34 
BULLETIN 45, HAWAII EXPERIMENT STATION. 
infested soil, this serving only to increase the number of the para- 
sites. If possible, a rotation should be practiced using nonsusceptible 
crops where such are suitable. The following susceptible crops are 
to be avoided: 
Alfalfa. 
Cowpea. 
Okra. 
Soy bean. 
Asparagus. 
Cucumber. 
Onion. 
Strawberry. 
Bean. 
Eggplant. 
Peach. 
Tobacco. 
Beet. 
Field pea. 
Pepper. 
Tomato. 
Cantaloup. 
Fig. 
Pumpkin 
Watermelon 
Carrot. 
Grape. 
Rape. 
( telery. 
Kale. 
Salsify. 
Clover. 
Lettuce. 
Spinach. 
There are a few crops which can be safely planted upon infested 
soils. A three-year rotation would probably be the shortest that 
would be at all effective in eliminating the pests. At the end of that 
time one planting of potatoes or other susceptible crop could prob- 
ably be made. Among the crops which are not seriously affected 
are the following: 
Barley. Peanut. Rye. Velvet bean. 
Corn. Pearl millet. Sorghum. Wheat. 
Iron cowpea. Redtop. Timothy. 
Corn and sorghum are particularly desirable, as they permit clean 
cultivation and the removal of weeds which might harbor the pest. 
NONPARASITIC DISEASES. 
Sux scald, Sunburn of Tubers. 
Under certain conditions of the weather the leaves of the potato 
plant may become sunburned. This condition may result when the 
sun comes out brightly after a period of cloudy or misty weather. 
The tender leaves wilt and later become dry and brown. This dis- 
ease has not been found of much consequence in Hawaiian fields. 
Young plants frequently appear drooping in the middle of the day 
if the sun is hot following showers, but little burning or permanent 
injury to the plants has been observed. 
When growing tubers become exposed to the action of the sun- 
light, they develop cholorophyll (leaf green) and are said to be sun- 
burned (locally called "moonstruck"). As a result of diseases like 
Rhizoctonia root disease (p. 24), which cause the tubers to develop on 
short stolons and in a bunch next to the stem, the tubers are fre- 
quently forced out of the soil. 
Control. — Hilling up the plants and attention to the control of 
such diseases will remedy the condition. 
Leaf Tipburn. 
The disease characterized by the drying up, dying, and rolling up- 
ward of the tips and the margins of the leaves during a period of 
