Flexible approach to weed control offers best results


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For Lancashire-based Agrovista agronomist John Ball, effective weed control in potatoes is down to getting the job done right first time.

He advises across a range of crops, including potatoes, vegetables, combinable crops and forage, grown on soil types which run from high organic matter Lancashire moss and black sands to light blowing sands.

These soils present challenges when it comes to herbicide use, with respect to both efficacy and crop safety.

“You have got to be quite careful about what products you use, particularly with metribuzin, depending on the variety. And on the moss soil it is difficult to get residuals to work,” says John. “On the moss you need something that is more robust if it is to work well, and on the light sand you want something that's a little bit kinder.”

Most of the potato growers John advises are producing maincrop ware for packing, but some are growing for the chip shop trade. Crops are grown mainly on either moss or light sands and varieties include Maris Piper for chipping, Sagitta, Nectar, Melody and Estima for pre-pack.

Agrovista agronomist John Ball

Field pansy and groundsel are the predominant broad-leaved weeds seen, while annual meadow-grass is the main grass-weed problem. Ryegrass is an increasing threat, adds John.

While Maris Piper’s sensitivity to metribuzin on lighter soils is well-documented, one of the challenges this season will be the limited herbicide sensitivity data – or in some cases complete lack of data – available for several of the newer varieties that being grown because of seed shortages in more mainstream varieties.

“This is going to a be a massive challenge,” says John. “We are going to need products with excellent crop safety on all soil types. It is just going to make this season a little bit more difficult.”

It is not simply a case of matching herbicide programmes to soil types, as some growers will have crops on light sand as well as organic soils but will not want the hassle of different mixes, he adds.

His starting point this season, as in previous seasons, will be a ‘tailored mix’ comprising three litres per hectare metobromuron (in Praxim (sold as Soleto by Agrovista) and 3l/ha prosulfocarb (Defy).

“That will be my standard safe mix if I am going with just a residual,” says John. “And then I will build around that depending on the weed spectrum I’m expecting.” On the moss soils this might see some metribuzin incorporated into the soil pre-ridging for a little more ‘bite’, he adds.

Soleto +Defy will then be applied to the ridges, before cracking, with Gozai (pyraflufen-ethyl) also likely to be included. Where groundsel, mayweed or field pansy are present, Gozai (pyraflufen-ethyl) (marketed as Albis by Agrovista) has a clear advantage over alternatives such as carfentrazone (Shark), he adds.

Soleto brings broad spectrum activity and good tank mixability to the mix, providing excellent control of annual meadow-grass, as well as brassica weeds such as charlock, chickweed, mayweed. Where bindweed is likely to be a problem, adding pendimethalin (stomp aqua) to a Soleto + prosulfocarb mix is a good option, John adds.

After the long, wet winter, he has some concerns around the prospects for good soil conditions at planting.

“Much depends on what growers have had in the ground ahead of the potato crop. I’ve seen an increase in use of cover crops before potatoes, especially for potato cyst nematode control, and that will only increase with the SFI multi-species cover crop options coming in. These seem to leave the ground in a lot better condition for planting.”

However, while concerns are focused presently on the impact of the wet weather, a prolonged spell of dry weather starting soon after plantings has posed significant problems in recent seasons, which has limited the efficacy of some residual herbicides.

Soleto will provide continuing control providing conditions do not become too dry for too long, says John. Dose rates should not drop below 2.5l/ha, he adds. “If you are getting down to that level, that's when you want to put in a mix partner in. If I was going with a really kind mix, then I would be looking at 3.0l/ha at least.”

Get things right pre-emergence and the need for costly later sprays is reduced, says John. “You are better off getting the job done and doing it right first time,” he concludes.