PGRO Crop Update (15.05.14)

Becky Ward, PGRO principal technical officer, comments on the latest situation for insect pests and for diseases in pulse crops:

INSECT PESTS ...

Bean bruchid alert        Bruchids are present in crops, and some winter beans are at first pod-set. Maximum daily temperature is forecast to reach 20°C on Friday and Saturday in some regions and crops should be sprayed when temperature has reached 20°C for two consecutive days and when crops have set first pods (when 50% pods on the bottom trusses are 2cm long). Growers can sign up for bruchid spray forecasts by going to: http://www3.syngenta.com/.../BruchidCast.aspx

Pea moth damage in peas        Pea moth is one of the most damaging pea pests in this country and in Europe. The caterpillars feed on peas within the pod, and in combining peas for premium markets - including human consumption or seed - damaged peas are removed by the merchant and the price paid to the grower is reduced in proportion. Although pea moth caterpillar damage can reduce quality, the yield loss is rarely significant.

A system of accurately timing the application of insecticides is commercially available in the form of pheromone traps. Pea moth traps should be placed in crops from the middle of May and monitored every two days. Spray timing should be related to insect development rather than crop growth stage. Therefore, insecticides should be applied while the larvae are exposed: from the time of hatching to the time of entering the pods. The timing of application is critical for maximum control. Because pea moth can be a localised problem, overall spraying of peas over a wide area on any one date is not advisable as local conditions influence the behaviour of the pest.

PGRO runs a forecasting system for pea moth control and updates will be available on the PGRO website at www.pgro.org from the middle of May. The traps, which were developed by Rothamsted Research and fully tested by PGRO and ADAS, are manufactured by OECOS Limited, 11a High Street, Kimpton, Hertfordshire SG4 8RA. They are available from several merchants and growers should telephone 01438 832481 (www.oecos.co.uk) for their nearest supplier.

Aphids    The Rothamsted insect survey shows that, as predicted, most aphids are flying two to four weeks earlier than usual. This is mainly as a result of the mild winter, helped by the favourable conditions of spring. The very wet winter does not appear to have had a major impact. Spring crops, especially if sown later than usual are expected to be at higher than usual risk from aphids.

Pea aphids are present in some crops and early infestations may lead to greater incidence of virus infection in both peas and beans. Where aphids are present, early aphicide applications will help to reduce virus transmission.

DISEASES ...

Field beans    Some winter beans are developing high levels of downy mildew as conditions have remained favourable. In cases where 25% or more plants are infected in winter or spring beans, particularly on new growth, SL567A (metalaxyl-M) will give good control of downy mildew and should be combined with a partner fungicide product. Live forecasts for bean downy mildew risk in your area are available on the CropMonitor website at www.cropmonitor.co.uk.  The current forecast is for moderate risk of infection in all areas.

Chocolate spot is present in winter bean crops at relatively low levels. The disease is encouraged by long periods of overcast and humid weather. Winter beans are more susceptible to infection, especially where plant populations are higher than currently recommended. Spring and broad beans may also develop chocolate spot, particularly during damp summers.

The disease develops as small, circular, chocolate coloured spots on the lower leaves. This becomes larger and may coalesce to form a lesion extending over the leaf surface, severe infection resulting in defoliation. Stems and pods can also develop spots and flecks.

Protectant fungicides should be applied as soon as first spots are seen, particularly during flowering. A second spray should be applied 4 to 5 weeks later if spotting continues to develop on new growth. A range of products and mixtures are available.

Post emergence herbicide applications        Bentazone is the only active ingredient available in beans. Bentazone and MCPB are options in peas. Unless known herbicide-sensitive varieties are grown, i.e. those noted on the label, the newer varieties that do not appear on the label cope well. Sensitivity scores are based on full-rate applications. At the more commonly used half rate of bentazone, with the option of a second application in beans, few crop sensitivity issues are reported. It is important to check that there is adequate leaf wax on peas as both bentazone and MCPB are mainly contact materials.