DISEASES OF VARIOUS CROPS 1 54 9 



the first symptoms appear. In Trinidad the disease has never so far been 

 discovered on rubber, but now that this plant, is fairly widely cultivated 

 there and in some cases among cacao trees, the surrounding cacao should 

 be carefully watched, so that in case the fungus should appear precautions 

 colli d be promptly taken to prevent its spreading to the rubber. 



1133- Phoma Lavandulae on Lavender (^Lavandula officinalis) in En- 

 gland. — Brierly, W. B., in Bulletin of Miscellaneous Ihfonnation, Royal Botanic <iay- 

 dens, Keu\ Xo. 5, p. 113-1^1, Figs. 1-9, PI. V-VI, ii)i6. 



Phoma lavandulae Gab. was recorded for the first time in Rnglaitd in 

 1 915. It is the cause of a serious disease in Lavandula officinalis. The di- 

 seased buds and shoots are brown in colour, the leaves wither and fall, and 

 the epidermis sphts away in minute silver^' flakes. The infection spreads 

 very quickly from one plant to another so that it readily attacks and 

 destroys whole beds. 



In pure cultures the fungus produces pycnospores and conidia, which 

 are hyaline with thin walls (which later on become brown while the walls 

 thicken), and characteristic brown chlamidospores, with very thick walls. 

 The thin walled spores germinate quickly ; they are not very resistant to 

 drought and are killed by frost. The thick walled spores on the other hand 

 are very resistant and only germinate after a resting period. 



Inoculation experiments gave positive results, and confirmed the pa- 

 thogenic properties of the fungus which is ver^^ probably confined to the 

 genus Lavandula. The mycelium branches freely through the host tissues, 

 causing disintegration of the peridermis and phloem. It also penetrates into 

 the xjdem and the hyphae often reach the inside of the cells through the 

 pits in the walls. The pycnidia are formed immediately below the epidermis 

 which splits away from the cortex. The optimum temperature for the 

 gro\\4;h of the mycelium is about 18° to 20° C. 



To check the infection the diseased shoots should be cut out and es- 

 tro3'ed as soon as they appear. 



1 134 - Fusarium sp. ("die-back disease") a Pest on Hibiscus in the Federated 



Malay States. — Sharples, a., in The AriHcultural Bulletir ni the Federated Malay 

 Stales, Vol. VI, No. 7, pp. 217-218, Sin,s;apore, 1916. 



Several species of Hibiscus winch are cultivated in the Federated Ma- 

 lay States for ornamental purposes are attacked by a fungus that kills the 

 shoots. The disease, whose common name is " die-back disease ", develops 

 principally in hedges of H . Rosa-sinensis which are periodically pruned. The 

 shoots blacken and die from the top onwards, the leaves wither and fall, 

 and finally the plant is reduced to a cluster of dead branches. The author 

 has been able to isolate from infected material two fungi in pure cultures 

 {CoUetotrichum sj). and Fusarium sp.). Inoculation experiments showed that 

 Fusarium sp. is the specific cause of the disease described above. The my- 

 celium of the }:)arasite penetrates the host by means of the numeroas lesions 

 and cuts which result from pruning. It is therefore suggested that this o])er- 

 ation should always be followed by an immediate dressing with Bordeaux 

 mixture. 



