The Time is Now to Apply Pre-Emergent Herbicides in Asparagus

Kristen Obeid, OMAFRA, Weed Management Specialist – Horticulture

Asparagus growers are lucky because they have a large number of herbicides available to control weeds. This sometimes causes confusion. Most other horticulture producers would love to be confused by which herbicide to choose! The best rule to follow is: only apply herbicides in the very early spring before asparagus spears emerge or after all of the harvesting has been completed.

Depending on which part of the province you are in, asparagus spears will likely emerge soon especially with the warm weather coming. Therefore, get your herbicides on now to make sure you follow all of the pre-harvest intervals (PHI) outlined on the herbicide labels. This is particularly important with the food safety requirements of the retail chains.

Controlling weeds that are present in the field requires the use of a post-emergence herbicide. If you do not have any emerged weeds you could apply a pre-emergence herbicide, based on your weed problems in previous years. Before selecting your herbicide make sure you identify the weed problems in your field and determine the herbicide that will best control those weeds. For example, if you have a yellow nutsedge problem you should use Sandea; if you have a wild buckwheat and nightshade problem you should use Authority; if you have velvetleaf and nightshade you should use Callisto; if you have your standard annual grasses and broadleaves you can stick with Lorox + Sencor.

Unfortunately, many of the most widely used herbicides that are best matched to the weed mixes found in asparagus fields have relatively long PHIs. Make sure you read the labels carefully. If there is a sudden turn in temperatures with several days above 80^oF you will need to select a herbicide with a shorter PHI.

NS – not stated

*Early spring or after harvest

**May be used as a stale-seedbed technique – applied before direct seeded or established asparagus emerges