Six insights for crop agronomy in June and July in the south

Crop Progress

Virtually all flag leaf sprays in wheat were applied by the middle of May as crops, especially forward varieties like Extase and Graham raced through growth stages.

We’ve had fairly regular showers in the south west which will only help with yield potential, which is looking good.

Some varieties are starting to break down with yellow rust, but decent robust rates of fungicides had been holding it well and it was possible to get good protectant chemistry on the top two leaves on all varieties.

Disease pressure was such that most growers were using the newer, more curative chemistry, although some of the later drilled crops were fine with a second dose of Ascra (bixafen + fluopyram + prothioconazole).

Matt’s agronomy tips for June and July

1. Decide on T3 fungicide choice in wheat

Ear spray product choice in wheat will potentially depend on what programme has already been applied.

Where no or only one SDHI-containing product has been used there will be an option to use a second SDHI as an ear spray. That would open the opportunity to use Aviator (bixafen + prothioconazole) at 1.0 L/ha which would provide enough prothioconazole for good Fusarium control – you need at least 150 g/ha – while the bixafen will extend Septoria protection, which can be important if there is a long gap between spraying and harvest.

Timing for Fusarium should be early to mid-flowering – usually around 6 June in the south west, but maybe earlier this season.

Where two SDHI fungicides have been used, there are a number of prothioconazole containing products to choose from. In some varieties, such as Insitor, which is riddled with yellow rust in some areas, and Crusoe with its susceptibility for brown rust, then the addition of tebuconazole might be useful.

2. Plan potato blight programmes

Potato crops are all up in the row, and blight programmes will be starting soon. With warmer and humid weather, it’s potentially good conditions for blight development, but check the various forecast tools and Hutton Criteria for local risk.

Infinito (propamocarb + fluopicolide) provides excellent foliar and tuber blight control. It can be used a maximum of four times in the programme, so it makes sense to plan its use through the season from canopy complete stage through to haulm destruction.

On varieties susceptible to early blight (Alternaria), Caligula (fluopyram + prothioconazole) provides the best control, according to Euroblight trials results.

3. Desiccate oilseed rape to help with harvest efficiency

Some oilseed rape crops look to have huge potential. If weather is good, it can be left to die back naturally, but desiccation with Roundup (glyphosate) does help with combining speed and efficiency, especially if there are weeds at the bottom of the crop or uneven ripening.

Many varieties now have pod shatter resistance, but where not glyphosate can be combined with a pod sticker application.

If you do decide to spray, timing is crucial to avoid losing yield or quality, which obviously you want to avoid with the price of oilseed rape this season.

You’re looking for the seed to be below 30% moisture content. Once the crop starts to senesce, usually in around mid-June, take 20 pods from the middle part of the canopy across the field, and if two-thirds of the seed has turned from green to brown in at least 15 of the pods, it is ready to spray.

Around 1080 g/ha of glyphosate should be sufficient if you’re targeting desiccation and annual weed control, or 1440 g/ha if there are perennial weeds. Keep forward speeds to 10-12 km/h to maintain boom stability and help the spray penetrate the canopy. There’s a 14 day statutory harvest interval after application, and don’t use on seed crops.

4. If necessary, also use harvest management in cereals

While I’d generally try to avoid using glyphosate applications in cereals, it can be helpful where there has a been a flush of annual meadowgrasss or other late weeds, particularly in wetter climes keeping the bottom of crops damp and slowing harvest. It does ensure when the crop is fit, you can get on with combining efficiently.

Again, timing is critical, with too early applications limiting yield. Use the thumbnail test in cereals – if a selection of grains from across the field just hold a thumbnail press, you’re about 30% moisture, although it’s always worth checking with a moisture meter.

For desiccation only, apply 540 g/ha of glyphosate, dosing up to 1440 g/ha depending on weed spectrum, with the higher rates for perennial grasses and thistles.

In cereals, the statutory harvest interval is seven days after application, and again don’t use on crops destined for seed. Always check with end users, for example, maltsters, as well.

5. Spray off heavily infested grassweeds in crops

Early June is about the latest time for spraying off areas of fields with high infestations of grassweeds, including headlands where bromes are invading.

Heading is a better time for this than stem extension, but once you see the head you need to get on with it before the seed becomes viable. Some grass species set seed within 3-7 days, particularly bromes.

Brome is more of a problem in the south west, especially with direct drilling becoming more popular. But it’s not an easy decision with the current price of wheat. Consider what seed return you’re going to get and calculate whether the future problems and costs of herbicides are going to outweigh the price of wheat from that patch.

If you’re spraying off a patch, using FieldView’s satellite imagery to find and map target areas to create an application map that can be uploaded into the sprayer makes the job easier, particularly if you have section or individual nozzle control. One other advantage doing that is it will automatically give you an area to spray and the amount of glyphosate required.

It's worth monitoring the patch after application for survivors to see whether any further cultural controls are required.

6. Take out weeds in maize

Any later drilled maize just coming up in early June may still need a herbicide to take out weeds competitive with the crop. Maister (foramsulfuron + iodosulfuron + isoxadifen) is a good option with a particular strength on grassweeds. You can mix with 0.5 L/ha of Calisto (mesotrione) to broaden out the broadleaf weed spectrum, if required.