CORN
Crop Observation and Recommendation Network

May 14 to May 20, 2001
C.O.R.N. 2001-13

In This Issue:

A) Check Fields for Weeds
B) Winter Wheat Heading; Dry Conditions Restrict Disease
C) Cutworms Feeding on Ohio Corn
D) Alfalfa Weevil and Re-growth Following Harvest
E) Slug Eggs Are Hatching and Bean Leaf Beetles Active
F) Diagnosing Emergence Problems in Corn
G) Drift Can and Should Be Reduced to Minimum

A) Check Fields for Weeds (J.Stachler) CORN Questions

Parts of the state, especially central and south central Ohio, have not received enough rainfall to properly incorporate and activate preemergence herbicides. If you have not received at least one inch of rain within a 3 to 5 day period, then the preemergence herbicides may not effectively control weeds. These fields need to be scouted for the emergence of weeds. Fields receiving less than 1.5 inches of rain should be checked also to make sure the herbicides are working. If corn or soybeans have been planted within the last 5 to 10 days, then a rotary hoeing can be effective in controlling the early emerging weeds and allow for more time before a rain is received. Look at previous newsletter articles to explain this further. If rotary hoeing is not an option, as discussed before an early postemergence spray may be necessary and effective. The best advice right now is to scout, scout, and scout.

B) Winter Wheat Heading; Dry Conditions Restrict Disease (P. Lipps) CORN Questions

Wheat in southern Ohio (south of I-70) is heading with most County Agents reporting 90% or more fields in head. Counties in the central part of the state have a few early fields beginning to produce heads (Feekes growth stage 10.1) but most fields are in mid to late boot stage (growth stage 10). The most advanced wheat in far northwest Ohio are in boot stage, but most have flag leaves fully emerged (growth stage 9).

Much of the state will be in various stages of head emergence over the next 7 days, but extreme northern counties may see heading next week. Predicted cooler temperatures this week (highs in mid 60- 70s) will slow the heading progress and improve pollination of the crop.

When looking at your wheat fields you may notice that the fields do not look as even as the fields have been over the last two or three years. You will see short and tall plants and notice that the plants are not all in the same growth stage. The variation in plant development is probably due to winter injury, mostly soil freezing and thawing problems that occurred in late February and March. As reported in earlier articles, we have seen a lot of heaving injury throughout the state. Affected plants have struggled to develop new tillers this spring; thus the age of tillers on a single plant may be quite different. Plants having tillers of different ages will cause them to have an uneven appearance, giving a 'ratty' look to the field. We can not predict the effect this will have on yield, but we do know that secondary tillers produce fewer seed than the main tillers. It will take more of these secondary tillers to make the same amount of seed (yield) as a main tillers. Good weather during pollination and grain fill will be essential for good yields.

Continued dry conditions during the past week throughout the state have limited the development of most diseases. Powdery mildew is still spreading in fields of susceptible varieties in north central and northeast sections of the state. Fields with powdery mildew on the lower leaves should be checked again at head emergence to see if the disease has spread upwards on the plant. Mildew will be favored by the high humidity in the wheat canopy as plants get taller. Most importantly check fields planted to susceptible varieties. See last weeks article for scouting instructions and fungicide recommendations. Tilt fungicide (4 oz/A) can be applied through flowering. No other diseases are of significance at this time. The dry conditions in southern Ohio will prevent the development of head scab south of I-70. We will be watching the weather as the wheat goes into head over the next week or so to see what predictions we can make for head scab in northern Ohio.

C) Cutworms Feeding on Ohio Corn (B. Eisley) CORN Questions

Cutworm larvae ranging in size from 3rd instar (caterpillar that is 1/2 inch long) to early 6th instar (more than an inch in length) were reported feeding on field corn in the in central and southern Ohio last week. If cutting is above ground, cut plants will likely recover if a timely rescue treatment is applied. In contrast, below ground feeding is generally characterized by wilting plants that have been cut below the growing point, or plants cut off before emergence.

Early detection of cutworm infestations and timely application of rescue treatments are the keys to achieving effective stand protection where preventive treatments have not been applied. Where visible cutworm injury is observed on 3% or more of a stand, application of a timely rescue treatment is warranted, will arrest cutworm feeding, and prevent additional stand losses. If a significant cutworm infestation is detected too late, cutting has occurred below ground and below the growing point, then a rescue treatment may achieve marginal results.

In a 1999 field trial, early detection of 6 to 8% visible stand injury by cutworm on VE to V1 stage corn enabled timely application of Pounce, Lorsban and Warrior treatments which significantly reduced stand loss compared to the untreated check plots.

For more information, visit the following images: Black Cutworm Below Ground Damage on Corn Plant
(http://www.ag.ohio-state.edu/~ohioline/icm-fact/images/8.html)
Black Cutworm Larva in Base of Corn Plant
(http://www.ag.ohio-state.edu/~ohioline/icm-fact/images/9.html)
Black Cutworm above Ground Damage on Corn Plant
(http://www.ag.ohio-state.edu/~ohioline/icm-fact/images/10.html).

Cutworms can occasionally infest soybean fields and cause stand loss. An instance of a dark-sided cutworm infestation in soybeans was reported in 2000 in Madison County. If you find problems with cutworms in soybeans, would you let your county agent know or call me at 614-292-3851 or email at: eisley.1@osu.edu.

D) Alfalfa Weevil and Re-growth Following Harvest ( Eisley) CORN Questions

Alfalfa fields that had large numbers of alfalfa weevil larvae and were cut instead of being treated, should have the re-growth check for alfalfa weevil feeding. In cases where re-growth appears to be retarded 7 to 10 days after harvest due to feeding activity of weevil adults or larvae, application of a stubble spray may be warranted. Although a harvest of alfalfa will generally decimate the weevil population, surviving larvae will continue feeding on re-growth and show the second cutting. For more information, visit the Fact Sheet on Alfalfa Weevil on the Web at:
http://ohioline.ag.ohio-state.edu/ent-fact/0032.html.

E) Slug Eggs Are Hatching and Bean Leaf Beetles Active (Hammond) CORN Questions

Because slug eggs have hatched throughout the state, growers, especially those with past problems, should begin monitoring their fields for the presence of slugs and injury. In fields with a slug population, growers might see an increase in defoliation over the next few weeks.

If the crop has emerged, observations on the level of feeding need to be taken. If feeding is moderate to heavy on new leaf tissue, and plants begin to appear stunted, treatment is warranted. Currently, treatment thresholds are not available. A major consideration will be the growing conditions over the next few weeks. If good crop growing weather continues and corn and soybeans grow well, the likelihood of crop damage will be lower because the plants will put on sufficient leaf tissue to compensate for any slug injury. If the weather turns cold and wet and limits plant growth, slugs could gain the advantage. Thus, growers should also monitor weather conditions. If treatment is warranted, the primary molluscicide available is Deadline MPs, which should be broadcast at 10 lbs per acre.

Although no reports of soybean stand problems have been received at this time, growers should begin to monitor plant emergence. If replanting becomes necessary due to slug injury, treatment prior to replanting will become a consideration.

Growers should also continue monitoring their soybean fields for the possible presence of high populations of bean leaf beetle. Reports have been received of fields having light to moderate size populations. Although these early beetles usually do not reach economic levels in the spring, we did see many fields last year with extremely high populations. Growers should visit fields to make sure that the bean leaf beetle are not reaching high levels. In fields where defoliation is over 50% and plants are not growing well, insecticide treatment would be recommended. Growers should remember that bean leaf beetles tend to be most numerous in early planted fields, and thus, these fields should be scouted first.

F) Diagnosing Emergence Problems in Corn (Thomison) CORN Questions

Diagnosing emergence problems early helps to identify solutions and develop replanting plans. Corn should begin emerging after about 100 to 125 GDDs have accumulated following planting. This can be anywhere from one to three weeks after planting depending on the temperature. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.

1. No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.
   
2. Coleoptile (shoot) unfurled underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, or may be due to extended cool wet conditions alone.
   
3. Seed with poorly developed radicle (root) or coleoptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor.
   
4. Seed swelled but not sprouted. Often poor seed-to-soil contact or shallow planting - seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.
   
5. Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.
   
6. Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm. Note the patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information will be valuable in the future.

G) Drift Can and Should Be Reduced to Minimum (Erdal Ozkan) CORN Questions

This time of the year is the time when Ohio Department of Agriculture (ODA) receives more complaints about spray drift than other times of the year because this is the season for spraying. About 75% of the pesticide non-compliance calls ODA receives annually are related to spray drift. The situation may get even worse as the acreage of genetically modified crops increases.

The bad news is: Spray drift occurs wherever liquid sprays are applied. The good news is: Although complete elimination of spray drift is impossible, problems can be reduced to a minimum if chemicals are applied with the proper equipment under favorable weather conditions.

Regardless of where it occurs and what causes it, drift is undesirable because:

• A. It results in inefficient use of application equipment and applicator time.
  
• B. It may result in under?application of chemicals and ineffective pest control, which leads to additional applications, reduced yield and higher production costs.
  
• C. It may result in over?application if the applicator knowingly over?applies chemicals to compensate for drift losses and to ensure the desired level of control.
  
• D. Losses and/or costly litigation may result if sensitive crops in adjacent fields are damaged.
  
• E. Unintentional contamination of foodstuffs from unacceptable pesticide residues can result in mandatory destruction of the crop.
  
• F. It may contribute to pollution of air and water resources.
  
• G. It may affect the health and safety of susceptible human and livestock populations.

Drift is influenced by many factors that usually may be grouped into one of the following four categories:

1. Spray characteristics (too many small drift-prone droplets discharged from nozzle, small droplet size, volatility of the chemical applied, etc.)
   
2. Equipment and application techniques used.
   
3. Weather (high wind, low relative humidity and high ambient temperature).
   
4. Operator care and skill.

Operator's knowledge of what causes drift is perhaps the key element in reducing drift potential. Conscientious and experienced operators rarely get into serious trouble with drift damage because they understand drift and take steps to avoid it. Here are some management strategies to reduce spray drift from boom sprayers:

• I. Use nozzles that produce large droplets whenever possible, if biological effectiveness can be maintained (obtain copies OSU Extension Fact Sheets AEX-523 and AEX-524 to learn more about the new nozzles and their effectiveness in reducing drift).
  
• II. Keep the boom close to the spray target.
  
• III. Use greater spray volume and use nozzles with larger orifices.
  
• IV. Use lower system pressure and check pressure gauge accuracy.
  
• V. Use drift retardants if droplet size cannot be controlled with nozzle selection.
  
• VI. Follow label recommendations to avoid drift with highly volatile pesticides.
  
• VII. Avoid spraying on extremely hot, dry days, especially if sensitive vegetation is nearby.
  
• VIII. Do not spray when conditions are favorable for an atmospheric inversion.
  
• IX. Although the distance droplets will drift is a function of many other factors such as droplet size, relative humidity, temperature and boom height, it is best not to spray when wind speeds are greater than 5 miles per hour.
  
• X. Avoid spraying near sensitive areas located downwind. Leave a buffer strip 50 to 100 feet wide and spray this strip later when the wind shifts.
  
• XI. Be sure to keep good records (wind speed and direction, temperature, relative humidity, etc. and evaluate spray results.
  
• XII. New label requirements may use a drift model to determine the required buffer width. Travel slower (and lower boom height) and use nozzles to produce large droplets near sensitive areas. This will reduce the required buffer zone width, then, as distance from the sensitive area increases, nozzles can be changed to produce smaller droplets, if desired, and boom height raised so travel speed can be increased.
  
• XIII. Select the time when drift is likely to be low for spraying the parts of the field near sensitive areas.
  
• XIV. In the future, label requirements may specify nozzles that produce a certain droplet size spectrum, such as fine, medium, coarse, very coarse, etc. Carefully check the label to determine the optimum droplet size and proper nozzle size for a spray application.
  

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: Steve Prochaska        Web Editor: Tom Rosati

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

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