How to monitor and manage aphids that cause yellow dwarfism in wheat

In 2019, at the time of wheat crop implementation, there were questions whether it would be a favorable year for the occurrence of aphids and transmitted viruses. In a scenario of above-average temperatures in April, May and June, it was suspected that problems associated with aphids on wheat would occur this harvest and one of the questions was how to manage them.

Temperature is one of the main factors that regulate the development and reproduction of insects. The closer temperatures are between 18°C ​​and 25°C, the higher the development and reproduction rates of winter cereal aphids (aphids). On the other hand, rain is harmful to insects. The month of April had precipitation close to the historical average, however, May was marked by above-average volume. Thus, until that moment temperature and precipitation were opposing each other. Until April, aphid populations were moderate, but in May there was a significant reduction.

Historically, due to the decline in temperature from autumn to winter (June and July) the aphid population reduces. For the Middle Plateau region, a critical point in determining the importance of yellow dwarf epidemics in the wheat crop is the timing and intensity of the aphid peak during winter. The earlier and the larger the populations, the greater the incidence of the virus and the greater the damage associated with yellow dwarfism. Therefore, after the first 20 to 30 days of wheat emergence, it is essential to monitor and apply insecticides if the level of 10% of plants with aphids is reached.

In 2019, the resumption of population growth occurred earlier than that recorded in the last decade. Furthermore, population growth was intense, reaching the highest non-autumn peak in the last decade. The reasons for this intense growth are debatable. The drier winter may have contributed. June, July, August and September were marked by rainfall well below the historical normal average (only 261,7 mm accumulated in this period this year, against 680,9 mm of the historical normal). Furthermore, lower populations of natural enemies (especially parasitoids) may have been unable to contain the rapid growth of aphid populations in a favorable environment.

Associated with this population growth, there was a high incidence of yellow dwarfism. In plots without insecticides, the average incidence reached 28% of plants with symptoms (varying according to the susceptibility of the genetic material). The most efficient management strategy, which came closest to treatment with weekly application of insecticides, combined application on aerial parts and seed treatment (average incidence of 5%), followed by application only on aerial parts (8%) and seed treatment (18%). In 2019, in this region, seed treatment (TS) contributed to management, with an average reduction of 10% in the incidence of the virus, but it was not enough, as population growth occurred strongly in August, when the action of TS was already was reduced.

The damage associated with viruses is varied and depends on genetics. The symptom normally seen by producers and technicians is the yellowing of the leaves from the apex to the base. But the virus has its effects long before it is visualized by this yellowing. When introduced into the plant's vascular system during aphid feeding, the virus promotes the degeneration of phloem cells. One of the first symptoms is the reduction in root growth due to the difficulty in translocating photoassimilates to this organ. With less developed roots, the plant's entire growth and ability to resist biotic and abiotic stresses is compromised. The plants have reduced growth of the entire mass of the aerial part. During earing, a decrease in the size of the ears and also basal and apical sterility are evident, which can often resemble other types of injuries. An end-of-cycle symptom associated with infection is the darkening of the ears, a phenomenon known as “chocolate ears”. The chocolate ear was very common in the Middle Plateau in 2019 and, generally, technicians and producers confuse the diagnosis of this phenomenon. The severity of symptoms varies depending on the material. Viral infection at the beginning of the cycle compromises, on average, 40% to 50% of the productive potential of infected wheat plants. In field plots, the average yield in 2019 for adequate management of yellow dwarfism (seed treatment + application in part of the area when 10% of plants with aphids was reached) yielded 71 bags per hectare. In contrast, in the control without insecticides the yield was 48 bags/hectare.

Initiatives for monitoring and managing aphids

The Winter Cereal Pest Monitoring Network is an action coordinated by Embrapa Trigo, created in 2015 together with partners in the states of Rio Grande do Sul, Paraná, Minas Gerais and Mato Grosso. The objective is to monitor, through traps and field experiments, insect pest populations, relating population levels to the economic damage caused to establish alert systems for decision-making on crop management. The aim of the work is the monitoring of aphids, insects popularly known as aphids, which can cause direct and indirect damage to wheat. When feeding on plants, aphids transmit the Barley yellow dwar virus, a virus that causes yellow dwarfism in several winter cereals. On average, wheat plants infected by the virus at the beginning of their development can have their grain yield compromised by between 40% and 50%. As the name suggests, the infected plant suffers from stunting, reduced growth, a degenerated vascular system and yellowing of the leaves, which impairs photosynthesis and grain production. Biological and chemical control of aphids and genetic resistance (to the vector and the virus) are strategies for managing this virus.

Use of Information Technology

The need to develop a tool to record all the information collected in the experimental network brought researchers in the Information Technology (IT) area closer to researchers in the agronomic and biological area (entomologists and virologists). Thus, within the scope of the project Integrated platform for monitoring, simulation and decision-making in the management of epidemics caused by viruses transmitted by insects, three pieces of software were developed to support both the creation of the database and support for pest control decision-making. in crops.

Integrated platform for monitoring, simulation and decision-making in the management of epidemics caused by insect-transmitted viruses

TrapSystem: platform that stores, organizes and allows you to view insect monitoring data. Developed in partnership with IFSul Passo Fundo.

Address: http://gpca.passofundo.ifsul.e...

AphidCV: software that automates the counting, classification and morphometry of aphids. Developed in partnership with the University of Passo Fundo. https://www.upf.br/noticia/pes...

ABISM: insect population simulation model. Developed in partnership with IFSul Passo Fundo and University of Passo Fundo. http://200.132.58.15:6538/ABIS...

 

Douglas Lau,
José Maurício Cunha Fernandes and
Alberto Luiz Marsaro Júnior,
Embrapa Wheat

 Alexandre Tagliari Lazzaretti,
Federal Institute of Education, Science and Technology Sul-rio-grandense

 Paulo Roberto Valle da Silva Pereira,
Embrapa Forests

Robert Wiest,
Federal Institute of Education, Science and Technology Sul-rio-grandense

 Rafael Rieder,
University of Passo Fundo

 Marcus Vinicius Sampaio,
Federal University of Uberlândia

Alfred Stoetzer and
Marielli Ruzick,
Agricultural Research Foundation

 I filmed Teresinha Riffel,
Três de Maio Educational Society

 Elderson Ruthes and
William Iordi do Anjos,
ABC Foundation

 Janine Palma,
Central Gaucha Cooperative

Ayres de Oliveira Menezes Júnior,
State University of Londrina

Luiza Rodrigues Redaelli and
 Simone Mundstock,
Universidade Federal do Rio Grande do Sul

 Carlos Diego Ribeiro Dos Santos,
UFRGS

Juliana Pivato,
PIBIC/CNPq - Embrapa Trigo

Monique D’Agostini and
José Roberto Salvadori,
University of Passo Fundo

Patrícia Sobral Silva,
Federal Institute of Education, Science and Technology of Mato Grosso

Paulo Eduardo Branco Paiva,
Federal Institute of Education, Science and Technology. from the Triângulo Mineiro