Cultural and environmental factors associated with winter injury to apple trees in Quebec

Abstract
A survey was conducted in 1995/1996 to identify factors responsible for apple tree mortality in Quebec during the winter of 1993/1994. Data were collected on environmental factors, cultural practices and tree characteristics. There was an interaction between the cultivar, rootstock and some cultural and environmental factors. 'Golden Delicious', 'Wealthy', 'Mutsu', 'Red Delicious', 'Golden Russet' and 'Yellow Transparent' were severely injured or killed in all regions, the mortality of other cultivars was mainly affected by certain combinations of cultural and environmental factors. Generally, percent mortality was lower in higher altitude and in density orchard with good snow cover and low density trees (e.g. larger distance between the rows and between the trees within the rows). Higher mortality was observed for very young or very old trees, specially those which had a heavy crop in the previous year or were exposed to wind. Vigorous trees and weak trees were more susceptible to winter injury than tree of moderate vigor. Less mortality was observed of trees which had been harvested early in the season. Trees on dwarf rootstocks planted in sandy soil, sandy loam, gravel loam, or any soil in combination with sandy or gravel soil type were more susceptible to winter damage. The orchard site and the location of trees in each orchard were the most important factors which affected apple tree mortality. The maximum tree mortality was observed for trees which were exposed to cold air accumulation or prevention of flow of cold air due to local obstructions like a natural windbreaks or land topography. Least damage was observed in orchards planted on a slight slope. More than 50% mortality was observed in orchards on level land away from a body of water. The absence of a river, or a large body of water near by increase mortality in all regions.
In short, selection of a good site is the most important factor in controlling winter damage. Knowledge of tree physiology and proper pruning is the key in a high density orchard. For example, irrigation in dry season specially in sandy type soil, mulching during the winter in certain orchard, proper pruning and training system, fertilizer requirement, etc. in necessary in a high density orchard. Our results revealed that even the most hardy cultivar rootstocks combination can undergo winter damage when they planted in an unsuitable site specially for dwarf and semi-dwarf rootstocks.

Introduction
Apple production potential in Quebec is between 5.5 and 7 million bushels per annum. In 1986 and 1987 there were severe low temperature injuries, and yields were reduced to 2.83 million bushels and 4.0 million bushels respectively in Quebec. This represents a loss of approximately $18 million in 1986 and $12 million in 1987, and a concomitant increase in the volume of apples imported to the province. Recently similar damage was reported by Quebec apple growers in 1993 and 1994.
One of the major problems affecting apple trees in Eastern Canada is low temperature injury occurring during the winter and spring (Granger 1981, Asnong 1982). Cold tolerance of many plant species has been extensively reviewed and studied (Chen and Li 1980, Gusta et al. 1982, Li 1987, Sakai and Larcher 1987, Khanizadeh 1991, Khanizadeh et al. 1989a, Khanizadeh et al., 1989b, Khanizadeh et al. 1992a, Khanizadeh et al. 1992b, Khanizadeh et al. 1994).
Our previous studies have compared the content of the amino acids, protein, sugars, starch, sorbitol, N, P, and K of cropped and noncropped trees in relation to cold hardiness (Khanizadeh et al. 1989b, Khanizadeh et al. 1992a, Khanizadeh et al. 1994). It has been shown that cropped trees with lower nutrient levels in their buds are more vulnerable to low temperatures than those on noncropped trees (Khanizadeh et al. 1989b, 1992a).
Short days and low temperatures are the main factors which induce cold hardiness, dormancy and subsequently cause biochemical changes in plants (Chen and Li 1980). It has generally been accepted that development of cold hardiness is associated with metabolic changes during cold acclimation (Levitt 1980).
While there have been many studies of cold resistance and metabolic change in Malus woody tissue, (Brown 1978, Sakai and Larcher 1987, Li 1987, Khanizadeh et al. 1989a, 1989b, 1992a, 1994), types of freezing injury (Weiser 1970, Granger 1981); breeding hardy varieties or using hardy intermediate framestocks (Stushnoff 1972; Spangelo et al. 1974, Granger et al. 1991, 1992, 1993); inactivating icenucleating bacteria (Lindow and Connell 1984; Lindow et al. 1989); use of chemical cryoprotectants (Ketchie and Murren 1976); cultural manipulation to slow growth and induce wood maturity in early autumn (Collins et al. 1978, Stang et al. 1978); and autumn sprays of growth regulants to delay bud break, no study has been done of the relationship between the cultivar, rootstock, environmental conditions and cultural practices in relation to winter injury in Quebec orchards.
The aim of this research was to identify the factors (rootstock/cultivar combination, environmental factors, cultural practices, etc.) which have a direct or an indirect impact on winter injury to apple trees. The precise objectives of the project were:

 - To determine the hardiness of common cultivar/rootstock combination, in Quebec orchards in relation to the orchard site.

 - To determine if there is a relationship between environment (i.e. geographical location, soil type, topography, minimum and maximum temperature) and cold injury.

 - To determine if there is a relationship between cultural practices (pruning, fertilizer application, ground cover, planting system, spray program etc.) and cold injury.

 - To determine if there is any similarity between regions in terms of cold damage, cultural practices and environmental factors.

 - To determine if orchards with similar winter damage had similar cultivar/rootstock combinations, cultural practices and environmental factors.

 - To determine what is/are the difference(s) between winter damaged orchards vs orchards with no damage in terms of cultivars/rootstocks, cultural practices and environmental factors.

The longterm goals are to develop a strategy to control winter damage by using hardy cultivar/rootstock combinations, optimal cultural practices and controlling environmental factors. This will help the apple industry in Eastern Canada to reduce annual crop fluctuations, stabilize the apple market and improve farm income.

 

Results and Discussions
There was some disagreement between the data provided by FPPQ and data collected directly from the orchards. The total number of trees and percentage of tree mortality reported to FPPQ were not the same as the data collected directly from the selected orchards. This might be due to the fact that some growers thought this information would be used for insurance purposes or tree cost compensation or they included trees which were killed by factors other than the winter of 1993/94. After removing these outliners and performing the preliminary analysis we observed a significant correlation between the results obtained from the three data sets. This indicates that information collected from the growers and provided by FPPQ are similar to that collected through the literature and that the primary factors which affect tree survival in Quebec are the choice of proper site followed by certain cultural practices after selecting proper cultivar and rootstock. More than seventy factors were analyzed in this survey (Table 1, Table 2 and Table 3). Some cultivars were deleted from the data before final analysis, since they were found only at one site and could not provide general information for the entire province.
With exception of Golden Delicious, Wealthy, Mutsu, Red Delicious, Golden Russet and Yellow Transparent which showed >50% mortality in all regions (Table 4), the other cultivars were mainly affected by combinations of certain cultural and environmental factors.
After removing the outliers, 2290 observations were selected from data set one and used for the analysis . A total of 40 cultivars (Bancroft, Close, Cortland, Early Geneva, Empire, Fameuse, Golden Delicious, Golden Russet, Hume, Idared, Yellow Transparent, JerseyMac, Jonagold, Jonamac, July Red, Lawfam, Liberty, Lobo, Lodi, MacSpur, McIntosh, McIntosh Summerland, Melba, Melrose, Mutsu, Northern Spy, Paulared, Quinte, Red Cort, Red Delicious, Rhode Island Greening, Royal Gala, Spartan, Trent, Tydeman Red, Vista Bella, Wealthy, Wellington, Wolf River) and ten rootstocks (EM26, EM7, M26, M7, M9, MM106, MM111, Ottawa3, Robusta 5, Standard) were observed in five agricultural regions (Laurentide, Eastern Townships, Québec, South West of Montréal, Montérégie) of Quebec. There were significant interactions between the regions and rootstocks indicating that the effect of low temperature injury on a rootstock varies depending on different region (Table 5) and in some cases on site within a region.
For example higher mortality was observed in areas exposed to wind (r=0.4^**). Trees on dwarf rootstocks planted in sandy soil, sandy loam, gravel loam, or any soil in combination with sandy or gravel soil type were more susceptible to winter damage (Clay=5.26% de mortality, Gravel=2.63%, lime garvel=12.50%, Clay loam=3.95%, Gravel loam=23.03%, Sandy loam=26.97%, Sandy=11.18%, Gravel sandy=6.58%, and Black soil=0.66%). This might be due to the shallow root system of dwarf rootstock in sandy soil and possibility winter damage in sandy type soil due to freezing and dryness in the summer where there was no irrigation. The orchard site and the location of trees in each orchard were the most important factors which affected apple tree mortality. The maximum tree mortality was observed for trees which were exposed to cold air accumulation or prevention of flow of cold air due to local obstructions such as natural windbreaks or land typography (Fig 1B and Fig 2D). Least damaged was observed in orchards planted on a slight slope or for the trees which were planted on a slope in an orchard (Fig 1D, Fig 1E, Fig 2E, Fig2F). The most damage (>50%) was observed in orchards set up on level land (Fig 2B) away from a body of water. The absence of a river, lake, or a large body of water increased mortality in all regions.
Generally percent mortality was negatively correlated with altitude, snow cover, distance of planting between the row and between the trees in the row (planting system, e.g. high density vs low density orchard), and positively correlated with tree age and total yield in the previous year. Higher mortality was observed in areas exposed to wind. Vigorous trees or weak trees were more susceptible to winter injury than trees with optimum vigor. Less mortality observed on trees which had been harvested early in the season.
Deficient soil drainage in combination with heavy soils increased mortality. Late application of soil applied or foliar fertilizers, use of herbicides, or mechanical weed control also increased tree mortality in some orchard possibly due to the increase in the vegetative growth and late development. Damage caused by deer or rodents increased the percentage of tree mortality but it was not consistent in all tested orchards.
In spite of a large variation in mortality among the rootstocks in each region and observed sites in region M9, EM26 and M26 showed little variation in percent mortality, indicating these rootstocks are the most reliable rootstocks and they seem to perform well in most regions (Table 6). When we grouped the rootstocks according to their planting distance, higher mortality was observed on dwarf than vigorous rootstocks (Table 7). It is postulated that the higher mortality on dwarf rootstocks is due to the lack of proper cultural practices required by these rootstocks e.g. no winter protection (e.g. straw or any other ground cover), lack of drip irrigation during the summer. The position of the trees in the orchard and location of the orchard seem to be the key factors for high mortality.
Cultivars variability was similar in different region but were less variable than rootstocks in terms of mortality. Mutsu, Jonagold, Tydeman’s Red, Hume, Wealthy, Northern Spy, Fameuse, Golden Delicious, Golden Russet, Red Delicious, Wolf River and Bancroft had more than 50% mortality overall region. The South West of Montreal had higher cultivar mortality followed by Montérégie, Eastern Townships, and Québec and Laurentide was the region least affected by the harsh winter of 1993 (Table 4). With the exception of Liberty, Quinte, Yellow Transparent, Jersey Mac, Vista Bella, Idared, Empire and Lawfam which showed lower mortality than those cited in the literature, our observation were similar to reports in the literature. Some cultivars however, like Hume, Wealthy, Jonamac, Close and Royal Gala, showed more mortality than was reported in the literature (Table 4). The contradictions between our results and those reported literature may be due to the effect of region and site rather than thatof cultivar/rootstocks. It seems that even the hardiest combination of rootstocks and cultivar can undergo winter damage when they are planted in an unsuitable site. Trees pruned in mid winter (December and January) were more vulnerable to the winter damage but it was not consistent in all region. In short the most important factors after cultivar and rootstock which affect tree mortality are, site and the location of the individual tree within each site, specially if the land is irregular or is far away from a large body of water. Our observations is very similar to the report of Krueger (1990) who performed an excellent study on orchard industry in Canada and Quebec and emphases on the effect of cultural practices to minimize winter injury.

Conclusion and Recommendation

Following are the conclusion and recommendation for improving winter damage based on the observed tree mortality in Quebec. Note that, some of these information already diffuse through provincial publications and Agriculture and Agri-Food Canada factsheet (Read 1983), regarding the cause for apple tree mortality, and might be repeated here again based on our observation of 300 orchards in Quebec.

 - Select local hardy cultivars and rootstocks or plant cultivars and rootstocks that were already tested at your region.

 - Perform proper cultural practices to protect dwarf rootstock which have shallow root system, e.g. mulch around the trees and irrigate especially in sandy type soils. Immaturity of the trees due to the late growth caused by rain fall and high temperature late in the season and premature dormancy due to the lack of moisture and available water in the soil make the dwarf and semi-dwarf rootstocks vulnerable to the low temperature injury. Lack of snow cover increased the mortality of trees on dwarf and semi-dwarf rootstock.

 - Do not set up an orchard on a level land, specially if the site is far away from a large body of water.

 - Use windbreak if the site has no natural protection from the wind.

 - Fruit thinning increase tree survival due to accumulation of nutrient in the bark and buds.

 - Trees which harvested late in the season or not harvested are more vulnerable to the winter damage.

 - Summer apples and early cultivars like 'Lobo' were less affected by the low temperature even though they were not rank very hardy compared to other cultivars. This might be due to the early harvest of these trees which help them to start their dormancy earlier than late cultivars as reported previously (Buszard 1981).

 - The older trees were more susceptible to the winter injury, however mortality on young trees was mainly associated with the use of dwarf and semi-dwarf rootstocks as explained previously.

 - Mortality was observed in orchards on soils which are not perfect for apple production. For example they have lack of drainage or the soil have excessive gravel or sand, which require irrigation.

 - Last but not the least, remember that the hardiest combination of rootstocks and cultivar can undergo winter damage when they are planted in an unsuitable site specially if the rootstocks is dwarf or semi-dwarf.

	Alden, J. & Herman, K. K. 1971. Aspects of the cold hardiness mechanism in plants. Bot. Rev. 37:37-142.
	Asnong, J. 1982. L'industrie de la pomme au Québec: Etat de la situation. Conférence socioeconomique sur l'industrie de la pomme. Min. Agr. Pêcheres et alimentation du Québec.
	Brown, G. N. 1978. Protein synthesis mechanisms relative to cold hardiness. in Plant cold hardiness and freezing stress, (P. H. Li and A. Sakai, eds.), pp. 153-163. Academic Press, New York, NY.
	Buszard, D. 1981. Winter injury to apple trees. Macdonald Journal. 42(11):9-11.
	Chen, H.H. & Li, P. H. 1980. Characteristics of cold acclimation and deacclimation in tuber bearing solanum species. Plant Physiol. 65:1146-1148.
	Collins, M. D., Lombard, P. B. & Wolfe, J. W. 1978. Effects of evaporative cooling for bloom delay on Bartlett and Bosc pear tree performance. J. Amer. Soc. Hort. Sci. 103:185-187.
	Granger, R. L. 1981. Notes concerning the harsh winter of 1980/1981. Fruit Notes. 46:14-16.
	Granger, R. L., Rousselle, G. L. ,Meheriuk, M. & Quamme, A. H. 1991. Promising winter hardy apple roostock from a breeding program at Morden, Manitoba. Fruit Var. J. 45(3):185-186.
	Granger, R. L., Rousselle, G. L., Meheriuk, M. & Khanizadeh, S. 1992. Performance of 'Cortland' and 'McIntosh' on fourteen rootstocks in Quebec. Fruit Var. J. 46(2):114-115.
	Granger, R. L., Meheriuk, M., Khanizadeh, S. & Groleau, Y. 1993. Performance of 'Starkspur Superm Delicious' on 25 rootstocks in Quebec. Fruit Var. J. 47(4):226-229.
	Gusta, A. L., Fowler, D. B. & Tyler, N. J. 1982. Factors influencing hardening and survival in winter wheat. in Plant cold hardiness and freezing stress, (P. H. Li & A. Sakai, eds.), pp. 23-40. Academic Press, New York, NY.
	Ketchie, D. O., & Murren, C. 1976. Use of cryoprotectants on apple and pear trees. J. Amer. Soc. Hort. Sci. 101:57-59.
	Khanizadeh, S. 1991. Controlling temperature by microcomputer. HortScience 26(5):607.
	Khanizadeh, S., Buszard, D. & Zarkadas, C. G. 1989a. Seasonal variation of proteins and amino acids in apple flower buds (Malus pumila Mill. McIntosh/M7). J. Agr. Food Chem. 37:1246-1252.
	Khanizadeh, S., Buszard, D. & Zarkadas, C. G. 1989b. Effect of crop load on seasonal variation in chemical composition and spring frost hardiness of apple flower buds. Can. J. Plant Sci. 69:1277-1284.
	Khanizadeh, S. & Fanous, M. 1992. Statistical Methods: A computer program to calculate orthogonal polynomial coefficients. HortScience 27(4):367.
	Khanizadeh, S., Buszard, D., & Zarkadas, C.G. 1992a. Effect of crop load on hardiness, protein and amino acid content of apple flower buds at several stages of development. J. Plant Nutrition 15(11):2441-2455.
	Khanizadeh, S., Buszard, D. & Zarkadas, C. G. 1992b. Comparison of three methods for calculating protein content in developing apple flower buds. J. Assoc. Off. Anal. Chem. 75(4):734-737.
	Khanizadeh, S., Buszard, D. & Zarkadas, C. G. 1994. Seasonal variation of hydrophilic, hydrophobic, and charged amino acids in developing apple flower buds. Journal of Plant Nutrition 17(11):2025-2030.
	Krueger, R. R. 1992. The low temperature hazard to the Quebec orchard industry. Dept. of Geography, University of Waterloo, pp. 154.
	Levitt, J. 1980. Responses of plants to environmental stresses. Vol. I. Chilling, freezing, and high temperature stresses, 2nd ed. Academic Press, New York, NY.
	Levitt, J. 1956. The hardiness of plants. Academic Press, New York, NY.
	Li, P. H. 1987. Plant cold hardiness. Alan R. Liss, Inc., New York, NY.
	Lindow, S. E., & Connell, J. H. 1984. Reduction of frost injury to almond by control of ice nucleation active bacteria. J. Amer. Soc. Hort. Sci. 109:48-53.
	Lindow, S. E., Panopoulos, N. J. & McFarland, B. L. 1989. Genetic engineering of bacteria from managed and natural habitats. Science 244:1300-1302.
	Pomeroy, M.K., Siminovitch, D. & Wightman, F. 1970. Seasonal biochemical changes in the living bark and needles of red pine (Pinus resinosa) in relation to adaptation to freezing. Can. J. Bot. 48:953-967.
	Read G. 1983. Reducing cold temperature injury in apples by site selection. New Brunswick Department of Agriculture and Rural Development. Factsheet, Agdex 111/11.
	Sakai, A. & Larcher, W. 1987. Frost survival of plants. Responses and adaptation to freezing stress. SpringerVerlag, New York, NY.
	Siminovitch, D. 1963. Evidence from increase in ribonucleic acid and protein synthesis in autumn for increase in protoplasm during the frosthardening of black locust bark cells. Can. J. Bot. 41:1301-1308.
	Spangelo, L. P. S., Fejer, S. O., Leuty, S.J. & Granger, R. L. 1974. Ottawa 3 colonal apple rootstock. Can. J. Plant Sci. 54(3):601-603.
	Stang, E. J., Ferree, D. C, Hall, F. R. & Spotts, R. A. 1978. Overtree misting for bloom delay in Golden Delicious apple. J. Amer. Soc. Hort. Sci. 103:82-87.
	Statistical Analysis System, 1988. SAS/STAT, SAS/BASIC guide for personal computers. Version 6.04 (ed.). SAS Institute, Inc. Cary, N.C.
	Stushnoff, C. 1972. Breeding and selection methods for cold hardiness in deciduous fruit crops. HortScience 7:10-13.
	Weiser, C. J. 1970. Cold resistance and acclimation in woody plants (A review). HortScience 5:403-408.