Plant Protection 3 : Selected Ornamentals, Fruit and Vegetables

Delphinium
Larkspur
Delphinium grandiflorum
Family Ranunculaceae (crowfoot family)
PESTS AND DISEASES
Parasitic
Virus and virus-like diseases
Bacterial diseases
Bacterial leaf spot, black leaf spot
Fungal diseases
Fungal leaf and stem spots
Powdery mildew
Root and stem rots
Nematode diseases
Insects and allied pests
Aphids
Mites
Snails and slugs
Non-parasitic
PESTS AND DISEASES
Parasitic
Rhizoctonia root rot (Rhizoctonia solani)
Sclerotium stem rot (Sclerotium rolfsii)
See Annuals A 5, A 6, Vegetables M 7.
NEMATODE DISEASES
Root knot (Meloidogyne sp.) has been recorded on
Delphinium cultorum. See Annuals A 7.
INSECTS AND ALLIED PESTS
Aphids (Aphididae): Green peach aphid
(Myzus persicae) may infest shoots. See Roses J 4.
Mites (Acarina): Twospotted mite (Tetranychus
urticae) may cause whitish leaf speckling. Broad
mite (Polyphagotarsonemus latus) and cyclamen
mite (Phytonemus pallidus) may also infest
delphinium. See Annuals A 9.
Others: Caterpillars (Lepidoptera), leafhoppers
(Cicadellidae), root mealybug (Rhizoecus falcifer).
VIRUS AND VIRUS-LIKE DISEASES
Cucumber mosaic virus, tomato spotted wilt virus
and tomato big bud mycoplasma (greening). See
Annuals A 4.
SNAILS AND SLUGS
Protect delphiniums from snails and slugs in
spring. See Seedlings N 70.
BACTERIAL DISEASES
Bacterial leaf spot, black leaf spot
(Pseudomonas syringae pv. delphinii) is a minor
disease. On leaf uppersurfaces spots are black,
shiny and irregular in shape and size; on leaf
undersurfaces they are brown. Symptoms also
occur on stems, leaf stalks and flowers. They
begin on lower parts of plants. See Vegetables M 5.
FUNGAL DISEASES
Fungal leaf and stem spots
Anthracnose, stem canker (Colletotrichum acutatum)
Fungal leaf spot, crown rot (Diplodina delphinii)
See Annuals A 5
Powdery mildew (Oidium sp.) affects leaves.
See Annuals A 6.
Root and stem rots
Damping off (Pythium, Rhizoctonia solani)
Grey mould (Botrytis cinerea)
Sclerotinia rot (Sclerotinia sclerotiorum)
Non-parasitic
Seedlings are frost sensitive, established plants are
tolerant. Tall varieties need staking and/or wind
protection. Delphiniums contain poisonous
substances (Frohne and Pfander 1983).
SELECTED REFERENCES
Edwards, C. 1981. Delphiniums : The Complete Guide.
J. M. Dent, London.
Frohne, D. and Pfander, H. J. 1983. A Colour Atlas of
Poisonous Plants. A Wolfe Science Book, London.
Jones, R. and Moody, H. 1993. Caring for Cut Flowers.
Dept. of Agric. and Rural Affairs, Melbourne.
Larson, R. A. (ed.). 1992. Introduction to Floriculture.
2nd edn. Academic Press, San Diego, CA.
Nowak, J. and Rudnicki, R. M. 1990. Postharvest
Handling & Storage of Cut Flowers, Florist Greens,
& Potted Plants. Timber Press, Portland, Oregon.
Pirone, P. P. 1978. Diseases & Pests of Ornamental
Plants. 5th edn. John Wiley & Sons, NY.
Sacalis, J. N. 1993. Cut Flowers : Prolonging
Freshness. Postproduction Care & Handling. 2nd
edn. Ball Pub., Batavia, Illinois.
See Annuals and herbaceous perennials A 10
Remember, always check
MANAGEMENT
for recent references
Delphinium is a tall, stately and hardy perennial flower. It is best treated as an annual but in cold climates plants
will last for several years if summers are mild. They prefer an open sunny position and well drained fertile soil.
Propagated by seed, cuttings or by division. Harvest cut flowers for direct sale when florets are
1/2 open. Growers may treat flowers with an anti-ethylene agent as they are sensitive to ethylene and florets
drop easily or 'shatter'. Keep flowers cool (Jones and Moody 1993). Flowers may be stored in preservative
solution for 1-3 days in water. Spikes must be transported in an upright position as they bend upwards
(geotropism) when kept horizontal (Nowak and Rudnicki 1990). Cut stems underwater and add a preservative.
A 30
ANNUALS AND HERBACEOUS PERENNIALS