Canada thistle in peach orchard

Kristen Obeid, OMAFRA weed management specialist – horticulture, offers timely advice for post-harvest treatment of problem weeds. She indicates that the spectrum of weeds in orchards and vineyards is changing.

Alion herbicide is a very useful tool for weed management in orchards and vineyards in Ontario, providing strong residual activity on annual broadleaf and grass weeds. In some cases, growers who have been continuously using residual herbicides such as Alion, may be starting to see an increase in perennial and biennial weeds such as Canada thistle, common mallow, wild carrot and curled dock to name a few.

“This is an example of a species shift and can occur when herbicides that are very effective at controlling certain weeds, such as annual weeds, allow an opportunity for other weeds -- in this case perennial and biennial weeds -- to become more prevalent,” she says.

In these situations, she advises identifying which weeds are present in the orchard or vineyard so they can be properly controlled. Management options may include using spring or mid-season burndown chemistries such as Roundup herbicide or Ignite SN herbicide; or may involve alternative chemistries such as Lontrel 360 herbicide or 2,4 -D. 

Post-harvest fall applications of Lontrel can be an effective management tool for thistles and research suggests would have some activity on wild carrot as well. Using 2,4-D post-harvest can be a useful tool against dandelions.

“In 2019, wild carrot seems to have flourished in many perennial crops, probably due to this year’s weather conditions,” Obeid says. “Alion continues to offer strong residual control of many annual broadleaf and grass weeds, however incorporating additional chemistries into an Alion program where needed -- to protect against perennial and biennial weeds -- can keep your farm looking its best.”

Source:  Kristen Obeid, OMAFRA weed management specialist – horticulture.