Pest Patrol: More and more hairy galinsoga

#PestPatrol with Mike Cowbrough, OMAFRA

Figure 1. Hairy galinsoga seedling.

Q: I’m seeing more of a weed called hairy galinsoga, and I’m struggling to control it. Any suggestions?

A: Historically, we have found this annual plant mainly in horticultural crops throughout the southern portion of the province, but in the last five years, there have been more inquiries on managing hairy galinsoga in field crops. Although there are effective herbicides to control emerged seedlings, this weed has characteristics that make it a challenge to eliminate throughout the growing season and capable of a rapid buildup in population when left uncontrolled.

Hairy galinsoga’s lack of seed dormancy or any special requirements for germination and its fast seedling growth, along with its ability to flower after a short period of vegetative growth, mean it can produce several generations and many viable seeds in a single growing season.

Figure 2. Hairy galinsoga that has begun flowering. photo: Supplied

In infested fields, it is not uncommon to see seedling plants (Figure 1 at top) amongst flowering plants (Figure 2 above). Both photos were taken in early September and both sets of plants produced viable seed before the first killing frost.

Simply put, because this plant can produce a lot of seed that will germinate from April to October, multiple methods of control are needed throughout the season. Let’s walk through the integrated strategies that can be used to manage this species.

Herbicides: Dr. François Tardif, Peter Smith (University of Guelph) and I have evaluated hairy galinsoga’s sensitivity to several active ingredients (Table 1 above). Field studies conducted in 2019 by the Tardif lab showed very effective control with Acuron when compared to the unsprayed check (Figure 3 below). There is also a novel active ingredient that shows promise on very young seedlings (Figure 4 at bottom) and provides us with some optimism for the future.

Figure 3. Control of hairy galinsoga and green pigweed with Acuron (right) compared to the un-sprayed check (left). photo: Supplied

Cultural control: Some studies indicate that the seed does not germinate when buried deeper than 2.5 cm (one inch). Therefore, tillage implements that bury the seed should serve to significantly reduce population density. Since hairy galinsoga can reproduce from rooted up stems, if you are using tillage to control emerged plants it should be done when plants are small, and with an implement that is aggressive enough to remove as much soil from the rooted plant as possible in order to reduce the chance of regrowth.

Crop rotation: Since seed dormancy is low or non-existent, planting a perennial forage crop has resulted in significant reductions in the population of hairy galinsoga within infested fields.

Figure 4. Control of hairy galinsoga with a new active ingredient (right) compared to the un-sprayed check (left). photo: Supplied

Have a question you want answered? Hashtag #PestPatrol on Twitter to @cowbrough or email Mike at [email protected].

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