Noxious weed life cycles

Noxious weeds can be annual, biennial or perennial plants. The plant life cycle is an important consideration when deciding how to best control noxious weeds.

Annual weeds have a life cycle that lasts only one year. They grow to maturity, produce seed and die in one season. Annual weeds often regrow in the same area due to seeds that drop and germinate the next year, starting the life cycle again. Annual weeds usually have a less vigorous root system than biennial or perennial weeds and are easier to control.

Biennial weeds take two years to complete the life cycle, while perennial weeds live for more than two years. Perennial weeds come back year after year to flower before going dormant again in the cold winter months. Due to their extended life cycle, perennial weeds often have a much hardier root system than annual or biennial weeds.

Just as there are varied life cycles for weeds and other plants, there are various control methods that can be effective. Many times a combination of mechanical, cultural and chemical control methods is what it takes to eradicate, or greatly reduce, a weed infestation. The control method best suited for your situation takes into consideration the kind of weed and the stage of growth. Another important consideration is surrounding vegetation, such as trees and shrubs, which can be negatively impacted by certain chemical applications.

Mechanical control methods can be very effective against annual weeds, provided that weeds are removed and bagged prior to seed set. If seeds have already dropped, removal of all above ground plant parts will not prevent seeds on the ground from germinating the next growing season. A combination of plant removal and the application of a pre-emergent herbicide can be helpful for annual weeds. The pre-emergent herbicide must be applied early the next growing season before seeds germinate.

Cultural control methods can help keep weeds from becoming established. These methods include having a strong stand of grass or growing other competitive, desirable vegetation.

Important aspects of chemical weed control for weeds of all life cycles include timing of the application, use of the proper herbicide for the target weed and assurance that equipment is properly calibrated to get the most from the application. When using pre- or post-emergent chemical control methods, you must carefully read and follow all instructions on the herbicide label. The importance of understanding the herbicide label cannot be overstated – it is paramount to safe and effective treatment of the problem weed.

If you have questions about noxious weeds or need help identifying a plant, please feel free to call our office at (509) 754-2011, Ext. 4710, or visit our website at www.grantcountyweedboard.org.