Managing weeds, particularly with chemicals, is more complicated than most people realize. A neighbor was spraying cheatgrass recently. He didn’t realize that with the cheatgrass already going to seed and turning brown, his use of chemicals was ineffective and costly in time and money. The seeds will still spread, and he will still have to mow or weed-eat the dead plant residue. A better course of action would have been to just weed-eat or even pull by hand in the first place. The best strategy would have been to apply a pre-emergent herbicide that targets cheatgrass (not all pre-emergents work on all weeds) in the late fall to early winter before the plants germinated.
To manage weeds effectively, identify the weed to be controlled and understand these important concepts. Weeds are grasses (such as foxtail, saltgrass, cheatgrass, even lawn grass to name a few) or broadleaf plants (dandelion, tall whitetop, tumbleweed, etc.). Some plants, such as cheatgrass or redstem filaree, are annual weeds that grow from seeds and live one year. Others are biennials, usually forming a rosette of leaves the first year and flower stalks and seeds the second year. They include mullein and many thistles. There are also perennials, such as tall whitetop, Russian knapweed, saltgrass, bluegrass, etc., which live for three years or longer.
Annuals are best managed before they germinate or when they are young. Biennial management usually occurs during the rosette stage.
Because of their persistence, perennial weeds are more challenging to manage. Many will propagate not only from seeds, but also from root or stem pieces. Timing perennial weed management varies depending on the weed. Some are best controlled at seedling stage, others at pre-bloom or post-bloom, with still others somewhere in between.
Be knowledgeable about herbicides. Is an herbicide non-selective (kills not only weeds, but also desirable plants, whether grasses or broadleaves); or is it selective for either grasses (this includes desirable ones) or broadleaf plants? Does it kill weeds prior to germination (pre-emergent) or must weeds be actively growing (post-emergent)? Is the herbicide translocated (i.e. Roundup — apply it and it moves through the entire plant killing both leaves and roots) or is it a contact spray, killing the top of the plant, but not the roots? Is an herbicide a soil sterilant? Be leery of sterilants; they often kill nearby plants and contaminate water, both on and off a property.
Read and understand the entire label before using an herbicide for the safest and most effective results.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.