PGRO Crop Update (06.06.13)

becky wardBecky Ward, PGRO principal technical officer, gives the latest update on pests and diseases for peas and beans ...

In summary ...

Pests
There have been no reports of Pea Moth yet.  Silver Y Moth traps should be placed in crops as soon as possible. There have been no reports of Pea Midge yet in any areas. There have been no reports of Pea Aphid yet.  While Bruchid beetles are active in both winter and spring beans, first insecticide applications should only be made when beans have reached first pod-set following two days at 20°C.

Diseases
Downy mildew is present at low levels in spring beans.  A few reports of low levels of Chocolate Spot in beans.

Detailed report ...

PESTS

Pea moth
Pea moth traps should be placed in crops now if they are not already in place. Traps should be monitored three times a week, and a threshold is reached when 10 moths are caught in either trap on two consecutive occasions. When a threshold is reached, a spray date can be forecast by going to the PGRO web site  www.pgro.org  and checking the latest tweets.
Insecticides should only be applied when first pods are set. 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, available on the website www.pgro.org for details. Traps are available from Oecos tel: 01438 832481.
 
Silver Y Moth
Traps are available from Agralan Ltd., the Old Brickyard, Ashton Keynes, Swindon, and should be placed in crops as soon as possible.

The threshold for spraying is a cumulative total of 50 moths per trap by the time peas have reached first pod stage.

Further information can be found in PGRO technical update 169, available on the website.
 
Pea midge
Vining peas are more severely affected than combining peas due to their determinate growth habit, producing a short flowering period.

Susceptible crops are those which are at enclosed bud stage. In areas where midge has been a problem in the previous year, crops should be examined for midge adults by pinching the outer leaves of the growing point together and peeling back the leaves to reveal the bud. If adult midges are found, an insecticide should be applied as soon as possible to reduce the risk of eggs being laid.

A monitoring trap is available from Oecos Ltd, 11a High Street, Kimpton, Herts, SG4 8RA. It comprises 4 sticky traps complete with pheromone lures.

By monitoring catches of newly emerged midge in the overwintering site - in last year’s pea field - the peak activity of pests can be determined. This will provide advance warning of infestation in the nearby pea crops. Traps should be placed in last year’s pea field 10m apart as soon as possible.        
 
Pea aphid
Although there have been no reports of pea aphid yet, it is likely that they will soon be present in crops whilst the weather remains warm. Many spring crops are late due to late drilling and slow development and aphid impact may be high.

Viruses may be transmitted by the pea aphid into both peas and beans and sprays may be necessary to prevent a damaging virus infection. To prevent yield loss caused by direct aphid feeding, combining peas should be sprayed when around 20% plants are infested, and vining peas should be sprayed when 15% plants are infested.
 
Bruchid beetles in beans
Winter beans are flowering in many areas but have yet to set pods. Spring beans may have first flower buds present.

First insecticide applications should only be made when beans have reached first pod-set following two days at 20°C.
 
DISEASES
Downy mildew in spring beans
Plants develop pale patches on the surface, with grey-mauve fluffy mycelium on the underside of leaves. Crops should be treated when a threshold of 20% of the tops of plants are infected. Forecasts of disease risk can be found at www.cropmonitor.co.uk

Folio Gold is no longer approved for field beans under the new label and only stocks with the old MAPP label can be used this year. An EAMU (Extension of Authorisation for Minor Use) has been granted for SL567A in field beans. This is a straight metalaxyl-M product and should be mixed with a partner product to prevent the development of downy mildew resistance to metalxyl-M.
 
Chocolate spot in beans
The disease is encouraged by long periods of overcast, humid weather. Winter beans are more susceptible to the disease and spring beans may develop chocolate spot if the weather has been poor during the late spring and early summer.

The disease develops as small, circular, chocolate coloured spots on the lower leaves. These may coalesce and form larger, aggressive lesions on the whole plant.
Protectant fungicides should be applied as soon as the first signs of disease are seen, especially if first flower buds are present and weather is forecast to be unsettled. A second spray should be applied 3 to 4 weeks later if the disease develops on new growth. A range of products and mixtures are approved for use.