Crop Residue Invites Seedcorn Maggot

Seedcorn maggot is now one of the biggest below-ground threats to soybean production. Changes in agronomic practices in recent years have contributed to the increasing prevalence of this pest in fields in eastern Canada. This includes reduced tillage, green manure (cover crops) and fresh manure applications. “These practices leave residue on the field, creating conditions that attract this pest,” says Abhi Deora, Seedcare Technical Lead at Syngenta.

Attracted to degrading organic matter

As Deora explains, seedcorn maggots overwinter as pupae and emerge as flies in the spring. “They can sense the degrading organic matter in the soil and will fly into those fields to lay their eggs,” he says. Larvae hatch in seven to 10 days and begin feeding on seeds and young seedlings.

Seedcorn maggots cause damage by attacking the seed and tunneling through the shoot. As a result, some plants will wilt and others never even emerge, leaving large gaps in the soybean stand. Cotyledon feeding is another damage symptom of seedcorn maggots.

Image: Tunneling damage caused by seedcorn maggot

Image: Cotyledon feeding by seedcorn maggot

Unpredictable pest

What makes seedcorn maggot so threatening is you can’t always predict when they will appear. “You can scout for some pests more easily like wireworms and white grubs as they overwinter as larvae, but seedcorn maggots overwinter as pupae in the soil, which are very small in size – similar to a grain of wheat. This makes them difficult to locate,” says Deora.

Even if you don’t have residue in your soybean field, they could be attracted by a neighbouring field that does. “They can fly far distances and devastate whole fields when conditions are conducive,” says Deora. “You need to be proactive. Insecticide seed treatments are the only option that we have to protect against this particular pest.”

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Image: Seedcorn maggot larvae. The translucent, yellowish-white maggots are small (< 5 mm), legless and oblong-shaped with a pointed anterior. They lack heads but have small black mouth hooks in front.

Management tips

• Scout for pupae of seedcorn maggots in the fall
• Fields with a history of persistent seedcorn maggot pressure should consider late and shallow planting and higher seeding rates
• Plant only once the soil has reached an appropriate soil temperature
• Avoid heavy manure applications in the three to four weeks before planting
• Kill or plough down green manure or cover crops at least three to four weeks ahead of planting

Protect your soybeans from below-ground feeding

Early-season protection against pests like seedcorn maggot is critical to give your soybeans a strong start. Fortenza^® is a new non-neonicotinoid soybean seed treatment that is applied as a commercial seed treatment that protects soybean seeds and seedlings from below-ground insect feeding. It’s formulated with cyantraniliprole (Group 28 insecticide) for control of seedcorn maggot, European chafer, June beetle larvae and wireworm. Even under heavy insect pressure, Fortenza helps producers build a strong soybean stand with faster, more uniform growth.

What other pests could be lurking below ground in your soybean field and putting your young crop at risk? Watch for more articles on white grubs and wireworms to get to know these damaging pests and plan your defence.

Always read and follow label directions. Fortenza^® is a trademark of a Syngenta Group Company. © 2019 Syngenta.