BYDV and Aphid Control in Cereals

By far the most significant damage aphids cause to cereal crops is the transmission of Barley Yellow Dwarf Virus (BYDV). BYDV is most damaging to plants infected in the early growth stages and large yield losses can result (as shown in Figure 1 below).  While all cereals are equally susceptible, Barley is generally the most severely affected due to sowing dates (Winter Barley sown earlier in the autumn and Spring Barley later in the spring when aphids are more active).

The initial symptoms of BYDV infection are normally seen as individual plants scattered through the crop with bright yellow upper leaves. Later, as infection spreads, larger areas of the crop become infected appearing as patches of bright yellow and severely stunted plants.

Life cycle
BYDV can be introduced into cereal crops in two ways:-
• By direct transfer by wingless aphids living on grass or on volunteer cereals which survive cultivation and move through the soil colonising the following cereal crop. This is more common in southern coastal areas where cereals tend to be milder.
• Indirect transfer by winged aphids migrating into newly emerged crops from grass or volunteer cereals elsewhere. This is the more common and important method of transfer but it requires certain conditions e.g. warm temperatures (ideally 14-15oC but not below 10oC) and light winds. These conditions tend to from mid-May to early October.

The virus exists as several strains and is transmitted by various species of aphids; the most important in Ireland is the grain aphid (Sitobion avenae).

Ploughing well before drilling (3+ weeks), burying or destroying trash completely and preparing well consolidated seedbeds will minimise the risk of direct transfer. Delaying sowing in the autumn (until after mid-October) and sowing early in the spring (before April) will minimize BYDV issues. Where this is not possible, or unusually mild weather is prevalent, control is heavily dependent on chemicals.

Spring Cereals

• Crops sown before the end of March should not require an aphicide. 
• Treat crops sown from early April once with a contact aphicide at GS 13-14.
Sowing date is crucial, there can be up to 20 times more BYDV in April sown crops compared to crops sown in March.

Winter Cereals
• Treat crops sown in September with a contact aphicide at GS 12/13 (unless treated with Redigo Deter) and again in early November (first aphicide if treated with Redigo Deter). 
• Treat crops sown from early October with a contact aphicide in early November unless treated with Redigo Deter or sown very late and weather is cold.

Pyrethroid Aphicide Resistance

All crops should be checked for the level of control 3-4 days after applying an aphicide. This is because partial resistance of certain populations of the Grain Aphid to Pyrethroids (Karate, Sumi Alpha, Decis, Cypersect etc.) has been confirmed in Ireland. Where control is unsatisfactory apply Dursban/Clinch (remember to observe tank mix restrictions with Dursban/Clinch). 

Key point: nearly all crops will require at least one aphicide. Check crops 3-4 days after spraying to ensure the product has worked as the presence of the Grain aphid with resistance to certain products has been confirmed in Ireland.

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