Key advice for disease and weed control in the south this April

Crop Progress

Cereals continue to look in good nick in the southwest. Early drilled winter barleys are thick and lush, so there is a lot of mildew kicking about and some early brown rust.

There’s also plenty of Septoria in winter wheats both on the older leaves and on some newer leaves, according to early results from our free CropCheck service in conjunction with NIAB, which provides qPCR latent disease testing for Septoria and yellow rust in winter wheat leaves.

Oilseed rape is the proverbial mixed bag – there are some decent-looking crops currently around knee height as we approach the last week of March, others that have been hammered by winter frosts, and / or pigeons or cabbage stem flea beetle larvae.

CropCheck results for oilseed rape disease have been coming back mostly low – there’s not much light leaf spot about, especially where prothioconazole was applied previously.

Matt’s agronomy tips for April

1. Finish off grassweed herbicide programmes in wheat

Residual programmes appear to have done a good job, so there’s not a huge amount of weeds around generally.

There was a decent window for applying spring grassweed herbicides, where needed, in February, while March was a bit more unsettled, albeit with some potential spraying opportunities.

If you haven’t been able to get on, it needs to be a priority in April as grassweeds are growing away and heading through the growth stages, and control will be more difficult the larger the weeds get, especially difficult ones like black-grass and Italian ryegrass.

Remember when using a mesosulfuron-based product you cannot mix it with tebuconazole, and with that a key option at T0 for yellow rust control, it could mean a separate application. Check other tank mix options on the Bayer website or FieldMate app .

2. Consider disease risk when deciding winter barley programme order

Nothing has really changed around building winter barley disease control programmes around prothiconazole – it still has good efficacy against net blotch and Rhynchosporium, provides activity against mildew.

It’s also worth remembering brown rust in winter barley is a completely different pathogen than in winter wheat, and prothioconazole is very effective against barley brown rust.

With prothioconazole as the base, what else can you add to strengthen disease control and provide disease resistance management? In Siltra Xpro (bixafen + prothioconazole) there’s the SDHI fungicide, bixafen, while some other products have the strobilurin trifloxystrobin, which has been shown to be unaffected by the F129L net blotch resistant strain.

But if you have a really thick, lush crop that needs the best for disease control, I would be looking to use the one application of Ascra (bixafen + fluopyram + prothioconazole) allowed in the season, as that’s when you are likely to get the best return on that investment.

The exception could be if the field has a history of Ramularia, as fluopyram has shown decent results against that disease from a T2 spray, so you could save it for that timing.

3. Watch out for more hidden diseases in winter wheat

Winter wheat disease control programmes will start in April with T0s, if appropriate, and then later in the month with T1s. There are fewer good choices for T0 fungicides available now, but if you have active yellow rust or susceptible varieties, then tebuconazole is worth using to keep on top of that before T1. You could consider using an azole, multi-site or elicitor at T0 for early Septoria control.

When we get to T1 timing it is important to use a scalpel to dissect plants rather than just using calendar date as your guide for correct timing. Ideally you’re wanting the majority of the field to have leaf three fully emerged. If you go a week too early you can lose at least 0.5t/ha in yield and risk a long gap until T2, and similarly there’s a threat to yield from going too late, so it pays to slice stems with a scalpel and check timing.

Also assess disease risk – if you are in a protectant situation on leaf three, then Ascra from 1.0-1.25 L/ha should cover you. Use the higher rate depending on disease risk, but it’s more likely to be needed the further west you are.

Ascra gives complementary benefits of fluopyram and bixafen, and at the higher rate 150g/ha of prothioconazole, which will help cover both types of eyespot.

Hidden diseases like eyespot and Fusarium are a threat, some varieties with higher Septoria resistance scores have low eyespot resistance ratings, so building prothioconazole into the programme will help cover the bases.

4. Oilseed rape flowering sprays provide a return on investment

Although it’s been a reasonably mild winter overall, there have been enough cold snaps to hold oilseed rape growth back and it is looking like a more normal April timing for oilseed rape flowering sprays.

Timing for flowering sprays is ideally just before petals start dropping – usually when the majority of the field is around mid-flowering, and before any rain as that combined with petal fall is what creates the risk from Sclerotinia infection.

We’ve seen really good benefits from using Aviator (bixafen + prothioconaozle) over and above other options at the timing, with the bixafen adding another mode of action for both disease control and resistance management. We’ve also seen bixafen improves flowering – we think it might help facilitate the movement of micronutrients into the flower giving a brighter yellow flower.

In trials Aviator has given a 0.3 t/ha yield response over other options, which is a good return on investment even with the higher cost of Aviator and oilseed rape prices being back on where they were last year.

5. Take care with mixing procedures when using Emerger

Plenty of early varieties of potatoes have been planted in West Cornwall already, with main crops to follow in April in other parts of the southwest.

When building pre-emergence herbicide programmes, check varieties to make sure they are metribuzin-tolerant. If they are I would build a programme around Artist (flufenacet + metribuzin) and Emerger (aclonifen) – it’s a mix that’s shown good wide-spectrum broadleaf weed activity and grassweed control.

Remember to use Emerger best use guidelines – aclonifen is a bigger molecule that needs careful attention when filling sprayer. Make sure the tank is half full of water before adding Emerger and use constant agitation. Avoid using fine filter meshes, switching to a larger size for this application, and once the sprayer is filled up and ready to go, don’t delay spraying. Once finished make sure the sprayer is cleaned out well.

Emerger also needs to be applied at least seven days before crop emergence, which gives an opportunity to add in a contact herbicide in Roundup (glyphosate) if it will be a long gap between ridging up and emergence and weeds are emerging. Just make sure you’re not going to hit any emerging potato crowns.

If your crop isn’t metribuzin tolerant, Emerger can still be used as the base with other residual options, such as pendimethalin, metobromuron and prosulfocarb.

6. Combat disease in spring barley and winter oats

February-drilled spring barley particularly could be looking at first disease control sprays in April. Again it’s a decision about what potential the crop has and disease risk, but we’ve seen good results from Ascra in programmes and even more so when only used a single spray. As in winter barley, Ascra will cover all bases in terms of disease.

In winter oats, crown rust is the primary disease challenge. Siltra (0.4 L/ha) has shown good results in trials over the years with the SDHI bixafen also providing stem strengthening properties helping reduce lodging risk.

If you’re planning to drill spring cereals or other spring crops in April and will be using Roundup (glyphosate) pre-drilling to clean up seedbeds, remember to match glyphosate rate to the growth stage in the field. Perennial weeds and grassweeds that are going through stem extension, for example, will need more than the usual 720g/ha of glyphosate normally associated with volunteer control in stubbles.

7. Consider new Dekalb maize varieties

If you haven’t selected maize varieties, then three new Dekalb varieties might be worth considering. They won’t be for everyone as the FAO numbers are around 200-210, meaning they are slightly later maturing than some competitors, but if early harvest is not the main criteria they have excellent other characteristics and are suitable for forage or anaerobic digestion production.

I wouldn’t consider them for the far southwest, but they could be a good option for growers in Dorset or around the Salisbury plain where it is a bit warmer and soils are a bit kinder for travelling later in autumn.