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Use winter to wage war on weeds

Posted 10/21/2011

UNCE Specialist offers advice for getting a head start on next year’s weed invasions

For northern Nevadans, October is the end of the line for growing crops and time to put away shovels and hoes. But while most Nevada gardeners retire for the winter months, Area Extension Specialist Sue Donaldson is getting a head start on spring weed outbreaks, and offers her advice to others.

Fall rains can contribute to an exponential outbreak of weeds if winter annual seeds sprout. According to Donaldson, additional steps need to be taken in order to prevent the germination and growth of these garden invaders.

"The traditional method for controlling weeds is to physically remove them before they flower," said Donaldson. "While this works in many cases, sometimes problems are too big for mechanical controls, or the weeds are growing in areas where you just can’t pull them out, such as rock mulches. Then, you might consider using another tool, such as a pre-emergence herbicide."

While pulling weeds by hand before they flower eliminates the possibility of adult plants leaving seeds, there are other means by which weeds encroach on gardens. Wind, irrigation water, animal fur or droppings, soil amendments and vehicles can transmit weed seeds to gardens and other parts of a yard. In cases where weed seeds may be present in soil, the use of pre-emergence herbicides can stop the elongation of root hairs in sprouting seeds, killing them. However, Donaldson says gardeners must be strategic with how they use these products.

"Most (pre-emergence herbicides) will not control weeds that are already up and established or dormant, so timing is everything. If you want to decrease the number of winter annual weeds, such as cheatgrass, redstem filaree and mustards, next spring, you need to apply the product before fall rains result in seed germination."

When considering using an herbicide, start by reading the entire product label. The label will tell you how long the product will be effective after application, and will give any precautions about potential damage to adjacent vegetation. When applying the recommended amount to the area, be sure to spread the product evenly. Following the product directions, water in the herbicide using a sprinkler or hose. This usually means applying about a half inch of water.

During this process, take steps to be mindful of human safety. Pre-emergence herbicides can remain in soil for weeks or months, and can contaminate shallow groundwater if not used correctly. Always read the product label to learn how to use the product safely.

To guarantee success, Donaldson recommends leaving the targeted areas undisturbed, and to avoid planting seeds where pre-emergence herbicides have been applied.

"The herbicide must remain intact or weeds will grow through the gaps," said Donaldson. "If you drive through the area, or your dog runs across it, you can expect weeds to show up. Also, it’s not a good idea to use pre-emergence herbicides in areas where you plan to grow something from seed, as these herbicides do not discriminate among ’desirable’ and ’unwanted’ seeds."

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