Seed Corn Maggot

Delia platura

Insectalso: Seedcorn maggot, Bean seed maggot

A small fly whose maggots tunnel into sprouting seeds and seedlings in cool, wet spring soil, hollowing out the seed before it can emerge. It is a common cause of poor, gappy stands of beans, corn, peas, and many other vegetables, especially in rich soil where manure or green matter was recently turned under.

🔎 How to spot it

The adult is a small grayish-brown fly about a fifth of an inch long, resembling a slender housefly, with wings that overlap over the back at rest. The maggot is white to cream, legless, tapered to a point at the head end, and up to about a quarter inch long, found burrowing in the seed or the base of the seedling. The brown, seed-sized pupae rest in the surrounding soil.

🥀 Damage it causes

The maggots bore into germinating seeds and eat the contents, often leaving only an empty seed coat so the seed never comes up, which shows as bare gaps in a freshly sown row. Seedlings that do struggle up are spindly, with few leaves, and may wilt and die, a symptom sometimes called snakehead in beans where the growing point is destroyed. Damage is worst in cold, wet springs that slow germination and give the maggots more time to feed.

🛡️ Prevent it

Plant into warm, well-prepared soil and wait for conditions that let seeds germinate fast, since quick emergence is the best defense and shallow planting in warm soil helps. Avoid sowing soon after turning under manure, cover crops, or heavy weeds, because decaying organic matter attracts egg-laying flies; let such material break down for several weeks first. Where the pest is chronic, use treated seed or set transplants instead of direct seeding.

🧯 If it is already here

There is no rescue once maggots are in the seed, so control is preventive: if a stand fails, wait for warmer, drier soil and replant, which usually escapes the problem. Insecticide- or fungicide-treated seed protects high-risk early sowings, and starting plants indoors for transplant sidesteps the vulnerable germination window. Good seedbed preparation and timing matter far more than any spray.

💡 Good to know

Seed corn maggot is a classic cold-wet-soil problem, so the same early planting that risks frost also risks this pest; warm soil and rapid germination are the cure. Because the damage happens underground before emergence, gardeners often blame old seed or rot when maggots are the real cause. Letting incorporated organic matter decompose before sowing greatly reduces egg-laying.

🌱 Plants it attacks

78 plants in the library can be attacked by this pest

Atlantic Giant Pumpkin

Black Bean 🥕Black Spanish Radish

Black-Eyed Pea

Bloomsdale Spinach

Blue Lake Green Bean 🥒Boston Pickling Cucumber

Broad Windsor Fava Bean

Delicata Squash 🥒Diva Cucumber 🌸Easter Egg Radish

Egyptian Walking Onion 🥒English Cucumber

English Shelling Pea

Field Pea

Fordhook 242 Lima Bean 🥕French Breakfast Radish

Golden Bantam Corn

Green Cabbage

Hubbard Squash

Jack-O-Lantern Pumpkin

January King Cabbage

Kabocha Squash

Kentucky Wonder Pole Bean

Pinto Bean 🌱Provider Bush Bean

Red Cabbage

Red Noodle Yardlong Bean 🧅Red Onion

Snow Pea 🥬Space Spinach

Spaghetti Squash 🧅Spanish Onion 🌱Sugar Daddy Pea 🎃Sugar Pie Pumpkin

Sugar Snap Pea

Suyo Long Cucumber

Sweetheart Cabbage

Tromboncino Squash 🥬Tyee Spinach

Vidalia Sweet Onion 🧅Walla Walla Sweet Onion 🥕Watermelon Radish

White Onion

Yellow Crookneck Squash

Yellow Summer Squash

Yellow Sweet Onion

For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.