Crop Watch: Frosts welcomed for disease control

A couple of frosts over the last weeks will not only curtail rising levels of mildew and net blotch seen in winter barley crops, says Patrick Stephenson, but have also brought soil temperatures down to those suitable for propyzamide applications for blackgrass.

In the South, Kevin Knight says soil temperatures are still a couple of degrees off ideal, but soil moisture deficits of as much as 130mm are of bigger concern.

Marcus Mann reports yellow rust and powdery mildew in susceptible cereal crop varieties, and although the frosts should eradicate both, he recommends treating barley for mildew if mild weather returns before spring.

While in the West, all field work has stopped as wet ground conditions mean quad bikes are struggling to spread slug pellets. Giles Simpson says this reiterates the importance of an early maize harvest.

See also: How to give maize the best possible start

Kevin Knight

Kevin Knight

South: Kevin Knight

Zantra (Kent)

“We won’t need an insecticide on the wheat now there’s been a couple of frosts will we?” is a question which has frequently come up over the past 10 days.

Barley yellow dwarf virus (BYDV) vector aphids will fly in daytime temperatures above 10C, maintain high levels of activity and reproduction above 4C, and they’ll still be walking between plants above 1C.

To achieve a significant kill of the population, particularly the bird cherry-oat aphid, temperatures below -3.5C for several concurrent nights are required.

If you have single purpose or “from the shed” seed in the ground, or your Deter (clothianidin)-treated wheat has been out of the ground for approaching five weeks, you really do need an aphicide.

Rothamsted’s suction trap network is showing around 10% of those tested are BYDV carriers.

Given environment secretary Michael Gove’s commitment to do away with neonics altogether, we’d best get used to several passes of broad spectrum insecticides when the bees are still flying.

Dry at depth

The sniff of rain we’ve had over the South-East corner has brought soil temperatures at 30cm down from as high as 15C to 10C and falling, though it’s done little to address soil moisture deficits of as much as 130mm.  

Propyzamide (Kerb) applications work best at ideally 8C and falling, though there is an argument that the aminopyralid component of AstroKerb works better in slightly warmer conditions.

Given how effective propyzamide is for weed control on lettuce crops in summer, I’m less concerned over the temperature and more about the lack of moisture.

It doesn’t adhere well to dust-dry soils and can wash down below the grassweed rooting zone if heavy rain arrives post application.

Rain last weekend dampened the surface, though we’re still worryingly dry at depth, so my recommendations are now on farm to hopefully be applied in short order.

There’s a lot of phoma around now, with many oilseed rape crops at threshold, and the odd hint of light leaf spot in very thick and forward crops.

Given that this disease is now almost a racing certainty, even in the South, most winters I will be including a fungicide with activity against both.

For what looks like the last time (another revocation) it will be a penthiopyrad (SDHI) + picoxystrobin (strobilurin) co-formulation (Cypher) as this has proved its worth over the past three seasons in terms of disease control, rooting benefits and uptake/utilisation of nitrogen in backward crops.

Patrick Stephenson

North: Patrick Stephenson

AICC (Yorkshire)

One grower described this drilling season to me as “we had October’s weather in September, and September’s weather in October”.

October was on the whole dry and we made more progress drilling than we ever thought possible. Not only that, but considering the conditions, we had minimal slug damage.

This confirmed to me that the best way of limiting slug damage is to ensure that germination is rapid. Unfortunately, easily written but not always that easy to achieve in practice.

I have heard reports that yellow rust can be found in some wheats, but in this era of fake news I will await my own observations.

Every week my clients and I agree what will be the last field drilled, and suddenly the wind blows or the maize and fodder beet are harvested and another field is popped in.

The question most commonly asked is: How much wheat yield do you lose by drilling late?

There are multiple caveats to this conundrum, but a good rule of thumb is just below 1% a day after mid-October, and just over 1% after the start of November.

If conditions remain good, then winter wheat can still achieve over 7t/ha, and priced at £150/t, this looks very competitive compared to the vagaries of spring cropping.

These late-drilled wheats, with hopefully a greatly reduced blackgrass burden, will receive a pre-emergence herbicide. I shy away from complex stacks at this time of year as I believe the potential crop check/damage outweighs the lift in performance.

Early phoma infection

Phoma has certainly been the star disease of the early season in oilseed rape. I cannot remember the last time we had such an early infection.

Imagine my joy when the latest soil temperature figures showed that it was now suitable for propyzamide applications. Sad though it is, spray applications at this time of year are even more strongly influenced by weather and travelling conditions.

This often means sprays are combined to limit the number of passes, hence fungicides and herbicides are put together. This is my excuse for leaving the Kerb recommendations until the end of October, where I believe you get the best compromise.

Winter barley crops have good levels of mildew and some net blotch. I was starting to get a bit nervous over the rising levels but fortunately a couple of hard frosts of -4C, with more forecast, will curtail its development.

Winter beans are nearly all drilled now with pre-emergence herbicides applied, so just about completing the drilling – and then maybe not.

Marcus-Mann

Marcus Mann

East: Marcus Mann

Frontier (Essex)

Soil temperatures are beginning to decline. However, soil moisture levels in the East remain lower than usual for this time of the year.

Most wheat crops are now drilled and the good travelling conditions have enabled well timed pre-emergence sprays.

However, the drier conditions have affected some residual persistency and earlier drilled crops have received a follow-up before the blackgrass becomes any bigger.

Recent colder weather and the odd frost certainly appears to be aiding efficacy, even if there is a moisture deficit in some areas.

Where autumn-germinating brome is being found in winter wheat, remember the earlier applications of pyroxsulam are more effective. Ensure good coverage as the small hairs on the leaf can affect the uptake of the product.

National monitoring for bird cherry-oat aphids suggests numbers are declining in response to cooler weather. However, they can still be found within untreated cereals. Crops drilled during early October treated with Redigo Deter will begin to need a follow-up insecticide.

This also is a good opportunity to treat the areas which have historically shown manganese deficiency.

Providing adequate control

Yellow rust and powdery mildew are being found in susceptible varieties of cereal crops. Frosts will generally eradicate both, but if mild weather returns and higher levels of powdery mildew continues in barley this may require treating ahead of the spring.

Winter oilseed rape crops are beginning to slow down in their growth with cooling temperatures. Disease pressure has increased with new phoma infections and early signs of light leaf spot being found.

Symptoms of light leaf spot may not always be evident in the autumn, but spring-only treatments often do not provide adequate control and programmes must begin in the autumn to target the disease early.

Crops not already treated will certainly now require it and, with soil temperatures beginning to near the 10C mark, this may enable a tank mix with propyzamide.

Be mindful of both the soil temperature and moisture levels as the persistency of propyzamide is critical in ensuring good longevity in the spring as the canopy begins to close.

For larger crops it may be beneficial to split the application and delay the propyzamide to allow the canopy to open up, giving better coverage. This is particularly important when applying AstroKerb (propyzmide with aminopyralid) for added broad-leaved weed control.

Giles-Simpson

Giles Simpson

West: Giles Simpson

Pearce Seeds (Somerset)

I can honestly say that all field work has now stopped as ground conditions no longer allow anything to travel. Even the quad bikes spreading slug pellets have struggled in a place or two.

There is a small area of cereals that have not been sown behind maize. The majority of this has been cultivated, which is good in terms of reducing soil erosion or leaching but will make drilling impossible now until probably the spring.

Some later-drilled cereals behind maize have struggled in the waterlogged conditions of the past couple of weeks and there will certainly be bare areas in the spring due to seed rotting in the ground.

This shows how important variety choice is as well as drilling date to make sure maize is ready to harvest as early as possible, as the wheat drilled earlier looks well.

I have had some hybrid barley drilled on some lighter better soil behind the maize on the 25 October; it was up within a week and looks good. It will be interesting to see how it performs.

The early-drilled cereals generally look very well, although slugs have been a problem where the crop has followed oilseed rape or grass. Second wheats have also come under attack.

Compaction concerns

All crops that were sprayed pre-emergence have had a follow-up of aphicide, manganese and herbicide, if required. I have some crops drilled behind maize where the chemical is still in the spray store and I can’t see it being applied now.

Oilseed rape crops vary immensely from ankle high to knee high, sometimes in the same field. I think compaction is a main concern as you can see exactly where trailers travelled across the fields.

I had one customer say he knew exactly where he had stacked a small heap of straw for a few days because the tractor almost stalled when he was ploughing that area of the field. This compaction will need sorting next summer if conditions allow.

If you are a cider drinker you will be pleased to hear that the apple harvest is almost complete. It has been a good year due to the rain in July and August, so even though the combines struggled, the cider trees didn’t. So all you need to do is have a pint or two and all this year’s struggle will be a distant memory.