How to control weeds when conditions are dry and hot

• Dry spring slows crop growth

• Many crops at different stages

• Strategic approach to weeds

Lack of rain continues to create challenging conditions for sugar beet – with hot weather adding to the challenge of what and when to spray for weed control.

While the dry weather helped growers expedite drilling, with most finished by the end of March, it has slowed crop development and left plants at different growth stages, says UPL head of technical services Stuart Jackson.

“Continuing dry weather coupled with relatively high temperatures is leading to – in some cases – stressed, variable crops and difficult conditions to achieve successful weed control,” he says.

“It’s not in every situation. Where growers were able to get a good seedbed, drilled a little earlier, crops are generally looking healthy, and weed control has been good.”

Drought stress

Emerged weeds are generally pretty tough to control because they are waxed up and drought-stressed, adds Mr Jackson. In these scenarios, we need to load more contact activity into programmes.

“Typical residual mixer partners, such as Venzar (lenacil), are less effective in dry soils, where root uptake is restricted, and should be replaced by more contact-acting herbicides.”

“For example, you can look to add products such as Shiro (triflusulfuron-methyl) and/or Vivendi (clopyralid) to base mixes of Betasana (phenmedipham), plus Bettix Flo (metamitron) + Efeckt (ethofumesate).

“Shiro will be helpful on polygonum weeds and brassicas, while Vivendi is stronger on mayweeds and black bindweed,” explains Mr Jackson.

Tank mixes

Adding oil to herbicide mixes will help pep up weed control, but it can come at the cost of crop safety. Use the forecast maximum temperature on the day of application to help guide decisions, with anything over 21ºC as the cut-off for not adding it into tank mixes.

Where growers want to use oil at their own risk in temperatures above 21ºC, rates should be cut to no more than 0.5 litres/ha and spray first thing in the morning or the evening, says Mr Jackson.

“If crops have flagged or flopped during the heat of the day, avoid spraying in the evening and leave them until the morning.”

With aphids arriving earlier than originally forecast at the beginning of May, many growers might need to tank mix an insecticide with their weed control spray.

The three insecticides available for use are Teppeki (flonicamid), Insyst (acetamiprid), and Sivanto Prime (flupyradifurone), all of which are compatible with the three-way mix of Betasana, Bettix Flo, and Efeckt.

“What we don’t know yet is the compatibility of Sivanto Prime with the bigger multi-way mixes where you add in Shiro or Vivendi. Insyst or especially Teppeki are better options if you’re looking to do that type of bigger mix.

Flexibility

“Obviously, you also need to consider advice around the sequence order of the insecticides, which says to avoid using two sprays with the same mode of action in a row.

Depending on that, it may be the case of spraying the weeds first, waiting for a few days before spraying the insecticide to give more flexibility.

“If you are tank-mixing an insecticide, don’t add oil. However, it may be worth replacing the oil in these conditions with a biostimulant like Vitalroot to help the crop thrive.

Vitalroot is seaweed extract with phosphorus and potassium. It can be used at 1-2 litres/ha in conjunction with a broadleaf spray programme.

It won’t pep up herbicide activity like an oil, but it will help with crop growth,” concludes Mr Jackson.