- Symptoms appear at any stage of growth and many of the cultivable varieties are susceptible.
- Prominent dark green streaks occur in the petioles, midribs and along the leaf veins. This is the most characteristic symptom for early diagnosis.(Image 1,2)
- The leaf margins turn wavy and roll upwards.(Image 3)
- Irregular dark green streaks appear on leaves .
- Leaves become dark green, small, brittle and erect with prominent veins (Image 4).
- The leaves become bunched together at the apex of the pseudostem to form a rosette or bunchy top.(Image 5)
- The whole plant gets stunted as the leaf stalks fail to elongate .
- Subsequently produced leaves become smaller. Finally leaf production stops .
- Newly produced suckers become infected, stunted and produce numerous thick, dark green necrotic leaves.
Select five rows at random from 10 cent plot. Observe plants showing typical virus symptoms.
Primary spread through use of infected planting material / rhizome / suckers. All the rhizomes / daughter suckers produced by a diseased plant carry the virus.Secondary spread is through the banana aphid Pentalonia nigronervosa in a non-persistent manner. Colocasia esculenta is the symptomless reservoir of the virus .
- The most important measure is to use only disease free planting material for propagation.
- The diseases should be detected early in the field and immediately eradicate infected plants including suckers.
- Affected plants can be destroyed by spraying kerosene or by injecting herbicides like 2-4 D
- Do not take suckers from infected fields
- Use tissue culture plants and certified disease free suckers for planting.
- Avoid growing leguminous and cucurbitaceous vegetables as inter crops.
- Before planting spread lemon grass in the pit,(if available)
- Apply cartap hydrochloride 4 G @ 25 g per plant 20 days after planting. A second and third dose of the chemical are to be applied in the leaf axil @ 12.5.g each at 65 days and 165 days after planting.
- Spray Verticillium lecanii to control aphid vectors @ 20 g or 5 ml /l at 25,65 and 165 days after planting . Where ever insecticides are applied 10 day gap should be given for biocontrol application.
- Apply neemcake @ 1 kg in two split doses – 25 -30 days after planting and the second at 60-65 days after planting.
- Predators of banana aphids include lady bird beetles (Symnus nubilus, Pseudaspidimerus circumflexa , Micraspes crocea, Menochilus sexmaculatus) Syrphids (Paragus serratus, Ascarina spp.) and a Hemerobid. Protect these natural enemies.
- Varieties such as Karpooravalli,kanchikela, Njalipoovn and koombillakannan are tolerant against bunchy top infection.