This is ragweed. Beginning in the late summer and early fall (usually between mid-August and October) many people suffer from seasonal allergy symptoms because of ragweed.
The two varieties which are mainly responsible for the allergic rhinitis are common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida). Common ragweed grows erect and up top 5 feet tall. Its leaves are long and with deeply-toothed divisions. Flowers are numerous spikes with small, greenish florets. Giant ragweed grows much taller, with rough leaves that are more rounded and shallowly toothed. Both plants reproduce annually by seed.
Ragweed thrives during hot dry summer weather. Almost no place in the northeast of North America is immune because ragweed can grow almost anywhere. It is commonly found along roadsides, in vacant lots or on recently disturbed soils. Seeds can survive for 40 years.
If you find ragweed on your property, do yourself and your neigbours a favour by pulling it out — before it flowers, if possible. It’s the pollen of the flowers pollen that causes the respiratory problems for so many. Continue to remove ragweed plants whenever you see them. The long life-span of seeds means ragweed may return for many years to come.
This information sheet was prepared at the request of local residents with ragweed allergies.