Crop wastes from crucifers left in the field after harvest have been found to be effective in the control of soil-borne diseases of potato such as bacterial wilt (BW) and root knot in Bukidnon. This is the finding of a team of researchers led by Ms. Fe Abragan of the Department of Agriculture-Northern Mindanao Integrated Agricultural Research Center in Dalwangan, Bukidnon.

This ingenious approach of using crop wastes from crucifers for disease control is anchored on the concept of biofumigation. Biofumigation is a process by which soil-borne pests and pathogens are suppressed by naturally occurring biocidal compounds called isothiocyanates (ITCs). These ITCs are released into soil when tissues of crucifers such as broccoli, radish, cauliflower, cabbage, etc., decompose in the soil.

In crucifer-growing areas in Bukidnon, the survey showed that 60-80% of crucifer stems and leaves are left in the field after harvest. To evaluate the potential of these crop wastes as biofumigants against BW and root knot, the team gathered leaves, stems, and roots of crucifers left from the previous harvest. These were chopped, shredded, and incorporated in the soil at a rate of 50 t/ha or 5 kg/m2.

The team found out that when soil is incorporated with a mix of different crucifers, BW incidence could be as low as 21%. If untreated, BW incidence can reach up to 58%. The mixed treatment also gave the highest yield of 11 t/ha. Without these mixed crucifers as biofumigants, yield could be as low as 6 t/ha.

The use of mixed crucifers also showed the highest reduction of 87% in nematode counts on-farm. Nematode population increased to 17.2% without biofumigation.

Based on the on-farm trials for BW in Lantapan, Bukidnon, the use of mixed crucifers as biofumigants resulted to higher yields of 8-11 t/ha, net income of P198,000—P286,000 and return-on-investment (ROI) of 133-193%. Without biofumigation, low yield of 6.67 t/ha, net income of P166,750, and ROI of 114% were noted.

BW caused by Ralstonia solanacearum and root knot caused by nematodes (Meloidogyne spp.) are major constraints in potato production. In Benguet, Bukidnon, and Davao del Sur, BW infection can reach up to 90%, while root knot accounts for 25-50% yield loss in many crops including potato.

Results of the project have been documented by PCARRD through its nationwide monitoring and evaluation activities.