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Plant Text Book by DRD.

TRANSCRIPT

  • Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

    Diagnosing and Managing Diseases of Herbaceous Perennials . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    General Types of Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

    Diseases by Host Plant Genus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

    Common-Latin Name Directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

    References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

    Photo Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

    Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

    Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

    Contents

  • 27

    AcanthusAcanthaceae

    Acanthus, known by the colorful name of bears breeches, requires rich soils that are light and well-drained, and sunny locations in the garden. Plants can be killed by overly wet conditions during winter. Mulches can be important for helping winter survival in the north.

    Plants in the genus Acanthus are rarely troubled by diseases, although slugs and snails may visit them in spite

    Distortion and adventitious bud development on the leaf of an acanthus infected with Rhodococcus fascians.

    of their formidable foliage. Acanthus species are suscep-tible to root knot nematode (Meloidogyne), which can cause small bump-like galls on the roots. Powdery mildew caused by a fungus and shoot proliferation caused by the bacterium Rhodococcus fascians (previously known as Corynebacterium fascians) have also been reported on Acanthus species but appear to be rare.

    Diseases by Host Plant Genus

    A

    Clump of adventitious buds developing on acanthus stem infected with Rhodococcus fascians.

  • 28 D I S E A S E S O F H E R B A C E O U S P E R E N N I A L S

    Achillea, or yarrow, is a popular and reliably performing perennial. Many varieties and hybrids are available; the flowers vary in color from species to species. These plants appreciate sunny or partly shaded sites, and tolerate poor soils as long as drainage is good. If night temperatures are too warm the stems will topple, and some flowers will fade in hot weather. Dividing plants and replanting will rejuvenate them if they have ceased to flower well.

    Yarrows are generally disease-free in favorable cli-mates, but insects can cause some symptoms that may be mistaken for diseases. The foliage can be browned by feeding injury and droppings from lacebugs and thrips. White foamy spittlebug masses are sometimes observed on stems. Few problems occur on yarrow during produc-tion and most can be controlled through judicious use of cultural and chemical controls.

    A rust disease caused by Puccinia millefolii will cause chocolate brown bumps to appear on the leaves. Wet sum-mer conditions favor this fungal disease, which is most often seen in the western and southwestern states. In wet-ter climates, Botrytis cinerea can attack flowers or stems, or leaf spots may occur after infection by species of the

    fungi Alternaria, Cercospora, Leptosphaeria, Pleospora, or Septoria. All of these are kept in check by careful atten-tion to irrigation practices. Powdery mildew, crown gall and root knot nematode are also possibilities. Yarrows are sometimes troubled by lower stem cankers caused by Rhizoctonia solani, especially if mulched too deeply. Pythium root rot and Phymatotrichopsis root rot can also occur. Avoid excessive overhead irrigation of yarrow to prevent foliar and root rot disease problems.

    AchilleaAsteraceae/Compositae

    Rust pustules on yarrow may be fairly inconspicuous because the leaves are so narrow.

    Close-up views of chocolate-brown rust pustules on yarrow.

  • D I S E A S E S B Y H O S T P L A N T G E N U S 29

    Aconitum, or monkshood, is a genus of plants with an aura of mystery about them due to their hooded flowers and the poisonous character of both the roots and above-ground parts. Monkshoods are not appropriate plants to grow adja-cent to root crops in the vegetable gardenbut these flowers have an unusual advantage in that they are left alone by deer, and their curiously hooded form is enchanting. The two-petaled flowers help to separate them from delphiniums, which have a similar leaf. They tolerate some later afternoon shade. Dry to moist (but not soggy) soils are acceptable, and richer soils are preferred. Aconitums are better adapted to growing in the northern United States or higher elevations in the south, as cool nights are best for their health. Winter mulching with a layer of leaves helps survival in the north. If plants become crowded, their flowering will decline, so make divisions and replant every few years, in the fall. Plants may need a season to fully recover from transplanting.

    Aconitums are quite susceptible to Verticillium wilt caused by Verticillium albo-atrum. The affected plants will perform poorly in the gardentheir leaves will turn brown and dry, and flowering will be reduced. Cutting across the stem of an affected plant will reveal dark discoloration of the vascular bundles (water conducting tissues). If this disease is detected, do not try to replant monkshood in the same part of the garden, as the micro-sclerotia of the fungus will remain in the soil for several years to attack new specimens.

    Monkshoods are susceptible to many of the same dis-eases as their close relatives, delphiniums. These include black leaf spots caused by Pseudomonas bacteria and the white colonies of moldy growth on leaves caused by the powdery mildew fungi. Foliar nematodes (Aphelenchoides) may cause discolored areas in the leaves. Stem rots may be caused by the fungi Sclerotinia sclerotiorum, Sclerotium rolfsii, S. delphinii and Rhizoctonia solani, and root rot caused by Phymatotrichopsis omnivora can cause problems in the extreme southern United States. Root knot nematode, rust, smut and downy mildew diseases have also been reported for Aconitum species. Aconitum

    AconitumRanunculaceae

    Foliar nematode infestation (Aphelenchoides sp.) has caused the blackened, aborted sprout on this monkshood transplant.

    The underground stems of monkshood show blackening of the vascular system due to Verticillium wilt.

    is susceptible to Impatiens necrotic spot virus (INSV), a thrips-borne virus that can cause a variety of symptoms including leaf spots and mottling of foliage, as well as Cucumber mosaic virus (CMV), which is spead by aphids and can cause mottling of leaves.

    Mottling of monkshood leaves, caused by CMV.

    Swollen areas on the roots of monkshood are symptomatic of infection by root knot nematode, Meloidogyne hapla.

  • 30 D I S E A S E S O F H E R B A C E O U S P E R E N N I A L S

    Actaea (previously called Cimicifuga), known as cohosh or baneberry, features some poisonous partsthe roots and the handsome berries. These plants appreciate a woodland environment, so they should be grown in rich, moist soils with plenty of organic matter, in shade. Similarly to astilbe, actaea will be subject to injury from dry periods in the summer and will need supplemental irrigation in many climates.

    ActaeaRanunculaceae

    A fungal leaf spot caused by an Ascochyta species on actaea.Yellow mottling that indicates a possible virus infection on actaea.

    The globose white structures in the swellings on this actaea root are the swollen bodies of root knot nematode females (Meloidogyne).

    Vein-limited necrotic areas in actaea leaves infested with foliar nematodes (Aphelenchoides).

    Few diseases are known for these plants. Some fungal leaf spots caused by species of Ascochyta, Ramularia, and Phyllosticta have been reported. Leaf spotting may also be caused by foliar nematodes, which cause brown patches between the veins when they feed within the leaf tissue. Actaea spp. are susceptible to some rust fungi, including Puccinia recondita that has certain grasses as its alternate hosts. Smut diseases caused by species of Urocystis have also been reported. These foliar problems along with foliar nematode injury will be kept in check by minimiz-ing periods of leaf wetness.

  • D I S E A S E S B Y H O S T P L A N T G E N U S 31

    The genus Aegopodium contains a single species, A. podagraria, whose common names include snow on the mountain and bishops weed.

    The variegated form A. podagraria Variegatum is not as vigorous as the species and appears to be especially susceptible to Septoria leaf spot, which is the most impor-tant disease on aegopodium. This fungus infection causes irregular brown spots or marginal scorched areas on leaves, and the dead areas usually ar