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Forest pests associated with silvicultural problems

Some companies, in order to reduce production costs, have drastically reduced or simplified forestry operations, often to the detriment of quality.

10.11.2015 | 21:59 (UTC -3)

The occurrence of forest pest outbreaks has a direct link with planting quality control. Aspects relating to the choice of species and most suitable origins, soil-climatic conditions, quality of seedlings, physical conditions of the soil, site, soil preparation, planting techniques, nutrition, silvicultural treatments are fundamental for creating environmental resistance factors to pest attack. Other factors beyond human control are also responsible for predisposing forests to attack by pests. Phenomena of an abiotic nature, such as hailstorms, heavy frosts, prolonged droughts, as well as factors of a biotic nature such as attacks by primary pests, can also stress plants, favoring the appearance of pests.

In the event of outbreaks of

Pissodes castaneus

, experience has shown that, in at least 90% of cases, plants present serious problems with curling or casing, which occurred during the seedling production phase or during planting. In other words, it appears that, in many cases, old seedlings are being planted, whose roots have already become tangled in the tube and/or, cases of tangling and encasement, caused by the mirroring or vitrification of the soil, by the use of troughs in shallow soils. or clayey, preventing normal root development. There are also problems in plantations located in places with hydromorphic soils that stress the plant.

It is clear that companies, in order to reduce production costs, have drastically reduced or simplified forestry operations, often to the detriment of quality. However, this will reflect on the resistance or susceptibility of plants to the biotic and abiotic factors to which they are exposed. Furthermore, as we are dealing with long-rotation crops, it is essential that implementation is carried out with as few technical nonconformities as possible, as the results will be obtained in the long term, in the case of pine, twenty years, on average.

The choice of site is another extremely important factor, so that you have a plantation that is resistant or withstands pest pressure. There is no point planting in bad places that have shallow soils with rock outcrops, poorly drained soils, as these plantations will be targets for pests. For many years this was not taken into consideration in pine forestry in Brazil. However, after the introduction of the wood wasp in the country, in 1988, of the aphids of the genus Cinara and Essigella, of the Adelgidae, Pineus boerneri and Pissodes castaneus, this became an indispensable condition, to provide conditions of resistance to plantations. .

Plants damaged by hail become susceptible to attack by Pissodes castaneus, due to the emission of allelochemicals that will attract the weevil. Likewise, water stress caused by prolonged droughts and damage caused by heavy frosts can predispose plants to attack by the pest.

Pruning, a very important silvicultural practice, when carried out at an inappropriate time, may compromise planting. The wounds caused by this practice exude chemical compounds that attract pests. For this reason, it must be carried out during periods of low population density of pests associated with planting. Furthermore, pruning remains should be eliminated and, if possible, chopped to prevent the proliferation of insects. Care must also be taken during thinning.

The application of herbicides to control weeds, in young plantations, must be carried out carefully, at times that avoid possible drifts, with the use of regulated spray nozzles, keeping the tractor speed constant, which if not If obeyed, they can stress the pine plants and predispose them to attack by the pine weevil, due to the excess product released in the plants. It is also essential to maintain native vegetation between planting lines, as they will provide places for shelter, feeding and reproduction of natural enemies, which will help in the biological control of pests, especially in the first year. Even one of the most effective agents in controlling giant pine aphids, the fungus Lecanicillium lecanii, needs this vegetation to protect itself from ultraviolet rays and remain in the environment. To do this, invasive plants that compete with the crop must be controlled only in the row, leaving secondary vegetation between planting rows.

Another important factor to be noted is that plants attacked by Sirex noctilio are also an ideal substrate for the development of P. castaneus. In many cases, it can be said that the presence of some pests, including the pine weevil, is an important indication that there is a silvicultural problem in the plantation, which must be identified and corrected, to ensure health to the plantation. Therefore, during the preparation of a Forest Management Program, in its planning phase, all biotic and abiotic factors that may favor pest attacks must be analyzed. In this particular, only climatic factors cannot be manipulated, but the geographic distribution of species/sources must also be considered, aiming to plant those adapted to each bioclimatic region, that is, those ecologically suitable for the region where the planting will be carried out.