29 March 2002

Forward planning can reduce input costs this spring

Competitive wheat crops, timely autumn treatments and new herbicide introductions

should make weed control straightforward this spring, as Louise Impey reports

LARGE populations of broad-leaved weeds are unlikely in cer- eals this spring, after widespread use of well-timed autumn treatments, says Chris Bean, of UAP.

"Crops are forward and competitive, too. And thats half the battle. They will be able to tolerate weeds."

That means low numbers of broad-leaved weeds can be ignored, especially if the threat to current or future crops is negligible, says Mr Bean. "The exception to this rule is cleav-ers, which must be kept at very low levels to prevent seed return.

"And there may be situations where mayweed and chickweed are a problem, or where rotational weeds such as volunteer oilseed rape need controlling."

Product choice for cleavers control includes early, mid and late season herbicides, so growers can choose a treatment to suit soil type, previous herbicide use and tank-mixing needs, he says.

The key consideration is where you want to make use of an herbicide containing sulfonylurea chemistry, such as Eagle (amidosulfuron), or one classed as an ALS inhibitor, like Boxer (florasulam).

Where youve used an SU in the autumn for blackgrass, such as Lexus (flupyrsulfuron), there are restrictions, he warns. "Make sure youve taken this into account.

"And if youre planning to make use of one of the new brome products this spring, which are based on the same chemistry, your cleavers spray must be different chemistry."

Spring grassweed control

With the chemical and cultural control options available, grassweed control should also be an easy task, believes Farmacy agronomist Mark Taplin.

Key targets are wild oats, ryegrass, brome and couch, he suggests. "Blackgrass control from the autumn has been very good, so it shouldnt be an issue."

Where ryegrass is a problem, autumn is the best time for action. Crystal (flufenacet + pendimethalin) used pre-emergence, or a spring spray of Grasp (tralkoxydim) or Tigress Ultra (diclofop-methyl + fenoxaprop-P-ethyl), are the main options. "But make sure there is no resistance in your ryegrass population where these herbicides are to be used."

Bob Bulmer, of Dalgety Arable, adds that spring emergence of ryegrass is likely, so crops must be checked even if autumn herbicides were used.

He advises using the full rate of 1.4 litres/ha of Grasp (tralkoxydim). "Where you have other weeds, you can add IPU or chlortoluron, but reduce the Grasp rate to 1 litre/ha with these."

Grasp will provide additional wild oat control, says Dr Bulmer. "If Avadex or IPU was used in the autumn, there will already have been some control of wild oats. The spring spray can then be done with Topik, Cheetah or Grasp, depending on the other weeds present."

Knowing what species you are dealing with is important when it comes to brome control, says Mr Taplin. "Different cultural control measures are effective on individual species.

"Stale seed-beds and delayed drilling will help, but at this stage of the season there are two new herbicides which can help – Monitor and Attribut."

Of the two, he favours Monitor (sulfosulfuron) where brome plants are big, and adds that it offers good control of some broad-leaved weeds, including cleavers. "But its an SU, which will be a problem for sugar beet growers. You cant sow sugar beet the following spring where it has been used."

Attribut (propoxycarbazone-sodium) is stronger on couch, but will control brome and is a useful over-spray for blackgrass. "It is classed as an ALS inhibitor, so shouldnt be mixed with an SU."

But both products represent a big step forward in brome control, he says.

UAP trials show sterile brome control will vary from 70-95% with the new herbicides, adds technical adviser Brin Hughes. He recommends using a split dose of Monitor where high levels of brome control are required.

"Monitor is probably a better choice where there are different brome species present, and also where oilseed rape will be the following crop." n

Weed control should be relatively straightforward this spring. But growers need to plan ahead to avoid problems with sulfonylurea sequences and to make the most of potential cost savings.

1 Competitive crops Benefit from forward wheat crops by leaving low numbers of broad-leaved weeds uncontrolled.

2 Autumn treatments On in good time and in optimum conditions, so weed numbers low.

3 Cleavers Main broad-leaved weed target. Choose different chemistry to that already used in the autumn and check restrictions where SU or ALS inhibitors are planned.

4 Ryegrass Pre-em Crystal will have worked well, use Grasp for the spring spray providing no resistance.

5 Wild oats Avadex or IPU mixes have activity in autumn, choice in the spring is between Topik, Cheetah and Grasp.

6 Blackgrass Should not be tackling it in the spring, but Topik or Attribut can be useful.

7 Brome Cultural control can now be reinforced with either Monitor or Attribut. Use Attribut where sugar beet is grown, Monitor for different brome species and large weeds.

8 Couch Both Monitor and Attribut are effective, but growers should have couch in hand with pre-harvest and stubble glyphosate treatments.

9 Sequencing Restrictions apply to sulfonylureas and ALS inhibitors. Seek advice where necessary.

10 Resistance Experts predict target-site resistance to sulfonylureas will be identified in 3-5 years. Use herbicides carefully and according to guidelines.