Prays citri is currently considered the most harmful pest of the lemon tree because it destroys the floral organs of the trees. However, the moth can also damage shoots and small fruits.
Since the damage produced is mainly when the flowers are in bloom, the plants that are attacked the most are those that bloom in various stages, as is the case of the lemon tree. Within this species is the Verna variety that have several consecutive blooming periods a year. Damage has also been observed in orange trees and occasionally in the Clemenules (variety) mandarin trees that have a long blooming period.
MORPHOLOGY AND BIOLOGY
The adult is 10 mm wide and a grey colour, its wings have dark spots and frayed edges. The larvae are a whitish or greenish colour with a brown head.
The adults fly at night and twilight, laying eggs preferably on the petals of the flowers that are still closed. They also lay their eggs in the sepals, shoots or small fruits. They normally pupate inside the flower in which they have already fed, then joined with silk threads. They usually hibernate as a chrysalis and can produce between 3 and 5 generations a year.
Prays citri adult
Prays citri egg on a flower
Prays citri caterpillar
Prays citri pupa
The eggs can be seen individually on the rose-pink petals as a whitish speck. If the amount of eggs that are laid over the floral buds is high, the damage will be severe during the flowering period. The caterpillar, born from this egg, bores into the chorion and enters directly inside the flower, between the egg and the petal.
Source: Profesores F. García Marí, J. Costa Comelles y F. Ferragut. // Fotografías de E. Llácer en http//gipcitricos.ivia.es
DETECTION AND MONITORING
1 to 2 traps per hectare should be placed at the same height as the crops or on a specific support.
The traps should be placed at the exact moment when the blossoming starts and the first floral buds appear.
The males of this species are specifically captured in order to reduce mating, meaning that the unfertilised females will lay unviable eggs. In this way, the pest population is reduced.
For mass trapping, the amount of traps per surface area must be increased, depending on the location and uniformity of the plots. One trap controls a surface area between 500 and 1.000 m2. This means a density of 10 to 20 traps per hectare.
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PERIOD OF USE
To obtain good control of Prays citri it is advisable to combine two methods: detection and monitoring; and mass trapping.
In spring, 1 to 2 traps per hectare should be placed for the detection of the pest and observation of its population levels. With tolerance thresholds established in each area, the moment to adopt control measures, in this case mass trapping, can later be defined.
The tolerance threshold for Prays citri is very low and varies depending on the area. In general, it is between 7 and 21 captures per trap and per week. For mass trapping, traps should be placed throughout the plots.
The most serious damages are produced in the Verna variety of lemon trees during the two main blooming periods: in spring, from April to May, it is known as Cosecha and summer, in September, it is called Rodrejo. The “Sanjuanera” blooming period that takes place in June is not as abundant and the damages are also to a smaller extent.
In the case of attacks on flowers, the larva feeds on the anthers and pistils inside of the flower. It then moves on to other flowers and binds the damaged area with silk threads, forming a mass on the inside in which dried petals and lots of dark-coloured excrement can be found. This type of damage could be confused with that of the Cacoecia caterpillar, with the difference being that this last pest has a preference for newly ripened fruit and not flowers. Besides, Cacoecia does not produce sawdust and excrement.
Damages caused by Prays citri in a floral shoot
The larva feeds on the epidermis of the leaves. It excavates a gallery along the shoot with resin secretions. Attacks on newly ripened fruit tend to create a gallery in the style and Cacoecia caterpillar ends up by eating all the fruit.
Damages to growing fruits appear as superficial spots, which are caused by the larva feeding on the peel. In the centre of these spots, the chorion of the egg can be found.
Sometimes, the larva can cause damage to the scions in all types of citrus fruits, by entering under the grafted scutum and feeding on the cambium. Therefore, the scion dries up. Once the damage is caused, the larva abandons the fruit to pupate in the ground, although it can also pupate near the damaged bud. Some pylarid moths such as Ephestia sp. or Cryptoblabes can cause similar damage to the scion.
FACTORS THAT INFLUENCE THE NUMBER OF TRAPS NEEDED
The pest population, the bordering crops, the level of control required, etc…
One important factor is the size of the crop. In small and irregular crops, a greater number of traps are required than in larger and more uniform plots.
Another important factor is the distance between plots that have the same pest. In cases like this, the borders of the plots must be reinforced, so it could be necessary to place up to 20 traps per hectare or even more for mass trapping.
If specialists or farmers use the traps and pheromones correctly, as previously described, especially during the early stages when adults of the first generation appear, then this monitoring system is very effective. A very low level of damage, mainly on organic land, has been demonstrated.
A level of control of more than 95% is very common, especially in large areas of crops. A limiting factor of this system could be when there are small plots distributed in many areas and the neighbours have a high level of this pest infestation.
Despite some important basic rules for the effective monitoring of Prays citri, farmers or specialists have to find their own system to achieve it. They can experiment with this system, even establishing their own tolerance thresholds.
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