Spring Spray Pressures Blessing In Disguise For Set Aside Weed Control

July 2006 - Don't worry about set aside spraying. Prioritise your foliar fungicides, PGRs and herbicides in this spring's particularly tight spraying window. Your set aside can easily wait for its treatment. Indeed, it will probably be all the better for the delay.

This is the timely advice from Agrovista technical manager, Mark Hemmant who insists that particular pressures on spraying resulting from the poor spring are likely to be a blessing in disguise for set aside management.

"The biggest mistake most people make with set aside is spraying it off too early," he insists. "They then have to go to the trouble and extra expense of over-spraying later onin the summer.

"A single dose of high activity glyphosate, Roundup Ultra will almost certainly give you complete control of most grass weeds at tillering or at full ear emergence. Spray in between these stages during stem extension, though, and even the best formulations will give you very variable control. The strong upward sap flow tends to accumulate glyphosate in the aerial parts, giving a good initial kill but allowing tillers to re-grow.

"For every flowering stem in early May it's important to appreciate there will be many more tillers still in the less vulnerable stem extension phase. And, since seeds in early emerging ears commonly take a good six weeks to mature, there's no rush to spray them."

Mark Hemmant stresses that the best time to spray grass weeds is once all the ears are fully emerged but while the seed heads and leaves are still green. With annuals like black-grass, brome and ryegrass this is likely to be from mid-May to early June. In contrast, it may be late June or even early July with common couch, onion couch and other perennials.

For the most cost-effective volunteer cereal and annual grass weed control, he recommends a single 2.4 litre/ha application of Roundup Ultra, with higher rates for couch and other perennials.

He advises adding the specifically developed adjuvant, Companion Gold to the tank prior to the glyphosate to reduce spray drift as well as maximising herbicide efficacy, stressing that boom height, forward speed, spray pressure and nozzle choice must also be spot-on for the most effective spray targeting.

"Avoid spraying in hot weather as weed glyphosate translocation can be restricted under these conditions," he adds. "And, with light intensity also important in governing herbicide movement in the plant, spraying in the morning is always better than later in the day."

"Where volunteer cereal or grass weed growth is excessive, you may need two glyphosate applications - one before ahead of main stem extension in May and the other at full ear emergence in June/July. In most cases, however, a single spray of Roundup Ultra with Companion Gold will be quite sufficient. Providing, of course, you get the timing is right."