Latest PGRO pulse crop bulletin: Post-emergence herbicides, pest control, disease control, pea moth

Becky Ward, PGRO senior technical officer, advises: 

Post-emergence herbicides

In beans, post-emergence options are limited to bentazone. If it is used at full rate, then applications are from 3 nodes.  Full rate applications are expensive but split options at reduced rates can be both effective on small susceptible weeds and significantly reduce costs. Weeds beyond 2 true leaves will probably require a full dose application, and those species classed as moderately susceptible may not be controlled adequately by the half rate. To avoid excessive crop damage, there is a temperature restriction (21C). When considering using bentazone, temperatures in the mid to high teens positively influence the effectiveness of bentazone in terms of weed control. Its use when temperatures are relatively low can give disappointing results.

In peas, the hormones MCPB and MCPB + MCPA are available for use in conjunction with bentazone. They can control thistles, volunteer OSR and docks and boost the control of fat hen, knotgrass and poppy when used in mixes with bentazone.

In both vining and combining peas, Skirmish can be used up to the 2nd node of the crop at early post-emergence timing. If weeds are already present, then low rates of bentazone can be added, 240 g ai/ha if weeds are cotyledons – 2 true leaves and 480g ai/ha if they are beyond this. However, using bentazone at this timing with Skirmish strictly speaking means no further bentazone can be applied – there are no split application approvals in peas.

In some pea crops, volunteer borage can be a problem and post-emergence herbicide applications have been found to be more effective than pre-emergence sprays. Making up a bentazone + MCPB mix equivalent to the old Pulsar applied at 4.0l/ha was very effective in PGRO trials, as was bentazone alone at rates above 0.85kg.

In some bean crops, volunteer beet has been reported to be a problem. If used at around 1.65l/ha of a liquid formulation, or approximately 1kg/ha of the granular product, bentazone has been seen to be effective if used when the beet has 2-4 leaves.

Disease control

In winter beans, there are very few reports of chocolate spot following the continued dry weather in most parts of the country. Some crops may be flowering, particularly where they have been under severe pressure from weevil attack but, if there is no sign of disease development, delay spraying until disease is present. This will extend the period of protection later into the season.

Pea Moth

Pea moth traps should be ordered now ready for placing in crops in the next couple of weeks. 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).

PGRO is the non statutory levy body which promotes and carries out research and development in peas and beans. PGRO growing guides and recommended lists of varieties are the national references for growers. The PGRO publishes ‘The Pulse Magazine’ quarterly, the ‘Pulse Agronomy Guide’ annually, issues bulletins during the growing season, provides education and training courses, and runs grower / agronomist meetings around the UK.