What is the difference between systemic and non-systemic pesticides?

avocado technique

 1- BOTANICAL PRESENTATION OF THE PLANT 

 1-1 General 

The avocado tree: Persea americana Miller, belongs to the laurel family is native to Central America. Three botanical races are recognized: the Mexican race, the Guatemalan race and the Caribbean race whose main characteristics were identified by BERGH in 1975 (Gaillard, 1987).

1-2 Morphology

The tree can reach a height of 10 to 15 meters. The growth habit is very variable; spread out, erect or even in a ball with numerous branches from the base of the trunk.

The bark is smooth, ashen and the young wood is green in color.

1-3 The roots  

The roots of the avocado are superficial, constituting a root hair located in the first decimeters of the upper zone of the soil.

1-4 The leaves 

The foliage is evergreen and very ornamental, the leaves are whole, tough, usually acuminate 10 to 20 cm long and 5 to 8 cm wide with a shiny dark green color, it contains a substance called Abacatine which has diuretic properties, some give off an aniseed smell when crumpled.

1-5 The flowers :

They are small, always very abundant on a tree in production. They are grouped in panicles on the terminal part of several branches.

The flower of the avocado tree is of type 3, the perigoneum is composed of six sepals in two whorls. The 12 stamens are arranged in four whorls, three of which are fertile on the outside and the inside sterile. The anthers have four boxes superimposed two by two opening through valves. The ovary is sessile, surmounted by a hail style with a simple stigma.

The central whorl of the stamens is reduced to a staminode state which together with the two rows of glands secrete an abundant nectar when the flower opens.

 1-6 Floral biology

The avocado flower is protogynous with a dichogamy synchronized daily; the dichogamy is characterized by an asynchronism of the states of maturity of the stamens and the pistil. This behavior is similar for all open flowers on a tree and for each flower it is the pistil that is ripe before the stamens. Thus the flower of the avocado tree being structurally bisexual (hermaphrodite), it is functionally unisexual since the flower goes through two situations which are repeated in time. This can be explained as follows:

- Female flower: At first, the flower is open, with the pistil alone in the center; the stamens are removed at 45°; the stigma is then receptive and the egg can be fertile. This opening lasts for two hours, then the flower closes for the rest of the day and night.

- Male flower: In a second stage; The next day the flower opens again, but then it is functionally male, the valves of the stamens open and release the pollen. 

The pistil is discolored withered and is no longer receptive. The flower remains open in the male state for several hours.

This differential evolution of the reproductive elements has led to the classification of varieties and seedlings into two groups or types, each with a particular floral biology.

-Group A : The flower opens in female phase in the morning, then closes at noon. The following day, it opens in male phase at midday, then closes definitively around 6 pm. The total duration of the cycle is 34 to 36 hours. 

-Group B: The first opening takes place in the afternoon, can be at 1 or 4 pm, the second opening takes place in the afternoon, can be from 8 am to 1 pm. The total duration of the cycle is 24 hours. But the climate can cause significant disturbances in the course of the floral cycle. 

Therefore the conventional definitions of type A and B varieties are only valid at certain temperatures; whereas in some localities it becomes an exception rather than a rule. The floral cycle normally only takes place under well-defined temperature conditions.

1-7 parthenocarpy

Normally the growth of the fruit is dependent on hormonal factors produced by the seed but the degree of dependence varies from fruit to fruit. 

Fruits are characterized by an abnormally high level of auxin in their ovary. Some fruits can develop without the need for fertilization and seed development, this is called parthenocarpy. In our farm this phenomenon is observed especially in the variety Fuerte in which parthenocarpy rates up to 70% have been found (see appendix H1).