Causes of variation in weed control

Excerpt taken from Crop Production Magazine written by Tom Allen-Stevens.
Mark Hemmant of Agrovista suggests the weed control difficulties growers are having are partly due to withdrawal of key pesticides. “Certain Weeds, like groundsel, were kept in check with isoproturon and chlorotoluron.  
Some growers are now switching out of pendimethalin because they believe their blackgrass is becoming resistant to it, but it's a very effective herbicide for poppies and still contributes significantly to blackgrass control.
The tight OSR/wheat rotations are making cranesbill more of a problem in cereals, he continues. "They're not easy to control in OSR and in cereals post-emergence, especially if they're a good size. Putting Duplosan in with an SU herbicide, such as metsuifuron or amidosulfuron, is a good option on cereals,.
In the past, growers have achieved good between results from even low rates of SU herbicides and he feels these should now be raised.
"All products, whether using SUs or alternatives, should be applied at robust rates, But if you've got confirmed resistance, even a high rate of an SU herbicide won’t offer any control."
He advises using Larke (MCPA 750) against poppies, which can also be used beyond the normal out-off timing of G831 in winter wheat (but not other cereals). "You wouldn't necessarily want to apply it as late as May, but it gives you flexibility in case variable weather causes delays."
Chickweed is “easy”, he says. “Fluroxypyr is a good alternative, while an HBN herbicide, such as Oxytril (bromoxynil+ ioxynil) has activity on mayweed."
While growers will always be dependent on herbicides to control broadleaf weeds, Mark Hemmant believes tight rotations aren't helping.  “If you broaden your rotation you increase the options you have for control without selecting out weeds and making those weeds more of a problem."


12 May 2014

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