Effects of fungicide dosages, staking and plant densities on development of late blight on tomatoes in Tigoni
Kinyagia, Benson M.
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Tests were conducted in the field to investigate the effects of (i) fungicide, dosage and frequency of application, (ii) staking and (iii) different plant densities on development of late blight disease (Phytophthora infestans) on tomato (Lycopersicon esculentum). All the tests were replicated four times and arranged in a randomized complete block design. In order to investigate effects of fungicide dosage on disease development, tomato plants were sprayed with metalaxyl-mancozeb (Rodomil-MZ) at 100% dosage (160 gm/20 l. of water), 75% (120 gm/20 l. of water) dosage, 50% (80gm/ 20 i. of water) and non-fungicide control after every 7 day intervals. To investigate the effects of reduced frequency of fungicide application on the disease, spraying was done after 7, 14 and 21-day intervals. To investigate the effects of staking on late blight plants were staked using 2-m long sticks. To determine the effects of different planting densities on late blight disease development, tomato plants were planted with spacing of 120 cm by 80 cm, 90 cm by 60 cm and 60 cm by 40 cm. Plant performance assessment was based on plant height, fruit weight, number of fruits, and number of culls and expressed in tonnes per hectare. Fungicide dosages influenced disease development differently. The 100% dosage had significantly (p=0.05) the lowest mean disease severity index (MDSI) of between 1.25 and 2.63 and mean disease incidence index (MDII) of between 2.13 and 5.13, while the non-fungicide application (control) had the highest MDSI of between 4.25 and 5.5 and MDII of between 5.5 and 6. However, those sprayed at 100% and 75% did not differ significantly (p=0.05). There was a significant difference in MDSI and MDII when spraying was done after 7, 14 and 21-day intervals. The 21-day interval treatment had significantly the highest MDSI of between 3 and 4.75 and MDII of between 4.25 and 5.63. The MDSI of between 1.75 and 3.38 and MDII of between 2.38 and 4.63 associated with spraying after 7 and 14 days during the long rains were found to be significantly (p=0.05) different. Staking plus fungicide gave MDSI of between 1.25 and 2.38 and MDII of between 1.25 and 4.55 that were significantly (p=0.05) lower than those associated with fungicide alone, staking alone, and no-fungicide no-staking treatments (control). Significant (p=0.05) differences in MDSI and MDII were detected among various plant spacing. The lowest MDSI of between 1.13 and 3.5 and MDII of between 1.25 and 5.5 were associated with 120 cm by 90 cm spacing. The highest MDSI of between 3.25 and 5.38 and MDII of between 4.13 and 6 were associated with 60 cm by 40 cm spacing. In conclusion it can be noted that fungicide dosage and frequency of application are critical in management of late blight disease. Staking plus fungicide treatment was found to be highly effective in control of the disease, however, staking alone not a sufficient measure of control. Plant densities were to have notable influence on development of late blight disease.