A pest that we have received many questions about the last couple of years is the Hydrangea scale or Pulvinaria hydrangeae.. This pest is often mistaken for mealybugs, but it is a woolly scale insect, which belongs to a different group of pests.
The confusion arises in the month of June when woolly egg masses are formed by the female scale. These structures are white and fluffy, and very similar to mealy bugs.Hydrangea scale has a single generation per year in which a single female can produce up to 1000 new scales. After hatching, the young scale insects reside on the leaves. They move to the woody part of the plant in late Fall. In Spring, when the leaves have sprouted completely, the scale insects return to the leaves and feast on the plant juice.
Nuisance from Hydrangea scale
The name suggests that the pest only occurs on Hortensia (Hydrangea) but that is not the case. You can also find the Hydrangea scale in trees, such as lime- and maple trees. The production of sticky honeydew causes a lotof nuisance, for example on cars that are parked underneath the trees. Incase of heavy infestation, the black sooty mold will strart to grow on the leaves. This hinders the photosynthesis and leads to growth reduction. When the whole plant is affected it will weaken and become more susceptible to other diseases and pests.
Combating Hyndrangea scale with natural enemies
To control the Hydrangea scale, you can use two native natural enemies. The most famous of these is the pine ladybird (Exochomus quadripustulatus). This beetle feeds on the scales and lays its eggs near or even in the woolly egg masses of the Hydrangea scale. When the eggs hatch, the young larvae immediately start eating the eggs in the egg mass. This way you can prevent the scale from spreading very quickly.
The other natural enemy that you can use to combat Hyndrangea scale is a small parasitoid: Coccophagus. The condition is that the correct stages of the scale insect must be present, because the parasitoid only parasitizes the smaller stages.
When can you use biological control agents?
The best time to release the larvae of the pine ladybird (product name EXOCHOMUS larvae) is when the egg mass is found, usually in May and June. Coccophagus (product name SAISIN-C) can be used from the end of July to the end of September. That is when the smal stages of the Hydrangea scale can be found.
You can apply the natural enemies in trees, in the cultivation of hydrangea, but also in your garden. Both products can therefore be ordered for both private and business customers.
Hyndrangea scale in lime tree