CORN
Crop Observation and Recommendation Network

For Week of July 6-12, 1998
C.O.R.N. 98-17

In This Issue:

A) Fungicide Treatment for Sclerotinia White Mold
B) Soybean Herbicide Injury During Flowering
C) Corn Rootworm Activity in Corn
D) Detecting Adult Corn Rootworm Activity
E) Protection of Stored Wheat Grain
F) Frequently Asked Questions on Late Applications of Nitrogen to Corn

A) Fungicide Treatment for Sclerotinia White Mold - Anne Dorrance CORN Questions

Rains that occur during soybean flowering may enhance the development of Sclerotinia white mold. Sclerotinia white mold is a fungal disease of soybeans. This fungus survives in fields as hard black sclerotia. During wet rainy periods these sclerotia will produce light tan apothecia or "mushrooms" which are the size of the head of an eraser. Environmental conditions that favor apothecia development include soil temperatures that range between 55-65°F and when soil moisture levels are high for 10-14 days prior to flowering. Environmental conditions that favor infection of the blossoms are cool temperatures (<86°F) and plant surfaces that have been wet for 12-16 hrs. Under these favorable environmental conditions, spores will land on decaying blossoms and begin to colonize soybean plants. There are no varieties that are totally resistant to Sclerotinia white mold. There are varieties which do get less disease than others, for example, Vertex will have approximately 10% of the plants infected where as Williams 82 will have 60% under the same conditions.

For those fields where Sclerotinia has been a recurring problem on soybeans and only on very susceptible varieties, producers may want to consider fungicide applications. Topsin M is labeled for Sclerotinia white mold at the R2 growth stage. However, it is very important to get the fungicide on the blossoms. Cobra has a label for white mold suppression. However, control has been erratic in several studies. Studies in Wisconsin and Iowa have found that when Cobra was applied with water to soybeans that were moderately susceptible to white mold, at the R1 growth stage, there was suppression of white mold.

B) Soybean Herbicide Injury During Flowering - Mark Loux CORN Questions

We have often been asked whether herbicide application during soybean flowering will cause yield loss. Our experience has been that large soybean plants are more tolerant of soybean herbicides in general, compared to small plants. As we stated in recent weeks, our greatest concern is application of "hot" herbicide mixes to small soybeans late in the season. This scenario has occasionally resulted in yield loss in OSU plots, but large soybeans seem to be considerably more tolerant. While we do not know whether herbicides cause flowers to drop off, abort, etc, plants are usually fairly large when flowering is at its peak. Application during flowering may not be the issue - the issue is probably whether plants are able to regain enough growth following herbicide application to reach maximum yield potential. If damage to foliage on large plants is minimal and overall plant development is not greatly inhibited, we would assume that yield potential has not been reduced.

C) Corn Rootworm Activity in Corn - Hal Willson CORN Questions

Western corn rootworm beetles were observed in abundance (up to 5 beetles per plant) in first year corn fields of Van Wert County on Thursday, July 2nd. In contrast, no adult activity was observed in heavily infested continuous corn plots at the Western Branch station on the previous day. Curtis Young (NW District IPM specialist) reports that lodging (ranging from 2% to 50% of stand) was observed in Van Wert corn fields. However, it should be noted that part of the lodging injury may be due to severe weather conditions.

At our continuous corn trials at the Western Branch, lodging has become more evident following the heavy rains of the past week. Late plantings are exhibiting more injury than earlier plantings, especially in plots where corn has been planted for three years.

D) Detecting Adult Corn Rootworm Activity - Hal Willson CORN Questions

Given current conditions, field efforts should be underway at this time to detect rootworm problem fields and determine the distribution of the first year corn rootworm. At the present time, first year corn stands should be checked for lodging and root systems examined for rootworm injury and presence of larvae. In addition, observation of adult rootworm beetles in abundance in first year corn fields by mid-July also indicates the presence of first year corn rootworm, since the migration of beetles from continuous corn is unlikely to occur until late July.

Deployment of yellow sticky traps in soybean fields to detect unusual rootworm activity should begin in mid-July. A number consultants, dealers, corporate representatives and Extension personnel will be operating traps this year to evaluate adult rootworm activity in soybeans. Due to recent corporate purchases of yellow sticky traps, sources of the Pherocon AM traps are currently out of stock and waiting on factory production.

Ohio Extension personnel will be using both Pherocon AM and Multigard traps to monitor rootworm this summer (if our shipment of Pherocon traps arrives). It should be emphasized that the Multigard trap collects many more beetles that the Pherocon AM trap (5 to 10 fold more). In Illinois and Indiana, where the first year rootworm problems has been active for a number of years, preliminary thresholds have been developed to related beetle catch in on the Pherocon trap in soybeans to forthcoming rootworm injury in first year corn. The threshold may range from 2 to 7 beetles per day per trap depending on the level of root injury tolerated. Thus, the threshold may range form 15 to 50 beetles per trap per week in a soybean habitat.

In Ohio, we have used the Multigard trap to monitor rootworm in corn for a number of years, but data applicable to the first year rootworm problem is limited. We do know that the average catch of adult rootworms on Multigard traps in a soybean fields lacking the first year rootworm problem averages about 5 beetles per trap over a two week time period. In contrast, the beetle catch on Multigard traps in a soybean field having the first year corn rootworm problem will increase to 100 or more beetles per trap, which is equivalent to the activity we would normally observe in a first year corn field without the first year rootworm problem. In first year corn fields with the new rootworm problem or in continuous corn fields, the catch on Multigard traps averages more than 300 beetles per trap per two week period.

Western Corn Rootworm Beetle

E) Protection of Stored Wheat Grain - Hal Willson CORN Questions

Wheat is currently being harvested and reports have been received that growers may store more wheat on-farm this year. Given the hot temperatures and periodic moist conditions, good grain management practices should be emphasized this season to prevent potential stored grain pest problems.

First, one should begin with a clean and pest free storage facility. A 1994 survey of Ohio storage manager's practices indicated that less that half of on-farm wheat storage facilities were treated with an empty bin treatment prior to grain storage. Furthermore, most of the empty bin treatments applied used malathion in contrast to more effective treatments such as Reldan or Tempo, which would improve control of the total storage pest complex in an empty storage facility.

Second, wheat grain at storage should be clean and grain moisture reduced to an optimal level that can be economically maintained. Effective management of the grain environment with timely aeration is essential to prevent development of insect pest populations and microbes on stored grain.

The 1994 survey also indicated that only one out of five on-farm wheat storage managers applied a grain protectant to their stored wheat. Although two products, Reldan and malathion, are registered for use as grain protectants on wheat, a grain manager should check on whether the market targeted prefers grain that has not received a protective treatment. In areas where Indian meal moth infestations have been a primary problem, grain surface treatments with a Bt formulation such as Dipel or the protectant Reldan should be considered. Malathion is generally not effective against Indian meal moth.

F) Frequently Asked Questions on Late Applications of Nitrogen to Corn - Peter Thomison and Jay Johnson CORN Questions

Excessive rainfall has forced many growers to sidedress their nitrogen (N)on corn this year - in some cases much later than what is considered normal. The following includes part of an 1996 article by Dr. Dave Mengel (formerly Extension Soil Fertility Specialist at Purdue University, now chair at Kansas State), which addresses various questions concerning N applications to corn after planting.

How Late Can N Be Applied?

• Corn utilizes large quantities of N during the grand growth stage. From the 8 leaf stage through tasseling N uptake is 4 to 8 pounds per day. For most corn hybrids N uptake is complete shortly after pollination. So, most of the N should be applied prior to the 10 leaf stage, with any supplemental applications complete by or shortly after tasseling. Under conditions of severe N deficiency, some response would be expected to low rates of N (30 to 60 pounds) as late as three weeks after pollination.

What Is the Best N Source to Use?

• Ammonia or N solutions knifed in, or ammonium nitrate over the top are preferred in most situations, especially high residue fields. Granular urea can also be applied over the top in clean tilled situations. Both granular urea and ammonium nitrate broadcast in standing corn will cause some foliar burn when granules fall into the whorl. While it may appear unsightly, little yield decrease normally occurs if the fertilizer is applied prior to the 10-leaf stage.

How Much N Should Be Applied?

• If the corn has gotten too tall to sidedress by this point (late June and early July), it has probably not been severely stressed and yield potential is still good. An example would be rotation corn after beans which had some starter or 28% applied with herbicides with good green color. Supplemental N rates at this point should probably be in the 0.5 to 0.7 pounds N per bushel of expected yield.

How Can I Apply N to Four Foot Tall Corn?

• Tall corn requires the use of high clearance ground equipment such as a high boy. Care must be exercised to ensure that N solutions applied are not sprayed directly on the foliage as they will cause extensive foliar burn. Fitting the machine with drop hoses which deliver the fertilizer in a solid stream on the ground is preferred. Hoses should be long enough to drag on the ground. A weight attached to the hose helps it to drag true through the row.

Can I Broadcast Urea and 28-0-0 Solutions "Over the Top"?

• Using broadcast applications of urea and 28% N solution to sidedress N will cause some burn to foliar tissue of corn plants. Damage results when urea granules or 28% UAN solution get inside the leaf whorl of corn plants.
• The severity of injury is determined by the plant's stage of growth, the amount of N used and form of N. If the plant growing point is at or below the soil surface (or when plant has six fully expanded leaves or less), the extent of foliar injury caused by burn will usually be negligible if the N rate is kept below 50 lb/acre. Even at higher N rates and later vegetative growth stages (up to V6) the injury from leaf burn is normally not so severe that it outweighs the potential benefits received from the N addition. The degree of this plant burning is less with urea granules than with other N products.
• Dribbling 28% solution with drop nozzles as a narrow band on the soil surface is an alternative approach that can help reduce foliar burning. Dribbling 28% is also a more efficient use of N than broadcast surface application because it helps reduce N volatilization.

Can I Apply N to Every Other Row?

• Research in Indiana, Illinois and Iowa has all shown that farmers can knife ammonia or N solutions in every other row middle (60 vs. 30 inch spacing) with no reduction in yield. The only caution is that extra attention must be paid, especially in wet conditions, that no knives plug with soil. A plugged knife in 60 inch spacing gives 4 rows with no N and will seriously reduce yields.

What About Aerial Application?

• Aerial applications of granular fertilizers such as urea or ammonium nitrate can be made to growing corn. Unsightly burn spots will result where fertilizer granules fall into the whorl. However yield reductions will be minimal. N solutions should not be applied by air due to the problem of foliar burn. Even at higher N rates and later vegetative growth stages the injury from leaf burn is normally not so severe that it outweighs the potential.

Readers can subscribe electronically to this newsletter bysending an e-mail message to: listserv@agvax2.ag.ohio-state.edu with the message: subscribe corn-out. A successful subscription message will receive a reply from listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Contributors to C.O.R.N. this week include: State Specialists: Ann Dorrance (Plant Pathology), Jay Johnson (Soil Fertility), Mark Loux (Weed Science), Jeff M. Stachler (Ext. Asso., Weed Science), Peter Thomison (Corn), and Hal Willson (Entomology). Extension Agents: David A. Jones (Allen), Steve Prochaska (Crawford), Greg LaBarge (Fulton), John Barker (Knox), Howard Siegrist (Licking), Ray Wells (Ross), Clark Hutson (Seneca), and Rodger Bender (Shelby).

Editor: David A. Jones - Web Editor: Steve Lichtensteiger

Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868

| C.O.R.N. | Newsletter | Archive | Search | Questions? | Ohioline | Publications |