Phytophthora Spot in Taro ( Leaf Blight)

The cause of this disease is Phytophthora colocasiae, one of the downy mildews, closely allied to late blight of potato.  The fungus produces its spores on the spots,the above-mentioned fuzz consisting of many thousands of conidia or sporangia,as the spores are termed.  The sporangia are blown by the wind or splashed by rain from diseased to healthy leaves,where they germinatein the presence of moisture to reproduce the disease in 3 to 5 days.  There is a close connection between these verity of phytophthora spot and abnormal atmospheric conditions, particularly rainy weather accompanied by high winds which whip the leaves about and scatter the sporangia.  The practice of close interplant-spacing is conducive to the development of leaf spot,due to poor air drainage and maintenance of a high humidity a round the leaves of the taro plant,which permit the sporangia to germinate easily and abundantly.

The disease can be controlled by spraying with 4-4-50 bordeaux as fungicide  at 10- to17-day intervals.   A spreader must be added to the Bordeaux for the waxy surface of the taro leaf is not easily wetted. (1)


Six fungicides were evaluated under greenhouse, laboratory, and dryland field conditions for control of Phytophthora leaf blight of taro incited by P. colocasiae. Five separate criteria were utilized to evaluate these fungicides: fungicidal activity in vitro; and fungicidal activity in vivo under conditions of simulated dew, simulated rainfall, greenhouse, and dryland field environments. In in vitro tests zoospores were killed at the following concentrations: Dithane M-45, 5 ppm; Difolatan, 9 ppm; Polyram, 65 ppm; Tribasic Copper Sulphate, 145 ppm; Benlate, 210 ppm; and Dyrene, 260 ppm. Excellent control was obtained with Difolatan; good control with Dithane M-45 and Polyram; and poor control with Benlate, Tribasic Copper Sulphate, and Dyrene. Results of in vivo tests correlated with those of the in vitro tests. Difolatan, Benlate, and Dyrene were the most phytotoxic while Tribasic Copper Sulphate, Polyram, and Dithane M-45 were the least phytotoxic.(R.R Bergquist 1971)(2)


Intended for readers from Indonesia,...please

Cara membuat larutan 4:4:50 bordeaux :
Untuk membuat 5 liter larutan 4:4:50 bordeaux
Siapkan 400 gr CuSO4 (Tembaga sulfat) dan 400 gr Ca(OH)2 ( Kapur hydrate) 

• Buat Larutan kapur : 400 gr Ca(OH)2 dalam 1 Liter air dan diaduk hingga terbentuk larutan seperti susu, kemudian buat larutan tembaga sulfat : 400 gr CuSO4 dalam 1 liter air dan aduk beberapa menit hingga terlarut sempurna (larutan berwarna biru).
• Siapkan ember atau wadah plastik, kemudian diatasnya letakan kain saringan dan ikat dengan karet ban, tuangkan larutan kapur dan tembaga sulfat. Penyaringan diperlukan agar padatan yang belum terlarut tidak menyumbat nossel sprayer.
• Setelah itu tambahkan air dalam ember hingga total volume menjadi 5 Liter dan aduk rata, larutan fungisida ini siap digunakan.(fungisida ini dibuat pada saat akan digunakan)

Kapur hydrate bisa di buat dari kapur bakar atau kapur mati  yang memiliki kemurnian n % CaO, dan umumnya kemurnian berkisar antara  60-85% CaO
CaO+ 2H2O (excess)==> Ca(OH)2 (mengendap) + H2O
(Reaksi eksotermis atau melepaskan panas)
untuk mendapatkan 400 gr Ca(OH)2 , 
diperlukan Kapur bakar sebanyak = 400/74 x 56 x (1/n%)= 303 gr x (1 / (n % CaO)), kemudian ambil endapan dan keringkan.
Ref :

1. DISEASES OF TARO IN HAWAII AND THEIR CONTROL With Notes on Field Production by G. K. PARRIS, Plant Pathologist Honolulu , 1941 
2. Efficacy of Fungicides for Control ofPhytophthora Leaf Blight of Taro, R. R. BERGQUIST, 1971