Insects: soil pests

Primary symptoms

Soil pests primarily cause root damage leading to reduced plant density and weakened or stunted plants . Physical damage to the roots is a clear indication of damage. Because of the effect of these insects, along with nematodes, on plant roots, they can cause problems of drought stress or lodging.

Confirm the problem by checking below.


Causes of soil pest problemsAdditional evidence required
High natural level of infestatation, or high level of insects due to constant maize cropping. Dig up area around affected plants early in the morning. Look for larvae. A laboratory test is required to confirm nematode infestation. Ask the farmer about rotation patterns.
Poor weed control, or poor incorporation of previous crop residues. Ask the farmer about weed populations during the fallow period and about land preparation. Look over the field for persistent weeds, which serve as insect hosts, or for residues on the soil surface.
Termites tend to prefer maize over other crops. Check if maize fields are more severly affect than adjacent fields planted to other crops.

Soil insects can be particularly damaging in maize because they reduce plant density, and maize cannot easily recover from low densities. These insects, along with nematodes, can also affect the plant roots and cause problems of drought stress or lodging.

Note: This section does not attempt to describe all soil insects—rather it describes the overall effect and possible management of such insects.

Are soil insects a problem?

Evidence: observations.

  1. Is plant emergence irregular? Dig up seeds in the areas where emergence is poor and use the problem key to interpret what you find.

  2. Are the plants wilted even though soil moisture is adequate? Pull lightly on the plant. Cutworms or white grubs may have eaten through it at the base. Dig up a wilted plant and examine the roots. Look for larvae inside the roots or sections which have been chewed. Cut open the plant all the way down the length of the stem and look for larvae or tunnels where they have been.

  3. Another possible (though not common) cause of root damage is nematodes. These tiny organisms can cause stunted, discolored root systems, but the definitive diagnosis of nematode problems requires laboratory analysis.

  4. Look for plants that have curved stems or which are root lodged. Pull on the stem of the plant lightly; if many roots are damaged, the plant can easily be pulled out of the ground. Dig up some plants and look for clipped roots and tunnels. Dig up the soil around affected plants-cutworms are often found in the soil near the plant.

  5. Look for termite mounds in the fields in areas where termites are common. These insects cut maize roots and can cause lodging at or after the VT stage.

Possible solutions

Note: All solutions require the correct identification of the insect. Use the pest key or request help from an expert if you are uncertain.

  • Treat the seed with a protective chemical or apply a systemic insecticide.
  • Rotate with another crop to reduce the infestation.
  • Change tillage practices to reduce insect populations.
  • Plant a resistant variety if one is available.
  • Move maize away from termite infested fields.