Pest Update – Whitefly

August 14, 2008
engage_agro_sept
 
 

Pest Update – Whitefly
October 30, 2008  |  by Sean Valk
Overview
Whiteflies are small insect pests with sucking mouth parts.  They belong to the family Aleyrodidae   (Suborder Homoptera) and are related to other sucking insects including aphids, scales, leafhoppers, and mealybugs.  There are several different types of whiteflies that commonly occur in the greenhouse, the main types being the greenhouse whitefly (Trialeurodes vaporariorum) and the silverleaf whitefly (Bemisia argentifolii and Bemisia tabaci). 

Greenhouse whitefly adults hold their wings nearly parallel to the leaf surface and appear broader-winged; adult silverleaf whiteflies hold their wings at a 45-degree angle similar to the roof of an A-frame house. Pupae of the greenhouse whitefly appear coin-like in shape (with sides perpendicular to the leaf surface). Silverleaf whitefly pupae typically appear more rounded with edges that slant slightly toward the leaf surface.  Two biotypes, Q and B, of silverleaf whitefly occur in Canada.  The Q biotype is becoming more prevalent and causing concern for some Canadian growers.  These whitefly biotypes are identical in appearance and have virtually identical life cycles, host plants, etc, but differ in body chemistry. The only way they can be correctly identified is by conducting laboratory tests.



whitefly_1

     
whitefly2

 
Adult Greenhouse Whitefly - Trialeurodes vaporium    
      Greenhouse whitefly nymph
 


Damage
Feeding damage by both the nymphs and adults results in the accumulation of honeydew on the leaves and the subsequent growth of sooty black as well as other molds.  Other forms of damage include the removal of plant sap; vine, leaf and plant breakdown; chlorotic spots; yellowing; leaf shedding; and abnormalities of fruiting structures. It is believed that the pest injects foreign enzymes into the host plant while feeding, affecting the normal physiological processes. The pest is also known to vector virus diseases to many crops.

Controlling Whitefly
While the adults only live for about 10 days, they can lay in excess of 200 eggs during that time. The life cycle begins with the eggs which are laid  hatching into larvae, 5 to 6 days after being laid. For 12 to 14 the larvae feed and molt.

Keeping records, scouting and being proactive are essential to winning the battle against whitefly.  Using a program like SprayScout to record pest pressure and pest management applications will provide an invaluable look at what is happening in your greenhouse, and what is working to keep pests at manageable levels; therefore making your control options more effective. 

The first step in control whitefly is to maintain a weed-free area around your crop to help eliminate breeding areas.  Other cultural controls include using a vacuum to physically remove the whitefly from the crop.  

There are many commercially available biological control insects to help combat whitefly, such as Encarsia formosa and Eretmocerus eremicus.  Before entering into a biological control program for whiteflies, you should consult your local extension specialist or a sales representative knowledgeable in using beneficial insects.

Insect growth regulators (IGRs) is a chemical group that is most effective against the young developing nymphs and can work in one of several ways:

1) they can mimic juvenile hormones, so that insects never enter the reproductive stage of development;

2) they can interfere with the production of chitin, which makes up the shell of most insects; or

3) they can block the formation of ecdysone, a essential molting hormone. 

Enstar® II (s-kinoprene) and Distance® (pyriproxyfen) are examples of products that are juvenile hormone mimics; they affect the insects’ hormonal balance, suppressing the development of eggs, metamorphosis, and adult formation. 

Along with the above options there are also a number of registered insecticides for the control of whitefly.  Endeavor® (pymetrozine) is a selective feeding blocker that paralyzes the sucking mechanism immediately and irreversibly as soon as the whitefly feeds on a treated plant.  Tristar™ (acetamiprid), which belongs to the neonicitinoid class of chemistry, is locally-systemic, translaminar, works on all life stages of the whitefly, and is widely used as a clean-up product. Other chemical control options include; Dyno-mite, Forbid™, Intercept, and Opal Insecticidal Soap.  Each of these options is designed to work in a specific way; so it is important to read the label and understand the chemistry to get the most out of each application.  Also, by understanding the chemistry, you will be able to know which products to rotate and alternate to develop a more effective resistance management program.



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