Mexican marigold as Cover Crop for Pest and Weed Control
Answered by: Inge Poot and Conrad Richter
Question from: Jesse and Gary Woodward
Posted on: August 8, 1999

I am interested in growing mexican marigold (Tagetes minuta) as a commercial cover crop on northern Vancouver Island, BC, Canada.

What soil temperature is required for germination?

The seeds need light to germinate and a soil temperature of 10 degrees Celsius.

What weeds are adversely affected by Tagetes minuta? What crops? Are family Rosaceae (ie.: orchard trees) vulnerable to damage?

Among others it destroys ground elder, bindweed, couch grass, ground ivy. It will not damage any trees. The plant grows upwards to 6-8 feet high and when grown as a tight cover crop it literally chokes weeds out.

What pests or other invertebrates are killed or repelled? Slugs (hopefully!)? We have a soil pest unique to this part of North America: symphylans. Any information regarding these and T. minuta is welcome. We’ll report any results and observations gladly.

We would be delighted to hear of any results from you. Unfortunately, we have not heard that slugs or other molluscs are affected by this plant. A plant we used to be able to offer as seed, an Egyptian ragweed, Ambrosia maritima is the only plant we have heard of that kills molluscs. You might like to try Scanmask (predatory nematodes) for the symphylans.

The best studied pest control feature of the plant is its nematocidal property. Studies have shown that a cover of T. minuta can reduce soil nematode populations significantly.

What about fleas, ticks, mosquitoes - or other pests?

Tagetes minuta is reported to be effective for mosquito control. We have no information on its effect on other insects. There is plenty of anecdotal information that it repels insects but proper scientific trials are needed to verify and characterize this effect.

We’ll want to sell any marketable product deriving from a cover crop of T. minuta. Suggestions welcome.

In Kenya, fresh T. minuta extracts are made from the plant to treat nematodes in the field. Possibly, you could develop an anti-nematode product and commercialize it in North America.

How soon after sowing will we get some effective pest control?

The anti-nematode effect requires a full season. The insect repelling effect should be active within a month or so of planting. The weedkilling effect requires a full season.

How many lbs. per acre of seed for cover crop?

The recommended seeding rate is 150 grams to 3 kilograms per hectare, with the latter rate for a cover crop. This would be about 3 lbs (1.5kg) per acre.

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