Managing BYDV Risk

Planting a mix of crops, having a range of sowing dates and applying fungicides to control disease are all examples of how tillage farmers can manage risk to their income. This autumn has demonstrated how people view risk. Ciaran Collins, Teagasc Crops Specialist has advice on BYDV risk management

Managing risk is second nature to tillage farmers. Everybody is aware that delayed sowing of winter cereals reduces the risk of BYDV, take-all and the incidence of grass weeds, yet some farmers are finished planting. Some have gambled with a proportion of their planned area and others have not started sowing yet.

The wet autumn of 2019 is fresh in the memory of many growers where the area of winter wheat fell from the traditional 60,000ha to 35,000 for the 2020 harvest. Some growers have taken a calculated risk that the afore mentioned risks associated with early sowing will outweigh the risk of poorer establishment or none, later in the season.

While early sowing removes some of our integrated pest management (IPM) tools, IPM does not end once the crop is in the ground. In crop inspections, decision making on whether pesticide application is required or not and the employment of anti-resistance strategies are all valuable IPM practices that can contribute to reduced pesticide use.

BYDV

Temperature governs aphid flight, migration and reproduction. Therefore, earlier sown crops are at the highest risk of infection and it is difficult to avoid insecticide application in these scenarios. In crop, monitoring is essential before an insecticide is applied to check if aphids are present. Inspect headlands first, because aphids are three times more likely to land near headlands than further out the field.

Aphids are visible on volunteers and this is no surprise as mean temperature for September are above average. Mean temperature to September 27 in Oak Park was 15.8°C compared to the long-term average of 13.2°C.

Location also affects BYDV risk. In Teagasc experiments during the 2016/17 season untreated experimental plots in Carlow had 4% BYDV infection whereas a similar sowing date in Cork had 40% infection. 

If aphids are present, apply an insecticide at the 2-3 leaf stage of the crop and a follow up may be required for September sown crops in early November, but it is important to check if aphids are actually present in the crop. Pyrethroids (Karate, Sumi Alpha etc.) will be effective for most growers but if resistance is suspected, use an insecticide from an alternative group eg. Sulfoximines (Transform). 

There is no known resistance to the sulfoximine class of insecticides. Transform has a maximum individual dose 48g/ha and can only be used once in a crop and is only allowed on winter cereals from GS 12 to 21 during November, December and January.

Currently there is a lack of thresholds to guide farmers on insecticide application for BYDV. Teagasc are currently researching a decision support system to inform farmers whether they need to spray or not.

The decision support system has two parts. Firstly, a network of suction towers (fixed 12.2m towers) to monitor aphids will build a better understanding on the impact of climatic conditions on aphid movement (see photo). Secondly, when we see aphids in a crop, we do not know if they are carrying virus or that viral load, so digital droplet PCR will be used to quantify BYDV loads in aphids. Virus threshold levels in combination with aphid movement will amalgamate to create a decision support system to inform future IPM based spray decisions. This research has started and will be a valuable tool for farmers in the future.

Weed Control

Pre-emergence and early post emergence herbicide applications in wheat and barley will give the best weed control this autumn.

This is particularly relevant for the control of annual meadow grass (AMG) in winter barley where pre-emergence or early post emergence timings are required to achieve the most reliable control.  The currently available suite of active ingredients can give excellent control of AMG (Flufenacet, eg. Firebird; Prosulfocarb eg. Defy; Pendimethalin eg. Stomp, Chlorotoluron eg.Tower) when used early. Control will be reduced after AMG reaches the two-leaf stage.

Brome is an increasing problem in winter barley and needs careful management to prevent a build-up of the weed seed bank. Herbicides approved for winter barley will not give complete control of brome species even when applied pre-emergence. Therefore, any effective control strategy needs be based largely on cultural control techniques.

There are more post emergence options available for wheat but we need to be careful of resistance. Recent herbicide resistance work done by Teagasc researcher Vijaya Bhaskar has confirmed resistance in Italian ryegrass to ALS herbicides Pacifica Plus and Broadway Star. Sterile brome was also tested for resistance and the results confirm early stages of resistance evolution within sterile brome populations, which may be hastened by the repeated use of reduced rates

Whether a farmer is trying to prevent BYDV or controlling weeds it is important to only use pesticides when required and to get effective control and to reduce the risk of resistance use a mix of actives at recommended rates.

If you liked this you might also be interested in Projected higher costs to hit Tillage margins in 2022.
Find out more information and advice from the Teagasc Crops team here. 
The Teagasc Crops Specialists issue an article on a topic of interest to tillage farmers every Thursday on Teagasc Daily.