PLANTING tomato and garlic near cabbage farms reduces damages caused by diamondback moth (DBM), cutworms, and other harmful pests attacking the crop.

The technique, called companion planting, is planting two or more plants close to the main crop so that some biological and cultural benefits, usually pest control and higher yields, could be derived.

The profitability of using tomato and garlic as companion crops of cabbage was proven in a study conducted by researchers Lucricia Conchita G. Cocson and Lagrimas J. Flojo of the MMSU Research Directorate. The test was done in one of MMSU’s experimental farms during the October-February dry season.

Results showed that the cropping combination of cabbage and tomato markedly reduced the damages caused by DBM and Hellula pests, while the cabbage and garlic combination reduced the damages inflicted by cutworms.

DBM and Helllula are two main pests that feed on cabbage shoots at the early stage of the plant. This incident causes the plant not to produce heads, or leads the plant to produce multiple heads that are non-marketable.

In terms of yield, the cabbage-garlic combination gave a total head yield of 14.86 tons per hectare, while the cabbage-tomato combination gave 13.86 tons per hectare.

“These cropping combinations have produced marketable yields of 12.58 and 13.54 tons per hectare, respectively,” the researchers said, adding that in terms of net income, the combinations gave P251,190 and P284,560, respectively.

Companion planting is one approach in the Integrated Pest Management (IPM) technology which the university is aggressively advocating to help combat the incidence of pests and diseases in crops. It aims to manipulate the environment to take advantage of the insects’ dispersed activities and on their preference for one host plant to another. IPM is a harmonious combination of cultural, biological, and chemical methods of controlling pests and diseases. Its ultimate aim is to reduce the application of pest control chemicals to a minimum.    

The strategy of companion planting in cabbage attempts to divert the attention of the insects from the main crop by presenting them a more favorable substitute, or a crop that would be deterrent to them.

The researchers said that this technique is a very effective way to increase environmental health and productivity while reducing pest problems. In IPM, companion crops repel or confuse the pests that use their sense of smell to find their host. Research showed that the strong smell of garlic, marigold, daisies, ginger, and fragrant herbs are good to intercrop in backyard gardens.

Allicin, the active compound in garlic, is sulfur and is produced when the clove is broken. This serves as defensive mechanism of the plant in deterring birds, insects, and worms from eating it.

On the other hand, tomatoes contain a toxin called tomatim, which makes the plant unpalatable to some worms. The compound repels DBM larvae, and caterpillars that chew cabbage leaves.

To determine what other companion crops could be suitable for cabbage, the researchers also tested marigold and onion in separate plots. They also established a farm without a companion crop to serve as control plot.

Results showed that among the companion crops tested, only tomato and garlic were proven to have lessened the damages caused by insects, resulting in a higher yield for cabbage than the control plot.

In selecting a companion crop, one should consider the following agronomic characteristics of the plant: 1) it should have repelling properties such as strong aroma and unfavorable taste; 2) it should not share common pests with the main crop; 3) it should not compete with the main crop for nutrients, space, and sunlight; and 4) it should be early maturing and high yielding so that it could give additional income.

Its application on cabbage

Companion crops should be planted three weeks before transplanting cabbage to enable them to develop enough leaves so that they will readily deter insect pests away from the newly transplanted cabbage.

These crops must be planted near the cabbage farm, about 0.8 meters along the perimeter and one meter apart from the main crop to avoid competition for nutrients and sunlight.

Cabbage must be transplanted in sunken beds which measure 0.4 meters wide at 40 x 40 centimeter distance between hills. Before transplanting, furrows should be watered to moisten the soil. Newly transplanted seedlings along the furrows should be watered again to establish good root contact with the soil.