Vegetable Press
Vol. 00 No. 02 February 18, 2000
Vegetable Specialist
The 10th annual Greenhouse Tomato Short Course will be March 16 & 17 (Thursday & Friday) in Jackson, Mississippi.
The complete Agenda is included in this issue of the Vegetable Press Newsletter. To register in advance, send in the Registration form with your check as indicated.
For more information, call (601) 892-3731 or your local Mississippi County Ag Agent. Or, take a look at the new Greenhouse Tomato Short Course Web Site at http://www.msstate.edu/dept /cmrec/GHSC.htm .
Dr.
David M. Ingram Extension Plant Pathologist
Central Mississippi Research & Extension
Center
Tomato spotted wilt virus (TSWV) has recently become more prevalent in greenhouse tomato production in Mississippi. Tomato spotted wilt was first described in 1915 in South Australia and was later found to be caused by a virus. TSWV is closely related to another virus called Impatiens Necrotic Spot Virus (INSV). Tomato plants can be infected with one or both of these viruses. TSWV is a very destructive disease resulting in a variety of symptoms including stunting, yellowing, wilting, premature death of plants, and fruit with uneven ripening and yellow blotchy areas. The disease has occurred more frequently in the last few years. In 2000, TSWV has been observed in several greenhouses in Mississippi. The virus affects many crop and ornamental plants as well as several weed species growing near greenhouses.
Symptoms of TSWV vary depending upon when infection occurs. Young leaves usually will take on a bronze appearance, quickly followed by small, dark-brown spots on the upper surface of the leaves. Plant growth is immediately stunted, and frequently, plants will show wilting symptoms with the terminal or growing points drooping down. After a couple of days, affected areas may die, and leaves and growing points will dry up. Occasionally, plants will show yellowing in the tips of the growing points.
Plants infected early in the season may not produce fruit. Tomato fruit produced on virus-infected plants will usually have spots that take on a target appearance, especially on ripening fruit. As the fruit ripens, rings become obvious and will often be red and white or red and yellow. Many times the fruit shape is deformed. Infected fruit is not marketable.
TSWV causes more damage on crops, ornamentals, and weeds than any other virus. The disease can affect more than 160 species of plants, including tomato, pepper, celery, eggplant, and lettuce. The virus is carried on numerous weeds and ornamentals plants. Spread of the virus is accomplished through insects called thrips. Thrips are tiny insects that feed on the leaves of tomatoes and suck the juices from them. The thrips acquire the virus in the immature stage of life. Only fifteen minutes of feeding on an infected plant, and the thrips can acquire the virus. Once the thrips becomes an adult and feeds on a healthy tomato plant, the virus is transmitted into the healthy plant and the disease process is started. Symptoms begin to show up within 4-5 days after the virus has been introduced into a tomato plant.
Nine species of thrips are known to transmit the virus, of which at least three species are known to occur in the southeastern United States. The virus may remain within the thrips for its entire life span.
Control of this disease is difficult. When TSWV is diagnosed in the greenhouse, infected plants should be removed promptly and disposed of far away from the greenhouse. Initially, it would seem that insecticides to control thrips would help prevent the transmission of TSWV. However, since the feeding time for acquiring the virus is so short, pesticides may not act quickly enough to prevent spread of the disease before the virus is moved to healthy plants. However, several insecticides are effective in controlling thrips. The use of reflective mulches and floor coverings, such as white plastic, may help to deter thrips from feeding on tomatoes in the greenhouse, but the effectiveness of this treatment has not been determined. Install thrips barrier netting over any intake vents in the greenhouse. Make sure that the greenhouse is well sealed to prevent thrips from entering. Keep tomato transplants separate from other plants that may harbor the virus. Control weeds both inside and outside adjacent to the greenhouse. Many weed species carry the virus, and thrips feeding on the weeds can bring the virus inside the greenhouse. If you suspect a TSWV problem in your greenhouse tomato operation, contact your county extension office or plant pathology specialist.
Dr.
J. Pat Harris
Extension Entomologist
Whiteflies continue to be a common and persistent problem of greenhouse tomatoes. We generally have the regular greenhouse whitefly in our Mississippi greenhouse tomatoes and should not confuse it with the troublesome strain of sweetpotato whitefly presently occurring on vegetables in California. Some refer to sweetpotato whitefly as silverleaf whitefly, but actually they are two differentstrains. We found a strain of sweetpotato whitefly in a couple of our greenhouse tomato operations. This whitefly strain is much more difficult to control than the regular greenhouse whitefly. Whiteflies are related to aphids (plant lice) and are not true flies.
Adults are about 1/16 inch long, white in color and have four powdery wings. Feeding and egg laying generally occur on the underside of leaves. Adult females lay 150 or more minute eggs on the underside of the leaves. Under greenhouse conditions, eggs hatch in about ten days into tiny, white, oval "crawlers". These move about on the underside of leaves for 1 to 2 days searching for a suitable feeding site. On finding a site, the crawlers lose their legs and stop all movement for the remainder of the nymph's development. Nymphs go through three instars and a pupa stage before reaching adulthood. Full development generally takes from 25 to 30 days in greenhouses. Adults may live up to 30 days. Under greenhouse conditions generations overlap and all stages of the insect may be found on infested plants at any time.
Adult and immature (nymph) stages suck fluids from plant foliage with their piercing-sucking mouthparts. Further injury may result from the sticky honeydew secreted by whiteflies, which adheres to foliage and fruits. This can result in a black sooty fungus (mold) growing on the honeydew that can interfere with leaf respiration.
Whiteflies can reduce yields of greenhouse grown tomatoes. To prevent yield loss, these insects must be controlled or kept to a low level during the growth period. Several insecticides are recommended for whitefly control on greenhouse grown tomatoes. These include dichlorvos (DDVP, Vapona) fog or mist; Thiodan WP, EC; malathion WP, EC; and naled (Dibrom EC, fog). Generally it is better to spray when temperature is 70o to 80o F. Spray applications every second day may be needed for 21 days in order to break their life cycle.
Alternate insecticides if necessary.
A product called M-Pede Insecticide (contains potassium salts of fatty acids) produced by Mycogen Corporation is cleared for use on several greenhouse vegetables including tomatoes. Use of it will increase control of whiteflies. Use 1 part M-Pede per 100 parts of spray solution containing the companion pesticide. If small volumes of water are used, apply 1 ounce M-Pede per gallon of water. Overuse of M-Pede may cause phytotoxicity, especially when temperature is above 90o F.
Two of our major concerns in controlling whiteflies have been coverage and timing of our insecticide applications. Pyrellin EC (pyrethrin + Rotenone + cube resin) and Pyronone (pyrethrin + PB) may also be used alone or tank mixed with a companion insecticide. A product called Azatin EC (biological insecticide) may also be used on greenhouse tomatoes. This product produced by AgriDyne controls targeted immature (nymphs) whiteflies after they ingest or come in contact with it, by interfering with the insect's ability to molt. It is effective on all immature stages. This product can enhance your whitefly control if used properly. Use Azatin EC at least once per week when whiteflies appear, with an adulticide, and get complete coverage underneath and atop leaf surface.
Keep in mind whitefly eggs and pupae are generally not controlled with insecticides and only Azatin EC is effective on immatures. Therefore, a grower must carry on a good IPM control program. If not, he or she will be over-run with whiteflies. Correct timing and thorough coverage of insecticide is a must if whiteflies are to be kept under control in greenhouses. Read and observe all label usage and precaution statements.
SHORT COURSE
Mississippi Music Hall of Fame
Mississippi Agriculture & Forestry Museum
Thursday, March 16
(Fee includes Short Course, Coffee, Refreshments, Lunch both days, Dinner both days, admission to the MS Ag Museum and grounds, and various publications; $75 in advance / $90 at the door; this is the fee per person for 1 day or both days.)
9:00 Start the Session
Moderator: Dr. Richard G. Snyder, Vegetable Specialist, MSU.
9:15 Welcome from the Mississippi State University Extension Service.
Mr. Butch Withers, Head, Central Mississippi Research & Extension Center
9:30 Overview of Raising Greenhouse Tomatoes.
Dr. Richard G. Snyder, Vegetable Specialist, Mississippi State University.
10:15 Grower's Perspective.
Michael Pierce, Conroe, TX
11:00 A Budget for Greenhouse Tomatoes
Dr. Ken Hood, Ag Economist, Mississippi Food & Fiber Center.
11:30 Getting Organized In The Greenhouse
Mike Morton, President, Hydro-Gardens, Inc., Colorado Springs, Colorado.
12:30 LUNCH - Mississippi Ag Museum Café (a short walk over the bridge to the east)
2:00 Exhibitor Show & Tell.
Exhibitors Present Their Products.
2:30 Tomato Types and Their Fertigation Needs
Howard Wener, Grower Agrotechnical Support, Hazera Seed Company
3:30 BREAK (coffee, soda, cookies)
Visit Exhibitors!
Dr. Richard G. Snyder, Vegetable Specialist, Mississippi State University.
4:30 Social Hour / Tourist Activities
Come back for Dinner and Entertainment
6:30 Entertainment
Friday, March 17
8:30 COFFEE and registration
Moderator: Dr. Richard G. Snyder, Vegetable Specialist, MSU.
8:55 Welcome To Day #2
9:00 Stuff Your Greenhouse Needs
Mr. Mike Morton, President, Hydro-Gardens, Inc., Colorado Springs, CO.
9:45 IPM - Insect Management in Greenhouse Tomatoes.
Dr. Pat Harris, Extension Entomologist, Mississippi State University.
10:30 Disease Management for Greenhouse Tomato Growers.
Dr. David Ingram, Extension Plant Pathologist, Mississippi State University.
11:15 Israeli Greenhouse Growing Techniques
Howard Wener, Grower Agrotechnical Support, Hazera Seed Company
12:30 LUNCH - Mississippi Ag Museum Café (a short walk over the bridge to the east)
2:00 Panel - General Discussion; Questions and Answers.
Howard Wener, Ken Hood, Mike Morton, David Ingram, Pat Harris, Michael Pierce, and Rick Snyder.
3:00 Optional Tour A (you drive)
Courtesy of Wayne & Debbie Smith, Growers west of Brookhaven, MS.
Highway 55 South to first Brookhaven exit. Take a right and keep going to end. Take right on 550 West. Take right at sign _ mile down on Noah Trail Road. Greenhouse is on left. Coordinate with Wayne Smith after the Short Course.
Optional Tour B (you drive)
Truck Crops Experiment Station Greenhouses, Crystal Springs, MS.
Highway 55 South; 2nd Crystal Springs exit - number 68; left from exit; right on Highway 51 South for 1_ miles; left at Truck Crops sign; proceed to plastic greenhouses.
5:30 Crawfish Boil - Cajun Style - at the Truck Crops Experiment Station, Crystal Springs (directions immediately above).
March 16 & 17
Truck Crops Research & Extension Center
Crystal Springs, MS
Central Mississippi Research & Extension Center
Raymond, MS
Mississippi State University Extension
Mississippi State University
Mississippi Agriculture & Forestry Museum
Held at
Mississippi Agriculture & Forestry Museum
Country Music Hall of Fame Building
1150 Lakeland Drive
Jackson, MS
Greenhouse Tomato Short Course
Registration
1)Name:
Business Name:
Mailing Address:
Town: State: Zip:
County (if from Mississippi): Phone Number: Email:
2)Name:
Business Name:
Mailing Address:
Town: State: Zip:
County (if from Mississippi): Phone Number: Email:
{Please photocopy registration sheet for more than 2 people from your business.}
Please return this registration sheet by March 10, 2000 to the following address:
Greenhouse Tomato Short Course
c/o Dr. Richard G. Snyder
Truck Crops Research & Extension Center
P.O. Box 231
Crystal Springs, MS 39059
TOTAL NUMBER ATTENDING:
TOTAL AMOUNT ENCLOSED ($75/PERSON IN ADVANCE):
WHAT HOTEL WILL YOU BE STAYING IN?:
(Please make check out to "Greenhouse Short Course".)
Dr. Rick Snyder, Vegetable Specialist
Vegetable Specialist
Truck Crops Research & Extension Center
Mississippi State University
P.O. Box 231
Crystal Springs, MS 39059
PHONE: _ (601) 892-3731
Fax: (601) 892-2056
Internet: RickS@ext.msstate.edu
Web
Pages
Central
Mississippi Research Extension Center
http://www.msstate.edu/dept/cmrec/
Greenhouse
Tomato FAQ
http://ext.msstate.edu/anr/plantsoil/vegfruit/tomato/ghtomato/faq.html/
Vegetable
Resource Page
http://www2.msstate.edu/~ricks
Greenhouse Tomato Short Course
http://www.msstate.edu/dept/cmrec/GHSC.htm
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Last Modified: Thursday, 15-Apr-04 12:03:54
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