Autumn applications give spring weeds time to grow

Reports and experience of weather-related poorer control from spring Atlantis applications, increasing instances of resistance, and a concerted campaign from its manufacturer and agronomists appear to have encouraged growers to apply a bigger proportion of Atlantis this autumn.

Ever since its launch in 2003/04 the split between autumn and spring Atlantis use has been at least 75:25 in favour of spring – driven partly by good results, as well as the opportunity to take out later germinating wild oats, bromes, and ryegrass in one hit.

But the poorer control last spring, and trials evidence suggesting autumn applications were more reliable, has brought a relatively conclusive response from growers. Estimates from both manufacturer and agronomists suggest the split this season will be much closer to 50:50.

For example, ProCam’s Nick Myers says his firm has sold 48% of the 2005/06 total Atlantis sales this autumn. That compares with a 23% autumn, 77% spring split in 2005/06. Assuming there isn’t a dramatic increase in total Atlantis sales this year, something he isn’t anticipating, it indicates a substantial increase in the amount sprayed this autumn.

Hutchinson’s Dick Neale backs those figures up with his own firm’s experience. “A large percentage has gone on this autumn – it might be up to 60% – although it is tricky to say exactly.”

Where it has been applied, particularly following a strong residual treatment, such as Crystal, it has worked extremely well, Mr Neale says. Indeed he is confident that most Atlantis sprays shouldn’t need following up for blackgrass. “Where it has been on for 10 weeks it has done pretty much 100%, and quite frankly, what can you put on that will pick up any stragglers in any case.”

Right approach
Tackling blackgrass in the autumn has been the right approach, according to Syngenta’s Rod Burke.

But autumn applications of Atlantis are likely to have an impact on wild oat, ryegrass and brome control. All three weeds were typically taken out relatively effectively by spring applications, but spring germinators are unlikely to be controlled by the autumn timing.

Industry market research data suggests around half of fields treated with Atlantis in the spring of 2006 also contained wild oats, Mr Burke suggests. “And around half the fields targeted for ryegrass also contained blackgrass. It is likely we will now have situations where ryegrass and wild oats will be germinating after autumn Atlantis use.”

The situation is likely to re-energise the contact graminicide market, he believes. Before the launch of Atlantis just under 600,000ha were treated with the likes of Topik, Cheetah and Grasp. But that fell to just under 300,000ha last season, almost exclusively because of spring-applied Atlantis, Mr Burke says. “A lot of people are going to have to rethink their approach this spring.”

He estimates about 150,000-200,000 more hectares might be vulnerable to spring germinating wild oats and ryegrass this season and require a contact graminicide treatment.

A complicating issue is the implications of the Pesticides Safety Directorate’s decision to impose restrictions on both ALS (sulfonylureas) and ACCase (fops/dims/dens) grassweed herbicides, he suggests.

One application
Those restrictions now only allow growers to apply one application of a grassweed sulfonylurea herbicide, such as Lexus or Atlantis, to a crop, and only one application of an ACCase inhibitor active ingredient to a crop, he explains.

The latter is complicated by the decision to allow two applications of ACCase inhibitor actives to a crop but the second application must be a different active ingredient and be targeted at a different grassweed at a separate timing to the first.

“Effectively that means you wouldn’t be able to follow a Hawk treatment [because it contains clodinafop] with Topik this spring, but you could follow Hawk with Cheetah or Axial [as neither contain clodinafop, although both are ACCase inhibitors].”

Similarly, under the ALS restrictions, you can’t follow one grassweed sulfonylurea application – such as Atlantis – with another such as Lexus or, probably more realistically if you have brome, Attribut or Monitor.

While those particular combinations have never been legally approved in any case, growers don’t have any alternative non-sulfonylurea brome options, Mr Myers says. “Soft bromes, in particular, do have a largely spring germinating pattern so could be a problem if you’ve already applied Atlantis. The options in that case are legally zero. But it might be why there is still 50% of Atlantis left to spray.”

Fortunately spring-germinating wild oats and ryegrass are not quite so tricky to control if Atlantis has been applied, according to Mr Burke. “Axial is a simple solution to spring grassweed issues and the PSD restrictions.” It can be used in all situations except where it has previously been applied, provided it is targeted at a different grassweed to any autumn application, he explains. “The only place where Axial is likely to have been used in the autumn is against blackgrass in barley,” he notes.

Last season the product was used on about 100,000ha for wild oat control – around a third of the specific spring wild oat market. Mr Burke hopes the market will grow this season. “It is a step forward for wild oat control.”

Mr Myers had little personal experience of Axial against wild oats last season, but says it was excellent against ryegrass. “The feedback from our other agronomists has also been positive – its level of control is up there with Hussar.”