|
January
16, 2002
Salt
damage in the landscape and near roadsides is common. Each year, a
single lane of well-traveled highway can receive 40-80 tons of rock
salt per mile. Salt-weakened trees are more susceptible than healthy
trees to attack by insects and pathogens, and can also fall prey to
environmental tresses, such as drought, wind, and ice.
How Salt Damages Trees
Salt damages trees through two pathways: via airborne salt spray,
as on a busy highway, and via the soil. Salt spray that lands on a
dormant twig can enter the tissue through leaf scar and kill the dormant
bud.
When salt in the soil dissolves, it separates into sodium and chloride
ions. The ions act differently to damage the tree. In early spring,
the chloride ions can be taken up by the roots, enter the sap, concentrate
in the shoots, and prevent buds from opening. Later, they can be transported
to actively growing leaf margins, causing leaf scorch, curling, or
death.
Sodium ions use the same "chemical route" as necessary tree
nutrients. As George Hudler, professor of plant pathology at Cornell
explains, the sodium can "tie up the plant's shuttle system and
restrict uptake of magnesium and potassium, two chemicals that are
essential for making chlorophyll." Potassium deficiencies are
common in plants suffering from salt injury, says Hudler.
Salt in the soil can create a physiological drought. Brine near underground
tree roots can be a more concentrated solution than the sap in the
roots. The roots therefore can't take in water through osmosis. Water
is so unavailable to salt-stressed tree that they are actually dying
of thirst.
Diagnose a Salt-Damaged Tree
Salt spray damage can occur in trees that are up to fifty feet from
a fast moving, salted highway. Salt spray will damage exposed branches
more severely than branches covered by snow. Suspect soil salt damage
in trees that are near salted streets and sidewalks.
Conifers damaged by salt spray, show the greatest damage in early
spring. On branches facing the road starting from the tips, needles
become yellow or broken, and perhaps drop off. Soil salt can cause
the needles of conifers to take on a blue-green cast.
Deciduous trees affected by salt spray can develop tuft-like "witches'
brooms." Bunches of lateral branches grow to compensate for a
terminal bud that was killed by salt. Deciduous trees growing in salty
soil might have flower buds that don't open. Leaf scorch, whereby
margins of the leaf turn prematurely brown can arise in the spring
or during hot, dry weather. Foliage can be sparse, stunted, or yellow
and twigs can show dieback.
Spice up your options
People who maintain paved surfaces can choose from a range of products.
If you choose low-cost but toxic products, you might have to factor
in the replacement cost of future plantings.
Rock salt, consisting of 98.5% sodium chloride, is the cheapest and
most widely used of deicing agents, so for highway departments, it
is king. The biggest drawback? Corroding bridges and cars and damaging
tress. The long-range cost of rock salt damage could be 10-15 times
the initial cost.
Calcium chloride, an effective deicer, works best below 15 degrees
F. Eight times more expensive than rock salt, it tends to cake, making
spreading difficult. It reportedly doesn't damage plants but still
contains chloride, which could damage trees.
Potassium chloride is a naturally occurring material that is a fertilizer
and a food salt substitute. It also has the potential to harm plants.
Calcium magnesium acetate (CMA) is made from dolomitic limestone and
acetic acid (the main acid of vinegar). It poses few problems to plants,
but unfortunately, is expensive: a ton of CMA costs twenty times more
than a ton of rock salt.
Alternatives to salt, such as urea fertilizers, gravel, cinders and
ground peanut shells have proven effective in small-scale applications.
Homeowners could try a mixture of 3 pounds of urea to 50 to 100 pounds
of sand or cinders.
Keep trees out of the brine
Whatever your choice of deicing agent, especially if you've chosen
rock salt as the preferred option this winter, but mindful of the
following ways to minimize negative effects on your plants.
Cut down
Avoid salting when trees are active particularly in the fall and spring.
In late October an dearly March, many tress in New York are taking
of nutrients. A salt application could damage roots and prevent the
uptake of nutrients. Dormant trees are less likely to be harmed by
salt than growing trees.
Consult weather forecasts to determine when ice formation will be
problematic, and salt only when necessary.
Store and apply salt efficiently.
Erect a snow fence or guard to limit the amount of snow and salt reaching
plants.
Shovel salt-laden snow away from plants whenever possible.
Mound the root area with mulch or if a large open are is available,
plant the tree into a raised bed.
Keep the tree happy
Improve the drainage around tree roots. Poor drainage can create underground
pools of salty water that won't go away. Good drainage allows salts
which are highly soluble to be flushed through the soil.
Fertilize properly to keep your tree growing vigorously; a healthy
tree will manage stress more easily than an unhealthy tree.
If soils get salty
Leach salted areas thoroughly in the spring with water. If drainage
is good you can wash the salt away from the top 18 inches of soil
that the roots inhabit.
For a new landscape
Plant salt-tolerant species and avoid salt-sensitive species. Remember
that younger trees are more susceptible to soil injury than older
trees because they have fewer roots.
Plant intolerant species at least 30 feet from a salted surface.
This article was previous published in an issue of Gardening Gazette
and was provided by Acres ' N Gardens, Cornell Cooperative Extension
of Wayne County, November 2000.
Master
Gardeners are available all year round to answer your home, garden
and grounds questions. Please contact the Master Gardeners by calling
the Cooperative Extension office at 315.536.5123. To visit past articles
written by Yates County Master Gardeners visit
www.cce.cornell.edu/yates/mgindex.htm.
Cornell
Cooperative Extension Yates Association
Last updated: 1/11/02
top
|
