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 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.
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).
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.
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.