Common Ragweed-Sunflower Family

 

Ambrosis artemisiifolia

 

Characteristics.  This native western annual is one of if not the most common sources of hay fever in those areas where it is common.  This species if not aggressive and causes minimal problems in cropping situations.  Ragweed is fairly commonly found along roadsides, ditches and in wastelands. There is a perennial species (western ragweed) that is more prevalent in perennial cropping situations. In the fall ragweed produces a large amount of pollen from many terminal flowers.

Identifying Characteristics.  This weed grows erectly to 5 feet with pinnately divided leaves and blue-green stems.  The leaves are covered with fine hairs with the bottom sides gray in appearance. A large number of flowers occur in the fall.

 

 

Images courtesy of Oklahoma State University

 

Poisonous Plants-Dermatitis. One effect that immediately comes to mind is irritation of the skin caused by certain weed types.  Common examples are poison oak, ivy and sumac.  The actual skin irritant occurring in these plants is uriushiol, which is a mixture of several derivatives of the chemical catechol.  This oil occurs in the sap of most of the parts of these weeds, including roots, stems, leaves and fruit.

All three plants belong to the cashew family. Poison ivy (Figure 2) grows plentifully in parts of the United States and southern Canada.  This plant will forms upright bushes if it has no support to climb but also occurs as a twining vine on tree trunks or straggling other plants over the ground.  Poison oak (Figure 3) occurs commonly in California, the Pacific Northwest and nearby regions of Canada, and poison sumac (Figure 4) is primarily an eastern United States species. Poison oak and poison sumac both are shrubs.

 

 

Figure 2.  Poison ivy.  Image courtesy of Jil Sinon.

 

 

Figure 3.  Poison oak, Image courtesy of Jim Dunphy.

 

 

Figure 4.  Poison sumac.  Image courtesy of Jim Dunphy.

 

The irritating may brush onto the clothing when coming in contact with the plants. Many people have been poisoned merely by taking off their shoes or clothing after walking through poison ivy. In cases of extreme sensitivity the mere presence of the plant in the general vicinity may result in skin irritations.  In addition the disease can be passed from individual to individual if the oil remains on the skin. The eruptions ((Figure 5.) themselves are not a source of infection.

 

 

Figure 5.  Symptoms of exposure to urioshiol.

 

Control and Treatment. If exposed to any of these plants it is important to wash thoroughly several times with soap and water.  Because the oil can be transferred by mere contact, avoid touching any part of the body, as even tiny amounts of the oil will cause irritation.  Blistering and red, itching skin may be treated with dressings of calamine lotion, Epsom salts, or bicarbonate of soda. There is a vaccine that is available (oral or injection) that is effective when taken prior to exposure.

 

There are a number of other weeds (for example stinging nettle) that can produce less severe dermatitis if exposed to the skin.  In some cases these weeds are much more common than those discussed above but unless allergic reactions are involved, the symptoms are much less severe and short term.

 

Additionally, there are a number of species of plants, including weeds that are quite toxic (even deadly) if consumed.  The question may arise as to why a plant would contain toxic materials.  Of course the answer is that these toxins are a form of natural protection against plant-eating insects, birds and any of a number of other animals.