Galls & Burls Explained…Sort of

Trees and other woody plants often have large or interesting swellings on their trunks or branches.   The cause is often difficult or impossible to determine.  Possible causes include fungi, bacteria, insects, mechanical or environmental injury, or genetic mutation.  The terms gall, tumor and burl are commonly applied to describe these abnormal swellings. 

Galls and tumors can be any size or shape and may occur on both woody and herbaceous plants and plant parts.  The swelling occurs as cells divide more rapidly than normal (hyperplasia) and/or due to excessive cell enlargement (hypertrophy).  Burls are generally considered to be large woody swellings that are basically hemispherical in shape.  They often bear many buds and sometimes sprouts.   The burls of black walnut, coast redwood, sugar maple and black cherry are highly prized by woodworkers for their beautiful swirling or ‘bird’s eye’ grain.   This relatively small burl from an apple tree (cause unknown) has an interesting surface pattern and interior grain showing bud traces.

Burl from an apple tree trunk.

 

Tiny brown lines are bud traces.

An individual tree may have one or many swellings.  On this maple tree, the many swellings are of unknown origin.  Often, a tree with large or numerous galls will decline earlier than a tree without them. 

The most common bacterial gall disease is crown gall caused by the bacterium Agrobacterium tumefaciens.   This soil-borne bacterium enters the roots of the host plant through wounds caused by planting, cultivation, frost heaving, insects or nematodes.  The bacteria, upon attaching to the plant cell walls, send DNA that causes production of plant growth hormones into the plant cell where it is incorporated into the plant cell chromosome.  Affected cells begin to multiply at an uncontrolled rate, resulting in visible tumors within 2-4 weeks.   More than 600 plants are susceptible to crown gall.  One of the most common, where galls occur on both roots and stems, is Euonymus, shown in the photo. 

Crown gall of Euonymus.

 

Examples of galls caused by fungi include azalea gall (Exobasidium vaccinii), black knot of plum and cherry (Apiosporina morbosa), and Fusiform rust of pine (Cronartium quercuum).    More information on these diseases is available by clicking on the name of the disease. 

 A close up of a leaf gall on azalea . (Plant Disease Diagnostic Clinic, Cornell University)

Black knot of plum and cherry.

 

 Fusiform rust (USDA Forest Service – Region 8 – Southern Archive, USDA Forest Service, Bugwood.org)

Insects and mites cause some very interesting galls on leaves as shown in the photo.  These usually cause little damage to the host plant or tree and control measures are not normally recommended.  A new theory is being explored by scientists that the swellings associated with these arthropods may in fact be caused by bacteria transferred to the plant tissue during feeding.   Fascinating! 

Hickory gall phylloxera.

 

Galls can be caused by cultural, mechanical and environmental factors including graft incompatibility, wounding, and freeze injury.   Galls on some conifers that vary from small to huge (several times wider than the trunk) are thought to originate when the trees are young seedlings from a single cell and enlarge for many years.  Low temperature injury is suspected, but not proven, as the cause. 

J Allen

 

Winter Salt Damage on Woody Plants

Ladybug Blog Winter Salt Damage on Woody Plants February 10, 2009

Last week on February 2, 2009 Punxsutawney Phil saw his shadow. This date for winter weather prognostication has its origin in both European folkloric traditions and the Christian celebration of Candlemas. Six more weeks of winter was to be expected if Candlemas day was sunny. The same weather pattern was predicted if a hibernating animal, initially a hedgehog, was frightened by its shadow. This belief was brought to this country by German settlers during the 18th Century. They adopted the groundhog for their predictions as there are no native hedgehogs.

Be it startled ground hogs or terrified hedgehogs, New Englanders can usually expect at least six more weeks of winter.

 

This winter has been especially trying, bringing us freezing temperatures and weekly snow storms since mid December. With the storms come the snow plows and deicers. Starting in the winter of 2006-2007, the State of Connecticut implemented a new snow and ice control program, an all-salt regime using sodium chloride in solid and liquid form, in combination with liquid calcium chloride. Unfortunately the de-icing salts used during the cleanup efforts to maintain ice-free roadways, driveways, and sidewalks can cause severe damage to woody trees and shrubs.

 

Woody plants growing along roadways or side walks may be impacted by direct contact of deicing salt spray and by chemical changes in the soil due to a build up of salt ions that accumulate in the soil and are eventually absorbed by the plant roots. Salt ions can injure plants at any time, but late winter applications may accumulate and be more damaging since there is less time for winter snow and precipitation to leach away the salts.

 

Salt damage increases with the plant’s proximity to the road and is more severe on the side of the tree or shrub facing the road. The chlorides ions in these salts can be absorbed by roots and leaves resulting in the accumulation of toxic levels. Salt damage symptoms include marginal scorch of leaves, tip burn and dieback of buds and stems, foliar browning or the death of entire leaves, needles or twigs. In addition plants weakened by excessive salt exposure can be more susceptible to disease and pest problems.

 

These are some methods that can be employed to remedy the impact of deicing salts on trees and shrubs:

Wash salt spray off plants with fresh water as soon as possible after salt exposure.

Flush out excess salts from the root zones. This can be done as soon as the ground is no longer frozen. Repeated applications may be necessary.

Construct a physical barrier made of plastic, burlap, or snow fencing , or a berm of soil between the pavement and the plants

Plant salt tolerant plants in high risk areas.

Maintain vigorous growth in plants.

 

 

 

LA

Leaf scorch on maple

Winter salt damage on white pine

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