Effect of weed killer on galvanized steel columns

To control grass growth around the base of galvanized steel streetlight columns, maintenance contractors have traditionally used weed killers. While effective on grass some weed killers, or herbicides, can seriously affect the life span of the columns.

The most common weed killers, such as Roundup, contain a pelargonic acid which is a type of organic carboxylic acid. Pelargonic acid, like all organic carboxylic acids, is corrosive to many metals, including galvanised steel.

The Material Safety Data Sheet (MSDS) for Roundup warns against the contact of the herbicide with galvanized steel. The herbicide Roundup is water-based and the presence of an acid in the chemical formulation ensures that the corrosive compound leaches into soil affecting the galvanized coating of the in ground section of the light column.

As a result of using a weed killer such as Roundup there is accelerated corrosion of the galvanized streel streetlight columns in the areas that have come in contact with the spray. This corrosion can shorten the expected life span of the column, from the usual 25 years down to as low as 10 years. It can also cause the column to fail by breaking at the site of the corrosion.

CSP recommend the use of an alternative method of grass control around galvanized steel columns such as a mowing strip.

If a herbicide is used to control vegetation at the column base, the formulation should be assessed by a specialist to ensure that the chemicals contained are not corrosive to galvanized steel.

Truely organic herbicides do not contain harmful chemicals but, depending upon the application, they may be less effective than synthetic herbicides and therefore are usually used in conjunction with mechanical weed control practices.

For more information: email: cspcustomerservice@csppacific.co.nz or phone CSP on 0800 655 200