Effective antidotes for horsetail milkweed poison have neither been 

 discovered nor developed; hence, prevention is the only control. 

 Areas heavily infested with horsetail milkweed should not be grazed. 

 Wherever practicable this plant should be eradicated from hay fields 

 and pastures and other grazing lands. The prolific seeding habit 

 of this species, together with its ability to grow from even small 

 pieces of root, make it difficult either to control or eradicate the pest. 

 However, mowing and burning the plant secures temporary protec- 

 tion and also tends to reduce seed distribution. The most satisfac- 

 tory method of eradication on tillable land 4 is to plow or grub areas 

 infested with horsetail milkweed early in August, just before the 

 plants seed. This should be followed by another grubbing or plow- 

 ing when the green shoots appear in September. Artificial reseeding 

 oners promise as an aid in controlling reinfestation of areas from 

 which this plant has been eradicated. Where the plant occurs on 

 ditchbanks, along fencerows, or on rocky hillsides, either grubbing 

 or spraying with sodium arsenite are very effective. However, since 

 sodium arsenite is extremely poisonous, livestock should be prohibited 

 from, areas sprayed with this chemical until the following season. 



Horsetail milkweed has gained recognition as a possible source of 

 commercial rubber, the leaves of the plant containing as much as 

 5.2 percent of rubber according to Hall and Long. 5 



As is characteristic of its genus, horsetail milkweed is admirably 

 adapted to insect pollination. The five stamens are united by their 

 stalks into a tube which surrounds the pollen-receiving organ 

 (stigma). The paired pollen masses (pollinia) are waxy and pear- 

 shaped, and each pollen mass is suspended on a short, slender stalk 

 (translator) from a stick body (corpusculum) located on the stigma 

 between adjacent stamens. These corpuscula are connected by trans- 

 lators to the pollen masses of the two adjacent pollen sacs (anthers). 

 The pollinating insect in crawling over the stigma gets one or more 

 of these corpuscula stuck to its feet and thus carries away the two 

 attached pollen masses to the next flower visited. Doubtless the local 

 name beeweed resulted from the numbers of bees present during the 

 pollination period. The seeds are well fitted for wind dissemination, 

 being numerous, light in weight, and crowned by a tuft of long, silky 

 white hairs; however, they are also often water-borne for consider- 

 able distances, especially along irrigation ditches. 



* May, W. L. CONTROL OF THE WHORLED MILKWEED IN COLORADO. Colo. Agr. Expt. Sta. 

 Bull. 285, 24 pp., illus. 1923. 



6 Hall, H. M., and Long, F. L. RUBBER-CONTENT OF NORTH AMERICAN PLANTS. Carnegie 

 Inst. Wash. Pub. 313, 66 pp., illus. 1921. 



