Growing fresh runner and dwarf beans in Western Australia

Introduction

Beans (Phaseolus vulgaris) originated in Central America and belong to the pea (Fabaceae) family. They require warm temperatures for growth and yields. The immature pods are eaten as a fresh vegetable. They contain good levels of carbohydrates, proteins, vitamin A and vitamin C.

Two types of fresh beans are grown, with production divided between the climbing or runner bean and the dwarf bean, which has a number of names, such as French, bush, snap or stringless beans.

Dwarf beans are lower yielding, more difficult to pick and have a shorter bearing season than runner beans. However, dwarf beans do not require supports, have earlier maturity and are usually stringless and of good quality. They may also be harvested by machine.

Beans are a quick maturing crop but need considerable labour for picking.

The industry

The main production areas for runner beans are Carnarvon and Perth, with small areas in the south-west and Albany.

The main growing area for dwarf beans is Gingin and Broome, where beans are harvested by machine. Dwarf beans are also harvested by hand in Perth and the South-West. Production occurs throughout the year and demand is highest in the cooler months.

Fresh bean production has declined in recent years due to competition from frozen-packaged dwarf beans.

Other types of beans, such as butter beans, are grown in small quantities. Italian or borlotti beans are grown for the mature seeds that are used in soups and stews. Mung beans are grown under hydroponic-type conditions for their sprouts, which are used in salads.

Soils

Use well drained, uncompacted soils with a pH_Ca of 5.5 to 7.0. Apply lime at 2.5 to 5.0t/ha at least three months before planting if the pH_Ca is less than 5.3.

Beans are very sensitive to high salt levels. High salinity causes a scorch on the edge of the leaves, yellowish leaves and poor growth. The soil should have a low salinity with an EC25 (1:5) less than 15mS/m.

Beans may also be affected by high boron levels in the irrigation water and/or soil. Toxicity symptoms include yellowish leaves and small, crinkled pods.

Water quality

Beans have a lower salt tolerance than most vegetable crops. The salinity of the irrigation water should be less than 100mS/m (550mg/L total salts) for highest yields and quality.

Climate

Optimum air temperatures for good yields and quality are 16°C to 30°C. A frost-free period of 120 days is required. Where temperatures exceed 35°C, pollination of flowers may be poor and beans may be short, flat and curled with many second grade and reject beans. Temperatures below 10°C during flowering and pod setting may result in curling and russetting of pods.

The optimum soil temperature for germination is 24°C, with a minimum of 15°C and a maximum of 35°C.

Plant beans in a sheltered area. Winds damage leaves and destroy flowers, and pods are deformed when they rub against supports, leaves and stems.

Varieties

Climbing

New varieties of most vegetables are regularly introduced to the market. Check with your seed supplier for varieties best suited to your area and market.

The traditional local variety is Westralia, which is flat-podded and slightly stringed. It is tolerant to rust and mosaic virus. In recent years, production of Kentucky Blue has increased markedly, especially from Carnarvon. This is a high yielding, stringless, bean, with pods which are slightly more rounded than Westralia.

Blue Lake is a high yielding stringless variety with a roundish pod and is grown only in small areas. It needs more picking than Westralia as it has a smaller pod. It is susceptible to summer death and rust diseases. Storage life is good.

Dwarf

Most dwarf varieties are green, stringless, white-seeded and round-podded, with resistance or tolerance to rust and summer death. Jade is a popular variety, but check with your supplier as new dwarf varieties are common.

Seed

Growers normally purchase seed from local suppliers. Growers may also keep their own seed by collecting seeds from the highest yielding, true-to-type plants.

Collect seeds after the pods have dried on the plants. Further drying is required for two weeks inside a warm shed. Store seed in an airtight container in a cool place and keep a watch for weevils. Seed kept in good conditions will last for up to three years. Just before planting, dust seed with thiram (Thiram®) to prevent rotting.

Growing the crop

Planting

Times of planting and production in the different areas are shown in Table 1.

Plant every two to four weeks to obtain a succession of harvesting periods. Plant by hand or by machine, 3 to 4cm deep.

Depending on season, beans will emerge in 5 to 14 days. Do not thin the seedlings.

Climbing beans

Space climbing beans in single or double lines per row. In single lines, space at 15 to 25cm, with two seeds at each site and 1.0 to 1.3m between the rows. If planted in two lines per row, plant 0.6m between the lines and 1.5m between the rows, with two seeds planted every 30 to 40cm. About 40kg of seed per hectare is required.

Dwarf beans

With dwarf beans, aim for a plant population of 30 to 40 plants per square metre. About 45kg of seed will be needed per hectare. Plant rows 50cm apart with single seeds spaced at 7.5 to 10cm.

In Carnarvon, plant in rows 1.2m apart with two lines 60cm apart per row and two seeds planted every 15cm.

Beans for mechanical harvesting are planted with rows 30cm apart and 50 to 75cm between seeds in the row. Seeding rates are around 90kg/ha.

Watering

Most growers use overhead sprinklers in Perth and the south-west. This has the advantages of cooling plants in hot weather and increasing the humidity around plants. Trickle irrigation can also be used, especially in Carnarvon, and leads to large savings in water, weeding and labour. Growers in Carnarvon use a combination of low volume trickle watering (1.5 to 2.0L per hour per dripper) and black polythene mulch, 0.9 to 1.2m wide.

Beans require moist soil at all times but must not be waterlogged, especially for the first week after planting. Do not overwater for the first month after planting, as this can result in excessive vegetative growth.

Increase watering from two weeks before flowering to two weeks after flowering. As a guide, irrigate as shown in Table 2 from flowering onwards.

Fertilisers

Nitrogen is the main fertiliser needed, although some nitrogen is supplied to the plants from Rhizobium bacteria in nodules on the roots. Plants short of nitrogen are stunted, with small pale green leaves. Excess nitrogen will produce too many leaves and lower yields.

Beans also need phosphorus and potassium. Plants low in phosphorus have small, dark green leaves turning to bronze, with some defoliation and poor flowering. Plants short of potassium have stunted growth, with curled yellowish leaves and scorched leaf margins.

To improve soil organic carbon levels, apply compost at 30 to 50 cubic metres per hectare sometime in the rotation. This will supply organic matter, add nutrients and help retain moisture in the soil.

Analyse soil and irrigation water before planting, plus one to two analyses of the youngest mature leaves during the first half of the growing season. This will enable some adjustments to the fertiliser program and provide information on nutrients that are deficient or toxic. Some of the suggested nutrients may be deleted or reduced if they are sufficiently high in the irrigation water and soil, including sources from compost and fertilisers from previous cropping.

Do not apply excess fertilisers, because nitrogen, phosphorus and potassium are easily washed through sandy soils by rainfall and irrigation. This may lead to pollution of surface and groundwater.

In Perth and the Swan Coastal Plain, apply the following rates of magnesium and trace elements before planting:

• 50kg/ha magnesium sulphate to supply magnesium
• 20kg/ha manganese sulphate to supply manganese
• 18kg/ha borax to supply boron
• 18kg/ha iron sulphate to supply iron
• 18kg/ha copper sulphate to supply copper
• 18kg/ha zinc sulphate to supply zinc
• 2kg/ha sodium molybdate to supply molybdenum.

South-west

• On heavier textured soils such and loams and gravelly loams, phosphorus requirements should be applied based on soil test results and banded at sowing. Some potassium and a small amount of nitrogen may also be banded at sowing. Seek advice from DAFWA advisers or your horticultural consultant regarding a specific fertiliser program.

Perth

• On sands with yellow subsoil, apply phosphorus before planting according to soil test. Phosphorus fertilisers may be broadcast and incorporated.
• A simple fertiliser program on sands is to follow with weekly dressings of 50kg/ha urea and 70kg/ha of sulphate of potash.

Carnarvon

In Carnarvon, the soil and irrigation water supply adequate levels of potash. Apply fertiliser as follows:

• Apply double superphosphate at 1.5kg per 60m row and incorporate into the soil to 15cm before planting, if soil test phosphorus is less than 100mg/kg.
• Apply urea at 1kg per 60m row one week after emergence and again at the same rate just prior to flowering. Sulphate of ammonia (2.1kg per row) can also be used.

Trellising

Climbing beans require support from the four leaf stage onward, using one of the following systems:

1. Place vertical stakes (25mm square and 2m long) every 30 to 50cm.
2. Use ti-tree (Melaleuca uncinata) stakes, 2 to 2.25m high. Dip the bottom 45cm of the stake in tar to prevent rotting. The stakes form an inverted ‘V’ trellis and are supported by a central wire 1.6 to 1.8m high.

Where Fusarium disease has caused damage in previous years, dip stakes in a bath containing sodium hypochlorite (1% chlorine) for ten minutes, two weeks before use. Wash excess soil off the stakes before dipping them.

Four to six weeks after planting, it may be necessary to assist some of the plants to climb around the sticks in an anti-clockwise direction.

Weed, pest and disease management

The registration and availability of chemicals for weed, disease and pest control change regularly. Consult a trained and experienced horticultural consultant or the Australian Pesticides and Veterinary Medicines Authority (APVMA) website for chemicals which are currently registered or have a permit for use on this crop. The information on the label or permit for a chemical must be followed, including the directions for use, critical use comments, withholding period and maximum residue limit. Quality assurance (QA) schemes for horticultural crop production require producers to have current information on chemical registrations and permits at their fingertips. The information to be found at the APVMA website allows this requirement to be met.

Weed control

Weed control is essential for good yields and quality, especially during the first four weeks with runner beans and the first six weeks for dwarf beans.
Some growers use a contact herbicide to control existing weeds before the beans have emerged through the soil or before planting.

Pests

Two-spotted mites are just visible to the naked eye. They can be devastating in warm weather. Numerous dry white spots appear on the leaves. Pods may be stunted, whitish and shrivelled.

Early application of miticides is essential to obtain good control. After picking, remove old crops to prevent spread of two-spotted mite to other crops.

The false wireworm or vegetable beetle is grey to brown, 10mm long and 4mm wide. It may severely damage seedlings by ring-barking the lower part of the stem. Damage is more severe in warmer months. No chemicals are registered for control.

Pests that occasionally damage beans include bean fly (young stems), cutworm (leaves, young stems), dragonflies (Carnarvon-puncture young stems during egg laying), grasshoppers (leaves), caterpillars, (leaves, pods), leafhoppers (leaves), snails (leaves), Rutherglen bug (leaves), thrips (flowers) and whitefly (leaves).

Nematodes

Beans may be damaged severely by root-knot nematodes. Damage is seen as swollen lumps on the roots. Nematode damage should not be confused with the nitrogen-fixing nodules on bean roots. These nodules are up to 2mm wide and are attached by a single point to the root, which is of normal size and not swollen.

Where possible, avoid land known to be infested with root-knot nematodes for growing beans.

Diseases

Root rots (Fusarium and Rhizoctonia) are soil-borne diseases that may kill up to 20% of plants. Normally, single plants are affected, the surrounding plants being healthy. The diseases are not transmitted through seeds. They will infect other bean crops grown later on the same ground. Fusarium will not affect other vegetable crops, but Rhizoctonia may.

Symptoms mainly consist of rotting and development of lesions at the base of the stem. The diseases may be increased by nematodes, root damage caused by weeding or applying fertiliser close to the stem, deep planting, waterlogging —  especially in soil high in salt — and compacted soils.

No chemicals are registered for controlling Fusarium and Rhizoctonia on beans. There should be a minimum of six years rotation between successive bean crops, where possible.

White mould (Sclerotinia sclerotiorum) usually causes more damage in cool, wet or humid weather. It attacks leaves, stems and pods, especially on maturing crops, and results in a soft watery rot. A white fungus growth develops on infected tissue and black bodies, 1 to 5mm in size, may be found in the rotted tissue. These carry the disease over in the soil to following crops.

Do not over-water or over-fertilise with nitrogen.

Rust (Uromyces appendiculatus) is occasionally seen on susceptible varieties, but seldom warrants chemical control.

Mosaic viruses are occasionally transmitted to individual plants by aphids but many varieties have mosaic virus resistance. Virus-infected plants are stunted with small twisted leaves.

Harvest, yields and packing

Harvesting

Beans are self-pollinated and bees or other insects are not necessary to produce pods. Harvesting occurs about two weeks after flowering.

First picking occurs 7 to 11 weeks are planting, depending upon season. Some people experience skin allergies when picking beans and must wear gloves and a long-sleeved shirt.

Pick beans early in the morning in hot weather and keep them cool. This is especially important with the stringless dwarf varieties, which wilt more readily than the Westralia variety.

A total of 4 to 12 picks is obtained with climbing beans over 10 to 30 days, depending on season. Pick beans when they are over 15cm in length, with half-sized seeds. Younger beans wilt rapidly. Best quality beans are straight with smooth pods.

Do not market over-mature, small, misshapen or blemished beans. Reject beans may amount to a quarter of the crop.

Dwarf beans are picked two to five times over 7 to 15 days, when the beans are 10 to 13cm long, depending on variety.

Baby beans can be picked for gourmet markets. These are less than 10cm long.

Dwarf beans can be harvested by machine in one pick. Harvesting machines are expensive and a minimum of 10ha of beans is needed to justify the purchase. Yields and quality can be lower than with hand picking and hand grading is required after harvesting.

Yields

Climbing beans usually yield 6 to 10t/ha and a yield of 15 to 25t/ha is high. Dwarf varieties yield slightly less than climbing varieties.

Packing and storage

Cool beans to 4.5 to 6.0°C immediately after harvesting. Grade beans during picking. Pack into 22L or 36L plastic crates or 10kg cartons.

For good presentation and extra life, dwarf beans and baby beans may be packed into 300g punnets and covered with clear plastic, with 12 punnets stacked on a tray.

Store beans at 4.5 to 6.0°C at 90 to 95% relative humidity for one to three weeks. Bacterial soft rot and Sclerotinia may appear in the middle of packages if beans are packed when wet.

Transport

For best results, consign dwarf beans to distant markets in refrigerated trucks. Beans are consigned from Kununurra to Perth by air.

Acknowledgement

This material was originally authored by John Burt.