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 yellow bud mosaic virus to almond trees.

RESISTANT ROOTSTOCKS

Rootstocks for almonds differ in response to various plant-parasitic nematodes. Nemaguard peach rootstock, almond-nemaguard hybrids, and Marianna 2624, which are resistant or immune to most common and injurious root knot nematodes, are susceptible to ring nematode and root lesion nematode, common pests in old orchard and vineyard soils. Peach-almond hybrid rootstocks are particularly susceptible to ring nematodes 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 rootstock has ring nematode tolerance similar to Lovell. Other peach rootstocks (S-37, rancho resistant) offer resistance to one root knot species but not to others. Almond rootstock is rated susceptible to root knot, root lesion, and ring nematodes. Use of resistant rootstocks may be limited by soil and horticultural considerations.

MONITORING and WHEN TO TREAT
When planting or replanting an orchard, be sure to sample for nematodes, especially if the land was previously an orchard or a vineyard. If sampling indicates that any of the pest nematodes of almond are present, plan to preplant fumigate using the following time schedule:

Summer/Fall: Remove trees or vines, destroy residues, and deep cultivate to remove residual roots and break up cultivation pans or soil layering.

Winter/Spring: Fallow or plant grains.

Spring/Summer: Level (if necessary), cultivate, and do other operations required for next year's planting. Dry the soil.

Late Summer/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. Do not apply chloropicrin or Telone II after mid-November.

Winter/Spring: Observe waiting period on fumigant container label; plant young trees on resistant rootstock if root knot nematode is present.

Make a solid application of methyl bromide or Telone II 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 the orchard has soils that are not conducive to the development of high populations 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.

Apply nematicides at the rates listed in the table below. 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.

To determine application rates:

Using the soil and moisture chart, determine the number code based on your soil type and its percent moisture. Use the top number if treating with 1,3-D and the bottom number for methyl bromide treatments.
In the second table, use the number code to determine application rate. For example: If your soil is a loamy sand with 5% moisture, the number codes are 1 and 8. If using methyl bromide, the application rates for soil in the temperature range of 40–77°F are 200 lb/acre or 400 lb/acre, depending on the type of control desired.

Number code from soil and moisture chart	Soil temp. (°F)	Application rates (lb/Ac)
		1,3-D Nematicides *(92% 1,3-D)²
		A	B
1	40–77	50–100	350
2	40–77	75–125	350
3	50–77	100–150	350
4	50–77	125–175	—¹
5	60–68	150–200	—¹
6	60–68	200–250	—¹
7	60–68	250–300	—¹
		Tarped Methyl Bromide (98% a.i.)³
		C	D
8	40–77	200	400
9	40–77	250	400
10	40–77	300	500
11	40–77	350	—¹
12	50–77	400	—¹
13	50–77	500	—¹

KEY
A.	Controls soil pests, such as nematodes outside roots, throughout the surface 2.5 feet of soil.
B.	Controls pests or nematodes in smaller (less than 2 in. diameter) roots throughout the surface 5 feet of soil.
C.	Controls pests or nematodes in smaller (less than 2 in. diameter) roots throughout the surface 5 feet of soil.
D.	Eradicative treatment to control nematode virus vectors throughout the surface 5 feet of soil.

1	If soil moisture is this high, maximum legal rates are not effective.
2	Permit required from county agricultural commissioner for purchase or use.
3	Any use of methyl bromide after Dec. 31, 2004 must be allowed under a critical use exemption. Additional chloropicrin may be present.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Nematodes
M. V. McKenry, Kearney Agricultural Center, Parlier

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How to Manage Pests

UC Pest Management Guidelines

Almond

Nematodes

Scientific names: Root knot nematode: Meloidogyne spp. Root lesion nematode: Pratylenchus vulnus Ring nematode: Mesocriconema (=Criconemella) xenoplax Dagger nematode: Xiphinema americanum

DESCRIPTION OF THE PESTS

RESISTANT ROOTSTOCKS

PUBLICATION

Scientific names:
Root knot nematode: Meloidogyne spp.
Root lesion nematode: Pratylenchus vulnus
Ring nematode: Mesocriconema (=Criconemella) xenoplax
Dagger nematode: Xiphinema americanum