32 BULLETIN 45, HAWAII EXPERIMENT STATION. 
" phytoptosis " on the tomato in Florida by Rolfs. 1 The mite attack- 
ing the potato is quite different from the one found by Rolfs, how- 
ever, this being Eriophyes or Phytoptus, while that infesting potatoes 
probably belongs to the same group as the so-called red spider 
(Tetranychida?). 
The mite disease was first noted by the writer early in May, 1917, 
in the vicinity of Honolulu and Castner, Oahu. It was soon found 
to be very prevalent and destructive after the weather became too 
dry and warm for the late blight disease. It is now recognized as a 
disease of considerable importance during dry seasons in the main 
potato sections, and has probably been destructive to the potato crops 
for many years. During the drought of the summer and fall of 1917, 
this disease caused losses estimated at as high as 25 per cent in some 
fields in the Hamakua district of Hawaii and the Makawao and Kula 
districts of Maui. Practically total losses were observed in gardens 
in the vicinity of Honolulu, where the conditions were not favorable 
to the crop, the weather being too dry and warm. 
That this disease is caused by mites is established by the following 
facts: These organisms are always present in sufficient numbers on 
plants with the recognized symptoms to be considered responsible 
for the trouble; the reaction of the plant is such as has come to be 
associated with mite injury; if the mites are kept off potato plants 
by spraying or dusting with sulphur the plants grow normally, while 
adjacent unprotected rows are devastated; increases in yield of tubers 
of 100 per cent by weight have been obtained by spraying with lime- 
sulphur. (See PL XIII.) 
The mites are oval shaped and almost colorless when young, be- 
coming slightly brownish with maturity. When young they have 
three pairs of legs, later four pairs (PL XII). The eggs, which are 
numerous on the affected leaves, are sculptured or papillate. 
Control. — Experiments (PL XIII) have shown that the mite dis- 
ease can be almost if not entirely prevented by dusting the plants 
with sulphur or spraying them with a lime-sulphur spray. In dry, 
warm weather watch the potato plants carefully, and as soon as any 
of the small young leaves at the tip show signs of turning brown or 
becoming bronzed on the under surface, spray the entire surface of 
the plants with the lime-sulphur spray (p. 13) or dust the plants 
thoroughly with dry sulphur. Repeat as often as necessary. 
The mite disease is entirely different in its symptoms from the 
late blight or wet blight disease and likewise from the early or dry 
blight, and there should be no confusion of these types. The mite 
disease can be confused with Fusarium wilt or other wilt disease 
unless careful examination is made. It seems that there has been 
1 Rolfs, P. H. [Tomato diseases.] Florida Sta. Buls. 21 (1893), pp. 23, 24 ; 47 (1898), 
pp. 143, 144. 
