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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-28

Dates Covered: 
August 23, 2004 - August 31, 2004
Harold Watters

Soybean Reaction to Cool Summer 2004

Authors: Jim Beuerlein

All chemical reactions in soybean plants increase with temperature up to about 95º degrees F and then decrease because one or more inputs needed for the reaction becomes limiting. Between about 55º and 85º photosynthesis and all other chemical reactions double with each 13-degree increase in temperature. Temperature affects the respiration process in the same way it affects photosynthesis. Respiration is the controlled burning of glucose that provides energy for the plant to use in the production of new compounds and for nutrient uptake. While photosynthesis occurs only in light, respiration occurs in both light and darkness. Therefore, both are most rapid during daylight hours when temperatures are high. With the onset of darkness photosynthesis stops but respiration only slows. If night temperatures are high, the respiration rate is high and more sugar is consumed which reduces the net amount of energy produced during the previous day. When night temperatures are low, the respiration rate is decreased, less sugar is burned and yield loss is reduced. Thus, cool night temperatures during grain fill tend to increase yields. Higher night temperatures during the vegetative stage tends to be positive because plants grow faster and reach the reproductive stage at an earlier date.

As of mid-August most of our crop is in the grain filling stage. Lower than normal day and night temperatures reduce the photosynthesis rate and also the respiration rate, so there should be only a small reduction in the net accumulation of dry matter, and that loss could be offset with a 1 to 2-day delay in maturity. Cooler temperatures have a positive effect in that they reduce the water requirement of the crop so that any drought stress will be delayed. Moisture stress late in the grain fill period hastens maturity and reduces yield as does stress from disease and temperature extremes. Therefore the cooler than normal temperatures of early August could have either no effect on yield or a small negative effect depending on rainfall amounts, temperatures, and the amount of sunlight energy fixed between mid August and mid September.

Bean Leaf Beetle and Soybean Pod Feeding

Authors: Ron Hammond, Bruce Eisley

Bean leaf beetle (BLB) populations have been large in some areas of Ohio this year. The concern with this insect should now shift to pod feeding as we go into late August and early September. Pod injury will become more evident as the second BLB generation becomes more numerous and green pods become more attractive to feeding than foliage.

When pod injury occurs on 10-15% of pods, seed injury will become evident and yield losses are possible. If the pod injury occurs during periods of wet conditions this may enable infection by seed diseases, the development of moldy bean seeds may then lead to a loss in seed quality. The assessment of a field infestation depends on (1) determination of the current level of pod injury, (2) the abundance of adult BLB activity using a sweep net, (3) consideration of weather factors that may enable infection of the damaged pods by disease agents, and (4) the amount of time remaining before total leaf drop and dispersal of a BLB population from the field. In terms of this last point, many early-planted fields are already in the full pod stage, and should be maturing in the next few weeks. Although growers should continue to monitor these fields, these soybeans should mature before much pod feeding occurs. Later planted fields, however, will stay green with succulent pods well into September. Although these fields might not have much of a beetle population at this time, you might see a large migration of BLB into them as earlier planted fields mature. Growers are advised to pay close attention to their late maturing fields.

Growers should continue to sample their fields weekly for the remainder of the summer. Hopefully visits have been made the past month to determine the relative size of the first generation to help with treatment decisions. Those fields that had large BLB populations in the past few weeks should be monitored closely, although as mentioned above, later planted fields also warrant close attention. The percentage pod injury should be determined by randomly counting the total number of pods and those with feeding injury on about twenty plants (see Adult BLB population should be estimated by taking 10 sweeps with a sweep net at three to four locations in a field.

Rescue treatment to prevent excessive development of seed damage may be warranted when pod injury exceeds 10%, fresh feeding scars predominate, and adult BLB are still present and actively feeding. Less than two BLB per sweep (20 per 10 sweep sample) are unlikely to cause significant injury. Three to five BLB per sweep (30 to 50 per 10 sweep sample) indicates a potential problem possibly warranting rescue treatment. More than five BLB per sweep (50 per 10 sweep sample) may result in significant injury especially if two or more weeks remain 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. Growers also should be aware of the harvest interval with the insecticide that is used for BLB control. Many of the materials have waiting periods of between 45 and 60 days, which would probably limit their use for use at this time.

Do Not Overlook Potassium

Authors: Robert Mullen

Considering the importance of nitrogen (N) and phosphorus (P) fertilization, potassium (K) is sometimes overlooked. Even though K does not get the same attention as N and P, it is an important nutrient for crop production. Potassium serves two major roles in higher plants, 1) enzyme activation and 2) osmotic potential maintenance (water dynamics). Plants that are K deficient are less able to regulate transpiration (water exchange between the plant and air) resulting in poor water use efficiency. Thus adequate levels of K are needed to support high-yielding crops.

Because K exists as a monovalent cation (K+) (a single, positively charged element), it is not extremely mobile in the soil, and its mobility increases as soil texture becomes coarser. Thus heavier textured soils have a greater capacity for adsorbing K. When identifying if soil K levels are adequate, cation exchange capacity (CEC) is considered. Based on Tri-State Recommendations, the following table shows the relationship between K critical values and CEC:

CEC (meq/100g) ___ Critical Value (lb/acre)
5 _________________ 175
10 ________________ 200
20 ________________ 250
30 ________________ 300
Potassium levels below the critical value are deficient and are likely to respond to application of K fertilizers. To see current state recommendations for K, refer to the Tri-State Fertilizer Recommendations available at your local Extension office or on-line at

Lime Applications This Fall

Authors: Robert Mullen

As fall quickly approaches, many are beginning or contemplating lime applications to adjust soil pH. Here are some simple rules for liming this fall:

1) Remember all liming materials react with the soil the same way to neutralize soil acidity, but not all liming materials are equal. The Ohio Department of Agriculture regulates all liming materials and labels each based on its Effective Neutralizing Power (ENP). The higher the ENP, the more effective a material is at neutralizing soil acidity. Make sure to compare cost when it comes to selecting a liming material, a high ENP lime may not be the most economical choice.
2) Consider magnesium (Mg) levels when selecting a source. If soil Mg is low (less than 100 lb/acre), a dolomitic source may be necessary. Dolomitic lime contains approximately 10-12% Mg which makes it an excellent source of Mg. If soil Mg levels are adequate, base material decision more on cost.
3) Apply the recommended rate of lime. Applying more lime than necessary to neutralize soil pH will not be beneficial to subsequent crops. Additional amounts of lime neutralize more soil acidity and can actually cause micronutrient deficiencies.
4) If 4 or more tons/acre of lime is recommended, split the application into two events. Make the first application and incorporate the lime, then apply the second half. This will promote good mixing of the liming material and soil. Do not apply more than 8 tons/acre of lime in a single year.
5) Application of lime in no-till production systems should be adjusted to a depth of 4 inches. This will cut recommended rates significantly. Do not surface apply urea based fertilizers for at least a year after surface application. Surface applications of these fertilizer materials can result in significant N loss by volatilization.
6) Consider subsoil pH when identifying the target pH. Acid subsoils (pH < 6) require higher rates of application. To increase these rates, the target pH is increased (see Tri-State Fertilizer Recommendations,

North Central Ohio Conservation Field Day and Precision Ag Olympics- August 26

Authors: Steve Prochaska

Crawford County will be the site for a Conservation Field Day focusing on practices that are profitable. The program includes field demonstrations
(several different tillage implements will be demonstrated) of current agronomic technologies with on-site experts to answers questions on a variety of topics and the Olympics of Precision Ag (what practices will return gold to your farm business).

Grain producers and crop advisors are encouraged to attend this premier agronomic program on August 26 from 1 to 8:00 PM. Topics include the following:

- Tillage demonstrations with comparisons of tillage equipment
- Soil pits to evaluate field performance of various tillage equipment (eleven) with Frank Gibbs
- Auto-Steer tractor demonstrations and adoptability to the farm (Miller Brothers)
- The Olympics of Precision Ag - What practices will return gold, silver and bronze to your farm

Sessions start promptly at 1:45 PM and continue on a regular basis through 5:00 and repeat from 6:30 to 8:00 PM. A free dinner will be served at 5:00 PM. The location for the field day is the Frost Farm located on the corner of State Route 4 and Scioto-Chapel Road, 4 miles south of Bucyrus. The Field Day is sponsored by the following: OSU Extension, Crawford SWCD and Upper Scioto River Watershed Project.

Archive Issue Contributors: 

State Specialists: Anne Dorrance and Dennis Mills (Plant Pathology), Jim Beuerlein (Soybean Production), Robert Mullen (Soil Fertility), Jeff Stachler (Weed Science), Ron Hammond & Bruce Eisley (Entomology) and Ed Lentz (Agronomy). Extension Agents and Associates: Glen Arnold (Putnam), Roger Bender (Shelby), Greg Labarge (Fulton), Harold Watters (Miami), Dusty Sonnenberg (Henry), Ray Wells (Ross), Mark Koenig (Sandusky) and Steve Prochaska (Crawford).

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.