In This Issue:
- Wheat Harvest Progressing - Grain Quality Issues
- Septoria Brown Spot Is Prevalent in Many Soybean Fields
- Sclerotinia Update
- Rootworm Larval Feeding Evident in Some Fields
- Tissue Testing for Nutrient Management
- Not Too Late to Doublecrop Soybeans After Wheat
- Will Poor Root Development Impact Corn Yield Potential in 2004?
Authors: Patrick Lipps
Harvest reports from the southern counties in Ohio indicate that harvest moistures are 14 to 17%, yields are about average (60-80 bu/A) and test weights are reasonable (generally 58 to 59 lb/bu) with some test weights as high as 60 lb. Although this may not be a 'bin buster' year for wheat, these reports indicate that the scab problems resulting from fungal infection during the wet periods in May have not caused overwhelming problems. The incidence of Fusarium head scab is quite variable from one county to another and from one field to the next. You should expect field to field variability in yield and test weight. Differences in the amount of head scab from one field to the next can be associated with planting date, variety, fertility and previous crop. These factors influence when the crop flowers and how much Fusarium is in the field to infect the crop. For example some counties are reporting fields with a little as 2% infected heads to fields with as many as 38% infected heads. Growers should expect differences in test weights from these fields.
So far we have only little information about the level of vomitoxin, or DON, in the harvested grain. In those regions of Ohio with higher levels of head scab, wheat buyers will likely be testing for DON in the grain. The best ways to deal with the DON is to limit the time when the fungus can produce this toxin in the grain. The way to do that is to harvest the grain as soon as possible by starting harvest a higher moisture levels (about 20%) and then dry the grain to 14% by low temperature or air drying. Additionally, turn up the blowers in the combine to get rid of the small shriveled seed. This will eliminate the severely-diseased, shriveled kernels that contain most of the DON. Since nearly all wheat growing areas of the state are reporting damage from head scab we expect to see some DON problems. Those growers in the north central area of the state that experienced high risk potential from head scab due to excessive wet weather, should do all that is possible to harvest early to help minimize lower test weights and DON in the grain. Drier weather during this wheat harvest season would certainly be welcome.
Authors: Anne Dorrance
This wet weather has provided a perfect environment for early season Septoria again this year. This fungus survives on the old soybean stems on the soil surface. These serve as sources of inoculum. The wet rainy weather provides a perfect environment for this fungus to infect and colonize soybean leaves. Symptoms are very apparent on the lower leaves, especially the unifoliates. Leaves are yellowing with small brown spots. The spots soon grow together to form a dark brown color. In general the spots occur more frequently near the margins of the leaflets. We place the leaves in a moist chamber to look for the fungal spores. It is unusual to have this much Septoria this early season, but disease severity is not high enough to require fungicide applications at this time. Save your money for problems later down the road. For more information and images of this disease go to : http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/septoria.htm
Authors: Anne Dorrance
Many fields were planted relatively late this spring which may impact the development of Sclerotinia stem rot or white mold. This disease requires moisture during the flowering period AND cool temperatures AND thick and early canopy closure. We will have to wait until the plants reach reproductive period to better predict what will happen. Historically, the years with delayed planting tend to set us up for these events. I have been asked about the use of Cobra for reducing white mold. We know from some recent work at OSU by Dr. Terry Graham that the effects of Cobra for protecting the crop are fleeting or short lived. So if you apply Cobra one week and then the following week you have a fog bank roll into your field for a couple of days, the effect of the Cobra will not be there- it will be gone and you will get white mold. This is why this material has worked in some fields and not in others. Another limitation that must be considered this year – is the severe stress these beans have been under. They are already behind – any further stresses will translate into further yield hits at harvest. Whenever you experiment with new methods – don’t forget to leave those controls – or strips that are not treated. And leave several of them in the field – this way you can make comparisons in the same field. Sclerotinia stem rot is notorious for sitting in pockets. It is generally not uniform across the field making valid comparisons difficult. So plan accordingly.
Authors: Bruce Eisley, Ron Hammond
We are seeing and receiving reports of rootworm larval feeding damage to corn roots in some fields in Ohio. The next couple of weeks will be a good time to check for corn rootworm larval feeding injury. Corn fields to check include fields where corn follows corn or those fields in NW and west central Ohio where corn follows soybeans and the possibility of first year corn damage might be possible.
The reason to check in the next couple of weeks is because the maximum larval feeding damage will be during this time and larval feeding will be ending as the larvae pupate and new adults begin to emerge. After larval feeding has ended, the roots on some hybrids will begin to regenerate and when this happens, rootworm larval injury is more difficult to detect.
We suggest the following method to check for rootworm injury:
1. Carefully dig plants, don’t pull them, from the field taking as much soil as possible with the plant.
2. Carefully remove as much soil as possible from the plant without damaging the roots and also look for any larvae that might still be in the soil or on the roots. Rootworm larvae are white, about 1/2 inch in length when full grown with a brown head and brown plate on the tail http://ohioline.osu.edu/icm-fact/images/43.html (see picture).3. If there is still soil on the roots you can either soak the root system in a bucket to loosen this remaining soil or you can spray the root system with a hose to remove the remaining soil.
4. After the soil has been removed, check the roots for feeding injury, either roots chewed back to the stalk or tunneling in the roots.
Root systems can be rated using either a 1 to 6 scale or 0 to 3 scale. In both ratings, the scale indicates the amount of damage to the root system and can be used to determine if economic injury has occurred.
Iowa 1 to 6 Scale: (Economic injury normally occurs at a rating of 3 to 3.5)
Rating by damage to roots
1. No damage to the roots.
2. Slight feeding scars present.
3. One root chewed to within 1-1/2 inch of the plant.
4. One node of the roots destroyed.
5. Two nodes of the roots destroyed.
6. Three nodes of the roots destroyed.
Modified Node-Injury Scale.
Rating by damage to roots
0 no visible damage to roots
0.05 slight scarring
0.08 moderate to severe scarring, no roots chewed to 1.5 inches of stalk
0.1 one root chewed to 1.5 inches of stalk
1 one node of roots destroyed
2 two nodes of roots destroyed
3 three nodes of roots destroyed
Authors: Robert Mullen
Although soil testing is the best way to determine crop nutrient needs (especially the immobile elements like potassium and phosphorus as well as soil pH), tissue testing is an excellent way to determine how well the current nutrient management program is addressing crop needs during the growing season. When collecting plant samples for tissue analysis, timing of sampling and which portion of the plant that is sampled becomes important. For younger plants (seedling stage), collect 15 whole plant samples and allow them to dry prior to shipping them to an analytical lab. The 15 samples should be randomly taken from the field, but make certain to avoid areas not representative of the field (i.e. drowned out portions of the field or other areas clearly different). If you wish to sample the field in different sections, collect samples from areas of the field that are similar. If the crop is further along in the growing season, then use the following table to collect plant samples.
|Number of Samples
|Upper fully developed leaf
|Upper fully developed leaf
|Alfalfa & forage legumes
|Top 6 inches
Once lab results are known, refer to the Ohio Agronomy Guide to determine if nutrient levels are sufficient or marginal. Tissue analysis can have the greatest impact on nitrogen, sulfur, and micronutrient management. Most of the analytical labs in and around Ohio can analyze plant samples.
Authors: Steve Prochaska
With wheat harvest under way across Ohio and very adequate soil moisture, doublecropping of soybeans after wheat is an option to consider. For example, in north central Ohio there will be around 12 weeks of growing season after wheat harvest (from about July 1 to the average date of first frost which is around Oct. 5). This is adequate time to grow a crop of soybeans. Check the Agronomy Guide for dates of average first frost for your area. Dr. Jim Beuerlein, Ohio State University Soybean Specialist, offers additional information on soybean maturity to select, last planting date to doublecrop and other pertinent production points in this fact sheet http://ohioline.osu.edu/agf-fact/0103.html.
Authors: Peter Thomison, Robert Mullen, Patrick Lipps
In early July, nearly all our attention is focused on corn canopy development - canopy closure, plant height, tasseling, etc. Unseen, but probably of greater importance to the crop’s long term success and productivity is the root development. The corn crop’s access to soil moisture and nutrients during the growing season depends on establishment of an effective root system. Understanding root development can help with diagnosis of various production problems, from nutrient deficiencies early in the season to stalk rots at maturity. Estimates of root growth and penetration are complicated by a number of factors because growth is dependent upon soil moisture, aeration, texture, structure, and fertility.
Research by Dr. Stan Barber at Purdue University indicated that corn will produced similar total amounts of roots each year. The difference between years is mainly where in the soil profile the roots predominate. Warm dry soils will promote deeper root development, whereas cold, dry soils promote shallower root development.
In a year such as 2004, when the surface soil moisture after planting was above optimum for an extended period in many fields, corn roots are usually confined to the surface eight or twelve inches of soil. Lateral roots are short and less abundant, very little branching, and essentially all of the root development is horizontal. In contrast, in a year where there is a period of three to four weeks with light rainfall after planting, a deeper root system is favored. Lateral roots are longer and more abundant, considerably more branching, and they likely “turn down” earlier. Such root systems generally enable the crop to tolerate late season water deficits much better than shallow root systems. Unfortunately, cool rainy weather conditions and wet soils are often the norm after planting in Ohio.
Well drained soils favor penetration of roots better than compacted soils with a hardpan and poor aeration. In one past study, a well drained soil was characterized by a general root distribution of 70% in the upper 10 inches, 19% in 10-30 inch depth, 8% in 30 to 48 inch depth and 3% in the 40 to 72 inch zone. However, for a poorly drained soil, the general root distribution was 56% in the upper 8 inches, 42% in the 8 to 28 inch depth, and 2% in the 28 to 48 inch depth.
Root development can be related to different stages of vegetative development. Under favorable growing conditions in a well drained soil the following rules of thumb would usually apply.
1. Up to the 7th or 8th leaf stage (knee high) the roots will be almost parallel to the soil surface with little penetration more than a foot deep.
2. Between knee-high and four feet, the roots may extend 2 to 3 feet from the base of the stalk, where they usually turn down abruptly. Penetration at this stage can range from 1 foot to over 4 feet in depth. Since roots have likely reached the row middles by about the V8 stage, they are more vulnerable to pruning by cultivation.
3. As maturity approaches, roots tend to branch and penetrate deeper. Maximum root spread from the stalk is often 3.5 feet in all directions. Maximum penetration of very fine roots may be from 4 to 8 feet.
4. Root mass reaches it’s maximum size at silking
5. Brace roots (above ground nodal roots) are initiated from the lowest 3 to 4 stalk nodes during late vegetative development and usually penetrate the soil surface by silking. Brace roots provide support to the stalk and are of considerable importance in “resurrecting” plants root lodged by strong winds.
How will root development impact this year’s corn crop? Although excessive rainfall this year has certainly limited root development in many corn fields, the relatively moderate to cool temperatures have been beneficial and probably promoted root growth. If we had experienced a prolonged period of high temperatures with little rainfall, root development would have been severely inhibited. Root growth declines at temperatures above 86 degrees F, and soil temperatures in corn fields, which have not yet canopied, often exceed this temperature on hot days with air temperatures in the 90 degree range.
Fortunately, cooler than normal temperatures after sidedressing have probably also reduced the nitrogen losses associated with denitrification. Although water-logged plants have a chlorotic appearance which is indicative of nitrogen stress, the problem is probably more attributed to the small root system than actual N deficiency of the soil (this is dependent upon N management). In fact, some fields that receive sidedress applications of N may not “green up” very quickly depending upon the placement of N. The root systems have not grown large enough to capture the N that has been applied, or the roots are not actively taking up N (depending upon how wet the soil actually is). This problem can be more prevalent in fields that are sidedressed with anhydrous ammonia. The primary form of N taken up by the corn crop is nitrate and anhydrous is strictly ammonia. The bacteria that convert ammonium to nitrate prefer aerobic (oxygen rich) conditions and excessive moisture can slow their activity dramatically.
Based on corn performance in past years, the impact of a wet spring on corn prospects is largely influenced by weather conditions later in the growing season especially during grain fill. Despite the adverse effects of saturated soil conditions on root development during vegetative growth, with moderate temperatures and frequent rainfall during grain fill, a corn crop still has the potential to generate excellent grain yields; this was the case in 2003 when a new, record high corn yield was achieved.
If frequent and heavy rains provide near continuous saturated conditions in fields during the first few weeks after silking, soil pathogens like Pythium and Fusarium will continue to reduce effective root systems. Under these conditions early deterioration of root systems will likely hasten premature ripening of the crop leading to lower yields and light weight kernels. The best situation we can hope for is sufficient moisture to eliminate any moisture stress on the plants with alternating soil drying to allow air to penetrate the soil profile. Continuous high moisture conditions or excessive drying will both limit the yield potential of the crop. The key to adequate yields from this point on is avoiding any additional stress on the crop.
References:Zublena, J.P. and C.L. Parks. 1980. Nutrient and volume of water available to the corn plant are influenced by volume and depth of root development. Coop. Ext. Serv. Clemson Univ. Soils & Plant Nutrition Information Sheet.
State Specialists: Pat Lipps & Anne Dorrance, (Plant Pathology), Peter Thomison (Corn Production), Jim Beuerlein (Soybeans & Small Grain), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology); Extension Agents and Associates: Woody Joslin (Shelby), Barry Ward (Champaign), Howard Siegrist (Licking), Gary Wilson (Hancock), Mark Keonig (Sandusky), Harold Watters (Miami), Dusty Sonneberg (Henry) and Steve Prochaska (Crawford).