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Futures

Managing weeds in the fall

10/01/2020
Managing weeds in the fall

By Jason Migchels CCA-ON, CCS, 4R NMS
Crop Sales Specialist
Wanstead Farmers Co-operative
AGRIS Co-operative

Every year we run into a problem with weeds throughout the growing season. Often on winter annuals and perennials, we are dealing with some big weeds in the spring that are hard to control. Some of these weeds we can gain better control if we start in the fall.

Fall applications of herbicides effectively control the most common weeds that I run into:

  • Dandelion
  • Sow thistle
  • Canada thistle
  • Chickweed
  • Fleabane
  • Wild carrot

Dandelion flowering plant.jpg

Dandelion

dandelion_seedling.jpg

Dandelion

Sow Thistle flowering plant.jpg

Sow thistle

Sow Thistle seedling.jpg

Sow thistle

Canada Fleabane seedling.jpg

Canada fleabane

Canada Fleabane flowering plant.jpg

Canada fleabane

canada_fleabanef2_HairySeedlingLeaves.jpg

Canada fleabane

The herbicide application you use in the fall will be determined by the crop you plan to grow in 2021. If you are growing wheat in the fall and you want to grow clover in the spring, a successful herbicide application of double rate Eragon® plus roundup plus merge before or after wheat planting but before crop emergence is advised to reduce the overwintering population. This will assure next spring you are only dealing with smaller emerged weeds which enhances control with spring applications. The choice of spring herbicides is critical as some herbicides that control Fleabane in the spring will also damage under-seeded red clover.

Canada Thistle seedling.jpg

Canada thistle

Canada Thistle flowering plant.jpg

Canada thistle

WildCarrot-plant.jpg

Wild carrot

WildCarrot-flower.jpg

Wild carrot

An application of Roundup and Classic™ / Chaperone® in the fall is successful at keeping the fields clean from thistles, dandelions and wild carrot. The residual will carry through fall and early spring so that seedling perennials or biannuals will not germinate. For existing perennials, the glyphosate application needs to be taken down into the root systems for an adequate kill. This seems to work well for established dandelions, sow thistle and Canada thistle. Wild carrot is also controlled by Classic/Chaperone/glyphosate with fall applications. The problem with this chemical program is that you are forced to grow soybeans the following year.

Applications of straight glyphosate in the fall also control dandelions, sow thistle, Canada thistle and most established perennials. Timing is crucial. The best control is accomplished by waiting for cooler, consistent temperatures or one light frost before starting applications. This tells the plant its time to store nutrients for the winter in the crown, which is a great time for it to pull glyphosate to the root and kill the plant by the roots. When using straight glyphosate in the fall, it gives you options to plant whatever you choose next spring. Of course, any other glyphosate-tolerant weeds in the fall will not be controlled.

Common Chickweed flowering plant.jpg

Chickweed

Common chickweek before flower in hand.jpg

Chickweed

When controlling chickweed, refine M works well in the spring and fall. Also, double rate Eragon works well in the fall to control existing weeds and newly germinated ones through late fall and early spring. The problem with chickweed in the spring is that it sets seeds before we have an opportunity to enter the field. Therefore, it gets away on us.

There are many options to control weeds and manage weed resistance with multiple modes of action. Applying at different times of the year at different growth stages with different chemistries keeps weeds off-balance.

These are some of the scenarios that worked best for my area. If you have any questions, please do not hesitate to contact your local Wanstead or AGRIS Cooperative crop specialist to go over these options in greater detail on a  site-specific field by field basis.

If you have any questions or concerns with anything you are seeing in your fields, contact your local Wanstead Farmers Co-op.

Reference Source OMAFRA.

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