Get herbicide options for pulses right this spring

Despite losing several options over recent years, there are still various pre-emergence herbicides available.

“But, as they are generally more expensive, you have to get it right,” says PGRO principal technical officer, Jim Scrimshaw.

Pre-emergence options in both crops are reliant on products such as Nirvana (imazamox + pendimethalin), Skirmish (isoxaben + terbuthylazine), Stomp (pendimethalin), Centium (clomazone), Lingo (clomazone + linuron) and Afalon (linuron). Defy (prosulfocarb) and Stomp have SOLAs for use in spring beans.

“If conditions are good, all can perform. Some offer a fairly wide spectrum of weed control on their own; others are quite limited.

“Materials such as Afalon, Centium and Stomp are more sensibly used within mixes to address weaknesses in partner products and broaden the weed control spectrum generally,” says Mr Scrimshaw.

Afalon and Stomp are relatively low cost products - but robust pre-emergence sprays at effective rates of one product or a mixture can easily cost £30-£45/ha (£12-£18/acre).

Some pendimethalin formulations are permitted for mixing with Afalon, and may offer useful control in some situations. Afalon would specifically strengthen 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 controls cleavers and helps to control fools parsley. However, it is not cheap and although the maximum application rate in spring is only 0.25l/ha (0.1l/acre), this represents at least £25/ha (£10/acre) before consideration of the partner product, says Mr Scrimshaw.

Tank-mix options

When tank-mixes are considered, there are opportunities to adjust product rates down. This controls costs, but acceptable levels of weed control need to be maintained.

“For example, work has indicated that, 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. 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.

“Defy shows a similar dose response if the recommended rate of 5.0 l/ha is reduced too much below 4.0l/ha when in a tank-mix with Stomp. The reduced control, especially of cleavers, is noticeable,” he says.

Recent dry springs have illustrated how important the presence of adequate moisture is. If it is too dry, nothing works well, no matter how much it costs. If the forecast is to remain dry after application, perhaps it is worth considering delaying application. A prolonged dry spell may well mean emergence before any useful spray can be applied.

“In these cases, if you feel the need to get something on, a cheap and cheerful option is the most sensible choice,” says Mr Scrimshaw.

Application window

“Skirmish, with or without Basagran, can be considered up until the second node of the pea crop, increasing our application window if conditions do remain dry up to emergence.”

This timing is not an option in bean crops.

In beans, Basagran remains the only post-emergence option. It can be expensive at full rates, but work has shown that using it with some adjuvants at reduced rates can achieve acceptable levels of weed control. Such applications are at the growers’ own risk.

Along with Basagran, the use of MPCB (Tropotox) or MCPA + MCPB (Impetus) is permitted post-emergence in combining peas. These hormones are useful against thistle, docks and larger oilseed rape.

PGRO hopes work in 2010 will begin to identify more specific Basagran rates to tackle particular species.

“Then this expensive post-emergence herbicide can be used at its most economic rate for any given situation,” says Mr Scrimshaw.

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