Mayweed in oilseed rape

Mayweeds — Matricaria spp. and Tripleurospermum spp. — are common and high profile annual or hardy-annual composite weeds of superficially similar white daisy like flowers.

There are several widely distributed species including scented mayweed (Matricaria recutita), scentless mayweed (Tripleurospermum inodorum) and pineappleweed (Matricaria matricarioides).

Mature plants are large, fleshy and robust and can be competitive with the crop. Their presence can have a significant impact on crop harvesting, moisture of the seed at harvesting and the level of admixture left in the harvested sample.

Biology

Scented mayweed germinates all year, with particular flushes in early autumn, spring and late summer. It has a small seed that can only germinate from shallow depth and its prevalence may be favoured by minimum tillage cultivation systems. Characteristic flowers with yellow centres and white petals are normally seen in late spring and early summer. One plant can produce 10,000 seeds.

Scentless mayweed will germinate at most times of year. Peaks of germination are normally August to October and March. Germination of seed only occurs if they are near the soil surface. Flowering can occur from late spring through to autumn with each plant capable of producing up to 5,000 seeds.

The germination pattern of pineappleweed is similar to that for scented mayweed but with the main flush being in spring. It appears to thrive in soil that is constantly disturbed and compacted, often being particularly prevalent in gateways and on field headlands. Plants flower in summer, without the characteristic white petals of other Mayweed species, and can produce 5,000 seeds per plant.

Why is mayweed a problem?

Mature plants are large, fleshy and robust and can be competitive with the crop. Their presence can have a significant impact on crop harvesting, moisture of the seed at harvesting and the level of admixture left in the harvested sample.

How do I control mayweed?

Corteva Agriscience has a range of products for the control of broad-leaved weeds, including mayweeds in oilseed rape. The key is to using products with different modes of action such as Belkar®, Astrokerb®, Korvetto® or Shield Pro®.

ALS resistant populations of scentless mayweed have been recorded in England and Scotland and the non ALS containing products, Belkar, Astrokerb, Korvetto or Shield Pro will control these populations and provide an important opportunity to introduce different modes of action for weed control.

Product choice

• Belkar (picloram and halauxifen methyl) can be applied as a single application or a sequence providing a flexible solution for weed control.
• Astrokerb (propyzamide and aminopyralid) can also be used to control mayweeds from the 1^st October once crops have reach 3 true leaves up until the end of January. 
• Alternatively, mayweeds can be controlled in the spring with Korvetto or Shield Pro. 
• Korvetto (clopyralid and halauxifen methyl) can be applied from 1^st March until before 1^st June and, applied at 1 L/ha, will control mayweeds and a wide range of other broadleaved weeds.