This spring’s prolonged dry period is creating challenging conditions for sugar beet weed control, with large swings between night and day temperatures adding to the issue.

While the dry weather helped growers complete drilling in good time, with most finished by the end of March, the lack of rain has since slowed crop development and left plants at variable growth stages.

See also: How a new test helps tackle herbicide-resistant weeds

Coupled with relatively high temperatures, many crops have been left stressed, leading to variable growth stages which makes weed control difficult, explains UPL head of technical services Stuart Jackson.

“It’s not in every situation. Where growers were able to get a good seed-bed, drilled a little earlier, crops are generally looking healthy.”

However, hot weather adds to the challenge of knowing when and what to spray for weed control. 

Emerged weeds are generally more challenging to control in dry conditions because they are waxed up and drought-stressed.

Stuart Jackson © UPL

Oil mixes

Adding oil to herbicide mixes is one way of helping promote weed control.

However, growers should consider daytime temperatures when applying as too high temperatures can come at the cost of crop safety.

Stuart recommends using the forecast maximum temperature on the day of application to help guide decisions, with anything over 21C as the cut-off for not adding oil to tank mixes.

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

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

Stuart notes that typical residual mixer partners, are less effective in dry soils, where root uptake is restricted, and so contact-acting herbicides may be a useful replacement.

“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).

Earlier aphid arrival

With aphids arriving earlier than originally forecast at the beginning of May, some growers may consider 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 phenmedipham, metamitron, and ethofumesate.

“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,” says Stuart.

“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.”

Stuart notes if growers are tank-mixing an insecticide, to not add oil. It may be worth replacing the oil in these conditions with a biostimulant to help the crop thrive.

Biostiumlants containing seaweed extract with phosphorus and potassium and can be used.

“It won’t pep up herbicide activity like an oil, but it will help with crop growth,” says Stuart.