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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-21

Dates Covered: 
July 6, 2004 - July 12, 2004
Steve Prochaska

Wheat Harvest Update: Grain Quality And Scab Levels

Authors: Patrick Lipps, Dennis Mills

Wheat harvest is progressing rapidly in Ohio with much of the wheat already harvested in the southern part of the state and harvest has begun in many of the more northern counties. Reports indicate that yields are about 10% less than last year, with some counties reporting 15 to 20% lower yields due to Fusarium head scab and Stagonospora glume blotch. Most reported yields are in the 60 to 70 bu/A range with some fields in the 50's and a few in the 80 to 90 bu/A range. The most interesting aspect of these reports is the considerable variability in yield among fields across a location. Variety, planting date, planting depth and drainage had a profound impact on yield as did variety resistance to disease.

Test weights are much better than expected, probably due to the vigilance of our wheat growers attempting to harvest as early as possible to maintain grain quality and adjusting combines to get rid of as much shriveled grain as possible. Test weights are generally in the 58 to 60 lb/bu range except in the areas more affected by scab and Stagonospora glume blotch where test weights were as low as 54 lb/bu. There are few reports of elevators checking the crop for DON (vomitoxin), but few reports of growers being docked for DON. This indicates that the levels being found in the grain are not limiting the usefulness of the crop for milling and baking purposes. Considering the wet weather that occurred across the state during the flowering and grain filling period this is not too bad; it could have been a lot worse.

Over the past three years the OSU County Extension agents have assessed the level of Fusarium head scab in the state. This year 116 fields in 19 Counties were surveyed. The average scab incidence (percentage of diseased heads in a field) of the 116 fields was 13.1% and incidence in individual fields ranged from 0.0% to 61.0%. Some counties like Tuscarawas, Henry, and Van Wert reported relatively low incidence levels (2.6% to 4.7%) and other counties like Crawford, Morrow and Licking reported higher than average incidence levels (27% to 40%). Obviously this corresponded to the duration of favorable weather for scab infection during flowering of the crop experienced by these counties. Although, Ohio experienced slightly more head scab this year than last year, the potential problem with DON contamination of the grain was not as great as last year in many areas. This difference was due to the very wet conditions that delayed harvest and promoted deterioration of grain quality in 2003.

Wheat Variety Resistance To Fusarium Head Scab

Authors: Patrick Lipps

The wide spread occurrence of Fusarium head scab in Ohio and other midwest states has prompted many wheat pathologists and wheat breeders to increase their efforts in developing varieties with usable levels of resistance. Generally, few varieties have been available with reasonable levels of resistance to scab and due to the incomplete nature of the resistance, these more resistant varieties have been classified as having only moderate levels of partial resistance. This means that none of the varieties are immune to scab, but under moderate disease pressure these varieties have fewer heads affected and fewer spikelets on the head killed by the fungus. Thus, the moderately resistant varieties had overall less disease symptoms and less yield loss. However, under very high disease pressure due to the presence of a lot of fungal spores in the field (from surface corn residue) or long durations of wet weather that favor infection of the wheat heads during flowering, even varieties with higher levels of partial resistance would have significant disease and yield loss.

The moderate levels of head scab Ohio wheat field experienced this season has provided us an opportunity to evaluate the reaction of the varieties planted in the Ohio Wheat Performance Test at three locations (Pickaway Co., Crawford Co. and Wayne Co.). Data from these locations were combined to determine the varieties that had the least amount of head scab across locations. Using the Public Certified variety 'Freedom' as the moderately resistant check for comparison, the following varieties could be classified as having moderate levels of resistance to head scab: Rupp 'RS 947', Gries Seeds 'Brazen', Thompson Seeds 'TS3060', AGI '538', Wellman Seeds ' W150', Hylamp 'Wonder', Pioneer Brand '25R35', NK 'Coker 9474', Steyer Seeds 'Hartman', and the Public Certified 'Cecil'. Of the 70 or more varieties planted in these tests at the three locations, these varieties had the lowest levels of head scab. We have learned from experience that an accurate evaluation of scab resistance for any variety can not be obtained in one year even from tests conducted at multiple locations. Regardless, these are some varieties to watch over the next few years. Look for their yield performance and other important characteristics (test weight, lodging potential, resistance to other diseases) after harvest when the Ohio Wheat Performance Test is published.

Pollination Well Ahead of Normal in Many Corn Fields

Authors: Peter Thomison

Corn growth is well ahead of normal in many Ohio corn fields. Tasselling and silking were evident in many April planted fields last week. We don’t usually expect to reach this stage of development until mid July. The flowering stage in corn is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Stress conditions such as drought or hail damage have the greatest impact on yield potential during the reproductive stage. The following are some key steps in the corn pollination process.

Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. Under very dry conditions, silk emergence may be delayed, and such “asynchronization” of pollen shed and silking may result in poor kernel set and reduced grain yields. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon.

This year I’ve seen many corn plants that have started to silk prior to tassel emergence and pollen shed. This atypical pattern of flowering may be related to the unusual growing conditions we’ve experienced, at least up until recently, relatively moderate temperatures and abundant moisture (i.e. minimal stress). Differences in flowering patterns among hybrids may also be contributing this early silking.

The tassel is usually fully emerged and "stretched out" before any pollen is shed. Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. This year, in another departure from the norm, I’ve seen many corn plants with tassels that have started to shed pollen before they have completely emerged from the whorl.

Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.

Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains.

Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours.

A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.

Pollen of a given plant rarely fertilizes the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant are pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought. As noted above, poor seed set is more often associated with poor timing of pollen shed with silk emergence (silks emerging after pollen shed). However, modern hybrids seldom exhibit this problem in Ohio unless they experience extreme drought stress.

Pop-up Fertilizers

Authors: Robert Mullen

As planters get larger and the use of conventional starter attachments decrease, the use of pop-up liquid fertilizers has gained popularity.

The concept of pop-up fertilizer has been around for quite a while. Pop-up fertilizers are meant to provide adequate nutrients in close proximity of the developing roots to allow for better early season growth and potentially quicker emergence. Despite the fact that early season growth and nutrient uptake typically does increase with pop-up fertilizer, most research shows the advantages of pop-up is somewhat limited to soils with low P levels. Thus soils with high P do not benefit much from addition of pop-up fertilizers. Cool soil conditions at planting also increase the likelihood of response due to decreased early root development. Minimum tillage and no-till operations have the greatest opportunity to respond to pop-up fertilizer due to cool soil conditions.

Caution should be used, however, when utilizing pop-up fertilizers. Excess salts applied as N and K2O can inhibit germination and cause emergence problems. Dry soil conditions at planting increase the potential for poor emergence. As a general rule do not apply more than 5 pounds of N and K2O in the row on low CEC soils (5 meq/100g), and no more than 8 pounds of N and K2O on soils with higher CEC (8meq/100g).

So should you use pop-up fertilizer? Pop-up fertilizer may have some beneficial effects in minimum and no-till operations on soils that are low in P, but based upon the cost of pop-up fertilizer and the potential emergence problems, the benefits may not outweigh the risks. If pop-up is going to be used, take care when setting rates and assess soil moisture when planting.

Gearing Up for Wheat This Fall

Authors: Robert Mullen

I know the last thing on everyone’s mind this time of year is wheat (unless you have some still in the field that needs to be harvested), but if you are planning on planting wheat this fall it is not too early to start thinking about your fertility. Soil sampling is the best way to gage current fertility levels and make the best economic decisions on nutrient applications for next year’s crop. Although soil sampling is typically conducted in the fall, fields that are going into wheat this fall can be sampled over the next couple of months. The primary concern should be P and K levels as well as soil pH. Soils that are sampled should be sampled to a depth of 8”. Remember it is never too early to start planning for the next crop.

Archive Issue Contributors: 

Pat Lipps, Dennis Mills & Anne Dorrance, (Plant Pathology), Robert Mullen (Soil Fertility), Peter Thomison (Corn Production), Jeff Stachler (Weed Science); Extension Agents and Associates: Roger Bender (Shelby), Barry Ward (Champaign), Todd Mangene (Mercer), Glenn Arnold (Putnam), Mark Keonig (Sandusky), Harold Watters (Miami), Dusty Sonneberg (Henry), Ray Wells (Ross) 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.