Rotational control basis of weed-free pulse crop - farmers weekly

19 FEBRUARY 1999 ------------------------- ROTATIONAL CONTROL BASIS OF WEED-FREE PULSE CROP THERE is a good choice of herbicides for keeping pulse fields weed free. But it is often more

economic to tackle specific problems elsewhere in the rotation, says Cathy Knott of the Processors and Growers Research Organisation. "That applies particularly to couch. It is

inadvisable to grow peas on couch-infested land," she warns. Post-emergence graminicides Falcon (propaquizafop), Fusilade (fluazifop-P-butyl) and Laser (cycloxidim) can be used on both

peas and beans. "But the couch dose rate is costly and does not provide long-term couch control. So growers will be better off relying on pre-harvest glyphosate sprayed on the previous

cereal if they want to eradicate the problem." Volunteer potatoes cannot be killed in pulse crops, she adds. "It is better to deal with them elsewhere in the rotation."

Choosing the most appropriate in-pulse herbicide involves understanding the properties of each and assessing which is most suitable for ones own conditions, soil type and weed spectrum.

"The cheapest may not be the most cost-effective." The PGRO issues free information sheets for both crops detailing available choices. Peas have a relatively short growing season

and rarely justify more than one herbicide treatment, she advises. "Pre-emergence application to take out weeds early is usually a good strategy. But treatments need soil moisture and

so may not be suitable for later sowings. They are also ineffective at economic rates on high organic soils, and none are recommended on sands or gravelly soils, because they may cause

damage. Rolling to remove soil clods before spraying is essential for good weed control." Some pea varieties are more sensitive to certain products than others, so it is important to

consult the label or the PGROs information sheet on the subject. "Forage peas and some pigeon feed types are especially at risk of damage." Opogard and Battallion (terbutryn +

terbuthylazine) are the most widely used pre-em products, says Ms Knott. Other options include Bullet (pendimethalin + cyanazine) which is useful against volunteer oilseed rape, Peaweed

(terbutryn + prometryn), Remtal (trietazine + simazine) and Senate (trietazine + terbutryn) which can be used on organic soils. Reflex T (fomasafen + terbutryn) is also good on volunteer

oilseed rape and can be used on soils too light to accept Opogard. "But it must be on before the crop emerges, and following cereals cannot be drilled for at least four months."

Skirmish 495SC (terbuthylazine/isoxaben) pre- or early post-emergence is safe and has no variety restrictions. "Unfortunately it is no longer manufactured though some stocks may still

be available." In dry springs, post-emergence sprays may be required. But all must applied as soon as possible and certainly before the enclosed bud stage, which can be checked on the

PGRO growth stage guide, she warns. "Apart from MCPB alone, which has a limited weed spectrum, they are all contact-acting. So treated crops must be healthy and the leaves well waxed to

avoid damage." A crystal violet test with a kit, available to herbicide buyers, can be used to determine wax levels. Wild oats can cut yields badly and may be tackled with pre-sowing

Avadex (tri-allate). But unless severe infestations are expected it is more economical to use one of several fop and dim herbicides once the target can be seen, she suggests. Once again a

wax test is advisable. PULSEWEEDSTRATEGIES _&#8226 Think rotational control._ _&#8226 Pre-emergence focus._ _&#8226 Post-em limitations._ _&#8226 Detailed PGRO guides._