VegNet News

VegNet Vol. 8, No. 4, March 21, 2001

Predictions for Corn Flea Beetle and Stewart's Wilt on Sweet Corn:

C. Welty

Sweet corn growers can expect fewer problems with Stewart's wilt in Ohio this summer compared to the past few years. Stewart's wilt is a bacterial disease that causes reduced yields, and when severe it can stunt or kill an entire planting. The disease is transmitted by the corn flea beetle. Yield is affected the most if plants are infected at the 3- to 5-leaf stage.

A traditional rule for predicting severity of Stewart's wilt is to calculate a 'corn flea beetle index' by adding the average temperatures (degrees Fahrenheit) for December, January, and February. If the index is below 90, then wilt should be negligible. If the index is 90 to 95, then wilt should be light to moderate. If the index is 95 to 100, then wilt should be moderate to severe. If the index is over 100, then wilt should be severe. Flea beetle index values for 11 Ohio locations for the current winter and the previous 5 winters are listed in Table 1. The number of Ohio sites in each of four categories of predicted disease severity are shown in Table 2 for this year and recent years as well as the long term average. Averaged over the 11 Ohio locations listed, December 2000 was 9 degrees lower than normal, Januray 2001 was 1 degree higher than normal, and February 2001 was 4 degrees higher than normal, making this year's index values about 4 points lower than normal.

Table 1. Corn flea beetle index values for 11 Ohio locations in years 1996 to 2001, plus the long-term average. ___________________________________________________________ Site Flea beetle index value __________________________________________________ Long term average 1996 1997 1998 1999 2000 2001 ___________________________________________________________ Piketon 100 95 108 116 111 107 94 Jackson 96 93 107 116 110 105 93 Ripley 96 90 105 111 106 101 87 Columbus 92 84 98 110 102 96 88 Oxford 92 85 97 110 105 101 86 S.Charleston 90 81 96 111 101 95 82 Delaware 87 80 95 106 105 95 83 Kingsville 85 80 93 105 98 96 82 Wooster 84 80 96 106 98 96 83 Hoytville 81 75 91 105 93 90 76 Fremont 80 71 86 98 94 87 76 .. .. .. .. ... ... ... ... ... ... ... ... ... ... .. .. .. Table 2. Summary of predictions for severity of Stewart's wilt based on corn flea beetle index values for 11 Ohio locations for years 1996 to 2001, plus the long-term average. Stewart's wilt prediction Number of Ohio sites _____________________________________________ Long term average 1996 1997 1998 1999 2000 2001 Severe (>100) 1 0 3 10 7 4 0 Moderate to severe (95-100) 2 1 5 1 2 5 0 Light to moderate (90-94) 3 2 2 0 2 1 2 Negligible (<90) 6 8 1 0 0 1 9
Cultural control: The most important management option for Stewart's wilt is to use resistant varieties. Some hybrids that are most resistant to Stewart's wilt are Eliminator (yellow su), Sweet Sue (bicolor su), Miracle (yellow se); the se bicolors Ambrosia, Buckeye, Encore, Lancelot, Seneca Nation, and Table Treat; Argent (white se); and Trigger and Zenith (yellow sh2).

Editors Note: For the complete updated listing on variety resistance to Stewart's wilt, go to: http://www.ag.ohio- state.edu/~vegnet/vegipm.htm

Chemical control of corn flea beetle by seed treatment with Gaucho: In 2001, Ohio growers are allowed to buy sweet corn seed treated with Gaucho in Idaho, the state where most of our sweet corn seed originates. Gaucho does not yet have a federal registration for use on sweet corn, but Idaho has been allowed an emergency exemption (called a Section 18 registration) for its use. Ohio is one of several states included as an end-use destination in the Idaho registration. Gaucho-treated seed might not be available for all sweet corn varieties or from all seed companies; growers should contact their seed supplier to find out about availablity. Gaucho-treated seed is about $1 more per pound than untreated seed. Gaucho is an insecticide with the active ingredient imidacloprid, the same ingredient as in Admire and Provado. It has systemic action when applied to seed or to soil in the root zone. Gaucho is made by Gustafson.

Tests done by Dr. Jerald Pataky at the University of Illinois showed that incidence of Stewart's wilt in susceptible varieties was reduced by about 70% by Gaucho. Severity of symptoms was also reduced by Gaucho. The degree of control by Gaucho was roughly equivalent to using a hybrid with one higher level of resistance, among 4 levels: resistant, moderately resistant, moderately susceptible, and susceptible. For example, using Gaucho on a susceptible variety was equivalent to using a moderately susceptible variety without Gaucho.

Gaucho is thus not a product that alone will control corn flea beetle and Stewarts wilt. The primary strategy that should be used is host plant resistance. The secondary strategy is insecticide. Gaucho is the easiest insecticide to use since it is comes already on the seed. The second best insecticide option is Furadan 4F at planting. Other options are Counter or Thimet at planting, or waiting until seedlings emerge when they can be sprayed with Sevin, Pounce, or other non-systemic foliar insecticides.

Online Edition of the 2001 Ohio Vegetable Production Guide - Now Available.

R. Precheur

World Wide Web users can now access this bulletin either through the Home page of the VegNet website, http://www.ag.ohio-state.edu/~vegnet/index.html

from 'bulletins online' in 'The Library' Section at the vegnet website
http://www.ag.ohio-state.edu/~vegnet/library/libr.htm

or through OH State Cooperative Extension's Ohioline http://www.ag.ohio-state.edu/~ohioline/b672/index.html

Be sure to go to the bottom portion of the Table of Contents for a listing of the bulletin's charts and tables including the insecticide efficacy tables for each chapter and the chart on the Basic Guide to Pumpkin Production. Most of the charts and tables are available in PDF file format for downloading. You will need Adobe Acrobat Reader to view them.

As mentioned in earlier issues, hard copies of this bulletin are available through your local extension office or through Janis Cripe, Publications Office at 614-292-1607. The base price is $4.50 to which you must add taxes and postage. Ask for Bulletin # 672-01.

Spring Vegetable Calendar

March 29 Hydroponic Study Group, Toledo Botanical Garden, Toledo, Ohio, 6-9 p.m. Contact: Mary Donnell, OSU Extension Agent, ABE Center, 800-358-4678, or 419-354-6916, donnell.8@osu.edu April 5-7 International Fresh-cut Processor's Association 14th Annual Conference and Exhibition in Phoenix, Arizona International Fresh-cut Produce Association, 1600 Duke St., Ste 440, Alexandria, Virginia 22314-3400, tel 703-299-6282, fax 703-299-6288 April 10. FDA Food Safety Workshop, East Lansing, MI. United Fresh Fruit and Vegetable and FDA. Contact Anita Ragan, 703-836-3410, aragan@uffva.org


Predictions for Corn Flea Beetle and Stewart's Wilt on Sweet Corn: C. Welty
Sweet corn growers can expect fewer problems with Stewart's wilt in Ohio this summer compared to the past few years. Stewart's wilt is a bacterial disease that causes reduced yields, and when severe it can stunt or kill an entire planting. The disease is transmitted by the corn flea beetle. Yield is affected the most if plants are infected at the 3- to 5-leaf stage. A traditional rule for predicting severity of Stewart's wilt is to calculate a 'corn flea beetle index' by adding the average temperatures (degrees Fahrenheit) for December, January, and February. If the index is below 90, then wilt should be negligible. If the index is 90 to 95, then wilt should be light to moderate. If the index is 95 to 100, then wilt should be moderate to severe. If the index is over 100, then wilt should be severe. Flea beetle index values for 11 Ohio locations for the current winter and the previous 5 winters are listed in Table 1. The number of Ohio sites in each of four categories of predicted disease severity are shown in Table 2 for this year and recent years as well as the long term average. Averaged over the 11 Ohio locations listed, December 2000 was 9 degrees lower than normal, Januray 2001 was 1 degree higher than normal, and February 2001 was 4 degrees higher than normal, making this year's index values about 4 points lower than normal. Table 1. Corn flea beetle index values for 11 Ohio locations in years 1996 to 2001, plus the long-term average. ___________________________________________________________ Site Flea beetle index value __________________________________________________ Long term average 1996 1997 1998 1999 2000 2001 ___________________________________________________________ Piketon 100 95 108 116 111 107 94 Jackson 96 93 107 116 110 105 93 Ripley 96 90 105 111 106 101 87 Columbus 92 84 98 110 102 96 88 Oxford 92 85 97 110 105 101 86 S.Charleston 90 81 96 111 101 95 82 Delaware 87 80 95 106 105 95 83 Kingsville 85 80 93 105 98 96 82 Wooster 84 80 96 106 98 96 83 Hoytville 81 75 91 105 93 90 76 Fremont 80 71 86 98 94 87 76 .. .. .. .. ... ... ... ... ... ... ... ... ... ... .. .. .. Table 2. Summary of predictions for severity of Stewart's wilt based on corn flea beetle index values for 11 Ohio locations for years 1996 to 2001, plus the long-term average. Stewart's wilt prediction Number of Ohio sites _____________________________________________ Long term average 1996 1997 1998 1999 2000 2001 Severe (>100) 1 0 3 10 7 4 0 Moderate to severe (95-100) 2 1 5 1 2 5 0 Light to moderate (90-94) 3 2 2 0 2 1 2 Negligible (<90) 6 8 1 0 0 1 9 Cultural control: The most important management option for Stewart's wilt is to use resistant varieties. Some hybrids that are most resistant to Stewart's wilt are Eliminator (yellow su), Sweet Sue (bicolor su), Miracle (yellow se); the se bicolors Ambrosia, Buckeye, Encore, Lancelot, Seneca Nation, and Table Treat; Argent (white se); and Trigger and Zenith (yellow sh2). Editors Note: For the complete updated listing on variety resistance to Stewart's wilt, go to: http://www.ag.ohio- state.edu/~vegnet/vegipm.htm Chemical control of corn flea beetle by seed treatment with Gaucho: In 2001, Ohio growers are allowed to buy sweet corn seed treated with Gaucho in Idaho, the state where most of our sweet corn seed originates. Gaucho does not yet have a federal registration for use on sweet corn, but Idaho has been allowed an emergency exemption (called a Section 18 registration) for its use. Ohio is one of several states included as an end-use destination in the Idaho registration. Gaucho-treated seed might not be available for all sweet corn varieties or from all seed companies; growers should contact their seed supplier to find out about availablity. Gaucho-treated seed is about $1 more per pound than untreated seed. Gaucho is an insecticide with the active ingredient imidacloprid, the same ingredient as in Admire and Provado. It has systemic action when applied to seed or to soil in the root zone. Gaucho is made by Gustafson. Tests done by Dr. Jerald Pataky at the University of Illinois showed that incidence of Stewart's wilt in susceptible varieties was reduced by about 70% by Gaucho. Severity of symptoms was also reduced by Gaucho. The degree of control by Gaucho was roughly equivalent to using a hybrid with one higher level of resistance, among 4 levels: resistant, moderately resistant, moderately susceptible, and susceptible. For example, using Gaucho on a susceptible variety was equivalent to using a moderately susceptible variety without Gaucho. Gaucho is thus not a product that alone will control corn flea beetle and Stewarts wilt. The primary strategy that should be used is host plant resistance. The secondary strategy is insecticide. Gaucho is the easiest insecticide to use since it is comes already on the seed. The second best insecticide option is Furadan 4F at planting. Other options are Counter or Thimet at planting, or waiting until seedlings emerge when they can be sprayed with Sevin, Pounce, or other non-systemic foliar insecticides.

Online Edition of the 2001 Ohio Vegetable Production Guide - Now Available. R. Precheur
World Wide Web users can now access this bulletin either through the Home page of the VegNet website, http://www.ag.ohio-state.edu/~vegnet/index.html from 'bulletins online' in 'The Library' Section at the vegnet website http://www.ag.ohio-state.edu/~vegnet/library/libr.htm or through OH State Cooperative Extension's Ohioline http://www.ag.ohio-state.edu/~ohioline/b672/index.html Be sure to go to the bottom portion of the Table of Contents for a listing of the bulletin's charts and tables including the insecticide efficacy tables for each chapter and the chart on the Basic Guide to Pumpkin Production. Most of the charts and tables are available in PDF file format for downloading. You will need Adobe Acrobat Reader to view them. As mentioned in earlier issues, hard copies of this bulletin are available through your local extension office or through Janis Cripe, Publications Office at 614-292-1607. The base price is $4.50 to which you must add taxes and postage. Ask for Bulletin # 672-01.

Spring Vegetable Calendar
March 29 Hydroponic Study Group, Toledo Botanical Garden, Toledo, Ohio, 6-9 p.m. Contact: Mary Donnell, OSU Extension Agent, ABE Center, 800-358-4678, or 419-354-6916, donnell.8@osu.edu April 5-7 International Fresh-cut Processor's Association 14th Annual Conference and Exhibition in Phoenix, Arizona International Fresh-cut Produce Association, 1600 Duke St., Ste 440, Alexandria, Virginia 22314-3400, tel 703-299-6282, fax 703-299-6288 April 10. FDA Food Safety Workshop, East Lansing, MI. United Fresh Fruit and Vegetable and FDA. Contact Anita Ragan, 703-836-3410, aragan@uffva.org

What's New At The VegNet Web Site

Online Edition of the 2001 Ohio Vegetable Production Guide - Now Available

Sweet Corn Disease Resistance Ratings

The following are summarized lists of Dr. Pataky's work at the Univ. of IL on disease reactions of sweet corn. In these summaries, all experimental and processing varieties have been removed and only named varieties which were rated for common rust or MDM are included. The first list are those named varieties rated for common rust. The second list are only those named varieties rated for Maize Dwarf Mosaic virus (MDM).For a complete report, E-mail: Bob Precheur: precheur.1@osu.edu

Common Rust of Sweet Corn
MDM of Sweet Corn

Do You Know Us?

Find out what we've been up to. The OSU Vegetable Team Report is available in PDF file format for downloading from the VegNet homepage.

Sources of Pheromone Traps Used in Vegetable Pest Management.

Do you need to find traps, lures or suppliers, click on the Vegetable IPM button on the left side of the homepage, then click on the 'Sources' document in the Vegetable IPM section.

IR-4 News

Also in the Vegetable IPM section, you can link to the IR-4 website. Read the results of the 2000 food use workshop, monthly and quaterly newsletters. Find out the latest on pesticide registrations for minor crops. Learn about biopesticides plus much more. Click on the Vegetable IPM button on the VegNet homepage and then click on the IR4 link in the Vegetable IPM section.

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We appreciate very much the financial support for thisseries of vegetable reports which we have received from the board of growers responsible for the Ohio Vegetable and Small Fruit research and Development Program. This is an example of use of Funds from the "Assessment Program".

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