Scale pests: still an increasing prolem in roses

Scale pests are still an increasing problem in roses as result of the withdrawal of broad-spectrum insecticides. This is stated by Trudie Coenen, PlantDoctor at BLGG. A scale pest that often occurs on roses is the rose scale Aulacaspis rosae.

This species can only multiply on plants of the Rosaceae. "It is difficult to combat scale pests with chemical crop protection products because they hide underneath their impervious scale", says Trudie Coenen. "It is necessary to spray repeatedly in order to control the pests. However, it is not possible to combat these pests by spraying. Therefore, it is necessary to employ biological crop protection products. The parasitic wasps and beetles that are often used to combat scale insects can also be employed in this case."

A nice example is the ladybug Rhizobius lophantae. Using an integrated approach of chemical crop protection products, when having a small population of scale insects, and afterwards releasing the natural enemies is probably the best option.

When using chemical crop protection products, it is important to keep in mind that all natural predators can be killed by the chemicals.

Upper left: underneath the scale the female with eggs, upper right: damaged stem caused by the scale pests. Bottom left: male nymphs, bottom right: female with eggs and damage on the stem.

Growth inhibition
The rose scale is located on the stems underneath the plant and stay alive by sucking plant juices. This causes growth inhibition. When heavily damaged the plant might even die.

Often, pulvinaria and scale pests are mixed up. However, they can be distinguished. The scale insect does not leaves honeydew behind and the pulvinaria does. The scale of the scale insect is not fixed to the body, but the scale of the pulvinaria is grown together with the body.

Spread via cultivation proceedings
Trudie Coenen: "Scale insects are mainly spread through cultivation proceedings or transport of plants. The insects are immobile for the largest part of their live. They are only able to move in the first larval stage. The females stay their entire lives on the same spot. The peel a couple of times and lay eggs. In the final stage of their growth, the males get wings and are looking for females to multiply. Annually, more generations occur in a greenhouse.

The female rose scale insect can be recognized by their white-grey scale with a size of 1,5-2,5 mm that covers their 1mm sized orange-red body. The scales of the male nymphs are white, oblong and flat with two serrations.

What can you do?
Working hygenically is very important. When scale insects are noticed, active approach is neccessary in order to prevent a plague. Keep checking your plants!

For more information:
BLGG AgroXpertus
Trudie Coenen
Binnenhaven 5
Postbus 170
6700 AD Wageningen
The Nethelands
T: +31 88 - 876 1010
Fax +31 88 - 876 1011

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