PGRO Crop Update No. 3 - 23 May 2017

PGRO CROP UPDATE NO. 3 23 MAY 2017

bruchid beetleBruchid beetle
Bruchid beetles have been active in field bean crops for some time, particularly winter beans that are flowering. Winter beans are at or almost at the first pod formation stage, with pods forming inside flowers on bottom trusses. Insecticide sprays should be applied when the temperature threshold has been reached and around 50% of pods on bottom trusses are 2 cm long. Sign up for the Syngenta BruchidCast® forecasting service by going to www.syngenta.co.uk/bruchidcast The forecast predicts when the critical temperature threshold of 20°C for two consecutive days has been reached and indicates suitable conditions for applications. Growers should check that first pods have set. BruchidCast® is currently indicating that the temperature threshold will be reached this week. In order to avoid risk to foraging bees spraying should be carried out very late in the evening or at night time.

Aphid monitoring
Aphid populations are likely to increase over the next few days as warm weather settles across the UK. For those crops approaching the first flower growth stage, presence of aphids should be checked and the following thresholds use for spray applications: 15% plant colonisation in vining peas, 20% plant colonisation in combining peas, 10% plant colonisation in field beans. Updates on suction trap catches and activity of crop aphid species can be found in the summaries provided by AHDB on the PGRO website at www.pgro.org or at https://cereals.ahdb.org.uk/monitoring/aphid-news. The AHDB Aphid News bulletins provide information about when aphids are migrating at key times of the year. Information in the newsletters should be used to optimise the use of insecticides, time treatments better and reduce harm to beneficial insects. This will also lower the risk of selection for insecticide resistance by reducing unnecessary or wrongly timed sprays. Support for this project is provided by BBSRC, The Lawes Agricultural Trust, PGRO, BBRO, AHDB and other industrial supporters. For further information call the PGRO technical advisory line on 01780 782585.

pea aphid on pea podsPea moth
Remember to order your pea moth traps ready for monitoring in May and June. If you haven’t already put pea moth traps in place, you can order them from OECOS Limited, 11a High Street, Kimpton, Hertfordshire SG4 8RA. An alternative monitoring system is available from Agralan Ltd., The Old Brickyard, Ashton Keynes, Swindon, SN6 6QR. Control of the larvae must be carried out following egg-hatch and before they reach the pod, and the monitoring system will accurately predict spray date. When traps are in place they should be monitored three times each week and a threshold is reached for combining peas when 10 or more moths are caught in either trap on two consecutive occasions. Timing of sprays is related to egg development and this is affected by temperature. Starting from the day on which the threshold is reached, record the daily maximum and minimum temperature and set these on the outer scales of the calculator supplied with the Oecos traps. The figures exhibited in the window are added each day until the total reaches 90. Alternatively, a spray date can be obtained from the PGRO website - www.pgro.org, based on a computer prediction, 3 - 4 days after reaching a threshold.

Silver Y mothSilver Y caterpillarSilver Y moth
Silver Y moth caterpillars feed on the foliage and pods of peas and beans, but most of the economic impact is felt through contamination of vining pea produce at harvest, causing crop rejection by the processors. The moths are large, grey-brown, day-flying Noctuid moths with distinct silver ‘Y’ markings in the middle of each forewing. They migrate from North Africa during early to mid-summer and are attracted to a wide range of plant hosts. The caterpillars are bright green with a white strip along each side of the body and a darker line along the back. When disturbed the caterpillars roll into a ball. A monitoring system consisting of traps containing a pheromone attractant is available. The system is available from Agralan Ltd. In peas the trap should be placed at crop height in the field in late May and moths, caught in the base, are counted on three occasions during each week of monitoring. A threshold is reached when a cumulative total of 50 moths has been reached by the time that the peas have reached the first pod stage. When the threshold has been reached, a single spray of a pyrethroid insecticide, approved for pea moth control, should be applied 10 - 14 days later. This application will control both large and small caterpillars, which fall off the plants before the crop is harvested.

Chocolate spot in beansChocolate spot and Cercospora in field beans
Disease pressure in field beans has remained relatively low, with sporadic reports of chocolate spot and Cercospora. While the weather forecast is settled for a period, chocolate spot development may be suppressed in crops. Chocolate spot can be seen as small, round discrete chocolate coloured spots on the lower leaves of plants. Under the right conditions these lesions may coalesce to form unevenly shaped grey-brown patches on the foliage as the disease develops. Both winter and spring beans may develop aggressive chocolate spot and brown streaks may appear on stems. In severe infections plants may defoliate. The disease is favoured by overcast, humid conditions and particularly when long periods of wet and overcast weather are experienced during the summer. Fungicides applied at the first signs of disease help to prevent rapid infection.


PGRO Technical Information
All PGRO Technical Updates have been revised to include the changes in pesticide availability for peas and beans. PGRO publications are available as free downloads from the PGRO web site www.pgro.org. User passwords are available on request through the web site.
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