Guide to growing a successful spring bean break crop

Spring beans make an excellent break crop, fixing nitrogen and improving soils to provide a helpful entry for subsequent cropping, and successful production rides ultimately on conditions at planting.

Drill timing is absolutely critical to getting crops off to the best start, with warm and moist soil conditions required for seeds to germinate and grow effectively.

Calculating optimal seed rates, deploying a two-pass fungicide spray strategy and the close monitoring of pest threshold levels also play key roles in achieving good harvest yields.

See also: Somerset grower wins gold with precise wheat production

Bean benefits

  • Nitrogen fixing with yield benefits of 0.6-0.9t/ha in following crops
  • Rotational benefits that increase microbial populations
  • Good for pollinating insects
  • Source of home-grown protein (26-30%)
  • Cut costs, energy use and CO2 emissions
  • Reasonable feed market

Establishment

Becky Howard, research and development manager at the Processors and Growers Research Organisation (PGRO) explains that growers should wait to drill spring beans into the right conditions.

“The optimal sowing date for spring beans is between mid-February and late March. If soils are cold and wet, don’t force them into difficult conditions – wait,” advises Dr Howard.

Seeds should be placed at the optimum drill depth of 10-12.5cm, ensuring the seed is deep enough to stay protected from bird attacks and herbicide residues, but not too deep to prevent germination.

A target density of 50-55 plants/sq m is recommended on most land types, but where ground is particularly fertile a target density of 40 plants/sq m is more appropriate.

Seed rates should take into account target population, germination rate and a 5% field loss, and can be calculated using the PGRO app or the formula below:

Seed rate (kg/ha) = (thousand grain weight x target population divided by % germination) x (100/100-field loss).

Soil success

Dr Howard continues that beans do not require particularly fine seed-beds, just level seed-beds with good seed-to-soil contact.

“As minimum tillage techniques are becoming more common, growers must ensure they cover the seed well and coulters do not leave open slots in the ground,” she warns.

After last year’s wet autumn the area of spring beans rose sharply. However, in 2020 some spring bean crops established unevenly, with multiple waves of emergence due to the spring drought.

Although spring beans have the ability to improve soils with their nitrogen-fixing abilities and strong roots that grow to 1m in depth, or more in some cases, poor soil structure can lead to significantly higher levels of infection from soil-borne pathogens.

Good soil health is paramount for beans to tolerate extreme weather. Compaction will otherwise restrict root development and penetration – limiting access to water and essential nutrients – and make crops more susceptible to environmental influences.

“At times when soil water deficits are high, roots become heavily restricted and unable to reach the subsoil. This causes severe moisture stress and where there is high plant stress there is greater disease pressure,” she says.

Disease

Beans are an effective disease break crop in cereals and oilseed rape, but a long history of bean production results in a higher pathogen burden, so only growing beans once every five years is key.

A two-spray fungicide programme should be sufficient to control the three main diseases: chocolate spot, rust and downy mildew.

“Preventative sprays are important when conditions are suitable for disease, but during seasons of low disease pressure a single spray may provide enough control,” highlights Dr Howard.

The first spray should take place at mid-flowering when the first pods appear and focus on chocolate spot control, using either Signum (boscalid + pyraclostrobin) or azoxystrobin + tebuconazole/metconazole or cyprodinil + fludioxonil.

“If downy mildew is present on 25% or more of plants, metalaxyl-m should be included as well,” she states.

The second spray should occur three to four weeks later, with either Signum or azoxystrobin + tebuconazole/metconazole.

“Remember that only one application of tebuconazole is permitted, so growers may leave this for use at this stage to control rust.”

Pests

Dr Howard encourages growers to monitor key pest levels, such as the pea and bean weevil and bruchid beetle.

“Pea and bean weevils have developed partial resistance to pyrethroids, so as temperatures begin to warm up growers should be monitoring pest movement in fields to ensure threshold levels are reached,” she says.

This can be achieved by placing five weevil traps into last season’s legume field margins during mid-February or current crop margins and check three times each week.

When the threshold average of 30 weevils a trap is reached, the crop should be sprayed at the first sign of weevil notching if the crop has emerged in the past 10 days or will do so in the next 10 days. Repeat sprays are not always necessary.

Furthermore, insecticide sprays for bruchid beetle should take place when maximum daily temperature has reached at least 20C for two consecutive days and crops are at the first pod stage (50% of pods are 2cm long). A second spray may be required seven days later.

“Adult beetles emerge at harvest and overwinter in field margins, moving into flowering crops during late April,” explains Dr Howard.

She recommends growers check insecticide product labels for flowering restrictions and use water volumes of 200 litres/ha.

Harvest

Crops are fit to combine at 18% moisture content, when only a few stems remain green. If beans are to be stored long term, moisture content at harvest should be 14%.

“It’s also worth noting that, in many cases, field beans may not require desiccation, especially if the crop is not weedy.

“Glyphosate is a weed-control product in crops, not a true desiccant. Glyphosate should not be used for seed crops as it can damage germination capacity,” reports Dr Howard.

Weed control

A range of pre-emergence products is available for weed control in spring beans, with some having extension of authorisation for minor use (EAMU), (see table).

However, post-emergence herbicide use is somewhat limited, with only bentazone available for broad-leaved weed control. Currently, too much bentazone is being detected in ground and surface water. For this reason, stewardship guidelines are in place to help reduce levels in water.

These include: a maximum recommendation dose for bentazone of 1,000g/ha; applications taking place from April onwards; and in high-risk areas with shallow light soil types bentazone should not be used.

“Although these are not label recommendations, it really is important that growers follow the guidelines, otherwise there is significant risk the active will be lost,” reports PGRO’s Becky Howard.

For blackgrass control, exploiting stale seed-beds remains an important control measure as there is widespread resistance to the fop and dim graminicides currently available.

Available herbicides for spring bean use

Products (active)

Application

Nirvana (imazamox + pendimethalin)

Pre-emergence

Centium (clomazone)

Pre-emergence

Stallion (clomazone + pendimethalin)

Pre-emergence

Stomp (pendimethalin)

EAMU pre-emergence

Dual Gold (S-metolachlor)

EAMU pre-emergence

Defy (prosulfocarb)

EAMU pre-emergence

Basagran SG (bentazone)

Post-emergence


Becky Howard was speaking at a recent webinar hosted on the BASF Virtual Farm website

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