Tomato Ringspot

Tomato ringspot virus is a soilborne virus that is capable of infecting certain stone fruit rootstocks (peach, almond, Mahaleb and Mazzard cherry, Myrobalan plum) when virus-infected nematodes feed on the roots. Depending on the combination of scion wood and virus strain, either yellow bud mosaic or prunus stem pitting may result. Because the pathogen is spread from tree to tree by nematodes in the soil, symptoms tend to appear on trees in one area of an orchard, rather than being scattered about at random.

Yellow Bud Mosaic
Foliage symptoms slowly spread throughout the canopy as the virus moves up into scion wood. Trees grown on peach, almond, Mahaleb or Mazzard cherry, and Myrobalan plum rootstocks are affected. Yellow bud mosaic occurs on peaches, nectarines, and cherries in the Sacramento and northern San Joaquin Valleys.

On cherry trees, a bare-limb appearance starts at the bottom of branches and moves upward as the virus kills spurs, twigs, and small branches. Affected leaves have an elmlike appearance because the prominent, whitish veins are at right angles to the midrib. Leaflike growths (enations) develop along the midrib on the underside of these leaves.

Prunus Stem Pitting
Prunus stem pitting affects peaches, nectarines, plums, and cherries. Infected trees leaf out later than normal. Foliage appears pale green or yellowish and wilted in early summer. In late summer, foliage may prematurely develop reddish or purple fall coloration. Fruit size and yield are reduced greatly, and fruit may fall prematurely. Foliage and fruit symptoms are caused by a reaction at the graft union that interferes with the flow of water and nutrients. Poor water availability causes foliage symptoms similar to those caused by root-destroying fungal pathogens and girdling or root destruction by rodents. A distinguishing characteristic of this disease is an abnormally thick and spongy bark at the base of the tree just above and below the soil line. The wood underneath is deeply grooved and pitted. The wood may be weakened to the point that the tree falls over.

Tomato ringspot virus is spread by budding and grafting and by dagger nematodes, Xiphinema spp., in the orchard soil. The virus is seedborne in dandelion, Taraxacum officinale, and infects a number of other broadleaf weeds as well as grapevines and caneberries. The nematode vector acquires the virus by feeding on the roots of infected weed hosts. Xiphinema larvae remain infective until they molt. Adults remain infective for 3 to 8 months. Disease spread in the orchard may follow the movement of soil water. Cultivation and irrigation may assist in the spread of both the nematode and the disease.

Susceptible rootstocks become infected with Tomato ringspot virus when infected dagger nematodes feed on their roots. The virus moves upward in the roots until it reaches the graft union. In susceptible scions infected with yellow bud mosaic, the virus moves upward into the scaffold slowly, infecting buds and causing symptoms as it progresses. In the case of prunus stem pitting, the virus moves up the tree slowly and causes pitting in the sapwood, but affected trees usually die before the virus reaches the lowest branches.

Tomato ringspot virus management requires a combination of tactics: the use of clean planting stock, planting resistant rootstocks where possible, removing diseased trees, controlling the nematode vector, and strict sanitation to avoid spreading nematodes with infested soil.

When disease develops in the orchard, remove the affected trees and adjacent trees from the next two rows, which may already be infected with the virus. If you do not remove the stumps immediately, kill any suckers that sprout. This prevents the roots from staying alive and supporting the nematode vector. Take care to avoid moving infested soil when you remove the trees from the orchard. Leave the ground fallow for 2 years to allow all remaining root fragments and nematodes to die out. Control weeds during the fallow period because they may host both the nematode and the virus. Fumigate the soil before replanting, or replant with resistant rootstock (Colt may have some resistance). If several sizable areas within a block are affected, it probably is best to replace the whole block.