Crops Management Notes – September

September 1, 2020

CEREAL MANAGEMENT

Variety selection

The starting point for effective disease control to achieve high yielding crops is variety selection. Consider varieties with good disease resistance scores and favourable agronomic profiles as part of an integrated pest management strategy.

Unfortunately due to COVID-19 the annual variety trial tours could not take place this year. You can however view the AHDB funded trail plots at AFBI Crossnacreevy with Dr Lisa Black by visiting https://youtu.be/Mz0QmdBUY7s for winter barley and https://youtu.be/kjsrhWwLefM for winter wheat.

Aphid monitoring and virus control

Good planning is essential to reduce the risk from BYDV transmitting aphids in an era without insecticide seed treatment and pyrethroid resistance in aphid populations.

Cultural control of weedy stubbles and volunteers by destroying the ‘green bridge’ for wingless aphids is achieved by burning off seven to ten days before ploughing or allowing 14 days between ploughing and sowing. 

Infection by migrating winged aphids is the most common route for BYDV infection in autumn cereals. To assess this threat AFBI, using a suction trap, monitor cereal aphid migration. Aphid migration is updated weekly, along with advice on control, and is available at https://www.afbini.gov.uk/cereal-aphid-monitoring. Historically data shows, as the season progresses, aphid migration and consequent BYDV infection pressure diminishes. Therefore, early drilled autumn crops are at greater risk and growers should balance this risk against later sowing, slower emergence and potentially poorer establishment. Concerns about pyrethroid resistance means you only apply pyrethroid sprays when aphid colonies, not individual aphids, are present on leaves.

A few winter barley varieties show tolerance to BYDV. This means they can be infected without displaying symptoms and suffer less of a yield penalty in severe outbreaks than non-tolerant varieties. Small quantities of tolerant seed are available this autumn so consider these for early sown high risk situations.    

Cultural weed control

This year’s prolonged dry and wet spells have caused a flush of weeds in more open crops. Stale seedbeds are a useful way of reducing the weed seed bank. Lightly cultivate immediately after harvest to encourage a flush of weeds which can be burnt off before ploughing and drilling. 

Slug monitoring

Now is the time of year to assess slug numbers before winter crops are sown. Set traps on damp soil using dry bait under a tea tray sized cover, leave overnight and check for slugs the next day. Removing green cover reduces their habitat and feed source. A clod free, firm seedbed allows seed to germinate quickly whilst restricting slug movement, making it harder for them to find seed and seedlings. If slug numbers exceed four per trap in cereals or one per trap in oilseed rape consider applying ferric phosphate slug pellets if emerging crops are still at risk. 

POTATO MANAGEMENT

Late season management

Maintain blight spray programmes until after haulm desiccation to avoid late blight developing. Blight strains insensitive to Fluazinam are common in Northern Ireland meaning this active should no longer be relied on for tuber blight control. The EuroBlight late blight fungicide table, www.agro.au.dk/forskning/internationale-platforme/euroblight/control-strategies/late-blight-fungicide-table/ provides alternatives to Fluazinam which have high tuber blight ratings and good antisporulant activity.

Desiccation

Regular trial digs indicate when tuber size has reached market specification, allowing desiccation to be timed accordingly. Without Diquat growers have PPO Inhibitors, Spotlight Plus (carfentrazone) and Gozai (pyraflufen-ethyl) as desiccation spray options. These can take longer to give the same effect as Diquat so plan to make the first application seven to ten days earlier than usual. They work best in bright, sunny conditions. Good spray penetration into the canopy is key so use slow forward speeds, high water volumes with forward and backward facing nozzles applying a medium quality spray. Both products are compatible with the fungicide Ranman Top, which can improve the desiccants efficacy whilst also having good activity on tuber blight.

Store and equipment preparation

Spores of many storage diseases lie dormant in the dust and debris remaining in stores, boxes and equipment. Thorough cleaning and disinfection is one of the most effective ways to avoid carryover of disease from previous years. Significant reductions in infection can be achieved by thoroughly power hosing or vacuuming stores and equipment before the new crop is harvested.