Companion planting helps control insects

Tomato and garlic planted around cabbage plants can control major insect pests like diamondback moth (DBM), Hellula, and cutworms, among others.

Researchers of the Mariano Marcos State University (MMSU) in Ilocos Norte, led by Dr. Miriam Pascua, found in a three-year study that companion planting with tomato or garlic results in higher marketable yields and net income on cabbage. 

This strategy, called companion planting, tries to divert the insects from the main crop by presenting to them a more favorable substitute or a crop that would be deterrent to them, said Lucrecia Cocson and Lagrimas Flojo. It is also a very effective way of protecting environmental health and increasing farm productivity. 

Results of the study showed that cabbage plus tomato combination significantly reduced the damages caused by Hellula and DBM. On the other hand, the cabbage plus garlic combination reduced cutworm damages.

Hellula is an insect that feeds on cabbage shoots at the early vegetative stage of the plants. Its damages come in either of two ways: one, the crop does not produce any head at all; two, the plants may produce multiple heads that are not marketable.

DBM larvae are voracious feeders on cabbage heads. This insect may cause farmers to lose 80 to 100 percent of their expected yield if left uncontrolled. Damaged cabbage heads become unmarketable.

Cocson and Flojo harvested a total cabbage head yield of 14.86 tons per hectare (t/ha) in the cabbage plus garlic combination, and 13.86 t/ha in the cabbage plus tomato combination.

The percentage of marketable yield was higher in the cabbage plus tomato combination (97.7 percent or 13.54 t/ha). In contrast, the cabbage plus garlic combination had only about 85 percent marketable yield (12.58 t/ha), resulting in a difference of almost one ton per hectare.

Translated into net income, the cabbage plus tomato combination had higher net income of P284,560/ha, while the cabbage plus garlic combination had only P251,190/ha. 

What is it in tomato and garlic that makes them effective companion crops? Cocson and Flojo said tomatoes contain a toxin known as tomatin, which makes the plant unpalatable. Tomatin repels the DBM larvae or caterpillars from chewing the cabbage leaves.

On the other hand, garlic contains an active ingredient known as allicin, a sulfur compound produced when the garlic glove and leaves are broken. Allicin deters insects, birds, and worms from feeding on cabbage plants.

The two ladies recommend that a companion crop should be planted at least three weeks before transplanting cabbage. By then the companion crop has produced enough leaves and could readily deter insects away from the newly transplanted cabbage. 

Plant the companion crop around the cabbage crop – about 0.8 meter along the perimeter and one meter away from the main crop to avoid competition for nutrients and prevent shading.

The main crop – cabbage – must be transplanted at the bottom of the furrows, 40 cm x 40 cm. The furrows must be moist to facilitate transplanting. Water the newly transplanted seedlings along the furrows to establish good root contact with the soil. — Sosimo Ma. Pablico