Stem nematode – Dictylenchus dipsaci
Stem nematode lives in the plant tissue and seeds and can withstand severe desiccation. It also lives in the soil and can survive several years without a host crop. Hosts include beans and oats but will also infect sugar beet, peas, maize, strawberries and many weeds including red dead nettle and knotgrass. It is recognised that the Giant race is the one which affects beans most.
It is best to avoid cropping pulses too closely together in the rotation to help prevent infection, although if this coincides with a year of high rainfall particularly in the spring then chances of infection are increased.
Infected plants become swollen or distorted, later becoming dark brown in colour. This dark colouration usually starts at the stem base and stops at a leaf node. Infestations in the podding area result in infested seed. Heavily infested seeds have a blemished, darkened and cracked seed coat. One seed can carry 1500 to2000 nematodes in more severe situations and is capable of infesting clean soil.
A seed test exists for stem nematode. Results are indicated as either present or absent although more detailed scoring is available from PGRO and NIAB. Uninfected land should not be planted with seed at any level of infection, low infection in dry years will not normally cause further issue, although this is not a risk that many growers should take.
Where infection has been notably present in the field in the past then this may prevent pulse from being grown on those fields for 6 or 12 years.