How to keep crops disease-free in Scotland this May

1) Monitor for yellow rust efficacy at T1

With wheat varieties unexpectedly being infected with yellow rust this spring, monitoring the efficacy of T0 sprays in the run up to T1 to make sure they have worked is important.

Try not to go too soon with T1 sprays though, as it risks leaving too long a gap between T1 and the flag leaf spray. You’re looking for final leaf three to be fully emerged before spraying T1s. If there’s yellow rust in the crop at that point, you’ll need to consider a more robust rate of a product with activity on this disease.

The combination of Septoria and yellow rust risk leads towards using Vimoy® plus a partner. While the weather has been dry through most of April, that can change quickly to increase Septoria pressure. Vimoy® provides excellent control of both diseases.

Alternatively, if weather remains dry and Septoria pressure is lower, Ascra® Xpro®, for example on varieties with good disease resistance, is another option, while on very susceptible varieties, early drilled, with higher levels of yellow rust or Septoria, Plaxium® could be used.

Recent rain could also bring another flush of weeds, especially cleavers, for which Eagle® or fluroxypyr as the weather gets warmer could be necessary tank mix additions.

2) Flag leaf spray choice will depend on several factors

Lots of different factors will help determine what will be required for flag leaf sprays, which will likely start towards the end of the month.

It will depend, for example, on the effectiveness of the T1 spray, its timing, and weather in between T1 and T2, because even with a well-timed T1 spray, leaf two will have been unprotected once it emerges and can easily spread disease to the flag leaf.

Other factors include what the disease levels were before the spray, what product was used at T1, variety susceptibility and drilling date.

In a worst-case scenario where you applied a weaker product at T1 on a susceptible variety with disease already present, then you’ll need a robust T2 spray. Whereas if you went robust at T1, the crop’s clean and the weather has been dry then maybe you can use Ascra® Xpro® at T2.

Products where more Septoria activity is required include Univoq^TM and Miravis® Plus, while Jessico® One plus Vimoy® is a very strong combined Septoria and yellow rust choice. Each of the key actives in the products can only be used once in a programme though, so can only be used if that active wasn’t used at T1.

3) Multiple modes of action help versus Ramularia

Ramularia is typically the key target for T2 sprays in winter barley but watch out for net blotch and Rhynchosporium too.

In barley, the more active ingredients you can apply to control Ramularia the better, as no one active does a 100% job. Stacking multiple mode of action products, such as Ascra® Xpro® plus a multi-site product, where you didn’t use Ascra® Xpro® at T1, is a good option. Don’t discount the value of adding a strobilurin fungicide either, for improved greening and net blotch control.

4) Two sprays for spring barley disease control

It is as much about quality as quantity with spring barley, with it vital to achieve the malting barley quality specification to qualify for a premium.

Start programmes early at the end of tillering or GS30 using a prothioconazole-containing product such as Siltra® Xpro® or Ascra® Xpro®. Again, adding a strobilurin fungicide could have value for added net blotch control, as well as greening for protecting bushel weight.

Controlling disease early will reduce stress on the plant, which can be a key risk factor for Ramularia.

Also look out for trace element deficiency in spring barley, especially manganese on fields which have been limed in the past year or two. With a higher pH, the more likely you are to see manganese deficiency.

Most variable rate lime applications are determined by one or two samples per hectare, while pH can change by the footstep almost. That means you’ll almost certainly have areas that are over-limed and over pH 7, even if you were targeting pH 6.5. You often see it most in the second year after lime.

5) Consult AHDB Sclerotinia forecast tool

Oilseed rape looks like it will be flowering for quite a while. We had decent sunny week in mid-April and then it turned a bit cooler, and the crop stopped growing, so I think there will be a prolonged flowering period.

Sclerotinia risk will increase as temperatures increase and we’ve had some showers. AHDB’s showed a near miss near Edinburgh over the Easter weekend, and is a good tool to see current forecast and risk.

Where crops need spraying, a first fungicide should be applied at the start of petal fall. The aim is to coat the petals and help avoid creating the food source for sclerotia to infect stems when they stick to the oilseed rape plant.

Fungicides, such as Aviator® Xpro® protect crops for around three weeks with an initial application of 0.75 L/ha. A follow-up application of 0.5 L/ha is worthwhile even if petal fall is nearly over after three weeks, as the later emerging flowers will be unprotected by the first spray.

6) New insecticide offers welcome aphid control in potatoes

Controlling virus levels in seed potato crops in recent seasons has been challenging, partly due to a lack of active ingredients, so hopefully it is positive news that Bayer has a new insecticide that controls aphids that transmit viruses approved.

Sivanto® Prime contains flupyradifurone, and provides contact and translaminar activity. The translaminar activity means the product moves from the upper leaf surface to help control aphids hiding under leaves.

It’s best used early in programmes as it has good knockdown activity, and also a positive beneficial profile allowing beneficial insects and predators to build up.

Sivanto® Prime can only be used once in a season with a latest date of application of 13 July.

-----

Aviator® Xpro® contains bixafen and prothioconazole. Ascra® Xpro® contains bixafen, fluopyram and prothioconazole. Eagle® contains amidosulfuron. Jessico® One contains fenpicoxamid. Miravis® Plus contains pydiflumetofen. Plaxium® contains isoflucypram, fluopyram and prothioconazole. Siltra® Xpro® contains bixafen and prothioconazole. Sivanto® Prime contains flupyradifurone. Univoq^TM contains fenpicoxamid and prothioconazole. Vimoy® contains isoflucypram.

Aviator®, Ascra®, Eagle®, Jessico®, Plaxium®, Siltra®, Sivanto®, Vimoy® and Xpro® are registered Trademarks of Bayer. All other brand names used are Trademarks of other manufacturers in which proprietary rights may exist. Use plant protection products safely. Always read the label and product information before use. Pay attention to the risk indications and follow the safety precautions on the label. For further information, including contact details, visit www.cropscience.bayer.co.uk or call 0808 1969522. © Bayer CropScience Limited 2025