468 Handbook of herbs and spices
significant and real risk to stable commercial peppermint oil production. The incidence
of TSM has increased annually in commercial peppermint crops. Under dry conditions
high levels of TSM infestation result in excessive leaf loss, particularly lower leaf
and can affect the oil quality.
Bienvenu conducted a field survey of commercial peppermint crops to establish
which pests are present in peppermint fields and the range of controls currently used
or available. Evaluation of the potential to develop an effective integrated pest
management program for peppermint production in south eastern Australia based on
effective control of TSM was successfully completed. It was noted that the predator
mite Phytoseiulus persimilis can survive and reduce TSM populations during the
critical months of peppermint production (http://www.rirdc.gov.au/comp02/
eoi1.html#DAV-178A, Project Title: Potential for IPM in Peppermint growing in
South East Australia, RIRDC Project No.: DAV-178A).
Shukla and Haseeb (1996) evaluated some nematicides (aldicarb, carbofuran,
ethoprop) and oil cakes (linseed, mustard, neem) against Pratylenchus thornei infesting
Mentha citrata, M. piperita and M. spicata in glasshouse experiments. All the treatments
were effective in increasing herb weight and oil yield, and minimizing nematode
reproduction of all the test species of mint as compared to untreated-inoculated
plants. Neem cake was most effective in reducing the reproduction rate of P. thornei.
The humid-adapted species Neoseiulus fallacis (Garman) was the most common
phytoseiid mite collected in either humid (>100 cm annual rainfall) or arid (20–45
cm annual rainfall) mint growing regions of Washington, Oregon, Montana, Idaho,
and California during 1991–1995. In experimental field plots, this predator gave
excellent biological control of Tetranychus urticae Koch on peppermint grown under
arid conditions in central Oregon when evaluated by an insecticide check method or
by the caging of mites (Morris et al., 1999).
28.3.5 Harvest and post-harvest management
The herb is cut just before flowering according to local conditions. Sometimes when
well irrigated and matured, a second crop can be obtained in next 60–75 days.
Harvesting should be carried out on a dry, sunny day, in the late morning, when all
traces of dew have disappeared. The first crop is always cut with the sickle to prevent
injury to the stolons. In India, the crop planted in January–February, becomes ready
for the first harvest in April–June, depending upon crop management. The second
harvest is taken after 60–70 days of the first harvest. After harvesting, the herb is
spread in shade to reduce the bulk and increase the recovery of oil. The average yield
varies around 15–20 t/ha of herb and 60–70 kg oil/ha. The oil yield depends upon the
period of wilting, period of stalking (between wilted hay and distillation) and efficiency
of distillation.
Changes in essential oil content, CO 2 exchange rate and distribution of
photosynthetically fixed^14 CO 2 into essential oil, amino acids, organic acids and
sugars were determined in developing peppermint leaves by Srivastava and Luthra
(1991). The incorporation of^14 CO 2 into sugars was maximal followed by organic
acids, amino acids and essential oil at all stages of leaf development. The incorporation
into sugars and amino acids declined as the leaf matured whereas that in essential oil
and organic acids increased with leaf expansion and then decreased. The seasonal
variations in fatty acid composition were studied by Maffei and Scannerini (1992) in
developing peppermint leaves. Chalchat et al. (1997) studied the effects of harvest