fruit ( Manners et al., 2003 ). The degree of freeze damage to the fruit of a particular orchard subjected to mild to moderate freezing conditions usually cannot be readily determined by the eye as navel oranges often do not show obvious injury to the
David Obenland, Dennis Margosan, Sue Collin, James Sievert, Kent Fjeld, Mary Lu Arpaia, James Thompson, and David Slaughter
James O. Denney and George C. Martin
Record low temperatures were experienced in California during the last 10 days of December, 1990. Olive trees in both the Sacramento and San Joaquin Valleys suffered damage from the freeze. The lowest minimum recorded in these areas was -11.6C at Willows (Glenn Co.). Types of damage included death of succulent growing tips, defoliation, bark split, and bark and xylem discoloration. Tree death to the ground was uncommon. Defoliation continued throughout the growing season, and many leaves that persisted became chlorotic. Major outbreaks of olive knot disease caused by Pseudomonas savastanoi were seen in damaged trees, especially in `Manzanillo.' Anatomical studies showed evidence of ice nucleation events in the phloem, xylem, and leaves, but the cambium was usually left intact. Refoliation and healing of bark splits progressed rapidly once growth resumed in the spring, except in cases of olive knot infestation. Cultural practices that predisposed trees to freeze damage were those leading to late-season vegetative growth, namely fall pruning and late or excessive irrigation or fertilization. `Manzanillo' is the least cold-hardy of California cultivars and the most susceptible to olive knot. `Barouni' is the most hardy.
Jan Schooley and John T.A. Proctor
The Lake Erie counties of southern Ontario, Canada are the major producers of ginseng (Panax quinquefolius) in North America. In this area there is about 1740 ha (4299.5 acres) of ginseng and an annual production of 1455 t (1603.8 tons). Spring freeze damage to the crop is rare as the mean date of last freeze in spring is 12 May. On 21 May 2002, following three to six nights when air temperatures dropped below freezing, extensive damage to the crop was evident. A survey by the Ontario Ginseng Growers Association showed that 78% of growers had gardens showing freeze damage. The extent of the damage was variable across the growing area, and on individual farms. Most damage to plants occurred in low-lying areas where heavy cold air collected. Recently germinated seedlings that were exposed above the straw mulch were severely damaged, and many did not survive because they did not have leaves and no perennating bud was formed. Damage to 2-year-old plants was expressed as leaves wilting and turning black. In some cases stems froze and the plants toppled. In 3-year-old and older plants, damage was variable with some leaf collapse and stems broken, or damaged with corking-over taking place. Damage to inflorescences ranged from death and abscission, to distorted flowers and shriveled and split peduncles. Plant health was a concern following the freeze episode, and throughout the subsequent growing season. The fungicide fenhexamid received emergency registration to combat recurring problems in Botrytis control. The seed crop for 2002 was light. Damaged seedling gardens were replanted. Older gardens will undergo a period of adjustment. Root yield in 2002 was reduced by 30%, a 500 t (551.1 tons) loss. The full extent of the damage and associated financial implications are unknown and could impact the industry until 2005.
Japanesesnowbell(Styrax japonicus Sieb. & Zucc.) is an outstanding small ornamental tree that is underutilized in the United States. Many of the cultivars of this Asian native frequently suffer spring freeze damage, especially when grown in the areas of the country that routinely experience dramatic fluctuations in late winter and early spring temperatures. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants with reduced susceptibility to spring freeze damage. In 1998, 224 open-pollinated seedlings were planted in the field. Percent budbreak was evaluated weekly during a 6-week period in Spring 1999 and 2000. While weather conditions varied greatly between the 2 years, there was good consistency between mean budbreak ratings in 1999 and 2000. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003, and 2004. All of the selections broke bud later and suffered less freeze damage than `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper, and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.
Sandra M. Reed
Japanese snowbell (Styrax japonicus Sieb. & Zucc.) is an outstanding small ornamental tree that is underused in the U.S. One of the reasons this Asian native is not more widely planted is that it is subject to spring freeze damage. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants better adapted to areas of the country that frequently experience late spring freezes. During Spring 1999 and 2000, budbreak was evaluated weekly in 224 open-pollinated seedlings. While weather conditions varied greatly between the 2 years, there was good consistency between 1999 and 2000 data. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003 and 2004. All of the selections broke bud later and suffered less freeze damage than the cultivars `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.
M. Lenny Wells
between measured parameters of damaged and nondamaged trees within each cultivar. Results The shoot length of ‘Desirable’ was significantly reduced on trees exhibiting severe freeze damage at 32, 47, 91, and 147 DAF ( Table 1 ). The shoot length of damaged
L.J. Grauke and J.W. Pratt
Seven open-pollinated pecan [Carya illinoinensis (Wangenh.) K. Koch] stocks were grown in a nursery in blocks. Bud growth of ungrafted seedlings was influenced by rootstock, with growth being more advanced on `Curtis', `Elliott', `Apache', and `Sioux' seedlings than on `Moore', `Riverside', and `Burkett'. Bud growth of grafted trees was influenced by scion, with growth of `Candy' being most advanced, while `Cape Fear' trees were more advanced than `Stuart'. Growth of `Candy' grafted trees was affected by rootstock, with growth being more advanced on `Elliott' and `Curtis' seedling rootstock as compared to `Apache', Sioux', `Riverside', and `Burkett' seedling rootstock. Tree damage caused by a May freeze was directly related to bud growth and was influenced by scion and rootstock.
M.J. Willett, E.L. Proebsting, and R.E. Redman III
Flower buds of peach, apricot, and sweet cherry are killed by low temperatures during winter and spring. Frost protection measures used commonly in the spring are applied to freeze protection during the winter in the Yakima Valley of Washington. Critical temperatures change rapidly during winter. To succeed, winter freeze protection requires adequate inversions, equipment that operates at temperatures below -15C, and reliable estimates of critical temperatures for flower bud survival. Observations and experience have shown that inversions develop on most critical winter nights. Wind machines and orchard heaters will operate under severe low-temperamre conditions. Winter freeze protection has been practiced successfully on an increasing scale in the Yakima Valley for more than 20 years. Five packinghouses operate laboratories to measure critical temperatures. A computer model that estimates critical temperatures from daily or hourly air temperatures is being incorporated into these estimates.
Reeser C. Manley and Rita L. Hummel
The index of injury (It) and tissue ionic conductance (gTi) formulas for analyzing electrolyte leakage data from freeze-stressed tissues of cabbage (Brassica oleracea L. Capitata group) were compared. The two formulas produced similar results in calculating the relative freezing responses of stem pith, lamina, and petiole tissues. Disagreement occurred only with lamina tissues when the magnitude of ion leakage was low. Vital staining of pith and petiole tissues with triphenyl tetrazolium chloride indicated that the tissue TK50 (the temperature resulting in 50% injury), derived from It data, was a reliable indicator of the freeze-killing point. These results support the use of the simpler It method for analyzing electrolyte leakage data in studies of cabbage freezing tolerance.
W.R. Okie, T.G. Beckman, G.L. Reighard, W.C. Newall Jr., C.J. Graham, D.J. Werner, A.A Powell, and G. Krewer
This paper describes the climatic and cropping conditions in the major peach [Prunus persica (L.) Batsch] producing areas in the southeastern United States in 1996. The peach and nectarine crop was the smallest since 1955 due to a series of unusually cold temperatures in February, March, and April. Crop set was not strictly a function of late blooming. No variety produced a full crop across the region. Many reputedly hardy peaches cropped poorly. The only peach or nectarine varieties that produced substantial crops in multiple locations were `La Premiere', `Ruston Red', and `Contender'. Cropping ability of some breeding selections shows that peach frost tolerance may be improved further.