Get on top of grass weeds early

With growers coming up against a delayed start to the spring spraying season, on account of the cold temperatures, the priority must be to get on top of grass-weed problems before turning to other spraying operations.

However, while clear spray days will be needed for the remainder of March and early April to enable growers to catch up, the late start has delivered some management benefits.

That’s the advice from Nottinghamshire-based agronomist Andrew Wells, of the recently formed crop advisory group Arable Alliance.

“A late start from an agronomic viewpoint is actually good to manage,” says Mr Wells. “The long winter has stopped crops getting forward and, in addition, it hasn’t favoured the rusts as yet. Foliar disease levels are generally not as high as they could be but we know yellow rust will be there this season.”

The urgency, however, is the control of grass-weeds in winter wheat, particularly where there are higher populations of black-grass, ryegrass and sterile bromes, he says.

“Where an autumn pre- or post-emergence herbicide treatment went on, then I think they appear to have worked well, and where autumn treatments were applied I don’t think the black-grass situation is any worse than last year.

“But those areas where herbicide treatments didn’t get on, or went on in less than ideal conditions, then these should be prioritised as soon as suitable temperatures allow.”

On hold

If Atlantis (mesosulfuron + iodosulfuron) or Broadway Star (pyroxsulam + florasulam + cloquintocet-mexyl) are planned for grass-weed control, then growers must wait for conditions when active weed growth is taking place. Until this happens, grass weed control must be put on hold.

“It’s also worth remembering that where you are treating grass weeds with Atlantis or Broadway Star, both products have broad-leaved weed activity and, while these applications may not give 100 per cent kill of all broad-leaved weeds, they will help slow down their growth,” says Mr Wells.

“The autumn’s early post-emergence treatments will have taken the pressure off early broad-leaved weed control for this spring anyway, and, as long the key target weeds are sprayed by the T1 timing, crop competition should be avoided.”

Autumn’s early post-em treatments will have taken the pressure off early broad-leaved weed control

Andrew Wells

Tank mixes must also be kept simple and growers shouldn’t feel pressurised into putting everything in the tank because it’s a late start to the season. “Crop growth stages are not advanced right now and it might just mean going in the field one week for black-grass and, 7-10 days later, going back in for something else. But most growers can achieve this and it results in better product performance, giving improved weed control.”

Higher water volumes should also be a focus this spring.

“150-200 litres per hectare of water will result in a better penetration of the crop canopy, particularly when plants really start to grow.”

Speed is also critical, says Mr Wells, highlighting that although 12km/hr will seem slow to many operators, it will help in gaining optimum spray coverage.

“Right volumes and speeds should be a priority this spring - you have one chance to do grass-weed control, so do it properly.”

Avoiding

Mr Wells says he is trying to avoid mixing fungicides with Atlantis and Broadway Star this spring but, if forced, he will include a rust-active triazole such as cyproconazole and avoid chlorothalonil completely.

Priorities for oilseed rape revolve around applications of Galera (clopyralid + picloram) or Dow Shield (clopyralid) as temperatures rise but, importantly, before the crop’s flower buds extend above the leaf canopy to ensure crop safety.

“There are concerns about the spread of light leaf spot and although some say put a fungicide in the tank at the same time as the herbicide, you can go later at the green-yellow bud stage.”

Tebuconazole and prothioconazole on their own (or combined, as in Prosaro) both have good activity on light leaf spot.

Beet drilling in Nottinghamshire has begun with the last of the 2009/10 crop being harvested in neighbouring fields, but Mr Wells believes growers should ignore calendar dates for their sugar beet drilling and be guided by soil conditions.

“There’s still a lot of wet land about so wait until soil conditions are right. Also, aim for slightly higher plant populations when drilling beet as modern varieties have a higher genetic potential, enabling more plants per square metre to reach harvestable size.”

Interestingly, Mr Wells says the large number of frosts over the winter has meant that there is some poor root-to-soil contact in winter cereals this season. “There’s a lot of ‘fluffy’ soils on the lighter, sandy land because of the high number of frosts, and the poor root-to-soil contact can cause manganese deficiency.

“It would be worthwhile getting the Cambridge rolls out onto these cereal crops as soon as conditions allow as this will help overcome manganese deficiency and provide a better root base, anchoring it against lodging later in the season.”

Mr Wells concludes: “Where spring barley is being drilled now and black-grass is expected, go with a Defy (prosulfocarb) and Stomp (pendimethalin) mix pre-em. I have used them in this situation for the past two years (on SOLAs) and this herbicide combination has worked well.”

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