), Peter Thomison (Hort and Crop Science), and Hal Wilson (Entomology); District Specialists: Bruce Eisley (Entomology) and Ed Lentz (Agronomy); Extension Agents: Dave Jones (Allen), Steve Prochaska (Crawford), Dennis Baker (Darke), Larry Lotz (Fayette), Glen Arnold (Putnam), Ray Wells (Ross), and Roger Bender (Shelby).
Editor: Ed Lentz 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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