CORN
Crop Observation and Recommendation Network

June 2-8, 2003
C.O.R.N. 2003-16

In This Issue:

A) Wheat Disease Update
B) Corn Seedling Blight Causing Stand Losses
C) Tips for "Patching In" Poor Corn Stands
D) Corn Yellowing Concerns
E) Sidedress Nitrogen Considerations
F) Insect Update
G) PONCHO Labeled on Corn

A) Wheat Disease Update - Lipps and Mills CORN Questions

The cooler weather is affecting the development of wheat diseases in most areas of Ohio. The cool weather diseases, powdery mildew and Septoria tritici leaf blotch, continue to develop, but the warmer weather diseases, Stagonospora nodorum leaf and glume blotch are much lower than expected for this time of year. Additionally, the cooler weather also means much less risk from head scab even though it has been raining. Those fields in southwest Ohio that went into flower early (May 12-17) the scab risk is moderately low. The later flowering wheat in this area and the wheat in central Ohio have a low scab risk. Wheat in NW Ohio is moving through the heading and flowering stages very slowly and the weather later this week and early next week will impact the risk of scab in those areas. When the temperatures return to more normal levels growers in northwest Ohio can expect the wheat crop to head and flower quickly. The cooler weather has not hurt the wheat crop at all, and probably has helped the wheat in most areas.

A final note on spraying fungicides for disease control: do not spray wheat after flowering. If disease threshold levels have not been reached by flowering then the cost of fungicide and application is usually not returned by the yield response from disease control. At this time only the wheat in northwest Ohio should be evaluated for a fungicide application because the crop is in heading and early flowering stage in this area. Secondly, the fungicides labeled for use on wheat in Ohio are not very effective against head scab. They only suppress head scab and at best can reduce the severity by 50%. This may not improve yield and just as importantly they may not lower DON levels in the grain enough to avoid dockage when selling the wheat. Besides, the risk of head scab is low due to the cool weather we have had over the past two weeks when the wheat crop was flowering. It is important to visit fields and evaluate for leaf and head diseases at the flowering growth stage because what has occurred on these plants up to this point will impact yield.

B) Corn Seedling Blight Causing Stand Losses - Lipps and Mills CORN Questions

We continue to see corn seedlings die in many fields throughout Ohio. Much of the affected corn is in the V1 to V3 growth stages. The soil temperatures have not been favorable for rapid corn growth. In most locations the soil temperature has been fluctuating around 60 degrees F. The wet and cool to cold weather this weekend has not helped this situation. It appears that these young corn plants are very slow in producing nodal roots and thus are relying on the seedling roots (seminal roots) associated with the seed for nutrients and water. We have recovered several disease causing fungi, mostly Pythium, from young seedling roots and from seedlings that were killed prior to emergence. Most recently it appears that Fusarium is attacking the roots and the mesocotyl (stem internode between the seed and the crown) of emerged plants. The mesocotyl is a very important structure for young plants and if rotted the plants wilt and die rapidly if nodal roots are not available to provide the plant with water and nutrients. Unfortunately, if soils remain cool and wet more seedling blight diseases can be expected. Seed treatments are only effective for about 10 to 14 days under most circumstances and many of the fields with seedling blight problems were planted three to four or more weeks ago. The severe wind damage some of these plants received a couple of weeks ago have left them even more vulnerable to attack by these soil fungi.

C) Tips for "Patching In" Poor Corn Stands - Thomison CORN Questions

Ponding and poor drainage conditions have reduced corn stands in many Ohio fields. Moreover, the remaining plants in affected fields are usually unevenly spaced within rows and not developing uniformly. Questions often arise as to whether to patch-in these poor stands, replant stands with poor emergence, or to protect late emerging plants during row cultivation. The following are some guidelines to consider in these situations based on findings of Illinois and Wisconsin research. A good source for more information on this subject is the National Corn Handbook Chapter 36, "Effects of Uneven Seedling Emergence in Corn" which is available on-line at http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-36.html

WHEN SHOULD YOU PATCH-IN A POOR STAND?
Growers will sometimes attempt to plant over or "patch in" a poor stand rather than kill the existing plants and replant at a full population. However,"patching in" is generally of limited benefit unless the surviving plant population is less than one half that of the original. The success of such an approach is even less likely late in the planting season (i.e. after June 1). Later planted corn cannot compete effectively with the remnants of the original plant population for sunlight, water, and nutrients. In these late planting situations, late emerging plants often function more like weeds, and contribute little to grain yield.

· If you replant within 2 weeks of planting the original, patching-in may be a viable option. Yields will be similar to those from a uniform-emerging replanted stand, if you can get relatively uniform plant spacing within the row between the old and new plants. However, within 2 weeks of planting, it probably will be too early to determine what the final stand will be (and whether patching will be needed).
· If you replant within 3 weeks after the initial planting, yield potential is about 10% greater if you tear up the field and start over with an even emerging stand rather than just patch-in the original stand. Balance this possible yield increase against the additional cost of tillage, seed, and dryer fuel.

SHOULD YOU REPLANT STANDS WITH UNEVEN EMERGENCE?
· If the delay in emergence is less than 2 weeks, replanting will have a minimal effect on yields, regardless of the pattern of unevenness.
· If one half or more of the plants in the stand emerge 3 weeks late or later, then replanting may increase yields by up to 10%. To decide whether to replant in this situation, estimate both the expected economic return of the increased yield compared to your replanting costs and the risk of emergence problems with the replanted stand.
For more information on replanting corn, check the CORN newsletter of May 19-26, 2003 C.O.R.N. 2003-14 ("Guidelines for Replanting Corn") available on-line at
http://corn.osu.edu/archive/2003/may/03-14.htmlout

SHOULD LATE EMERGING PLANTS BE PROTECTED DURING ROW CULTIVATION?
· If the delayed plants emerge only 1 " to 2 weeks late, use shields and avoid burying the late-emergers during cultivation.
· Protect plants emerging 3 weeks late if one half or more of the plants in the stand are late-emergers.
· If less than 1/4 of the stand emerges 3 weeks late or later, it probably will not pay to encourage their survival. Yields will be about the same whether or not these delayed plants are buried during cultivation.

D) Corn Yellowing Concerns - Thomison CORN Questions

Cloudy, cool, rainy weather has slowed growth of early planted corn. Corn seedlings often turn yellow (due to low nitrogen uptake and/or limited chlorophyll synthesis) or purple (reduced root development) under cool, wet conditions. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool. Yellowing or purpling of corn plants at this stage of development generally has little or no effect on later crop performance or yield potential. If it's induced by environmental conditions, the yellow or purple appearance should change to a healthy green after a few sunny days with temperatures above 70 degrees F. If plants remain yellow then closer inspection and assessment is needed to determine if yellowing is caused by nutrient deficiency or some other factor. Given our weather conditions this year a nitrogen deficiency is most likely responsible for leaf yellowing.

E) Sidedress Nitrogen Considerations - Lentz and Thomison CORN Questions

The ability to adjust N rates after planting is one of the main advantages of a sidedress program. Rate adjustments should be made at sidedress when the yield goal has changed since planting or significant N losses occurred early in the season. Some areas of the state have had to replant some fields or were not able to plant by the first part of May. These areas should expect lower yields than the earlier planting date and should reduce sidedress N rates accordingly. Even though the earlier planted corn has had slower growth this year, it should receive its original rate of N since it still has the ability to reach its full yield potential.

Sidedress N may be applied any time after planting; however, keep in mind that the corn plant does not require large amounts of N until after the 6th - 8th leaf collar stage (V6-V8). We often sidedress N before this time because corn may become too tall for some application equipment and the concern of an extended wet period at V6. It may be several weeks before a response is seen from sidedress with early applications since the roots have not had time for extensive growth. This would be more of a concern during cool and wet or very dry soil conditions. A response may be seen sooner from anhydrous ammonia than 28% solutions during dry weather.

Anhydrous ammonia and urea-ammonium nitrate (UAN) solutions knifed-in are the preferred N sources. Broadcast urea would be susceptible to volatilization losses unless timely rains occur (a urease inhibitor would allow a greater window for a timely rain). Ammonium nitrate and ammonium sulfate would have minimum volatilization loss as a broadcast but ammonium nitrate is unavailable in many parts of the state and cost would limit the use of ammonium sulfate. If unable to inject, a dribble band application of UAN would be preferred over broadcast to diminish volatilization losses and burn potential.
Research in Indiana, Illinois Iowa, and Ohio has shown that producers can knife anhydrous ammonia or UAN solutions every other row (60 vs. 30 inch spacing) with no reduction in yield. Extra attention should be given that no knives plug under this approach, especially during wet conditions. A plugged knife in 60 inch spacing gives 4 rows with no N and will seriously reduce yields.

F) Insect Update - Eisley and Hammond CORN Questions

Alfalfa - Checks in first cutting alfalfa at the Western Branch last week found all stages (adults, 1st, 2nd & 3rd instar larvae and pupae) of alfalfa weevil present. Weevil damage was showing on the upper parts of the alfalfa but because of the late surge in population and the growth of the alfalfa, little damage was occurring. The field will be cut this coming week and the new growth will need to be checked because of the large number of small and medium larva present. If a field is cut this week that had large numbers of AW larvae present, then the alfalfa should be checked to make sure the larva are not damaging the new regrowth.

Potato leafhopper (PLH) adults were also found in this first cutting of alfalfa. PLH adults have been in the state for the past several weeks having migrated from the south but we do not worry about PLH damage to first cutting because the insect shows up too late in first cutting to do any damage. However, we need to begin checking second cutting alfalfa for PLH as soon as new regrowth can be swept. Checks should be made with a standard sweep net by taking several 10 sweep samples randomly across the field and counting the number of PLH adults and nymphs found in each 10 sweep sample. Treatment for PLH is based on the number of adults and nymphs found when sweeping versus the height of the alfalfa. For example, treatment is warranted if the number of adults and nymphs in 10 sweeps equals or exceeds the height of the alfalfa in inches (8 adults & nymphs in 10 sweeps in 6 inch alfalfa would justify treatment for PLH). The following table gives numbers for treatment. Additional information about PLH can be found in a fact sheet on the web at: http://ohioline.osu.edu/ent-fact/0033.html

Action thresholds for control of potato leafhopper.

Chemicals labeled on alfalfa for PLH control:

Corn - A slight amount of black cutworm damage was observed in 6 leaf stage corn at the Western Branch last week. The worms were 1.5 inches in length and would have been very difficult to kill if the population would have been economic.

Common stalk borer was also observed in this field. The worms were about 3/8 inch in length and feeding was in the top of the plant.

European corn borer (ECB) moths have been flying for the past week in Ohio. So far moths counts are light but should pick up this coming week. Early planted corn will need to be watched in the next couple of weeks for ECB feeding.

Common armyworm (CAW) feeding and worms were also found this past week in central Ohio. The worms were about ¾ to 1 inch in length and feeding along the edges of the leaves. Corn that was planted no-till in a field with a lot of grasses should be checked beginning this week for armyworm.

Soybean - Bean leaf beetles have been active in some early-planted fields across the state causing light to moderate injury. Most fields should not need treatment at this time, especially if the beetle population is going down. If feeding is heavy and continuing, treatment might be warranted. Furthermore, bean leaf beetle injury at this time is an indication that a population exists in the field, and that the field should be watched carefully later in the summer for a larger than normal first and second-generation beetles.

Slugs on Corn and Soybean - Numerous corn and soybean fields have significant slug injury that is requiring a molluscicide treatment, with some replanting being necessary. If replanting because of slugs, remember that the slugs will be larger and could be a problem again. Thus, replanting might require a treatment. Prior to treating a soybean field showing feeding injury to the leaves, growers should make sure that injury is from slugs and not from bean leaf beetles, and that any stand reduction is not from seedcorn maggot or other causes. The presence of slugs will be obvious from slime that will be present on the plants and feeding that makes the leaves ragged in appearance.

G) PONCHO Labeled on Corn - Eisley and Hammond CORN Questions

Bayer CropScience has informed us that PONCHO (clothianidin) has been labeled on corn. PONCHO is a seed treatment that is commercially applied to corn seed at either 0.25 mg/seed or 1.25 mg/seed.

PONCHO 250 (0.25 milligrams of active ingredient per kernel) is labeled for control of chinch bugs, black cutworm, flea beetle, wireworm, seedcorn maggot and white grub.

PONCHO 1250 (1.25 milligrams of active ingredient per kernel) is labeled for all of the above and also labeled for control of corn rootworm.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the 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.

Editor: Clark Hutson        Web Editor: Nathan Watermeier

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination 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 |