10 September 1999

WAGING WAR ON GRASS

ENEMY No 1

BLACKGRASS

ALWAYS use mixed chemistry when tackling blackgrass, but make sure each element packs a punch, advises Suffolk-based crop consultant Paul Morris.

With over 20 years experience in the area, the past seven with Sherriff Crop Care, he finds most heavy land farms he visits have a blackgrass problem. "But on most of my long-standing clients farms it is an easily managed problem, and I believe that is because we have always used mixtures or sequences. Even in the early days with isoproturon we often mixed in some Hoegrass."

Branding blackgrass problems easy to control may be somewhat optimistic, he admits. But only farms with "difficult" blackgrass, for example high populations on organic soils, does his standard approach of isoproturon (ipu) + Stomp (pendimethalin) merit significant modification.

"For a mixture to be effective you must make sure each component has a good effect against blackgrass. Over the years a lot of ipu mixtures, for example with diflufenican as Javelin, have one part, in this case the dff, which has little or no effect on blackgrass."

A similar criticism can be levelled at trifluralin, which is often used in mixtures, says Mr Morris. "It does have a place, but it is certainly not as effective as pendimethalin, which costs more, but gives you extra broad-leaved weed control as well."

There are several limitations to an ipu/pendimethalin mixture, he acknowledges. "It needs to be applied relatively early, usually before the blackgrass has three leaves, and on to a good seed-bed. It cannot be expected to deal with more than moderate blackgrass infestations, and I dislike using large quantities of ipu on lighter soils." Maximum dose, whether achieved through the product Trump + ipu or as a straight tank-mix should be about 1650g/ha, he believes.

"That said the big advantage is that in 80% of cases on mineral soils in my area you can spray and shut the gate." The pendimethalin, as Stomp, should go in at the full 3.3 litres/ha dose, he advises.

"At £15-£16/acre last year the mix looked expensive compared with straight ipu or trifluralin + ipu. But if you take the view that a follow up treatment, say on meadow soils or for cleavers, is unlikely to be needed more than 20% of the time, it is really quite cheap."

Many hard-pressed growers welcome the easing of spring workloads, he adds. "And not having to follow up means you do not have to worry about choosing the right herbicide to mix with your growth regulator and fungicide."

Two local weeds have recently emerged to threaten the dominance of ipu + pendimethalin mixes. Both can be controlled with sulfonylureas in the spring, but modification to autumn programmes may be more practical, he believes.

"I have several fields where groundsel has become a big problem. We seem top have selected it out and it can be quite competitive." Replacing the pendimethalin with dff is one option, but using Lexus (flupyrsulfuron) would retain maximum effectiveness against blackgrass, he says.

Shepherds needle, which seems to like clay soils, especially old airfields, which lie cold and wet in spring, is the other spur which might lead him to introduce Lexus to replace the ipu.

Unfortunately Lexus/Stomp mixes are unlikely to be as effective against wild oats, he notes.

For harder-to-control blackgrass Mr Morris advocates 15kg/ha of Avadex (tri-allate) pre-emergence, ahead of either ipu + Stomp or preferably Lexus + Stomp at 20g and 2 litres/ha respectively. "It is a good first step, backed up by our trials, and means we do not have to wait until the weed is at the right stage for contact-acting products. A good take-away message is: Always take the first opportunity to hit blackgrass."

Ploughing preferred

Little minimal cultivation is undertaken in the area, ploughing being the primary route to seed-beds. Where possible stale seed-beds sprayed off with Sting (glyphosate) are a valuable way of easing the task for following herbicides, he says.

"For really difficult to control blackgrass and where we have very high populations a stale seed-bed is well-nigh essential. In a few fields I see the blackgrass can be like the hairs on a cats back and I estimate we have up to 3000 plants a sq m."

Again Avadex provides first hit. Main blow, at the two- to three-leaf stage of the blackgrass, is with 20g/ha of Lexus plus 2.5 litres/ha of Hawk (clodinafop-propargyl + trifluralin) and oil.

"That is getting towards the ultimate hammer and was a very expensive treatment at £28-£30/acre last year. But extreme problems need extreme solutions, and I think it should get on top of the problem."

To avoid its customers over-spending, Crop Care operates a blackgrass resistance testing service, he notes.

ENEMY No 2

WILD OATS

YIELD losses, reduced sample quality and long seed dormancy mean the wild oat is not a weed to take chances with, says a leading agronomist.

"Wild oats are a close second to blackgrass, the number one weed where blackgrass is not an issue," says UAPs technical manager for the west, Peter Gould.

"The dormancy mechanism is the problem – they just keep on germinating. That showed up particularly well this year with wild oats emerging in late April and May through cracks opening up in the soil," he says.

By that time, autumn applications of Avadex (tri-allate) have run out of steam, and getting a contact product to the target under the crop canopy is extremely difficult.

Nonetheless, Avadex as the granular Excel formulation, is the cornerstone of Mr Goulds programme on any field with a moderate or severe history of the weed. Residual activity overcomes the problems of shading with contact acting products, and it is an anti-resistance strategy.

"If there have been no wild oats for three or four years, then perhaps go without Avadex and take a look-see approach," he says.

For conventional second-half September or early October sowings, where wild oats are expected, a full-rate of Avadex is recommended pre-emergence or at 1-2 true-leaves of the crop at latest. Reducing the rate is likely to be a false economy, he warns. "Even with full-rates control is never 100%. It is in the 90s at best, and can slip to 75%."

Following Avadex, pendi-methalin, diflufenican and even ipu in moist growing conditions, reinforce the control.

On very early sown wheats Avadex is omitted. "The crop and wild oats come through so fast and vigorously that there is a risk of them escaping the Avadex," he says.

Instead, a low rate of a contact product, such as Puma X (fenoxaprop-P-ethyl + ipu), is recommended early post-emergence, at the 2-4 leaf stage of the crop. "That often fits in with the first BYDV spray," he notes.

In spring Cheetah Super (fenoxaprop-P-ethyl) plus oil, or Topik (clodinafop-propargyl) if onion couch is present, is used to tackle any late emerging wild oats. For weeds at 2-3 leaves, 0.3litres/ha of Cheetah, or 80ml of Topik is recommended. If they are starting to tiller that is increased to 0.5litres/ha and 100ml respectively.

"I tend to use Li700 rather than mineral oil with the Cheetah as it is safer in multi-product tank-mixes," he adds.

However, if treatment is delayed and the wild oats have reached first node, it is essential to increase to full-rate applications. "Thats were a lot of people come unstuck – translocation past the node is poor, and the side-tillers re-grow."

In late drilled crops, growers can leave control to contact products in the spring, and for normal drilling dates, where only low numbers of wild oats are anticipated, 2 litres/ha of Stomp (pendimethalin) early post-emergence can be sufficient. "It is a very good suppressant of autumn germinating wild oats."

For winter barley the Avadex component of the programme becomes even more important, as the dense barley canopy makes effective application of contact materials impossible. Any field with a history of the weed gets a full-rate. "You dont muck about – lower rates are very variable, they cause too many complaints."

As with wheat, pre-emergence application is preferred, or at 1-2 true leaves of the crop at the latest. Vapour activity with the granules means moisture is not too critical.

Spring clean up

Hopefully the Avadex does the job, but if growers do find wild oats escaping the Avadex, then a spring application of Grasp (tralkoxydim) or Tigress (diclofop-methyl + fenoxaprop-P-ethyl) is recommended. Grasp should be used with adjuvant Output, and has the edge on onion couch, while Tigress is slightly better in cooler conditions.

"They need to go on early while the crop canopy is still open and the when the wild oats are actively growing – the first mild period in February or early March," he says.

In oilseed rape, better control of bromes and volunteers means Fusilade (fluazifop-P-butyl) or Falcon (propaquizafop) are preferred to Kerb (propyzamide) by Mr Gould. "There seems to be a lot of rate flexibility with Falcon – down to 0.3 litres/ha for early tillering wild oats and volunteers," he notes.

Ideally applications should be delayed to late October to ensure most wild oats have emerged. But vigorous volunteers may mean an early and late low-dose split is needed.

More robust rates are required in spring breakcrops due to rapid growth of wild oats emerging with the crop. "They can be growing like the clappers," he warns. However, a spring crop means seedbanks can be depleted with stale seedbed techniques during the autumn.

ENEMY No 3

BROME GRASSES

YIELD losses to brome can be as high as any grassweed.

Where it is a problem, a control strategy integrating cultural and chemical approaches is required, says Fieldcares David Kirkham.

"It is the major grassweed on certain farms," he stresses.

A history of minimal cultivation and long runs of cereals is often to blame. But a simple switch back to the plough is not the answer, or even an option for some. "These are often stony, shallow, difficult to plough soils."

But herbicides alone are ruled out too. "We should not rely on chemicals alone, but want to look at an integrated policy. The best control comes from a combination of all factors."

Cultivation, rotation, drilling date, and chemical control make up his four-pronged plan. Chemical control itself breaks down into four opportunities to tackle the weed: In stubble, pre-emergence, autumn post-emergence, and spring.

"Due to seed dormancy brome may emerge over an extended period, so a programme of herbicide treatments is most effective," he says.

That starts before the crop goes into the ground, with Sting or another glyphosate based product. "The advantage of Sting is that it requires less time before you can cultivate."

Sterile brome seeds dormancy is broken most rapidly by mixing with soil, so a light cultivation immediately behind the combine is advised. But with meadow and soft brome species, dormancy seems to break faster with seed left on the surface.

Pre-emergence Avadex (tri-allate) or Fortrol (cyanazine) is the next step. "The crop can be through with Avadex, but it is best done as soon as you can after drilling for best control of brome."

A pneumatic spreader is preferred for the granules. "A spinner does not have accurate enough placement really," he warns.

Cutting application rate with Avadex is not advised, but there is some flexibility with the Fortrol, he says. Full-rates of 3.5 litres/ha and 4.5 litres/ha for medium and heavy soil types, respectively, are usually only necessary on severely infested headlands. "I tend to use 2-2.5 litres/ha for the middle of the field," he says.

Such pre-emergence applications can have variable results, but they are worthwhile even in dry conditions, when Avadex has the edge. "Though you might get some brome coming through, the Avadex makes it more susceptible to post-emergence ipu."

The value of a competitive crop should not be overlooked either. "We have tried increasing seed rates on headlands and it did help," he notes.

Post-emergence ipu should be applied at a minimum of 2000g/ha, 6-8 weeks after drilling. Even at that, control can be inconsistent, particularly with meadow and soft bromes, so a sequence of Avadex or Fortrol followed by ipu is essential to achieve some reliability.

"A fundamental problem with brome is that you can never guarantee the level of control you are going to get. But you only realise how much good applications have done when you miss a patch. Control is much higher from a pre-emergence/post-emergence sequence, than an either/or approach," he adds.

Growers with blackgrass problems should beware of missing brome, as some products such as Hawk (clodinafop-propargyl + trifluralin) or Lexus (flupyrsulfuron-methyl) are not strong on the weed. "In their own right they do not offer any inherent brome control."

Subject to approval this season growers will have an effective spring herbicide to tackle brome in Monsantos MON375 (sulfo-sulfuron). "It is the only effective spring option. Some say ipu can work in the spring, but quite honestly growers are wasting their time."

There are some caveats with the new product. As a sulfonylurea it cannot be used on crops treated with any other sulfonylurea, it is only for use on winter wheat, and it cannot be used until Feb 1.

"By then there is four months growth and likely to be a considerable population of brome if nothing has gone before. Personally I do not see it as a single hit product, but in sequence with Avadex and ipu."

If Mon375 has a weakness, it is on sterile brome, whereas on rye, soft and meadow brome it is particularly effective, he says.

That complements Avadexs strengths on sterile brome, but weakness on the other species. Which species is present is best identified in May or June when the weed heads.

On set-aside, applying gly-phosate before seed is produced is a good opportunity to get at the weed, and other crops in the rotation should be used to reduce the weed seed bank.

"Spring crops such as peas are particularly good, as desiccants and cultivations can be used to kill successive flushes of the weed in the autumn, and then you can have another go in the peas themselves," he says.

Similarly, delaying drilling date of cereals will allow more time for weeds to chit before spraying off, or ploughing in.

"Ultimately ploughing is by far the best method of control as the longevity of the seed is not great. But growers have to look at their cultivation costs, and not every field is suitable for ploughing," he concludes.

ENEMY No 4

RYEGRASS

ITALIAN and perennial ryegrasses are becoming more prevalent in cereals, mainly because they are not specifically targeted often enough. The right choice of herbicide and the accurate timing of treatments are essential for successful control, says Jon Harrington, Countrywide Farmers crop protection manager.

In the past, the problem was confined mainly to mixed farms in the west as a legacy of rotational leys on former dairy and beef farms. But over the past 10 year or so, the weed has become established on farms with a long history of arable cropping.

Mr Harrington recommends two residual and two contact herbicides for combating the weed in cereals. The former are full-rate Avadex (tri-allate) pre-emergence or medium-rate clorotoluron, pre-emergence or early post-emergence.

"Chlorotoluron gives about 90% control of ryegrass at medium rate, but thats not high enough against blackgrass and it can be used only on a limited number of cereal varieties," he explains. "Its effective up to the weeds mid tillering stage and is slightly better against perennial ryegrass than Italian."

Generally Avadexs control is not quite so good, about 85 to 90%, he reckons, and so if the ryegrass population is high it might need following up with a contact herbicide.

Hoegrass (diclofop-methyl) can do a 95 to 100% job provided the weed has completely emerged when it is applied and its timing is spot on, he maintains. At 1.5l/ha plus Headland Intake or Headland Fortune adjuvants, the product will eliminate plants up to mid-tillering.

"To ensure the spray hits the target its best to turn up the pressure a bit," suggests Mr Harrington. "I certainly wouldnt advise using low-drift nozzles. Although Hoegrass can be quite hard on barley its a bit softer on wheat."

His second contact option is Grasp (tralkoxydim) at 1.0 to 1.25l/ha applied up to the weeds second node stage. But again good spray coverage is essential, he stresses. If the timing is also right the product will give close on 100% control.

If earlier control opportunities are missed, pre-harvest glyphosate can prevent viable seed return because ryegrass is often still green then, particularly in winter barley. Ideally, however, it should be eliminated by mid-March because although not as competitive as blackgrass, it is a darned nuisance, asserts Mr Harrington.

That view is not shared by Cyanamids agronomy consultant, Roger Allen. He reckons both species are very aggressive in the crops early stages and the Italian type is probably more competitive than wild oats during the autumn and winter as is it more erect then. Unless controlled early it can be 15-20cm (6-8in) tall by January or February.

"Ryegrass has become quite a common weed everywhere, particularly on mixed farms in the west," he confirms. "Unless well controlled it soon becomes a major problem; being finer seeded than wild oats you get higher populations more quickly."

Arguably just as important is the weeds ability to germinate right through to April, he notes. This means that if the earlier flushes are eliminated with an autumn-applied contact herbicide, a follow-up treatment might be required in the spring, particularly where the ryegrass population is high.

Far better to use a long-acting autumn residual, advises Mr Allen. He recommends a tank-mix of 3.3l/ha of Stomp (pendimethalin) plus 4.2l/ha of IPU, applied when the ryegrass has one or two leaves. This combination provides enhanced activity against the initial larger ryegrass flushes and then Stomp continues to work long after the IPU has disappeared.

"You must go in early with this mixture because its no good against sizeable ryegrass," he admits. "Ive used it against ryegrass populations as high as 500/m2 and its taken out the lot. Chlorotoluron can replace IPU but youve got to be aware of its varietal restrictions."

Mr Allen says that apart from late-drilled cereals there is no point in ignoring ryegrass until the spring.

As an autumn herbicide generally is necessary to control broad-leaved weeds and other grass weeds, it is best to use a treatment that eliminates the whole lot.

"Topik and Grasp will take out ryegrass up to 10in tall in the spring provided its actively growing," he affirms, "but this might not be until late April or early May, and if the weeds population is high it will have hit crop yield by then."

Mr Harrington considers that combating ryegrass in break crops is a cakewalk as it is so well controlled by the translocated graminicides, like Falcon (propaquizafop) and Laser (cycloxydim), and in oilseed rape by the residuals, Carbetamex (carbetamide) and Kerb (propyzamide) too. &#42