http://www.ag.ohio-state.edu/~corn/

CORN
Crop Observation and Recommendation Network

For June 7 to 13, 1999
C.O.R.N. 99-12

In This Issue:

A) More Comments about Postemergence Herbicide Applications
B) Cutworm Activity on Corn
C) Slugs on Corn and Soybeans
D) Time to Monitor Leafhopper on Alfalfa
E) No Scab, Little Stagonospora Leaf Blotch or Leaf Rust on Wheat
F) Wheat Field Days Planned for Northwest Ohio

A) More Comments about Postemergence Herbicide Applications - Jeff Stachler CORN Questions

Do not put off applying herbicides. As weeds get larger and more drought stressed, they will become more difficult to control. All weeds will be easier to control this week than next week if we stay dry. Waiting for rain seems like a good idea, but we have been too dry too in most of the state already. This has created drought stressed weeds and the hot temperatures will cause the weeds to be more stressed. Annual weeds in corn should not get over 3 inches tall and annual weeds in soybeans should not get over 4-6 inches tall, especially weedy fields. If rain does return soon, be sure to scout fields that have small crops in them now as additional weeds may emerge. For every passing day, the chance for new weed emergence is minimal with a few exceptions, like foxtails and fall panicum, giant ragweed, burcucumber, waterhemp, and eastern black nightshade.

Do maintain high additive loads in herbicide mixtures. All ALS herbicides and Flexstar should have a methylated seed oil (MSO) and a nitrogen source added to the spray mixture. We have seen an increase in weed control when using MSO's, especially under dry or drought conditions. Crop Oil Concentrates (COC) or MSO's should be used with all postemergence grass herbicides in soybeans (examples: Fusion and Select). The MSO and COC can increase crop injury with certain herbicides, but soybeans have a long time to recover from any herbicide injury now, but will not recover from weed competition due to escaped weeds.

Increased crop injury will occur when applying herbicides in hot and humid conditions, but injury and good weed control is better now than later. Spray in the early mornings and late evenings to decrease the injury potential and decrease stress on the weeds. Do not apply Liberty after dusk as poor weed control is likely. Spraying postemergence grass herbicides in the middle of the day during these hot and humid conditions can cause a reduction of weed control.

Do not let weeds get over 8 inches tall in Roundup Ready soybeans with our current dry spell. Velvetleaf over 4-6 inches tall with our current dry conditions may not be controlled with Roundup Ultra. They "harden off" very quickly. Large morningglory and eastern black nightshade will also be more difficult to control with Roundup Ultra during these conditions. We know that the tendency is to wait for large weeds in Roundup Ready soybeans, but this year is different compared to the successful weed control in previous years. Because of our dry conditions, weed competition will cause yield loss faster than when adequate moisture is present.

B) Cutworm Activity on Corn - Hal Willson CORN Questions

In central Ohio, black cutworm activity on corn declined during the past week. Cutworm larvae are in the late instar stages and pupating. Evidence of fresh cutworm injury was clearly evident following the Memorial Day weekend, and then the occurrence of additional injury declined as the week progressed. In a trial at the Western branch comparing 3 granules treatments to 4 broadcast treatments applied as pre-emerge and rescue treatments, stand loss in the untreated check plots peaked at 31% while stand loss in the planting time granule treatments averaged about 2%, stand loss in the pre-emerge treatments averaged 10%, and application of a timely rescue treatment on May 19th at the first leaf stage stopped stand loss at 14%. The timing of the rescue treatment was important to achieve such results. If the rescue treatment had been delayed a week, stand loss in the rescue treatments would have increased to about 24%.

Black cutworm larva in base of corn plant.

C) Slugs on Corn and Soybeans - Hal Willson CORN Questions

Although central Ohio continues to be very dry, some regions of the state have had enough moisture to support slug populations on corn and soybeans. Ron Hammond (OARDC entomologist) reported in late May that gray garden slugs began hatching in late May and activity of dusky slugs is increasing. During the past week, Ron has reported that slugs in some Wayne County fields have reached a point where rescue treatment with a commercial slug bait is warranted.

No-tillage fields with a history of slug activity should be monitored at this time. Late planted fields will presumably be more susceptible to slug problems than fields that have gained a head start in growth and can tolerate defoliation of the lower leafs. If slug activity is heavy enough to defoliate the new foliar growth, bait treatment may be warranted. Where bait treatment is needed to reduce slug activity, the baiting should selectively target areas of a field having a severe problem and the bait should be applied prior to an evening when slugs are active. Given the cost of commercial slug baits, treatment of areas of a field with marginal slug activity may not be cost effective.

Slug damage to no-till corn.

D) Time to Monitor Leafhopper on Alfalfa - Hal Willson CORN Questions

The hot weather appears to be suppressing potato leafhopper activity on alfalfa. However, the hot and dry weather is causing extreme stress to alfalfa stands and such stands may be very susceptible to leafhopper feeding activity. In general, our threshold for treatment of alfalfa is exceeded when the catch of leafhoppers in ten sweeps exceeds the height of alfalfa (i.e. 6 PLH per 10 sweeps is the economic threshold on 6 inch high alfalfa). However, when alfalfa is under extreme stress, the threshold should be reduced by half. In contrast, if weather conditions are favorable to vigorous growth, the threshold may be increased nearly two-fold.

Potato leafhopper damage to alfalfa.

E) No Scab, Little Stagonospora Leaf Blotch or Leaf Rust on Wheat - Pat Lipps CORN Questions

Spotty rains and dry weather further limited development of disease in the wheat crop over the past week. Leaf rust can be seen in a few fields, but at very low severity levels. We have no major reports of scab this year, but you may find an isolated head with an infected floret if you look close. The continued dry weather predicted for this week will keep the crop relatively disease free through the grain filling period. We could use some rain later this week to help grain filling to meet full yield potential.

F) Wheat Field Days Planned for Northwest Ohio - Clark Hutson CORN Questions

The Northwestern Ohio Wheat Field Day will be held on Thursday, June 10, 1999 from 1:00 p.m. to 4:00 p.m. at the Ohio Agricultural Research and Development Center - Northwestern Branch, 4240 Range Line Road, Custar, Ohio. For additional information call Paul Houdashelt or Matt Davis at: 1-419-257-2060.

Another field day is planned for Wednesday, June 16, 1999 at the Unger Farm, 1335 Nevada Road, Bucyrus, Ohio. This Twilight Tour of Modified Relay Intercropping and Ohio Wheat Performance Test Plots will begin at 6:30 p.m. Call the Crawford County Extension office at: 1-419-562-8731 for additional information.

Modified Relay Intercropping

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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: Pat Lipps (Plant Pathology), Anne Dorrance (Plant Pathology), Jeff Stachler (Weed Science), and Hal Willson (Entomology); DISTRICT SPECIALIST: Ed Lentz (Agronomy, Northwest); EXTENSION AGENTS: Dave Jones (Allen), Barry Ward (Champaign), Steve Prochaska (Crawford), Dennis Baker (Darke), Larry Lotz (Fayette), Gary Wilson (Hancock), Howard Siegrist (Licking), Ray Wells (Ross), Clark Hutson (Seneca) and Roger Bender (Shelby)

Editor: Clark Hutson Web Editor: Clark Hutson

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.

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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.

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