Efficacy of mono-dipotassium phosphite against Phytophthora palmivora (Butl.) Butl. on durian
1990
Kuakoon Bunyanupappong
Fungitoxicity of m-dKP was compared in term of DR-curve and ED50 values with the assistance of poisoned food techniques. The m-dKP ranked at fourth position. The ED50 values of tested fungicides were 0.07, 0.07, 0.21, 10.59 and 35.48 mg./l. for metalaxyl, ofurace, etridiazole, m-dKP and fosetyl-Al, respectively. Regarding the role of spore formation inhibition, toxicity of m-dKP is seconded to only metalaxyl (with ED50 values 0.028 and 39.81 mg./l. respectively). All tested fungicides moved upward to mature leaves and within 15 days after soil treatment the infection of P. palmivora via disc-inoculation was inhibited. Considerably, the m-dKP performance was ranked at third position after metalaxyl and ofurace. The diseased tree with heavy leaf-fall and declined symptom at the age of 10-15 year-old, after receiving 30 ml. of m-dKP plus equal amount of distilled water revealed the discovering and became healthy withing the period of 2 months. Further treatment with same dosage 6 monthly for one year provided a steadily discovering from patch canker and root rot. Persistency of m-dKP in leave after injection was also studied in durian. Maximum toxic could have lasted upto 3 weeks and later on the toxicity declined with 5-7 weeks which means that the m-dKP moved to the lower tree parts and resulted in curative effect. Finished product (Foli-R-Fos 400) when kept at various temperatures (viz. 20, 25, 30, 35 and 40 deg. Celsius) for 7 days could have the same level of fungitoxicity, at the concentration of 5-10 mg./l. Besides, the diluted m-dKP when kept at particular 30+-5 deg. Celsius for 25 weeks provided the toxicity decreasing.
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