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Capsids

Timing treatments against capsids

The European tarnished plant bug (Lygus rugulipennis), more commonly referred to as ‘capsid bugs’, feeds on new plant growth, causing distorted leaves, destroyed growing points and malformed fruits. They became an important pest of cucumber crops in the mid-late 1990s. At that time, there were no effective IPM compatible control measures and growers were forced to apply broad spectrum insecticides that disrupted the whole IPM programme.

Adult capsid bugs survive the winter in plant debris and become active in April / May. There is a second generation in mid-summer but the timing varies from year to year depending on weather conditions. Cordon-trained crops planted during the summer are particularly vulnerable when they are growing up to the ‘wire’, while high wire crops remain vulnerable until the end of the season. We witnessed some extremely serious damage to the latter during 2010.

Work in HDC-funded Project PC 123 in 2000, developed an IPM compatible control measure based on the anti-feedant chemical pymetrozine (Chess). This has since become the standard treatment against capsid bugs in cucumber crops. The treatments remain effective for about 7 days, which means repeat applications are required to provide protection throughout the vulnerable periods. It was clear that an effective monitoring system was required to determine when capsid bugs were active and thus minimise the number of treatments required.

We demonstrated that male capsid bugs were attracted to live females in traps, which indicated that they were producing a pheromone which acted as a sex attractant. Prof David Hall’s research team at the Natural Resources Institute identified the three chemical components of the pheromone and Tom Maynard (GSK Blackcurrant Growers’ Association) subsequently led a LINK project (CSA7520 / HL0184LSF) aimed at developing monitoring techniques for a wide range of crops. Both the HDC (Project PC / SF 276) and the CGA have been partners in that venture.

The research was fraught with difficulties; the quantity and ratio of the three chemical components, as well as the trap design, all proved to be extremely critical. However, thanks to the hard work and persistence of Dr Michelle Fountain (East Malling Research) we now have a reliable monitoring system. Our own work on several cucumber nurseries in 2010 has shown that pheromone-baited traps positioned outside the glasshouses can give at least one week advance warning of crop damage.

Example of Capsid damage