Nematode in Field Beans
Thursday 5th April 2018
This pest has now become one of the major pests of both winter and spring bean production.
The nematodes are usually introduced into the field through infected seed stocks and once established in the soil, can remain viable for many years.
Damage is often first seen in the plants as they reach the flowering stage, although earlier symptoms can be found at any stage after crop emergence. Plants will be stunted and the stems thickened and twisted. Leaves may take on a bronze discolouration in the petioles; the area where the leaf attaches to the stem. Later the stems become brown or rust red and will usually swell, twist and then break. Pods will fail to fill evenly and seeds will become black and shrivelled as they mature.
The appearance of single isolated plants across a field would indicate that infected seed is the source; more general crop damage would indicate the soil has become infected from a previous bean crop. Multiplication is always greatly enhanced during a wet spring.
Yield loss can be severe. In 2000 we saw infected crops return yields as low as 0.8 tonne / ha. Infested crops are unsuitable for use as seed, but the beans are still usable in animal feed compounds and blemish free produce is still suitable for export.
Nematodes can be detected in seed under microscopic examination. They are generally 1.4 - 1.8mm in length, virtually transparent and usually found in vast numbers within the stem and leaf tissue.
Test for nematodes before farm saving beans.
An adequate crop rotation will help to prevent the build-up of the pest in the soil. Once detected the land should not be used for ten years for the production of beans, peas or lupins.