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Crop Advice & Expertise

East: Light leaf spot and grassweed control are priorities

The mild conditions have done little to check diseases and pests in the East of England. Sam Harvey gives some advice on controlling these problems

This month’s key messages:

  • Prioritise a light leaf spot fungicide in susceptible OSR crops before stem extention
  • Take the opportunity to apply outstanding post emergence grassweed herbicide recommendations in optimal spraying conditions
  • The objective of any grassweed control strategy is minimising potential seed return at harvest. Don’t cut corners
  • Double check crops aren’t outstanding an aphicide for BYDV control
  • Novel new liquid nematicide available for potato growers

Crop Progress

The colder spell in late January was certainly welcome, but unfortunately is forecast to subside. The mild back end led to advanced canopies of oilseed rape, but similarly encouraged the development of light leaf spot. In the main, most residual herbicide stacks have performed well in later drillings of cereals, where cultural measures were fully deployed, but the mild autumn has favoured grassweed development as residual herbicide activity subsides.

Sam’s agronomy tips for February

1. Protect OSR crops against light leaf spot

Light leaf spot  should be the priority in oilseed rape crops and remember that just because you can’t see the disease, it doesn’t mean it isn’t there. Conditions before the cold spell were ideal for development, typically taking 30 days for initial infection to show visible lesions.

In terms of strategy, it is important to understand risk in individual circumstances based on the variety’s resistance score and what fungicides have already been applied for light leaf spot pre-Christmas. Around half the leaf samples submitted to the Bayer/ADAS SpotCheck initiative in January have tested positive for light leaf spot, which confirms that conditions were ideal for development pre-Christmas.

It is particularly important to make sure new growth is protected before buds extend upwards. If inoculum isn’t managed at this time before stem extension, it will make it very difficult to keep the disease off flowing buds for the remainder of the season. My recommendation if susceptible crops haven’t received a light leaf spot fungicide until now is an application of Proline (prothioconazole) at 0.46L/ha is well overdue. Where a light leaf spot active fungicide has already been applied or a variety has a higher resistance rating, remain vigilant and treat if symptoms become visible.

2. Make outstanding grassweed herbicide applications

Prior to the cold spell we had continued active growth of grassweeds and ideal ground conditions and some growers may have taken the opportunity to apply post-emergence herbicides. Milder temperatures are forecast again, so if conditions for travel allow, take the opportunity to apply any outstanding recommendations. There is one caveat, which is to ensure that you are applying to a dry leaf and there is a couple of hours drying time post application for maximum efficacy. It’s imperative not to compromise potential control by sub-optimal application practice.

For product choice, there are a number of different options. Hamlet (diflufenican + iodosulfuron + mesosulfuron) can be applied at 1.5L/ha plus Biopower up until the end of February at the latest, but I would caution against application once we start to see any meaningful spring growth. Other options include Atlantis OD at 1.2L/ha plus Biopower or Monolith at 0.33kg/ha plus Biopower. Match product choice to spectrum of grassweeds and broad-leaved weeds.

When making grassweed post emergence decisions, remember, the objective of the control strategy is ultimately minimising potential seed return at harvest to enable a continued sustainable rotation. So manage expectation on a field by field basis and have your weed seedbank in mind at all times. In some cases it might mean sacrificing patches of crop completely. Remember pernicious grassweeds will ambush inputs such as nitrogen ahead of the crop so make decisions sooner than later.

3. Protect at-risk cereals from BYDV threat

Due to the mild autumn, it is worth considering if any follow up aphicides remain outstanding to protect cereal crops from barley yellow dwarf virus. Despite the recent cold weather, temperatures were not low or sustained enough to take bird cherry or grain aphid out, so if they were present before Christmas they will still be there now. Aphicide decisions should be based upon reaching a T-Sum threshold.

4. New nematode control tool available

Ahead of the planting season decisions around potato cyst nematode (PCN) and free living nematode (FLN) control strategies are well under way and our new nematicide Velum Prime adds an entirely new dimension to the pest control armoury. Based on SDHI fluopyram, it provides a new mode of action with high intrinsic activity and favourable soil mobility. It’s a compelling proposition for those potato growers used to applying 30-55kg/ha of granular nematicides as Velum Prime is applied in-furrow at a dose rate of just 0.625L/ha.

Velum Prime is recommended as a base treatment for low to moderate PCN infestations and used in conjunction, or in sequence with, a half rate granular products in moderate to high PCN infestations.

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