Dry Beans XIII-1
Seedcorn Maggot
Gary L. Hein & Frank B. Peairs
Seedcorn maggot eggs, left; larva, center;adult, right
Seedcorn maggot is a sporadic pest of dry beans that is most often seen when beans are planted into fields with high organic matter, especially recently tilled small grain stubble.
Identification (and life cycle/seasonal history)
The seedcorn maggot overwinters in the pupal stage, and the first adult activity in the spring occurs in April or early May. The adult seedcorn maggot is a hairy, gray fly about 1/5 inch long that lays eggs in areas high in decaying organic matter (i.e. manure, plant residue) that have just been tilled. In this region, small-grain stubble increases the risk of damage. The maggot is yellowish white, legless and about 1/4 inch long. Offspring of these adults mature to form a second generation of adults in late May or early June, and another generation is produced that is most likely to affect dry beans.
The maggot has a minimum developmental temperature of 39oF, and it takes 677 F degree-days (about 4 weeks) to develop from egg to adult. Adults are active in temperatures down to the mid 40’s. But, when temperatures consistently reach above the mid 80’s, adults do not survive well, and pupae become dormant until the following spring.
Plant Response and Damage
Seedcorn maggots have a wide host range and even feed on organic matter in the soil. In dry beans, maggots feed on the germinating bean seed and hollow out or otherwise damage the cotyledons. Severely damaged seeds may not emerge. If maggots damage the growing point of the plant, a “snakehead” plant may result. Snakehead plants are characterized by much reduced cotyledons and ragged edges at the growing point where feeding occurred. They will be very slow to produce their first leaves, if they produce them at all. Later, maggots feed by burrowing within the stem. This feeding may increase the incidence of secondary disease within the stem. Damaged seedlings will be stunted and have reduced vigor.
Management Approaches
Seedcorn maggot is most likely to cause serious problems during periods of cool and wet conditions. Typically, dry beans are planted later in the spring when soil temperatures are optimal for emergence and establishment of the beans. To reduce the risk of damage from seedcorn maggot: plant when soil conditions will enable rapid emergence of seedlings and plant establishment, use seed treatments when planting in a high risk field, such as, recently worked small grain stubble or other fields with high organic matter, and manage areas with high crop residue by fall or early spring tillage to avoid attracting flies for fly egg laying just before planting.
Products for Seedcorn Maggot:
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Insecticide |
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Preharvest Interval, remarks |
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Thimet 20GR |
4.5-7.0 oz/1000 row ft |
Apply at planting; drill to side of seed, not in contact with seed; PHI 60 days; REI 72 hrs. |
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RRestricted use pesticide 1Labeled for chemigation |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Dry Beans, Insects, Seedcorn Maggot
Date: 04/24/2006