Host Status of Herbaceous Perennial Ornamentals to the Northern Root Knot Nematode


By Dr. James A. LaMondia
Department of Plant Pathology and Ecology
The Connecticut Agricultural Experiment Station
Valley Laboratory
153 Cook Hill Rd.
Windsor, CT 06095

Telephone: (860) 683-4982 Fax: (860) 683-4987

Perennial herbaceous ornamentals are a rapidly expanding segment of the floriculture and nursery industry. Herbaceous perennials are a diverse group of about 2,500 species in about 500 genera with annual gross receipts of approximately $1 billion in the United States alone.

The northern root-knot nematode, Meloidogyne hapla, is the most important nematode pathogen affecting a wide range of flowering herbaceous perennial ornamentals in the major market area of the northern United States and Canada. Perennials are propagated by seed, division, and cuttings. Vegetative methods of propagation such as division are often easier and may produce better, more uniform plants as well as reducing variation within cultivars. Unfortunately, vegetative propagation may result in increased spread and distribution of plant-parasitic nematodes. M. hapla is of particular concern for the major market area of the northern United States and Canada, as this species can readily over-winter and increase in number over time on perennials in these areas.

The concept of damage threshold levels may not apply to nematodes on perennials. Low initial nematode densities may greatly increase on susceptible perennial hosts after the planting year and may cause damage over time. Because of this, control of root-knot nematodes in perennial ornamentals presents a particular challenge. The lack of nematicide management options requires nursery and landscape nematode management programs based on sanitation and rotation. Sanitation, accomplished by identifying and eliminating M. hapla-infested planting stock, and rotation with nonhost species can be effective, especially for field-grown perennials, although successful use of rotation requires knowledge about the host status of a large number of plant species. Much of this information has not previously been available. The objective of this report was to evaluate the host suitability of common perennial ornamentals grown in the Northeast to M. hapla.

To do this, perennial ornamentals supplied as 1-2 year-old potted plants or bare root plants were grown in the greenhouse in pots, inoculated with nematodes, and host status determined. 'Rutgers' tomato plants were grown for 2 months from seed and used as nematode-susceptible controls. Meloidogyne hapla inoculum consisted of a mixture of isolates originally recovered from lettuce in New York and strawberries or cranesbill geranium in Connecticut. Eggs were produced on tomato in the greenhouse and extracted with NaOCl. A suspension of 10,000 or 20,000 eggs and second-stage juveniles was placed in four holes per pot for 700 and 1,400 cm3 pots, respectively. Five to seven replicate pots of each plant species were infested and three uninfested plants served as controls.

Plants were grown in the greenhouse on a peat bed for two months. When galls and egg masses were apparent on nematode-susceptible tomato controls, roots of test plants were washed free of soil and rated for galls. Root galling was rated on a 1-4 scale, as follows: 1 = no galls; 2 = 1-10 galls; 3 = 11-100 galls; and 4 = >100 galls per root system. In some cases, such as when small root galls were present on fine roots, the roots were soaked in dilute phloxine B to aid in the identification of egg masses. Gall ratings were subjected to the nonparametric Kruskal-Wallis test and analysis of variance. Means were separated by the LSD technique.

Results are presented in the following table. The identification of species or cultivars resistant to M. hapla is an important first step in nematode control by rotation as a considerable percentage of perennial ornamentals are field-grown in nurseries. In our experiments, rotation with a few M. hapla-resistant species has been a successful means of root-knot control in infested field soils (LaMondia, unpubl.). Rotation may also be of use to landscapers and home gardeners planting or replanting in areas infested with M. hapla. The long-term effects of nematode infection on herbaceous perennial plant growth and performance remain to be determined.

Galling response of perennial ornamentals grown in media infested with Meloidogyne hapla after 2 months under greenhouse conditions. J. A. LaMondia, Dept. Plant Pathology & Ecology, CAES Valley Lab., Windsor CT

Genus species Cultivar Common name a Gall rating b literature
Acanthus spinosissiums --c bears breeches 4.0 NT
Achillea sp. Coronation gold yarrow 1.0 +
Aconitum arendsii -- monkshood 4.0 +
Adenophora confusa ladybells 3.6 NT
Ajuga reptans Burgundy glow bugleweed 4.0 +
Alchemilla mollis1. Improved form lady's mantle 7 NT
Althea rosea Chater's doubles hollyhock 1.7 +
Anchusa azurea Dropmore alkanet 3.8 -
Anemone sylvestris Queen Charlotte windflower 4.0 -
Aquilegia sp. Blue star columbine 2.6 +
Arabis caucasia Compinkie rockcress 1.5 -
Artemisia sp. Silver mound wormwood 4.0 +
Asclepias tuberosa butterfly weed 1.0 -
Aster novae-angliae September ruby aster 1.0 +
Aster novae-angliae Harrington's pink aster 1.0 +
Astilbe x arendsii Peach blossom feather flower 4.0 -
Astrantia major Rose Symphony masterwort 4.0 NT
Belamcanda chinensis -- blackberry lily 1.0 -
Boltonia asteroides Pink Beauty Bolton’s aster 4.0 -
Campanula poscharskyana -- bell flower 4.0 +
Centranthus ruber Albus valerian 4.0 -
Chelone obliqua -- turtlehead 1.0 -
Chrysanthemum coccineum Giant hybrids painted daisy 3.6 +
Chrysanthemum x superbum Polaris Shasta daisy 3.0 +
Chrysanthemum x superbum Exhibition Shasta daisy 1.0 +
Chrysanthemum parthenium -- feverfew 2.7 -
Cimicifuga acerina -- fairy candles 4.0 +
Cimicifuga dahurica - -- fairy candles 4.0 +
Cimicifuga simplex White pearl fairy candles 4.0 +
Clematis sp. Hagley hybrid clematis 4.0 +
Coreopsis verticillata Moonbeam tickseed 4.0 +
Delphinium grandiflorum Blue mirror delphinium 3.2 +
Dianthus barbatus Indian carpet sweet william 1.0 +
Dicentra sp. Alba bleeding heart 2.8 -
Digitalis ambigua -- foxglove 1.4 +
Digitalis purpurea Excelsior hybrids foxglove 1.0 +
Doronicum sp. Magnificum leopardbane 2.3 +
Echinacea purpurea Bright Star purple coneflower 1.0 -
Echinops bannaticus Taplow Blue globe thistle 1.5 -
Epimedium versicolor Sulphureum yellow barrenwort 1.0 NT
Filipendula venusta Venusta magnifica meadowsweet 1.8 -
Gaillardia x grandiflora- Goblin blanket flower 1.0 -
Gentiana sp. Benichidori gentian 3.6 -
Geranium dalmaticum -- cranesbill 3.0 -
Geranium x magnificum -- cranesbill 3.8 -
Geranium x oxonianum Thurstonianum cranesbill 3.7 -
Helenium autumnale Brilliant sneezeweed 1.0 -
Helicotrichon sempervirens -- blue oat grass 2.0 NT
Heliopsis helianthoides Karat orange sunflower 4.0 -
Hemerocallis sp. Bright Banner daylily 1.5 +
Hypericum polyphyllum -- St. John's wort 3.4 +
Iris germanica Afternoon delight bearded iris 4.0 +
Iris pumila Elfin queen dwarf iris 1.6 +
Iris siberica Maranantha siberian iris 1.0 +
Lathyrus latifolis -- sweet pea 2.7 +
Lavandula angustifolia Munstead dwarf lavender 3.0 +
Liatris scariosa White spires gay feather 1.0 +
Ligularia dentata Desdemona strain senecio 4.0 NT
Liriope muscari Variegata lilyturf 1.0 NT
Lithosperum diffusa Grace Ward lithodora 1.0 -
Lobelia cardinalis Complement scarlet cardinal flower 4.0 +
Lupinus sp. Russell hybrids lupinus 3.0 +
Lycopersicon esculentum Rutgers tomato 4.0 +
Lysimachia clethroides -- circle flower 3.2 +
Lythrum sp. Morden's pink purple loosestrife 4.0 -
Malva alcea Fastigiata rose mallow 2.4 -
Malva moschata Alba musk mallow 1.7 -
Miscanthus sinensis Silberfeder silver feather 4.0 NT
Monarda didyma Cambridge scarlet bee balm 1.0 -
Myosotis alpestris Indigo Blue forget-me-not 1.0 -
Pachysandra procumbens -- alleghany spurge 1.0 +
Pachysandra terminalis -- pachysandra 2.4 +
Papaver orientale Carousel oriental poppy 1.0 +
Penstemon digitalis Husker Red beard tongue 1.0 +
Perovskia atriplicifolia -- russian sage 3.8 NT
Phlox paniculata Fairest one garden phlox 1.0 +
Phlox stolonifera Bruce's white creeping phlox 1.0 +
Physostegia virginiana Summer Snow false dragonhead 1.2 -
Polemonium reptans Firmament Jacob's ladder 2.0 -
Potentilla nepalensis Miss Wilmott cinquefoil 3.0 +
Primula x polyanthus Crescendo mix primrose 1.0 +
Rudbeckia sp. Gold drop coneflower 1.0 -
Salvia azurea Grandiflora meadow sage 2.3 +
Salvia haematodes -- meadow sage 4.0 +
Salvia jurisicii -- meadow sage 3.4 +
Sanguisorba obtusa -- Japanese burnet 3.4 -
Scabiosa caucasica Fama pincushion flower 4.0 -
Sidalecea hybrida Party Girl miniature hollyhock 1.0 +
Solidago sphacelata Golden Fleece goldenrod 1.0 -
Stachys byzantina Lantana lamb's ear 4.0 +
Stokesia laevis Blue Danube stokes aster 1.4 -
Thalictrum speciosissimum -- meadow rue 3.4 -
Thymus serpyllum Album thyme 3.2 -
Tradescantia sp. J.C. Weguelin spiderwort 1.0 +
Trollius hybrida Lemon Queen globe flower 3.0 -
Verbascum phoeniceum Benary's hybrid mullein 1.4 +
Veronica spicata Icicle speedwell 4.0 +
Vinca minor Bowles variety periwinkle 1.0 +
Viola cucullata Priceana swiss violet 2.0 +

a Gall ratings: 1 = no galls; 2 = 1-10 galls; 3 = 11-100 galls; 4 = >100 galls per root system. Numbers are the mean of five or six observations.

b Host status in the literature: + = reported as a host; - = not reported as a host; NT = not reported or not tested.

c no cultivar name given.


Root-knot nematodes are parasitic roundworms that infect a large number of plants, causing stunting and poor growth.  One way to manage these parasites in nursery or landscape soils is by selective planting or rotation to nonhost or resistant species.  We evaluated the host status of a large number of common herbaceous perennial ornamentals to establish a base of knowledge for nonchemical management of root-knot nematodes.