510 Handbook of herbs and spices
31.4 Diseases, pests and their control...................................................
31.4.1 Fungal and viral diseases
Spearmint, like other mints, is susceptible to a variety of diseases. These diseases are
major bottlenecks in production that affect both yield and overall quality of the
essential oil. Some of these diseases reduce the yield of spearmint crop, especially
when virulent forms of one or more diseases attack the monoclonal spearmint crops
spread over wide areas. The most economically threatening diseases of spearmint are
caused by the fungi Puccinia menthae (rust), Sphaceloma menthae (anthracnose),
Rhyzoctonia solani (aerial blight) and R. bataticola (stolon rot), (reviewed by Kalra
et al., 2004).
Rust (P. menthae)
This disease has been reported from all mint growing countries. P. menthae, a
macrocyclic autocious organism produces uredosori on leaves, stems and stolons.
The uredospores (17–28 mm ¥ 14–19 mm) of the disease are borne singly. The aerial
stage, though observed in other countries, has not been observed in India (Gangulee
and Pandotra, 1962). Teliospores (37 mm ¥ 20 mm) are brown, 2-celled, pedicellate,
obtuse to slightly pointed.
A high degree of physiologic specialization has been observed in P. menthae
(Walker and Corroy, 1969; Bruckner, 1972). Rust isolates from M. spicata have been
observed to infect M. cardiaca, but not P. ¥ piperita. The biotypes that infected M. ¥
piperita were avirulent on M. spicata (Roberts and Horner, 1981). In France, eight
races of P. menthae were identified during the early part of the last century (Cruchet,
1907). A total of six races were detected in the north-eastern United State (Neiderhauser,
1945), nine races were detected in England (Fletcher, 1963), and three races were
detected in New Zealand (Breesford, 1982). In the United States, 15 physiologic
races have been observed on mints (Baxter and Cummins, 1953). In another study, a
high degree of physiological specialization was observed on mint hosts with 17
collections of P. menthae (Johnson, 1965).
Rust has been noted to persist as uredospores on the stolons of the host (Wheeler,
1969). Maximum germination of uredospores occurs at 20 ∞C (El-Zayat et al., 1994)
and the bottom and middle leaves of the plant are most prone to rust disease (Bhardwaj
et al., 1995). The disease increases in severity when cultivation is continued in the
same area for several years (Kral, 1977). Rust can be avoided by using the disease-
free planting material (stolons). Sometimes stolons are treated with hot water at
112 ∞F for ten minutes (Staniland, 1947) or at 45.4^ ∞C for ten minutes to obtain rust-
free planting material (Ogilivie and Brian, 1935; Neiderhauser, 1945). However,
planting clones resistant to rust is the most economical and environmentally friendly
approach to control the disease (Kalra et al., 1997).
Application of nickel chloride (Molnaz et al., 1960), tebuconazole, belixasol (Margina
and Zheljazkov, 1994), mancozeb (Melian, 1967; Bhardwaj et al., 1995), plantovax
(Mancini et al., 1976), propiconazole, and diclobutazol (Nagy and Szalay, 1985)
offer reliable protection against rust. Good control of rust has also been obtained
from spraying the soil surface with denitroamine (Campbell, 1956) at pre-emergence
and Krezonit-E (DIVOC) at shoot emergence (Suab and Nagy, 1972).
Anthracnose (S. menthae)
Anthracnose disease is a common disease of spearmint grown on a large scale in
areas of the United States and Yugoslavia. It causes stunting, defoliation and economic