Introduction

The global atmospheric concentration of greenhouse gases has increased largely due to anthropogenic influences, affecting agriculture and natural ecosystems. The increasing concentration of CO₂ interacting with climatic elements such as temperature and rainfall is influencing plant growth and productivity in a changing climate. It is well known how the effects of pest infestations and plant diseases in crops may hinder the quality and quantity of agricultural products; therefore, threatening food security. Despite its importance, there are few studies on the impact of climate change on pests and diseases so far (^{Hamada and Ghini, 2011}).

There is clear evidence that climate change is altering the distribution, incidence and intensity of plant and animal pests and diseases such as bluetongue, a disease of sheep moving from the north to more temperate zones of Europe. ^{Cannon (2008)} has found examples of plant pests whose distribution has changed in the UK and other places of Europe, most likely due to climatic factors, as in the case of bollworm (Helicoverpa armigera) which had a phenomenal increase in the United Kingdom between 1969-2004 and there have been outbreaks at the northern end of its range in Europe, and also the cottony cushion scale (Icerya purchasi) whose populations seem be spreading northward, perhaps due to global warming, as well as camellia Pulvinaria (Chloropulvinariafloccifera) which has become a more common problem in the UK, which has spread northward in England and increasing its host range in the last decade, which is almost certainly in response to climate change. In Sweden this species was known only as a problem of greenhouse crops, but it has already been established as an outdoor kind (^{FAO, 2008}).

In temperate regions, most insects have their period of growth during the hottest part of the year. Because of this, the species whose niche is defined though the climate system will respond more predictably to the change (^{Bale et al, 2002}), whereas those in which the niche is limited by other biotic or abiotic factors will be less predictable (^{Jenkinson et al., 1996}). The studies on global warming are based on historical temperature data, computer models and mathematical equations. These investigations aim to forecast the weather trend for the next hundred years. Almost all of our experts converge that unknown is asymmetrical; for example, is likely to be increasingly reluctant to accept climate change as the time goes. Uploading a heating from 2 °C to 4 °C is much more disturbing than 0 °C to 2 °C. The higher the heat, the more we move away from the current temperature and is even more likely that significant events might happen unanticipated. However, is expected the increase in the occurrence of extreme events such as droughts, hurricanes, heat and cold waves, overflowing ofthe rivers and lakes freezing, phenomena that are currently causing the greatest economic losses. These considerations have been addressed from the theory of global climate change (^{Contreras and Galindo, 2009}).

Diseases in plants and crops are an important component of agricultural production as they have the potential to significantly reduce crop yields, recent estimates indicate that this reduction consistently obtain an annual average of 12-13% achievable harvest in the eight maj or crops for food and industry, which together occupy more than half of the cultivated area in the world. In addition, some re-emerging diseases have caused devastating attacks associated with certain environmental and technological changes in crop production over the last decade, even in countries that possess improved agricultural technology (^{Jiménez-Díaz, 2008}).

^{Magaña (2007)} mentioned that in Sonora there will be an increase in mean annual temperature ranging between 1 and 2 °C by 2020 and 1.5 to 3 °C by 2050m, a situation that led to the subject of this study, which characterized and quantified the impact of climate change on the incidence of favourable conditions for one of the most important pests of pecan in Hermosillo, Sonora, the pecan nut casebearer. Also, favourable conditions were assessed for infections by leaf rust and stripe rust in wheat, in valleys Yaqui and Mayo (Southern Sonora).

Materials and methods

The average monthly temperature data were used for the 2000-2050, period generated by techniques of downscaling of the outputs of the model CGCM3^_1 and published by the interdisciplinary group comprising the Lawrence Livermore National Laboratory, the California Nevada Applications Program, Climate Central and the University of Santa Clara in United States of America (http://gdo-dcp.ucllnl.org/). Data shared in NetCDF (Network Common Data Form) files were downloaded and stored in adatabase using MySQLas amanager ofthe database to streamline the queries. Similarly to delineate the agricultural regions we used the borders of the Costa de Hermosillo and Valleys Yaqui and Mayo (Southern Sonora) provided by the State Committee on Plant Health of Sonora.

Overall for Sonora, data from 1076 nodes were downloaded, which are shown in Figure 1. 27 nodes covering the Costa de Hermosillo and 24 nodes for covering the agricultural region in the South of Sonora (Figure 2) were identified. With these average monthly temperatures and using the technique ofleast squares, we obtained regression models between data of the stations of the Agroson network and nodes data. All available data for each station and the corresponding nodes during the period 2000-2010 were used. Regression models allowed us to obtain the statistical parameters for calculating daily temperatures ofthe nodes in2020and2050underthe assumption that, the temperature variation is maintained. This assumption becomes quite important, since in orderto calculate the relative humidity (RH) per hour, we made a regression between temperature date and RH at different lags. Time lags chosen were those where the maximum positive correlation was found.

Figure 1 Nodes selected for the State of Sonora. 

Figure 2 Nodes selected for Costa de Hermosillo and Valleys Yaqui and Mayo. 

Since the pecan nut casebearer (GBN) is currently only present in the agricultural region of Costa de Hermosillo, we proceeded to evaluate the possible change of the incidence of under scenarios of change climate. For this, we used the model proposed by ^{Nava (1994)} , using the technique of heat units for calculating the number of generations through the residual method (-3.3 °C mean temperature). Each generation was obtained with a total of 907 accumulated UC corresponding to the life cycle of GBN (^{García, 1986}). The period between January and November was selected, period historically monitored by the Local Board of Plant Protection of Hermosillo, Sonora.

Wheat rusts are important in southern Sonora (Valle delYaqui and Valle del Mayo), especially leaf and linear. That is why the model temperature outputs proceeded to evaluate the possible change in conditions favourable to its occurrence. In the leaf rust Puccinia triticina Erikson, we used average temperatures between 15 ° and 22 °C, while for the stripe rust Puccinia striiformis f. sp. tritici, we used the temperatures between 9 and 11 °C considered optimal, in both cases, a relatively humidity higher than or equal to 80% in more than 4 hours per day in the period from 06:00 to 12:00 h (^{Jiménez, 2008}). The period from December to March was considered.

Results and discussion

Casebearer (A. nuxvorella)

According to the results with the isolines of Figures 3 to 5, an increasing number of generations of a larger number of heat units are noted, observing in the Figure 3 that the recent situation (2010) of generations of GBN, ranges from 4.9 to 6 with an average of 5.4, while for the year 2020 (Figure 4) and 2050 (Figure 5), ranging from 5 to 6.8 with an average of 5.9, although in 2050 is the same value but in the high-incidence regions (yellow and orange areas) will be higher than in 2020; i.e., covering larger areas of the producing area of walnuts, so if eradication campaigns or at least suppression of the insect are not made, there will be major problems in its control which affects production costs for the producer. This agrees with the statement by ^{van Oudenhoven et al. (2008)} , who indicated that, the temperature increases in the Netherlands in 2050 (0.3 - 2.3 °C), will make the processional worm (Thaumetopoea processionea) disperse almost throughout the whole country.

Figure 3 Map of generations of GBN during 2010. Costa de Hermosillo, Sonora. Roya de la hoja (P triticina)  

Figure 4 Map of generations of GBN for the 2020 scenario. Costa de Hermosillo, Sonora. 

Figure 5 Map of generations of GBN for the 2050 scenario. Costa de Hermosillo, Sonora.  

Leaf rust (P. triticina)

According to the results in terms of days of favourable conditions for infection with this disease, we can see that, according to graphics of isolines shown in Figure 6, relates to the recent situation (2010), between 30 and 90 days, being lower in the wheat areas of the north closer to the urban area of Ciudad Obregón, while the greatest risks occur in the coastal area especially towards the Valle del Mayo, which have a great influence on moist ocean currents, besides that they are low areas that have better low temperature conditions that favour the development of fungus. It is also clear that the region ofthe Valle del Mayo in general has better favourable conditions for the disease and is very common in this area to start the infections for Southern Sonora.

Figure 6 Maps of the numbers of days with favourable conditions for infection of leaf rust of wheat in southern Sonora. Scenario 2010. 

In 2020 (Figure 7), is shown that the days of favourable conditions are between 10 and 110, highlighting the fact that in areas near Ciudad Obregon such as San José de Bácum and Cócorit as well as the coastal part, the number with favourable conditions is reduced, this as an effect of rising temperatures, a situation that discourages fungal growth. Similar to this, it is a notable increase in this value in the region of the Valle del Mayo; increased in the reddish stain, indicating a higher number of days of favourable conditions. On the other hand, the 2050 scenario shows a similar trend to 2020, ranging favourable days between 10 and 110, but there is a geographical redistribution for different levels of risk, as there is even a small reduction in those areas in the Valley Mayo (Figure 8). Similar results were found by ^{Hijmans (2000)} and ^{Kaukoranta (1996)} point out that for every degree Celsius increased in temperature, the late blight (Phytophthora infestans) the infection will start 4-7 days earlier, in addition that the susceptible period is extended from 10 to 20 days, which could result in a larger number of spray applications (1-4), resulting in increased costs and environmental risk in the northwestern United States.

Figure 7 Maps of the numbers of days with favourable conditions for infection of leaf rust of wheat in southern Sonora. Scenario 2020. 

Figure 8 Map of the numbers of days with favourable conditions for infection of leaf rust of wheat. Southern Sonora. Scenario 2050. 

Stripe rust (P. striiformis f. sp. Tritici)

Regarding this disease, the favourable conditions in days for the current or recent situation are presented in Figure 9 (2010), where it can be seen that, the range is between 10 and 45, noting that the areas of greatest risk are located on the coasts of the valley of Huatabampo and the region of Júpare. The valley Yaqui had better conditions in the regions of San Ignacio Río Muerto and San José de Bácum. The areas around Ciudad Obregón have low risk.

Figure 9 Map of the numbers of days with favourable conditions for infection of stripe rust of wheat. Southern Sonora. Recent situation, 2010. 

Because for the years 2020 and 2050 there were no days with favourable conditions for the presence ofthis disease, the maps do not show information, which may reflect the temperatures are increasing. This is consistent with the views expressed by authors like ^{Magaña (2007)} , who mentioned that there will be an increase in the average temperature of Sonora ranging between 1 and 2 °C in 2020 and 1.5 to 3 °C in 2050.

Conclusions

According to the outputs of the proposed scenarios, the number of generations of screwworm's apple would increase 5.4 to 5.9 on average for the region of Costa de Hermosillo, Sonora. This may indicate that control costs would increase, since an application currently costs about 1 100 pesos / ha, for those years and having an area of recommendation domain of 9 000 acres, prices are 5 million pesos only additional for this item.

An increase on days with favorable conditions for leaf rust (60-120), which could cause applications of fungicides remain as an economical method of control, especially in varieties that do not have good tolerance was observed to the disease, but due to its higth productivity, are still used.

Stripe rust, because the conditions necessary for its development, is a case that will not be problema in the future according to temperatura increases are predicted.