Whitefly
- GardenMaestro
- Feb 28, 2023
- 3 min read
Common name: Whitefly
Classification: Insecta, Order: Hemiptera, Species: Several
Physical description
Adult stage: Small flies are between 1 and 2mm long, Most Whitefly species that occur locally are white or white/ cream in color, although they can occur in other colors. They have two pairs of wings that extend beyond the end of the abdomen; magnified, the adults look like very small moths due to their coloration
Nymph stage: Small flattened nymphs can be found upper and lower leaf surfaces of the plant leaf and measure about 0.2 - 0.3mm in size, and can only be seen under magnification. This is the most conspicuous stage and when damage is normally noticed - yellow blotches and speckles on the upper leaf surface.
Life Cycle and Description of damage
The insect causes physical damage to the plant tissue during both the nymph and the adult stages of its life.
The eggs hatch between 3 and 7 days after being laid, they are extremely small and cannot be seen with the naked eye. After hatching, the insects enter the nymph stage of the life cycle, these nymphs are partially mobile and can move away from the hatching site to a more suitable feeding site. The nymph then anchors itself to the feeding spot by inserting its mouth parts into the leaf surface, once in this location, it cannot move again. The nymph will remain in this location and feed for a period of about 20 days.
During feeding the nymph will secrete digestive juices into the leaf surface to facilitate the feeding process, this causes surrounding tissue to break down and results in the small yellow stipple marks common on the upper surface of the leaf. As the nymphs cannot move, the amount of damage is commensurate with the number of nymphs feeding in this location.
The plant experiences stress and stunting due to the attack as well as the reduction in photosynthetic tissue. Tissue damage is aesthetic and permanent in nature, even if the insects are killed the damage will still be visible until the leaf is replaced; damaged leaves can be removed as long as not too many are removed which may impact the photosynthesis of the plant as a whole.
Plants affected
A very common problem on seasonal plants and vegetables: Vinca, Petunia, Marigolds, Lettuce, Cabbage, Tomato, Strawberries, etc. Anything with a soft leaf that is fast growing. It will also affect some perennial plants, especially those with soft foliage.
General comments
The eggs are immune to chemical controls, so these have to be repeated for at least 3 spray cycles to eliminate any eggs that hatch between spray applications. One of the most serious problems with Whitefly is that they build up resistance to insecticides very quickly, in agriculture the chemical controls (the active ingredient of the poison) are alternated in order to reduce this effect.
Control methods - Natural
Simply removing (and discarding) damaged foliage can keep the problem at a manageable level. Damaged tissue does not repair, so the blemishes will remain even if the insect is killed.
Control methods - Cultural
The effects of whiteflies can be minimized (not prevented), by using cultural methods such as "catch crops" or "Companion planting". Sticky insect cards can also be placed between high-risk crops to catch as many flying adults as possible, thereby reducing the effects of the pest.
Control methods - Organic
Insecticidal oils such as Neem are also effective in controlling and breaking the breeding cycle, but only when used in a program with an emphasis on prevention not curing an existing problem.
Control methods - Chemical
Plants can be treated with a combination of systemic and contact insecticides. Care needs to be taken as most chemical treatments will have a residual period, so should not be used on edible crops.
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