golden cornflower, guild weed, yellow daisy, yellow ox-eye
Chrysanthemum segetum L.
An annual weed of acid arable soils, locally common throughout the UK but decreasing and described as a vulnerable species by the BSBI. Corn marigold was probably introduced in the Neolithic period and was formerly one of the worst weeds in cornfields on sands and lighter loams. Seed cleaning, liming and herbicides are thought to be responsible for the decline. There were laws in Scotland and Denmark that obliged farmers to root out the weed.
In early surveys of Bedfordshire, Hertfordshire and Norfolk it was confined to non-calcareous sands where it was locally dominant but elsewhere was not very frequent. Although absent to rare in most areas it was still common to abundant at 18% of sites when surveyed with other arable weeds in 1971-73. It was most troublesome on loamy and sandy soil. It is said to like acid conditions and is thought to be an indicator of soils that are low in calcium, but other factors may be involved. Corn marigold is not recorded above 1,100 ft in the UK.
Corn marigold flowers from June to September, or even into October. The average number of seeds per flower head is 176 and there is an average of 7 flower heads per plant. Seed numbers on individual plants can be very high, 13,500 seeds have been recorded on a single plant. A plant will continue to ripen seeds even when pulled up.
Light, nitrate, chilling and alternating temperatures interact to promote germination. Seeds germinate from March to October but the main seedling emergence period is March to April. In sandy soils the majority of seedlings emerged from the top 30 mm of soil with the odd seedling emerging from down to 70 mm.
Corn marigold seeds can lay dormant in the soil and have retained 12% viability after 5 years burial. Seeds in dry storage gave 11% germination after 5 years. Seeds broadcast onto the soil surface, ploughed to 20 cm and followed over a 6-year period of cropping with winter or spring wheat had a mean annual decline rate of 67%. The estimated time to 95% decline was 3 years. Under a grass sward, corn marigold seeds showed a mean annual decline rate of 36% and a half-life of 1.5 years.
The seeds are light and may be distributed by the wind. Corn marigold seedlings have been raised from the droppings of various birds. It is said the seeds can pass through the digestive system of a horse without loss of vitality. Corn marigold seed has been found as a contaminant of cereal seed. The seeds may also occur in threshing waste and this should be thoroughly steamed to destroy viability if it is being fed to stock, otherwise it should be burnt.
Corn marigold was said to be a difficult weed to eradicate. Control is aided by sowing only pure crop seed. Hand pulling of large plants and hoeing in two successive root crops should prevent seeding and reduce future populations. As corn marigold prefers soils deficient in lime, liming can help to reduce its frequency.
Small seedlings are susceptible to flame weeding but large plants are not.
Updated October 2007.