Dry springtime posers for spud weed control
Dry springtime posers for spud weed control
By Andrew Blake
CONTROLLING weeds in potatoes this season, especially in crops from unchitted seed, is set to be trickier than usual, despite the arrival of three new herbicides.
"If very dry conditions persist we could have real problems and some growers may even have to resort to the old cold steel, tickling ridges mechanically," says SAC weed specialist Ken Davies.
The main concern is that several weeks of dry weather are likely to reduce the effectiveness of residual herbicides, and two of the new trio fall into that category.
Artist (flufenacet + metribuzin) and Centium (clomazone) offer better cleavers control than previous pre-em products, but both still need moisture to work well, notes Dr Davies.
"The other problem is that where potatoes are going into dry soils their growth may be checked." Canopies that normally help smother weeds will be slower to develop, reducing the suppression of later weed flushes.
"In these circumstances it should pay to hold off with your residuals as long as possible and include a contact herbicide such as PDQ."
The third newcomer, FMCs carfentrazone-based Shark, works slightly faster than PDQ (diquat + paraquat), but may only be used up to 5-10% crop emergence, says the firms Stuart Hill. Late approval means little will be available this season, he adds.
Some first earlies may have a head start on weeds and provide good suppression, believes Simon Bowen of Abbey Growers. Chitted crops will help in this respect, says Dr Davies.
"The real concern is for later plantings," says Mr Bowen. "If it stays dry and residuals do not work we could see the crop and weeds developing together.
"In those cases you have to be looking at a true post-emergence treatment, for example Titus or low dose Sencorex. I would recommend keeping something up your sleeve for post-ems."
But Sencorex (metribuzin) and another post-em option, Basagran (bentazone), are both restricted to certain varieties and soil types, says Dr Davies.
Neither Basagran nor Titus (rimsulfuron) can be used on seed crops, he adds. "And they are both relatively limited in the range of broad-leaved weed control they offer."
Where moisture permits, Artists recent approval for use on seed crops is a plus, he notes.
But some crops planted on light land in the past seven days have gone into dust and will struggle to get going, says Greenvale AP technical manager Paul Coleman.
One useful option for growers normally re-ridging after planting is to incorporate Sencorex, he suggests. "It should work better like that than if you leave it on a bone dry surface.
"But not everybody re-ridges, and my advice for them is to hold off until the very last minute before applying a cheap and cheerful residual like linuron with an appropriate dose of PDQ to deal with any weeds coming through from deeper down." *
SPUD WEED CONTROL
• Herbs choice harder in dry soils.
• Concern for role of residuals.
• Poorer crop smothering effect.
• Post-em products to the fore?