Tuta absoluta (Lepidoptera: gelechiidae) is one of the major challenges facing tomato farming in Kenya. The pest is a serious threat to tomato production and can lead to total losses in a farm especially if one fails to deploy control measures early enough. Let’s discuss how you can manage Tuta absoluta on your tomato farm in Kenya.
Understanding How Tuta absoluta Develops
The pest has four stages of development including egg, larva, pupa and adult. When an adult moth lays eggs on the underside of the stems, leaves and sepals, the larva emerges and creates mines in the plant where they hide or produce large galleries. That is why you will see many people and resources mentioning tomato leaf miners in place of Tuta absoluta.
The larva may also burrow into tomato fruits exposing them to fungal infections and causing rotting before or after harvest. The larva is the most destructive stage of the Tuta absoluta and lasts for 12-15 days. After this period, the pest begins to pupate either in the mines, on the soil or the leaf surface. The pupa does not cause damage to the crop. After 10 days, an adult will emerge from the pupa.
Adults hide between the leaves during the day. The total lifecycle takes 30-35 days, therefore, Tuta absoluta can have up to 12 generations in one year.
How to Detect Tuta absoluta Attack in Your Tomato Field
Below are symptoms of Tuta absoluta attack in tomato crops:
- Irregular mines and galleries on leaves (these mines emerge because the larva feeds on the mesophyll tissue)
- Dark-coloured frass accumulation in designated areas of the mines
- Fruits with small entrance point marks often below the calyx and larger obvious exit points
- Premature fruit drop and shedding of flowers and leaves
- Abnormally shaped fruits
- Fruits have reduced size
- The entire plant may die back when larvae penetrate the auxiliary buds of young plants
Control Methods for Tuta absoluta
You will need to implement integrated pest management to sustainably control Tuta absoluta in your tomato field. Combining cultural, biological and chemical methods increases your chance of success in controlling Tuta absoluta.
Cultural Control
Some cultural practices to consider include:
Crop Rotation
Avoid planting tomatoes and other crops belonging to the solanaceous family e.g., potatoes, tobacco, black nightshade and capsicum continuously in the same land. You can plant beans, maize and onions for about two seasons before you embark on tomatoes or any solanaceous crop.
Control Weeds
Ensure you maintain a weed-free field because some weeds such as Datura can serve as hosts for Tuta absoluta.
Destroy Infested Plant Parts
Destroyed infested leaves through solarization. Further, you can bury infested tomato fruits in deep holes. Do not dump them at the farm edges or harvest collection points since they may re-introduce the pest into the field.
Biological Control
Biological pest control involves using living organisms and natural compounds to manage pests. Popular biological organisms that can help control Tuta absoluta are predatory mirid bugs (Nesidiocoris tenuis and Macrolophus pygmaeus). Biopesticides can also help control Tuta absoluta. Examples are Bacillus thuringiensis (BT) based insecticides.
You can also control the eggs, larvae and adult moths using fungal species such as Beauveria bassiana and Metarhizium anisopliae or entomopathogenic nematodes Steinernema feltiae.
Sex Pheromone Traps
The use of sex pheromones to control Tuta absoluta has proven to be effective. Sex pheromones are chemical signals emitted by an organism to attract individuals of the opposite sex and encourage them to mate with them.
A trap with Tuta absoluta sex pheromones will attract adult males who get trapped. The males moves towards the trap expecting to find female pests but they end up getting trapped. Sex pheromone traps can help mass trap the pests or monitor their population. You can use pheromone traps regardless of where you plant your tomatoes i.e., greenhouse or open field. By trapping the male adults, you disrupt the mating activity thus reducing the population.
Chemical Control
Several pesticides available in the market can help manage Tuta absoluta. However, the cryptic behaviour of the pest including concealing itself in the translaminar and fast development of resistance reduces the effectiveness of the insecticide. Farmers need to alternate the pesticides to combat insecticide resistance. When buying your pesticides, you can look for those with the following active ingredients:
- Emamectin benzoate
- Abamectin
- Chlorantraniliprole
- Flubendiamide
- Spirotetramat
If you want to effectively manage Tuta absoluta, you need to use a combined approach. First, prevent infestation by practicing cultural practices. Second, regularly scout and monitor your tomato field. You can monitor the pests by physically checking your plants in the field or using sex pheromone traps. Depending on the pest population you encounter, you can introduce biological control agents, use biopesticides, or proceed to chemical control.