Plant Sanitation. 



[Jandart, 1909. 



thrips' attacks have ceased or have 

 become much reduced with the advent 

 of rains after a drought. 



The description of cacao thrips, its 

 habits and manner of attack, and the 

 remedies to be used in its control have 

 appeared in the pablications of the 

 Imperial Department of Agriculture 

 (West Indian Bulletin, Vol. II, pp. 175, 

 289; Vol. Ill, p. 235 ; Vol. VI, p. 94 ; Vol. 

 VIII, p. 143 ; Agricultural News, Vol. 

 Ill, p. 90) and are only briefly reviewed 

 here. 



Thrips are small insects of the order 

 Physopoda. The cacao thrips [Helio- 

 thrijis (Physopus) ruhrocincta] is from 

 l-18th to l-25th inch in length. The adults 

 are dark-brown or black, the young are 

 pale-green or yellowish-green with a 

 bright-red band across the abdomen. 

 These insects make minute incisions in the 

 plant tissues on which they feed. They 

 are generally to be found on the under 

 surfaces of the leaves and on the pods. 

 They injure the plant by feeding on the 

 sap, and the incisions made by them 

 may afford entrance to fungoid diseases. 



The pods are discoloured by these 

 attacks, and it often happens that pods 

 picked as ripe are merely discoloured. 

 This sometimes occasions considerable 

 loss. This however is less a source of 

 loss than formerly, as cacao pickers are 

 learning to be careful, and discoloured 

 pods in thrips-infested areas are tried, 

 before being picked, by scratching or 

 slightly cutting the surface so that the 

 tissue .just under the skin can be seen. 



It will sometimes happen that cacao 

 thrips will occur in such abundance 

 that it is desirable to spra^ to bring 

 them under control as quickly as pos- 

 sible, while the effects of cultural 

 methods are becoming apparent. For 

 this purpose any of the sprayers of the 

 knapsack or barrel types might be 

 used. The following mixtures are recom- 

 mended as being useful in this con- 

 nexion : — 



1. Rosin Wash. 

 Powdered rosin ... ... 4 lb. 



Caustic soda (77 per cent.) ... 1 ,, 

 Fish oil ... ... | pint. 



Mix these, cover with about 2 inches 

 depth of water, and boil till all is 

 dissolved. Then add water very slowly 

 to the liquid, keeping it continually 

 boiling until the whole is made up to 

 about 3 gallons. This is stock solution. 

 For use, add 6 gallons of water to 1 

 gallon of stock solution. 



Amount of wash, 21 gallons. 



2. Kerosene Emulsion. 

 Hard soap ... ... \ lb. 



Kerosene ... ... 2 gallons. 



Boil the soap in 1 gallon of water till 

 it is dissolved. Take it off the fire, at 

 once pour in the kerosene and churn the 

 mixture with a force pump or syringe 

 for ten minutes. This is stock solution. 

 Add 9 gallons of water to 1 gallon of the 

 stock solution. 



3. Kerosene Emulsion with Whale 

 Oil Soap. 

 Use 1 lb. whale oil soap in place of \ lb. 

 hard soap and make and use as in No. 2. 



4. Rosin and Whale Oil Soap 

 Compound, 

 Rosin ... ... 4 lb. 



Washing soda ... ... 3 ,, 



Whale oil soap ... ... 10 ,, 



With the rosin and soda make 4 gallons 

 of rosin compound stock solution as 

 above. Stir the whale oil soap in 5 

 gallons of hot water ; mix the two while 

 hot. This is stock solution. To every 

 gallon add 4 gallons of water. An 

 alternate method is to make the rosin 

 compound stock solution. For use, mix 

 1 gallon with 10 gallons of water and stir 

 in 2J lb. of whale oil soap. Every 45 

 gallons of wash should contain the above 

 ingredients, however mixed. 



Of these, Nos. 1 and 3 are recommended 

 as likely to be most effective. 



Discussion. 



Hon. H. Grahame Lang (Grenada) said 

 that in Grenada some years ago they 

 suffered badly from attacks of thrips ; 

 but now they had found that whenever 

 thrips appear, it was due to some 

 cultural defect. As soon as the land was 

 well tilled, the thrips disappeared. The 

 chief cause was want of a system of 

 proper drainage. To get rid of thrips a 

 good system of cultivation must be 

 adopted. The burial of husks or shells 

 should also always be insisted upon on 

 cacao estates. 



Mr. J. H. Hart (Trinidad) said that 

 their experience of thrips was that it 

 was a matter of no consequence what- 

 ever to cultivation in Trinidad. There 

 was some there, but they attributed 

 their comparative freedom largely to 

 the presence of shade.— Journal of the 

 Imperial Agricultural Department for 

 the West Indies. Vol. IX, No. 2. 



