The cool and humid conditions in winter favour incidence of some seasonal specific pest and diseases on mulberry and silkworms which affect silk production.
Powdery mildew caused by the fungus, Phyllactinia corylea. It is a common disease of mulberry during winter season. In initial stage of infection, white powdery batches appears on lower surface of the leaf and then spread to cover the entire leaf.
Finally the leaf turns black in colour. Such leaves are not preferred by the silkworms. Further, growth of this fungus results in loss of leaf moisture and nutrients which reflect adversely on growth of silkworms and cocoon yield.
The leaf webber, Diaphania pulverulentalis is a serious pest of mulberry in winter. It attacks the apical shoot and defoliates the tender leaves which lead to stunted growth of plants.
Farmers face shortage of tender leaves to rear young silkworms besides reduction in volume of silkworm rearing due to poor leaf yield. The silkworms also suffer from a fungal disease in winter called muscardine caused by Beauveria bassiana. After contact of its conidia with the integument of silkworm, mycelia penetrate into the body and grow vigorously absorbing the body fluid and finally mummify the larvae. This disease causes mortality of silkworms in mass during winter when the temperature comes down to 20 degree celsius.
Severity in powdery mildew is found more on plant maturity. Therefore, timely harvest of leaves for silkworm rearing in winter helps to avoid the disease.
Spray of 0.2 per cent carbendazim (2g/litre) is effective.
To control leaf webber, spraying of dichlorovos (1ml/litre) is recommended. The pupal parasitoid, Tetrasticus howardii at 20,000 per acre and egg parasitoid, Trichogramma chilonis at 4 cc /acre are also promising.
Muscardine in silkworms can easily be controlled by manipulating the temperature and humidity inside the silkworm rearing house.
(Dr. N.Sakthivel, Scientist, Research Extension Center, Central Silk Board, Srivilliputtur – 626 125, Tamil Nadu and Dr. Chikkanna, Scientist, Regional Sericultural Research Station, Salem – 636003, email: firstname.lastname@example.org, mobile: 098427 61789)