Diseases of English Ivy

D. J. Norman, Ph.D.*

University of Florida/IFAS
Central Florida Research and Education Center
CFREC-Apopka Research Report RH-96-4

Over 40 species of plant pathogens have been found associated with English ivy (Hedera helix L.) in Florida (Alfieri et al., 1994). Six of these pathogens can consistently cause extensive damage to ivy production. They are: Xanthomonas campestris pv. hederae; Colletotrichum trichellum; Botrytis cinerea; Phytophthora palmivora; Rhizoctonia solani; and Fusarium spp.; however, these six pathogens can easily be controlled by following sound horticultural recommendations and with prudent pesticide applications.

1) Xanthomonas leaf spot: Xanthomonas campestris pv. hederae infections on English ivy are characterized by the formation of irregular dark brown to black necrotic lesions on leaves. These lesions usually have water-soaked margins and also may have chlorotic halos. When plants are heavily infected, new growth may be twisted and malformed.

Disease Management Practices: It is important in ivy production that stock plants be free of Xanthomonas infections. Stock plants from which cuttings are taken should be under covered structures and drip irrigated. This is because the primary mechanism of movement of Xanthomonas within the nursery is in splashing water. If English ivy is grown under covered structures with drip irrigation, infected plants can easily be removed and spread of the disease can be halted. When infected leaves are observed, these should be removed in order to lower inoculum in the nursery. If outbreaks occur, applications of cupric hydroxide (Kocide®, Blue Shield®, Champ®, Champion®) or fosetyl aluminum (Aliette®) will help control the spread of infections within the production facility. Streptomycin sulfate is recommended for control of xanthomonads in many crops; however, it should not be applied to English ivy due to a phytotoxic reaction. After applications of streptomycin sulfate, English ivy leaves can become chlorotic.

2. Colletotrichum leaf spot: Colletotrichum trichellum produces brown lesions on English ivy leaves. As the lesions age, small dark structures form on the lesion surfaces. These structures are referred to as acervuli and within each acervuli thousands of spores are produced. These spores are easily spread from plant to plant via water and wind movement

Disease Management Practices: As with Xanthomonas, planting under covered structures and using drip irrigation substantially aids in disease control. Leaves with lesions should be clipped and placed in plastic bags, to limit spore movement, and subsequently removed from the nursery. High humidity is conducive to disease development; therefore, lowering humidities in the production facility will aid in disease control. Copper oxychloride and copper sulfate are effective in Colletotrichum control as well as mancozeb (Manzate® 200) and iprodione (Chipco® 26019 WP).

3. Botrytis blight: Botrytis cinerea infections occur under humid conditions producing brown to tan lesions on ivy leaves. Within these lesions, abundant sporulation occurs with masses of brown spores being produced on hyphal tips, giving infected tissue a fuzzy appearance. This fungus can readily colonize ivy tissue which has been damaged by cold or improper chemical applications.

Disease Management Practices: Lowering the humidity in the greenhouse is important for disease control. Plants which are heavily damaged should be removed in order to lower inoculum concentrations in production facilities. Registered pesticides which aid in the control of Botrytis blight are vinclozolin (Ornalin® 50wp) and iprodione (Chipco® 26019 WP).

4. Phytophthora root rot and leaf spot: Phytophthora palmivora is an opportunistic soil inhabitant which can get into production facilities via contaminated soil mixes, or may gain access if plants are set onto soil surfaces. Ivy plants infected with Phytophthora palmivora can exhibit leaf chlorosis, wilting, root die-back and discoloration. Phytophthora palmivora can gain access to leaf surfaces by either zoospores, which are highly mobile spores capable of swimming across wet leaf surfaces or via splashing contaminated soil onto leaf surfaces. When this happens, dark water-soaked lesions can appear on leaves similar in appearance to lesions caused by Xanthomonas infections.

Disease Management Practices: Plants should always be kept on raised benches or in hanging baskets to avoid Phytophthora infestations. If infections are detected, leaf surfaces should be kept dry, plants which are heavily infected should be discarded and remaining plants should be treated with either ethazol (Truban®, Terrazole®), ethazol-thiophanate-methyl (Banrot®), or metalaxyl (Subdue®).

5. Rhizoctonia root rot and aerial blight: Rhizoctonia solani also colonizes soil readily and usually gains access to production facilities via contaminated potting mix. If potting mix components such as bark, compost or peat moss are stored on soil surfaces, Rhizoctonia can readily grow into these products and contaminate future plantings. Rhizoctonia solani, under normal cultural conditions, produces few spores, although it may produce small hyphal mats (sclerotia) which can be splashed between plants.

Disease Management Practices: Rhizoctonia should not be a problem in ivy production if soil mixes and plants are kept on raised benches and ivy cuttings for propagation are taken from disease free stock. However, if soil becomes contaminated, highly infected plants should be discarded and remaining plants should be treated with triflumizole (Terragard®) or ethazolthiophanate-methyl (Banrot®).

6. Fusarium root rot: When Fusarium infections occur, ivy plants are usually wilted, chlorotic, and stems may rot-off at the soil surface. Additionally, stems may be covered with a thin layer of white dust-like material. This dust-like material is actually millions of spores which have formed on the exposed surface of the plant. These spores are easily splashed or blown to nearby plants. Fusarium spp. also can readily colonize soil mixes thus contaminating future plantings of ivy.

Disease Management Practices: Plants with severe infections and abundant spore production on stems should be placed into plastic bags and removed from the production facility. Remaining plants should then be drenched with ethazol-thiophanate-methyl (Banrot®).

References

Alfieri, S.A., Langdon, K.R, Kimbrough J.W., El-Gholl, N. E., and Wehlburg, C. 1994.

Bulletin No. 14, Diseases and Disorders of Plants in Florida, Division of Plant Industry, Gainesville, FL. 114 pp.

Simone G., Elliott, M., and Mullin, R. 1994. Florida Plant Disease Control Guide, Volume 1. Plant Pathology Dept., University of Florida, Gainesville, FL. 362 pp.

Turf & Ornamental Reference for Plant Protection Products. 1995. 4th edition, C & P Press, N.Y. 747 pp.

*Assistant Professor of Plant Pathology, Central Florida Research and Education Center, 2807 Binion Road, Apopka, FL 32703-8504.

Pesticides should be applied according to label directions.

Regardless of the pesticide or mixture of pesticides used, it is
strongly recommended that the effects be evaluated on a few
plants, under your particular conditions before treating all plants.

Mention of a commercial or proprietary product in this paper
does not constitute a recommendation by the authors,
nor does it imply registration under FIFRA as amended.

Reference to University of Florida/IFAS Pest Control Guides