Valley Grows: A fungus is among us

I began research on boxwood shrubs as they are a big part of any formal landscape. They are used for boundaries, defining different areas and beautiful hedges. They are used for holiday decorations, like wreaths, bouquets, etc., to bring that rich deep green into homes in winter.

But as the keeper of boxwoods, you need to be informed to maintain healthy, thriving shrubs that will live for many years. We have several issues affecting our boxwoods these days. My aim is to help you investigate any evidence of disease, pest, and/or problems of your plants.

Boxwood blight is a fungus Calonectria pseudonaviculata usually transported from nurseries. In 2011, it was found in the United States, and is now in 20 states and parts of Canada. It attacks boxwoods, and Japanese and Allegheny pachysandra.

The leaves have brown spots that coalesce into dead areas on the shrubs.

Leaves drop within a few days. Boxwood blight can overwinter in plants and leaf litter. Water splash (rain or hose) can contribute to its spread. Plants diagnosed must be destroyed, including leaf litter and roots. Double-bagged plants can go into the garbage or burned if able. Never compost them.

Volutella blight (Volutella boxii) manifests like winterkill. In the winter, plants are susceptible as winds dry the dormant plants, and with frozen ground, the plant cannot take up moisture to replenish the loss. Thus the plant looks desiccated.

In humid, moist conditions, this pathogen produces a pink to salmon colored mass of spores.

Macrophoma Leaf Spot (Macrophoma candollei) causes dark leaf spots and straw colored leaves. Easily identified black fruiting bodies are found on dead or dying leaves.

Phytophthora root rot (Phytophthora spp.) is found in heavy clay soils that are constantly wet. The branches wilt and die back with areas of pale green to yellow, then brown leaves. Beds must be well drained, and do not overwater.

Fusarium canker (Fusarium spp.) is found in tips of branches (note that boxwood blight is found on base or middle of branches). The dark brown to black streaks run along branches that coalesce over the whole area.

Boxwood leafminer (Monarthropalpus buxi) consume the centers of leaves with markings that look like tunnels. These then turn brown.

Boxwood Psyllid (Pyslla buxi) are small green insects covered with waxy white secretion that covers their bodies to protect from parasitoids and pesticides. Eggs overwinter and hatch to feed on spring buds. The leaves yellow and curl, where psyllid nymphs hide.

An accurate diagnosis is vital to have healthy shrubs. Trim any suspect plant tissue, to include healthy to transitional tissue to dead tissue, dry tissue wrapped in dry newspaper, then wrap in two layers of plastic bags. Bring this to the extension office for a clinical diagnosis.

For details and pictures of boxwood blight, go to http://go.osu.edu/boxwoodblight.


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