Agriculture Reporter

TOMATOES are a horticulture crop that thrives all-year-round and grown by most local farmers.
As farmers strive to produce a quality crop, it is imperative they acquire relevant knowledge on the crop.
Local farmers have had to deal with the tomato leaf-miner, Tuta absoluta (Lepidoptera: Gelechiidae) a pest which has caused great losses in several countries.
Its primary host is tomato, although potato, aubergine, common bean, physalis and various wild solanaceous plants are also suitable hosts.
Tuta absoluta is characterised by a high reproduction potential as each female may lay up to 300 creamy coloured eggs and 10 to 12 generations can be produced each year.
In tomato, it can attack any plant-part at any crop stage and can cause up to 100 percent crop destruction, although the larvae prefer apical buds, tender new leaflets, flowers, and green fruits.
This pest is crossing borders and devastating tomato production in both protected and open fields.
Originating from Latin America, Tuta absoluta has recently spread via infested fruits and packaging material to Europe, Africa and the Middle East.
Given its aggressive nature and crop destruction potential it has quickly become a key pest of concern in these new geographies.
Infestation of tomato plants occurs throughout the entire crop cycle.
Feeding damage is caused by all larval instars and throughout the whole plant.
On leaves, the larvae feed on the mesophyll tissue, forming irregular leaf mines which may later become necrotic.
Larvae can form extensive galleries in the stems which affect the development of the plants.
Fruits are also attacked by the larvae, and the entry ways are used by secondary pathogens, leading to fruit rot.
The extent of infestation is partly dependent on the variety.
Potential yield loss in tomatoes (quantity and quality) is significant and can reach up to 100 percent if the pest is not managed.
Risk for insecticide resistance
development:
Pests like Tuta absoluta, with high reproduction capacity and short generation cycle, can develop resistance to insecticides.
This risk increases significantly when management of the pest relies exclusively on chemical control with a limited number of effective insecticides available.
This situation usually leads to an increase in the frequency of use and thus, increased selection pressure for resistance.
Tuta absoluta has been a key pest in tomato in Latin America for decades and is resistant to a range of mode of action groups.
Due to this resistance history, it is possible that introduced populations may express the same resistance profiles as found in Latin America.
Key management tactics:

– Allow a minimum of six weeks from crop destruction to planting the next crop to prevent carryover of the pest from previous crop.
– Between planting cycles, cultivate the soil and cover with plastic mulch or perform solarisation.
– Control weeds to prevent multiplication in alternative weed host (especially Solanum, Datura, NicoCana).
– Prior to transplanting install sticky traps.
– Use pest free transplants.
– Seal greenhouse with high quality nets suitable for Tuta absoluta.
– Place pheromone baited traps to monitor all stages of tomato production that is in nurseries, farms, packaging, processing and distribution centres.
– Start monitoring two weeks before planting.
– Inspect the crop to detect the first signs of damage.
Insecticide Resistance Management (IRM):
The recommendations for sustaining the effectiveness of available insecticides is centred on integration of as many pest management tools as possible, use of insecticides only when needed based on established thresholds and rotation of effective insecticides with different modes of action.
Mode of action window approach:
The basic rule for adequate rotation of insecticides by mode of action (MoA) is to avoid treating consecutive generations of the target pest with insecticides in the same MoA group, by using a scheme of ‘MoA treatment windows’.
A treatment window is a period of 30 consecutive days, based on the minimum duration of a single generation of Tuta absoluta.
Multiple applications of the same MoA or different MoAs may be possible within a particular window (follow insecticides label for maximum number of applications within a window and per crop cycle).
After first MoA window of 30 days is completed and if additional insecticide applications are needed based on established thresholds, different and effective MoAs should be selected for use in the next 30 days (second MoA window).
Similarly, a third MoA window should use different MoAs for the subsequent 30 days.
The proposed scheme seeks to minimise the selection of resistance to any given MoA group by ensuring that the same insecticide MoA group will not be reapplied for at least 60 days after a window closes, a wise measure given the potential of a longer life cycle based on temperature fluctuations throughout the growing season.
This scheme requires a minimum of three effective insecticide MoA groups but ideally more MoA groups should be included, if locally registered and effective against Tuta absoluta. – Source: www.irac-online.org