Cottony Scale on Hills Yew

(Question)

Hill’s yew question. The tree has little white balls about 2mm on the branches. Is this normal?

(Answer)

No, this is not normal. Its sounds like Cottony Camelia (Taxus) Scale, aka Pulvinaria floccifera, which lay thousands of eggs in a single, tiny, cottony white ball, usually on the underside of leaves and stems of yews, euonymus, holly and maples. There is only one generation per year, with the adults laying eggs in June, crawlers hatching in July and developing into nymphs which overwinter on the plants stems and branches. The brown coloured nymphs mature in the spring and the cycle begins again.

If you only have a small number of cottony balls you can remove them by hand when you are gardening.  In exchange for the honeydew which the scale produce, ants protect the scale from predators such as ladybugs- which lay their eggs near scale eggs to feed their emerging larva. If you can deter the ants from your infected yew, natural predators such as ladybugs and wasps will eat the scale eggs.  Your local garden centre can advise you on available ant traps and deterrents.

If your infestation is severe, the use of Horticultural Oil (available in garden centres) is recommended by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) as it poses a low risk to humans or wildlife. Yew foliage is sensitive to Dormant oil (Horticultural oil applied during the winter months), so apply as per manufacturers instructions as the crawlers hatch in July, and repeat after 10 days if necessary. If you shake a branch over a piece of paper you will notice tiny yellowy brown insects. Unlike adult scale which develop a protective shell, the crawlers have soft bodies and die when they come into contact with the sprayed oil.

Read the instructions carefully. Some mixtures require dilution and can burn your foliage. After treatment be sure to keep your yew mulched and watered over the summer months and consider applying a slow release evergreen fertilizer to improve your yews overall health.