Spearmint 511
loss in spearmint as well as the other species M. piperita (Baines, 1938; Dermelj,
1960). The anthracnose fungus grows well at temperature ranging from 4–28 ∞C,
while the most favourable temperature for development of the disease is about 21 ∞C.
Saturation of the atmosphere for 48 h at a temperature of >15^ ∞C, enhanced infection
that did not occur at a relative humidity of 80% (Dermelj, 1960). Overwintering of
the fungus is on infected mint debris (Baines, 1938). The use of planting materials
from healthy crops helps prevent anthracnose. Application of ferbam and copper
oxychloride controls the disease to some extent (Dermelj, 1960).
Aerial blight (R. solani)
Although aerial blight has been reported in several species of Mentha, maximum loss
of herb due to this disease has been reported in M. spicata as well as other species,
for example, M. arvensis. The disease is particularly damaging after the first plant
harvest (Bhardwaj et al., 1980) and when the crop is closely planted (Bhardwaj and
Garg, 1986). The disease first appears on leaf margins as faded patches that gradually
extend inwards under moist and humid conditions. Later, the blight broadens towards
twigs (stems) causing necrosis of above-ground parts (Bhardwaj et al., 1996). In
India, early planting of the crop before the rainy months reduces the losses during
crop maturation. One or two applications of mancozeb can also restrict aerial blight.
Stolon rot (multiple agents)
Stolon rot (also known as stolon decay) caused by R. bataticola was first recorded on
M. cardiaca (Green, 1961) and subsequently recorded on M. arvensis and M. spicata
(Husain and Janardhanan, 1965). That the stolon rot is, indeed, a complex of R.
solani and R. bataticola, was later reported by Singh (1991). The initial symptom of
the disease is a yellowing of the foliage with eventual death of the whole plant.
Underground stolons show pinkish brown lesions in the early stages of the disease,
which gradually turn to dark brown or black patches. The patches increase in size to
finally result in decay of a portion or entire stolon. The use of healthy planting
material and practices such as deep summer ploughing and crop rotation can control
the disease (Jain, 1995). Treatment of the stolons with Zineb, Mancozeb or Captan
before planting can also effectively control the disease (Sastry, 1969). To check the
spread of the disease, healthy stolons need to be grown in a disease-free plot.
Viral disease: tobacco ring spot virus
Severely stunted and deformed leaves are characteristic of spearmint plants infected
with a strain of tobacco ring spot virus (Stone et al., 1962). In China, two cucumo
virus, cucumber mosaic and tomato aspermy, have been isolated from spearmint
plants displaying mosaic symptoms and distorted leaves (Zhou et al. 1990).
31.4.2 Pests
Both aerial and underground parts of spearmint are attacked by insects. The aerial
part is affected by leaf folder (Syngamia abrutails), hairy caterpillar (Spilosoma
obliqua), bug (Nisia atrovenosa) and whitefly (Bemisia tabaci) whereas the underground
part is damaged by white grub (Holotrichia consaguinea) and termites (Microtermes
obesi) (Husain et al., 1988). Insecticides like dimenthoate (0.05%), quinalphos (0.05%)
and chloropyriphos (0.05%) successfully manage the pests of this crop (Khanuja et
al., 2004).