Continued dry weather could put pre-emergence herbicide effectiveness at risk in pea and bean crops this spring, PGRO‘s Jim Scrimshaw is warning.
Recent dry springs have shown moisture is essential for products to work, regardless of how much they cost, he says.
If soil is not moist enough, growers can consider delaying applications. “But be careful when using this tactic as prolonged dry weather may well mean crop emergence before a spray is applied,” he says.
“In these cases, where something needs to go on pre-emergence, a cheap and cheerful option is the most sensible choice. But keep an eye on crop development below ground as products containing pendimethalin do recommend a latest timing for application.”
Under the right conditions, however, Mr Scrimshaw says all recognised pre-emergence products can perform well – although some offer a fairly limited range of weed control.
Tank mixing different products can increase the weed spectrum covered, and offer the chance to reduce rates to control costs.
But striking the right balance between reducing doses and maintaining acceptable levels of weed control is not easy, Mr Scrimshaw warns.
“Rates within tank-mixes have to remain economic, but at the same time, still be effective, otherwise their application is pointless.”
Products such as Afalon, Centium and Stomp may be better used in mixes to broaden the weed control spectrum in peas, he advises. “Some pendimethalin formulations are permitted for mixing with Afalon, and this relatively cheap combination may offer useful control in some situations. Afalon specifically strengthens mayweed and orache control in most tank mixes.”
The use of Stomp in a mixture traditionally covers any polygonum weakness in the partner product.
Centium effectively controls cleavers and helps to control fool’s parsley. However, it is not cheap and although the maximum application rate in spring is only 0.25l/ha, this represents at least £25/ha before consideration of the partner product.
Mr Scrimshaw says reducing the rates too much can give disappointing levels of weed control. “When there is a level seedbed and enough moisture, Nirvana used at the maximum rate of 4.5l/ha can give excellent broad spectrum weed control,” he says.
“If there is a cleaver population to be controlled, Centium may be considered in a tank-mix. Both are expensive at full rates, but reduce rates of either too much and the results can be disappointing.”
Cutting Centium rates too far can affect cleaver control, while reducing the Nirvana rate to 2.5l/ha, can compromise polygonum control.
Pulse herbicide options
Product Active ingredients
Label rate (litres/ha)
Nirvana imazamox + pendimethalin
Skirmish isoxaben + terbuthlylazine