Sweetpotato Weevil

What it looks like

Adults are slender, ant-like weevils about 1/4 inch long with a blue-black head and wing covers and a red-orange middle. Grubs are legless, white, and curved, with a pale head.

Damage

Grubs tunnel through stems and storage roots. Damaged roots give off a bitter taste and smell, even with light feeding, and are often unusable. Damage keeps going in storage.

How nematodes help

The eggs, grubs, and pupae live inside the storage roots and the base of the stem, down in the soil where nematodes can reach them. Adults get to the roots through cracks in the soil.

Results are mixed. In lab tests in Sri Lanka, Heterorhabditis nematodes killed 80 to 90% of the weevils and S. feltiae (the nematode in Scanmask) killed 70 to 80%, with some benefit in the field. A Puerto Rico study found S. carpocapsae (the nematode in Ecomask) worked best, and an earlier one rated it above H. bacteriophora (the nematode in Heteromask). Field trials in Hawaii with S. feltiae didn't give a clear answer. All three kinds of nematodes have killed sweetpotato weevils in these studies.

In university research, the timing that worked best was from when the roots start to form (about 6 weeks after planting) until harvest, in mid to late summer, repeated every 3 to 4 weeks.

How to apply

Treat with Scanmask.

When: March to June, or mid to late summer from about 6 weeks after planting.

Where: Spray the soil along the sweet potato rows and around plant crowns, and water it in. Keep soil moist and fill cracks.

See How to apply for step-by-step directions, or use the calculator on the Scanmask Spray page to see how much you need.