By John Durham, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County
Gardeners in Colorado are warned often about the hazards of putting bedding plant transplants in too early. Who among us can't remember killing frosts in May?
There's also a good reason to delay the planting of certain vegetable seeds until late May - the seed corn maggot.
This insect attacks the seeds of many warm-season vegetables planted early when soil is still cool and often damp. Germinating seeds are eaten before seedlings appear above ground. Particularly vulnerable are the seeds of bean, corn and sometimes melon and cucumber.
Though pea is a cool-season vegetable recommended for early spring planting, the maggot will attack pea seeds if they take a long time to germinate because of saturated or cold soil. Young plants of cabbage, beet, onion, turnip, spinach, potato and radish occasionally may be nibbled as well.
The seed corn maggot is one-fourth inch long, and yellow-white in color. Maggots burrow in seed, either causing failure to sprout, or producing a weak, sickly plant. Additionally, the insect transmits a bacteria that causes soft rot.
The primary way to control the seed corn maggot is simply waiting until soil is warm enough to allow quick germination and rapid growth. In additional, avoid the application of fresh manure directly to your garden soil. The decaying organic matter from fresh manure attracts the egg-laying adult stage of the maggot.
In spring, apply only "aged" manure. You can use fresh manure, but only in fall. This allows adequate time for it to thoroughly rot before spring planting.
Photograph of seedcorn maggots Copryright Marlin E. Rice.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010