Introduction

In the state of Chihuahua, the cultivation of apple occupies an area representing about 50% of the just over 60 thousand hectares are estimated cultivated in Mexico, with a greater volume of production to 200 thousand tons per year, with a value of 1 913 billion pesos (^{SIAP, 2013}).

The apple tree is affected by a wide range of direct and indirect phytophagous (^{Gontijo et al., 2012}). A phytophagous causing indirect damage and has received increased attention in recent years is the woolly aphid apple Eriosoma Lanigerum Hausmann (Hemiptera: Aphididae) (^{Beers et al., 2010)}. This phytophagous can overwinter in the root and aerial part of the plant. The population that overwinters in the aerial part is more susceptible to extreme cold temperatures (^{Hetherington, 2009}). In infested trees, the first instar nymphs (walkers) are dispersed form new colonies in the tree (^{Asante et al., 1993}), walkers produced by overwintering females serve as source of infection for each new season, migrating root the aerial part of trees during the spring (^{Damavandian and Pringle, 2007}).

The increase of woolly aphid in apple orchards seems to be associated with a greater variation in the extreme and reduction temperatures in rainfall (^{Ramirez et al., 2011}), also with changes in programs pesticide use and alteration natural biological control (^{Gontijo et al., 2012}). This may have an impact on the geographical distribution of phytophagous, survival rates of population growth in the number of generations in the crop-pest synchrony in interspecific interactions (^{Lastuvka, 2009}; ^{Porter et al., 1991}; ^{Ramirez, et al., 2011}; ^{Stay et al., 2009}), increase in production costs (^{Ramirez et al., 2011}) and crop losses by pretending still to this day, fight it before understand and consider it as the source of the problem and not the result of a number of factors interacting (^{Barrera et al., 2008}; ^{Romero, 2004}).

With the use of pesticides has avoided the damage that could cause some pests (^{Headley 1968}; ^{Pimentel et al., 1978}), but its use has been associated with an increase in losses from them (^{Kogan and Bajwa, 1999}), environmental problems and human health (Sabitha and ^{Shetty, 2009}) and the selection of traits conferring resistance to pests (^{Lagunes et al., 2009}). In some farming systems it has documented the negative effect of broad-spectrum insecticides on populations of natural enemies (^{Matlock and De la Cruz, 2002}; ^{Romero, 2004}) and the ecological impact of farming systems of high performance is enhanced by the intensive use of insecticides, in these systems, the lack of information by decision makers, promotes actions that harm non-target species and eliminate organisms that serve as food for others in the food chain (^{Altieri et al., 1989}; ^{Holland y Luff, 2000}; ^{Romero, 2004}).

In any pest management program in which pesticides are used, one can determine the coefficient of environmental impact assessment (CIA) (^{Kovach et al., 1992}). Environmental impact studies and selection pressure for pesticide use, allow to estimate the consequences of management actions on one or more environmental indicators (^{Ramirez and Jacobo, 2002}; ^{Jacobo and Ramirez, 2006}). The assessment of the environmental impact resulting from the use of pesticides in agricultural systems, information of temperature and precipitation and timely detection of organisms that reduce crop production, strengthen decision making in designing programs pest and diseases. However, the omission of key elements in the management of pests and diseases, has meant that in eight sprayings of agrochemicals performed in apple tree in Chihuahua, Mexico, only three have technical support (^{Ramirez y Jacobo, 2002}).

Based on the above, in this paper objectives were: a) obtain and analyze information maximum, minimum temperatures and precipitation for the years 2010 and 2011; b) quantify immature woolly aphid rising from the roots to the aerial part of the tree and its relationship with the presence of air phytophagous colonies; and c) to estimate the environmental impact of pesticide use in apple orchard with different management.

Materials and methods

This work was done in Cuauhtemoc, Chihhuahua in apple orchards, located geographically between the 28° 25 '58' 'and 2° 28' 19 '' north latitude and between 106° 54 '25' 'and 106° 54' 37 '' length west, with an average height of 2 042 meters above sea level; with maximum distance between orchards of 5 900 meters. Three orchards were selected with the Golden Delicious variety of pattern Franco is susceptible to woolly apple aphid and were designated as: 1) no pest management (orchard irrigation, without hail mesh, restricted resources without technical advice: SM); 2) with integrated pest management (defined by garden with anti-hail net, irrigation, without restriction of resources, technical assistance, using sexual pheromone disruption of mating of codling moth and chemical pest control and disease management: IPM); and 3) garden with conventional management (with anti-hail net, irrigation, without restriction of resources, technical assistance and regular pesticide applications: MC).

The information maximum temperatures and minimum daily and precipitation was obtained during the period from April to October 2010 and 2011 of an automated weather station (Campbell Scientific^MR, with temperature probe and integrated rain gauge) with geographic location of the 28° 26 '49 '' north latitude and 106° 52 '40' 'west longitude and maximum distance of 5 300 m from the station to garden further away. the occurrence of maximum and minimum temperatures based on confidence intervals for the average described (^{Sincich et al., 2002}) and number of days with less than 4 °C above 30 °C and minimum temperatures. With a software called SICA (^{Medina et al., 2004}), daily heat units were calculated using the simple method with minimum temperature within critical of 4 °C (^{Asante et al., 1991}). Daily heat and precipitation, accumulated units per year and during the evaluation period and adjusted to the modified Weibull model (^{Pennypacker et al., 1980}), which is flexible to the parameters Y=1-exp (-UC o -pp)/b) ^c ; where Y= cumulative proportion of units heat or accumulated occurrence of precipitation (mm); UC, pp = heat units (or accumulated rainfall); b = estimator growth rate in its inverse (1 / b); c = parameter curve shape. For the same variable, the estimate of the rate of increase per year, to detect significant differences between them. Generated models were obtained with the SAS^MR (2002) statistical package.

Results and discussion

The recorded temperatures allowed noted that during 2010, the average maximum temperature fluctuated between 25.3 and 26.2°C, while in the year 2011 fluctuated between 26.9 and 27.6° C, so that, based on the interval with 95% confidence, stated that the average maximum temperature was statistically different between years and higher in 2011. For 2010, the confidence interval for the average minimum temperatures ranged between 9.2 and 10.4° C, while in 2011, the average minimum temperatures ranged between 8.8 and 10°C, declaring statistical equality between years for the average minimum temperature (Table 1). For 2010, minors days at 4° C were 23 and older days at 30°C were 34, while for 2011, the number of days with less than 4°C temperature were 25 days with temperature above 30°C were 37 (Table 1). In 2010 they quantified UC 2 958 with a rate of increase of 4.4X10^-3, while in 2011 they were joined UC 3 061 with a rate of increase of 4.6X10^-3. The gradual increase in the accumulation of heat units was statistically different between years (Table 1). It was also observed that precipitation occurred during 2010 was 322 mm, while in 2011 226 mm, a differential of 56 mm were accumulated. The Weibull model adjusted significantly accumulated rainfall with greater determination coefficients to 92% and lower coefficients of variation 27.5 (Table 1). In 2010 the rate of increase in the accumulated rainfall was 4.6 x 10^-3 and statistically different 3.6 x 10 ^-3 from which was the rate of increase in the cumulative rainfall for 2011 (Table 1).

Table 1 Intervals average temperatures maximum and minimum averages less days at 4 °C and 30 °C higher and indicators Weibull model in adjusting the heat and accumulated precipitation (mm) in Cuauhtemoc, Chihuahua units increase. During the years 2010 and 2011. 

Σ= valor acumulado durante el ciclo; Modelo Weibull de forma: Y=1-xp(-UC)/b)c o Y=1-exp(-PP mm)/b)c donde: Y= valor estimado; c= parámetro de forma del modelo Weibull; 1/B= estimador de la tasa de incremento; valores con misma letra en columna intervalos de confianza para temperaturas y en columna (1/B) significa igualdad de pendientes con 95% de confianza; R2= coeficiente de determinación; CV= coeficiente de variación en por ciento; Pr>F= probabilidad de encontrar un valor mayor a un valor de F tabulada.

Temporal occurrence of woolly aphid

The number of aphids trapped foil tape was statistically different between years and orchards. Among years, during the cycle 2010 were counted 2 049copies, while in 2011 were 11 269 units (Table 2). Among orchards, in 2010, the garden without pest management, the median trapped aphids was 140, in the garden with MIP was 330 copies, while in the garden with conventional management 283 copies were trapped (Table 2). For 2011, the garden without management, the median number of aphids trapped in aluminum foil tapes was of 4 461 copies; of 1 698 units in the garden with MIP and 7,831 copies in the garden with conventional management (Table 2). The significance was detected by comparing the number of air aphid colonies between years, since in 2010 a median of 1 and 46 colonies in 2011 was detected (Table 2). No consistent relationship between the number of aphids on the rise and the subsequent occurrence of colonies in the aerial part was detected. Similar point was previously reported by ^{Beers et al. (2010)}.

Table 2 Aphids trapped in aluminum foil tapes and air woolly aphid colonies per year and orchards (under different management) for the years 2010 and 2011 in Cuauhtemoc, Chihuahua. 

Valores en columnas por año con misma letra significa igualdad estadística entre ellos; valores en hilera para manejo de huerto dentro de un mismo año con misma letra significa igualdad estadística entre ellos.

The occurrence of higher temperatures, higher heat accumulation units and less precipitation could initially favor the survival of pests and subsequently increase their establishment or during the 2011 cycle, the previous marking coincides with the previously highlighted by ^{Ramirez et al. (2011)} and ^{Stay et al. (2009)}, deriving the above in greater use of pesticides and consequently greater environmental impact in apple orchards this year (Table 3).

Table 3 Pesticides applied during the years 2010 and 2011 in apple orchards and its coefficient of total environmental impact. 

In comparing aerial colonies among orchards, for 2010 statistical equality was detected in orchards without management and conventional management, since the presence of colonies was almost zero and in the garden with MIP were detected 77 aerial colonies value it was significantly different from the other two orchards (Table 2). In 2011, the number of aerial colonies in the garden without management and MIP were statistically equal, with values of 247 and 54 colonies respectively and different from the orchard with conventional management with only 1 detected colony (Table 2).

At least for the past 10 years, plant pathogens and herbivorous insects affecting apple orchards in the state of Chihuahua, have been exposed to the same chemicals that are used for combat, the result of comparing reported by ^{Ramirez y Jacobo (2002)} and the products used in apple orchards reported in this paper. During 2010 and 2011, pest management in apple depended on 20 chemicals in commercial formulation, of which 5 were insecticides- acaricides, 4 insecticides, 3 miticides, 6 fungicides and 2 bactericides (Table 3). Of all these chemicals, the use of sulfur was the most environmental impact with 209 IUA, followed in order of importance Mancozeb and Ziram fungicides with 122 and 76 IUA, respectively (Table 3). Regardless of pest management in the garden, use of sulfur had high impact on the levels of environmental impact, results coincided with the statement made by Covach et al. (1992), who compared the environmental impact of conventional organic pest management against in which the use of sulfur included detected a differential of 782 UIA top for the garden with organic management. The increase in the occurrence of woolly aphid and very likely other phytophagous and phytopathogenic, reverberated in 55 and 81% more UIA than for 2011 very possibly derived from the change in environmental conditions between 2010 and 2011.

Over the past 15 years, attention on climate change for the next 200 years and its effect, first organisms and subsequently in distribution, have distracted attention from what happens every year in relation to abiotic factors. In this work, significant differences in maximum temperatures that affected an increase of 3% in heat units and a 30% reduction in acumulative rainfall during the period from april to august between 2010 and 2011 to the west were evident Chihuahua state. This situation of temperature and precipitation that could be casuistry, provided evidence of variability in short period of time and its influence on the increase of copies of woolly apple aphid and the consequent environmental impact product handling, perhaps deficient pests and diseases on apple trees to the west of the state of Chihuahua, because even with changes in temperature, rainfall and incidence of phytophagous, activities orchard management, with combat phytophagous inclusive, it is based on an outdated and inflexible making decisions.

Conclusions

The incidence of higher temperatures during 2011, the highest number of accumulated and lower precipitation, heat units, could favor the establishment of woolly aphid and very possible other herbivores and pathogens in apple orchards that led to increase in the diversity of chemicals and number of applications for combat, which detonated in a coefficient of environmental impact than 2010. Of all the pesticides used in apple during the study period, the use of elemental sulfur was the most environmental impact with 209 UIA, they followed in order of importance Mancozeb and Ziram fungicides with 122 and 76 UIA, respectively.

No copies relationship between rising and air woolly aphid colonies were detected.