Drought? Don't cut back on weed control in onions

Despite the drought of the past period, many weeds on onion plots will soon raise their heads or may have already done so. That is why the approach to weed control now requires full attention, says Steven Dorrestijn.

"All the onions have been sown and I assume that most plots have already been burned," says Steven Dorrestijn. "Sometimes I see in practice that people tend to skip burning during droughts, but I would never do that myself. After all, you can tackle the first crop of weeds very cheaply and very effectively by burning. As far as I'm concerned, it's the most important weed spraying of the season. It gives you a clean start." 

Weed stage
The approach to weeds depends not only on the stage of the onion but also on the development of the weeds. And that can differ greatly between plots, Dorrestijn knows. "If there has been irrigation after sowing, the weed seeds from the first 2 to 3 centimetres will also have germinated and may already be above ground. But if there has been no irrigation, the seeds from the layer below that are on their way; they get their moisture from the solid subsoil. The weeds that come from deeper are fewer in number but often also larger in size and you have to take that into account. And on such plots, the weeds in the top layer will germinate after the rainfall last weekend. So you get weeds in multiple stages and that is enough reason not to economise on weed control."

Wide cocktail
The Syngenta advisor expects that this week a large part of the onion plots will be in the sprouting stage. "That is, as far as I am concerned, the starting signal for the soil herbicide spraying. With a cocktail of AZ 500, Stomp and/or Boxer you get a nice broad effect. Be careful with the dosages if a lot of precipitation is expected. Because then soil herbicides can still reach the roots of the seedling. But if you spray with a reduced dosage, you can repeat that after about a week if desired." 

Cutting back on soil herbicide spraying, which Dorrestijn sometimes sees happening in dry springs, is counterproductive, he believes. "We see in our tests, for example at the Rusthoeve experimental farm, year after year that soil herbicide spraying gives you a relevant long-term effect. So just do it."

Do not forget
In the Southwest, the first plots will probably reach the stage of the first pipe this week. For those plots, Dorrestijn advises spraying with Boxer-Lentagran-Starane Top or a combination of Wing P + Boxer. "Here too, the warning for heavy rainfall applies," he says. "You can repeat that spraying 2 more times, but the second time without the Starane Top because of the prescribed interval of 14 days." To round off the weed control, spraying with Boxer, with or without Wing P, is the best recipe for contact and soil duration effect, according to the crop protection expert. "The growers really shouldn't forget that last spraying. "I have seen too often that a plot is still covered in weeds if it rains a lot later in the season."

Adjust dosage to weeds
In weed control in onions, besides the choice of means, the regularity of spraying is also very important. "If possible, use an interval of a maximum of 7 days", advises Dorrestijn. "And if that is not possible due to circumstances, always spray earlier and certainly not later." His last tip is about the dosage: "Adjust it to the size of the weed. Some growers look too much at the onion plants or they use a lower dosage because there are few weeds. But then there is a chance that you will underdose with the result that you do not spray the weed dead but spray it sick. And a sick weed plant does not absorb anything during the next spraying. But an onion that has been standing still for a while will recover."