Mayweed and thistle threat to thin crops

UK - October 25, 2007

Mayweeds and sow-thistles pose a threat to yields particularly in thin rape crops warns a leading agronomist.

Late and poor germination of oilseed rape has resulted in thin, patchy crops, and while the recent rain has encouraged growth it has also helped problem weeds, such as mayweed and sow thistles, warns Dave Ellerton, Technical Director at Procam.

“A strong rape crop can shrug off most weeds. However where the crop is poorly established or patchy, mayweeds, sow thistles and cleavers are starting to grow well. This may lead to harvesting delays as well as threatening yield,” explains Dave Ellerton.

Growers have two options: Galera (clopyralid and picloram) at 0.35L/ha can be applied in mild weather while the weeds are growing. It can only be used once per crop, to gain good control of mayweeds and thistles, as well as suppression of cleavers. Alternatively Dow Shield (clopyralid) at 0.35-0.5L/ha can be used more than once and is the best solution where mayweeds and thistles are the problem. The higher rates of Dow Shield need to be used with bigger, or hardened-off, weeds.

“Provided most cleavers and mayweeds have germinated, then Galera is the best option,” advises Dave Ellerton. “The autumn timing is less critical than trying to hit the narrow spring window before buds are visible above the crop canopy. An autumn application also leaves the option of a follow-up treatment with Dow Shield in the spring.”