The willow is a temperature deciduous tree that produces narrow leaves and catkins, which are flowering spikes that hang down from tree branches. By providing a willow tree with ideal growing conditions, specifically full sun exposure and moist soils, you can help ensure that the tree does not succumb to disease or infestation. Apart from microorganisms causing problems, like the fungal spores that produce cankers, a variety of bugs can be detrimental to the health of a willow tree.
Armoured scales are small insects that have flat, hard, platelike covers shielding the tops of their bodies. When a large population of these sap-sucking bugs exist in a willow tree, the tree's leaves may yellow, wilt, curl and fall prematurely. Other symptoms of armoured scale infestation can include cracked bark and the secretion of gum -- or a viscous substance that hardens upon drying -- from those cracks. You can treat a willow tree with armoured scales using horticultural oil or systemic insecticides. The most common species of armoured scale that cause problems with willow trees include the San Jose, oystershell, latania and greedy scale.
Like armoured scales, aphids are small insects that suck the sap from tree tissues. However, unlike armoured scales, aphids have soft bodies and excrete a sweet, sticky substance known as honeydew. Apart from distorting, yellowing and curling willow tree leaves with their sap-sucking, aphids encourage the growth of mould on leaves when they release honeydew. Some of the most common species of aphids that appear on willow trees include the melon, giant willow and giant bark aphid. You can treat aphid infestations in willow trees using neem oil, narrow-range oil or insecticidal soap.
Mealy bugs are soft-bodied insects that have powdery, whitish coatings of wax covering their bodies. When a large population of mealy bugs invades a willow tree, symptoms can include twig dieback, slowed growth and the appearance of large, cottony masses on foliage. Like aphids, mealy bugs feed on the sap of willow trees and secrete honeydew, which means the bugs put willow trees at risk for mould. You can remove mealy bugs from willow trees using forceful streams of water, narrow-range oil or insecticidal soap. Common species of mealy bug that impact willow trees include the vine and the obscure mealy bug.
Blister Gall Mites
Unlike armoured scales, aphids and mealy bugs, blister gall mites are not insects. Instead, these tiny bugs are a species of arachnid, like spiders and ticks. In a willow tree, blister gall mites can cause the distorting, curling and blistering of leaves, while also producing wart-like swellings on twigs. Treating blister gall mites with insecticides is often unsuccessful. For best results, prune off the leaves and twigs of a willow tree that show signs of infestation.