Jingjing Yin, Commercial Ornamental Horticulture
Cornell Cooperative Extension
Capital Area Agriculture and Horticulture Program
Hairy galinsoga (Galinsoga quadriradiata) is a seed-producing summer annual. Seedlings are erect with round cotyledons and a multibranched stem. Stems are usually sparsely hairy. Mature plants’ densely hairy stems reach 4-28” (10-70 cm) in height. Coarse hairs are present on leaf stalks, the entire upper leaf surface and veins on the lower leaf surface. Roots are shallow and fibrous. Flower heads are clustered at branch ends; they have 4-5 small and white flowers.
Galinsoga has a few nicknames such as “quickweed”, “shaggy soldier”, or “gallant soldier”. It can be a troublesome weed in landscapes, container nurseries, and other agricultural production systems. It grows and matures very fast and can seed multiple generations within one growing season. In New York, there can be up to three generations per season. Each plant can produce up to 7,500 seeds within only 8 to 9 weeks after germination. One escaped galinsoga plant can lead to a serious infestation! Seeds can remain viable for more than two years and be easily transported by wind and water. Seeds germinate when the temperature is between 50º F and 95º F, especially after the soil is tilled or crops are planted. Galinsoga has a strong competitive advantage in high-light environments and prefers warm and sunny locations.
Due to limited herbicide options, prevention of weed establishment is the most successful method of management for galinsoga. Scout and monitor fields regularly and hand-weed escaped seedlings before flowering occurs. Make sure that roots are removed. Avoid building excessive levels of soil phosphorus from manure or compost amendments as this will favor galinsoga growth and reproduction. Because galinsoga goes to seed so rapidly, clean up fields immediately after harvest to reduce population growth. During summer fallow periods, either keep the soil clean cultivated at 3 to 4 week intervals to flush out seedlings, or plant with competitive cover crops. In the spring, a thickly-sown mustard cover crop may help suppress galinsoga. In the summer, tall and dense covers, like buckwheat or sorghum-Sudangrass, can compete with galinsoga for light, water, and nutrients. Make sure to sow the cover crop seeds extra thickly in order to reduce maturation and seed production of galinsoga. Since the seeds can only emerge from the top 0.4” (1 cm) of soil, a thorough cultivation at shallow depth can effectively deplete the surface seedbank without bringing up new seeds. A flame weeder can be used to kill galinsoga seedlings if the initial flush has happened. Galinsoga germinates very well in lightly disturbed soil, so once it is flamed try to minimize additional soil disturbance. A second flaming may be helpful after crops seeds have been sown but before they emerge.
References:
Biology and management of Galinsoga (Galinsoga Quadriradiata) in ornamental crop production. University of Florida. https://edis.ifas.ufl.edu/publication/EP593
Galinsoga management. University of Vermont Extension. https://www.uvm.edu/vtvegandberry/factsheets/galinsoga.html
Galinsogas. Weed Profiles. Cornell University. https://cals.cornell.edu/weed-science/weed-profiles/galinsogas