How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Plant parasitic nematodes are microscopic roundworms that live in soil and plant tissues. They feed on plants by puncturing and sucking the cell contents with a spearlike mouthpart called a stylet. Of the several genera of plant parasitic nematodes detected in California orchard soils, lesion and root knot nematodes are considered to be important factors in limiting plant growth. Dagger nematode can reduce growth, but is more important as a virus vector. Pin nematode is common, but effects on cherry have not been studied and it is not considered a pathogen on other stone fruits.

DAMAGE

Damage caused by nematodes is likely to become evident during the first year after planting. Feeding by nematodes can impair root functions such as uptake of nutrients and water. Lesion nematodes penetrate into the roots and cause damage by feeding and tunneling through the root 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. However, X. americanum is more important on stone fruit trees as a vector of the cherry rasp leaf virus, which causes raspleaf disease, and strains of tomato ringspot virus, which cause yellow bud mosaic, cherry mottle leaf, and Prunus stem pitting diseases. These virus diseases can reduce the productivity of the trees significantly, and infected trees may eventually die. Feeding by root knot nematodes causes swellings of the entire root, which impairs normal root functions.

SYMPTOMS

Symptoms described below are indicative of a nematode problem, but are not diagnostic as they could result from other causes as well. Symptoms of a nematode infestation are reduced vegetative vigor and fruit yield, and unevenly sized trees. Heavily infested trees are more susceptible to moisture stress. Lesion nematodes may cause reddish brown lesions on roots that later turn dark and ultimately black. Root knot nematode produces characteristic galls (swellings) on roots. Symptoms of dagger nematode infestation include reduced tree growth and vigor. If the tree is infected with cherry rasp leaf virus, characteristic enations, which are distorted tissue growths, develop on the underside of leaves. Affected leaves have normal color, but are deformed and initially found on the lower parts of the tree. If the strain of tomato ringspot virus that causes yellow bud mosaic is involved, infected trees produce bare limbs, small leaves, and enations adjacent to the midrib on the underside of leaves. Cherry mottle leaf infections are usually symptomless except on highly susceptible sweet cherry cultivars that exhibit chlorotic mottling, distortion, puckering of younger leaves, and small fruits that ripen late. Trees infected by the strain of tomato ringspot virus that causes stem pitting exhibit symptoms of delayed budbreak, yellow leaves, a wilted appearance early in summer, and reddish purple leaves by late summer.

FIELD EVALUATION

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

However, if nematode analysis has not been done, take soil samples to a diagnostic laboratory for identification. Divide the field into sampling blocks of not more than five 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 smaller roots when possible. Mix the subsamples thoroughly and make a composite sample of about 1 quart (1 liter) 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 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 1 to 2 years (3 to 4 years if lesion nematodes are present). Do not use cover crops that are known hosts of nematodes that damage 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. Both Mazzard and Mahaleb are susceptible to cherry rasp leaf virus and to the lesion nematode, Pratylenchus vulnus. Colt rootstock is the most susceptible to P. vulnus. Mazzard is immune to M. incognita and resistant to M. javanica. (Immune rootstocks are not attacked by nematodes, whereas resistant or nonhost rootstocks may be invaded by the nematodes and show damage, but do not allow population increases.) Mahaleb is resistant to M. incognita and susceptible to M. javanica. Stockton Morello is immune to M. incognita and susceptible to P. vulnus. Contact your local farm advisor to discuss rootstock options.

When to treat. Trees planted on fumigated orchard sites generally show improved growth and yields compared to those on nonfumigated sites. Preplant fumigate in fall when soils are dry and warm. For detailed information on soil fumigation, see IPM for Apples and Pears , UC/ANR Publication 3340.

Threshold levels of nematode pests for postplant treatment have not been established. Yield and vigor increases may not become evident for 6 to 18 months following treatment with fenamiphos. To help determine the effectiveness of postplant treatments, leave several trees or rows of trees untreated for comparison with treated trees.

PUBLICATION

UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440
Nematodes
B. B. Westerdahl, Nematology, UC Davis
Acknowledgment for contributions to nematode section:
U. C. Kodira, Plant Pathology, UC Davis

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