Physical removal of the parasite is the only known means of controlling it. In heavily infected stands it is usually necessary to depart from normal forest management practices to obtain adequate protection for the future forest exceptionally heavy harvest cuttings, followed by stand improvement designed to reduce mistletoe in the unmerchantable trees. At least one cleaning subsequent to the initial eradication will be desirable to remove the infections that originated before control work was started but which were invisible at the time. Economic justification for control will depend on the value of the stand attacked. A knowledge of the biology of the particular mistletoe species involved will aid in developing the most efficient control techniques.

DODDER belongs to the genus Cuscuta, a close relative of the familiar morning-glories. It is sometimes referred to as love vine, strangleweed, devil's-guts, goldthread, pull-down, devil's-ringlet, hellbine, hairweed, devil's-hair, and hailweed. It commonly appears as dense tangles of leafless, orange or yellow strands on its host plants. Sometimes it is tinged with red or purple. Occasionally it is almost white. The strands develop from seed, which germinate on the soil. The leafless yellowish stem gropes in the air until it makes contact with a host plant. The contact is made firm by one or more coils about the host stem after which haustoria the absorbing organs are produced. The haustoria invade the host tissues and absorb the food required for the dodder to continue its twining growth. The basal part of the parasite soon shrivels away, so that no connection with the soil remains. Growth continues with the aid of more and more haustoria, which are produced at intervals as the stem elongates. From the original host plant, the twining stems reach out to attack others in the vicinity, so that a single dodder plant may parasitize several hosts simultaneously. Many minute flowers occur in clusters on the stems; they develop tiny seeds, which fall to the ground at maturity. The seed may remain viable without germinating for 5 years.

Of the 100-odd recognized species of Cuscuta, 32 are reported as being native to the United States; 18 others have been introduced. The parasite is particularly troublesome in regions where clover and alfalfa are grown extensively, although it is not to be feared in America to the same degree as in some European countries, where the production of clover seed has been abandoned because of its ravages.

Dodder also attacks flax, sugar beets, and onions. A large number of both cultivated and wild plants also are its hosts, but little or no economic loss results from the association. Cereal plants are never attacked.

Dodder is most frequently carried to a farm in impure seed. It may also be carried in hay, manure, and irrigation water and on vehicles and animals. Prevention is therefore the first principle of control. Once established, it usually appears in small scattered patches. Cutting the patches before the seed matures will often eliminate the parasite. After the seed has matured it will be necessary to burn the infested area. Heavily infested fields should be plowed under or used for hay; the stubble should be grazed hay; preferably by sheep. The safest method is to cut the crop and burn it in place when it dries. If conditions Permit, an infested field can be planted to immune or resistant crops such as cereals, corn, soybeans, velvetbeans, or cowpeas. Chemical control is feasible but is not recommended because of the high cost.

THE NAME BROOMRAPE is generally applied to the genera Orobanche and Phehfiaea. The 90-some species are mostly in the temperate parts of the world. Both belong to the botanical family Orobanchaceae, all members of which are complete root parasites. The family also includes the genus Epifagus, commonly known as beech-drops, which appears under beech trees. From an evolutionary standpoint, the group is closely related to the snapdragons and foxgloves (Scrophulariaceae). Some species of the parasites produce just as showy flowers as their independent relatives. Several members of the Scrophulariaceae exhibit mild degrees of root parasitism similar to that previously mentioned in the case of sandalwood and falsetoadflax.

The broomrapes appear as clumps of whitish, yellowish, brownish, or purplish annual stems arising from the ground at or near the base of their host plants. The stems are 6 to 18 inches high. They have bractlike leaves and numerous showy flowers somewhat like those of the snapdragon. An abundance of minute seeds is produced in capsular fruits. The seeds germinate in the soil if the fibrous roots of a congenial host plant are nearby. Otherwise they remain dormant until they lose their viability, which can be retained as long as 13 years. When the primary root, or radicle, of a germinating seed makes contact with a fibrous root of its host, it forms a nodule of tissue, which becomes fused with tissues of the host. New roots and a stem of the parasite develop at that point. The stem emerges while the roots form new contacts with other host roots at each of which new roots and stems of the parasite are produced.

About 16 species of broomrape are regarded as pests of many crop plants. Three are found in the United States. The damage caused by broomrape in America does not approach the situation in Europe. Our most troublesome species, hemp broomrape (Orobanche ramosa), was perhaps introduced on hempseed from China or Japan. It attacks a number of unrelated crops, but it is serious only on our hemp. A native species, Louisiana broomrape (O. ludoviciana), sometimes damages tobacco. Beyond these, the losses caused by broomrape are negligible and sporadic.

CLEAN SEED is the best protection against broomrape in hemp culture. The seeds of the parasite can be separated mechanically. Contaminated lots may be treated with hot water or a strong bluestone solution, both of which kill the parasite without damaging the hemp. Rotation with immune or resistant crops is perhaps the most practical procedure in heavily infested fields, but it should be remembered that the seeds of the parasite remain viable in the soil for many years. Small infections of broomrape can usually be eliminated by destroying the aerial stems before the seeds ripen.

LAKE S. GILL, senior pathologist of the division of forest pathology, Bureau of Plant Industry, Soils, and Agricultural Engineering, is an authority on the diseases of forest trees in the Southwest and the Rocky Mountains. He has made comprehensive studies of mistletoe and developed methods for its control. He is stationed in Albuquerque, N. Mex. He contributed "Arceuthobium in the United States" to Transactions of the Connecticut Academy of Arts and Science (volume 32, pages 111-245, 1935). With Y. L. Bedwell he wrote "Dwarf Mistletoes" for Trees, the Yearbook of Agriculture 1949 (pages 458-461).