Scales are tiny, parasitic insects which adhere to plants and feed off the plant’s sap. They have scale/ shell like waxy covering which hides their bodies, making them appear like bumps and are easily mistaken for a disease.
There are very many scales species.
Types of Scales
Scales are majorly divided into 2 groups. These are;
- Soft scale– this is covered with a protective waxy substance and is easier to control. It produces honeydew.
- Armoured / hard scale– this secretes a hard shell over its body for protection from predators and does not produce honeydew. The shell also makes it difficult to control this pest by use of a pesticide.
Host Range
Scale insects feed on a wide variety of plants. However, there are particular species which are specific to particular host plants. Examples of plants attacked by scales are mango, pigeon peas, citrus, ornamentals, etc.
Life Cycle
Eggs are laid under the cover of the adult scale, which protects them as they develop. These hatch after 1-3 weeks into tiny legged insects usually referred to as crawlers (nymphs) which spread all over the plant and its foliage in search of a suitable place to settle until it matures.
NB; after it has laid its eggs, the adult dies.
The shell / scale develops after feeding begins.
Identification
Scale vary greatly in colour, shape and size. They are usually rounded and can be white, black, orange, green, brown etc. depending on the species. The size of a mature scale is approximately 3-5mm.
Depending on the species, they can be found on plant stems, trunks, twigs, foliage or fruits
Feeding & Damage
Scales feed by sucking sap from plants through their piercing and sucking mouthparts. This exercise causes yellowing and eventual wilting of leaves and stunted growth as plant losses growth vigour.
In severe cases of infestation, plants become weakened and susceptible to attack by other pathogens as well as unable to withstand adverse climatic conditions.
As they feed, scales secrete a sweet sticky substance (honeydew) which encourages the development of sooty mold on the plant parts. If on the leaves, this leads to reduced rate of photosynthesis.
Control
Scales can be controlled through a number of ways. However, due to their protective layer, they are not very easy to control.
The use of insecticides is the most preferred because it is more reliable than the others.
The following insecticides are very effective in the control and management of scales.
- EMERALD 200SL 20ml/20l
- LOYALTY 700WDG 10g/20l
- RANGER 480EC 30ml/20l
These chemicals have both contact and systemic properties and are thus very efficient. In order to prevent the pest from building resistant for either of the insecticides, alternating them is recommended.
In order to get rid of the sooty mold which develops as a result of the honeydew disposition by these insect pests, spray JAMBO CLEAN 100ml/20l.
It is highly recommended to always mix the insecticide with INTEGRA 3ml/20l whenever spraying. This is a spreader, sticker, wetter and penetrant which basically improves the efficacy of the chemical.
Apart from the chemical control method, the following ways can also be used to manage scales;
- Use of tolerant and resistant cultivars
- Crop rotation with non-host crops
- Maintaining field hygiene
- Pruning the infested plant parts
