Crop wastes from crucifers effective for pest control

A team of Filipino researchers from Bukidnon found crop wastes from crucifers as effective control for plant pests such as bacterial wilt (BW) in potato.

Crucifers are any of various plants in the mustard family (Cruciferae or Brassicaceae), which includes the alyssum, candytuft, cabbage, radish, broccoli, and many weeds.

The researchers, led by Fe Abragan of the Department of Agriculture-Northern Mindanao Integrated Agricultural Research Center (DA-NOMIARC) in Dalwangan, Bukidnon, found that crop wastes from crucifers left in the field after harvest effectively control soil-borne diseases of potato such as BW and root knot.

Based on research, root-knot nematodes (Meloidogyne spp.) are one of the three most economically damaging genera of plant-parasitic nematodes on horticultural and field crops.

On the other hand, bacterial wilt of potatoes (Pseudomonas solanacearum) is a destructive disease. It is most severe in tropical and subtropical climates with high rainfall like the Philippines.

Tomato is the most susceptible crop, but BW also infects tobacco, potato, eggplant, pepper, banana and over 200 other species.

The researchers said this ingenious approach of using crop wastes from crucifers for disease control is anchored on the concept of biofumigation — a process by which soil-borne pests and pathogens are suppressed by naturally occurring biocidal compounds called isothiocyanates (ITCs).

“These ITCs are released into the soil when tissues of crucifers such as broccoli, radish, cauliflower, cabbage, etc., decompose,” they said.

In crucifer-growing areas in Bukidnon, a survey showed that 60 to 80 percent of crucifer stems and leaves were left on the field after harvest.

To evaluate the potential of these crop wastes as biofumigants against BW and root knot, the DA-NOMIARC 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 tons per hectare (t/ha) or five kilograms per square meter (kg/m2).

The team found out that when soil was incorporated with a mix of different crucifers at the recommended rate, BW incidence could be as low as 21 percent.

“If untreated, BW incidence can reach up to 58 percent. The mixed treatment also gave the highest yield of 11 t/ha. Without these mixed crucifers as biofumigants, yield could be as low as six t/ha,” the researchers said.

The use of mixed crucifers reduced nematode counts on-farm by 87 percent. Nematode population increased to 17.2 percent without biofumigation, they said.

Nematodes belong to a phylum of worms having a long, round and generally smooth body. They are mostly parasites in plants and animals, but some are freely living in soil or water. They are also called Nematoidea.

Based on the on-farm trials for BW in Lantapan, Bukidnon, the use of mixed crucifers as biofumigants resulted in higher yields of eight to 11 t/ha, net income of P198,000 to P286,000, and return on investment (ROI) of 133 to 193 percent.

“Without biofumigation, low yield of 6.67 t/ha, net income of P166,750, and ROI of 114 percent were noted,” the researchers said.

The research project was funded by the Australian Center for International Agricultural Research and monitored by the Los Baños-based Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCARRD), an attached agency of the Department of Science and Technology.

According to PCARRD, bacterial wilt 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 percent, while root knot accounts for 25 to 50 percent yield loss in many crops, including potato, the agency said.