Organisms that derive a living from willow and poplar but have rarely caused extensive damage include; froghoppers, leafhoppers, weevils, gall midges, mites and viral capsids. Economically damaging pests and diseases include; stem aphids, leaf beetles, sawflies and rust. Of most concern to growers is consumption of leaf tissues (defoliation or skeletonisation), siphoning of sap (sugar and protein contained within the phloem and transported from leaves to woody tissue) from the new wood layer beneath the bark (stem infestation), leaf discolouration and damage by infectious fungal, viral and bacterial agents, and stem deformation by wood borers. .

Rust (usually Melampsora epitea although there are many other willow rusts) is the major disease affecting willow and poplar short rotation coppice (SRC) in the UK. The extent to which this disease affects trees varies considerably between and within plantations and clones. Rust is a complex of fungal species that attacks leaves and can defoliate early in the season. Resistant and tolerant willow clones are available and planting a selection of willow clones with varied resistance to different pathotypes should prevent large scale damage. Fungicides are available to control rust but large scale use is expensive and may encourage the development of resistant pathotypes.

Leaf eating blue, brassy and brown willow beetles of the family Chrysomelidae are reported to be wide spread and potentially damaging to willow and poplar. Both the larval and the adult stage consume the leaf epidermis often leaving only the nutrient and water transport system (or skeleton). Cases of infestation are rare but can lead to reduced yield and crop death, defoliation is usually periodic, late in season and causes no reduction in crop yield. Caterpillar-like sawfly larvae can also cause defoliation of poplar and willow varieties.

Sap sucking stem aphids (photographs courtesy of T. Collins, Silwood, Imperial College) are probably the most noticeable insect pest on willow because of their tendency to aggregate together in colonies along the trunk and stems of trees. They are found on older SRWC shoots usually in the 2nd-4th year of stem growth. Colonies produce sticky deposits that are often black from mould growth. Damage is rarely terminal but can lead to stem death and reduced productivity particularly if the plant suffers a secondary stress such as drought.

Damage to roots from slugs and insect larvae, such as leather-jackets, and fungi such as honey fungus is hard to anticipate and detect and can be commercially damaging in the establishment phase of the crop. An application of insecticide in conjunction with the pre-emergent herbicide (used for weed control as discussed in the willow management section) may be needed in situations where a problem is anticipated from previous experience of the site.