Peppermint 467
recommended for application just before shooting begins, while a mixture of Prometryn
and Simazin can be used in established cultures. Alloxydim-Na has proved effective
against undesired grasses and Bentazon against dicotyledonous weed. Using Simazin
after the first harvest of peppermint plants prevents the growth of weed in the autumn
and winter to come. A combination of Diuron and Propyzamid killed Agropyron
repens in established peppermint cultures in late autumn. In cultures laid out to
obtain new planting material Chlorbromuron proved successful, while in the period
of beginning growth Desmetryn was applied. The use of chemicals to fight the
weed did not result in any yield reduction or morphological variation and did not
influence the proportion of essential oil. Similarly, Vaverkova et al. (1987) did not
find any significant effect of Simazine application on essential oil constituents of
peppermint.
The essential oil content and constituent concentrations in various parts of M.
piperita during growth were studied before and after administration of Sinbar (terbacil).
The highest oil content was found in the leaves of the youngest upper part of the
stem. Menthol increased during growth with maximum concentrations observed in
the flowering stage. Sinbar application caused no changes in essential oil content or
in proportional amount of components (Vaverkova and Felklova, 1988). The results
of another study have shown that the beginning of bloom may be regarded as a
vegetation period giving the highest content of the essential oil in herb and leaves of
peppermint, and its greatest amount was found in the youngest leaves (Vaverkova et
al., 1997). Content of menthol gradually increased to its top in the blooming phase
while that of menthone was decreasing. The treatment of peppermint with Terbacil
did not influence the essential oil content and its changes during vegetation when
compared with that of untreated plants. Similarly, the application of a herbicide
formulation did not cause detectable changes in relative representation of main and
secondary components of the essential oil. To study Lindane residue dynamics,
peppermint was sprayed with a 0.05% formulation in May, and samples taken two
months later were found to contain 0.4 ppm lindane; which was reduced to below 0.1
ppm, similar to those in the untreated controls after four months (Beitz et al., 1971).
Diseases are generally not the major constraint in the cultivation of peppermint in
temperate conditions. Under Indian conditions, rust, powdery mildew, wilt, leaf blight
and stolon rot are the five major fungal diseases in regions with high humidity. Of
these, the recurrence of leaf blight and rust is more frequent. Leaf blight is caused by
Alternaria tenuis and Rhizoctonia species. These can be checked by application of
Mancozeb. The hilly regions are more prone to occurrence of rust, which can also be
prevented by Mancozeb. The broad-spectrum, systemic fungicides, Propiconazole
and Tebuconazole are used to control rust in peppermint. Garland et al. (1999)
determined their rate of dissipation in peppermint. At harvest, 64 days after the final
application, Propiconazole was detected at levels of 0.06 mg/kg and 0.09 mg/kg of
dry weight, and Tebuconazole was detected at 0.26 and 0.80 mg/kg dry weight, in
identical trials. Rates of dissipation of Propiconazole and Tebuconazole were lower
at a second trial site, where three applications of 125 g/ha a.i. for each fungicide
resulted in residue levels of 0.21.
A large number of insect pests attack the aerial and underground part of the crop.
Among these, the important ones are leaf roller, white fly and hairy caterpillar, which
damage the aerial part. The underground parts are damaged by white grub and termites.
Crickets, grasshoppers and caterpillars may also do some damage. Two spotted mite
(TSM) is one of the most difficult horticultural pests to control and constitutes a very