Many growers may be reluctant to apply cleaver sprays too early in the spring for fear of missing later-germinating plants. But there may be no need to worry

There is far more flexibility with the control timing of cleavers than many growers believe, Rothamsted Research weed scientist John Cussans believes.

Although cleavers have two distinct germination flushes, with 10% of the total population not emerging until the spring, the later-germinating weeds appear to have little or no effect on crop yield, he says.

“Even though 10% is a sizeable proportion, our work shows that it shouldn’t constrain the management decisions of farmers. The spring-emerging weeds do go on to produce viable seeds, but the numbers are very low, at about five seeds per plant.”

In contrast, an equivalent autumn-emerging population caused 23.3% yield loss in trials conducted by Dr Cussans.

“There’s plenty of evidence and trials data to show just how damaging cleavers can be,” he adds. “But to date, there’s been little work done to compare the characteristics of autumn and spring-germinating plants.”

His work concluded that as spring germinating cleavers do not contribute to the population dynamics of the species as a whole, it is not necessary to delay control measures to ensure that all the weeds are controlled.

“If an early herbicide timing fits in better with other agronomy or crop passes, then it shouldn’t be dismissed.”

By early, he still means a spring treatment. “It may be that you can deal with the problem two to three months earlier than your normal practice, without any detrimental effect,” he says.

“It is important to pick the right herbicide for the conditions on your farm. There have been a number of new cleavers herbicides and mixes launched in the past few years, so the choice is good.”

But Dr Cussans warns growers that there are situations where spring cleavers can become more problematic.

“If the seed production of these cleavers suddenly increases by 20-25%, then they are significant. So if crop competition is poor, or you’re in a specific rotational situation – such as following potatoes – then you might need to adopt a different approach.”

In this case, cleavers control may involve two timings one early and the other later, he suggests.

“Cleavers are unusual in emerging in two flushes. Most other weed species come up in one period following cultivation. But this different germination pattern doesn’t need to have a huge bearing on their control.”

Cut the cost of cleavers control

Independent agronomist Steve Harrison has successfully controlled cleavers with an early application of either Boxer (florasulam) or Eagle (amidosulfuron), but his reasons for doing so have been driven by economics.

“If you’re looking to use a February or March dose of Atlantis [iodosulfuron + mesosulfuron] for blackgrass, and cleavers are also present, then it’s possible to incorporate a reduced rate of Boxer or Eagle and cut the costs of your cleavers control.”

Mr Harrison is familiar with the Rothamsted work, but believes that there are other considerations to take into account. If just cleavers are present in February, he is not too bothered about controlling them then.

“It’s where it fits in with Atlantis that it is relevant. It halves the cost of the cleavers spray, bringing it down to about £8/ha.”

He warns that this approach is not always bombproof. “Occasionally the cleavers regrow and last year we had to re-treat a couple of fields with Starane [fluroxypyr]. But neither Eagle nor Boxer are too temperature dependent, so it works well in most situations.”

This approach also simplifies life later on in the season, when tank mixes become more complex, he adds.

Mr Harrison used 50ml of Boxer with Atlantis last year. “Eagle is now approved to mix with Atlantis, so this season I’ll be looking at the costs of both products before deciding which herbicide to use.”

He reminds growers that broadleaved weed control in February and March is more hit and miss than later on. “But it can save you money and help with the logistics of spring spraying.”