Will rain help growers in the south get new crops off to a positive start in September?

Crop Progress

Harvest was positive for most growers in the south, apart from the fire risk. No drying was required which was a bonus with the high energy prices and most growers seemed to have first wheat yields up on their normal average. Second wheats were perhaps slightly down on what farmers hoped, after being more vulnerable to the hot weather.

Oilseed rape yields were a mixed bag as always, but a decent number of strong yields of 4-4.5t/ha were reported in the region. Pigeon damage was quite often the reason behind lower yields.

Later drilled spring crops that missed the pockets of moisture in the spring were perhaps the poor relation this season, while beans also suffered in the 40C heatwave.

Richard’s agronomy tips for September

1. Conserve moisture when establishing oilseed rape

Where growers have been lucky and caught a localised storm or rain in August, some oilseed rape drilling has happened, but that’s certainly not the case for all as we reach the August bank holiday. In some, if not most of the south, not much oilseed rape has been drilled.

We could do with a slow and steady soaking for a few days to allow moisture to get into the soil. That needs to happen reasonably quickly for oilseed rape as growers will need to get going soon if the planned area is all to be established. Most growers consider the middle of September to be the cut off for oilseed rape drilling.

For September drilling focus attention on how to establish the crop as quickly as possible. Establishment method is crucial, especially if moisture remains limiting, with, where possible, direct drilling a good option to help keep moisture in the soil. Avoiding any cultivations that release moisture from the soil profile will not be helpful for rapid establishment and continued growth.

Choose a variety with rapid germination and early vigour to reduce vulnerability to cabbage stem flea beetle. Hybrid varieties, such as those in the Dekalb stable like DK Exstar, have shown increased vigour over conventional varieties, especially from September sowings.

Adding some nutrition either down the spout with the drill or in the form of organic manures will also help crops with germination and establishment speed.

2. Use stale seedbeds to start successful weed management

Successful weed management starts in September by getting a clean seedbed to drill into, free from grassweeds.

With hot, dry weather around black-grass seed maturation meaning freshly shed seeds will have low dormancy and rapid germination, stale seedbeds should be successful this autumn, provided we get some moisture.

If there has been some rain or is some on the horizon, it’s worth running some shallow discs or a stubble rake over stubbles to promote a chit of grassweeds. With black-grass, Italian ryegrass and sterile brome that can be any time after harvest, while for meadow, soft and rye brome wait for a month after harvest to give time for the weed seeds to ripen and break dormancy. With such an early harvest that’s going to be early in September for many crops.

Once there has been a good flush of grassweeds, spraying off with Roundup (glyphosate) is key to getting good control. It’s our best weapon against difficult grassweeds so use it carefully to maximise efficacy.

The ideal timing is when grassweeds have reached 1-2 leaf stage, when they can be treated with a minimum dose of 540g a.i./ha. If any grow beyond that to tillering then up the dose to a minimum of 720g a.i./ha to avoid applying a suboptimal dose of glyphosate for good resistance management.

Pay attention to sprayer set up and application practice – this isn’t a job to rush or do sub-optimally. Think about the small target you’re trying to hit and set the sprayer up with the right nozzles, boom height and forward speeds to maximise control.

Recent studies have shown up to two passes of glyphosate on stubbles is optimum for efficacy and resistance management. Time the last one for as close to drilling as possible, and use mechanical disturbance to take out any survivors between applications.

3. Consider new pre-emergence option for winter barley grassweed control

Assuming we do get some rain in September, winter barley drilling will likely commence later in the month. Moisture is important for getting the best control from residual herbicides as well as obviously for growth.

There will be a new option for growers to consider this season for pre-emergence weed control with Proclus (aclonifen) + Liberator (flufenacet + diflufenican). As in winter wheat it should only be used as a pre-emergence treatment, applied as soon as possible (ideally within 48 hours) of drilling to a fine, firm seedbed.

One difference is that the use rate is lower at 1.0 L/ha of Proclus plus 0.6 L/ha of Liberator, compared with 1.4 L/ha in winter wheat.

The combination’s strengths are against difficult grassweeds such as black-grass and Italian ryegrass, and some broadleaf weeds including cleavers and brassicas. When Proclus is applied, it binds to the soil forming a film through which the weeds grow and take up the chemical. That means it is less dependent on moisture levels in the soil for activity. However, the residual partner in Liberator is more dependent on soil moisture for its activity.

4. Ideally delay winter wheat drilling until October where grassweeds threaten

The question many of us is asking is when will the drought break, and when it does, will the rain stop? It’s enough of a concern that some growers may well decide to drill wheat in September, especially remembering back to two seasons ago.

Agronomically, though, delaying drilling wheat until at least mid-October where you have difficult populations of grassweeds is the best thing to do. If you do start drilling in September, obviously try to target fields with low grassweed pressure first.

A residual pre-emergence treatment will still be necessary in most cases, and especially where grassweeds are present. Liberator + Proclus has been tried and tested for the past couple of seasons to overwhelmingly positive feedback. If necessary, another residual, such as prosulfocarb, triallate or pendimethalin can be added to increase control of grassweeds in wheat.

One advantage of aclonifen in these earlier drilled crops is its longer half-life of around 90 days, which is about double that of flufenacet and other residuals on the market. That will give a longer period of activity in earlier drilled crops, although a top up of another residual might be required after 3-4 weeks, as the activity of flufenacet wanes.