Giant Buttercup

Botanical name: Ranunculus acris
Family name: Ranunculaceae

giant buttercup N1.jpg Overview

Buttercups tend to be a problem in moist dairy pastures. They can tolerate wet soil conditions better than many other species, including perennial ryegrass and white clover, allowing buttercups to out-compete more desirable species. Cows don’t like eating buttercup foliage because of the chemicals within the foliage, which also helps them dominate. Giant buttercup, while not as common as creeping buttercup, is generally the most aggressive of the buttercups found in New Zealand. In dairy regions where giant buttercup exists, it can be a major problem. Such areas include Taranaki, Nelson Bays and near Woodville.

giantB2.jpg Distinguishing features

The main species that giant buttercup is likely to be confused with is creeping buttercup. Creeping buttercup produces stolons, whereas giant buttercup has no stolons but instead grows in clumps from a crown at ground level. The leaf shape of the two species also differs slightly (see picture). Generally giant buttercup leaves are more jagged and deeply dissected than creeping buttercup leaves, and the three leaflets that make up each leaf aren’t as clearly defined in giant buttercup. Creeping buttercup generally has a longer stalk for its middle leaflet, while giant buttercup leaflets don’t really have much in the way of a stalk. As with many weeds, these differences in leaf shape refer mainly to leaves of the vegetative plants, as leaf shape can change up flowering stems. Note that hairy buttercup is also commonly found in areas occupied by giant buttercup, and although its leaves can differ in shape quite a bit, don’t tend to be as jagged as with giant buttercup. The flowers of hairy buttercup also differ as they have reflexed sepals (ie they point downwards), unlike with giant buttercup.

giantB3.jpg Control

The control of giant buttercup has never been particularly easy, and has usually required several sequential applications of MCPB and MCPA to give lasting control. Although MCPA is more effective than MCPB, it is also more damaging to clovers, which is why MCPB is alternated with MCPA when several applications are used. Since the 1980s, there have been problems in some areas with biotypes of giant buttercup which have developed resistance to both of these herbicides. After this problem had been identified, another couple of products became available on the market for controlling giant buttercup selectively in pasture, and both of these were effective against the resistant biotypes. One is thifensulfuron (eg Harmony) and the other is flumetsulam (eg Preside). These also need follow-up applications to give 100% control, with flumetsulam being more selective to clovers than thifensulfuron. However recent Massey University research has shown that farmers who have been using flumetsulam for many years in succession have now ended up with giant buttercup that is resistant to this herbicide too, with cross-resistance to thifensulfuron.  It appears the best strategy is to alternate between using MCPA and MCPB in one season and then flumetsulam in the following season.  For more information, there is also an AgPest page about the biology and control of giant buttercup.

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