Giant hogweed

About

A huge carrot-family plant from the Caucasus whose sap, with sunlight, causes severe burns, blisters and even blindness. It is a federal noxious weed: if you think you've found it, don't touch it, and report it.

Also called cartwheel-flower, hogweed

How to identify it

Look for

Plants reach 7 to 14 feet or more, with hollow stems 2 to 4 inches thick covered in purple blotches and coarse white hairs. Deeply cut, jagged leaves can be 5 feet across, and in summer it carries flat-topped white flower clusters up to 2½ feet wide. It usually grows for a few years as leaves only, then flowers once and dies.

Look-alikes

Native cow parsnip is smaller (5 to 8 feet), with stems 1 to 2 inches thick, fine hairs and flower heads about a foot wide. Poison hemlock has fern-like leaves and smooth stems, wild parsnip has yellow flowers, and Queen Anne's lace is only 1 to 3 feet tall; angelica and elderberry lack the coarse stem hairs.

Where it grows

Stream and river banks, damp roadsides, field edges, woodland edges and yards, often where it was once planted as an ornamental.

When

Leaves come up early in spring; plants bloom from late June to mid July, then set seed and die.

How it spreads

One plant makes thousands of seeds, often around 20,000, which float along waterways and can survive in the soil for several years; people spread it by moving seeds.

Most common in

Where it is regulated

A federal noxious weed, illegal to move between states without a permit; also listed by New York, Virginia (Tier 1), Ohio and Washington (Class A), among others.

What to do, gentlest first

Protect yourself first. Weed killers are a last step; always read and follow the label.

1. Report it and keep away Prevent

   Take photos from a distance and report the location to your state agriculture or environmental agency or county extension office. Don't move plants or seeds.

   Keep children and pets away. It is illegal to move this federal noxious weed.

2. Root cutting by trained crews By hand

   Crews cut the root below ground and remove flower heads before seed forms, starting early in spring when plants are small.

   Not a DIY job: sap can splash several feet. Never use a string trimmer or brush cutter. Work in shade or after sunset in full waterproof gear.

3. Grazing on large stands Natural enemies

   Sheep and goats grazing several times a year can wear down dense stands under an agency or professional plan.

4. Glyphosate or triclopyr by a licensed applicator Conventional spray

   Applied by trained applicators to young plants in spring, with follow-up for 3 to 5 years until the seed bank is gone.

   Read and follow the label. Many lawn and brush herbicides also kill garden plants, so keep spray and drift off anything you want to keep.

Uses, wildlife and pets

Pets

Not listed by the ASPCA under its own name; the ASPCA lists its close relative cow parsnip as toxic to dogs, cats and horses because its sap causes sunburn-like skin damage.