Effects of Fungicides on Earthworms
MetadataShow full item record
Fungicides use is one of the strategies to increase crop yields and production, minimizing postharvest losses and improving quality of harvest. These fungicides get in contact with nontarget organisms for example earthworms hence disrupting their ways of life, physiology, and functionalities which in turn affects the soil functions, productivity and health. There is a limited understanding of the impact of the use of these fungicides on earthworm abundance, growth parameters and species diversity. This study was conducted at Makerere University Agricultural Research Institute Kabanyolo (MUARIK) to evaluate the impact of 3 commonly used fungicides: coppermate (at two application rates: 2kg/ha and 2.5kg/ha), mancozeb (at four application rates: 1.8kg/ha, 2.2kg/ha, 3.8kg/ha and 4kgha) and azoxystrobin (applied at 500ml/ha) and method of extraction of earthworms at two levels: detergent (20g/l) and onion solution (175g/l) on earthworm abundance, growth parameters and species diversity. This gave eight fungicide treatments: control, coppermate1, coppermate2, mancozeb1, mancozeb2, mancozeb3, mancozeb4 and azoxystrobin. Each treatment was replicated thrice in a randomized complete block design, giving a total of 48 experimental units (8 fungicide levels x 2 extraction methods x 3 replications). The earthworm parameters investigated included; earthworm numbers, earthworm length, earthworm clitellum length, earthworm weight, and species diversity earthworm species. The data collected were subjected to ANOVA using GenStat Statistical Package 14th edition. The population density of earthworms was highest (3.8±0.53)/ft2 under tomato plots which received 2kg/ha coppermate and lowest (1.0±0.53)/ft2 in the control which was also comparable to 1.2±0.53 earthworms/ft2 for tomato plots which received 4kg/ha mancozeb. The mean number of earthworms from the lower mancozeb dozes (1.8, 2.2 and 3.8kg/ha), the higher coppermate doze (2.5kg/ha) and azoxystrobin (500ml/ha) were comparably lower than that under plots which received 2kg/ha of coppermate but relatively higher than the control and 4kg/ha mancozeb. The average length of earthworms was longest (5.7±0.31cm) per earthworm for earthworms under 2kg/ha coppermate which also tended to have the highest number of earthworms and shortest (2.77±0.31cm) for earthworms from plots which received 4kg/ha mancozeb. An increase in the application rate of mancozeb from 1.8kg/ha to 3.8kg/ha resulted in an increase in the length of the earthworms from 2.8±0.31cm to 5.5±0.31cm, higher dose than 3.8kg mancozeb/ha suppressed average earthworm length to 2.77±0.31cm which was the shortest. An increase in the application rate of coppermate from 2.0 to 2.5kg/ha also suppressed average earthworm length to 4.2±0.31cm below the average length for earthworms under the control (5.1±0.31cm) which closest to the highest mean earthworm length observed for earthworms under the 2kg/ha coppermate treatment. Average clitellum length was longest (0.4±0.02cm) per earthworm was from plots which received 2kg/ha coppermate and earthworms under the control. The shortest average clitellum length (0.1±0.02cm) was for earthworms from plots which received 4kg/ha mancozeb, 1.8kg/ha mancozeb and azoxystrobin. As it was the case for average earthworm length, increasing the application rate of mancozeb from 1.8kg/ha to 3.8kg/ha also resulted in increase in average clitellum length of the earthworms from 0.1±0.02 to 0.3±0.02. 9 Similarly, higher dose of mancozeb than the 3.8kg/ha also suppressed earthworm clitellum length to one of the shortest. There was also a drastic reduction in average clitellum length for plots which received 2.5kg coppermate/ha relative to those which received 2kg coppermate/ha. The highest mean weight (0.74±0.08 g) per earthworm was from tomato plots which received 2kg/ha coppermate whereas the lowest (0.04±0.08 g) was from tomato plots on which 4kg/ha mancozeb had been applied. Increase coppermate application rate from 2-2.5kg/ha and mancozeb from 2.2-4kg/ha resulted in a decrease in the weight of the earthworms. The mean of the number of earthworms extracted from detergent (3.08±0.53)/ft2 was higher than (1.37±0.53)/ft2 which was from onion solution. The mean length of earthworms, (5.64± 0.31cm earthworm-1) extracted from detergent was higher than (3.05±0.31 cm earthworm-1) from onion solution. The mean weight of earthworms extracted using detergent (0.410±0.08 g earthworm-1) was significantly higher than the (0.176±0.08 g earthworm-1) using onion solution. The higher mean clitellum length of earthworms (0.3±0.02 cm earthworm-1) was extracted from detergent while the lower mean (0.15±0.02 cm earthworm-1) was from onion solution. However there was no significant effect of the interaction between treatment and method of extracting earthworms on all the earthworm parameters determined in my study at MUARIK implying that the measured parameters depended on either the type of fungicide or method used to sample the earthworms rather than on the type of fungicide used. Mancozeb is a very toxic fungicide to earthworms and a threat to their lives. The use of coppermate at a rate of 2kg/ha should be more encouraged than the use of mancozeb and azoxystrobin or rates of coppermate higher than 2 kg/ha because of the positive effect it had on all earthworm parameters measured in this study. The order of toxicity of fungicides to earthworms in this study was Mancozeb > azoxystrobin > coppermate. For more accurate results when extracting earthworms from treated soils in the field, detergent should be used as an expellant of earthworms for study purposes.