Early Diseases in the Landscape

Last year was extremely wet and rainy. We had double the average rain fall. While most believe this was good for plants and the water table, it is not so good for the spread of disease. Here are three diseases to look out for this spring on your woody ornamentals (aka trees and shrubs) These diseases are a direct correlation to wet weather patterns.

Needle Blight- Septorioides

Needle blight most often develops as a needle tip blight where the base of the needle remains green. Over time, the entire needle becomes yellow-brown to brown and is prematurely shed from the canopy. This blight is prevalent in Eastern white pines, mugho pine, and Austrian pine. Like many needle blight fungi, S. strobi produces large volumes of spores that are blown and splashed to nearby branches and trees during wet weather. Climate studies have shown the northeastern U.S. is experiencing an increase in the frequency and amount of precipitation during the months of May, June and July, which is helping to fuel outbreaks. This coincides with the period of active needle and shoot development for many pines in the region. These immature needles are most susceptible to infection during periods of wet weather or high humidity. Once infected, symptoms may take many months to develop and may not be visible until the following spring, nearly one year after infection.

Active management for any needle blight pathogen of conifers should focus on protecting the current year's foliage from becoming infected in the late spring and early summer. Pruning of heavily diseased branches, especially those in the lower canopy, and removal of discarded needles can help to reduce disease pressure. Forest studies have shown a direct correlation between thinning density and needle blight severity. When diseased pines are provided more space, light and airflow, needle blight severity decreases. Please see an arborist if fungicide needs to be applied to large trees.

Edema- not a disease but worth noting.

Ever have one of those days when you feel a little sluggish and bloated? Well, your plants can have the same problem -- they retain water just like people do when conditions are not right. Edema in plants is not a serious disease and it's not a symptom of a bacteria, virus, or insect infestation. Edema on broadleaf evergreens such as Rhododendrons, Boxwood and Andromeda is caused by too much water taken up by the roots faster than the plant can process it. This is very stressful to the plant and presents itself by pushing tissue outwards underneath the leaf.

There is nothing to do to prevent this from happening other than ask Mother Nature to disperse the rains more evenly throughout the year :)

Cedar-Quince Rust

The juniperus family is the host and infects shrubs like Serviceberry, Hawthorn, Apple/Crabapple, Cotoneaster and Quince.

On Juniperus, the pathogen produces orange- to red-colored pads of fungal tissue (known as telia) that swell from infected stems and branches in the spring (late April to late May). After periods of rain, the pads swell and become orange, gelatinous masses of spores that are dispersed by wind and splashing rainwater. The spores (basidiospores) produced on Juniperus disperse on air currents to infect nearby hosts. By mid summer the effects show by stem cankering, leaf spots and canopy die back.

Rarely are fungicides recommended to control cedar-quince rust, mostly because none have been found to be very effective. This is due, in part, to the long period of time in which spores can disperse to infect either host, both in the spring (Juniperus to host) and in late summer and early autumn (host to Juniperus). Prune out and discard any girdled stems and branches that develop and prune to promote air flow and sunlight, especially in the lower canopy. Avoid planting hosts in close proximity to Juniperus. In areas where disease severity is high, plant resistant species or cultivars to avoid exacerbating disease pressure.