In his book, Allergy-Free Gardening, author Thomas Ogren uses a Plant Allergy Scale to rate plants from 1 (low) to high (10) for pollen and allergies. The book also provides many useful tips for reducing your exposure to allergens.
Many weeds are among the worst allergenic plants. Take Common Ragweed for example. One Common Ragweed plant can produce up to one billion pollen grains, and they have been tracked over 400 miles away! Other weeds that can cause allergy problems with their pollen include Pigweed, Bermudagrass, Annual Bluegrass, Dallisgrass, Dandelion, Dock, Lambsquarters, Nettle, Plantain, Ryegrass and Sagebrush, plus many others. Bottom line – control weeds in your lawn and garden and you can reduce your exposure to troublesome pollens.
Weeds are usually easiest to control in spring when they are small and actively growing. However, fall can also be a crucial time to control cool-season weeds in mild winter areas, especially in lawns. Hoeing, mulching and cultivating can help reduce weeds, but herbicides that prevent or kill weeds are often an easier, more efficient method of control, especially if weed pollen is a health concern. Mowing can reduce weeds in lawns temporarily, but unfortunately, they'll regrow. Just one missed mowing can result in abundant pollen, especially with weedy grasses like Bermudagrass or Annual Bluegrass. A herbicide like Season Long Weed Control For Lawns is a more effective and longer-lasting solution.