Wheat growers need to consider alternative disease control methods to cope with drought-stressed crops in the spring – such as inter-cropping, variety blends and grazing in the early part of the year.

A run of dry springs has seen poor uptake of fungicides by stressed wheat crops, prompting experts to look at how to make crops more resilient in dry conditions.

See also: Benefits of septoria tests in optimising T2 fungicide rates

Crops have also been stressed by big fluctuations in temperatures, typically with warm, sunny days followed by cold nights in the spring.

Aoife O’Driscoll, crop protection and agronomy specialist at crop consultant Niab, says growers need to look at how to manage wheat crops under these new conditions, in a season where yellow rust levels have been high while septoria infections have been more modest.

“Growers need to look at incorporating other methods along with variety choice and fungicides to manage disease in drought-stressed crops,” she says.

High stress

A good indicator of high stress in wheat crops this season is the increased incidence of powdery mildew, a disease that thrives in fluctuating temperatures. The disease is present on many lower wheat leaves, but is unlikely to cause major yield losses.

Dr O’Driscoll suggests farmers look at inter-row cropping such as growing wheat with beans, with the pulse crop helping to shade wheat in dry conditions, preserve soil moisture, fix nitrogen from the atmosphere and help suppress weeds.

Some growers have tried oats with beans, and she suggests wheat and beans together can reduce disease levels, although more work needs to be done on the best depth of drilling and whether crops are drilled or broadcast across the ground.

Variety blends

A second method to reduce disease pressure is by using variety blends, and four-way mixes have been tried, mirroring practices in France and Denmark, which greatly improves diversity compared with some farms that only grow one variety of wheat.

A milling Skyfall-Crusoe-Zyatt-Illustrious mix has looked good in trials, although the latter variety is a little taller than the rest, while a feed wheat Extase-Theodore-Graham-Saki mix has also impressed.

“These blends have shown a good level of disease resistance and given a good diversity in the parentage of the varieties,” Dr O’Driscoll adds.

Individual varieties that have shown a good performance under stress include the older wheat varieties Crusoe, Costello and Santiago and also the new variety Dawsum.

The third method is grazing wheat crops in the early spring with sheep to keep crops in check and reduce inoculum. This could lead to growers saving on an early T0 fungicide or the early use of plant growth regulators, which can stress crops.

High yellow rust pressure  

The season has seen high pressure from yellow rust and low to moderate pressure from septoria in the dry conditions. The good news is that there has been no major shifts in disease sensitivity to fungicides.

“Yellow rust has been particularly virulent and aggressive, especially in varieties such as Zyatt, emphasising that good resistance to the disease is very important,” she says.

Zyatt is particularly susceptible to yellow rust, with a score of 4 on the AHDB Recommended List, while Skyfall scores even lower at 3 on a 1-9 scale, where 1 is susceptible and 9 shows good resistance.

For yellow rust, the group is looking forward into 2023 to assess rust disease control if the very effective and relatively inexpensive azole tebuconazole is banned. The alternatives would be strobilurins, which can only be used once in a season, or the more expensive SDHI Solatenol (benzovindiflupyr) as in Elatus.

Septoria pressure has been low to moderate this season, with the disease only cycling very slowly due to the dry weather, resulting in septoria leaf blotches being seen, but often without black pycnidia fruiting bodies.

Aoife O’Driscoll was speaking at the Cereals 2022 event in Cambridgeshire.