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How to Manage Pests

UC Pest Management Guidelines


Apricot

Nematodes

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

(Reviewed 11/07, updated 2/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Nematodes are microscopic roundworms that live in diverse habitats. Plant parasitic nematodes live in soil and plant tissues and feed on plants by puncturing and sucking the cell contents with a spearlike mouthpart called a stylet.

DAMAGE

Damage caused by nematodes is likely to first become evident during the first year after planting. Feeding by nematodes can impair root functions such as uptake of nutrients and water. Root lesion nematodes penetrate into the roots and cause damage by feeding and migrating through the cortical tissues. Dagger nematodes feed from outside the roots, but can reach the vascular tissues with their long stylet and are capable of reducing vigor and yield of trees. Xiphinema americanum also transmits strains of tomato ringspot virus to apricots, but the disease is less severe and the symptoms less obvious than on peaches and almonds. Feeding by ring nematode increases the incidence of trees affected by bacterial canker (Pseudomonas syringae). Feeding by root knot nematode produces root galls, which disrupt root functions.

SYMPTOMS

The symptoms described below are indicative of a nematode problem but are not diagnostic as they could result from other causes as well. Lack of vigor, small leaves, dieback of twigs, and yield reduction are typical symptoms of nematode damage. Orchards infested with ring nematode may exhibit symptoms of bacterial canker and trees with root knot nematodes may have galls on roots.

FIELD EVALUATION

It is critical to know the nematode species present and to estimate their population to make management decisions. If a previous orchard or crop had problems caused by nematodes that are also listed as pests of apricots, expect population levels to be high enough to cause damage to the young trees.

If nematode species have not previously been identified, take soil samples and send then to a diagnostic laboratory for identification. Divide the field into sampling blocks of not more than 5 acres each that are representative of cropping history, crop injury, or soil texture. Within each block, take several subsamples randomly from the frequently wetted zones at the edge of the tree canopy. Take samples from within the root zone (6 to 36 inch depth) and include some feeder roots when possible. Mix the subsamples thoroughly and make a composite sample of about 1 quart for each block. Place the samples in separate plastic bags, seal them and place a label on the outside with your name, address, location, and the current/previous crop and the crop you intend to grow. Keep samples cool (do not freeze), and transport as soon as possible to a diagnostic laboratory. Contact your farm advisor for more details about sampling, to help you find a laboratory for extracting and identifying nematodes, and for help in interpreting sample results.

MANAGEMENT

Cultural practices. Before fumigating, remove old trunks and large roots brought up by ripping and fallow or plant green manure cover crops for 2 to 4 years. Do not use cover crops that are known hosts of nematodes that feed on the rootstock you plan to plant; contact your farm advisor for additional information. Use certified nematode-free rootstocks or seedlings to establish new orchards. When the orchard is developed, use procedures that improve soil tilth and drainage to help reduce nematode damage.

Rootstock selection. Use certified nematode-free rootstocks. Among peach rootstocks, Nemaguard is known to be resistant to root knot nematodes, but it is susceptible to ring and root lesion nematodes. Lovell is somewhat resistant to ring nematode but susceptible to root knot and root lesion nematodes. The apricot rootstock Royal (Blenheim) seedling is resistant to root lesion nematode but susceptible to ring nematode. Most apricot rootstocks are nonhosts for root knot nematode. Plum rootstocks Myrobalan 29C and Marianna 2624 are resistant to root knot nematode, but susceptible to ring and root lesion nematode. Contact your local farm advisor for additional information on rootstock selection.

When to treat. Trees planted on fumigated orchard sites are generally known to have improved growth and yields compared to those on nonfumigated sites. Preplant fumigate in fall when soils are dry and warm.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
Consider information relating to water quality when choosing a pesticide.
 
PREPLANT
A. 1,3-DICHLOROPROPENE*
  (Telone II) 33.7 gal/broadcast acre 5 days 0
  COMMENTS: This restricted use product is applied only by professional fumigation companies. It is effective at 33.7 gal/acre rate if applied to dried sandy soils or sandy loam soils with no more than 12% soil moisture content anywhere in the surface 5 feet of soil profile. In California the applications must be applied to soils having a moist surface; this task is difficult to achieve without use of sprinklers unless there is a fortunate rainfall. Do not flood irrigate prepared lands to achieve this surface moisture requirement. Broadcast apply where nematode resistance is unavailable for prevailing nematodes. Strip applications are permitted at higher treatment rates and effective where resistant rootstocks are available, the clay loam soil profile contains no more than 19% soil moisture, the field has been pre-ripped to 4- or 5-foot depth, and the delivery shank is winged to limit off-gassing. Fumigants such as 1,3-dichloropropene are a source of volatile organic compounds (VOCs), but minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available..
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Apricot
UC ANR Publication 3433
Nematodes
B. B. Westerdahl, Nematology, UC Davis
Acknowledgment for contributions to Nematodes:
U. C. Kodira, Plant Pathology, UC Davis

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