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OSU Nematode Testing Service - Pratylenchus on Oregon Crops

PRATYLENCHUS DAMAGE LEVELS FOR OREGON CROPS: A LITERATURE SURVEY.

DRAFT: JANUARY 1998

Contents of this survey:
Host ranges
Suppressive crops, poor hosts, and non-hosts
Damage levels
Peppermint
Forage legumes
Grain legumes
Grasses
Grains
Small fruits
Pomes
Stone fruits
Nuts
Grapes
Vegetables
Miscellaneous crops
Flowers
Literature cited

Root-lesion nematodes (Pratylenchus spp.) create holes in root cells and crawl inside. They move longitudinally through the cortex, piercing, sucking, and leaving behind a trail of cell-killing metabolites and eggs. Eggs deposited in both roots and soil hatch, and the life cycle continues through four molts to sexual maturity and reproduction. Root cell death results in brown longitudinal root lesions, which begin on one side but may eventually encircle a root and thereby girdle it. The overall effect is a weak, shallow root system with extensive dead areas. Pratylenchus spp. are disseminated by transportation of soil or plant parts and by surface or irrigation water (Evans et al. 1993). Pratylenchus species included in this survey are limited to those detected on Oregon agricultural crops: P. crenatus, P. neglectus, P. penetrans, and P. thornei.

Host Ranges

Pratylenchus species tend to have wide host ranges.
Pratylenchus crenatus
often occurs together with P. penetrans. It has been recorded from pear, sunflower, alfalfa, graminoids, and natural grassland (Kleynhans et al. 1996).
Pratylenchus neglectus
is primarily a parasite of pasture legumes and grains (Cook and Yeates 1993). It has also been recorded around temperate fruit crops, alfalfa, peppermint, and pasture and natural grassland plants (Kleynhans et al. 1996).
Pratylenchus penetrans
parasitizes nearly 400 plant species including many important crops (Evans et al. 1993). It is probably the most widely distributed and economically important species in the genus, and it interacts with with various fungi in disease complexes of peas, oats, alfalfa, potato, tomato, and strawberry (Kleynhans et al. 1996). It has been recorded around cereals, legumes, temperate fruit, vegetables, sunflower, and natural grassland and forest plants (Kleynhans et al. 1996). It is probably a problem only in cooler temperate climates (Evans et al. 1993). Pratylenchus thornei has been recorded around grasses, sunflower, pear, wheat, alfalfa, potato, and carnation (Kleynhans et al. 1996).
Pratylenchus vulnus
, not included in this survey, has rarely been seen in Oregon. It injures peaches and members of the carrot and pea families.

Suppressive crops, poor hosts, and non-hosts.

Sorghum spp. and their hybrids are possible rotation crops for suppression of P. penetrans in potato production; Tagaetes (marigold) suppresses lesion nematode populations, and some members of the mustard family are comparatively poor hosts (Evans et al. 1993). Agrostis palustris (creeping bentgrass) is a poor host for Pratylenchus penetrans (Sikora 1972). Asparagus is a non-host for P. penetrans (Potter and Olthof 1993).

Damage levels

Most nematode damage numbers listed below are from replicated studies. Those conducted in pots or microplots are indicated. Study conditions may deviate from local Oregon conditions in soil type, climate, moisture, and a host of other factors. Nematode numbers vary seasonally (Ingham and Merrifield 1996). In many of these studies, the season at which samples were taken is not indicated, but in some, Pratylenchus numbers are designated as initial or as final levels. Therefore, these data are presented only to give suggestions of nematode levels at which damage may occur.

If a particular crop is not included in the list, no information was found for that crop. If a Pratylenchus species of concern is not listed under a particular crop, no information was found on the species for that crop. A lack of information does not necessarily imply a lack of damage.

Information relevant to damage is included under specific hosts in some cases in which numbers were not available.

Nematode damage numbers in this survey are expressed in this survey as nematodes/100 grams (g) soil or number of nematodes/100 cubic centimeters (cm3 or cc) soil. Numbers/100 g soil may be multiplied by 20 to give the number of nematodes/2000 g soil (traditionally designated by the OSU Nematode Testing Lab as one "quart"). Nematode numbers from the OSU Nematology Lab are corrected for soil moisture.

Damage levels vary with species, climate, soil type, and host crop, but a density of one to two nematodes/g soil at planting is a reasonable guide; damage levels range from 50 to 1800/100 g soil (Potter and Olthof 1993), or 1000 to 36,000/2000 g soil.

Nematode numbers/100 cm3 soil can provide a rough estimate of numbers/100 g soil corrected for dry weight but should be divided by the soil bulk density for accuracy. Bulk densities of clay, clay loam, and silt loam surface soils range from about 1.0 to 1.6 g/cm3, and those of sands and sandy loams range from about 1.2 to 1.8 g/cm3 (Buckman and Brady 1969). However, the bulk density of the sample actually processed is dependent upon packing density during measurement. Since bulk densities are not frequently reported in studies in which nematode numbers are expressed on a volume basis, accurate conversion of numbers/100 cm3 to numbers/100 grams soil is not usually possible. Nevertheless, since the variation associated with bulk density conversions is generally less than the variation associated with field sampling, numbers/100 cm3 soil provide an acceptable approximation of numbers/100 grams soil for making management decisions.

Additional information may be added to subsequent editions of this survey.

PEPPERMINT

P. neglectus: Associated with reduced growth of peppermint (Kleynhans et al. 1996).
P. penetrans: One lb. of oil is lost for each 322/g root or 83/100 g soil (Ingham and Merrifield 1996).
P. thornei: Found in an irrigated Columbia Basin, OR mint field previously in wheat (W. T. Cobb, pers. comm.)

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FORAGE LEGUMES

ALFALFA

P. neglectus: Greatest yield reduction was at 800/100 cm3 soil, but damage observed at 200/100 cm3 (Griffin & Jensen 1997). In pots, 200 to 2000/100 cm3 reduced shoot weights of Ranger and Lahontan by 16 to 40%; 200/100 cm3 reduced Ranger by 12 to 38% at 15 to 30o C (Griffin and Gray 1990). Demonstrated to cause establishment losses in pots and to be associated with poorly growing field crops (Cook and Yeates 1993). P. penetrans: In microplots, mean yields were reduced 83% by 167 P. penetrans/100 cm3 soil (Willis and Thompson 1969). In pots, initial populations of 33/100 g soil resulted in 1200/g root and moderate necrosis on "Saranac" and 1080/g root and little necrosis on "Narragansett" after 3 months (Miller 1978). In pots, from 50 to 270 individuals of a mixed population including P. penetrans/100 cm3 soil significantly reduced root weight from 40 to 45% (Chapman 1958). In pots, 194/100 cm3 soil resulted in lower yields (Willis 1976).
P. thornei: Demonstrated to cause establishment losses in pots and to be associated with poorly growing field crops (Cook and Yeates 1993). Found in an irrigated alfalfa field previously in wheat (W. T. Cobb, pers. comm.)

BIRDSFOOT TREFOIL

P. penetrans: < 200/100 cm3 soil (Barker et al. 1976). In microplots, mean yields were reduced 50% by 167 P. penetrans/100 cm3 soil (Willis and Thompson 1969). 

CLOVER

P. neglectus: Damaged clover in Poland (Cook and Yeates 1993).
P. penetrans: In microplots, 166 /100 cm3 soil reduced mean yields of red clover by 73% and of white clover by 93% (Willis and Thompson 1969). In pots, 194/100 cm3 soil reduced yields (Willis 1976). In pots, from 25 to 135 individuals of a mixed population including P. penetrans/100 cm3 soil significantly reduced plant survival by 54 to 70% and root weight from 77 to 84% (Chapman 1958). In pots, initial population of 33/100 g soil on Penobscot red clover resulted in 440/ g root and moderate necrosis after 3 months (Miller 1978). In pots, initial population of 33/100 g soil on Alsike (T. hybridum) resulted in 1220/g root and little root necrosis (Miller 1978).

GRAIN LEGUMES

NAVY BEAN

P. penetrans: Initial populations of 50 to 300 (but not 25)/100 cm3 soil significantly reduced yield and shoot and root weight on Sanilac, Seafarer, and Tuscola but not on Saginaw, Gratiot, and Kentwood (Elliott and Bird 1985).

GRASSES

BROMEGRASS

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 40/ g root and moderate necrosis on Smooth Saratoga bromegrass after 3 months (Miller 1978).

CREEPING BENTGRASS

P. penetrans: In pots, inhibited top growth only when co-inoculated with Meloidogyne naasi (Sikora et al. 1972).

ANNUAL BLUEGRASS

P. crenatus: Has caused damage as a member of mixed populations (Cook and Yeates 1993).

ORCHARDGRASS

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 270/ g root and moderate necrosis after 3 months (Miller 1978).

REED CANARY GRASS
NOTE: REED CANARY GRASS IS A SERIOUS WEED IN THE PACIFIC NORTHWEST.

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 50/ g root and very little necrosis after 3 months (Miller 1978).

RYEGRASS

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 50/ g root and little necrosis on Oregon ryegrass after 3 months (Miller 1978).

SUDAN GRASS

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 40/ g root and very severe necrosis after 3 months (Miller 1978).

TIMOTHY

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 50/ g root and very little necrosis after 3 months (Miller 1978).

WHEATGRASS

P. neglectus: Initial density of 400/100 cm3 soil reduced shoot weights by 22 to 49% and root weights by 26 to 42% (Griffin 1992). Greatest yield reduction was at 800/100 cm3 soil, but damage observed at 200/100 cm3 (Griffin & Jensen 1997).

GRAINS

BARLEY

Pratylenchus spp.: Causes severe damage (Kleynhans et al. 1996).
P. crenatus: At 500/g root in controls at harvest, yield correlated negatively with initial population (Rivoal and Cook 1993).
P. neglectus: 150/100 cm3 soil at sowing decreased grain weight by 9% (Rivoal and Cook 1993). 150/100 cm3 soil significantly reduced root but not shoot or head weight at 20o C but not at 15o or 25o (Umesh and Ferris 1994).
P. thornei: 4/100 cm3 soil decreased grain weight by 10%. (Rivoal and Cook 1993). In pots, 42 and 420/100 cm3 soil decreased ear weight by 26 and 45 %. (Rivoal and Cook 1993).

CORN

Pratylenchus spp.: Causes moderate damage (Kleynhans et al. 1996).
P. penetrans: In pots, 25/100 cm3 soil significantly reduced root growth at 20 and 24 but not 16 and 28o C and top growth at 20o C only; stem diameter was not reduced (Dickerson 1964). In pots, initial populations of 33/100 g soil resulted in 70/g root and little necrosis on "Butter and Eggs" after 3 months (Miller 1978).

OATS

Pratylenchus spp.: Causes moderate damage (Kleynhans et al. 1996). P. crenatus: 33/100 cm3 soil (Barker et al. 1976).
P. penetrans: In pots, initial populations of 33/100 g soil resulted in 150/g root and little necrosis after 3 months (Miller 1978).

RYE

P. penetrans: In pots, initial populations of 33/100 g soil resulted in 220/g root and moderately severe necrosis after 3 months (Miller 1978).

WHEAT

Pratylenchus spp.: Causes severe damage (Kleynhans et al. 1996).
P. crenatus: Associated with yellowing and stunting of wheat (Kleynhans et al. 1996).
P. neglectus: Relatively weak pathogen on Stephens wheat (Mojtahedi and Santo 1992).
P. thornei: 50 - 100/100 cm3 soil (Rivoal and Cook 1993). In pots, 667/100 cm3 soil caused stunting and chlorosis on "Stephens". 67/100 cm3 caused no noticeable damage (Mojtahedi et al. 1988). Associated with wheat exhibiting unthrifty patches and stunted and chlorotic growth, sometimes in low spots, and in Madsen wheat with intermittent yield problems, in SE Washington (W. T. Cobb, pers. comm.) In Mexico, on wheat cultivars Tobari and Inia, 42, 420, and 4,200 P. thornei/100 cc soil reduced heat weight 26, 45, and 34%, respectively, after 60 days; yields of cultivars Inia, Tobari, Azteca, Norteno, Lerma Rojo, and Siete Cerros on fumigated soils were from 19 to 30% higher than yields on soils with 173-229 P. thornei/100 cm3 soil (Van Gundy et al. 1974).

SMALL FRUITS

CRANBERRY

P. penetrans: 75/100 cm3 soil significantly reduced runner number and root and top weight (Bird and Jenkins 1964).

RED RASPBERRY

P. penetrans: 100/100 cm3 soil at planting; 200 to 800/100 cm3 in established plantings (McElroy 1992). 1000/g root may be found in damaged plantings, and 50/g soil at planting will probably cause significant damage (Brown et al. 1993).

STRAWBERRY

P. penetrans: 15/100 g soil have decreased growth, but sometimes higher levels have no effect (Pscheidt, 1997). 50/100 g soil; damage is greatest on light soils (Brown et al. 1993).

POMES

Pratylenchus spp.: 25 to 150/100 cm3 soil are considered damaging but can vary depending on soil texture, climate, and additional pathogens (Nyczepir and Halbrendt 1993).
P. penetrans: Considered important on fruits in temperate areas (Nyczepir and Halbrendt 1993).

APPLE

P. penetrans: 20 to 50/100 g soil (Barker et al. 1976). Initial population of 15/100 g soil necessary for growth reduction (Nyczepir and Halbrendt 1993).

PEAR

Pratylenchus spp.: Pratylenchus is the only nematode genus considered important to pear production in North America (Nyczepir and Halbrendt 1993).
P. penetrans: Initial population of 30/100 g soil necessary for growth reduction; involved in pear replant problems in the USA and Canada (Nyczepir and Halbrendt 1993).

STONE FRUITS

P. penetrans: Considered important on fruit in temperate areas (Nyczepir and Halbrendt 1993).

CHERRY

P. penetrans: Initial population of 80/100 g soil necessary for growth reduction (Nyczepir and Halbrendt 1993). In NE U.S., reduced yield and shortened productive life of Montmorency cherry on Mazard and Mahaleb rootstocks; parasitized trees were less winter hardy (Nyczepir and Halbrendt 1993).

PEACH

Pratylenchus spp.: All commercial peach rootstocks are susceptible to root-lesion nematodes, but some evidence for resistance has been shown in Rubira, Pisa, Rutgers Red Leaf, Tzim Pee Tao, and in some hybrids of Rutgers Red Leaf X Txim Pee Tao (Nyczepir and Halbrendt 1993).
P. penetrans: 5/100 g soil (Barker et al. 1976). Root impairment results in loss of vigor and yields of mature trees, but P. penetrans' role in orchard replant problems is probably more economically important (Nyczepir and Halbrendt 1993).

PLUM (MYROBALAN)

P. penetrans: Initial population of 320/100 g soil necessary for growth reduction (Nyczepir and Halbrendt 1993).

NUTS

Pratylenchus spp.: 25 to 150/100 cm3 soil are considered damaging but can vary depending on rootstock tolerance, soil texture, climate, additional pathogens; they are primarily a replant problem on walnuts (Nyczepir and Halbrendt 1993).
P. penetrans
: P. penetrans is considered important on nuts in temperate areas (Nyczepir and Halbrendt 1993).

GRAPES

Pratylenchus spp. Several Pratylenchus spp. have been associated with poor growth in grapevines (Brown et al. 1993).

VEGETABLES

ASPARAGUS

P. crenatus: Asparagus is a host for P. crenatus; pathogenicity is unknown (Potter and Olthof 1993).
P. penetrans: Asparagus is a non-host for P. penetrans (Potter and Olthof 1993). In pots, initial populations of 45/100 g soil resulted in 0/ g root, 0% height reduction, and very little necrosis after three weeks (Miller 1978).

BEET (TABLE)

P. neglectus: Causes moderate damage (Potter and Olthof 1993).
P. penetrans: 1800/100 cm3 soil reduced fall yield by 27%; beet is recommended as a fall-maturing crop in soils with up to 600/100 g soil (Potter and Olthof 1974). 600-1800/100 g soil (Barker et al. 1976).

BRUSSELS SPROUTS

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 260-520/g root, 42% height reduction, and severe necrosis after three weeks (Miller 1978).

CABBAGE

P. penetrans: Losses in marketable yields ranged from 17% at 67/100 g to 25% at 1800/100 g soil (Olthof and Potter 1973). 200 to 600/100 g soil (Barker et al. 1976; Potter and Olthof 1993). In pots, initial populations of 45/100 g soil resulted in 180-360 g root, 22% height reduction, and moderate necrosis after three weeks (Miller 1978).

CARROT

Pratylenchus spp.: Threshold range is 30 to 180/100 g soil at planting, with moderate damage at about 100/100 g (Potter and Olthof 1993).
P. crenatus: Taproots are branched and reduced; side roots have lesions and dead tips; above-ground parts are thin and chlorotic (Potter and Olthof 1993).

CAULIFLOWER

P. penetrans: Losses in marketable yields ranged from 19% at 67/100 cm3 soil to 59% at 1800/100 cm3 soil (Olthof and Potter 1973). 200 to 600/100 g soil (Barker et al. 1976; Potter and Olthof 1993).

CELERY

P. penetrans: In pots, fresh weight was decreased 31, 48, and 83% by 61, 313, and 1565 P. penetrans/100 cm3 soil (Towhshend 1962).CORN (SWEET)

P. penetrans: Losses in marketable yields ranged from 30% at 67/100 g to 49% at 1800/100 g soil (Olthof and Potter 1973). 100/100 g soil (Barker et al. 1976). In pots, 25/100 cm3 soil significantly reduced root growth at 20 and 24 but not 16 and 28o C and top growth at 20o C only; stem diameter was not reduced (Dickerson 1964). In pots, initial populations of 33/100 g soil resulted in 70/g root and little necrosis on "Butter and Eggs" after 3 months (Miller 1978).

CUCUMBER

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 630-1260/g root, 40% height reduction, and severe necrosis after three weeks (Miller 1978).

DILL

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 110-220/g root, 30% height reduction, and moderately severe necrosis after three weeks (Miller 1978).

EGGPLANT

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 245-490 g root in "Black Beauty" and 150-300/g root in "Midway Hybrid", 15 to 18% height reduction, and very severe necrosis in both cultivars after three weeks (Miller 1978).

LETTUCE

P. penetrans: Losses in marketable yields ranged from 18% at 67/100 g to 33% at 1800/100 g soil (Olthof and Potter 1973). 1800/100 g soil reduced fall yield by 43% (Potter and Olthof 1974). 200 to 600/100 g soil (Barker et al. 1976; Potter and Olthof 1993). In pots, initial populations of 45/100 g soil resulted in 325-650/g root, 22% height reduction, and moderately severe necrosis after three weeks (Miller 1978).

ONION

P. penetrans: At 7-13o C, < 100/g root caused significant root weight reduction, but > 400 were required to produce injury at 16-25o C (Ferris 1970). Losses in marketable yields ranged from 14% at 67/100 g soil to 71% at 1800/100 g soil (Olthof and Potter 1973). 100/100 g soil (Barker et al. 1976; Potter and Olthof 1993). Cultivars vary in susceptibility, and wild Allium canadense may be more resistant (Ferris 1970).

PARSNIP

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 280-560/g root, 22% height reduction, and very severe necrosis after three weeks (Miller 1978).

PEA

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 500-1000/g root, 14% height reduction, and very severe necrosis after three weeks (Miller 1978). 100/100 g soil (Barker et al. 1976).

PEPPER

P. penetrans: "California Wonder": In pots, 625/100 cm3 soil reduced top fresh weight by 84% and root fresh weight by 87% (Shafiee and Jenkins 1963). In pots, initial populations of 45/100 g soil resulted in 40-80/g root, 8% height reduction, and severe necrosis after three weeks (Miller 1978). "All Big": In pots, initial populations of 45/100 g soil resulted in 150-300/g root, 33% height reduction, and severe necrosis after three weeks (Miller 1978). "Italian Sweet: In pots, initial populations of 45/100 g soil resulted in 40-80/g root, 8% height reduction, and severe necrosis after three weeks (Miller 1978). "Sweet Banana": In pots, initial populations of 45/100 g soil resulted in 180-360/g root, 8% height reduction, and severe necrosis after three weeks (Miller 1978).

POTATO

P. neglectus: Initial populations of 19 to 188/100 g soil on Russet Burbank suppressed marketable and total numbers and weight of tubers by 19 to 25%. 12/100 g suppressed total number and weight (Olthof 1990). 150/100 cm3 soil significantly reduced root but not shoot or tuber weight at 15o C but not at 20o or 25o (Umesh and Ferris 1994). Threshold may be lower than for P. penetrans (Brodie et al. 1993).
P. penetrans: Losses in marketable yields ranged from 35% at 67/100 g soil to 43% at 1800/100 g soil (Olthof and Potter 1973). In field plots, initial populations over 10/100 g soil and harvest populations over 72/100 g soil significantly reduced total yield during over two years and marketable yield in one of two years (Olthoff 1987) 1000 to 2000/100 g soil measurably reduce yields (Potter and Olthof 1993). In microplots, initial populations of 38 to 211/100 cm3 soil significantly reduced tuber yields of Kennebec and Superior but not Russet Burbank; Katahdin was insignificantly reduced (Bernard and Laughlin 1976). 100, or 200 to 600,/100 g soil (different experiments) (Barker et al. 1976). In microplots, 185/100 g soil significantly reduced marketable Russet Burbank tubers by 15.7%. Kennebec, Monona, Norchip, superior, and Yukon Gold did not differ significantly from control (Olthof 1983).
P. thornei: Found infrequently; little known about damage.

PUMPKIN

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 440-880/g root, 17% height reduction, and very severe necrosis after three weeks (Miller 1978).

RADISH

P. penetrans: In pots, initial populations of 45/100 g soil resulted in 300-600/g root, 57% height reduction, and very severe necrosis after three weeks (Miller 1978).

SPINACH

P. penetrans: 1800/100 g soil reduced fall yield by 21% (Potter and Olthof 1974) 600 to 1800/100 g soil (Barker et al. 1976; Potter and Olthof 1993).

TOMATO

P. penetrans: Unspecified cultivars: In pots, initial populations of 36/100 g soil appeared to stimulate fruit production, but 201, 458, and 1436/100 g suppressed fruit production by 38% and weight by 44% (Potter and Olthof 1977.) In pots, 8 to 55 P. penetrans/100 g soil at planting significantly reduced subsequent growth of tomato seedlings 20 to 66% after 2 months (Miller 1975). Beefeater: In pots, initial populations of 45/100 g soil resulted in 200-400/g root, 54% height reduction, and severe necrosis after five days (Miller 1978). Bonny Best: In pots, initial populations of 45/100 g soil resulted in 21 in the 0.1-0.2 g root system, 22% height reduction, and very severe necrosis after five days (Miller 1978). Fantastic: In pots, initial populations of 45/100 g soil resulted in 75-150/g root, 32% height reduction, and very severe necrosis after five days (Miller 1978). Fireball: In pots, initial populations of 45/100 g soil resulted in 115-230/g root system, 30% height reduction, and severe necrosis after five days (Miller 1978). Hybrid 980: In pots, initial populations of 45/100 g soil resulted in 65-130/g root, 21% height reduction, and moderate necrosis after five days (Miller 1978). Heinz 1350: In pots, initial populations of 45/100 g soil resulted in 105-210/g root, 30% height reduction, and severe necrosis after five days (Miller 1978). Red Plum: In pots, initial populations of 45/100 g soil resulted in 205-410/g root, 30% height reduction, and moderate necrosis after five days (Miller 1978). Wonder Boy: In pots, initial populations of 45/100 g soil resulted in 75-150/g root system, 15% height reduction, and very severe necrosis after five days (Miller 1978).

MISCELLANEOUS CROPS

RAPE

P. neglectus: Moderate damage (Evans et al. 1993).

GINSENG

Pratylenchus spp.: Growers in Ontario, Canada have zero tolerance (R. Releeder, pers. comm.)

FLOWERS

CARNATION

P. neglectus: Associated with rapid decline (Kleynhans et al. 1996).

DAFFODIL

P. penetrans: 0.2 to 1.0/100 g soil (Barker et al. 1976).

FOXGLOVE

P. penetrans: < 10/100 g soil (Barker et al. 1976).

LITERATURE CITED

Barker, K. R., and Olthof, T. H. A. 1976. Relationships between nematode population densities and crop responses. Annual Review of Phytopathology 14: 327-353.

Bernard, E. C., and Laughlin, C. W. 1976. Relative susceptibility of selected cultivars of potato to Pratylenchus penetrans. Journal of Nematology 8:239-242.

Bird, G. W., and W. R. Jenkins. 1964. Occurrence, parasitism, and pathogenicity of nematodes associated with cranberry. Phytopathology 54:677-680.

Brodie, B. B., Evans, K., and Franco, J. 1993. Nematode parasites of potatoes, pp. 87-132 in: Evans, K., Trudgill, D. L., and Webster, J. M., eds. Plant Parasitic Nematodes in Temperate Agriculture. CAB International, Wallingford, England.

Brown, D. J. F., Dalmasso, A., and Trudgill, D. L. Nematode pests of soft fruits and vines. pp. 427-462 in: Evans, K., Trudgill, D. L., and Webster, J. M., eds. Plant parasitic nematodes in temperate agriculture. CAB International, Wallingford, England.

Buckman, H. O., and Brady, N. C. 1969. The nature and properties of soils. Macmillan, New York. 653 pp.

Chapman, R. A. 1958. The effect of root-lesion nematodes on the growth of red clover and alfalfa under greenhouse conditions. Phytopathology 48:525-530.

Cook, R., and Yeates, G. W. 1993. Nematode pests of grassland and forage crops. pp. 305-350 in: Evans, K., Trudgill, D. L., and Webster, J. M., eds. Plant Parasitic Nematodes in Temperate Agriculture. CAB International, Wallingford, England.

Dickerson, O. J., Darling, H. H., and Griffin, G. D. 1964. Pathogenicity and population trends of Pratylenchus penetrans on potato and corn.

Elliott, A. P. and Bird, G. W. 1985. Pathogenicity of Pratylenchus penetrans to navy bean (Phaseolus vulgaris L.) Journal of Nematology 17:81-85.

Evans, K., Trudgill, D. L., and Webster, J. M., eds. 1993. Plant Parasitic Nematodes in Temperate Agriculture. CAB International, Wallingford, England. 648 pp.

Ferris, J. M. 1970. Soil temperature effects on onion seedling injury by Pratylenchus penetrans. Journal of Nematology 2:248-251.

Griffin, G. D. 1992. Pathological effects of Pratylenchus neglectus on wheatgrasses. Journal of Nematology 24:442-449.

Griffin, G. D., and Gray, F. A. 1990. Biology and pathogenicity of Pratylenchus neglectus on alfalfa. Journal of Nematology 22:546-551.

Griffin, G. D., and Jensen, K. B. 1997. Differential effects of Pratylenchus neglectus populations on single and interplantings of alfalfa and crested wheatgrass. Journal of Nematology 29:82-89.

Ingham, R., and Merrifield, K. 1996. A guide to nematode biology and management in mint. IPPC Publication 996, September 1996. Oregon State University, Corvallis, OR 97331-2915.

Kleynhans, D., Van den Berg, E., Swart, A., Marias, M., and Buckley, N. 1996. Plant nematodes in South Africa. Agricultural Research Council, South Africa.

McElroy, F. D. 1977. Effect of two nematode species on establishment, growth, and yield of raspberry. Plant Disease Reporter 61:277-279.

McElroy, F. D. 1992. A plant health care program for brambles in the Pacific Northwest. Journal of Nematology 24: 457-462.

Miller, P. M. 1975. Effect of Pratylenchus penetrans on subsequent growth of tomato plants. Plant Disease Reporter 59:866-867.

Miller, P. M. 1978. Reproduction, penetration, and pathogenicity of Pratylenchus penetrans on tobacco, vegetables, and cover crops. Phytopathology 68:1502-1504.

Mojtahedi, H., and Santo, G. S. 1992. Pratylenchus neglectus on dryland wheat in Washington. Plant Disease 76:323.

Mojtahedi, H., Santo, G. S., and Kraft, J. M. 1974. First report of Pratylenchus thornei on dry land wheat in Washington state. Plant Disease 72:175.

Mountain, W. B., and Z. A. Patrick. 1959. Canadian Journal of Botany 37:459-470.
Nyczepir, A. P.,and Halbrendt, J. M. 1993. Nematode pests of deciduous fruit and nut trees. pp. 381-425 in: Evans, K., Trudgill, D. L., and Webster, J. M., eds. Plant Parasitic Nematodes in Temperate Agriculture. CAB International, Wallingford, England.

Nickle, W. R., ed. 1984. Plant and Insect Nematodes. Marcel Dekker, Inc., New York. 952 pp.

Olthof, Th. H. A., and Potter, J. W. 1973. The relationship between population densities of Pratylenchus penetrans and crop losses in summer-maturing vegetables in Ontario. Phytopathology 63:577-583.

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