C.O.R.N. Newsletter 2004-19

Dates Covered: 
June 22, 2004 - June 28, 2004
Editor: 
Greg LaBarge

Ear Formation Well Underway In Early Planted Corn

Authors: Peter Thomison

There is considerable variability in corn growth and development across the state - with some of the early corn (planted in April) at or beyond V12 (12-leaf collar stage), and corn planted in late May/early June at V4-5. As early as the V4/V5 stage, ear shoot initiation is completed and the tassel is initiated on the top of the growing point. During the rapid phase of corn vegetative growth, now evident in the early planted corn, ear yield components are being determined. Kernel row numbers per ear are generally established by about V12 (the 12 leaf collar stage). Kernel row numbers are usually less affected by environmental conditions than by genetic background. Corn hybrids characterized by "girthy" ears exhibit more kernel rows (ex. 18 or 20 rows) than hybrids with long tapering ears (ex. 14 or 16 rows). Determination of kernels per row (ear length) is usually complete about one week before silking (R1) or about the V17 stage. Unlike kernel rows per ear, kernels per row can be strongly influenced by environmental conditions, so severe stress such as a drought occurring during the two weeks prior to pollination can reduce kernels per row and ear length.

Use Appropriate Herbicide Rates Based On Weed Sizes

The continued soggy conditions throughout most of the state and the warm temperatures are making weeds and crops grow quickly, presenting weed control issues.

Use the appropriate glyphosate rate for the weed size in all Roundup Ready crops!

- 0-8 inch annual weeds use 0.75 lb ae/A (22 oz/A of Roundup WeatherMax or 32 oz/A of most generics at 3.0 lb ae/gal)

- 8-15 inch annual weeds use 1.125 lb ae/A (33 oz/A of Roundup WeatherMax or 48 oz/A of most generics at 3.0 lb ae/gal)

- 15 –24 inch annual weeds use 1.5 lb ae/A (44 oz/A of Roundup WeatherMax or 64 oz/A of most generics at 3.0 lb ae/gal)

- If nothing has been done to field and not planted with weeds > 24 inches in height use greater than 2 lbs ae (61 oz/A of Roundup WeatherMax or 80 oz/A of most generics at 3.0 lb ae/gal)

For certain weeds in Roundup Ready soybeans, the glyphosate rates need to be adjusted accordingly. Below are glyphosate recommendations for three problematic weeds.

Lamsquarter & Velvetleaf

* 0-6 inch use 0.75 lb ae/A of glyphosate

* 6-12 inch use 1.125 lb ae/A of glyphosate

* > 12 inch use 1.5 lb ae/A of glyphosate

Giant Ragweed

* 0-10 inch giant ragweed use 0.75 lb ae/A of glyphosate

* 10-18 inch giant ragweed use 1.125 lb ae/A of glyphosate

* > 18 inch giant ragweed use 1.5 lb ae/A of glyphosate

Some other notes on control:

Insects boring in large plants can decrease control of translocation herbicides, including glyphosate. If insects are present in plants increase the translocation herbicide rate whenever possible to maximize control.

“Transplanted” weeds, especially lambsquarters and giant ragweed, from a single tillage pass are very difficult to control with translocated herbicides, including glyphosate. Use higher glyphosate rates for the “transplanted” weeds compared to weeds that germinated after the tillage.

In non-GMO soybeans, use the maximum labeled rates of herbicides, consider tank-mixes, and use the maximum adjuvant rates for control of large weeds. Soybean injury will occur when doing this, but yield loss will be greater from not controlling the weeds compared to not injuring the soybeans.

For height restrictions in corn and other large weeds refer to http://corn.osu.edu/story.php?setissueID=41&storyID=193

Wheat Harvest And Head Scab Issues

Authors: Patrick Lipps, Dennis Mills

Wheat head scab continues to be the topic of interest among wheat growers throughout the state, especially now since harvest has started in the southern Counties. Essentially every field has some level of head scab. Thanks to the County Extension Agents we have data on the incidence of scab from many counties. Overall, disease incidence (the percentage of heads with head scab) varies greatly within Counties and throughout the state. Some Counties in northwest Ohio report fields with as little as 1% of the heads affected where as Counties in central Ohio report fields as high as 30% to 40%. Overall the state will likely average about 10 to 13% incidence of head scab.

According to the relationship between scab incidence and severity (percentage of diseased spikelets per head), the severity of scab will likely run between less than 1% to as high as about 7%, with a state wide average of about 2% to 3%. Because the scab heads appear so evident in contrast to the green healthy heads most people tend to overestimate the incidence and severity of the disease. The amount of scab in the wheat crop this year is only a bit higher than what we saw last year and the year before, but in no way is it as bad as the major epidemic the state endured during 1996 when up to 80% incidence was detected in fields and yield were cut by up to 40%. Growers, elevator operators and the milling industry will likely deal effectively with the problems this year.

The relationship between scab level in the field and yield is not very predictable when disease moderate to low, only when scab gets very severe is the relationship more predictable. Therefore, it is difficult to estimate the level of yield loss this year, but yield loss is likely not too great. Most important at this time is grain quality issues. The presence of DON (vomitoxin) in the grain will likely be near the critical 2 ppm level in fields. At this point the amount of DON in the grain will be greatly influenced by the amount of scab in the field, how quickly the field can be harvested, and how quickly the grain can be dried to prevent further accumulation of the toxin. DON begins to accumulate in the grain soon after the fungus enters the plant and continues through harvest or whenever the moisture content of the grain is favorable. In general the fungus stops growing when grain moisture levels drops below 20%. However, the fungus can grow again, and produce DON when grain is rewetted due to rain or heavy dew.

Wheat growers are advised to harvest fields as soon as possible to prevent further deterioration of grain quality and to maintain test weights. Turn the combine blowers up high to remove as many small, shriveled kernels as possible. These kernels will likely contain higher levels of the DON. Dry grain to 14% moisture as soon as possible to prevent any further fungal growth and to prevent further accumulation of DON. Grain harvested from relatively disease free fields with low DON levels will likely sell at a premium. Take time and plan to take this opportunity.

Saving Wheat Seed For Planting In The Fall

Authors: Patrick Lipps

The wheat crop will come off earlier than normal this year, but not without some serious grain quality issues. Several diseases that affect grain quality also impact the ability of the crop to be saved as seed. Most importantly, head scab and Stagonospora glume blotch are widespread in the state and they will affect seed quality and germination. Any grain that will be saved for seed will need to be thoroughly cleaned to remove all small, shriveled seed and the seed will need to be stored under dry conditions until planting time to avoid mold and further deterioration of the seed. Air cleaning will not be sufficient to remove all diseased seed, but a gravity table will do a much better job if set to clean out sufficient light weight seed. Growers that do not have the facilities to adequately clean seed, store the seed and have it treated with an effective fungicide probably should not save their seed this year.

The fungi that cause head scab and Stagonospora glume blotch will remain on the seed during storage and when planted may cause increased problems with seedling stand establishment. Fungi that cause both diseases can kill seedlings under environmental conditions favorable for seedling blight. Additionally, Stagonospora nodorum, the fungus that causes glume blotch, will produce spores on the young plans in the fall that may contribute to the overall level of Stagonospora leaf blotch next spring. Therefore, all saved seed will need to be treated with as seed treatment that contains fungicides effective against these fungi. Dividend XL, Raxil MD, Raxil XT, Raxil-Thiram have excellent http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/seedtreatmentefficacy.htm activity against Stagonospora on seed and also provide good control of seed borne Fusarium from head scab. If additional protection from Fusarium is needed you can choose to apply LSP Flowable with the other seed treatment product. LSP Flowable is very effective in eliminating Fusarium from seed.

Lastly, all seed should be tested for germination before planting. The final germination test should be run on treated seed because treatment will frequently improve germination. It is not wise to plant seed with germination percentages much under 80%. A germination test is an indication of the level of possible problems that may arise from using poor quality seed and it can be reflected in the yield of the crop. Do not take chances with poor seed, the risks are too expensive.

Nutrient Management for Forage Production

Authors: Robert Mullen

Proper nutrient management can pay dividends when it comes to forage production systems. Supplying adequate nitrogen (N), phosphorus (P), and potassium (K) can go long way for both forage quality and yield. Much like N management for grain production systems, identifying a yield potential or yield goal helps identify an N recommendation. As rule of thumb, assume that for every ton of grass forage produced 40 pounds of N should be applied. Nitrogen application should also be split throughout the growing season. Apply slightly more in the early spring (70 lbs/A) and make N applications after each cutting (approximately 40-50 lbs/A).

Phosphorus management for legumes is also very similar to phosphorus management for grain crops. Soil test levels should be above the critical range to ensure that P is 100% sufficient. The critical range for most forage crops is 50 lb P/A. If soil test levels are below this value, P fertilizer should be applied. Because P is immobile in the soil, it is best if it is applied prior to seeding and incorporated. If P is added to an existing stand, simply broadcast apply a granular form. Subsurface injection of P may also be an option, but knifed P should be applied while the crop is dormant.

Potassium may need to be managed a little more intensively for forage production systems. Because most forages remove substantially more K than grain crops, K fertilization may need to occur more frequently. In cases where high yielding forages are grown on sandy soils, K should be managed more like N and applied after every cutting. The critical level for forages is a function of the soil cation exchange capacity (CEC), thus finer textured soils require more soil K to be 100% sufficient. Keep the magnesium (Mg) saturation of the soil CEC in mind when applying fertilizer K, too much K relative to Mg can contribute to grass tetany. To avoid tetany problems, keep the Mg to K ration above 2 to 1.

Sulfur (S) may also need to be considered for coarse textured soils low in organic matter, especially for alfalfa production.

Remember to determine your nutrient needs - soil test! Plant analysis can also be used to identify nutrient deficiencies.

Later Season N Applications for Corn

Authors: Robert Mullen

With all the rain that has fallen in the recent weeks, coinciding with the time most want to apply sidedress N, some fields have not received enough N to carry corn through to meet current yield potentials. The corn may be too tall now for conventional applicators, and so the question is “what do I do now?” The easiest answer would be the use of clearance spraying equipment, if it is available. Even if it is available, the ground may still be to wet to allow field activities.

Aerial application of urea may be a reality that some will have to face. If urea is applied over the top aerially, producers may want to stay away from the fields for a while. Some of the granules will get got in the whorl which is moist from all the rain and burning can occur. Does this burning hurt the crop’s yield potential? Probably not, but depending upon the rate of application it can look pretty ugly for about a about a week or so. The other concern with broadcast application of urea is N losses associated with the application. Nitrogen losses from broadcast applications can be significant, especially in no-till fields (greater than 20% in some cases). So if given the choice between aerial application and the use of a high clearance applicator, the high clearance applicator is probably the best choice from an efficiency standpoint. It will allow for dribble application of liquid N which is far less susceptible to loss. Obviously, economics must also be considered.

If faced with this decision consider all points. If the field is too wet for applicator traffic but the field does not look too N stressed, you may want to wait and allow the field to dry and make the application with a high clearance sprayer. If the field is obviously N stressed and it may not dry for a while, aerial application may need to be looked at more seriously. Research has shown that corn can respond to N application all the way up to tasseling and beyond. So even though you have missed the boat with earlier applications, the boat is not so far out into the harbor that you can not swim out to it (not yet anyway).

Soybean Aphid Update

Authors: Bruce Eisley, Ron Hammond

Currently, we have heard of no reports of soybean aphid in Ohio, and reports from other Midwestern states have been mostly of low to non-existent populations. Other than a few reports from Iowa of moderate population densities in a few fields, none of the other more northern states where soybean aphids are thought to overwinter are reporting any findings as of last week. Thus, there is no reason to begin taking action other than sampling fields and keeping up-to-date of the latest information available here in the C.O.R.N. newsletter.

When searching fields, growers should make sure of the correct identification of the soybean aphid which is often confused with small potato leafhopper nymphs or even thrips. Aphids will usually be found in groups of 3-10, are more oval, and are somewhat sedentary (slow moving), while potato leafhoppers are usually found singly, are elongated, and tend to move rapidly over the leaf surface (http://ohioline.osu.edu/icm-fact/images/113.html). Thrips are extremely small and very elongated. All three are best identified with the use of a hand lens.

Because of the current lack of aphids in most states, and especially in Ohio, there is no reason to begin making insecticide application either alone or in combination with Roundup or other post-emergent herbicides. Unnecessary insecticide application not only wastes money, but can lead to other problems including environmental contamination, possible resistance concerns, or resurgence of insect pests.

We still do not have a good prediction as to whether soybean aphid populations will increase to economic levels this summer. We hope to have a better idea by mid-to-late July. Thus, we recommend keeping abreast of the changing situation through this newsletter. Also, in a previous C.O.R.N. newsletter, we discussed a bulletin that was released on the soybean aphid. The correct address for this web sit is http://www.ncsrp.com. The address listed two weeks ago might have been wrong. Sorry for any inconvenience.

Phytophthora sojae Is Impacting Soybean Stands

Authors: Anne Dorrance

The downpours of last week are clearly evident in many fields this weekend. A drive through the state – you could really see the tile lines in the soybean fields. Plants were deep green and taller on top of the tile lines while those in the wetter areas of the field were yellow and stunted. In walking through several fields—the characteristic stem lesion of P. sojae was evident – but in my field plots – it is only occurring in varieties with partial resistance scores of 5 or greater. (Some companies use the reverse score—so check the fine print on your seed catalogue). Some of the beans were truly flooded out. The area of the field smells – soggy – like dead worms. The Rhizobium nodules are dead. When you dig he plants up – the nodules, those round bumpy things on the roots can be crushed between your fingers if they are dead. If they are healthy- they will be firm and a nice pink color on the inside. If the plants have a Rps gene that is effective or if they have high levels of partial resistance – it will take some time for them to grow new roots. Last year, we had several cases where folks sent stunted, yellow seedlings in to see if they had root rot. During the 2 days in shipment- the plants grew new roots! Some of these soybeans could use some oxygen in the root zone and they will be in much better shape. Those plants that were attacked by Phytophthora will continue to die throughout the summer – thinning the stands in the wetter areas of the field.

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance, Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Jeff Stachler (Weed Science), and Ron Hammond (Entomology); Extension Agents: Ray Wells (Ross), Barry Ward (Champaign), Steve Foster (Darke),Todd Mangen (Mercer), Greg La Barge (Fulton), and Steve Prochaska (Crawford).

About the C.O.R.N. Newsletter

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.