Efficiency of Selected Fungicides on Blast and Blight of Rice Leaves

The effect of pathogens on grains is closely related to the severity of the disease on plants. Similarly, infection of leaves is very important in epidemic of blast and blight. The objective of this study was to develop a treatment program suitable for different fungicides to protect the leaves of rice plants throughout the vegetative phase against blast and leaf blight by determining the required dose and the duration of protection for each fungicide.

The results showed that Pyricularia oryzae was drastically inhibited on the leaves of rice at 300 ppm combined dose of Carboxin + Thiram, whereas Helminthosporium oryzae was completely inhibited at a dose of 750 ppm with the same fungicide combination. However, this product caused a total leaf yellowing and requires repeated applications So it is not recommended. Pyrazophos has no effect on Helminthosporium oryzae even at very high doses. However, this product completely inhibited Pyricularia oryzae at a dose of 750 ppm per an experimental unit. To protect against rice leaf blast throughout the vegetative phase, the product should be applied every two weeks. On the other hand, the 750 ppm Tricyclazole totally inhibited the severity of Pyricularia oryzae on rice leaves. Whereas, a dose of 1500 ppm of the product was required to achieve the same level of protection against Helminthosporium oryzae. When this product was combined with Mancozeb, the H. oryzae was completely inhibited at 750 ppm.

Furthermore, Mancozeb inhibited both pathogens at a dose of 1000 ppm. However, when Mancozeb was applied each week to protect rice leaves until the end of the vegetative phase, a single application of Tricyclazole or a combination Tricyclazole + Mancozeb continued to protect rice leaves against P. oryzae and H. oryzae until the emergence of panicles. A treatment program with the most effective fungicides is then established taking account into the duration of rice plants protection throughout the vegetative phase against blast and leaf blight. The appropriate time for application for effective results is shown as follows:

Foliar treatment from the sixth week (from the day of planting) either by one treatment of Tricyclazole at 750 ppm against P.oryzae or Tricyclazole + Mancozeb at 750 ppm related to H. oryzae, one application of Pyrazophos at 750 ppm every 15 days against P. oryzae, or one application of Mancozeb at 1000 ppm every week against both pathogens.