June 10, 2003
Are you growing carrots in your nursery? For most of you, the answer
is probably YES!. We are going to focus on 3 plants in the carrot
family this week (some call it the parsley family). Technically called
the family Apiaceae, the carrot family is known for about 1/2 dozen weeds,
as well as your garden variety carrots. We are going to focus on just
3 that I see commonly in the northern Willamette Valley including: cow
parsnip (Heracleum lanatum), poison hemlock (Conium maculatum),
and wild carrot (Daucus carota). All three species are in
bloom right now (in Oregon). Cow parsnip has been blooming for about
4 weeks and is starting to go to seed, poison hemlock has been blooming
for about 2 weeks and is now in peak bloom, and wild carrot has just barely
Cow parsnip is not a weed of economic importance, in my opinion. This plant is native
to the Pacific Northwest, and mostly seen growing along roadsides and in
drainage ditches. I mention it here just because it is so prevalent
in Western Oregon, and because it shares many similar characteristics (especially
floral) to the other plants which are major weed problems for the nursery
Cow parsnip is prevalent along roadsides now, though the flowers on the
patch that I drive by each day are just beginning to fade.
Flowers occur in massive heads called compound umbels. Leaves
are enormous, growing up to 16 inches long and 12 inches wide. Each
leaf is made of 3 leaflets, with the terminal leaflet being much larger than
the 2 basal leaflets. Stems are pubescent and slightly ridged.
For more images of cow parsnip, click
Poison hemlock is common throughout the Willamette
Valley, and is in full bloom right now making it easy to spot. This
weed is common throughout the United States, though only to a limited extent
in the northern Great Plains. Poison hemlock was, by some accounts,
the poison used to killed Socrates. It is quite toxic to humans and
animals when eaten.
Poison hemlock is a biennial that spreads by seed. Seed germinate
in late summer or early spring, and in the first year a rather bushy rosette
is formed. During the second year the plant generates an impressive
floral display that can be up to 6 feet tall, with a highly branched array
of compound umbels (flower heads). The most distinguishing characteristic
of this plant is its red blotched stems. These purple-red blotches
are evident during all stages of growth,
from rosette to flowering stalk.
Poison hemlock can be controlled with herbicides or tillage. Cultivation
and/or herbicides will prevent rosettes from developing the first year
(from seed). However, I often see rosettes grow in nurseries because
they germinate during the wet season when it is difficult to get equipment
into fields. At the very least, remove the seed heads before flowers
mature. I often see this plant along roads and fencerows. Maintain
these areas to prevent seed from entering nursery production areas.
For more images of poison hemlock, click
Wild carrot is becoming an increasing problem in the valley. Wild
carrot has flowers similar to those described for poison hemlock and cow
parsnip. However, plants are much smaller in stature. Wild carrot
is a biennial that develops a rosette the first year and flower stalks the
second. Flower stalks on wild carrot are lower growing than those mentioned
above (up to 3 feet tall), and generally contain only a single flower cluster
per stalk with little branching (in contrast to poison hemlock).
Similar to poison hemlock, wild carrot spreads only by seed. Proper
use of preemergence herbicides will prevent new plants from germinating.
Use postemergence herbicides or other control measures to prevent seed
from maturing on plants and entering production fields.
For more images of wild carrot, click
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