Thursday, 24 May 2018
AHDB has issued late-spring guidance for the management of fast-moving cereal crops.
Tim Isaac, AHDB Head of Arable KE, said: “Both the autumn and spring cropping seasons got off to a challenging start and crops are now racing through their growth stages.
“But, with extremes of hot and cold, crop growth has neither been smooth nor predictable this season and this makes field work hard to plan.
“The AHDB website contains a wealth of information but it can be overlooked during the busy late-spring period. So we’re reminding people to take advantage of our resources to make the most out of the 2018 crop.”
Challenging early season weather means many people are playing catch-up with their disease control programmes. To determine the most appropriate time for spraying, people should view the cereal growth stage information published at cereals.ahdb.org.uk/wheatgg
Paul Gosling, AHDB Crop Protection Scientist, said: “In wheat crops, even if the timing interval between T1 and T2 is short, it’s vital to make sure the timing of the T2 is correct. The flag leaf should be fully emerged (GS39). Any delay in treatment increases the chance of infection.
“With hints of declining SDHI efficacy against septoria now evident in some places, it’s also important to include a multisite at T2 to manage resistance and improve control.
“In UK barley crops, ramularia isolates with strong resistance to SDHIs are now also common and SDHIs can no longer be relied upon for control, so it’s important to include chlorothalonil at T2.”
Earlier this year, AHDB published information on ramularia and its control on a dedicated web page – cereals.ahdb.org.uk/ramularia – to help people manage the disease this season.
In June, attention turns to the T3 wheat ‘ear wash’ spray to target fusarium head blight and ‘top up’ foliar disease control on the flag leaf
The decision to spray at T3 depends on many factors, including the weather and the target market, but those spraying will likely turn to azoles. AHDB fungicide performance work shows several are effective (epoxiconaozle, metconazole, prothioconazole and tebuconazole) but T3 sprays can select for azole-resistant septoria strains, even when septoria is not the primary target. In order to protect the azole, a multisite should also be included at T3.
“At T3, take particular care to note any timing and total dose restrictions on product labels,” added Paul.
The latest fusarium mycotoxin risk assessment can be downloaded from cereals.ahdb.org.uk/mycotoxins
Information on resistance management, including the 2018 Fungicide Resistance Action Group guidelines, is published on cereals.ahdb.org.uk/fungicidefutures
Fungicide performance information can be accessed via cereals.ahdb.org.uk/fungicide
With black-grass seed heads starting to show above winter wheat crops, severe patches can be sprayed off with glyphosate. AHDB guidance shows spraying or cutting the crop around the first week of June can prevent viable seeds being returned to the seedbank.
At this stage in the season, it is important to start evaluating the success of weed control strategies. The following resources can help with this:
Managing weeds in arable rotations cereals.ahdb.org.uk/war
Encyclopaedia of arable weeds: cereals.ahdb.org.uk/eaw
Black-grass management web page: cereals.ahdb.org.uk/blackgrass
The balance of nitrogen is usually applied to cereals in May. The AHDB Nutrient Management Guide (RB209) should be followed to ensure nitrogen applications are made in response to yield potential. Where wheat crops are judged to have high yield potential or have small, pale canopies, an early summer nitrogen application – around G39 (all flag leaf visible) – can be beneficial. Late-summer applications of urea can also be considered, especially when applied to potential breadmaking wheat with a good yield potential.
Nutrient Management Guide (RB209): ahdb.org.uk/rb209
At the end of April, EU Member States endorsed proposals to extend the ban of neonicotinoid insecticide seed treatments to include wheat and barley crops. The decision will put more pressure on pyrethroid chemistry, especially in the autumn. AHDB monitoring shows aphids can acquire widespread resistance to pyrethroids and the chemistry needs to be used with care, whenever in the cropping season it is used.
Several cases of pyrethroid resistance in grain aphid, from various locations, have already been reported. The pest can cause direct feeding damage to cereals over the summer. Crops should be monitored and a spray considered if half of tillers are infested at the start of flowering (GS61). If pyrethroids are used, full recommended field rates must be used. If control is poor, a pyrethroid-based product should not be used again.
Although no reported resistance cases in bird cherry–oat aphid have been found, best practice must be followed to help prevent issues arising. Late-sown spring crops can be particularly susceptible up until GS31 (first node detectable). There are no treatment thresholds and any bird cherry–oat aphids present should be assumed to be carrying barley yellow dwarf virus (BYDV).
Information on aphid monitoring and control, including what to do if resistance is suspected and how to sign up to AHDB Aphid News, can be found at cereals.ahdb.org.uk/aphids