Becky Ward, PGRO principal technical officer, gives the latest update on pests and diseases for peas and beans ...
Bruchid beetles in beans
Bruchid beetles are active in both winter and spring beans. Most winter beans have first pods and there have been several periods of two days at 20°C in many areas. Spring beans are setting first pods in many areas. Insecticides should be applied to any crop at first pod stage where temperature has been 20°C for two consecutive days. A second spray should be applied 7-10 days later.
A pea moth threshold was reached in traps at PGRO (at Thornhaugh, Peterborough) around 20th June and thresholds have been reported at some sites in Essex.
A threshold is reached when 10 moths are caught in either trap on two consecutive occasions. When a threshold is reached in combining peas, a spray date can be forecast using the PGRO pea moth forecasting service on the PGRO website forum.
Insecticides should be applied when first pods are set. A second spray application 10-14 days after the first will prevent damage from later arriving moths. Tolerance levels in vining peas are lower and crops should be sprayed at first pod where moths have been caught, even in low numbers, in traps.
See ‘PGRO technical update 149’ on our website for further information.
Silver Y Moth
A Silver Y moth threshold was reached at PGRO on Monday 24th June. The threshold for spraying is a cumulative total of 50 moths per trap by the time peas have reached first pod stage. When the threshold is reached, a single spray of a pyrethroid insecticide approved for moth control should be applied 10-14 days later. This will control both small and large caterpillars, which fall off the plant before harvesting.
Both pea aphid and black bean aphid colonies are present in crops and feeding impact may be high where crops are developing later than normal. To prevent yield loss caused by direct aphid feeding, combining peas should be sprayed when around 20% plants are infested and vining peas when 15% plants are infested. In beans, where a general infestation of 10% of plants are colonised, spraying should be carried out as soon as possible. Applications at early flowering, or when 5% plants are infested, reduces infections of aphid-transmitted viruses.
Disease levels in peas are still relatively low, but if conditions are unsettled it is likely that botrytis will develop as pods are setting and flowers falling. Flowers may stick to the pods which become infected, producing a watery rot and in some instances, grey furry mould. Flowers may also lodge in the leaf axils and grey mould develops around the stem and leaf node, causing early plant senescence and collapse. Several fungicides are available which reduce the risk of infection, and applications should be applied as soon as pods can be seen and the majority of flowers still have to fall when wet weather is forecast.
It is likely that powdery mildew infections could be high as crops develop later than normal. The disease is favoured by warm temperatures during the day and cool, humid nights. Later peas are more susceptible to infection. Cyproconazole/ chlorothalonil mixtures will give good control of powdery mildew, as will Thiovit Jet (EAMU), a sulphur based product.
Chocolate spot in beans
Protectant fungicides should be applied as soon as the first signs of disease are seen, especially if the weather is forecast to be unsettled. A second spray should be applied 3 to 4 weeks later if disease develops on new growth. A range of products and mixtures are approved for use.
It is likely that bean rust infection could be high as crops develop later than normal. Several products, including the triazole fungicides, will give good control of rust when applied at first signs of disease.