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WEED-PESTS. 



In many agricultural journals one may read of pestilential 

 plants accidentally or intentionally introduced by man from pther 

 parts of the world, which grow to such an extent that they 

 become a nuisance, and are often very difficult to eradicate. 

 In the "Journal d' A gri culture Tropicale, Paris {No. 35, May 31, 

 1904), M. des Grottes writes: " That the introduction of new 

 "plants into our Colonies requires much circumspection and 

 "careful preliminary study, for whilst some are useful others are 

 noxious." Among the noxious plants he places the Guava. 

 Other gardeners have the same cautious fear I find of introducing 

 a plant to their country which may possibly become a noxious 

 weed. It is, however, a fact that plants with the worst possible 

 reputation as weeds, often under apparently exactly the same 

 circumstances of soil and climate, refuse to take to the country 

 at all, and are quite harmless. A species of Oxalis is a pest 

 in the tea gardens of Ceylon. It grows by underground tubers, 

 and is difficult or almost impossible to eradicate. In the Malay 

 Peninsula, however, it hardly manages to exist, except on such 

 spots as Penang Hill, where it thrives but is quite easily disposed 

 of. Argemone Mexicana, an ornamental poppy, has established 

 itself as a pest in many parts of the world, and due caution was 

 exercised in introducing it as a bedding plant into Singapore. 

 It grew, flowered, seeded, apparently well the first year and 

 utterly vanished the second year. 



In the Antilles M. des Gkottes declares that the Guava has 

 run wild, is terrible prolific, and . the roots are very hard, sink 

 deep into the soil, and are very troublesome to (.'radicate. The 

 seeds are dispersed by cattle and pigs and also by birds. In 

 the Malay Peninsula the Guava is very widely cultivated, and 

 occasionally seedlings spring up here and there in waste ground, 

 but it is very far from establishing itself as a pest. It reproduces 

 very slowly in a half- wild state. The reason for this is probably 

 that civet cats and bats eat the fruit before it is ripe, so that 

 no seedlings are produced. I have but rarely seen a ripe fruit 

 on a half-wild seedling Guava here, though where the fruit 

 is protected to some extent in gardens it fruits very well. 



Among plants accidentally introduced into the Malay Peninsula 

 which have become more or less of a nuisance are the sensitive 

 plant Mimosa pudica, the large shrub M. sepiaria, the common 

 Lautana, Lautana mixta, lalang, Impcraia cylindrica, Limnochans 

 plumicri, an ornamental plant cultivated by the Chinese for pig- 

 food which has wandered into ditches and rice-fields, and some 

 other weeds. 



The most curious thing about many of these weeds is the way 

 that at first they seem to grow with great rapidity and prove a 

 general nuisance, becoming extremely abundant, and then seem 

 almost as fast to die. away and become scarce, or at all events not 

 more common than any other plant. 



