22 March 2002

Product choice and timing vital

Broad-leaved weed control

in peas and beans is the

focus for this weeks

baseline advice article

GOOD pea and bean weed control depends on careful product choice and good input timing.

Get those right and crop competition, weed return and harvest hassles should be minimal.

Spring bean herbicides

Growers must use a pre-emergence herbicide in spring because there is only one product that can be applied post-emergence, advises Jim Scrimshaw, technical officer at PGRO.

Basagran (bentazone) is the only post-em option, but Mr Scrimshaw warns: "It is expensive, has a limited weed spectrum and will not control annual meadowgrass, large fat-hen or black bindweed.

"There is also nothing that can be used to control thistles and docks because materials containing MCPB, MCPA and clopyralid are very damaging to beans."

Cost alone is enough to persuade growers of the importance of the pre-em timing, he believes. But crop damage is also more likely where a post-em spray is relied upon. "Application conditions and timing are more critical then and crop damage is more pronounced the later the spray is used."

The pre-emergence herbicides available for spring beans include Opogard 500 SC/Batallion, Reflex T, Bullet and Centium.

Opogard/Batallion (terbutryn/ terbuthylazine) is a popular mix with a good weed spectrum, he says. "Annual meadowgrass, black bindweed, knotgrass and mayweed are all controlled. It must be applied three days before emergence."

Reflex T (fomesafen/terbutryn) is a safe material on all varieties and has a wide weed spectrum, but planning and forethought are needed. "It is a good choice where volunteer oilseed rape control is needed.

"But if it is not applied before emergence, plant death may result. It is also persistent, so the following crop is restricted to cereals. The active ingredient fomesafen can only be used once every five years."

Bullet (pendimethalin/cyanazine) is applied at 5 litres/ha, regardless of soil type. "Apply it as soon as possible after drilling, before the growing point is within 13mm of the soil surface. It will give good control of knotgrass, but only moderate cleavers control.

"It is also useful on volunteer oilseed rape, but the control you get will depend on the depth from which the population is germinating and the numbers involved."

Centium is a new herbicide for 2002, containing the active ingredient clomazone. "Centium brings cleavers control into the pea and bean crop," says Mr Scrimshaw. "It also works well on chickweed, shepherds purse, fools parsley and red dead nettle, but control of other weeds is variable."

Best results with Centium have come from the product being tank-mixed with a pre-em material such as Opogard/ Batallion or Reflex T, he adds. "It is also very safe to all the varieties we have tested."

Spring pea herbicides

There are more choices for broad-leaved weed control in spring peas, especially when it comes to the post-em options, says Mr Scrimshaw.

The pre-emergence materials are the same for beans, but there is also Stomp (pendimethalin). Not for use on organic or gravelly soils, Stomp should be applied as soon as possible after drilling and avoided where surface water is likely to accumulate.

"There are two rates – 3.3 litres/ha or 5 litres/ha. The lower will control volunteer oilseed rape, whereas 5 litres/ha will bring in black bindweed and redshank and give useful cleavers control.

"But mayweed control is unreliable, and charlock and mustard wont be touched."

An early post-em herbicide for combining peas is Impuls (bentazone + pendimethalin), but it must be applied before the third node. "The contact action of bentazone complements the residual action of pendimethalin and controls cleavers, poppies and volunteer oilseed rape.

"Either apply one full rate application or use a sequence of half rate Impuls followed by a Pulsar + Fortrol mix. The other post-em options for peas are MCPB and Basagran, or mixes of Fortrol + Trifolex-Tra and Pulsar + Fortrol.

"MCPB should be used where thistles and docks are a problem and it will stunt volunteer oilseed rape. But a follow-up post-em application will probably be needed."

Basagran is good on cleavers, but care must be taken to adhere to application conditions. Do not use it where temperatures are likely to get over 21C, he says.

"The most popular post-em mix is Fortrol + Trifolex-Tra, which controls a wide range of weeds including volunteer oilseed rape and poppy, although you must check for varietal susceptibility. "It can be applied from four nodes but before flower buds have emerged," says Mr Scrimshaw.

Another popular treatment is Pulsar + Fortrol. Mr Scrimshaw recommends a full dose of 4 litres/ha + 0.4 litres/ha from three nodes, or 2 litres/ha + 0.2 litres/ha from two nodes.

"With all post-em sprays, it is important to check that there is adequate leaf wax before application takes place because all treatments have a contact-acting component." &#42

SULPHUR RESPONSE

Peas respond to sulphur similarly to cereals, says PGRO. Where sulphur deficiency is known, most likely on light free-draining soils, a pre-drilling application of 35-50kg/ha of SO3 is recommended. That equates to 110kg/ha of gypsum, 110kg/ha of keiserite, 25kg/ha of Thiovit or 80kg/ha of ammonium sulphate, it advises.

BROAD-LEAVEDWEED TIPS

1Pre-emergence timing Essential for spring beans, post-em options very limited.

2Centium New pre-emergence option. Good on cleavers, chickweed, shepherds purse, fools parsley and red dead nettle. Best results from tank-mixing with Opogard/Batallion or Reflex T.

3Reflex T Plan use carefully, as persistent and following crop restricted to cereals.

4Pendimethalin Can be used pre-em on spring peas, but not on organic or gravelly soils. Adjust rates to weed spectrum.

5Impuls Good early post-em option for combining peas, with both contact and residual action. Cleavers, poppies and volunteer oilseed rape controlled.

6Basagran Only post-em option for beans. Adhere to application conditions or crop damage will occur. Expensive.

7Thistles and docks No materials available for beans, use MCPB on peas.

8Pulsar+Fortrol Popular post-em treatment for peas, controlling wide range of weeds. Can be used in a sequence after Impuls.

9Crop damage Herbicide application at wrong growth stage is the main reason.

10 Post-em timing Check there is adequate leaf wax before application.