Originally Published In The Deseret News -- Wednesday, September 28, 1994
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-Remove Annual Pests First, Then Kill Pesky Perennials By Destroying Their Roots.
The last thing a gardener wants to hear about in the fall is weed control. In fact it is generally the last thing a gardener ever wants to hear about. Nevertheless every good gardener gives weeds their due or they will end up destroying the garden. Fall is an excellent time to address many aspects of weed control. Pesky weeds that have been bothering you all summer long can finally be dealt with as the temperatures cool and gardens stop producing.
It is a sad horticultural fact that thousands of weed seeds exist in every cubic foot of topsoil. This soil seed reserve accounts for the seemingly endless supply of annual weed seedlings that appear whenever you work soil for planting. Weed seeds remain until air, light and moisture are favorable for germination. Removing or killing the seeds is impractical in most situations, so we must suppress them or wait until they germinate. Then we can go on the offensive.
If you have gotten behind on your weeding, get out and pull any remaining annual weeds. Any that have formed seeds go directly to disposal, not into the compost pile. After seed heads are removed, the rest of the plant can be tilled back into the ground. Next, declare war against the perennial weeds that grow year after year. Although their tops die back, the roots live and return to infest your garden the following year. Knowing about the growth habit of these plants helps you use that knowledge to help control these lurking monsters.
In the fall perennial plants extract the proteins and minerals from the leaves and move them down into the roots. These are stored throughout the winter. They provide energy for the plant to send up new shoots the following spring. Fall is the preferred time to attack perennial weeds.
The real secret of controlling deep-rooted perennials is to destroy the roots. Perennial weeds are divided into two categories. Simple perennials have a single root and reproduce by producing seeds. These can be controlled by digging them out. It is difficult to get down and remove all the roots on some large, simple perennials, but complete removal is an effective control.
The more difficult weeds are creeping perennials. These produce horizontal stems that grow above or below the soil and form new plants at each node. Some of our most difficult weeds are reproduced this way. Field bindweed or wild morning glory, Canada thistle, whitetop and quackgrass are all sinister plants in this category. Digging is often detrimental when controlling these plants. The roots may extend over 5 feet into the soil and spread in all directions for many feet. Digging and severing the roots simply creates more plants and makes control even more difficult. These weeds must be controlled by excluding sunlight, competition or by using herbicides.
In the vegetable garden, the attack should begin as soon as frost damages the annual plants or temperatures drop below 40 degrees Fahrenheit at night. Clear away plant debris that may interfere with spray operations and decide which weeds are your targets. Broadleaved weeds can be controlled by using Trimec or other broadleaved herbicides. Grassy weeds are best controlled using Roundup (glyphosate). A mixture of the two is effective against both grasses and broadleaved plants. Carefully mix the materials according to the label directions and add an extra spreader sticker so the material remains on the leaves until it is absorbed. Spray the weeds so that the foliage is thoroughly wet but avoid using excessive amounts of herbicide. Mixing a chemical stronger than is recommended actually reduces the weed control. Excessive chemical burns off the top without translocating the herbicide down to the roots.
In turfgrass areas it is important to distinguish between the two different weed problems. Perennial grasses are controlled by using Roundup. This also kills any desirable grasses, so treat where only the weeds are growing. Broad-leaved weeds can be selectively removed from turfgrass by spraying with Trimec or related products.
It is important to use other cultural methods to help keep the weeds in check. Fertilizer is essential to help turfgrass out-compete broadleaved weeds. A good fall fertilizer is more beneficial to turf than fall weed control. In the garden, an aggressive attack against the newly emerging seedlings next year is equally important. Mulches are always a good idea, as they act as smoothing agents. Use landscape fabric in shrub areas to help suppress these difficult weeds.
As you approach weeds, the nemesis of all gardeners, don't be overwhelmed. Weeds have always been and will always be in your garden. Your challenge as a successful gardener is to suppress and control them. Use mechanical, cultural and chemical methods that give garden plants the upper hand. Weed control has always been and always will be one of the secrets of a successful garden.
© 1998 Deseret News Publishing Co.