How to deal with five potential cropping challenges this August

Crop Progress

Harvest, at least until mid-July, was very catchy. Some had started winter barley, and oilseed rape had been desiccated; early potatoes were also being lifted.

The heavy rain storms and strong winds had also caused some patches of cereals and oilseed rape to lodge, which will hit yields, quality and slow down combining. This is frustrating considering how challenging this season has been to look after crops.

Tom’s agronomy tips for August

1)      Moisture will help early establishment of oilseed rape

Over the past few years, there’s been a bit of a gamble for growers around oilseed rape drilling dates. You can sit in the camp where you establish the crop in early August and hope to get a large canopy that will tolerate adult cabbage stem flea beetle feeding and pigeon grazing.

The risk of earlier drilling is the crop is more exposed to adult cabbage stem flea beetle egg laying and as a consequence a higher larval burden a few months down the line for the plant to cope with. Other issues with earlier drilling include cabbage root fly and possibly higher lodging and light leaf spot risks.

If you drill later, you hope to avoid the worst of that feeding damage and lower larval burdens. In theory, there should be more moisture in seedbeds for an early September drilling, but that’s not a given. It does also help with having a period where you can flush of volunteers or grassweeds, but with reduced daylight hours you may not get the same size of canopy going into winter unless you have favourable autumn weather.

In either situation, moisture is critical for establishment. With current weather patterns at time of writing it looks like early August establishment should be possible. Minimising soil movement to retain that moisture will be important, and there can be a benefit from leaving longer straw for soil moisture retention too. Longer straw potentially can also help disguise the emerging crop from adult flea beetles, while applying manure or digestate is also said to have the same effect. Extra nutrition from digestate or by applying DAP down the spout also gives the crop the best possible start.

For early drilling, look for a slower developing variety. If it gets too leggy during autumn it can require excessive growth regulation, or get too forward and risk apical bud damage from frosts. Sheep are an alternative growth regulator.

There are suitable high vigour varieties for either window, or for other agronomic issues, such as clubroot pressure, Clearfield herbicide tolerance, or turnip yellow virus resistance within the Dekalb range, and they are all covered against failure under the Dekalb Establishment Scheme guarantee. 

2)      Manage grassweeds in stubbles

Grassweed control this season has been a bit mixed with high levels of black-grass and Italian rye-grass in some fields, along with some wild oats and various brome species. Managing those weeds will be a key part of your stubble management and cultivation decisions ahead of the following crop. With a wet spring and more rain latterly, there is even more of an emphasis to address field drainage, which is the first step in improving soils and creating an environment where the crop thrives and can compete more with grassweeds. 

Where you’ve had a really high weed infestation, then spring cropping has to be considered, and / or ploughing depending on when that tool was last used., Although as we’ve seen this year, later planted, thinner spring crops can also carry high populations of grassweeds because they can’t tiller sufficiently to compete.

Otherwise, if possible, I would leave black-grass, wild oats and Italian ryegrass seeds on the surface to allow ultraviolet light degradation and any predation by birds or mammals initially. When there is sufficient soil moisture to encourage germination, a light stubble rake or shallow disc cultivation to incorporate and stimulate a chit is ideal, before spraying off with a minimum of 720g/ha Roundup (glyphosate).

With attention to reducing the risk of glyphosate resistance, aim to limit Roundup stubble/stale seedbed applications stubbles to a maximum of two sprays and if possible, use cultivations between applications to mechanically destroy any surviving weeds.

With sterile and great brome try and incorporate seeds into the soil surface with shallow cultivation as soon as possible to get a chit, while the Bromus species, rye, meadow and soft brome, should be left on the surface for around a month to mature, before shallowly cultivating to encourage germination. The plough remains an effective tool to bury brome seeds after high infestations, but consider when you last ploughed and what weed seeds you may return to the soil surface.

The other reason to maintain soil moisture is that will help with the efficacy of residual herbicides when you do apply one post-drilling.

3)      SFI / CS makes cover crops increasingly attractive

Cover crops have an excellent place in the rotation introducing species to the soil with different rooting systems and enhancing the soil microbiome. They will also mop up any excess soil nutrients, protect against soil erosion and improve soil structure. With funding available through the Sustainable Faring Incentive and Countryside Stewardship schemes they have become increasingly attractive. Be selective with species inclusion with consideration of any pest or disease bridge, to minimise any unwanted consequences in the following cash crop.

Like oilseed rape, the small seeded cover crop species need enough soil moisture to establish as they run out of reserves in the seed quite quickly, and are best planted in August to build sufficient biomass, above and below ground. Do be mindful of previous herbicide applications – any legacy residues may affect the establishment of some species, particularly brassicas.

4)      Blight pressure increasing

Weather in the East Midlands in July did trigger Hutton criteria for blight infection risk, and there has also been an increased risk of Alternaria in susceptible varieties and stressed crops.   In August attention turns from not just foliar blight but to also protecting against tuber blight infections as zoospores can be washed down into the ridges to potentially infect tubers.

With options for products with activity against both foliar and tuber blight, limited to Infinito (fluopicolide + propamocarb) and quinone inside inhibitors (QiI) such as cyazofamid and amisulbrom, it is important to plan programmes carefully, as for resistance management reasons you’re limited to four applications of Infinito in a season and to not applying two QiIs consecutively.

Integrating Infinito into a late blight programme is also good resistance and risk management strategy, especially with the detection of the Phytophthora infestans strains EU_A1_43 in mainland Europe, to which resistance to CAA fungicides has been identified.

5)      Keep an eye on Cercospora alerts

The risk of beet yellows virus transmission should have passed in sugar beet crops, but August is the key month for Cercospora and other sugar beet diseases. 

With later sowing dates, keeping the crop green for as long as possible to harvest as much sunlight will be key to fulfilling yield potential. First disease control sprays will likely have gone in in late July and intervals are best kept to around three weeks.

Keep an eye on BBRO’s Cercospora alert system for conditions that might be suitable for that disease. If you need a third spray in September, Caligula (fluopyram + prothioconazole) is an option.