PGRO Crop Update (15.03.13)

becky wardBecky Ward, PGRO principal technical officer, comments on sowing rates for spring beans and peas, pre-emergence herbicides, peas and bean weevil ...

Sowing rate of spring beans and peas

The optimum density is 40 plants per sq m established for spring beans. Use the following to calculate seed rate (Allow for a 5 - 10% seed bed loss).

Required population x 1000 seed weight x 100

% germination   100-seed bed loss

The calculation is also used for peas, and optimum plant populations are as follows: Marrowfats: 65 plants per square m?; Large blues and whites; 70 plants per square m?; Small blues: 70 plants per square m; Zero 4 (small blue): 110 plants per square m.

Some growers may still be aiming to drill winter beans if they haven’t been able to do so already. Work carried out at PGRO showed that spring sown winter beans produced comparable yields to spring beans sown at the same time. These crops were drilled up to early March at similar seed rates to spring beans, but there are no data for winter beans drilled after this time. We therefore can’t advise that growers sow winter beans from mid-March onwards.

Spring beans can be sown to mid-April. Good soil conditions are more important than calendar date.

Pre-emergence herbicides

Cost effective pre-emergence herbicide options are dependent on moisture availability which, unlike recent seasons, should not be an issue for 2013 - although travelling on the land may be. Additional factors, such as cloddy seed beds, can also influence whether adequate weed control is achieved.

Some crops of spring beans are not rolled following drilling and some may not need it. Rolling helps conserve moisture and break up clods, giving a level surface to ensure the best ground coverage is achieved with the residual herbicide. If the surface is cloddy then application of pre-emergence herbicides with appropriate angled nozzles may help. Taking into account the amount of rainfall which has been received in some areas, it may be worth giving some consideration as to whether rolling is going to adversely affect below ground soil conditions.

Several pre-emergence products and tank mixes are available for combining pea and spring beans. In addition to Nirvana, Skirmish, Centium, pendimethalin (approved for peas, EAMU beans) and Defy (EAMU beans only), Afalon (linuron) and Linzone/Lingo (linuron+clomazone) are also approved for use in combining peas and spring beans.

Pea and bean weevil

Pea and bean weevils are not yet active due to cold weather. When temperature increases to 10-12oC over the next month, recently-sown spring beans may be at risk of damage as they emerge. Although foliar damage doesn’t generally cause a problem, crops can be held back if damage is severe at very early emergence. Spraying will prevent egg laying and larval damage to root nodules.

If you have a history of severe damage, particularly in drier areas, a pyrethroid spray should be applied at first signs of leaf-notching, and a second spray ten to fourteen days later where damage is persistent. Be aware that there is a limited range of products available for use later in the season for bruchid control. It is advisable to use different products for weevil control. Winter beans may suffer less damage as they are generally well-established by the time weevils are active.

Peas are susceptible and should be sprayed when first notching is seen, followed by a second spray ten to fourteen days later.