Galinsoga pressure in this field is so high that it has become a "cover crop" between the rows.  Photos by Vern Grubinger.

Galinsoga pressure in this field is so high that it has become a “cover crop” between the rows.
Photos by Vern Grubinger.

If you could design a weed that would flourish on vegetable farms, it would probably be a lot like hairy galinsoga (Galinsoga quadriradiata). This weed’s nicknames – quickweed, shaggy soldier, gallant soldier – suggest that it grows fast and is dangerous. Although it’s an annual, this weed is a perennial problem for many vegetable growers across the U.S. and beyond. It’s an especially tricky foe for organic growers, since cultivation seems to offer little control.

Appearance and life cycle

If you’re lucky enough to be unfamiliar with this weed, here’s a description: Hairy galinsoga is relatively modest in stature, with mature plants anywhere from 5 to 30 inches in height, but usually about 1 foot tall. It has erect stems with many branches, and there are coarse hairs on the stems and the leaf margins. The leaves are opposite one another and have toothed edges.

There are many small flower heads on this weed, each about 0.25 inch wide. The flower heads are composite, meaning they are made up of many individual flowers, each of which produces seed. The composite flowers appear white on the edges and yellow in the center. If you roll some of the flowers between your fingers, you may be surprised to find that the small black seeds have already formed, even though the flower doesn’t look like it has gone by.

Galinsoga reproduction is not affected by photoperiod, so it makes seeds whenever it can. A single plant can produce up to 7,500 seeds, and mature seeds can be formed in as little as six to seven weeks. This means that a single escaped plant can lead to a serious infestation. Further, there can be up to three generations in New England and New York, with four to five generations of this weed per season possible in the mid-Atlantic states.

In my neck of the woods, and most likely yours, hairy galinsoga appears to have become more and more widespread over the years. That may be due, in part, to seed being transported between farms via manure, compost, potting soil or transplants. Once it gets on an individual farm, it spreads quickly through the application of soil amendments, cultivation, field equipment, and anything else that moves soil. Galinsoga is one of the most difficult-to-control weeds of vegetable crops, but it’s also a weed in landscapes, gardens, ornamental beds and nurseries. It can even be found in urban settings, like sidewalks and vacant lots.

Left uncontrolled, galinsoga can spread quickly, often dominating an entire field, like some kind of cover crop run amok. It begins to flower and produce seed when it has just five or six pairs of leaves, and it continues until it’s killed by a frost. Fresh seeds drop onto the soil surface and soon sprout because there is little or no dormancy. The new seedlings repeat the cycle.

Cultivation is only partially helpful as a control because galinsoga plants root quickly and easily re-establish themselves from cut stems and uprooted plants unless conditions are very dry for several days after cultivation. Many of the herbicides used on vegetables are only slightly helpful for control of galinsoga, so conventional growers do not have a big advantage there. What they can do, however, is rotate to crops such as corn, where some labeled herbicides are more effective.

This weak stand of sorghum-Sudangrass is worse than no cover crop at all in terms of galinsoga suppression-the weed is flourishing within the cover crop.

This weak stand of sorghum-Sudangrass is worse than no cover crop at all in terms of galinsoga suppression-the weed is flourishing within the cover crop.

Management strategies

Keeping galinsoga at bay requires a multifaceted approach. Following are some tactics to consider using on your farm. The more, the better.

If you don’t have it, don’t get it. If you needed the description to know what galinsoga looks like, then you may not have it. Consider doing a germination test on manure, compost or potting soil you buy to see what sprouts in it before you spread it. If galinsoga is found, you may decide not to use the material, or you may be able to compost it some more to reduce the weed seed population.

Seek and destroy. It’s a really good idea to scout your fields regularly for galinsoga starting early in the season. Be sure to inform your workers about this weed and what it looks like. Maybe hang up “Most Wanted” posters. If and when you see galinsoga getting started in one small area, spend the time (and money) to thoroughly hoe or hand-pull it to eliminate it. Time spent on early intervention may save you a lot of frustration and expense later on. Do not drop pulled seedlings back in the field, as they may re-root; it’s better to remove the weed from the field in buckets.

Avoid spreading it. If you have galinsoga in some fields, don’t bring the problem to other fields. The better you can clean equipment after working in the infested fields, the less you will spread seeds or pieces of plants. Consider getting a pressure washer to clean equipment. Even a partial cleaning job, banging off the biggest clods, is better than nothing (but not much). Remember that cleaning field equipment also helps prevent the spread of some noxious diseases, like Phytophthora root rot.

Rotate your crops. Galinsoga is a particular problem in long-season, cultivated row crops. Try to rotate out of those crops to crops that are short-season (like lettuce), grown on black plastic, heavily mulched with straw, and/or are valuable enough to pay for frequent hand-weeding. Rotate with weed-suppressing cover crops.

Bare fallow. Prior to a summer smother crop, you might want to kill emerging summer annual weeds by repeated shallow cultivation for several weeks or more. This does beat up the soil, but if done frequently the depth of cultivation can be kept quite shallow, and subsequent cover cropping and/or compost additions can help rebuild soil health.

Use cover crops. Rotating with cover crops is one way to try to reduce galinsoga pressure. Vigorous cover crops can help compete with and suppress many annual weeds, so long as the weed is not thriving in amongst the cover. A period of bare fallowing may be necessary to reduce weed pressure before sowing a competitive cover crop. 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 weeds for light, water and nutrients. Such so-called summer smother crops need to be extra thick in order to reduce maturation and seed production of galinsoga. A thin or spotty stand, or a weak-growing cover due to poor nutrition or drought, may actually make a galinsoga problem worse by allowing it to grow and go to seed. Take a close look under your cover crops to make sure galinsoga is not running rampant there.

Stale seedbeds. These can be used to allow the initial flush of galinsoga and other broadleaf weeds to emerge, so they can then be killed with a flame weeder. 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 crop seeds have been sown but before seedlings emerge.

Conclusion

The extra cost of scouting, hand weed control, cover cropping, and even taking land out of production for bare fallowing may be well worth it to get a galinsoga problem under control before it takes over a field.