3/21/2023 - By Dr. Aaron Palmateer

When it comes to trees and shrubs, the most common and economically important pathogens are fungi that cause tip blight and often branch dieback diseases. It seems most conifers including cedar, cypress, fir, juniper, pine, redwood, spruce, and yew, are all susceptible to one or even several fungal diseases described as a tip blight.

What is Tip Blight?

A disease characterized by general and rapid killing is a blight. Thus, tip blight is a rapid killing of the branch tips, with small brown to black dots or fruiting structures of the fungi often visible on diseased tissue. Some of the names associated with these fungi include Diplodia, Kabatina, Pestalotiopsis, Phomopsis, and Sclerophoma.

Tip Blight and Branch Dieback Disease

One thing that tip blight and branch dieback diseases have in common is that they are mostly associated with plant stress and often occur under adverse environmental conditions such as temperature and moisture extremes (i.e., freeze or drought), pesticide damage (i.e., improper rate or host incompatibility) and nutritional disorders (i.e., deficiency or toxicity). In fact, some of these fungi are very much opportunistic, incapable of penetrating intact healthy plant foliage and must enter through wounds made by insects or injuries caused by ice or snow.

Examples include tip blight caused by Kabatina and Sclerophoma, which are both common in the early spring months on diverse conifers (i.e., junipers, pines, firs, arborvitae), causing the tips of young branches to turn chlorotic (yellow) and then necrotic (brown).

Other Related Diseases to Tip Blight

Here are a few of the other most common and deadly blight diseases to watch out for in the spring/summer months:

Phomopsis Blight

Another blight disease that appears in late spring and throughout summer, affecting many members of the cypress family, is Phomopsis blight. The fungal pathogen attacks young succulent shoot tips leading to twig cankers and often resulting in dieback, especially on plants that have been under stress due to drought or temperature extremes. This is one of the major diseases of junipers in both landscapes and nurseries. It reduces the aesthetic quality of plants and is often associated with transplant shock and failure in the landscape. Young, grafted nursery stock including seedlings are highly susceptible and affected hosts will often die.

Diplodia Blight

Diplodia blight (aka Sphaeropsis blight) is one of the most common diseases of two and three-needle pine tree species (i.e., Australian, Scots, Red, Mugo, Ponderosa). The disease can be devastating when trees are stressed due to water shortage, heat, compacted soil, shade, insect damage, and frost, making it a threat to pines through the majority of the year.

Although most severe on pines, the disease has been reported on other conifers including arborvitae, Douglas-fir, Norway spruce, Colorado blue spruce, noble fir, silver fir, cedars, and junipers. The most common symptoms are tip blight and death of the lowest branches, and the disease is more common during wet spring weather, which is highly favorable for spore production, infection, and spread.

Pestalotiopsis Tip Blight

One other common fungal tip blight disease that occurs on numerous trees and shrubs including conifers is Pestalotiopsis tip blight. Depending on the host plant there are many species of Pestalotiopsis associated with leaf spot, tip blight, twig dieback, and canker diseases. These fungi can be found colonizing and residing in healthy plant tissue as endophytes that will not cause disease until signals from the environment or host initiates the fungus to attack. This means that plants can appear healthy but are infected and will develop symptoms of disease when conditions are favorable. This can be problematic for nursery growers bringing in propagation material or for landscapers doing new installs.

How Can I Manage Tip Blight?

Management recommendations for all these fungal tip blight pathogens are generally the same.

·         Always purchase quality plant material that is pest and disease free. Starting healthy and using preventative measures requires fewer pesticide applications with lower rates as opposed to trying to control something already present.

·         The more favorable the environment is for the plant means there will be less stress and less stress means less disease. Most important is an attempt to minimize stress through ideal site selection and plant installation (i.e., the right amount of sun/shade, correct planting depth), proper horticultural practices (i.e., adequate water/nutrition, pruning), and judicious use of pesticides (i.e., follow the product label).

·         Prune only under dry conditions and use clean sharp blades to cut 2 – 3” into live wood to ensure diseased tissue is removed. All diseased tissue should be removed and discarded or burned. Tools should be properly sanitized using a commercial disinfectant such as Green-Shield® or Oxidate®.

·         Pruning should be followed with a fungicide application to protect freshly cut tissue and minimize the potential for reinfection. Products that are acropetal penetrants such as Azoxy 2SC and T-methyl are very effective as foliar sprays and should be applied in rotation for managing fungal tip blight pathogens.

Reach Out to Your Harrell’s Rep for More on Tip Blight

Managing diseases like tip blight is very tricky, but not impossible, and your Harrell’s Rep is here to help! Reach out for more recommendations, programs, products, and even diagnosis on your plants for a healthy and bright growing season.