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For Weeks of September 28 - October 4, 1998
C.O.R.N. 98-28
In This Issue:
A) Time to Control Perennial Weeds in Wheat Stubble
B) August Alfalfa Seedlings Attacked!
The time has arrived to apply herbicides in wheat stubble. For control of many perennial broadleaf weeds, except Canada thistle, apply Roundup Ultra at 1.0 to 2.0 quarts per acre or Touchdown at 1.6 to 3.2 pints per acre plus 2,4-D ester at 1.0 pint per acre. Apply Roundup Ultra at 1.5 quarts per acre or Touchdown at 2.4 pints per acre to control Canada thistle and perennial grasses. The addition of 2,4-D to Roundup or Touchdown can reduce the control of Canada thistle and perennial grasses. There is no need for additional surfactants with these herbicides, however it is HIGHLY RECOMMENDED TO ADD AMS AT 17 POUNDS PER HUNDRED GALLONS WITH ROUNDUP ULTRA AND TOUCHDOWN.
The size of the weeds and weather conditions at application can have a profound effect on weed control. All perennial weeds should be greater than 1 foot tall and have good green color for optimum control. Many places in Ohio are extremely dry at this time and these areas should wait for a rain, because control of water-stressed weeds will be reduced. However, warm-season weeds like milkweeds, hemp dogbane, and johnsongrass need to be sprayed at least 2 days prior to frost. Be sure to spray in warm weather so the weeds are actively growing. Waiting for another two weeks (as long as a hard freeze does not occur) may maximize control of Canada thistle and quackgrass. Too achieve good control of winter annual weeds such as purple deadnettle, field pennycress, and shephard's-purse wait until the end of October, as long as we don't enter a sustained period of temperatures below 45 degrees.
August seeded alfalfa that survived the torrential rainfalls of late August have seemingly disappeared over the past two weeks in NW Ohio. The culprit is an occasional insect pest which has boomed in population and has caused serious damage to the alfalfa stands. The insect is either the garden webworm or the alfalfa webworm, the caterpillar stage of a moth. Webworms feed on a wide range of host plants, including alfalfa, clover, corn, beans, and some major weed species.
Both webworms are native to North America and occur in many areas where appropriate host plants are located. In alfalfa during the growing season, webworms feed on foliage of mature plants. They spin webs around the foliage they are eating and pull additional foliage into their webs as they need it. Most of the time, this damage is not serious. Occasionally, high populations develop resulting in heavy defoliation that looks like alfalfa weevil damage and large amounts of webbing and fecal material that contaminates the hay. The most serious type of damage caused by the webworms and the type that is currently causing concern, occurs in the fall of the year. The fall generation of webworms can infest newly seeded alfalfa, where they act like cutworms and seriously damage the stand just prior to winter dormancy.
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Alfalfa Webworm Damage Seedlings One |
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Alfalfa Webworm Damage Seedlings Two |
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Alfalfa Webworm Damage Seedlings Three |
In NW Ohio, several fields have been identified as being infested with the webworms, and damage varied from slight to severe. Unfortunately, the infestations were discovered too late to take corrective actions. While searching for specimens,
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Alfalfa Webworm Larvae Pulling Plants into Soil |
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Alfalfa Webworm Larva Exposed in Burrow |
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Alfalfa Webworm Web Tube |
most caterpillars found were full-grown (about an inch in length),
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Alfalfa Webworm Larvae by Ruler |
several were found to be preparing to pupate and some were already pupated.
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Alfalfa Webworm Pupa in Ground |
The webworm passes the winter as a pupa or larva within a silk-lined cell in the soil. Thus, it appears the webworms have finished their feeding period and are preparing to overwinter. However, since we are not overly familiar with this pest, we need to continue to monitor fields to be certain that it is the end of their activity for this year. Additionally, if the same type of webworm activity is occurring in the southern portion of the state, there is a greater possibility of an additional generation in the southern region. If continued activity is detected, materials registered for rescue treatment use in alfalfa for webworms include, Baythroid 2, Lannate and Warrior.
Seriously webworm damaged areas of new stands will likely not survive the winter. Cut plants may put out new foliage but this will deplete any reserves in the roots. With the increasing chances of frost, the new foliage will not have time to replenish the reserves in the roots. It is also too late to attempt to reseed damaged areas this season.
Plans should be made to reseed bare spots next spring (NOTE: newly established alfalfa stands can be inter-seeded or re- seeded, no autotoxicity is present within the first 12 months). Damaged areas of fields should be scouted in mid- to late October for winter annual weed invasions. These weeds could further stress the stand and interfere with inter-seeding attempts next spring. These weeds are easier to control this fall rather than next spring. However, herbicides with residual soil activity (Pursuit or Kerb) should not be applied if inter-seeding or re- seeding are planned for next spring. Check herbicide labels for plant back restrictions. The best option in this situation for controlling winter annual broadleaf weeds this fall is probably 2,4-DB. If the weeds are missed this fall, Gramoxone would be another option as a dormant application in late winter.
The damage from the webworms may repeat itself next spring. Because there is a large population of webworms going into the overwintering period, alfalfa producers should also be watching for possible problems with webworms in the first crop growth next spring.
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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:Anne Dorrance (Plant Pathology), Jeff Stachler (Hort. &Crop
Science); DISTRICT SPECIALISTS: C. Young(Entomology) EXTENSION AGENTS: Roger Bender
(Shelby), Ray Wells (Ross), Clark Hutson (Seneca), Steve Prochaska (Crawford), Larry Lotz
(Fayette) and Dave Jones (Allen.
Editor: Steve Prochaska Web Editor: David Etzkorn
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
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