2 August 2002

Herbicide use helps to tackle grass troubles

By Andrew Swallow

PRE-EMERGENCE herbicide Crystal (pendimethalin + flufenacet) offers growers a step ahead of current standard Avadex (tri-allate) when it comes to blackgrass and ryegrass control, claims manufacturer BASF.

But before growers reach for that chemical crutch they must integrate all available cultural control techniques into their grass weed control strategies if they are to win the war, says technical business manager Rob Gladwin.

"Some growers are spending £75-100/ha on blackgrass control in wheat and they are still not doing the job. They need to change the way they are going about it."

Strategic rotation of crop and chemicals, considered use of cultivations, manipulation of drilling dates and seed rates, and stale seed-bed techniques all need to be deployed to support the herbicides in the armoury, he says.

Early drilling is a definite dont where grass weeds are an issue. "Drilling before Sept 15 will result in mediocre grass weed control from all products in severely infested fields," he warns.

In such situations growers tend to min-till, drilling into seed-beds with a high population of seed left on the surface from the previous crop. Weeds and crop germinate together putting pre and post-emergence chemistry under severe pressure. On top of that, seed-beds tend to be drier so residual herbicides are less effective.

Also, low seed rates in early drilled crops reduce crop competition with the grass weeds, giving them space to tiller, resulting in more heads/sq m. That is especially important with ryegrass, which tillers profusely given the chance.

"Two weeks delay could make a lot of difference to the overall success of your grass weed control. Prioritise your fields and delay drilling on the fields where you know you have a problem," he comments.

Break crops must be used as an opportunity to change the mode of action being used on the grass weeds.

Fops and dims should be reserved for use in crops such as oilseed rape, he maintains.

"Over reliance on fops and dims in cereal crops is leading to decreased control in oilseed rape. Farmers are not realising the level of blackgrass left in oilseed rape, especially if they are direct combining," he says.

In serious grass weed situations switching to spring cropping is an option some growers should take a seriously long hard look at, he adds. "It is a real option. Dont dismiss it out of hand just because of soil type."

Clever use of cultivations is needed too. "It is not just about ploughing. You have to balance what is in the seed bank from previous years with what fresh seed there is on the surface. It may be better to try to reduce this with a stale seed-bed than plough up a problem."

If growers are using stale seed-bed techniques to reduce the weed burden, obtaining a good quality seed-bed is very important to maximise the germination. Cultivation, if any, should be timed according to grass weed target (see table).

Only by integrating these cultural controls with herbicides will growers get on top of their grass weed problems, he stresses.

"Cultural and chemical controls have to be combined together and there is no substitute for doing that," he concludes. &#42

You wont beat blackgrass like this with chemicals alone, says BASFs Rob Gladwin. Well timed stale seed-bed cultivations can play a key role.

&#8226 Cultural controls essential.

&#8226 Integrate with herbicide use.

&#8226 Be clever with cultivations.

&#8226 Otherwise £75-100/ha programmes can still struggle.


Weed Immediate 4-week Timing

delay neutral

Sterile brome* 3

Volunteer cereals 3

Wild oats 3

Meadow/ soft/rye brome 3

Blackgrass 3

Ryegrass 3

* Straw cover can achieve the same effect.

Pre-emergence edge for newcomer

On average pendimethalin plus flufenacet product Crystal controls 75% of blackgrass and 70% of ryegrass when applied at the full 4 litre/ha rate, compared to 45% and 30% control from current standard Avadex (tri-allate), says technical business manager Rob Gladwin. "You can go post-emergence with Crystal but the level of control and reliability drops greatly. Ideally you should be on within 10 days of drilling. If the crop is germinating so is the blackgrass." Growers should regard the £32/ha (£13/acre) cost of such an application as an investment across the rotation, he adds.

For more top weed control advice check-out farmers weeklys Herbicide Supplement next week.