Late weed control in oilseed rape is running several weeks late due to the warm weather
Late weed control in oilseed rape is running several weeks late due to the warm weather, says Agrovista agronomist Craig Green (left).
Many growers have rightly delayed applying propyzamide to control black-grass in oilseed rape as soil temperatures have been too high for effective control, says Craig.
However, weeds have continued to grow strongly in the unusually warm autumn so any temptation to cut rates should be avoided, he advises.
Soil temperatures need to be at or preferably below 100C for optimum control, but at the time of writing (early November) they were still well above that level with a further week of warm weather to come.
“You’d think with all the rain we’ve had that soils would have cooled more than they have,” says Craig.
“Applications are going to be at least three weeks later than normal to ensure soils are cool enough to provide sufficient activity. Propyzamide breaks down more slowly at lower temperatures, so it remains in the soil for longer. Weed growth is also reduced.
“The cooler soils are, the better the active will work. However, given the ideal growing this autumn, black-grass is generally bigger than usual so full-rate applications are a must as efficacy starts to decline once plants begin to tiller.”
Mild weather has also encouraged more aphid activity than usual for the time of year, raising the threat of turnip yellows virus, Craig notes. “It will be worth adding an aphicide such as Biscaya (thiacloprid) when going through with Kerb if any aphids can be seen in the crop.
“Given the lateness of the timing growers might be tempted to tank mix with other products that are due to be applied. However, they’ll need to check compatibility – Biscaya cannot be mixed with Frelizon (penthiopyrad + picoxystrobin), which may well be earmarked to control phoma/light leaf spot. Other products such as Falcon (propaquizafop) to take out cereal volunteers and trace elements such as boron or manganese are also likely to be used at this time.
“I would apply the Frelizon, Kerb and Falcon in one application and the aphicide and trace elements separately. You can’t do everything at once.”
Maize growers may need to review their variety mix after this season’s “distinctly average” yields, says Craig.
“Crops have been reasonably tall but have matured more slowly than usual due to the cool wet summer. A lot of late varieties have been grown in the east as crops usually drought out, so people are chasing maximum yield. However, these later types have really suffered this year – they have not had enough heat units to mature.”
In Agrovista trials of 56 maize varieties at Great Ellingham, Norfolk, around 30 per cent of late varieties did not reach full maturity. “The cob accounts for about 40 per cent of yield – usually it’s a case of the more cobs the better in our drier climate. This season those varieties that put out more than one cob really struggled,” says Craig.
“Yields have still been decent because of the amount of growth, but energy/gas potential and dry matter will suffer as a result,” he adds.
To help avoid a repeat of this problem, growers might be better introducing some earlier/mid maturing varieties into their portfolio, he advises.
“Earlier varieties could be grown on poorer land, where they often do better than higher-yielding types. Varieties like Emblem, Cathy, Hobbit and Eurojet have performed particularly well at Great Ellingham this season, producing top yields on lighter soils and the highest cob weights,” says Craig.
“Growing a mix of early, intermediate and late varieties also helps spread the harvest workload,” he adds. “Harvest can start in September rather than mid-October or later.
*Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk ([email protected]).