POTATO DISEASES IX HAWAII. 35 
protracted dry weather is called tipburn (PL XV). The older, or 
lower, leaves are most affected. This trouble may possibly be mis- 
taken for early or late blight. The absence of definite spots with con- 
centric markings distinguishes it from the former, while the dry and 
upward-curling leaf margins of tipburn should serve to differentiate 
it from the late blight. Tipburn is most common on light soils 
which lose moisture rapidly. The disease results from the fact that 
under certain conditions the plant loses water faster by transpiration 
(evaporation from the leaves) than its roots can absorb water. 
Control. — Good surface cultivation to conserve the soil moisture 
and spraying with Bordeaux mixture have been found valuable means 
of preventing tipburn. 
Hollow Potato, Pkoxged Potatoes. 
The peculiarity known as hollow potato or black heart occasionally 
occurs in Hawaii. As the name indicates, the centers of the tubers 
are hollow or blackened. This trouble is considered to be due to 
peculiar conditions of growth. Uneven development, such as rapid 
growth following a period of cessation of growth or slow growth dur- 
ing drought, is thought to be a factor in the production of hollow 
potato and is also thought to encourage the formation of prongy 
potatoes. Large, overgrown tubers are more frequently hollow than 
average sized tubers, and in mainland States certain varieties seem 
to be more commonly affected than others. 
Aksexical Ixjuby. 
The application of Paris green to the leaves of the potato without 
mixing with it any neutralizing agent such as lime often causes the 
death of a portion of the leaf or of the entire leaf. Arsenate of lead 
is much less active in this way and is to be preferred for use on the 
foliage of plants. In a moist climate, basic arsenate of lead is prob- 
ably the best form to be used. Powdered arsenate of lead might 
well be substituted for Paris green in the flour poison bait used for 
the cutworms and army worms ("poko") where the bait is dusted 
over the foliage. If Paris green is used, an equal amount of slaked 
lime should be added to prevent burning. 
The application of arsenicals in spray form for pest control has 
been until recently but little practiced in the islands. Either Paris 
green or arsenate of lead can be used with Bordeaux mixture with 
little possibility of injuring the foliage. If Paris green rather than 
arsenate of lead is used, a small additional quantity of lime may be 
added to the Bordeaux to neutralize the Paris green. When a water 
suspension of Paris green is used for spraying, an equal amount of 
quicklime should be slaked and added to the water. 
