Agronomist notebook: Dealing with whiteflies, thrips on tomato farm

National Youth Service personnel in a tomato greenhouse at the farm named Tumaini Farm Unit in Nyandarua County.

Photo credit: Francis Mureithi | Nation Media Group

What you need to know:

  • Whiteflies suck the cell sap from plant leaves and produce a sticky substance known as honeydew.
  • The presence of eggs on the leaves is an indication of a new generation of whiteflies, hence the need to control them.
  • Yellow sticky traps can also be used to control the whiteflies as the pest are attracted to the yellow colour.
  • Thrips are attracted to white and yellow blossoms and easily transmit the tomato spotted wilt virus.

Apart from Tuta absoluta, which is also known as the tomato leaf miner, there are other pests such as whiteflies and thrips that affect tomatoes and lower their yields.

Whiteflies suck the cell sap from plant leaves and produce a sticky substance known as honeydew.

A high infestation of whiteflies on the plants makes them extremely weak. The honeydew makes it difficult for the plant to carry out photosynthesis, as it blocks the stomata on the leaves.

With time, the honeydew gives way to a black, sooty substance on the surface of leaves, a sign that whiteflies have been feeding on the plant sap.

One may also notice the presence of ants as they are attracted to the honeydew since it is sweet-tasting. The leaves wilt, turn yellow or pale as the crop gets stunted.

New generation of whiteflies

Moses scouts for whiteflies on the underside of the leaves, around the veins looking for white insects, eggs or the larva.

The presence of eggs on the leaves is an indication of a new generation of whiteflies, hence the need to control them.

The eggs hatch into larva, which also starts feeding on the cell sap. One may also easily notice the whiteflies by shaking the plant and small, white flying insects will fly away.

Whiteflies infestation is high during the warm season and affects a wide variety of crops, including French beans. They are usually active during the day.

Whiteflies should be controlled earlier to avoid a decrease in yields. To begin with, start by observing field hygiene as unwanted plants act as a breeding ground for the pests.

Avoid planting tomatoes in a field where whiteflies host plants such as beans had been previously planted as this helps in breaking the pest life cycle.

Rainy season

Go for systemic chemicals, which are absorbed by the plant’s leaves. The whiteflies, being sucking insects,  will suck the chemicals in the sap.

It is also important to use chemicals with a different active ingredient as the pests easily develop resistance.

While spraying, especially in the rainy season, use a spreader or sticker as this prevents the chemicals from being washed away by the raindrops. 

It also ensures the chemicals efficiently spread on the leaves’ surface and penetrate to the underside.

Yellow sticky traps can also be used to control the whiteflies as the pest are attracted to the yellow colour.

Market trends

Apart from whiteflies, Moses has battled thrips, a common tomato pest. They are small, black or slivery slender insects that suck juices from tomato leaves, flowers and fruits. Affected plants appear discoloured, twisted and sometimes scarred. 

The thrips leap or fly for shorter distances when disturbed. Affected fruits usually have marks on the surface of the fruit. Since thrips highly affect onions, it is vital to avoid planting tomatoes next to onions or where the previous crop was onions.

Thrips are attracted to white and yellow blossoms and easily transmit the tomato spotted wilt virus.

Mechanical method such as the use of the blue stick traps can be used to trap thrips as they are attracted to the blue colour. This is what Moses has been using.

In our next article, we shall focus on the current market trends of tomatoes.

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