Nematodes

There are three major species of nematodes affecting almonds: root knot, root lesion, and ring. The dagger nematode is also common and is capable of transmitting Tomato ringspot virus, causing yellow bud mosaic disease on almond trees.

Rootstocks for almonds differ in response to various plant-parasitic nematodes.

• Nemaguard and Guardian peach rootstocks, almond-Nemaguard hybrids (including Hansen 536, Nickels, Cornerstone, Bright's and Titan), and Marianna 2624 are resistant or immune to most common and injurious root-knot nematodes. Other hybrid rootstocks, including Viking, Atlas, Empyrean 1, Cadaman (a.k.a. Avimag) and Rootpac R are also considered to be immune to root-knot nematode.
• Peach-almond hybrid and most plum or plum hybrid rootstocks, including Krymsk 86, are particularly susceptible to ring nematode and the bacterial canker complex.
• Lovell peach rootstock is susceptible to root knot and root lesion nematodes but is more tolerant to ring than Nemaguard.
• Viking and Guardian rootstocks have ring nematode tolerance similar to Lovell.
• Almond rootstock is rated susceptible to root knot, root lesion, and ring nematodes.

When planting or replanting an orchard, be sure to sample for nematodes, especially if the land was previously an orchard or a vineyard. When sampling the soil:

• Use a soil probe or auger for best results.
• Discard the top few inches of soil. The majority of your sample should be from 4 -24 inches deep because nematodes live where the roots are.
• Pool together samples from several areas of the field because nematode populations can be spotty.

If sampling indicates that any of the pest nematodes of almond are present, plan to preplant fumigate using the following time schedule:

• Summer to Fall: Remove trees or vines, destroy residues, and deep cultivate to remove residual roots and break up cultivation pans or soil layering.
• Winter to Spring: Fallow or plant grains.
• Spring to Summer: Level (if necessary), cultivate, and do other operations required for next year's planting. Dry the soil.
• Late Summer to Early Fall: Rip the soil. You will be required to have surface moisture if applying Telone II. Fumigate preferably in September or October but before November 15. Fumigants are most effective in warm, dry soils. Efficacy is reduced and danger of damage to newly planted trees is increased if chloropicrin or 1,3 dichloropropene (Telone II) is applied after mid-November.
• Winter to Spring: Observe waiting period on fumigant container label; plant young trees on resistant rootstock if root-knot nematode is present.

Make a solid or strip application of Telone II or Telone C-35 if the rootstock to be used has no resistance to ring nematode (Mesocriconema xenoplax) or root lesion nematode (Pratylenchus vulnus) and sampling indicates either of these species is present. A solid application, when done properly, can provide control for up to 6 years.

If sampling indicates that only root-knot nematode is present, or if the orchard has soils that are not conducive to the development of high numbers of ring nematode, or the rootstock being used is resistant to these nematodes, a strip or spot fumigation can be made. Strip or spot applications provide about 6 months of control.

Formulations with chloropicrin may be used where other diseases are present, or because chloropicrin's odor helps to indicate the presence of the gas.

• Use the highest rate recommended for the soil conditions within the profile. For example, if a soil has a loamy sand surface layer with 5% soil moisture and a subsurface loam layer with 10% moisture, use the higher rate given for the loam.
• Do not plant for one month after tarps have been removed. If soils become cold (below 50°F) soon after treatment, an additional 30- to 60-day waiting period before planting may be necessary.
• Observe the waiting period on the fumigant container label, then plant young trees on resistant rootstocks, when available.