16 December 2000

All washed up? Rescue is at hand

Dont let the rain wash arable margins away. Heres our agronomy rescue package, in the aftermath of the wettest autumn ever…

North

T LEAST the wet weather has slowed up weed growth. But applying autumn residuals has been difficult, if not impossible.

David Booty, regional agchem manager with Dalgety Northern, reckons that residuals are still in the frame – even in flood-struck Yorkshire. "They give the most cost-effective response, so dont give up. Weeds are growing as slowly as the crop, but if blackgrass looks menacing by the time the land is fit for the sprayer, add a contact herbicide to the tank."

Where blackgrass is tricky and a pre-em wasnt used, a mixture of Stomp (pendimethalin) plus Lexus (flupyrsulfuron-methyl) is best, says Mr Booty. Where the weed is tillering, Lexus plus Hawk (clodinafop-propargyl and trifluralin) may be more appropriate.

Some of the residual activity of herbicides applied before the flooding may have been lost, so contacts could come in useful as backup, he adds.

In the absence of resistant blackgrass, and where the main target is broadleaved weeds, Panther (diflufenican and isoproturon) and Platform S (carfentrazone-ethyl and mecoprop-P) should feature. Both work well at low temperatures, and at low rates of use unless cleavers is a threat. Mr Booty is wary of recommending cheap and cheerful mecoprop products because they can scorch in the frosty weather typical of January and February.

As the season progresses and cleavers and other broadleaved weeds start to compete, he will recommend Eagle (amidosulfuron) or Boxer (florasulam), depending on the weed spectrum.

"Cereals are well behind, and so are more vulnerable than usual. Too many products in the tank might set them back further. But theres one mix partner that we are recommending for late drilled crops that can reduce scorch and should help to boost crop growth: hormone root stimulant Axis."

South and east

Where growers have managed to drill, weed control is pressing, says Laurence Power, technical agronomist with Bartholomews. The high water table did little to stunt weeds in the warmer south. Blackgrass and volunteer rape carried on growing throughout November and December.

Residuals which leach easily such as isoproturon are appropriate, and pendimethalin, diflufenican and chlortoluron may struggle to control tillering blackgrass, so will only be recommended on very backward fields. Mr Power suggests growers use contact graminicides such as Hawk or Lexus to tackle blackgrass. Normally hed opt for half rates; this season three-quarters to full rate will be needed.

Reduced rates may still be pertinent when using broad-spectrum herbicides such as Panther and Quantum (tribenuron-methyl) to control a range of weeds including meadowgrass, speedwell and chickweed – unless volunteer rape and cleavers are a threat.

"With crops struggling to tiller, weve got to prevent competitive weeds becoming established. My advice is to get something on as soon as you can travel, providing frost isnt forecast."

Central and south west

By late November, about 70% of the area planned for winter wheat had been drilled, and on the light soil types roughly half of that had been sprayed, says Clare Bend, technical manager for Masstock Arable. The far south west corner, however, is well behind.

"Obviously spraying progress varies enormously. Growers that got a crop in during August are well ahead with weed control. Generally those on the lighter land are finished, while those on the loams and clays have lots left to do. But theres still time to act."

Although some herbicides show reduced efficacy in cold weather, the majority can go on throughout the winter months provided frost is not imminent, she stresses. For example, you can get a dip in efficacy with Lexus under cold temperatures, but that can be lessened by adding an esterified rape oil such as Toil.

Mrs Bend urges growers with resistant blackgrass that have yet to drill, to take every opportunity to spray before the winter. "Obviously cultivating to produce a seedbed will control some blackgrass seedlings, but there could be others that transplant which are too large to kill using residuals. The best course of action would be to apply a total herbicide such as glyphosate before drilling, but I can understand why delaying further might be too much to ask!"

Lack of opportunity meant few pre-ems went on, but those that were have performed well, benefiting from the abundant moisture. Residuals such as Stomp/Claymore (pendimethalin) and Lexus Millenium (flupyrsulfuron-methyl plus thifensulfuron-methyl) appear to have done a good job so shouldnt need following up, she says.

Conventionally drilled crops yet to be sprayed may require a robust contact product, particularly where blackgrass or wild oats have started tillering. Topik mixtures such as Amazon (clodinafop-propargyl and diflufenican) or Hawk should do the trick, she suggests. Later drillings with smaller blackgrass that is slow growing due to the cold, wet conditions should still be susceptible to pendimethalin mixtures.