Help with weed and disease control decisions for Midlands growers this October

Crop Progress

Some regions of south Lincolnshire had more than 120mm of rain in a week in August, which caused a lot of issues, including as we’re seeing now, some quite serious problems with bacterial rot in potatoes. Some growers are having to plough in fields of potatoes because of it.

The rain in the region did help with oilseed rape planting in August with a decent amount planted. It’s still hit and miss, but generally the crops that went in earlier have got away quicker and looking well. Cabbage stem flea beetle has become more of an issue in September, particularly on later drilled crops with smaller plants, and there’s also been problem with slugs and turnip sawfly too, so it has not been all positive. But generally it’s pretty good compared with previous years and some other areas this year.

Cereal drilling is full steam ahead as we reach the end of September, and growers will only be stopped by rain. Winter barley drilling will be just about complete by the end of September, with winter wheat continuing into October. Hopefully we get the weather windows to get drilled up by the end of October.

Sugar beet and potato harvest have started with yields lower than average because of the summer drought. We have had positive feedback about the Conviso Smart herbicide tolerant system of growing sugar beet, however, with expectation of an increased area next season.

Adam’s agronomy tips for October

 1. Concentrate on weed control efficacy in stubbles

At the beginning of September there seemed to be a lot of volunteers coming through in stubbles but fewer grassweeds, despite low dormancy in black-grass. That seems to have changed now with more rain so it is a good opportunity to keep on top of volunteers and grassweeds and get the cleanest start possible for the following cereal crop.

For best efficacy use the correct dose of glyphosate for the target weed and size. Typically for grassweeds of 2-3 leaves this is a minimum of 540g a.i./ha, rising to 720g a.i./ha for tillering grassweeds.

Concentrate on best practice around applications, which will drive down the chance of resistance development as well as increasing efficacy. Don’t go too fast – 10-12 km/h is fine – which will help with boom stability at 50cm above the target and choose the correct nozzles to hit a small target.

2. Consider aclonifen for winter barley grassweed control

While most winter barley will have been drilled and hopefully treated pre-emergence in September, no doubt there will still be some being drilled into October.  

This season there is the option of using Proclus (aclonifen) in winter barley as a pre-emergence only treatment for controlling difficult grassweeds. It should be used in conjunction with 0.6 L/ha of Liberator (flufenacet + diflufenican) at the lower dose of 1.0 L/ha, and ideally applied within 48 hours of drilling.

It brings another active and mode of action into winter barley, which should be useful in higher pressure grassweed situations. Other options that can use in winter wheat such as cinmethylin and mesosulfuron are not available in barley.

For this year we are not recommending adding any additional herbicides to the tank mix but will review this year’s trials to see whether that can be safely done in the future.

Be careful if you’re considering using a generic flufenacet + diflufenican product rather than Liberator. They may look like-for-like but our experience and trials have highlighted there can be big differences in performance, especially on difficult weeds such as black-grass and Italian ryegrass. For example, in our weed screen a generic formulation only gave 50% control of Italian ryegrass from Kent compared with 80% with Liberator. Don’t underestimate the advantage of investment into well-formulated products.

3. Look for consistency in pre-em performance in wheat

In wheat the Liberator + Proclus has performed consistently well since its launch a couple of seasons ago. In trials, we’ve been impressed by its consistency, especially against black-grass, where it can even outperform the new products in the market.

The rate of Proclus for wheat is 1.4 L/ha, while there are options such as pendimethalin, prosulfocarb and liquid tri-allate available to bolster grassweed control if required. Prosulfocarb (3.0 L/ha) is a particularly useful one for Italian ryegrass and black-grass, while tri-allate whether liquid or granules will also be popular.

The same caveats around best practice remain – create the best seedbed possible, cover seed with at least 32mm of soil, and ideally get on within 48 hours of drilling.

There will also be situations in October that require a residual herbicide top up following the pre-emergence, especially in September drilled crops. Our metribuzin-based products Octavian Met and Alternator Met (flufenacet + diflufenican + metribuzin) are a good fit for this peri- or early post-emergence timing in grassweed situations.

The 0.5 L/ha dose that can be used from 1 October to the end of November delivers 120g/ha of flufenacet, 30-45g/ha diflufenican and 35g/ha of metribuzin. That’s a small amount of metribuzin compared with what it is applied in potatoes, but adds a little bit of contact as well as residual activity and helps out on grassweeds.

These products are also good options for annual meadowgrass and broadleaf weeds, especially groundsel and cranesbill, which some programmes are missing.

4. Monitor for oilseed rape diseases

Our SpotCheck programme will be running again this season, which enables growers to send off leaf samples from oilseed rape crops to be analysed by ADAS for diseases, such as Phoma and light leaf spot. If you’re interested in a sample pack please get in touch with me or one of my colleagues.

To break the life cycle of light leaf spot in the autumn, as well as giving good control of Phoma, there is the option of using a prothioconazole-based product such as Proline (prothioconazole), Prosaro (prothioconazole + tebuconazole) or Aviator (bixafen + prothioconazole).

Aviator (0.5-0.75 L/ha) is probably the strongest option to control both of those diseases, with the additional benefit of physiological benefits on rooting as shown by research with University of Nottingham. Glasshouse experiments showed greater root mass from plants treated with Aviator, which could be important in helping with nutrient and water uptake for plants affected by slugs or cabbage stem flea beetle, for example.