Thrips and Tospoviruses: The Basics and

Management

Diane E. Ullman

Michael Parrella

Logo by Eileen Rendahl

Overview of Presentation

• Biology of Tospoviruses and Their

Western Flower Thrips Vectors

•Monitoring/Physical control •sticky cards, sticky tape

• Biological control • predatory mites, EPNs (entomopathogenic

nematodes) & entomopathogenic fungi

• Chemical control

CONNECTING THE DOTS: INTEGRATING

MANAGEMENT STRATEGIES

A CONTEXT FOR RISK AND DECISION MAKING

Disease Pyramid by Eileen Rendahl, Photos Courtesy of J.Kelley Clark, J.L. Sherwood and J.J. Cho

WFT Life Cycle

68°-98° F

Pre-Pupal and Pupal Stages In the Soil

Egg

1st instar

2nd instar

Photos by J.K. Clark

1-3 days** 1-2 days**

2-4 days

1-2 days

2-4 days

30-45 days

Thrips/Virus

Relationship

Pupal Stages Do Not Feed

ACQUISITION

BY LARVAE IS

CRUCIAL

Egg

1st instar

2nd instar

VIRUS PASSAGE

Only adults that

acquire as larvae

can transmit.

TRANSMISSION

Photos by J.K. Clark

VIRUS PASSAGE

PRIMARY VS SECONDARY SPREAD:

WHEN THE PLANT IS A HOST FOR

THE VIRUS AND NOT THE THRIPS

x

PRIMARY VS SECONDARY SPREAD:

WHEN THE PLANT IS A HOST FOR

THE VIRUS AND THE THRIPS

Don’t Forget the Weeds!

Malva, commons.wikimedia.org Buttercup species, photo by Kim Willis

Photo from: www.designntrend.com

The Carlsbad Flower Fields: A Management

Case Study

FAMILY BUNYAVIRIDAE

Genus Tospovirus: the only plant infecting genus

THE TOSPOVIRUSES: TSWV IS THE

TYPE MEMBER

http://www.forestryimages.org

Chrysanthemum

http://www.forestryimages.org

Cyclamen and Begonias

http://www.forestryimages.org

Gloxinia

Approved Species (18 emerging not

yet approved)

Tospovirus Vectors (Ceratotripoides

claratris and Scirtothrips dorsalis

transmit emerging viruses)

Groundnut bud necrosis virus Frankliniella occidentalis, Thrips

palmi

Groundnut ringspot virus F. gemina, F. occidentalis, F. schultzei

Groundnut yellow spot virus N.D.

Impatiens necrotic spot virus F. occidentalis

Tomato chlorotic spot virus F. occidentalis, F. schultzei, F. intonsa

Tomato spotted wilt virus F. bispinosa, F. cephalica, F. gemina, F.

fusca, F. intonsa, F. occidentalis, F.

schultzei, F. setosus, T. tabaci

Watermelon silver mottle virus T. palmi

Zucchini lethal chlorosis virus F. zucchini

KNOW YOUR ENEMY

ELISA: Enzyme-Linked Immunosorbent Assay

Immunostrips

Illustration by Eileen Rendahl from Ullman et al. 2005, PNAS USA Commentary

Data from Sin et al. 2005, PNAS USA

Reassortment and Emergence of New

Tospoviruses and New Vectors

http://www.ipm.ucdavis.edu/PMG/r280301411.html

http://www.pestid.msu.edu/LinkClick.aspx?fileticket=MfLee5r8Jw8%3D&tabid=53

http://msue.anr.msu.edu/news/tomato_spotted_wilt_virus_found_in_fall_garden_mums

Egg Larvae Pupae Adults

UC IPM Guidelines for Monitoring Thrips

• Use yellow or blue sticky cards • yellow are easier to count and trap other insects

• Place vertically just above the crop canopy • Adjust height as the crop grows

• Use a minimum of 8 traps/100,000 ft2

• locate traps in more sensitive cultivars/doorways

• Check at least weekly - thresholds vary • Roses = 25-50 thrips per card

• Other Crops = 5-10 thrips per card

• Correctly identify the WFT and check plants

• Sticky tape to reduce thrips populations?

Biological Control Products with the potential to control WFT

Predatory Mites: Amblyseius cucumeris & swirski - released onto the

plant and regular releases are necessary

Stratiolaelaps scimitus – released into the soil with

only 1 or 2 ‘inoculative’ releases being necessary

Parasites – Entomopathogenic nematodes &

fungi

Steinernema feltiae – sprayed regularly on the soil

Beauveria bassiana – sprayed regularly on the plant

http://www.allaboutswirskii.com/

MANAGEMENT USING IPM An IPM strategy can be divided into three parts:

Before the Growing Season

During the Growing Season

After the Growing Season

MANAGEMENT USING IPM An IPM strategy can be divided into three parts:

Before the Growing Season

• Keep the area free of virus-infected plants and

potentially infected thrips—if you are growing

susceptible crops consecutively consider a crop-

free period

• Manage thrips populations on transplants if

necessary

• Practice good weed management in and around

the greenhouse

• Virus-resistant chrysanthemum cultivars are not

yet available, but may be coming

MANAGEMENT USING IPM During the Growing Season

• Avoid planting new crops adjacent to older crops

(especially those crops confirmed to have TSWV

infection).

• Monitor the greenhouse and surrounding areas for

the presence of thrips and manage populations

• Monitor for TSWV using immunostrips and

buffer bags: commercially available from

companies such as AgDia (www.agdia.com) and

EnviroLogix (www.envirologix.com).

MANAGEMENT USING IPM During the Growing Season

• Consider rogueing plants infected at the seedling

stage (remove from area completely)

• Practice good weed management in and around

the greenhouse.

After the Growing Season

• Destroy old crops and any volunteers after harvest

(e.g., plowing and physical removal). Ideally this

practice is followed on a regional basis.

• Control weeds and any volunteers on fallow fields

or unused land nearby

TSWV MANAGEMENT • Inspect incoming plant material for signs of thrips

feeding injury, or for symptoms indicative of

TSWV or INSV infection.

• Isolate incoming plants from all other plants in

the greenhouse until certain they are free of the

viruses. Hang yellow/blue sticky traps vertically

above the new plants to monitor for adult thrips.

TSWV MANAGEMENT

• Separate older crops from seedlings.

• Hanging baskets of infected crops over seedlings

can lead to bedding plant losses, since the young

seedlings are highly susceptible.

• Immediately discard plants showing distinctive

TSWV/INSV symptoms.

• Early destruction of a few infected plants may

prevent an epidemic through all the susceptible

plants in the greenhouse.

• If in doubt, throw them out. Infected plants cannot

be cured.

TSWV MANAGEMENT

• Be especially careful when producing

vegetable transplants, especially if they are

adjacent to ornamental crops

• Tomato and pepper, in particular, may be

severely affected by TSWV/INSV.

• Plants may act as reservoirs of the virus.

TSWV MANAGEMENT • Flowering pot plant crops such as cyclamen

can serve to carry the disease over from the

fall to the following bedding plant season,

weeds left under the benches may do the same

thing

• Eliminate weeds in and near the greenhouse

which may harbor thrips and/or the virus.

• Consider using indicator plants if they are

available

TSWV MANAGEMENT

• Losses in the greenhouse have been greatest

with gloxinia, double flowered impatiens,

New Guinea impatiens, begonia and

cyclamen crops.

• If you grow these crops, be particularly

careful to keep them isolated from potential

sources and other plants that may be

susceptible, such as chrysanthemums

Chemical Control

Materials registered/recommended for thrips

control in Michigan

Aria = flonicamid (Group 9c)

Avid = abamectin (Group 6)

AzaGuard = azadirachtin (unknown)

Azatin XL= azadirachtin (unknown)

Flagship = thiamethoxam (Group 4a)

Mesurol = methiocarb (Group 1c)

Orthene 97 = acephate (Group 1a)

Overture = pyridalyl (unknown)

Pedestal = novaluron (Group 15)

Chemical Control • A full volume wet spray is recommended; you

must get thorough coverage

• To eliminate/dramatically reduce thrips numbers in

the greenhouse, spraying every five days is usually

recommended

• Rotate between different classes of insecticides

after 4 applications of the same material

• Tanks mixes are usually not recommended because

of increasing problems with resistance, but to clean

up a particularly heavy infestation, tank mixes may

be useful: Orthene plus Azatin, etc.

Insecticides for Control of Western Flower Thrips

Questions?