8 September 1995

Mixes can beat blackgrass – provided timings just right

ADAS has undertaken four years of detailed MAFF-funded mixture trials with and without IPU. In 1994 few mixes performed as well against blackgrass as straight full rate IPU, particularly at the 1-3 leaf stage.

"One of the most reliable and effective mixtures is half rate Stomp and half rate Cheetah – but its very expensive," says Mr Orson.

In 1994 trials at four sites with different soil types it gave about 92% control of both young blackgrass plants and those sprayed at the 1-2 tiller stage. This was bettered only by IPU alone sprayed at the 1-3 leaf stage, which gave 97% control, "probably because of good rain a week or two after application that year".

However, later IPU alone at the full rate (2.5kg/ha) controlled only 90% of blackgrass plants with 1-2 tillers.

Young blackgrass

In contrast, straight IPU applied last autumn performed rather less well against young blackgrass than mixes of Cheetah (fenoxaprop-ethyl) and Stomp (pendimethalin) or IPU and Stomp at half rates.

The latter was the most effective treatment at Drayton, albeit with only 79% control, where resistance to fenoxaprop has been confirmed.

"One of the messages seems to be that you can get useful blackgrass control from post-emergence Stomp," says Mr Orson. But the application window for the chemical, previously thought to have little post-emergence activity, is quite tight.

The explanation seems to be that during emergence the blackgrass plants pick up the herbicide through the growing shoot. Sprays applied immediately post-emergence (at the 1 leaf stage) are ineffective because they do not reach the growing point in the needle-like first leaf.

However, at the 2-3 leaf stage there seems to be a "funnelling effect" as the leaves open up to channel the chemical to the meristem.

"Were continuing to look at mixtures with particular reference to the role of trifluralin." It is widely used as a cheap companion to IPU, he acknowledges.

Mixes with other herbicides may help enhance IPUs effectiveness at lower rates and combat weed resistance. ADAS has four years of trials results.