Top 5 Tree Diseases
Trees contribute mightily to a landscape's value, so it's important to keep them healthy. Here's how to deal with 5 of the most common tree diseases.
Anthracnose
Anthracnose is a common disease among deciduous trees, especially sycamore, ash and oak. It also affects shrubs such as privet. It causes unsightly dark, sunken lesions on leaves, stems, flowers and fruits.
Anthracnose fungi need water to spread and infect, so the disease is more prevalent during wet, cold springs. Because it’s more of a cosmetic issue than a serious tree health threat, anthracnose doesn’t normally require treatment.
Some cultural practices can help prevent it, including collecting and disposing of leaves and twigs, as well as increasing air circulation by pruning infected twigs and branches when the tree is dormant. Caring for your trees will help them grow quickly and fill out your yard.
Canker Diseases
A variety of canker diseases affect trees, including Cytospora canker on pine, poplars, spruce and willows. Canker diseases result when a fungal or bacterial pathogen enters bark or sapwood through a wound.
Eventually the tree’s vascular system becomes blocked and nutrients cannot flow. Depending on where the canker is, this blockage can cause branches to die. If it’s wrapped around the trunk, the entire tree may die.
Trees that are stressed — from environmental factors, animal browsing, mechanical injury, etc. — are most susceptible. Preventive measures include growing trees suited to the available space and conditions, avoiding injury to bark, proper maintenance and winter protection, and removing any branches affected by canker.
Sterilize pruning tools between cuts with a 10 percent bleach solution.
Diplodia Tip Blight
Blight can affect many different tree species, but this disease is common on stressed conifers. New growth is stunted, turns yellow and then brown, eventually dying.
Trees under stress are more prone to diplodia tip blight, so keep them mulched and watered, especially during dry periods. Remove and destroy infected cones and tips, as well as dead or dying branches, disinfecting pruning tools between cuts with rubbing alcohol or a 10 percent bleach solution.
Fungicides are applied three times in spring: when buds first break, when new shoots (called candles) are half emerged and again when they are fully developed.
Oak Wilt
Oak wilt is a fungal disease specific to oak trees. It is fatal to species in the red oak group (pointy leaf lobes), while those in the white oak family (rounded leaf lobes) are less susceptible.
Starting at the top of the tree, leaves rapidly wilt and turn brown. Oak wilt is passed from tree to tree through the roots of one oak tree to another, or by sap-sucking beetles who are attracted to freshly cut wood. Avoid pruning oak trees during the growing season. If you must prune an oak during the growing season, use a tree wound sealant to make the wound less attractive to beetles.
Properly caring for your oak trees will ensure spectacular fall foliage.
Phytophthora Root Rot
Phytophthora root rot is a fungal disease that attacks trees growing on poorly drained sites. Trees look as if they are drought-stressed, with wilting leaves turning pale green or yellow.
Although there are no treatments for root rot, there are things you can do to prevent it. Avoid planting trees in wet areas or near downspouts. Or plant water-loving species instead, including bald cypress, willow, sycamore and black gum.
Never plant trees deeper than they grew at the nursery — at the same level or slightly higher is preferable — and avoid piling soil against the trunk.