PGRO Crop Update (17.05.13)

becky wardBecky Ward, PGRO principal technical officer, comments on winter and spring bean disease control, bean seed fly, pea moth and post-emergence herbicide applications ...

Winter bean disease control
Winter beans are just starting to develop first flowers in some areas. There have been no reports of chocolate spot yet, but the current unsettled weather may encourage the disease. If disease appears in crops, fungicides should be applied to protect new growth. If disease pressure is high and weather remains unsettled, use full rates of fungicides. Reduced rates will not give adequate protection.

Spring bean disease control
There have been reports of early downy mildew in spring bean crops, encouraged by the cool, unsettled weather. 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. See the monitoring website www.cropmonitor.co.uk for current downy mildew forecasts.

Bean seed fly
Where drilling is delayed, weeds may have become well established and, particularly where weeds have not died off sufficiently before drilling, there may be a high risk of attack by bean seed fly.

Bean seed fly attacks later drilled peas and beans (May and June), and are attracted to fields with high levels of green material left in the soil. The larvae tunnel into seeds and stems causing the seedlings to die off or become severely deformed. There are currently no insecticidal seed treatments approved for use in peas in the UK, although some imported vining pea seed may be treated with thiomethoxam, and here the insecticide will reduce the risk of damage.

Otherwise control may be improved through cultural means – ensuring that green material in the soil is minimised by adequate weed control.

Pea moth
Pea moth traps should be ordered now ready for placing in crops at the end of May. Traps should be placed in early crops of peas as soon as possible. See PGRO Technical Update 149 (available at www.pgro.org) for details. The spray information telephone line will be available from the end of May on 01780 783099. Traps are available from Oecos. Tel: 01438 832481

Post-emergence herbicide applications
Bentazone is only available in beans. Bentazone and MCPB are options in peas. Unless known susceptible varieties are being grown - i.e. those noted as such on the label - the newer varieties that do not appear on the label cope well.

Sensitivity scores were based on full rate applications - these days few apply full rates. At the more common half rate bentazone -  with the option of a second application in beans - few crop issues are reported.

Checking there is adequate leaf wax on peas is important as both bentazone and MCPB are mainly contact materials.