by Sharon Morrisey, Consumer Horticulture Agent in Milwaukee County
In fall, weeds’ natural biology changes gears from growth mode to storage mode and they start moving carbohydrates into their roots for winter. By applying herbicides to weeds at this time, you trick them into doing some of the dirty work for you. They will carry the chemicals into their roots along with their carbohydrates where these products kill the plants, roots and all. Shorter days and a string of several evenings with temperatures in the 30s are the signals for plants to shirt to storage mode and for you to get out your sprayer.
Choose your weed killer carefully. Although some products can tell a dandelion from a blade of grass, they do not distinguish between that dandelion and your prized dahlia. That is why it is so difficult to use broadleaf herbicides in mixed flower and vegetable beds where the weeds and your precious plants are all broadleaves. Other herbicides kill everything green and living, dandelions, dahlias, and your lawn alike. Making this mistake for spot treating your lawn leaves dozens of little round dead spots where you sprayed.