02/10/2021
Banana rust thrips causing damage to banana plantations
Compiled by: National Banana Research program, National Agricultural Research Laboratories- NAR-Kawanda, National Agricultural Research Organisation – NARO.
A number of reports in the print media and social media concerning an outbreak of a suspected new banana disease were received by the National banana research programme at NARL-NARO Kawanda. A strange disease that makes the fruits rusty brown had been reported in a number of districts in western Uganda. Similar symptoms of fruit discolouration were first reported by extension officers in Ndeija sub-county in Rwampara district in 2017, however the symptoms later disappeared with the onset of the heavy rains. A team from NAROs banana research programme at Kawanda visited the affected areas to verify the reports, assess the occurrence and damage to bananas.
Banana scientists from NARO-Kawanda visited the district officials in Isingiro, including OWC and all extension workers from the 21 different sub-counties for a briefing about the suspected disease. Later, scientists visited farms in the worst hit areas of Rugaga and Kikagate subcounties. During their interaction, the farmers said intensity of the fruit discoloration increased when the rains became heavy between September 2019 and January 2020. The Chairman LC3, Rugaga Sub County, Mathias Tushabomwe and the Extension officer for Rugaga, Besiga Felix confirmed the information from farmers. Although in 2017, the symptoms disappeared at the onset of rains, the recent outbreak has persisted, and farmers reported an increase in number of bunches and farms affected during the rainy season.
Symptom Observations/ Description
Farmers in Insigiro reported that the symptoms are on the peel of the fruit and the pulp is not affected, they can peel and cook it for food. However, it is not as soft as it should have been.
Incidence
According to the extension workers and what the NARO scientists observed on the farms across sub-counties in Insingiro district, the incidence varies from 3% - 90% being both number of farms and bunches affected.
What is the cause?
The observed symptoms are caused by banana rust thrips belonging to Order: Thysanoptera, Family: Thripidae; Genus: Chaetanaphothrips Species: Signipennis. They are small yellow insects with narrow fringed wings. The insects attack by feeding on the green surface on the banana fingers. The bananas appear brown, purplish to black. The discolouration however is on the surface of the fruit peel. In extreme cases of severely affected fruits, the whole bunch appears blemish.
They cause more severe damage to younger fruits, often the symptoms do not manifest until after 2 months as the fruits begin to mature. When the peel gets damaged as a result of feeding by the thrips, the affected fruits first appear as grey and dusty, later turning rusty brown. As affected fruits continue to grow, sometimes the peel cracks causing scarring. The scars provide opening for opportunistic fungi including pathogenic [disease causing] ones especially anthracnose that take advantage and creep into the affected areas. In severe cases the fungus appears ashy or sooty or the fingers start to shrivel and rot starting from the cracked points due to the fungal infection. Available published scientific information about banana thrips indicates the female thrips lay eggs in the banana plant tissue which hatch and pupate at the base of the banana plant, maturing into adult thrips in a matter of two weeks.
Economic Contribution:
The rusty appearance of the banana fruits complicates marketing. Commercial farmers have had to destroy their bunches since traders refuse to pay for them. The Chairman of Rugaga Farmers Market, Hussein Sebanakita says the daily sales out of the market were 30,000 bunches, but due to the effect of the damage to the fruits, they now send out 25,000 bunches per day. When asked about the effect on prices for matooke, Hussein says the prices for the clean buches have not been affected both on farm gate and at their market because this is peak harvest season.
Spread of thrips
The thrips causing the observed symptoms are transmitted through infected planting materials. In already infected plantations management practices including cutting old leaves and detrashing within the same field aid the spread of thrips. To a less extent the thrips directly fly from one plant to another.
Hosts: Banana is the primary host of banana rust thrips, however alternate hosts are reported in immature fruits of citrus, tomatoes and green beans.
Research Investigation
Scientists from NAROs banana research team based at Kawanda took samples from infected fruits from affected farms to identify the causal agents of the problem. Once the cause has been confirmed, an appropriate management strategy will be communicated to the farming communities.
Preventive measures:
1. Use healthy planting materials from clean source.
2. Avoid cultivating host plants near or within banana plantations.
3. Immediately at flowering, use commercial
recommended clear polythene bags of 0.08mm thickness that is perforated at 76mm interval with hole of 12. 7mm to cover the bunch as it opens.
4. Cut down the affected banana fruits and burry them to reduce the population of insects in the fields
5. Remove neglected plantations as these can serve as ground for thrips to multiply
