Disease control priorities and advice for cereals and oilseed rape growers in the west

Crop Progress

Crops have responded well to early nitrogen, and to the 60mm of rain we’ve had so far in March. There are some oilseed rape crops with flea beetle or rape winter stem weevil larvae damage, but generally oilseed rape is looking pretty good – it’s now a question of deciding your level of input based on what potential you think your crops have.

Hopefully the last grassweed herbicides will be applied in March – if not that’s a priority for early April.

Gareth’s agronomy tips for April

1. Cover light leaf spot with flowering sprays in oilseed rape

One thing I am noticing a lot of is light leaf spot lesions on oilseed rape leaves in both treated and untreated crops. That probably means it will be really useful to include some light leaf spot activity with your flowering spray, as well as Sclerotinia activity.

Aviator (bixafen + prothioconazole) is one such option covering both diseases. Even in recent years when we’ve not had a major Sclerotinia outbreak, there have been yield benefits in trials – possibly from the SDHI element giving some physiological and yield benefits in the absence of disease.

With April notorious for showers, the superior rainfastness of Aviator could also come in useful, while rain or even heavy dews can increase risk from Sclerotinia. Aviator will give protection for around 3-4 weeks, so if there is an extended flowering period then you will also need to think about a second spray.

2. Don’t wait too long to apply winter barley fungicides

My big tip in winter barley is not to wait too long for T1 sprays. Tiller retention is key so getting protection on at GS30/31 will help minimise the risk of tiller abortion because of disease, as well as making sure the gap between T1 and T2 is not too short.

Net blotch is quite difficult to control, so short intervals, within reason, between sprays is good and use a combination of actives. Ascra (bixafen + fluopyram + prothioconazole) and Siltra (bixafen + prothioconazole) are options that will also cover the other diseases at T1, such as Rhynchosporium, mildew and brown rust.

Ideally I would use 0.9 L/ha of Ascra at T1 – the strongest option to help maintain tillers. You’re probably going to lose more yield by losing tillers at this timing than you would from a late attack of Ramularia.

Growth regulation is also likely to be important in winter barley – you want thick crops for yield and it can go through growth stages quickly. That means it’s easy to miss the latest before GS39 timing for growth regulation with Terpal (mepiquat chloride + 2-chloroethylphosphonic acid), and it’s perhaps better to go harder with early PGR. You don’t have many people regretting putting growth regulators on, but plenty regretting when they haven’t or undercooked it.

In spring barley crops go through growth stages even more quickly of course. For disease control, the first spray of a two-spray programme is usually around late tillering. In this crop I’d probably go Siltra first and follow up with Ascra as Ramularia risk is a little higher and you’re looking to keep the crop green for as long as possible.

For April drilled spring barley remember there is the option to use Liberator (flufenacet + diflufenican) as a pre-emergence for weed control.

3. Do you have yellow rust risk?

While it is not really proven with the current options that it is worth applying a T0 for Septoria, I’d definitely be considering it where there is a yellow rust risk.

If I thought there was a risk based on the variety score or the juvenile resistance rating, I think I would include something at T0. The decision is even easier if you’re already going through with a growth regulator. Keeping yellow rust out early makes management a lot easier through the programme.

Varieties such as Crusoe, Siskin and maybe Costello and Dawsum don’t appear to have a yellow rust risk so you probably don’t need to do anything at T0.

4. Use broad spectrum activity at T1 in wheat

The most important advice at T1 is to make sure you are targeting final leaf three. It’s time to practice your dissections again – it’s not the easiest thing to do, but it is worthwhile spending the time to make sure it is right.

With lots of diseases to target at T1 – Septoria, yellow rust, mildew and eyespot – you ideally want a broad-spectrum fungicide like Ascra to cover all of those. A rate of 1.0 L/ha should give you that broad spectrum activity.

You could add folpet – I’m quite neutral about it. Occasionally you see benefits, sometimes you don’t. But unlike with chlorothalonil in the past I’ve never seen a negative from putting it in. Unfortunately only hindsight will tell you if it was the right thing to do, but when you make the decision it’s really difficult to know.

5. Check for latent disease with our CropCheck service

Keep an eye out for reports about Septoria and yellow rust risk with our National Snapshot updates during the season. We’re using NIAB qPCR analysis to test for latent infections of both on a weekly basis from March onwards after doing one test each in January and February. In the west I’m testing crops of Costello and Crusoe drilled at similar times.

If you would like to do your own latent disease test through CropCheck then get in touch with me.

6. Pay attention to ridge formation in potatoes

If you’re planning to use Emerger as part of your pre-emergence weed control, pay attention to ridge formation. Well-formed ridges are important for efficacy as the product lays down a layer of chemical – if you haven’t got well-formed ridges it doesn’t work as well.

Advantages of Emerger include no varietal restrictions and that it is less affected by drier conditions than some other products. But you would use it with a partner product, which might be affected.

Use the guidance on Bayer’s website for spraying Emerger – the most important bits are to maintain agitation in the sprayer at all times and don’t leave the spray in the tank for a long time before spraying.