Biofumigation for control of bacterial wilt and root knot diseases in potato

To evaluate the potential of biofumigation against soil-borne diseases affecting white potato, Abragan et al. (DA-NOMIARC) conducted on-station and on-farm trials using locally grown crucifers as biofumigants in Dalawangan, Malaybalay City and Lantapan, Bukidnon [Philippines] from 2005 to 2006. The study was conducted in a 300 sq.m area naturally infected with BW [bacterial wilt]. Leftover crucifer leaves, stems and roots were gathered, chopped, shredded and applied at a rate of 50 t/ha or 5 kg/sq m per treatment. For the root knot nematode (RKN) study, a 300-g soil sample was taken from each plot for laboratory analysis before incorporation of shredded crucifers and 1 ½ months after incorporation. Nematodes were counted through extraction method from soil samples in each treatment. Findings of the study revealed the following: on-station trials utilizing chopped (radish, broccoli and cabbage) and shredded (broccoli and cabbage) crucifers showed that an initial Rolstonia solanacearum (Rs) population count of 81,050 cfu/g, mean population densities after harvest were significantly lowere in all treatments. Lowest mean population density after harvest of 45,341.95 cfu/g was noted in chopped broccoli followed by chopped cabbage (46,962.20 cfu/g). However, there was a dramatic increase in Rs population count of 190,641.55 cfu/g in untreated plots. BW infection (6.59 _ 9.95%), number of infected tubers (18-25), and yield (7.81 _ 8.75 t/ha) were comparable in all chopped and shredded treatments. However, untreated plots had the highest percentage of BW infection (32.48%), most number of infected tubers (31), and lowest yield (4.071 t/ha). On-farm trials in Lantapan, Bukidnon utilizing chopped radish, cabbage, broccoli, cauliflower, and mixed crucifers showed that soil incorporated with crucifers had significantly lower BW incidence (21.13 _ 44.27%) compared with untreated plots (57.79%). The lowest percentage of BW incidence was obtained with mixed crucifers ar 21.13%. The lowest number of infected tubers was obtained with chopped radish at 2.28 t/ha. The mixed treatment also gave the highest yield of 11.44 t/ha, but this was comparable to the yield in the cauliflower treatment (11.04 t/ha). The untreated plot had the lowest yield of 6.67 t/ha. On-station trials using shredded crucifers as biofumigants against RKN showed that at varying initial nematode counts ranging from 621 to 683 during pre-treatment, RKN population count was significantly reduced in all shredded treatments 1½ months after incorporation. Shredded mixed crucifers showed the highest percentage reduction in RKN population of 83.6% followed by radish (79.2%), broccoli (74.2%), and cabbage (68.4%). In untreated plots, however, a 24.1% increase in RKN population was noted. On-farm trials utilizing shredded crucifers as biofumigants against RKN in Lantapan, Bukidnon showed at varying initial nematode counts ranging from 684 to 712 during pre-treatment, nematode population decreased significantly with mixed crucifers by 86.7% followed by radish (85.4%), broccoli, (82.2%), cauliflower (71.3%), and cabbage (70.9%). However, a significant increase in nematode population of 17.2% was observed in untreated plots. Economic analysis based on the on-farm trials for BW in Lantapan, Bukidnon utilizing chopped radish, cabbage, broccoli, cauliflower and mixed crucifers showed that white potato grown in soil incorporated with crucifers gave higher yield (7.92 _ 11.44 t/ha), net income (P 198,000 _ 286,000), and ROI (133 _ 192.84%). Mixed crucifers obtained the highest marketable yield, net income, and ROI. Untreated plots had the lowest yield (6.67 t/ha), net income (P 166,750), and ROI (113.97%). The use of waste materials from locally grown crucifers was effective in suppressing BW and RKN in the soil. The use of mixed crucifers was recommended because it had the highest percentage reduction in nematode counts both in on-station (83.57%) and on-farm (86.7%) and lowest percentage in BW incidence (21.13%), highest marketable yield (11.44 t/ha), and ROI of 192%.