C.O.R.N. Newsletter 2005-16

Dates Covered: 
June 7, 2005 - June 14, 2005
Editor: 
Greg La Barge

Wheat Head Scab Risk Remains Generally Low

Authors: Pierce Paul, Patrick Lipps

The Wheat Head Scab Prediction Center http://www.wheatscab.psu.edu/ has indicated that the risk of head scab on wheat has been consistently low throughout Ohio for fields planted after soybeans due to prevailing cooler temperatures in late May and the first few days of June. Those wheat fields planted into corn residue have had a much higher risk of scab during this period of time, especially if located in the west central part of the state. However, any elevated risk of scab will depend on duration of precipitation that a particular field receives during the flowering period. The first wheat fields to began to flower did so about two weeks ago in southern Ohio and as of today (June 6) the latest fields in the state's most northern counties were in mid to late flowering. Wheat is most at risk during the flowering period, but persistent wet conditions, especially with warmer weather could cause later infections to the head as the wheat begins to go into grain fill. We are optimistic that head scab levels will be low this year since the wheat crop has generally been in its most susceptible stage when the weather conditions were unfavorable for infection and the numbers of spores of the Fusarium fungus in the air have been quite low. Growers in southern Ohio can begin to monitor wheat fields for symptoms of heads scab later this week and next week in central Ohio.

Development of Powdery Mildew and Leaf Blotch Slowed by Weather

Authors: Patrick Lipps, Pierce Paul

The warmer weather predicted for Ohio this week will limit the further development of powdery mildew. Powdery mildew generally spreads rapidly with high humidity and cool temperatures (50 to 73 degrees F). Temperatures above 77 degrees F stop spores from being produced and limit further spread of the disease in the field. Since all the wheat in Ohio is now past flowering no fungicides can be applied to fields.

Generally, leaf blotch diseases like Stagonospora leaf blotch and tan spot begin to spread rapidly as the wheat progresses from the flowering stages through grain ripening. However, leaf blotch diseases have been quite rare this year and we do not expect to see any great increase in these diseases over the next few weeks unless the weather conditions change to three to four days of rain each week through June. This amount of precipitation is not in the forecast, so there is likely a reduced risk of leaf blotch development on a state-wide basis.

A New Kind of Rust That’s Not Soybean Rust- Wheat Stripe Rust

Authors: Patrick Lipps, Pierce Paul

Those of you who may be scouting wheat fields may be finding some areas of fields affected by stripe rust. Stripe rust is a relative new-comer to Ohio so most of you probably have never seen this disease before. The Cereal Rust Lab at the University of Minnesota has been tracking this rust along with the other wheat rusts for many years. Each year we consult their monitoring system to see how far the wheat rusts have moved from the southern wheat growing regions toward our state. This gives us an early warning of when either leaf rust or stripe rust may be approaching our state. Over the past two weeks we have detected stripe rust in Ohio, but since it was not moving very rapidly, and not causing much of a problem, we have not reported it in this newsletter. Last week we received several reports of stripe rust in west central and south central Ohio and we have detected it here at Wooster. Therefore, it is likely that you might see it almost anywhere in the state at this time. So far it has been found only in 'hot spots' in fields. These are spots 1 to 5 feet in diameter where stripe rust is present on the upper leaves of affected plants. Obviously, only a few spores blew in from the south and landed in our wheat fields and then the disease spread to adjacent plants. It is a remarkably characteristic rust disease with bright orange pustules arranged in stripes on the leaves as seen in image at https://agcrops.osu.edu/images/wheat/wheatstriperust05b.jpg and https://agcrops.osu.edu/images/wheat/wheatstriperust05d.jpg. The bright orange is usually in stark contrast to the green leaf tissue on affected leaves.

Stripe rust spreads fastest during seasons with cool temperatures, but spread is restricted when the night time temperatures remain above 65 degrees F. Since our weather forecast is for much warmer weather we will probably not see this rust disease spread much further in our wheat crop. However, if you do detect stripe rust widespread in one of your fields, you should make a note of the variety and probably not plant that particular variety again. We are not sure how important stripe rust will be in the future, but it is obvious from looking at the spread of the disease from southern wheat growing regions to more northern states over the past few years that some day it may become an important problem for us. Time will tell.

Soybean Aphid Update

Authors: Bruce Eisley, Ron Hammond

Although we have not yet found aphids on soybeans in Ohio, other midwestern states, including Indiana, Michigan, Minnesota, and Iowa, have reported finding very low numbers of aphids on the crop. I would expect if we looked hard and long enough, we would also find the aphid in Ohio on soybeans.
The question that begs to be asked is, what does this mean? Are we going to have a bad aphid year? At this time, we still cannot answer this for certainty. However, these early finds are similar to the situation in 2003, which was a bad year for soybean aphid. The best thing for growers to do is to keep up on the situation through this C.O.R.N. newsletter. There is no reason to begin intensive sampling at this time, nor any reason to consider any type of treatment if indeed you find a few aphids in your fields. Entomologists from all the midwestern states are in weekly contact, so if something happens in one state, we all will know about it within a few days. If populations start to build up in any of the states, we will all hear about it. For those growers wishing to start looking for aphids, remember that their numbers will in all likelihood be very small; perhaps a single or a few aphids per leaf. Care should be taken so that you do not misidentify other insects as aphids http://ipm.osu.edu/soyaphid/sbapics.htm, including potato leafhopper nymphs http://ohioline.osu.edu/icm-fact/images/113.html and thrips http://entomology.osu.edu/ag/thrips.htm. As we get later into June and early July, we update growers on the scouting methods and thresholds for treatment along with treatment selection.

Soybean Rust Not Moving and Fungicide Clarification

Authors: Anne Dorrance

Soybean rust is still not moving or moving much slower than originally thought. Several reasons have been proposed over the past few weeks, primarily that there was just enough that survived the cold winter this past year, conditions in Florida have not been conducive to soybean rust development and third the weather patterns have really kept this thing in Florida and not allowed it to move along the coast to the remaining gulf states. The current recommendations for Georgia are “don’t treat”. Soybean rust has not been found in any of the sentinel plots – so we are still in a monitoring mode. For Ohio, the risk of soybean rust for the flowering period is very, very low.

Fungicides on soybeans. Numerous questions this past week and a few things probably need to be clarified. Headline and Quadris which are the strobilurin type compounds, have full section 3 labeling. These have a number of other soybean foliar and stem rot pathogens on their label. Strobilurins as a group of compounds must be applied as a preventative because their mode of action is on the spore – not on the actively growing mycelium. For all of the pathogens listed on the label – these are not yield limiting problems in Ohio: Cercospora leaf blight, Diaporthe stem canker, Frog-eye leaf spot. In field studies there is a great difference among the regions – Data from Mel Newman in Tennessee show a great return from applying fungicides; Don Hershman in Kentucky found a 50% of the time there was a positive yield effect; in Ohio last year, with one year of field data – we had one plot out of 16 that had a 5 bu/A. The remaining either had 1 to 3 bu plus or minus for fungicides. We will be evaluating the effects of these fungicides again in randomized strip plot studies at the recommended and labeled rates to determine if this is a regional or yearly effect. This work is funded through check-off support from Ohio Soybean Council.

Section 18 compounds. A section 18 is an emergency use label to help mitigate what could be a crop disaster. This would include the triazole compounds and the combination products. Bottom line – they can only be used on soybeans to manage soybean rust and any other use is off-label.

Conditions Favorable For "Rootless Corn Syndrome"

Authors: Peter Thomison

The recent hot, dry weather combined with poor root development in early planted corn may be setting the stage for rootless corn problems. Rootless corn (or "rootless corn syndrome") occurs when there is limited or no nodal root development. Plants exhibiting rootless corn symptoms are often leaning or lodged. Affected corn plants may only be anchored in the soil by seminal roots or by a single nodal root. This condition is generally observed in plants from about the three leaf stage to the eight leaf stage of development. The problem often becomes evident when corn is subjected to strong winds, which result in plants falling over because there is a limited number or no nodal roots supporting them. The force of strong winds can also break off nodal roots and inhibit establishment of a permanent root system. Leaning and lodged plants (sometimes referred to as "floppy corn") may also be wilted. When affected plants are examined, the nodal roots appear stubby, blunt, and unanchored to the soil.

Rootless corn problems are usually caused by weather related conditions that coincide with development of the permanent (or nodal) root system and various environmental factors. These include shallow plantings, hot, dry surface soils, compacted soils, and loose or cloddy soil conditions. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn. Nodal root development is inhibited by hot, dry compacted soils. During the protracted period of cold wet weather in late April and early May this year, compacted soil conditions also contributed to slow emergence and poor seedling root development in many fields.

The nodal roots develop above the seed and comprise the permanent root system of corn. The nodal roots, not the seminal roots (associated with the seed), are important in providing the water and the mineral nutrients that the corn plant needs for normal growth and development. If corn seed is planted 11/2 to 2 inches deep, then the nodal (or crown) roots begin develop at about 3/4 inches below the soil surface. However, if seed are planted shallower (1 inch or less), then the nodal roots may form near or at the surface where they are more exposed to fluctuations in soil moisture and temperature. Nodal root growth is very sensitive to high temperatures (w/ root growth slowing or stopping at soil temperatures exceeding 86 degree F ). When unshaded surface soil temperatures reach the mid 90's or higher on hot days, the nodal root growth of shallow planted corn may stop. Plants are forced to rely on the seed root system or limited nodal root growth until more favorable temperatures and moisture conditions allow nodal root growth to resume.

Certain types of herbicide injury (e.g. 2,4-D, Banvel) and insect feeding (e.g. corn rootworm) may also cause lodging to occur in corn plants during vegetative development. Generally they are not the major causes of the rootless corn problems. However, there may be situations where insect feeding and/or herbicides may be a contributing factor.

Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery. Of course, this is difficult to do in a no-till situation or when the soil is hard and dry. Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as soon as grain moisture conditions permit.

South Central Ohio Soybean Rust and Field Crops Pest Management Field Day June 16

Authors: Howard Siegrist

South Central Ohio Soybean Rust and Field Crops Pest Management Field Day program will be held on Thursday, June 16 from 5:00 - 9 P.M. at the Ruff's Seed Farm in southern Fairfield County. The program will feature concurrent "round robin" sessions on scouting for soybean rust, soybean aphids and economic thresholds, spray nozzle demonstration and mid season diseases and stress signs in corn. The evening will conclude with a light supper and a session "Making the Right Choice in Class of Fungicides for Rust Management".

The program is free; however, pesticide credits will be available at a nominal cost. The program is sponsored by the Fairfield, Pickaway, Ross, Perry and Licking OSU Extension offices. For additional information or directions contact the Extension offices or email siegrist.1@osu.edu.

Wheat Production Field Day in Northwest Ohio June 21

Authors: Greg LaBarge

On June 21st from 9 am until noon Wheat will be the featured crop at a field day hosted at the OARDC Northwest Agricultural Research Station in Custar. Topics include a Hands-on wheat disease identification, scouting and fungicide application session with Dr Pat Lipps, Plant Pathologist, Ohio State University; Wheat variety selection and row spacing interaction will be presented by Dr Jim Beuerlein, Soybean and Wheat Production Specialist; Managing nitrogen and sulfur discussion will be lead by Dr Ed Lentz, Extension Educator Seneca County; The program will finish with a wheat breeding progress report from Dr Clay Sneller, Wheat Breeder, Ohio State University.
The program is open and free to anyone. An afternoon session on scouting soybeans for insect and disease along with sprayer adjustment will be held. More information can be found below. The Northwest Agricultural Research Branch is located at 4240 Range Line Rd. A map can be found at http://www.oardc.ohio-state.edu/branches/Northwest.htm#Directions

Let’s Get Ready” Scouting and Sprayer Clinic June 21

Authors: Dusty Sonnenberg

Let’s get ready to SCOUT! The calendar page has turned to June, and now most all crops are in the ground for either the first or second time. Once an adequate stand is established, our focus turns to regular scouting for disease and insect pests that can reduce potential yields. A key to this scouting is not only knowing what to look for, but also identifying both agronomic and economic thresholds as well as effective control methods.

A free field scouting and sprayer adjustment clinic has been scheduled for Tuesday, June 21st, at the OARDC Northwest Research Station near Hoytville, from 1:00 p.m. – 4:00 p.m.

OSU Plant Pathologists, Dr. Anne Dorrance, and Dennis Mills will be on hand to help identify and discuss what diseases we are currently seeing in our crops and their associated thresholds. OSU Entemologist, Dr. Ron Hammon, will be discussing insect pressure and soybean aphid issues. OSU Agricultural Engineer, Dr. Erdal Ozcan, will be discussing sprayer set-up, adjustment, and tip selections.

Private and Commercial Pesticide Applicator Credits as well as Certified Crop Advisor CEU’s will be available that day. Industry representatives from Top Air and Hardy will be on hand with sprayer equipment on display and help producers with specific adjustment questions.

Hands-on field scouting for various insects and diseases, as well as an in field sprayer demonstrations utilizing various pressures, volumes and speeds will be conducted. A spray table will also be utilized to compare various nozzle types and spray patterns.

OARDC will be holding a Wheat Production Field Day that same morning, so producers can come and make a day of it. The Wheat Field Day runs from 9:00 a.m. – 12:00 noon. The McComb FFA Chapter will be on hand with a lunch stand so you can buy your lunch there and support the FFA, and then stay for the afternoon clinic.

For more information contact Dusty Sonnenberg at OSU Extension in Henry County at (419) 592-0806, or by e-mail at sonnenberg.2@osu.edu

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance, Peter Thomison (Corn Production), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology) Extension Educators: Roger Bender (Shelby), Steve Bartels (Butler), Steve Foster (Darke), Bruce Clevenger (Defiance), Gary Wilson (Hancock), Greg La Barge (Fulton), Howard Siegrist (Licking), Mark Keonig (Sandusky), Dusty Sonneberg (Henry) 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.