Eucalyptus trees, a diverse genus of over 660 species, are known for their rapid growth, aromatic foliage, and distinctive bark. Native to Australia, these evergreen trees have been introduced globally for timber, pulpwood, and landscaping. They serve as a food source for numerous organisms, impacting their health and survival.
Common Insect Pests That Eat Eucalyptus
Eucalyptus trees face challenges from various insect species that feed on different parts of the tree.
Eucalyptus psyllids, such as the red gum lerp psyllid, are common sap-sucking insects. They feed on phloem sap, creating distinctive waxy “lerps” on leaves, visible as small, white caps. Heavy infestations lead to sticky honeydew, sooty mold growth, premature leaf drop, and tree weakening.
Eucalyptus leaf beetles, including species like the blue gum leaf beetle, are defoliators that chew holes or irregular notches in leaves. Their larvae often feed gregariously, sometimes skeletonizing leaves or consuming most of the leaf surface. This extensive feeding can severely weaken trees, and repeated defoliation can lead to decline, especially in young or stressed trees.
Borers, such as the eucalyptus longhorned borer, tunnel into the wood, causing substantial structural damage. Larvae bore into the inner bark and cambial layer, disrupting the tree’s nutrient and water transport system. This feeding can girdle branches or trunks, leading to wilting foliage, dieback, and tree death. Scale insects also suck sap from stems and leaves, resulting in yellowing foliage and stunted growth.
Mammalian Browsers and Their Impact
Eucalyptus trees are a food source for various mammalian browsers, particularly in their native habitats and introduced regions.
Koalas are the most well-known mammalian consumers of eucalyptus, with their diet consisting almost exclusively of these leaves. They are highly specialized feeders, consuming 200 to 800 grams daily, and have unique digestive systems adapted to detoxify eucalyptus compounds. Koalas exhibit preferences for certain eucalyptus species, linking their presence to favored food trees.
Outside Australia, deer browse on young eucalyptus trees, particularly new shoots and sapling leaves. Where eucalyptus has been planted, deer may use them as a food source when other forage is scarce. This browsing can hinder the establishment and growth of young plants, damaging their developing structure.
In Australia, possums and wallabies consume eucalyptus foliage. Ringtail possums primarily eat eucalyptus leaves, sometimes stripping trees bare quickly. Brushtail possums also feed on eucalyptus, though they have a broader diet. These native marsupials can cause significant defoliation, especially on young trees or preferred species, impacting tree health and appearance.
Identifying Damage and Protecting Your Trees
Recognizing signs of damage is the first step in protecting eucalyptus trees. Chewed leaf edges, holes in foliage, or skeletonized leaves often point to insect activity, particularly from leaf-feeding beetles. Sticky residue on leaves and surfaces beneath the tree, known as honeydew, along with black sooty mold, indicates sap-sucking insects like psyllids or scale. Evidence of borers includes small holes in the bark, sawdust-like frass around the tree’s base, or oozing sap. For mammalian browsing, look for cleanly bitten or torn young shoots and leaves, especially on lower branches or saplings, and sometimes stripped bark.
Protecting eucalyptus trees involves cultural practices and physical barriers. Maintaining tree health through proper watering and soil care enhances natural pest resistance. Adequate moisture, especially during dry periods, helps prevent stress that makes trees susceptible to borer attacks.
For young trees vulnerable to mammalian browsing, physical barriers like tree guards or fencing deter animals. Regular inspection allows early detection of pest activity, enabling timely intervention. For significant infestations, consult local arborists or extension services for integrated pest management strategies.