How to Manage Maize Stemborers

Backgrounder

Is the maize stemborer a problem pest for you? If so, don’t despair. You can rescue your crop and reduce pest damage if you take the time to observe your crops and the stemborers carefully.

Start by watching the activity of the stemborers. You will see that they start by chewing holes in the leaves of corn, rice, and other grain crops. Then they chew into stems and stalks, cutting off the flow of nutrients and water to the rest of the plant. The worst part is that you might not know they are there until the damage is done.

Look for holes in the leaves to find out where the stemborers are. When you know where they are, it’s much easier to control them. For example, in the Philippines, farmers noticed that maize stemborers often begin by eating the tassels (male flowers) of the corn. So, after pollination, they pull out the tassels and burn or bury them to kill the stemborers.

The best time to control stemborers is while they are still chewing the leaves. If you don’t control them then, before they enter the plant stems, the stems break in the wind and the plants wither and die.

Here are some ways to manage stemborers:

Intercropping Growing your grains and legumes together in alternating rows is one good idea. In India farmers protect sorghum from stemborers by intercropping with legumes such as lablab beans (Dolichos lablab) and cowpeas (Vigna unguiculata). When low lying legume plants are mixed in with your grains it is harder for the pests to find the straight, tall, grain crops they want to lay their eggs in.

You can also try growing maize and sweet potatoes together. Tiny, friendly wasps called Trichogramma wasps are attracted to sweet potatoes. These wasps kill stemborers by laying eggs in the stemborers’ eggs. So it’s good to have them around.

Rotation It is also important to remember not to grow one kind of crop in the same place every year. Change the crops you grow in one field. For example, grow grains one year and legumes or vegetables the next year. If you grow crops that are attacked by stemborers followed the next year with crops that are not attacked by stemborers, it will be more difficult for the stemborers to survive from one season to the next. Rotation is a useful pest control strategy and one you can use with all your crops.

Encourage natural enemies Friendly insects can be your best friends in controlling stemborers and other pests. For example, ladybugs (Hippodamia convergens) can eat as many as 60 borer eggs in one day. Also try to grow some plants with small flowers. These flowers attract small, friendly wasps such as Trichogramma wasps.

A light trap Another way to help keep the stemborer population down is to kill the stemborers when they are moths, in otherwords at the adult stage of their life cycle. A light trap might do the trick. All you need is a lamp or lantern and a pan of water. Hang the lamp over the water on a simple tripod made of wooden poles. The moths will hit the lamp and fall into the water. You can make the trap more effective by adding a bit of kerosene or cooking oil to the water. The oil sticks to the bugs and they sink to the bottom of the pan. The best time to set up the light trap is before the maize or sorghum flowers because this is before the female adult has laid her eggs.

Sprays and dusts If you decide to use a spray to control stemborers it is important to spray while they are still outside the stems of your crops. Once they are inside the stems most sprays will not reach them.

Neem seed spray is one of the homemade pesticides you can use to control stemborers before they enter the stems. Collect seeds from ripe neem fruit. Dry and clean the seeds well. You will need one big double handful of seeds for every litre of spray you prepare. A double handful is the amount of neem seeds you can scoop up with two hands. If you want to prepare 10 litres of spray, crush or grind 10 double handfuls of seed into a coarse powder. Mix this powder with 10 litres of water. Stir the mixture well. Leave it covered overnight. The next day, filter the mixture through a fine cloth. Apply the spray with a sprayer, a watering can, or a small broom.

If you grow rice, you can use neem in a different way. Just take neem seeds, crush them roughly and mix them into the soil of your field. When it rains or you irrigate, the neem will mix with the water and go into the plant where it helps the plant protect itself against stemborers and other pests.

What if the stemborers are already in the stem? Once the stemborers have bored into the stems of your crops, it’s harder to control them. Here is one technique to try. Slit the stem and remove or kill the borer. Then pile the soil around the stem until it covers the hole in the stem and the next section of leaves if possible. What you are trying to do is make new roots grow higher up on the stem to better support the weakened stem.