Don’t Leave Your Best Bet On The Shelf

This week, I was browsing through the pesticides in a garden center when I overheard two ladies trying to figure out which herbicide to use on a particular weed.

Looking at the shelves of different brands and names, I could understand their dilemma. How do we determine which method is the best for controlling weeds, and if herbicides are used, which herbicide?

We need to start by familiarizing ourselves with the weeds in our garden. Weeds are usually divided into two classes - grasses and broadleaf (which include trees, shrubs and flowers). Since we’re familiar with grasses, we’ll direct ourselves to the broadleaf weeds. They are divided into three categories - annuals, biennials and perennials.

Annuals are plants that complete their life cycle in one year. There are summer annuals and winter annuals. Summer annuals include knotweed, pigweed, lambsquarter, ragweed and cockleburs. Their seeds lie dormant in the soil during the winter and germinate in spring. For best results, control summer annuals soon after they emerge in the spring.

Winter annuals include chickweed, shepherds purse, pennycress and cornflower. Their seeds lie dormant during summer months and germinate in the fall and over the winter. They set seed and die back during the summer. For best results, control these pests during fall or early spring.

Biennials complete their life cycle within two years. The first year they form a tap root and a clump of leaves resembling a rosette. The second year, they flower, mature and die. Examples include bull thistle, common mullein, common burdock and wild carrot. For best control, catch them during their first year of growth.

Perennials live more than two years - and some forever. They are the most difficult to control because of their persistent root system and seeds. Perennials are divided into two categories: simple and creeping.

Simple perennials are plants that spread by seed, cut root segments and crown buds. Examples are plantain, dock and dandelion.

Creeping perennials have roots that creep either above or below the ground. They include red sorrel, bindweed, strawberry mouseear chickweed, horsetail, Canada thistle and a grass, quackgrass. The creepers are the most difficult weeds to control. It takes repeated cultivation and/or sprays. Never let them go to seed and try to catch them in the seedling stage.

Once we have identified our weeds, we can determine our means of control. Mechanical control (digging, pulling etc.) is usually the preferred method, but sometimes chemicals are more effective.

That brings us back to the shelves of herbicides. How do we choose the proper herbicide?

Chemicals are usually divided into four categories: selective, non-selective, pre-emergent and ground sterilants.

Selective means just that: The chemical selectively kills out the broadleaf plants and leaves the grasses, OR it kills out the grasses and leaves the broadleaf plants.

Examples are Weed B-Gon, Lawn Weed Killer, Grass B-Gon, Ornamec, Hi-Dep and Weedmaster. The label will always tell you whether it kills grass or broadleaf.

Non-selective means the material will kill everything that it comes in contact with - both grass and broadleaf. Roundup and Kleeraway are good examples.

Pre-emergents do not kill the actual weed; they stop weed seeds from germinating. We apply pre-emergents to ground that has been cleared of weeds. Surflan, treflan, Casoron and dacthal are excellent examples.

Sterilants are used for permanent vegetation control in a given area - Triox or Noxall, for example.

Each of these products is formulated to be effective against certain weeds. The formulations are on the front of the label. The active ingredients are listed first, followed by the inert ingredients. The inert materials are not herbicidal but may improve the effectiveness of the active ingredients.

Hi-Dep, for example, is a 2-4-D product the same as Weed B-Gon. But Hi-Dep is more concentrated (indicated by the percentage) and it contains a sticker material to help penetrate the leaf surfaces of hard-to-control weeds. If you are trying to control dandelions, Weed B-Gon will work great. If you are trying to control knapweed, Hi-Dep would be the better choice.

For hard-to-control weeds in the lawn, perhaps you need a formulation that contains not just one active ingredient, but two or three. Lawn Weed Killer, for example, contains 2-4-D, MCPA and dicamba.

Controlling weeds can be an interesting challenge. Know the weed, know the proper time to control it and use the proper chemical. Ask if you aren’t sure, and READ THE LABEL.

Note: The WSU Master Gardeners will be hosting a free tour of the Duncan Gardens at Manito Park next Thursday, Aug. 10, at 6:30 p.m. Hear about the exciting new renovation of the gardens that will begin this month.

The following fields overflowed: CREDIT = Phyllis Stephens The Spokesman-Review