Early Pest Control in Wheat

Caterpillars, caterpillars, aphids and stink bugs are among the pests that attack the early stages of development of wheat cultivation. Correctly monitoring these insects is fundamental for adequate decision-making on control.

The pests that attack wheat cultivation in the initial stages of development, including the first four to six weeks, approximately in the period from seeding until elongation, they can be grouped into corós, surface caterpillars soil, aphids and stink bugs.

With a chewing habit (corós and caterpillars) or suckers (aphids and bedbugs), in general they are insects that cause concern for power to reduce the plant population and for the damage that may occur later, due to disease transmission, physiological changes and reduced the productive capacity of surviving plants. Due to the great potential to cause production losses, so-called initial pests require that special care is adopted before or immediately after the implementation of the farming, with the aim of choosing and applying the most appropriate means of control.

Os corós are underground larvae, with rhizophagous habits, considered resident pests since they have little mobility and are already present in the area during crop planning, before sowing. They are polyphagous (they feed on various plant species, whether cultivated or not), so the importance as a pest goes beyond a crop or harvest, depending on the phenological synchrony with crops.

The most common pest crow species in wheat, in Rio Grande do Sul, are the pasture choir - Dilobderus abderus (Sturm) and the wheat-horn - phyllophaga triticophaga Morón & Salvadori. Along with these species, it occurs with considerable frequency and high density, a preferably saprophagous species known by the name of coró-pequeno (Cyclocephala favipennis). This choir, due to the fact that it presents reduced potential for damage, it is not considered a pest.

The life cycle of corós is long, passing through the stages of egg, larva (coró), pupa and adult (beetle). Damage is caused exclusively by larvae passing through three sizes (stages or instars), mainly the large ones (3rd instar). The cycle of D. abderus and annual, while , P. triticophaga presents a generation to every two years. The first makes permanent galleries in the ground and is associated with crops under direct planting and pastures, since as soon as it hatches, the larvae consume plant remains and then gradually grow and become rhizophagous.

The wheatgrass does not make galleries in the ground. It occurs both in direct planting as in conventional and lives very close to the soil surface, close to the roots. Both species of corós consume seeds, roots and even parts green parts of the plant, which they pull into the soil. Infestations and damage occur in bumps (stains) which makes handling difficult. They can occur annually (pasture choir) or in alternate years (wheat corn), with the most critical period for culture lasts from May to September/October, that is, from sowing until the next the harvest.

Monitoring for verification and delimitation of infestations must be carried out from the presence of dead plants and the opening of trenches in the soil, in several moments, at any time of the year. Before wheat sowing, however, sampling more accurate soil measurements must be carried out in order to quantify the density of corós per unit area and identify the species present. A natural mortality of corós, mainly due to the action of entomopathogens (disease-causing microorganisms), is very significant, causing Infestations vary throughout the year.

caterpillars

These are insects that can already be present in the area at the time of sowing or come from posture carried out by moths, soon after the emergence of plants. It's more of a problem common in mild winter situations, caused mainly by the armyworm or fall armyworm - Spodoptera frugiperda (J.E. Smith). During during the day they shelter in the ground (under straw or clods) and at night they become active, attacking plants from the ground completely destroying them. The consequence is the reduction in plant population, which occurs in reboleiras that are expanding gradually. The wheat caterpillar (Pseudaletia sequax e P. adultera) occurs more at the end of the wheat crop cycle.

Aphids or aphids

These are sucking insects that reproduce quickly, developing numerous colonies on plants, depending on the species, it can be installed in practically all organs of the wheat plant (roots, stem, leaves and ears), from emergence to hard grain phase.

Wheat, as well as other winter cereals, is attacked by several species of aphids that occur at the same time or at different stages of cultural development. To the most frequent species are the stem aphid - Rhopalosiphum padi (Linnaeus), the green cereal aphid - Schizaphis graminum (Rondani), ear aphid - Sitobion avenae (Fabricius) and the leaf aphid - Metopolophium dirhodum (Walker).

When in high infestation (colonies), due to sap suction, can cause direct losses in grain and seed yield. Indirectly, even in low population levels, tend to cause significant damage, as vectors of phytopathogenic viruses, especially those that cause Stunting Virus Barley Yellow (VNAC). Due to the frequency that occurs and the efficiency as vector, R. pillow is currently considered the most important species in transmission of the causative agents of the virus.

The occurrence of aphids in the phases early stages of plant development tends to cause significant damage. Generally, in these phases the occurrence of R. padi quality S. graminum and, to a lesser extent, can also other species occur. In these situations, intense aphid attacks can cause the decrease in plant population as well as negatively affecting their growth. The species S. graminum has toxic saliva and causes typical yellowing of the leaves, which can evolve into tissue necrosis and seedling death. Aphid infestations originate from migrating alates. Black oats, grown in the fall, before wheat, for animal feed and Straw production for soil protection has important significance in relation to land management. vector-virus complex (aphid-VNAC), as it serves as a source of infestation of the vector and pathogen inoculum.

One of the main mechanisms for controlling aphid populations in Winter cereals are its natural enemies. The set of parasitoids (wasps), predators (ladybugs, lacewings, etc.) and fungi entomopathogens constitute an important brake on the population growth of aphids. Annually, high levels of dead aphids (mummies) resulting from the action of parasitoids, which represents effective natural control of the pest.

Bedbugs

Among the bed bugs that can be found in crops at the beginning of the development of wheat plants, green belly, Dichelops melacanthus (Dallas) and D. furcatus (Fabricius). The first species is more common in Paraná and in latitudes smaller, while the second is found mainly in Rio Grande do Sul. quite similar pentatomids, both with pronounced spines on the thorax, two pointed frontal projections on the head and ventral region of the colored body green.

Generally, in D. melacanthus the spines are larger and darker. Considered secondary as grain pests in soybeans, these species have adapted to use mulch (straw) as shelter in the system of direct planting and, without abandoning the area after harvest, began to act as Early cycle pests in corn crops, especially in the second harvest (“safrinha”) and wheat.

The damage of bed bugs arise from the sucking itself and from salivary toxins that cause deformations and changes in plant growth. Leaves with transverse, bent, curled and deformed perforations are typical symptoms from the attack of these bedbugs, which result in high losses in the yield of grains.

Pest management initial wheat production is based on a prior assessment of the real need for control measures, including the application of insecticides via seeds or by spraying plants, are adopted. This assessment It is based on monitoring pests through sampling. O Monitoring the areas allows identifying the pest species present, quantify the infestation and use criteria (population action levels) for decision making.

José Roberto Salvadori, FAMV-UPF

Article published in issue 231 of Cultivar Grandes Culturas, August, 2018