Becky Ward, PGRO principal technical officer, comments on the latest situation for pests and for diseases in pulse crops:
FIELD BEAN DISEASES
Chocolate spot is present in winter bean crops at increasingly high 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. Severe infection can result in defoliation and pod abortion. 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 3 to 4 weeks later if spotting continues to develop on new growth. A range of products and mixtures are available and under high disease pressure, reduced rates will not give adequate protection.
Responses to treatment can be expected where unsettled weather conditions continue to favour disease development.
Grey mould (Botrytis cinerea) is attracted to wet flower petals which, after pod set, either become detached and lodge in the leaf axils or remain stuck to the developing pods. The disease can penetrate and cause rotting of stems and pods. This has a direct effect on yield and can cause blemishing of the produce.
Leaf and pod spot (Mycosphaerella pinodes and Ascochyta pisi) causes infection after a prolonged period of wet weather and may appear at a slightly later stage than Botrytis. It causes purple-brown flecking of leaves and blackening of the stem before lesions develop on pods.
Botrytis and leaf and pod spot cannot be successfully controlled once established, and preventative sprays are more useful where weather conditions are unsettled. Because of the need to prevent development of disease, and if the outlook is for changeable weather at the first pod set stage, then sprays should be applied at this time. A second spray should be applied 10–14 days later if weather conditions remain unsettled. Fungicides such as azoxystrobin, metconazole, boscalid + pyraclostrobin (Signum), chlorothalonil + cyproconazole or chlorothalonil + pyrimethanil (Walabi) will give useful control of leaf and pod spot and Botrytis in the crop and can give yield increases when applied during flowering and pod set.
Powdery mildew may affect late maturing crops, and the disease may delay maturity. Cyproconazole + chlorothalonil will give useful control of powdery mildew at the second spray. Sulphur (Microthiol Special) has an Extension of Authorisation for Minor Use for peas to control powdery mildew.
Bean bruchid alert
Bruchids are present in crops and spring beans are flowering. Maximum daily temperature is forecast to reach 20°C on Saturday and Sunday 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).
Sign up for bruchid spray forecasts in your area by going to http://www3.syngenta.com/.../BruchidCast.aspx. BruchidCast is currently forecasting a threshold temperature and spray dates in some areas for Sunday 8th June and Monday 9th June.
Pea moth thresholds have been reached in some regions. For accurate forecasts of spray dates in your regions go to www.pgro.org Forecasts will be posted on the forum on our website
Pea aphid colonies are developing in many pea and bean crops. Where aphids are present, aphicides should be applied as soon as possible.
Pea and bean crop - nitrogen fixation assessment
Crop researchers based at the James Hutton Institute (www.hutton.ac.uk), are offering a free service which quantifies the nitrogen fixation capacity of pea and faba bean crops. The assessment, which involves minimal sampling of less than 10 plants per field, will determine the actual quantity of nitrogen which the pulses obtain from air, as this represents the efficiency of their nitrogen-fixing ability. Samples of root nodules will also be needed. This free assessment is offered to farmers throughout the UK, but especially to those cropping peas and beans close to and around the arable Scottish north east. For more information or to take part in the survey please contact either firstname.lastname@example.org, or email@example.com, as soon as possible.
Pea downy mildew
PGRO is investigating races of downy mildew present in UK pea crops and would like to request that growers send plant samples with downy mildew infection to our laboratory. Please send samples to Dr Kerry Maguire at PGRO, The Research Station, Great North Road, Thornhaugh, Peterborough, PE8 6HJ. Or call Kerry on 01780 782585.