Oilseed rape has been the surprise of the season so far – generally it looks good. Even crops that were quite badly savaged by adult cabbage stem flea beetle in the autumn, to the point where they were nearly written off, now have surprisingly few larvae in stems, despite the adult population.
So the forecast for the oilseed rape crop in the ground is promising – it’s just a shame there’s so little in the area. Maybe that is part of the reason it looks good – perhaps there’s something in the natural cycle of things that have come back into balance? Of course, as we have seen before, there’s still time for larvae to cause problems in the next month or two.
Also quite surprisingly there is very little wheat I’ve seen that looks horrific for grassweeds, even earlier drilled. That’s probably because the early drilled crops went into good seedbeds, which helps all round with emergence and herbicide efficacy, and then had plenty of moisture after drilling to allow residual herbicides to work well.
Some of the later drilled crops are a bit more iffy, although still generally OK. Seedbed quality on these was not so good, and / or could not be rolled, so there has been some interesting crop effects from certain active ingredients, especially pendimethalin. That’s particularly the case in Oxfordshire where there was 120-130mm rain in early October.
Wheat fields generally fall into three camps for weed control: early drilled with pre-emergence applied; later drilled with some weed control applied, and later drilled with nothing on.
The earlier drilled crops which have been treated are generally some of the cleaner ones, despite the earlier drilling. But earlier drilling and treatment does have other implications: herbicides run out earlier as higher temperatures mean shorter half-life for the active ingredient, anything that survives has more time to get to a decent size, so those are the fields you need to watch to see what happens.
If you’re really lucky that might be it for weed control on these fields, or just some broadleaved weed treatment later in spring. Just bide your time to see what follow ups are required.
In October or later drilled crops that had some herbicide applied in the autumn should be similar, although seedbed quality was likely poorer. That could mean clods breaking down over winter could see another flush of black-grass.
Generally these are also the fields where the damage is worst, so where plant thinning has occurred, weeds have more space to tiller into. It could be these crops end up coming out of winter with the worst problems.
With these it is again keep an eye on them, and as and when a decent population of any surviving grassweeds get to 2 leaf stage it will be time to treat, if you can travel.
Crops that are so far untreated will likely need treating, not least because residual herbicides in the autumn usually help with broadleaved weed control. For these, wait and see what happens with grassweeds.
Anywhere you have both broadleaved weeds and grassweeds, steers you towards Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron) as an option. In February, you can use it for mixed populations at 0.4 kg/ha. If you have brome as your major weed then from 1 March there is a higher rate of 0.5 kg/ha as an option.
Alternatively, Monolith (mesosulfuron + propoxycarbazone) at 0.33 kg/ha is an option for grass-weeds from February, but it controls a reduced range of broadleaved weeds.
Always look for opportunities to treat early in spring.. Obviously you need to be able to travel, and don’t consider spraying on a frost as this isn’t good application conditions for post-emergence herbicides.
We’ve seen surprisingly good results from applications during cold, but bright periods in February. The benefit is that if you can get grassweeds sprayed with two fewer leaves than you might a month later, it will help you out no end.
Just remember if you are changing between jobs and spraying oilseed rape for example, then you need to wash out thoroughly after applying sulfonylurea herbicides before spraying oilseed rape.
Oilseed rape is visually very clean. There was some Phoma about in the autumn, but now with most leaves a decent size it is no longer cost-efficient to treat for it specifically.
But while there are very few visual symptoms of light leaf spot so far, our Spotcheck results from November and December show some sites with reasonable levels after ADAS has done the 3-day incubation.
In many cases you can wait and see, while Spotcheck tests can help you monitor for any disease through the month.
With varieties rated a six or less for light leaf spot resistance, and these are less common than they used to be, you might consider treating with Proline (prothioconazole) at around 0.4 l/ha, particularly if nothing was applied in the autumn.
If you need growth regulatory effects as well, then that might point you more towards tebuconazole. That’s fine, but if you have a level of infection in the crop, remember that active isn’t as strong on the disease and could end up being too late by the time you’re applying for growth regulation at green bud.
I’m not going to give advice on when to spray off cover crops in advance of drilling spring crops, as there are so many factors that you need to take into account.
The one factor that can be overlooked and shouldn’t be is pest pressure. For example, if you’ve got oats or other cereals in a mix going into a spring cereal then the potential for green bridges for aphid and frit fly infections have to be taken into account.
That might mean needing to destroy the cover crop four to six weeks in advance of the new crop going in to give a decent break, this may be a longer gap than growers may be looking for with wet soils and using cover crops hopefully sucking some of that moisture out of the ground until closer to drilling date.
Decent formulations of Roundup (glyphosate) will help with efficacy in the more challenging spraying conditions early in the year, and if there is a lot of green material in the cover crop, don’t muck about with doses. The rate that will be needed will depend on the species in the cover crop, but think about dose in terms of grams of active ingredient rather than litres / ha of product because of the number of different products available.
There’s already some yellow rust appearing in wheat crops. We probably won’t have weather cold enough to remove the infected leaves, but just because there is yellow rust in crops in January and February it doesn’t mean that there will be a problem at T0.
Most varieties on the Recommended List are susceptible to yellow rust during the juvenile stages, but there is no need to panic. There’s nothing too bad at the moment, and while it might get worse, it might also disappear, and we still have cheap, effective yellow rust chemistry. The UKCPVS results meeting in March will hopefully give us some guidance on any significant changes in rust races.
Effective weed control is essential for any crop to fulfil its yield potential. However, the task is becoming harder as the chemical armoury shrinks and resistance reduces the effectiveness of some herbicides. There is now much more focus on integrating chemical and cultural weed control options. Take the test below to see how much you know about managing weeds in combinable crops.
We know that growing oilseed rape can be challenging so we have gathered together everything you need to know about oilseed rape here. From establishment to harvest we can provide insight about crop management and protection to help maximise yields.