10 BULLETIN 45, HAWAII EXPERIMENT STATION. 
vation of 2,000 to 3.000 feet or more on rather loose-textured, well- 
drained soils. In any case heavy wet soils poorly drained and hard 
to work are not suitable for potato culture. In some potato soils in 
Kula, Maui, the presence of a layer of hardpan a few inches under 
the surface indicates that shallow surface plowing has too long been 
practiced and that the conditions of apparent soil exhaustion might 
be largely improved in such fields by deeper plowing. Hilling up 
the plants might well receive more attention as an aid in checking 
attack by the potato tuber moth. Crop rotation should be prac- 
ticed more and more here, not only to increase the fertility of the 
soil but also to combat the prevalent diseases and insect pests. Seed 
selection is almost useless or is of temporary value unless combined 
with rotation. The organisms causing Fusarium wilt, rosette, black 
scurf, corky scab, etc., live indefinitely in the soil, but it is generally 
believed that in the absence of susceptible plants the virility of the 
organism is lessened and the number decreased. Similarly, the 
tuber moth, which is most serious in dry years, can possibly be held 
under control by clean cultivation and rotation combined with in- 
telligent spraying with arsenicals. Crop rotation, combined with 
the use of good seed and preventive sprays, offers promising oppor- 
tunities of improving the Hawaiian potato industry through in- 
creased yields and better quality. 
Soil reaction. — As certain organisms are favored by an acid soil 
while others are encouraged by an alkaline soil, the latter being 
favorable to the development of corky scab, lime or wood ashes 
should never be applied to potato fields, as they tend to produce an 
alkaline soil reaction and are sure to encourage scab. On the other 
hand, the plowing under of green-manure crops will tend to make 
the soil acid and thus reduce the damage from this disease. The 
Ehizoctonia diseases are thought to be worse on heavy, poorly 
drained, acid soils. Correcting the drainage and aeration of such 
soils is beneficial. 
SPRAYING, SPRAY MIXTURES, BAITS, ETC. 
In order to protect the potato plant against various insect pests and 
fungus diseases, sundry chemicals are sprayed or dusted thereon or 
used as baits. The chemical used varies with the nature of the pest — 
there are no cure-alls. The material may serve as a protection of the 
foliage against fungus infection or as a contact or internal poison for 
insect pests. In certain weather conditions, a coating of spray may 
act mechanically to prevent sun injury of the foliage. 
Bordeaux mixture for the control of foliage diseases. — The most 
widely used fungicidal spray for the prevention of foliage diseases of 
the potato is Bordeaux mixture. The experiments carried on with 
this spray by the writer alone and cooperatively with others in 
