Suspicious parasite


Ring nematode could be a culprit in loss of vigour being experienced by several fruits in the Okanagan.


By Judie Steeves


xenoplax) might be to blame for a lack of vigour in plants such as grapes, cherries, apricots, plums and peaches. Pacific Agri-food Research Centre soil ecologist Tom Forge specializes in nematodes and has been doing some work on these and other nematodes for the past few years in the Okanagan.


T


It is an ectoparasite, so soil cores from around the roots are being used as samples to monitor their populations. Forge says he is also working


on-farm with Mission Hill Family Estate to do some research on four different grape rootstocks, to see if they differ in their susceptibility to nematodes. He has been doing similar work at the research centre in Summerland. “It may seem like an emerging issue, but I think they may have been in the valley for a long time. These nematodes are also associated with Prunus species such as cherries and apricots, so they may have been brought into the valley decades ago with fruit trees,” he speculated.


This summer, he would like to take this work a step further and look at nematodes in cherry orchards, particularly trees between the ages of five and eight years, because they’ve been in the


hey likely have been in the region for decades, but only recently have growers and researchers begun questioning whether ring nematodes (Mesocriconema


They are recognized in most major grape-growing regions of the world as a pest of the vines, but not much work has been done yet in B.C., until recently when more notice has been paid to root issues and more sampling has been done. In other grape-growing regions the ring nematode is usually not the focus because growers are more preoccupied with root knot nematodes, but in B.C. root knot nematodes don't seem to be much of a problem.


The species of root knot nematodes (Meloidogyne hapla) found here aren’t as pathogenic, explains Forge. Similarly, a particular species of root lesion nematode


(Pratylenchus vulnus) is an issue in other regions, but the species found here is different (Pratylenchus penetrans) and scientists here don’t yet know just how much damage they are causing in vineyards.


In apple orchards they cause loss of vigour in newly- replanted apple blocks, and are known to be a problem in Fraser Valley raspberry fields.


As more old orchards are converted to vineyards, the issue of root lesion nematodes being present in the soil becomes more of a concern.


Dr. Tom Forge


ground long enough for chronic effects of nematodes to accumulate, but they’re young enough that other pests and diseases might not have begun to cloud the issue. “I hope to see if there is an association between tree vigour and nematodes,” he explained.


In fact, although Forge has lined up 20 sites in cherry orchards where there’s a good mix of varieties, he would like to monitor more young cherry orchard plantings throughout the valley.


So, if you would like to work with him on this project, contact him—whether you are having some issues with tree vigour or not. E-mail him at: tom.forge@agr.gc.ca. Nematodes are nearly microscopic in size, from 1/2 to 2/3 millimetres long and 30 microns in diameter, and they’re translucent, so difficult to see.


The fact they are underground makes it particularly challenging to study them and the damage they cause, without killing the plant by digging it up.


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A fumigant is available for use when replanting apples, but even if you do fumigate between crops, the nematodes will come back, Forge advised.


At present, there are no products such as nematicides registered for use on grapes, although there is a post-harvest product for raspberries.


Forge says he wants to assess the pathogenicity of root lesion nematodes in grapes, and says it is surprising how little information we have on this species here. There is evidence that the chronic, slow sapping of the plant’s strength by nematodes makes tree fruits more susceptible to winter injury, so he feels that may also be the case with grapes.


He’d like to do a longer-term study of their impact on plant physiology, and whether their presence pre-disposes those vines to environmental stresses, particularly winter injury. While nematodes can be frustrating for growers to deal with, and their presence and affect limiting the vigour of plants may leave the plant vulnerable to cane diseases or other issues, they are not what Forge calls an “emergency” in terms of plant health.


British Columbia FRUIT GROWER • Winter 2011-12


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