The expectation for 2023 is that the area sown with wheat in Rio Grande do Sul will register an increase of approximately 5%, according to information from the first survey of planting intentions by the agribusiness consultancy Safras & Mercado. Wheat cultivation has been a viable alternative in many properties, contributing to the sustainability of the production system. During the wheat implantation period, the monitoring and monitoring of crop development is important for identifying factors that may interfere with crop productivity and also for making decisions at the right time and assertively.
Among the factors that interfere in the definition of the productive potential, there is the attack of insect pests. Aphids are among the species that most cause problems in wheat productivity, as they reproduce quickly and can be present in all plant structures. When associated with the transmission and occurrence of Barley Yellow Dwarf Virus (VNAC) they can cause significant damage to crop performance, reducing grain yield by an average of 60%, and in less resistant cultivars, by around 80%.
Species that occur during wheat development
Aphids or aphids are sucking insects, causing significant damage to winter cereals. The most common species in wheat are Rhopalosiphum padi (oat aphid), Sitobion avenae (ear aphid), Schizaphis graminum (green cereal aphid) and Metopolophium dirhodum (leaf aphid). . Each species attacks a certain phenological stage in which the crop is found and can lodge in different parts of the plant.
The green cereal aphid and the oat aphid can start to appear soon after the emergence of the crop, being present on the stem, on the lower leaves and, sporadically, on the ears. Therefore, they are more relevant in the initial stages of crop development. On the other hand, the ear aphid appears frequently after the rubbering, settling on the wheat ear, but it can also appear on the leaves together with the leaf aphid. Unlike the other aphids, these appear later, mainly in the spring period.
Conditions that favor the occurrence
The increase in aphid pressure in the crop is favored by mild temperatures and dry weather (Lau, 2019). Parallel to this, the occurrence of cold temperatures ends up impacting the life cycle of aphids and reducing their multiplication rate. Thus, under suitable conditions, a female can produce 10 nymphs per day, showing the potential for rapid infestation of the crop. Another characteristic of the occurrence of aphids in high populations implies the emergence of winged individuals, which tends to facilitate dispersion in the crop, especially with the occurrence of winds.
Impacts on the wheat crop
The aphid affects wheat from the beginning of crop establishment to the grain filling period. The damage caused can be direct or indirect. Direct effects result from sap suction, affecting the grains by reducing size and weight. Indirectly, aphids, mainly Rhopalosiphum padi, transfer VNAC, transmitted through aphid saliva from one plant to another.
Among the most visible symptoms caused by VNAC, we highlight the reduction in crop growth and the yellow or purple coloration on the flag leaf, which can reduce grain production by around 20%, however, this number can increase depending on the variety. and environmental conditions. Thinking about the green cereal aphid and the oat aphid, in addition to the direct and indirect damage caused to wheat, they have toxic saliva, which can also cause the death of leaves and seedlings.
Monitoring and control strategies
Initially, the control strategy is based on seed treatment, mainly with insecticides from the neonicotinoid group. During the establishment of the crop and the development of the crop, monitoring is fundamental for observing the incidence and number of insects for recommending the application of insecticides in the aerial part. From emergence until booting, chemical control is indicated when, through direct counting, 10% of the plants are infested with the insect. Already during heading up to the mass grain stage, the introduction of insecticides can be recommended when an average of 10 aphids per ear is found (Meeting of the Brazilian Commission for Research on Wheat and Triticale, 2023).
For the control of aphids via aerial part spraying, the main insecticides available on the market belong to the chemical group of neonicotinoids, pyrethroids, organophosphates and sulfoxamines. For an assertive and adequate recommendation of the dosage and which product to use to control aphid species in the crop, it is important to consult an agronomist, as each chemical group has a formulation and is indicated for a certain target insect. Thus, it is necessary to obey the indicated concentration to be applied and the moment of correct decision-making for application in the plants.
Within the Integrated Pest Management (IPM) we have biological control strategies to be employed by means of natural enemies of these species, with the purpose of containing significant advances of infesting communities, in short consisting of insects of the families Coccinellidae, Dolichopodidae, Chrysopidae and Syrphidae , by fungi of the order Entomophthorales. Special forms of parasitoid control occur with microhymenopterans of the families Aphidiidae and Aphilinidae, which perform their egg laying inside the aphids, causing them to die.
Therefore, considering the management of aphids in wheat, it is essential to carry out recurrent monitoring of crops, especially in climatic conditions that favor the occurrence of aphids. Through monitoring, it is possible to obtain greater assertiveness in the control, since this is dependent on the number of insects and the different stages of development of the plants. In addition, it is recommended to look for cultivars that are more resistant to the virus transmitted by the aphid, as well as carrying out seed treatment and, if necessary, applying insecticides to the aerial part of the plant.
Text prepared by Lidiane Bilibio Bonfada and Máicon Luiz Kilpp, members of AGR Jr. Agronomic Consultancy, Junior Company of the Agronomy course at UFSM Campus Frederico Westphalen, under the guidance of Professor Dr. Gizelli Moiano de Paula.
Cover image: Pedro Bonini
