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 started blooming.

cow parsnip
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 industry.

Cow parsnip is prevalent along roadsides now, though the flowers on the patch that I drive by each day are just beginning to fade.

cow parsnip 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 here.

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 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, poison hemlock 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.

poison hemlock

For more images of poison hemlock, click here.

wild carrot
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.  

wild carrot

For more images of wild carrot, click here.

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