With the daily routines getting busier, the consumption of fast food in the last decade has been very high, while the intake of natural foods, due to the preparation time, ended up being pushed aside, and human’s health has been suffering the consequences of this change. Therefore, the WHO has encouraged people throughout the world to consume vegetables and fruits more frequently. These foods are rich in micronutrients, fibres and have a low energy density. By data presented in 2003, the minimum recommendation of energy consumed from these foods is 6 to 7%, and, due to this food "revolution", the volume of leaf vegetable production grows every day!
The cultivation of leaf vegetables often presents a high level of human poisoning by pesticides, from the chemical applicator to the vegetable consumer. This is due to the fact that many vegetable crops have a short cycle and consequently do not respect the amount of time needed between the last application of a chemical product and human consumption. Moreover, this crop is often not carried out on a large scale, but rather in family gardens, schools and small communities, which increases the risk of contamination, since these people generally do not have the technical knowledge and equipment to perform the application of the products without putting their health at risk.
Given this history of contamination, and also a change in the mentality of a large part of the population, which has lately been seeking healthier foods free of toxic substances, there is now a greater interest from farmers in different methods of pest control for leaf vegetables, such as biological and cultural control, but some barriers have been found. Biological control, for example, sometimes ceases to be exploited, again due to the short cycle of these crops, because there is a fear on the part of farmers that the predator or parasitoid will not act efficiently in a short period of time. Physical control, with luminous traps, with colours or pheromones, has been increasingly explored by producers, however, often associated with chemical control.
Therefore, the best solution for effective control, with a lower risk of contamination, is Integrated Pest Management, which consists mainly of 3 stages. Assessment of the ecosystem The first stage consists of sampling and monitoring of the area so that it is possible to define the population density of pest insects in that crop and also the level of economic damage. Considering that not every insect present in the crop is considered a pest, only those that are frequently present and causing harm to the farmer, these must be eliminated whenever they reach the level of control established for each species.
Decision-making At this moment, the data obtained in the sample are analyzed, regarding population density, level of damage, but also considering the parasites and predators of that pest, thus being possible to define the population growth of the pest. With this information, the producer can decide what will be more advantageous for his crop, regarding costs and financial return, the farmer may decide to use control methods, or not change that ecosystem. Selection of control methods Once the producer decided that it would compensate economically to initiate a form of control against that pest, the third step is reached, in which the control methods to be used are chosen.
There are many different tactics for integrated management of specific pests and these should be used together to make them more effective. However, for the control of leaf vegetables’ pests in general, there are a number of actions that can be taken, regardless of the pest or crop species, considered preventive controls. They are:
- Crop rotation: in successive years, the crops grown in the area should be changed, as long as they are not hosts of the same pests, decreasing populations and avoiding reinfestation. Polyculture, that is, the cultivation of different crops in the same area, can also be effective for reducing the population of pests, but only if the crops are not hosts of pests in common.
- The destruction of cultural remains: at the end of the harvest, plant residues must be transported to another area or incorporated at least 20 cm deep. This prevents pests present in fallen leaves, flowers, or remnants of any plant residue from surviving that crop and infesting the plants of the next season. Picking fallen flowers and fruit before, during and after the harvest also has the same effect.
- The increased spacing between plants: a high-density planting usually implies competition for light, generating dark and humid environments that can serve as shelter for pest insects, and hinder the application of insecticides and acaricides when necessary. However, the humidity of an environment with a slightly higher density may be favourable to the proliferation of entomopathogenic fungi, which decrease the population of pests. Therefore, the spacing between plants should be increased, but not excessively.
- Choice of a plant variety to be cultivated: there are some plant varieties that are more resistant to certain pests, and genetic modification is an interesting control solution, however, in some countries, dor instance Brazil, it is still not very much used for vegetables, since transgenic plant research presents high costs, and end up being directed to commercial crops such as corn, soy and cotton.
- Maintain the right balance of nutrients: adequate fertilization should be done since healthy and well-nourished plants tend to have a greater resistance to pests and diseases. However, excess fertilization can be extremely harmful, as excess nitrogen increases the sap concentration in the plant and can lead to an increase in the pest population, especially of sucking insects. With the i-Plant Nutrition software, you can get an instant assessment of the nutritional status of the crop and detect any deficiencies in a few clicks! (link to software tour)
- Selection of sites for growing the crop: vegetables should not be planted near other species that are hosts to the same pests, as this significantly increases the risk of infestation. Planting alongside forests can be an interesting alternative because forests often have nests of wasp species predatory of many pests. Planting should also be done in the opposite direction from the prevailing winds and away from roads, as the accumulation of dust in the leaves favours the oviposition of pest mites.
- Increase in host diversity: to intermediate, the cultivation with strips of plants of high flowering index, like corn, crotalaria and sorghum, or to create barriers around the field with flowering species like daisy and sunflower, can be beneficial for the planting of vegetables, because these plants are hosts to many natural enemies, and consequently, they increase natural biological control.
- Irrigation management: the water supply must be in accordance with the need of the crop, and if done properly, increases the humidity of the area, enabling the development of entomopathogenic fungi. The water deficit makes the plant more susceptible to pest attack, as it produces less chemical defences and more nutrients in the sap. Excess water increases vegetative growth, but decreases the morphological defences of the plant, also increasing its susceptibility to pest attack.
If the attack on the crop is already occurring, preventive management is no longer efficient, and therefore mechanical, biological, behavioural and chemical controls should be performed, taking into account the control level for each pest.
The mechanical control is based on the manual removal of insects. It can be done by collecting or crushing insects in the form of easily visible eggs, larvae, nymphs or adults.
Biological control can be done by conserving natural enemies by manipulating the environment with host plants and growing near forests, or by introducing parasites and predators into the crop, decreasing the pest population.
Behavioural or physical control uses attractive traps for insects. These traps can be adhesive, positioned at the top of the plants, where the insects stick together. Blue-coloured traps capture thrips and yellow-coloured traps, usually catch aphids and whiteflies. Light traps attract butterflies and moths, whose larvae are often vegetable pests, and usually have water at the bottom, capturing these insects. There are also pheromone traps, which attract and capture pests attracted by that specific pheromone.
Chemical control should be used as a last resource, or when the infestation is very large and requires a lot of care. When choosing the product, preference should be given to those who have lower human and environmental toxicity. In addition, it is ideal to rotate the insecticides’ methods of action, preventing insects from creating resistance. It is necessary to respect the application intervals and the grace period of each product, avoid mixtures, and only apply in the coldest hours of the day.
Keep in mind that well-nourished plants are less susceptible to disease and more efficient in fighting pest attacks. Leafy vegetables are in the i-Plant Nutrition software database and can be selected for the creation of fertilization plans when using the system. Take a look at our software and our leaf vegetable recommendation!