October, 1910,] 



319 



Plant Sanitation. 



number of the Agricultural News. He 

 came to the conclusion that this treat- 

 ment was thoroughly practical and 

 remunerative, and especially to be advo- 

 cated, in order to prevent spread of the 

 black rot fungus from the pods to the 

 trees, thus reducing the general pre- 

 valence of canker. Should the same 

 fungus be responsible for canker in the 

 other West Indian Islands, it is at any 

 rate evident that every possible means 

 for the suppression of black rob should 

 be undertaken, and that where the 

 nature of the ground permits, spraying 

 with Bordeaux mixture on a large scale 

 may even be found remunerative. 

 Another preventive measure is to plant 

 only those varieties of cacao which are 

 reasonably resistant to the disease. 

 These preventive measures, taken in 

 connection with the remedial measures 

 already in practice should be capable of 

 reducing the prevalence of the disease 

 to a minimum. Even if canker disease 

 is not always due to Phytophthora omni- 

 vora, but is in reality attributable to 

 Spicaria color ans, or some species of 

 Nectria in certain instances, yet the 

 practicability of spraying with Bor- 

 deaux mixture is worthy of consider* 

 ation, as it would certainly tend to 

 reduce canker, in addition to attaining 

 its main object, namely, the reduction 

 of pcd disease. 



THE CENTRAL AMERICAN 

 BANANA BLIGHT. 



By Dr. R. E. B. McKenney, 

 Department of Agriculture (Laboratory 

 of Plant Pathology). 



(From Science, XXXI., 802, May 11, 1910.) 



In 1904 the writer made a trip through 

 a nnmber of farms in Costa Rica and in 

 the Province of Bocas del Toro, Panama, 

 for the purpose of investigating a serious 

 banana disease reported by the planters 

 during the two previous years. Since 

 that time the disease has been more or 

 less continuously studied by him. 



" The disease," or " the blight," as it is 

 commonly called by the planters, spreads 

 rapidly. While in 1904 whole valley 

 districts were free from the disease, 

 there is now scarcely a single farm in the 

 regions above mentioned that is not 

 suffering from its ravages. The blight 

 occurs in the Panama Canal Zone ; also 

 by report on the Atlantic side of Nicara- 

 gua, Honduras and Guatemala. 



The disease has been known for many 

 years, but only within the last decade 

 has it alarmed the planters- As early 



as 1890 a few isolated spots were known 

 to be affected, and from these the spread 

 of the disease can be traced. 



In Panama at least 15,000 to 20,000 acres 

 ol banana plantations have been aban- 

 doned and many thousand more are 

 seriously affected, while iu Costa Rica 

 the damage has been eveu greater, so 

 that it is safe to estimate at least 

 $2,000,000 capital loss iu these two regions 

 in the last five years. 



Young and old plantations are attacked 

 with equal intensity. Plants are also 

 attacked on various soils— sand, clay.etc. 

 The disease seldom becomes evident 

 until the shoots have reached a height 

 of four to six feet at the collar (point 

 where the leaves diverge). Commonly 

 the first external sign is a rapid yellowing 

 and subsequently browning and wilting 

 of one or more leaves. Sometimes there 

 is a striking curvature and yellowing of 

 the terminal part of the leaf while the 

 remainder is still green. Eventually all 

 leaves die and fall back against the trunk, 

 leaving a crop of suckers which, in turn, 

 are killed and give place to still weaker 

 shoots. The fruit of diseased shoots 

 rarely matures and even when mature is 

 worthless with blotches, somewhat shri- 

 velled surface and dry, pithy interior. 

 Shoots which develop after one or two 

 suckers have died rarely reach the flower- 

 ing stage. When they do, however, 

 weak, distorted, worthless bunches are 

 produced. 



On cutting the pseudo-stem across and 

 longitudinally many of the bundles are 

 found to be of a yellow, reddish or 

 reddish-purple color deepening toward 

 the root-stock. In the last stages the 

 color of the bundles may be almost 

 black. While in recently affected plants 

 the vessels of the upper part of the stalk 

 and the leaves may be normal, those of 

 the root-stock are always colored. In most 

 cases the thin partitions separating the 

 air chambers are wrinkledaud collapsed. 

 The juice of diseased plants contains 

 much less tannin than that of normal 

 plants. A nauseating odour is often 

 given off when leaf-stalks which have 

 been diseased for some time are cut open, 

 though there may be no sign of rooting 

 in the trunk. 



It has been proved that the disease is 

 not due to local conditions such as too 

 wet or too dry soil, etc., yet some of 

 these conditions may predispose the 

 plants to the disease. 



There is a seasonal periodicity in the 

 activity of the blight corresponding to 

 the periodicity of giovvth in the banana 

 plants. It is during the stage of most 

 rapid growth that the plants most easily 



