Dry weather can hamper the activity of residual herbicides, while a lack of soil moisture will also slow the emergence of many key problem weeds until later in the season.
However, some of the sneakier ones may grow from depth earlier, unimpeded by a dry and disrupted herbicide layer.
This means growers are going to have to choose a robust post-emergence herbicide to tackle weeds when they emerge, said Craig Chisholm, field technical manager for Corteva Agriscience.
“Under normal conditions, starting with a clean field then tackling any late germination is usually the path forward,” he said.
“But this season, where a solely post-emergence strategy will be required, growers should wait for active weed growth for the best possible results.
While the primary concern over the presence of weeds in potato crops is one of yield, it can also increase blight risk through sheltering leaves, or contributing to a favourable microclimate for the disease.
Later in the season, larger weeds can have a serious effect at harvest – left unchecked, they get entangled in machinery and slow operations down.
Titus, containing the active ingredient rimsulfuron, has been valuable herbicide in the armoury for potato growers, particularly in dry seasons when pre-emergence activity will be negatively affected.
It may be used alone with a wetter to provide post-emergence activity across all potato varieties, excluding seed crops.
In fields where growers have failed to get a pre-em on, or conditions have been too dry, a mixture of Titus plus metribuzin and a wetter will broaden the weed spectrum.
Care should be taken to check that the variety is tolerant of metribuzin before adding to the mixture, though.
Mr Chisholm added: “Titus has consistently demonstrated that it delivered robust control of charlock, cleavers, chickweed, hemp-nettle, small nettle and volunteer oilseed rape. It is also active on polygonums and will supress couch grass.
“Being a sulfonylurea herbicide, it will work most effectively against small actively growing weeds, so application should target weeds at cotyledon four-leaf stage and before the crop reaches 15cm, to minimise weed shading.”
Source: The Scottish Farmer
Photo: Craig Chisholm