Weed of the Week

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Anyone see these really tall and slender weeds as you are driving around town? Or maybe you have some at the end of your driveway or growing out in your field? These common weeds are called horseweed/marestail (Erigeron canadensis) and dog fennel (Eupatorium capillifolium). Here is what you need to know about these weeds and ways to control them. 

images of tall weedsHorseweed is a winter annual weed in the aster family that can be found in waste areas, turf, roadsides, etc. It usually germinates in late fall and early spring, forming a small rosette of hairy leaves. In spring, the weed grows straight up and can get anywhere from 3 to 6ft tall. 

Horseweed has a taproot and anchoring fibrous roots so pulling them out by hand can be difficult. They can also grow back from damaged stems, so be sure you pull all plant parts up if you are hand weeding. Marestail also forms A LOT of flowers, which can produce A LOT of seeds if you allow it to do so. Therefore, try to control it when the plant is small (preferably in the rosette stage and ESPECIALLY before flowering) if you don’t want them to be a bigger problem next season.

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image of tall weedBest options for control are pre emergent broadleaf herbicides. Horseweed in many areas has developed a resistance to the chemical glyphosate (Roundup), so applications of 2,4-D, dicamba, glufosinate, or paraquat at that young growth stage is best. A great cultural practice that also helps is to maintain a thick, healthy lawn. That means, fertilizing at the right times at the right rates, mowing at the correct height, good watering techniques, etc. 

Dog fennel is an herbaceous perennial weed that is also in the aster family. It doesimage of tall weed well with many growing conditions and is especially drought tolerant, growing in fields, waste areas, roadsides, et. This weed is similar to horseweed in that it spreads rapidly from seed, can re-grow from broken stems, and can reach 3 to 6ft tall. Dog fennel has very thin, wispy, and deeply dissected leaves (kind of looks like a carrot seedling). I often think the best word to describe it is “fuzzy” when looking at the overall plant. These leaves are very soft and have a smell to them when crushed.

image of tall weed
Keys to management of this tall weed are good turf management, like those suggested for horseweed. Applying a pre-emergent herbicide containing isoxaben can reduce large amounts of dog fennel in lawns and landscape beds. Post applications of herbicides with active ingredients like 2,4-D, Mecoprop, or Dicamba and should be applied when weed is young and small.

As always remember that when using chemicals, please be sure to read and follow all labels and instructions! If you need any help or have questions about how/when to apply, or which chemicals you can use and where, just call our office (828-632-4451). We will be happy to help!

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