Fruit flies and white rot: major obstacles in peach cultivation

Currently, fruit fly control is carried out using contact and ingestion insecticides, malathion and deltamethrin, which act on the adult stage of the fruit fly. Despite being an alternative for controlling the pest, there is a great risk of losses, as the presence of a single adult female is enough to cause damage and in the conditions where peach production occurs, population pressure is very high due to the large number of fruit fly hosts (Salles, 1995). Furthermore, there is concern about the unsustainable use of agrochemicals (insecticides, fungicides and herbicides). In 2011/12, research and extension institutions implemented an alert system for the main phytosanitary problems in peach cultivation, based on monitoring pests, recording meteorological factors, training producers and disseminating results through a weekly newsletter.

Embrapa Clima Temperado (CPACT), together with the Technical Assistance and Rural Extension Company (Emater/RS), the Federal University of Pelotas (UFPel), the Association of Peach Producers of the Pelotas Region (APPRP) and the Union of Industrias de Conserva de Pelotas (Sindocopel), implemented in the 2011/12 harvest the alert system for phytosanitary problems in peach cultivation in the municipalities of the Pelotas region, in the south of Rio Grande do Sul, with the purpose of assisting producers in the establishment of management techniques to control fruit flies and brown rot.

The alert system is based on pest monitoring, dissemination of results and training of producers. Pest monitoring is being carried out in two locations (stations) in Pelotas: 1) Colônia Rincão da Cruz (coordinates: 31°25'54,99" S and 52°32'52,54" W, altitude 219m) and 2 ) Colônia Santa Áurea (coordinates: 31°29'47,87" S and 52°32'34,89" W, altitude 206m); and a location in the municipality of Morro Redondo, Colônia Colorado (coordinates: 31°36'38,21" S and 52°40'23,00" W, altitude 219m). Automatic meteorological stations were also installed in these three locations to collect climate data such as temperature, relative air and soil humidity, rainfall and hours of leaf wetness. The type of equipment used was the Vantage Pro 2™ Plus weather station (Davis Instruments Corp, Hayward, CA, USA).

To monitor fruit flies in each season, 30 McPhail traps were installed, baited with hydrolyzed protein. Every week, technicians from Embrapa and Sindocopel carry out assessments to count the flies captured in the traps. The counting of captured flies, changing the attractant and collecting climate data are carried out from Monday to Thursday. Once a week the project team meets to analyze the data and organize the information. A bulletin is provided with information regarding the fruit fly population and recommended strategies for its control. The bulletin is distributed via email, published on the Embrapa Clima Temperado website (http://www.cpact.embrapa.br/sistema_alerta) and Emater (www.emater.tche.br), on radio stations (commercial and community) in the region and on Embrapa Clima Temperado television programs (South Land) and Emater (Rio Grande Rural), in addition to being printed and distributed to producers. The Alert System Bulletin is always published on Thursday, so that, if control measures are adopted, producers can carry them out in a timely manner. In addition, text messages are sent weekly via cell phone, alerting producers about the pest population/infestation.

Data from fruit fly monitoring and climatic variables will also be used to implement an alert system, which in addition to informing the population of flies present in orchards, can be used to predict the occurrence of the pest, through of a mathematical model. This forecast will be made based on data collected in the last three agricultural harvests, the thermal requirements of the fruit fly and temperature data collected by meteorological stations, being essential for its control in peach cultivation.

Main results obtained

The fruit fly A. fraterculus It is the main pest of fruit growing in Rio Grande do Sul. With the establishment of the alert system, it was possible to quantify the population of this pest in the region's orchards and indicate to the producer the need to adopt control measures, based on the application of toxic bait during the harvest and the application of insecticides for coverage, mainly during the 40 days before peach harvest. It is worth noting that monitoring the fruit fly in the three seasons provides an indication of the pest population, but it is necessary for the producer to also carry out monitoring on his property, as depending on the alternative hosts cultivated or not in the vicinity of the peach orchards , the fruit fly population can vary.

During the two years the alert system was in operation, the fruit fly population behaved differently. In the 2011/12 harvest, the population was smaller than in the 2012/13 harvest (Figure 1). In peach orchards, the first flies were captured from the end of August, reaching the highest peaks in the months of November, December and January, when the population then decreased drastically, being collected in small quantities until the beginning of winter. This behavior is related to peach phenology, with the largest populations observed during the period in which the fruits are ready for fruit fly larval development (around 40 days before harvest). However, in addition to the population increase observed in the 2012/13 harvest in relation to the previous year, it was found that in this last harvest insects were captured earlier and, probably, one of the factors that have contributed to this anticipation was the increase in average temperature , during the period from August to December (Figure 2). In general, in this period (August-December), the months of 2012 were warmer than 2011 and this difference reached 4,5ºC in August and 3,7ºC in December. Thus, there was a greater accumulation of degree days, resulting in a shorter period for the insects to reach the adult stage. This condition of high temperatures demonstrates the need to monitor fruit flies and the importance of warning systems in informing about the occurrence or tendency to have greater population pressure of the pest.

For the Brazilian tropical and subtropical climate, models for predicting the occurrence of pests are not yet applied, as they were developed for countries with a temperate climate and, normally, do not adjust to our conditions. Although the peach tree alert system does not predict the occurrence of pests, it can help verify population increase trends and inform the producer what is happening in a short period of time.

Figure 1 – Population fluctuation of fruit flies in the Rincão da Cruz (A), Santa Áurea (B) and Colorado (C) colonies, during the 2011/12 and 2012/13 agricultural harvests. Pelotas and Morro Redondo (RS)

Figure 2 – Average monthly temperature from August to January in the Rincão da Cruz (A), Santa Áurea (B) and Colorado (C) colonies, during the 2011/12 and 2012/13 agricultural harvests. Pelotas and Morro Redondo (RS)

Brown rot alert system

Brown rot, caused by the fungus Monilinia fructicola, is the most important disease of the crop and very dependent on control with fungicides. The use of a system tool for predicting the occurrence of a brown rot epidemic is very important so that its management is carried out preventively and at the correct time, avoiding the damage that the disease could cause, in addition to avoiding the application of fungicides in a disorderly and unnecessary manner, optimizing their use.

For the disease prediction system, meteorological data such as temperature, air humidity, leaf wetness, rainfall and wind are necessary to be used in models to predict the risk of infection by the pathogen. In the case of brown rot there is a model developed by Tate et al (1995) in Australia and which has been validated and recommended in stone fruits in the region of Victoria, Australia (Holmes et al, 2008; Holmes et al, 2011; Holmes, 2012). The meteorological data needed to determine the risk of brown rot infection are the period of leaf wetness and the average temperature during that period. The calculation of the risk of infection of flowers and fruits by brown rot is done as follows: number of hours of leaf wetness x average temperature during the period of leaf wetness, which results in intensity of infection risk (degrees hour = °h ), value categorized according to Table 1.

Table 1 – Categories for the intensity of risk of brown rot infection, based on the number of hours of leaf wetness

Intensity of infection risk	°h range
Without risk	under 90
Marginal	90 to 120
Low	121 to 150
Moderate	151 to 180
Alto	Above 180

Intensity of infection risk

°h range

Without risk

under 90

Marginal

90 to 120

Low

121 to 150

Moderate

151 to 180

Alto

Above 180

Meteorological data to test the model developed by Tate et al (1995) were obtained from automated weather stations that were installed in peach orchards. In the locations of Colônia Rincão da Cruz (Pelotas) and Colônia Colorado (Morro Redondo) orchards of the Maciel cultivar were evaluated, while in Colônia Santa Áurea (Pelotas) the cultivar evaluated was Esmeralda. The leaf wetness sensors were coupled to the weather station at two heights: Colônia Colorado and Colônia Santa Áurea at 1,10m and 2,00m and in Colônia Rincão da Cruz at 0,90m and 1,70m (newest peach orchard – third year).

The period analyzed was from October 1st to December 10th, 2012 with leaf wetness and temperature data stored every 15 minutes. The result demonstrates that for the season analyzed, the maturation and harvest phase of early and mid-cycle peach trees, more than 50% of the days presented some risk of peach infection. M. fructicola, indicating that the environmental conditions of the period were very favorable for the occurrence of brown rot in peach fruits (Figure 3, Table 2). During the analyzed period, 19% to 25% of days presented a high risk of brown rot infection. This shows that in this situation, the application of fungicides is necessary throughout the pre-ripening period until harvest, with no reduction in the number of applications in relation to the fixed application schedule.

Figure 3 - Intensity of risk of brown rot infection in three peach producing locations in the Pelotas region (RS). Period analyzed: October 1st to December 10th

Table 2 – Number of days (%) with risk of brown rot infection in the three monitoring locations of the Alert System

Risco	Colorado	Santa Áurea	Rincão da Cruz
No Risk (0)	35 (49,3)	33 (46,5)	33 (46,5)
Marginal (1)	7 (9,9)	7 (9,9)	6 (8,5)
Low (2)	7 (9,9)	10 (14,1)	6 (8,5)
Moderate (3)	4 (5,6)	7 (9,9)	10 (14,1)
Viola (4)	18 (25,4)	14 (19,7)	16 (22,5)
Risky days	36 (50,7)	38 (53,5)	38 (53,5)
Total days	71	71	71

Risco

Colorado

Santa Áurea

Rincão da Cruz

No Risk (0)

35 (49,3)

33 (46,5)

33 (46,5)

Marginal (1)

7 (9,9)

7 (9,9)

6 (8,5)

Low (2)

7 (9,9)

10 (14,1)

6 (8,5)

Moderate (3)

4 (5,6)

7 (9,9)

10 (14,1)

Viola (4)

18 (25,4)

14 (19,7)

16 (22,5)

Risky days

36 (50,7)

38 (53,5)

38 (53,5)

Total days

71

71

71

Comparing with the data presented by Holmes et al (2008) and Holmes et al (2011), Brazilian environmental conditions are very favorable for the occurrence of brown rot, as in Australia the number of days with risk of brown rot infection M. fructicola is very low and there is rarely a high risk of fungal infection.

For the model adopted in Australia to be used in the Alert System in the Pelotas region, further studies are still needed. But, in any case, the data analyzed so far point to a very favorable scenario for the occurrence of brown rot, requiring greater attention from peach tree producers in the preventive management of the disease and the application of fungicides.

Positive results and challenges

The alert system for peach phytosanitary problems arose from the need of producers to obtain information on pest management and readjustment of the production system. After two agricultural harvests, the alert system made it possible to obtain advances related to the awareness of producers in the use of recommended control techniques, such as monitoring, applying toxic baits and using agrochemicals recommended by the Ministry of Agriculture, Livestock and Supply (Map). The alert system also provided greater cooperation between research institutions, canning industries and peach producers. Although these advances are significant, it must be considered that the removal of deep-acting phosphorus insecticides requires producers to take greater care of the orchard so that losses do not occur. These measures include greater attention to monitoring pests and applying toxic baits and covering insecticides as recommended by the research. On the other hand, there is a demand to develop more attractive and longer-lasting toxic baits in the field. Although the results are not immediate, research is also being carried out using parasitoids for biological control, in conjunction with other fruit production chains, the installation of a biofactory for the production of sterile insects and parasitoids.

It should also be considered that the alert system is another tool that aims to assist the producer in pest management.

Click here to read the article in Cultivar Vegetables and Fruits 82.