Crop Watch: Herbicide action needed as rain spurs late blackgrass chit

Extra residual herbicides are being applied in response to a swell in blackgrass emergence in Yorkshire crops, a switch to contact-acting herbicide has been made in some cases, says David Martindale.

Glyphosate may be the only cure for blackgrass-blighted crops in parts of Bedfordshire and Hertfordshire where Ryan Hudson is concerned about the potential for high populations of the grassweed next spring.

With soil temperatures falling and moisture levels rising, propyzamide herbicide applications are being recommended for oilseed rape crops across Kent, according to Kevin Knight.

See also: Map: View the light leaf spot risk in your area for this season

In Devon, Neil Potts says brome is germinating early and profusely in some crops and will require early treatment if it is not to become a major problem. 

David MartindaleNorth: David Martindale

Arable Alliance (Yorkshire)

The last 10 days has produced plentiful rainfall which has hampered spraying progress. All crops are generally looking good and cereals are finally emerging from the heavier patches in fields.

Those growers with nerves of steel who held off drilling until the second half of October stand the best chance of achieving good blackgrass control.

However, delayed sowing on its own is not the answer and now the planned herbicide programme needs to be applied, so let’s hope Mother Nature enables this to happen.

Wheat crops sown in mid-September are now at the two to three tiller stage, but on the heavier land, they are still at one leaf having just emerged.

These areas have been incredibly slow to appear, which has made for some tricky compromises on herbicide choice and timings.

While September and the first three weeks of October saw little blackgrass emerge, it has since appeared in abundance.

It has been a case of applying further residual herbicides or switching to products with more contact action.

Slugs have been an increasing problem in the past fortnight with cloddy seedbeds following oilseed rape the worst affected. Many second wheat crops and some winter barley has been attacked too.

Earlier sown winter barley looks exceptionally well. Mildew has become increasingly evident on susceptible varieties, but currently no fungicides have been required with some recent frosts slowing down its development.

Oilseed rape arguably looks too good in many cases with huge canopies knee high from early sown crops, aided by manure or slurry applications.

While such crops look tremendous now, they will require careful nitrogen management in the spring to prevent them from lodging with resulting yield loss.

Phoma is evident, but thankfully still at low levels, with fungicides being applied now more to target light leaf spot and mop up incidental phoma at the same time.

Soil temperatures are low enough for residual herbicides such as propyzamide to be applied, although some rain is going to be required to wash it from the leaves in dense crops.

Ryan HudsonEast: Ryan Hudson

Farmacy (Bedfordshire/Hertfordshire)

We received the first meaningful rain in months about 10 days ago with a very welcome 15mm falling as steady rain.

The early drilled wheat crops have blackgrass emerging with the wheat and due to the dry conditions, any activity from residual herbicides may well be less than expected.

Despite the dry conditions it has been possible to see herbicide effects on blackgrass with the distinctive white and purple banding around the leaf.

There are also several fields with significant blackgrass already emerged where glyphosate will be the only effective control.

Another concern is what plant populations we may have entering the spring. Due to the prolonged period of dry weather the number of seeds planted may well be too low for the time they emerge and this is likely to result in fewer tillers and potentially thinner plant stands.

This is something to be aware of in early spring if we are going to try and manage the situation, because many crops may not be able to afford to lose any tillers.

One benefit of the dry conditions has been root structure, which has been developing rapidly and to depth in order to seek moisture and nutrients.

The remaining oilseed rape has put on significant growth in many areas, although some light land and fields with low natural fertility have continued to struggle.

Phoma has only just started to show itself and with soil temperatures now falling and soil moisture slowly increasing, fungicides are due to be applied with propyzamide applications.

Dissecting plants over the past few weeks, it is encouraging that although there are cabbage stem flea beetle larvae in the petioles, there does not appear to be as many as in previous years. This may be as a result of significantly less oilseed rape in hotspot areas.

Beans and oats have been the main beneficiary of the decline in rapeseed area. Beans have been planted into some excellent seed-beds with rain arriving just in time for residual herbicides.

Kevin KnightSouth: Kevin Knight

Zantra (Kent)

With soil temperatures dropping after recent rains, propyzamide applications are now being recommended.

Local conditions must drive the timing – fit to travel, soil temperatures below 10C and falling, and no heavy rain forecast to prevent run-off should field drains begin to run.

Where Astrokerb (aminopyralid + propyzamide) is being used to target broad-leaved weeds as well, be aware that for best activity of aminopyralid it must be applied to a dry leaf of the target weed. Get your money’s worth and don’t go spraying too early when everything is sodden with dew.

With weather looking to be catchy for a while, I’m adding the autumn fungicide and some trace elements to the tank to ensure that all three get on.

Given levels of light leaf spot over recent years I stress the importance of ensuring your autumn fungicide controls this disease, as well as phoma.

Most of my oilseed rape is behind where I’d like it to be so I’m avoiding any growth regulatory effects and opting for an SDHI (penthiopyrad) + strobilurin (picoxystrobin) co-formulation.

There’s good evidence that nitrogen uptake and utilisation is boosted by the picoxystrobin, and tap and feeder root development gets a boost from penthiopyrad.

This should help the later germinating plants through the winter. The disease control provided is excellent, plus the enhanced plant development makes it a better bet than the market standard (prothioconazole).

In cereals, grassweed germination has been painfully slow. Where they emerged in dry conditions few showed any sign of taking up residual herbicides applied pre-emergence.

However, the rain over the past two weeks has made a significant difference, with small meadowgrass taking a hit from the activated residuals, and ryegrass and bromes significantly checked.

If weather prevents an autumn graminicide hereafter, I’m hopeful that this will hold the grassweeds back until we get on in the spring.

Where blackgrass is an issue, top-up herbicides have been applied to maintain levels of flufenacet, add prosulfocarb to the stack, or bring contact activity from a well-timed Atlantis (iodosulfuron + mesosulfuron) spray.

Neil PottsWest: Neil Potts

Matford Arable (Devon)

The weather has continued to be predominantly dry, allowing for continued planting of cereals after late harvested crops such as maize, fodder beet and potatoes. These crops, although going in late, are being planted into near perfect seed-beds.

Barley yellow dwarf virus, an ever present concern in the south west, still needs some attention. Early drilled crops with Deter (clothianidin)-treated seed are in the process of receiving an aphicide to top up control.

Later drilled crops treated with Deter should be in the clear, as far as follow-up treatment is concerned. This is because the temperature is now such that further aphid migration is unlikely.

This situation will still need to be monitored to ensure we do not end up being caught out.

The one situation where these later-drilled, Deter-treated crops will require a follow-up treatment is where there are significant numbers of volunteers growing from a previous cereal crop. 

These volunteers will be unprotected with no seed treatment and, therefore, likely to be holding aphids which will cross-infect the crop when the Deter runs out of steam. 

Cereal crops are now starting to show signs of slug damage in places, requiring treatment. The problem is worse in the direct-drilled and non-inversion tillage situations.

Straw management post-combining appears to be having a major impact on slug populations this autumn.

The worst slug attacks are happening in fields where there was a delay between combining and baling, and unsurprisingly in the fields where significant straw residues were left behind. 

Brome appears to be germinating early and profusely in some crops and will require early treatment if it is not to cause a major problem to the crop.

If populations are large this early in the season do not be tempted to leave control until the spring. It will be too late.

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