Whiteflies are a significant problem for global food production as they carry and spread plant diseases that cause significant economic losses. The most problematic species is Bemisia, which transmits the worst viral disease, tomato yellow leaf-curl begomovirus. Whitefly control is challenging as they rapidly develop resistance to chemical pesticides.
To reduce insecticide use and re-establish ecological balance, environmentally friendly integrated pest management systems and new crop varieties with increased tolerance to whiteflies and their transmitted diseases are being developed.
Whitefly management in Tomato
The life cycle of a Whitefly
- Whiteflies have a life cycle that consists of several stages. Female whiteflies lay up to 150 eggs attached to the undersides of leaves and hatch into first-instar nymphs after 8 to 10 days.
- The first instar nymphs crawl a short distance before settling to feed on plant tissue.
- There are four nymphal stages, with the last stage (red-eyed nymph or pupa) being the easiest to identify.
- The last nymphal instar stops feeding, pupates, and emerges as a fully developed adult.
- Adults are mainly responsible for spreading viruses from plant to plant.
- The life cycle of whiteflies takes 18 to 28 days in warm weather and 30 to 48 days in winter, from egg to adult.
Identification of Whitefly in Tomato field
- Pale and wilted leaves are a telltale sign of whitefly infestation as they feed on the juices from leaf undersides.
- The presence of hundreds of tiny white moths, a sticky substance known as whitefly honeydew, and ants (who feed on the honeydew) are additional indicators of whitefly damage.
Damage symptoms of Whitefly in Tomato field
- Whiteflies are small, soft-bodied insects that measure less than one-tenth of an inch and often rest on the undersides of leaves.
- They are identified as tiny white triangles. Different whiteflies can infest tomato plants.
- It is important to correctly identify the sweet potato whitefly and greenhouse whitefly as they are the only species that cause economic damage.
- Whiteflies feed on the sap from the undersides of leaves, causing the plants to become seriously weakened.
- Infested leaves show numerous chlorotic spots that grow together, forming yellow areas.
- In severe cases, only the veins remain green. Wilting and leaf drops may occur, and a sticky, black mold may form on leaves and stems.
Cultural control of Whitefly
- Handpick older leaves to remove early whitefly stages.
- Avoid using a lot of nitrogen fertilizer, including manures, as succulent growth will increase the whitefly population. It can be useful to check phosphorus and magnesium levels, as deficiencies in these are believed to contribute to whitefly infestations.
- Silver-colored mulches repel adult whiteflies. Place reflective polyethylene mulches on planting beds before seeding or transplanting to reduce the colonization rate significantly.
Biological control of Rice Gall Midge
- Encouraging the presence of these natural predators in your garden can help reduce the whitefly population.
- To control whitefly populations, you can also purchase and release predatory insects such as Encarsia formosa, a tiny parasitic wasp.
- Using beneficial nematodes is another option for controlling whiteflies in the soil.
- Avoid using broad-spectrum insecticides that can harm natural enemies and disrupt the balance of the ecosystem.
- Introduce plants that attract beneficial insects, such as marigolds, asters, and dill, to help maintain a healthy population of predators in your garden.
Chemical control of Whitefly
- Imidachloprid 70 WS can be used as a seed treatment at a rate of 5 g/kg of seed.
- Acetamiprid, 20% SP, can be applied at 100 g/ha.
- Neem seed kernel extracts 5% (50 kg); neem oil can be used at five ml/l of water.
- Fish oil rosin soap 25 kg at 1 kg in 40 liters of water and Notchi leaves 5% extract can also be used.
- Catharanthus roseus extract 5% can be used along with Imidacloprid and Thiamethoxam 25g a.i./ha. Chlorpyriphos, 20% EC, can be applied at 1250 ml/ha.