With recent springs becoming increasingly arid, barley growers will need to ensure weed control programmes provide effective protection in dry conditions.

That is the advice from ProCam’s head of crop production, Mike Thornton, who explains that with as little as 110 days between spring barley being drilled and harvested, it is important to ensure crops aren’t held back by weeds which will deprive crops of light, water and nutrients, and which could also reduce the number of viable shoots a plant puts down at early tillering.

“The majority of spring barley will hopefully go into a stale seedbed which is devoid of any active grass or broad-leaved weeds,” Mike describes. “However, whilst that’s the ideal scenario, it won’t be representative of all situations. Therefore, where blackgrass or annual meadow grass are problematic, a pre-emergence application of a multi-active product such as Tower (chlorotoluron, diflufenican and pendimethalin) will be essential as there are limited post-emergence options to control these difficult weeds.”

For weeds that can be controlled by post-emergence treatments, Mike recommends these should be applied sooner rather than later, with a series of 38 ProCam trials showing that applications made between GS13 (three leaves unfolded on the main shoot) and GS24 (main shoot and three tillers) will provide the best level of weed control.

“ProCam’s independent trials have shown that treatments made at GS13 can deliver an average yield increase of 2% compared to applications which are delayed until GS24 or later. It therefore pays to protect crops earlier, but it’s also important to remember that different weed species will be more or less competitive depending on their growth habit and germination timing. For example, weeds which grow from depth will be less effectively controlled by residual herbicides, making the need for early post-emergence treatments even more important. Meanwhile, any weeds which germinate after the crop has gone beyond GS24 will generally be over-shadowed and smothered by the developing crop.”

Mike also explains that the weather will impact the efficacy of herbicide programmes, with last year’s dry conditions causing weeds to develop a thick wax layer and keeping stomata closed for longer, both of which prevented herbicide uptake. “The dry conditions also reduced metabolism rates which slowed the translocation of herbicides within weeds,” he adds. “That’s another reason to control weeds while they are small. Herbicides should also be applied first thing in the morning when stomata are more likely to be open and don’t be tempted to reduce application rates. An adjuvant oil should also be used to help the herbicide penetrate target weeds.”

Herbicide recommendations

Mike explains that Quelex is the product of choice in many post-emergence situations “as its twin active ingredients (haluxifen methyl and florasulam) provide strong activity against a wide range of weeds, including some that are resistant to ALS chemistry.

“DP911 SX (metsulfuron-methyl and tribenuron-methyl) broadens the range of weeds and persistency, but growers should be careful when using metsulfuron as its half-life can range from 30 to 180 days which could impact a following crop of OSR.”

A third option is Supreme Max (florasulam and tribenuron-methyl) which brings in a different spectrum of weed control including field pansy and speedwell species. “It also has less of an effect on sensitive following crops such as brassicas and is an extremely flexible tank mix partner,” Mike describes.

For growers anxious to avoid ALS chemistry completely, Mike recommends Pixarro (halauxifen-methyl and fluroxypyr) which can be coupled with a phenoxy hormone containing product to eliminate any following crop issues. And in situations where ryegrass and/or wild oats are to be targeted, Mike advocates the inclusion of Kanaster (pinoxaden) which he recommends should be used at full-rate and can be applied one week prior to, or three weeks after, a broad-leaved weed treatment. “The latest timing for Kanaster is GS41,” he explains, “so work plans will need to be managed carefully. Alternatively, Foxtrot (fenoxaprop-p-ethyl) can be applied a week either side of a sulfonylurea herbicide, but it has an earlier cut off of GS31 and must be applied on its own.”

Mike concludes by explaining that growers shouldn’t be afraid to spray off any patches of poorly controlled weeds before seed is set. “If all else fails, herbicide resistant weeds such as poppy, chickweed and mayweed may need to be taken out with glyphosate. Destroying them before they have a chance to shed another consignment of seed will pay dividends in future years, especially as some weed seeds can persist for 10 or more years.”