Crop Watch: High blackgrass levels and T3 spray strategies

June is the month when any deficiencies in weed control become visible with blackgrass and other grassweeds waving above cereal crops.

This year, there seems to be more of them perhaps reflecting the difficult spring. 

Winter wheat ears are now starting to emerge in the earlier drilled fields and thoughts turn to T3 fungicide strategies, with sprayers heading out in 10-14 days in the South as flowering begins.

See also: Protein test sees Kent milling wheats hit breadmakers’ needs

North

Patrick Stephenson, AICC (Yorkshire)

Despite the prolonged wet spring, soils are already cracking after this short dry spell. May is a great month in the UK, as our countryside springs into life and is full of colour.

Unfortunately, from an agronomist’s point of view it is followed by June, when your season’s sins are revealed to the world, as the uncontrolled weeds wave to the passing public.

As much as I would like to say that this is all part of a new biodiverse farming policy, the reality is that it is the reflection of a difficult spring.

Winter wheat crops have at last filled out and on the whole look promising. Despite the epidemic of septoria seen early in the season, the top three leaves are clean.

Yellow rust is bubbling around, but most fungicide programmes and kind weather patterns have kept the disease under control.

It is many years since I treated any wheat crop for aphids, relying primarily on natural predators as primary defence.

This is a huge change from 15 years ago, when it was almost a standard application.

Aphids have certainly been about, and most wheat crops have a degree of barley yellow dwarf virus, although we are lucky that we have not got the level of infection seen in the South.

I will be very interested to see how the Recommended List trials reflect the level of disease seen in crops.

There are also questions over some lesions seen on leaf two which are not septoria and are randomly dotted across the field?

If we add to this various soil type-related colour variation in the crops, then the autumn post-mortem meetings will be fascinating.

The final fungicides will be applied when the ear emerges, and these will be dominated by prothioconazole and or tebuconazole.

Winter barley

The gates are now shut on winter barley crops, and they look magnificent, but sadly not all that glitters is gold. I fear that the combine will tell the true story of the 2022-23 season.

Spring barley crops are a real dog’s dinner ranging from excellent to “could do better”. Broad-leaved weed sprays have now been applied and the early drilled crops have received a fungicide.

Wild oats are always a challenge in spring barley crops, as finding them in the early season is almost impossible and then later in the season, they are waving at you above the crop!

Winter oilseed rape has finally stopped flowering. Again, there is tremendous contrast in the crops, some sadly are dire and others good.

All have one thing in common and that is they are short. The most forward and consistent crops are about four to five weeks away from desiccation.

The variation in flowering in some crops, courtesy of various vermin, means that the use of a pod sticker is likely to be a good idea.

Looking back at the season I fear that oilseed rape remains a high-risk crop and, consequently, plantings will be restricted for the coming year.

Winter beans have had a difficult spring, but are now well into flowering. The first chocolate spot fungicide has been applied and the second planned.

The loss of some main stems to foot rot has meant that many beans have tillered profusely and look very thick.

Spring beans have emerged well and at last are growing away from the pea and bean weevil. Downy mildew can easily be found, and some crops have been treated with phosphite.

The winter oats now have panicles emerging and the last fungicide is being applied. We are lucky that in the North crown rust is not common, however mildew thrives!

I am convinced that oats are the most sensitive crop we grow. Even talking about weed control in the field appears to make them flush red. At least they are all recovered and green now.

South

Oliver Bennetts, Zantra (Kent)

After the downpours of March and April, May has been kind, with seed-beds finally drying up. The remaining spring cereals and potatoes are now all planted and even these late-drilled cereals are now up.

As we move into the final days of May, all T2s which were aimed at full flag leaf emergence of the wheat are now applied.

The main focus for control so far has been septoria with very little in the way of rust compared with last year.

Winter wheat ears are now starting to emerge in the earlier drilled fields. T3s will be going on in 10-14 days as flowering begins.

Oilseed rape is just finishing flowering and compared with a couple of years ago crops look strong with plenty of pods set which means that the only decision left is the timing of desiccation.  

Chocolate spot

Beans are well into flowering stage with the first tiny pods setting on the lower parts of the plant. I’m seeing some chocolate spot on the lower leaves, but with a fungicide going on over the next few days this should help stop the spread up the plant.

I’m recommending a SDHI and azole mix. Low numbers of black bean aphids are starting to move in on some plants hiding away in the tops.

At the moment no action is needed, but I will be keeping an eye on these, in case colonies start to develop.

Spring crops that were drilled in those dry two weeks in February are really moving well, with awns visible on the barley.

With the later drilled crops that are emerging looking on the whole fairly well, the moist soils and now some warmer sunny weather they will race though their growth stages.

While the rain had been a pain for potato growers, fields are now planted, and earlier fields are emerging.

A warning for farmers to take control of their potato dumps and volunteers, as blight is already being found locally in these areas.

As we move to the later stages of the season, I am starting to plan for next year, and discussions around variety choice and agronomic challenges are beginning to happen.

This year has gone so quickly – we need to be ready for what happens next!

East

Marcus Mann, Frontier (Essex)

Finally, some long overdue sunshine! T2 fungicide applications to winter wheat are now complete and despite the higher septoria pressure this season, disease control so far looks to be preserving green leaf area of the key yield forming parts of the canopy. 

That said varieties with lower resistance ratings are expressing high levels of disease, with Skyscraper (4.9) for example expressing active septoria symptoms on both leaf three and leaf two. 

These symptoms are more apparent where spray timings have been stretched and or lower fungicide rates than required for this season have been used. 

While septoria has grabbed the headlines so far, yellow rust symptoms are now starting to express on untreated varieties of Zyatt, Skyfall and Gleam.

The focus is now turning to ear wash sprays, which on paper should be simple, but in reality, has to address a number of key areas. 

This year, we will be looking to top up levels of septoria protection, ensure we have the right actives to prevent yellow rust taking hold and as temperature increase manage brown rust and not forgetting the need to protect against fusarium infection if we get rainfall at flowering. 

Many crops have already received their two SDHIs and strobilurins (quinone outside inhibitors), so azole chemistry (prothioconazole and tebuconazole) will be the go to mode of action. 

Where T2 sprays have been based around fenpicoxamide (quinone inside inhibitor) and azole chemistry, there is an opportunity to use an SDHI/strobilurin at this later timing, labels permitting.

Keep in mind that while strobilurins will add to the level of rust protection at this timing as well as the recognised physiological benefits, they offer little protection against fusarium due to resistance.

Aphid pressure is continuing to increase in cereals with the rose grain aphid, grain aphid and bird cherry oat aphid all being caught within Rothamsted insect survey traps.

Threshold within crops is 50% tillers infested before growth stage 61 and 66% from GS61 to grain filling so will need monitoring around the T3 timing to decide upon the necessity of an additional pyrethroid insecticide application.

West

Gavin Burrough, Pearce Seeds (Dorset, Hampshire and Wiltshire)

The current hot, dry weather has allowed a lot of field work to be caught up with, but now the concern is when the next “sensible” dose of rain will arrive. 

Spring barley crops are very variable, with the early February drilled crops at awns emerging and would have had a late growth regulator applied where required compared with later drilled crops which are at early tillering stage and having a broad-leaved weed herbicide applied now.

Unfortunately, some of the later drilled cereal crops have also been hit by rooks which have thinned the crop out or heavy rainstorms which have not helped for an even emergence and capped some seed-beds.

Maize drilling has been carried out at a rapid pace. A handful of fields were drilled in April, but the majority have been drilled in May.

Weed emergence has been rapid so post emergence herbicides are being planned and applied in cooler temperatures in the morning or evening to avoid placing the maize crop under stress.

Winter cereals have grown well and should have had their T2 fungicides applied. The later drilled wheats have now caught up despite being a good two to three weeks behind at T1/leaf three emergence. 

Brome and blackgrass

Blackgrass and brome are now starting to show above the crop where grassweed control has not been 100%.

These areas will be noted and where possible the plants will be hand rogued or sprayed off. In extreme cases, larger areas could be mown off for whole crop. Every attempt needs to be taken to reduce weed seed return.     

Barley yellow dwarf virus is not difficult to find in winter cereals, even where an autumn aphicide was applied. I will be planning to grow more BYDV tolerant winter barley and wheat this autumn.   

Peas are looking well with very little damage from the pea and bean weevil. Where weeds have emerged through the pre-emergence herbicide, we will be looking to see if a post emergence herbicide is required or justified.

Where considering using bentazone, always first check to see if the fields to be treated are in high-risk surface or ground water areas and avoid their use if they are and follow the guidance provided. This information is found on the bentazone manufacturers website.

Tip of the week

Where considering using bentazone in peas, always first check to see if the fields to be treated are in high-risk surface or ground water areas and avoid their use if they are and follow the bentazone stewardship guidance. 

Gavin Burrough

 

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