Each spring there is one perennial weed species that dominates the urban and rural landscape like no other. It has a beautiful yellow flower that looks good but is always growing where it is not wanted. The lawn or sometimes crop fields. Yes, I am talking about dandelion.
Like clockwork, many home and property owners go to their local gardening stores to purchase a product that can eliminate the dandelions. In purchasing products when spraying on the plants which often appear to be control and/or eliminate.
However, that never seems to be the case. The apparent control of dandelions is only temporary, and the home or property owner has to continue this pattern year in and year out with frustrating results. And as usual, the dandelions are back again the following spring.
Is there a better way to control perennial weed species?
Yes, and it starts with a good understanding of plant biology. Knowing a little bit about the biology of plants, especially life cycle and reproduction characteristics. Helps in devising the most appropriate management techniques that will control the problem plants.
Plant lifecycles
- Plants with an annual lifecycle will germinate from seed and grow rapidly during the spring and summer. Eventually, producing new seed in the fall prior to dying off. With this knowledge, the target of control is to eliminate weed seed production. Control measures that can be design to prevent plants from producing seed is the primary strategy uses to manage weeds with an annual lifecycle. Furthermore, annual weeds are considering to be easier to control than either biennial or perennial weeds.
- Plants with a biennial lifecycle will typically germinate from seed, spend a year growing veg, and go to seed in the second year. Biennial plants require a period of cold weather, or vernalization. To prepare them from reproduction and are more challenging to control than annual weed species.
- Plants with a perennial lifecycle will emerge primarily from vegetative structures such as a deep root system, underground stems, bulbs, or other vegetative structure. Many perennial plants produce seed but rely more on their vegetative structures for reproduction and spread.
Okay, now that you know something about plant lifecycles, how can you use this information to control weeds? By understanding how to minimize weed seed production and vegetative reproduction.
Minimizing weed seed production
- Annual and biennial plants produce numerous seeds. It allow the plant species to establish itself within the habitat and spread to new habitats.
- Plants that rely on seed production for their survival. Also, spread within a habitat use much of their resources to produce seeds that can persist in the soil. This characteristic is refer as seed longevity.
- Seeds produced by most annual, and some biennial plants will not germinate uniformly even when conditions are favorable. Hence having the capacity to spread their germination over time. This characteristic is known as seed dormancy, and it is why there is the saying that ‘one year of weed seed production leads to many years of misery’ (Anon.).
- Perennial plants can reproduce by seed, but they invest far fewer of their resources into the production of seeds. Therefore, perennial weeds produce fewer seeds which have less dormancy. Perennial weeds, and some biennial weeds, invest most of the resources for reproduction in their vegetative structures.
Minimizing vegetative reproduction
- Plants that rely on vegetative reproduction have either biennial or perennial lifecycles.
- Typically, the vegetative structures used for reproduction by biennial and perennial weeds are usually underground. For example, dandelion has a deep root that serves as its reproductive structure. Other types of underground vegetative structures of perennial plants include, rhizomes, bulbs, and corms.
- Like most perennial weeds that reproduce by seed, dandelion has more than one strategy for establishing and spreading. However, preventing dandelion from producing seed does not halt its establishment. It is the root where the majority of resources for reproduction go.
How to target, and control underground vegetative structures of perennial weed species
First, you need to know which vegetative structure of the perennial weed species is the primary reproductive structure, e.g., for dandelion, it is the root.
Second, you need to know when the vegetative structure is most vulnerable, e.g., with dandelion, following a night when the temperature is below 32 F (0 C), the weed channels all of its resources from leaves to its root in preparation for winter.
Third, you need to select the best herbicide that will be translocated to the vegetative structure which will provide the best control of the perennial weed species. In this case, a systemic herbicide will be the best option, e.g., 2,4-D, dicamba, and glyphosate.
Fourth, you need to select an appropriate adjuvant that will enable the herbicide to spread on the surface of plant leaves and be retained long enough to penetrate the leaf surfaces. For example, Cide Kick™ or Cide Kick II™ are nonionic wetting, spreading, and penetrating agents that can be added to a mixture containing a systemic herbicide to improve the control the targeted perennial weed.
Fifth, make sure you read the herbicide label and follow all recommended instructions to get the best control of perennial weeds.
Sixth, where possible use the rosette method when targeting perennial weeds for control.
The Rosette Method
- Germination and emergence of biennial and perennial weeds is follow by the development of above ground
- structures that requires an environmental cue, in this case a season of winter (a process known as vernalization), to enable the species to reproduce. The above ground structure is refer as rosette.
- A rosette is a circular arrangement of leaves or of structures resembling leaves. In flowering plants, a rosette usually sits above the soil and is commonly refer to as a basal rosette. The formation of a basal rosette is a common feature among biennial plants and some perennials in the fall season.
- Perennial weeds that form a basal rosette are easier to kill in the fall than in the spring. Once they start growth in the spring, perennial plants develop rapidly with one goal which is to reproduce. For example, dandelions grow rapidly during early spring, produce those distinct yellow flowers that enrage many a homeowner, and which mature quickly and go to seed.
- Many people assume that applying herbicides to dandelions before they go to seed is the best approach. However, even if plants appear injured after herbicide application. That effect is merely temporary because the major reproductive part of the dandelion plant. Which is the root, has not been control.
Monitoring the extent of control of perennial weeds after herbicides have been applied using the rosette method will help determine if follow-up treatments will be necessary in the following springs before plants start to flower.
References
- Besanion, T. 2018. Fall Control of Perennial Weeds with Herbicides. Plant & Pest Advisory. Rutgers Cooperative Extension. https://plant-pest-advisory.rutgers.edu/the-season-is-over-for-blueberry-but-not-for-controlling-perennial-weeds/ (Accessed, Oct. 25, 2021).
- Lingenfelter, D. and W. S. Curran. 209. Biennial and Perennial Weed Control is best in the fall. Penn State Extension. https://extension.psu.edu/biennial-and-perennial-weed-control-is-best-in-the-fall (Access, October 25, 2021).
- North Dakota State University Extension Service. Perennial Weed Control. https://www.ag.ndsu.edu/publications/crops/north-dakota-weed-control-guide/resources/102-105-perennial-weed-control.pdf (Accessed, Oct. 25, 2021).
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