Obscure scales are pests that affect oak, hickory, walnut, willow and maple trees. These scaly pests live on branches and twigs, and they feed on sap using their piercing mouthparts. Obscure scales have one generation each year. Females lay eggs in June, July and August, and there is peak crawler activity during mid-July. Although small, these pests can wreak havoc on vulnerable trees. Interestingly, this pest affects trees in urban areas, not those in forests.

Let’s learn more about obscure scales and how you can protect your oak trees from an infestation.

What does Obscure Scale Look Like?

Obscure scales are small, about 3 mm in diameter and a dirty gray color. The females have a waxy coating. You won’t notice these pests unless you are looking closely for them. With their small size and dingy color, they can easily blend in with a branch or twig. What makes these pests unique is that the females are covered in a waxy coating. Newly hatched crawlers tend to settle under the waxy covering of the mature scales, so what happens in that layers of crusty material forms on the branches.

For the scales, these layers of coating provide extra protection, but for the trees, it only contributes to a greater infestation. It becomes much more difficult for the trees to be treated as well since the pests are protected from insecticides that are used. In fact, the wax coverings from past scales may still be being scraped from the tree several years later. With the above in mind, treatment methods can take years and be intensive.

What is the Life Cycle?

Obscure scales nymphs on branches and twigs in the winter. Females start to mature in April, while males start in May. Males emerge from their waxy cover and breed with the females, which then lay 50 pink eggs over the next several months. After mating, the males die off, and the females remain throughout the season. Most areas see only one generation.

When the crawlers are born, they are active for several weeks, and there may be activity through September. The early crawlers often settle underneath the waxy coatings so that they can feed, while late crawlers will travel to new territory. There is a second nymphal stage where more waxy coatings are secreted in the fall.

What Type of Damage Will They Do?

Obscure scale does a lot of damage during their infestations. The species takes plant fluid from the twigs and branches, which is why you’ll notice oak trees dropping their leaves and having premature dieback. There will be sunken areas on the tree where the infestation has been feeding, and infected branches will have an ash-like look to them. Severely infested trees can have three to four layers of wax coating, and some trees may have disfigured trunks. Since these types of pests have such pronounced damage but can be difficult to spot, it’s best to call in a professional arborist who can determine the nature of the infestation and the proper treatment methods.