POTATO DISEASES IN HAWAII. 25 
The name Rhizoctonia, as used here, is a group name for a number 
of closely related forms. This sort of fungus is a soil inhabitant 
which is thought to be favored by heavy, wet, sour soils, but in these 
islands it appears to be responsible for considerable damage even 
on porous, light, well-drained soils. 
Control. — The measures found effective in controlling this soil 
organism are seed selection and seed disinfection in corrosive-subli- 
mate solution (p. 9), combined with planting in uninfected soils or 
soils in which the liability of infection has been reduced by crop 
rotation. Root crops such as turnips and beets are susceptible to the 
parasite and should not be used in the rotation. The Rhizoctonia 
types of injury are very prevalent in Hawaiian fields, and attention 
to the control of these diseases will have to be given before any great 
increase in yield can be had in some localities. 
Sclerotium Wilt {Sclerotium rolfsii). 
The Sclerotium wilt disease is caused by the fungus Sclerotium 
rolfsii, described by Rolfs * as the cause of a wilt of tomato in Florida. 
Besides the tomato, this fungus causes a similar disease of the fol- 
lowing plants: Potato, peanut, eggplant, bean, cowpea, summer 
squash, cabbage, beet, and melon. It is reported to be very destructive 
to the Irish potato in heavy, wet soils. This fungus has been isolated 
from diseased peanuts growing on the farm of the College of Hawaii, 
Oahu, and also from Hilo, Hawaii, but as yet Irish potatoes attacked 
by this disease in the islands have not come under the writer's ob- 
servation. Larsen describes it as occurring on potatoes in the vicinity 
of Honolulu in 1913. He isolated the fungus and performed suc- 
cessful inoculations on potato plants. Since his publication is not 
generally available, and this disease is likely to be of occasional im- 
portance in some localities on the islands, the following quotation 
from his description is given : 
Sometime last January (1913) our attention was called to a field of po- 
tatoes in the vicinity of Honolulu which was being entirely destroyed as a 
result of some disease while the plants were still immature. On investigation 
it was found that the field in question, covering some 2 acres, was affected 
with a fungus malady known to mycologists as sclerotial disease. The same 
trouble was then found in other potato patches about Honolulu and occasion- 
ally on other host plants as. well. In most cases the trouble was fatal to the 
affected plants, causing severe loss wherever it occcurred. 
The first indication of sclerotial disease is a slight drooping of some of the 
younger leaves and leaf tips. On succeeding days the wilting becomes more 
pronounced, until in the course of two to four days the entire shoot wilts and 
fails to recover. * * * Sometimes several or all the shoots wilt simultane- 
ously. At the first indication of wilt, if one examines the base of an affected 
shoot, just below, and sometimes also a little above, the surface of the soil, one 
will find that the outer tissue through the cambium is decayed. * * * The 
decayed area may or may not extend clear around the stem. Eventually the 
1 Rolfs, T. H. Tomato diseases. Florida Sta. Bui. 117 (1913), p. 40. 
