One of the biggest challenges in farming watermelon in Kenya is controlling the melon fly. In fact, if not managed, it can cause up to 80% crop loss. Ignore it at your own peril. Therefore, how does a farmer protect their crop?
First things first, let’s learn about its life cycle. The melon fly (Bactocera cucurbitae) belongs to the Tephritidae family of fruit flies. The female fly lays its eggs under the skin of the watermelon. And after 2-4 days they hatch into larvae (maggots) and start to feed on the fruit flesh.
The maggots will then metamorphosis to pupae. The pupae will then leave the fruit and burrow 1-2 inches in the soil. It will take 7-13 days to mature into an adult.
In tropical and temperate conditions the life cycle of the melon fly is shorter. It averages 14 days. Hence, the cycle continues. Unfortunately, it continues to cause more damage to the young fruits.
However, all is not lost. This pest can be controlled. We are going to look at 4 ways on how to manage this pest.
1) Chemical control
This is the most popular method of control. It works by mimicking nature. Firstly, for reproduction to take place, the female secretes sex pheromones to attract the male. Therefore, using this biological trait, a vial is steeped in methyl eugenol (the attractant) to lure the male fly.
It is combined with an insecticide.
The male fly is attracted by the scent and ends up being captured in the trap. By eliminating the male, there will be no mating. Consequently, no eggs will be hatched. Eventually, the population of the fruit fly will be managed. Scientifically, it is called the male annihilation technique.
To ensure its efficacy, use 4-5 traps per acre. While installing, the trap should face the north of the plant. Additionally, the trap should be put 1 foot above the ground. This ensures the scent is carried further and attracts the males. Every 7 days the trap should be emptied. As for the wick, it is best to change after 14 days. However, in hotter climates it should be changed after 7 days.
Currently, in the market we have the Bactolure trap from Farmtrack Consulting.
2) Protein food bait
Whereas, the male annihilation technique targets the male, the protein food bait method focuses on the female. For the young female fruit fly to reach sexual maturity it has to feed on protein. It will also need it to develop eggs. They feed on protein found in the leaf and the fruit surface.
When the female start to lay eggs they stop consuming protein.
Just like the male annihilation technique, this method targets the behavior of the female. In this method a protein laced with a soft toxin is used to kill the fly. This method prevents the female from laying eggs. Hence, the population of the fruit fly is controlled.
Notably, at least two thirds of the captured insects are female and the other third are male.
For an acre, you will need 30 traps. The spacing from trap to trap should be 10 meters. The trap should be filled with 400 ml of the solution. Collect the catches every week and sieve. Just like the pheromone trap the changing of the solution should be done after 14 days. If there is a high rate of evaporation change the liquid after 7 days.
If you want to use this method there is the Cera trap that is sold by Amiran and Fruit fly Mania from ICIPE.
3) Bio pesticides
Unfortunately, the over reliance on synthetic pesticides has caused pesticide resistance in many parts of the world. The melon fly is no different.
The use of bio pesticides derived from fungi can help the situation. Metarhizium anisopliae is a form of fungus that occurs naturally in the soil. The fungi isolate strain 69 can be used to control the melon fly.
These fungi can be used as a soil inoculant or a spray. When applied to the soil, the granules of the fungi are raked in before fruiting. Since the pupae burrow in the soil before they mature into adults the fungi will kill them before they morph into adults.
The other way of using the fungi is through an oil based spray. When sprayed the fungus spores bind to the exoskeleton of the melon fly. Once the fungus enters the insect it grows rapidly and it dies. Insects that come into contact with the infected insect also become infected and die.
Available from Real IPM
4) Cultural control
To bolster the aforementioned methods, cultural control is important as well. This can be done through field sanitation and planting a trap crop.
While starting your season plant a border crop like maize that will serve as the host plant for pests. The crop will also help in managing aphids; another troublesome pest in watermelon.
For the infected fruit ensure it is collected and destroyed. The fruit should be put in a plastic bag to kill the fruit fly maggots or they be buried in a 3 feet deep hole. Add lime to kill the larvae. This should be done at least twice a week.
Finally, rotate the watermelon with non host crops (non cucurbits) for at least 3 seasons before planting again in the same spot. Ultimately, there should be no build up of pests.
The choice of control will depend on the level of infestation, method of production (organic or inorganic), and costs. It is best to start control at flowering i.e. week 4. Strive for prevention to stop any economic injury. In conclusion, always seek for an integrated pest management approach. It is more chilled out on the environment.
BY: Hilda Munjuri