Rain, rain go away…come back next month

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Aug 11, 2013. Courtesy leaf (Daphniphyllum himalaense ssp. macropodum) shoots (left) and shrub succumbs to root rot in the SC Botanic Garden.

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So, having experienced the driest of times, I’m now facing the wettest of times. What’s wrong with too much water? The SC Botanic Garden in Clemson experienced the wrath of 8 inches of rain that fell late Friday night into Saturday morning (July 12-13).  This torrential downpour was bookended by 20 inches of rain that fell 10 days before and rain that continued to fall almost daily afterwards.  As a result of the erosive forces of rainwater,  the SC Botanic Garden sustained $200,000 of damage. The cost to repair all of the damage from the rains is estimated to exceed $500,000.

This summer our waterlogged soils have contributed to a number of large trees toppling-over because of their insecure footing. Trees that survived past years’ droughts sustained root damage and become especially vulnerable to falling. Sadly, a magnificent, 100-year-old bur oak (Quercus macrocarpa) on Bowman Field on the Clemson University campus—coined the “hammock tree” for the many students who caught some shut-eye in its boughs—fell around 3 o’clock on a quiet, perfectly calm afternoon.  When I examined the root system of the tree to determine the cause of its failure, I was reminded of the importance of periodic inspections.  I wrote about do-it-yourself tree inspections in my July 22 entry (“A routine check-up of trees saves lives and property”).

Finally, these wet conditions have led to an increased occurrence of root rots. Various fungi fall under this category, including Phytophthora species, Rhizoctonia species and Pythium species. In the Southeast Phytophtora (means “plant destroyer”) is often the most common culprit, These deadly waterborne fungi attack a wide array of plants, including dogwood, deodar cedar, Fraser fir, white pine, and many others.

These fungi are often found in wet or poorly drained sites; however, they’ll also attack plants in moderate to dry sites if they’re planted too deeply.

Root rot symptoms include wilting, yellowing leaves. It may appear on a few branches or affect the entire crown.  Scrape the bark near the crown and look for a reddish-brown discoloration where the fungus has moved into the stem.

Examine the roots. The “outer skin” or cortex of the root can be slipped off easily like the paper-covering from a straw, leaving behind the threadlike core or stele (conducting tissue). Slice it open: a root rot-infected root is reddish-brown inside instead of healthy white in color.

When symptoms are evident, fungicides are often ineffective in controlling this disease. Here are some tips to avoid root rot disease:

1. Avoid planting in poorly drained sites.

2. Improve drainage in heavy clay soil by planting in slightly raised beds, or add organic matter such as composted pine bark prior to planting. Alternatively, raise the planting site by mounding the soil. This raised area will prevent the occurrence of “wet feet” or standing water.

3. Never plant shrubs or trees deeper than they were planted at the nursery.  Prior to planting remove soil from the crown to expose the root flare and the uppermost structural roots.

3. Finally, select plants that are highly resistant to root rot.  See “Suggested Plant Species for Sites with a History of Phytophthora Root or Crown Rot.”

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