If you could design a weed that would flourish on vegetable
farms, it would probably be a lot like Hairy Galinsoga (Galinsoga quadriradiata). Its nicknames suggest that this weed
grows fast and is dangerous; they include ‘quickweed’ and ‘shaggy soldier’ or
‘gallant soldier’. 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 worthy foe for organic growers, since cultivation
seems to offer little control of the persistent pest.
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 a foot tall. It has erect stems with many
branches, and there are coarse hairs on both the stems and the leaf margins.
The leaves are opposite one another, with toothed edges.
There are many small flower heads on this weed, each about a
quarter of an inch wide. The flower heads are composite, meaning they are made
up 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
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 6-7 weeks. That 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, too, Hairy
Galinsoga appears to have become more and more widespread over the years. In
part that may be due to seed being transported between farms via manure,
compost, potting soil, and transplants. Once it gets on an individual farm, it
spreads quickly via spreading 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 seed drops onto the soil surface and soon
sprouts because there is little or no dormancy. The new seedlings repeat the
Cultivation is only partially helpful as a control because
Galinsoga plants root quickly and easily reestablish 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 like corn where
some labeled herbicides are more effective.
Management strategies. Keeping galinsoga at bay requires a
multi-faceted approach. Here are some tactics to consider using on your farm.
The more, the better.
1. 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.
2. 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 hand-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 just drop pulled seedlings back in the field, as they may
re-root; it is better to remove the weed from the field in buckets.
3. 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.
4. 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. And of
course, rotate with weed-suppressing cover crops.
5. 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.
6. Use cover crops. Rotating with cover crops is one way to
try and 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 needed 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 problem. 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 galisoga is not running rampant there.
7. Stale seed beds. 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 crops seeds have been sown but before they
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
control of a field.