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Frequently Asked Questions


Historical Interest              Peaches in China          Commercial Production
General Interest                 Scientific Findings


Historical Interest

  • Where did peaches originate?
    Answer: Peaches originated in China.  They have been cultivated in China for more than 3000 years.
  • When did peaches first come to the New World?
    Answer: Spanish missionaries actually brought peaches to the "New World" in 1571.  This was to what is now known as St. Simon’s Island, Georgia.
  • How long have peaches been an important commercial crop in South Carolina?
    Answer: Since the mid 1800s.  Henry William Ravenal of Aiken, SC, is credited as the first commercial grower to ship peaches outside the state in the 1850’s.  Beginning in the late 1800’s, peaches were shipped by rail car in insulated cars kept cool with large blocks of ice. Most commercial packing sheds during this time were built next to the railroad to facilitate out-of-state shipping.  In 1935, there were 233 packing houses and over three million peach trees in Spartanburg county alone.
  • What are some historical similarities and differences concerning peach growing in Georgia and South Carolina?
    The Cherokee Indians grew peaches in this region in the mid 1700’s.  Commercial shipping (by train) out of the region began in the mid to late 1850’s. Georgia is commonly known as “The Peach State” where the peach was adopted by the state legislature as the state fruit in 1995.  South Carolina is commonly known as “The Tastier Peach State” where the peach was adopted by the state legislature as the state fruit in 1984.  Peach continues to be a vital fruit crop in the agricultural economy of both states. The primary growing regions enjoy similar soil types and climate and grow many of the same cultivars.  However, South Carolina currently produces more peaches annually than the state of Georgia.

Peaches in China

  • Is it true that in some peach orchards in China they put paper bags over the young fruit as they are developing and only remove them at harvest? Why would they do this?
    Answer: Yes, this is true.  I observed this practice at commercial orchards outside of Shanghai in August, 2009.  The paper bag protects the fruit from insects, disease, abrasion, etc.  Also, the paper bag significantly reduces the amount of sunlight that reaches the skin of the fruit.  In the orchards I visited, where yellow fleshed cultivars were being grown, the presence of the paper bag resulted in a beautiful, blemish-free peach with perfectly uniform yellow skin color.  Obviously, the yellow/orange pigments (carotenoids and xanthophylls) were being produced but no red pigmentation resulted.  In places where I saw bags on the tree that had partially come off the fruit or where the bag had been torn or deteriorated, the skin that was exposed to the sun turned red (i.e., anthocyanin pigments were produced).  This is obviously a costly and labor-intensive practice.  However, the extremely high quality fruit that resulted ensured a good price for the grower.  The average peach grower at this location maintained 1 hectare or less (1-2 acres) in production.
  • Is it true that the Chinese grow peaches and nectarines in greenhouses? Why do they do this?
    Answer: “Protected cultivation” as it is called, using simple, energy efficient solar greenhouses, is widely used in China for horticultural crops. In fact, by 2005, it was estimated that there was nearly 1.4 million acres of fruit, vegetable, flowers, etc. being grown using this technology. For peaches and nectarines, the estimated acreage is around 30,000. The beauty of this system is that it is energy efficient, it can enable fruit production beginning 1 year after trees are planted, fruit can be produced up to 2 months early getting high market price and the need for and cost of pest control measures is considerably reduced.

Commercial Production

  • What are the potential implications of improper fertility management? What do symptoms look like?
    Answer: The implications of improper fertility management are many!  Supplemental fertilization is expensive.  If nutrients are supplied in excess, luxuriant growth may result causing shading and reducing fruit quality and flower bud production for next year.  Excess nutrients may be leached from the soil or runoff the site and that is a waste of money and can cause environmental contamination. Further, some nutrients can actually create toxicities when in oversupply that can harm growth and development.  If specific nutrients are deficient in the soil, canopy growth may be stunted and fruit size and quality can be impaired.  If nutrients are applied at the wrong time, they may be unavailable when the feeder roots are growing and capable of absorption.  If the soil pH is incorrect, nutrients could be “tied up” and unavailable for root uptake (see image below).  If trees go into the winter nutrient deficient, early spring growth will be compromised. This is because much of the early growth is driven by “reserves” that were stored in the tree last summer/fall as opposed to new nutrient uptake in the spring that helps growth later on. Getting fertility right is not a simple matter but it is a critical one.
  • Are honeybees an absolute requirement for successful peach pollination and do you need two “different” cultivars for cross-pollination?
    Answer No.  Peaches have perfect flowers (including both male and female parts).  They are self-fertile and they can self-pollinate by wind.  Although honeybees can assist in pollination, they are not required nor is it necessary to plant two different cultivars near to each other for cross-pollination to set a crop of fruit.
  • When can peach thinning be done and how?  When is the best time and why? Are there any potential problems?
    Answer:  Under most circumstances, mature peach trees have a natural tendency to produce more fruit than the tree can adequately support.  Thinning is an attempt to reduce the crop load at some advantageous point in time during the year. There are three primary times of the year when peach thinning can be done.  These include the dormant season, during bloom, and prior to pit hardening when fruit are in the “green fruit” stage. The earliest thinning in the dormant season can be accomplished using fall applied ethephon or winter applied soybean oil to reduce the number of living flower buds on the tree. Another practice to “thin” at this time is actually pruning out and reducing the number of fruiting shoots on the tree.During bloom, flowers can be reduced by chemically burning and destroying them using chemicals such as ammonium thiosulfate or tergitol (a surfactant).  Also during bloom, flowers can be removed by hand or using a “toilet”-type brush or even mechanically using “Darwin” string thinner developed in Germany.  The latter is being tested at various sites in the U.S. for mechanical bloom thinning but uniformity of tree architecture is vital to the success of this device.Finally, the latest stage to do thinning is while the fruit are green and prior to forming hard pits.  At this stage, green fruit removal is by hand, using “wiffle ball” bats, a “Kentucky bumper”, or using a mechanical spiked drum shaker.  The latter is a prototype being developed and tested through scientists at the USDA-ARS in Kearneysville, WV.  The prototype green fruit thinner is based on a design originally created for mechanical harvesting of citrus. The best time to thin to maximize the impact on final fruit size is as early as possible. Because the tree has a finite supply of stored carbohydrate reserves to support growth of new fruits at a time when the leaf canopy has not developed sufficiently yet, the fewer fruits present, the more reserves that can be supplied to individual fruits that remain (less competition).  Initial fruit growth is primarily cell division. Fruits with more cells initially can then have those cells expanded in the final swell phase with water and solutes (sugars, acids, etc.) resulting in larger fruit at harvest.  This is the ultimate goal, large fruit size that will attain the highest market price possible to the grower. The one drawback of early thinning, however, is that there may be an unexpected spring freeze event that could substantially reduce the flower crop or developing fruit crop.  If this were the case, it would be best to have as many flowers/developing fruits on the tree as possible.  This is part of the reason that risk-averse growers often practice green-fruit thinning.  Their rationale then is that they “know what crop they have” by that point.  However, later thinning minimizes the impact on final fruit size, potentially resulting in smaller fruit that attain a lower market price usually.
  • If peach trees that have a “full crop” are not thinned properly, what can happen?
    AnswerFirst, the fruit that remain on the tree will be small, perhaps never attaining marketable size or quality. This can be financially disastrous for the commercial grower. Second, as fruits reach the final swell phase of fruit growth and they fill with water and solutes, they significantly weigh down branches.  In some cases, overloaded branches – and even scaffolds - that are not architecturally strong may actually break under the weight.  In the case of high density plantings [i.e., Kearney (Perpendicular) V or Quad V systems], a broken scaffold can reduce tree production capacity by up to 50%.  For a Kearney (Perpendicular) V tree where one of the two primary scaffolds broke at the point of attachment with the other scaffold, the entire tree could end up being lost.  This is an expensive mistake.
  • What are chilling hours and what do they have to do with dormancy?  Do cultivars differ in their chilling hour requirement?
    AnswerChilling hours are the number of hours below 45F accumulated by the tree during the winter to overcome dormancy.  Peach cultivars that can be grown in the subtropics (i.e., low-chill types) may require as few as 50-100 chilling hours while those grown in the temperate climates further north or at higher elevations (high-chill types) may require more than 1000 hours.  Knowing the typical chill hour accumulation of your geographic region should be one of the primary criteria you use in choosing cultivars that are suitable to grow there.
  • What is the difference between a public release and a patented peach cultivar?
    Answer: Breeding to develop new peach cultivars may be done by private individuals, companies, government organizations or even universities.  When a new cultivar (cultivated variety) is developed and made freely available to be propagated without restriction to the public, this is called a public release.  In years past, many public university or government (i.e., USDA-ARS) programs publicly released new cultivars.  Currently, private breeders and an ever increasing number of public breeders are seeking to protect their intellectual property (new cultivars) through the filing of a plant patent with the U.S. Patent and Trademark Office.  If a patent is awarded, the cultivar is protected for 20 years and the patent recipient can receive royalty payments for the sale of budwood, trees, etc.  Propagation of trees may be restricted to licensed nurseries.
  • What problems can result for peach trees during extended periods of very hot, sunny days during the summer?
    Generally speaking, high light and high temperature conditions in the summer can cause varying degrees of stress that are manifested in different ways. First, if there is inadequate rainfall or an inability to irrigate, such conditions can cause drought stress.  Foliage may wilt, especially in the afternoons, and, under very severe conditions, some premature defoliation can result. Second, ripening fruit may actually drop off the tree prematurely. Third, fruit that are well exposed to the sun can also experience sunburn causing them to be unmarketable. Fourth, larger branches or scaffold limbs that are not shaded by in-canopy foliage and that are directly exposed to the sun may be sunburned. This is evidenced by bark cracking, peeling and even exposure of underlying wood. Finally, flower buds for next year’s crop are initiated this summer. Sustained periods of high temperature during the flower initiation phase can cause the production of 1, 2, or 3 pistils. If pollinated, this may cause single, double, or triple fruit. These double and triples (twins or triplets) are fused together and need to be thinned off because the resultant fruit are unmarketable. Sometimes with doubles (twins), one fruit may abort and the resultant peach will have a malformed suture at harvest also making it unmarketable.
  • What problems can result if a peach tree is planted too deep?
    Answer: Most fruit trees are grafted in the nursery about 2-4 inches above the soil line.  Bareroot grafted trees that you purchase from the nursery should have a visible “soil line” – that line on the trunk where the soil came up to at the time the tree was dug prior to shipping.  Ideally, when this bareroot tree is planted in your orchard, you should ensure that the same soil line on the bark is at the actual level of the settled soil after planting.  A good, rule-of-thumb, therefore, is to ensure that the graft union is 2-4 inches above the soil once planted.  Because of the convenience of using tractor-mounted tree planters to plant thousands of trees per day, if the resulting furrow is too deep, many trees can be planted incorrectly in a short period of time.  In some cases in commercial orchards, I have observed trees planted 8 or more inches too deep.  This is particularly a problem on heavier soils.  Planting too deep can stunt tree growth, lead to soil compaction and a lack of oxygen for feeder roots, and even adversely impact tree stability.  Under conditions such as these, if soils become saturated because of excess rain, trees may die from waterlogging or may be predisposed to infection by phytophthora root rot.
  • What can happen if peach trees get flooded or if the soil they are planted in remains saturated for more than 48 hours?
    Answer: Peach trees definitely do not like wet feet. Soil saturated conditions for 48 hours or longer is enough to kill a peach tree. Ideally, trees should be planted on sites where there is good surface drainage during periods of torrential rains and also good internal drainage. Trees should not be planted in low spots – for one, water can stand there, for two, cold air can settle there and cause spring frost damage. Heavy clay soils or sites with a hard pan near the surface of the ground impede water drainage and can result in soil-saturated conditions following rainfall.  In some cases, use of raised beds can help if the site is otherwise suitable. Under non-saturated conditions, oxygen in the soil air spaces is available to support root respiration and good root health. However, when the soil becomes saturated with water, aerial oxygen is displaced from the soil air spaces. Under these conditions, root respiration is impaired, free nitrates are lost and the toxic end-products of bacterial respiration can build up. Further, trees may be predisposed to infection by phytophthora root and crown rot since this fungus can spread by motile (they can swim) zoospores.
  • How does hail adversely impact peach trees?
    Answer: Peach trees and hailstorms do not go well together.  Hailstorms can vary in intensity, duration and when they occur during the growing season.   Hailstones can vary in size and structure.  Some commercial growers have hail cannons in their orchard for use when a hailstorm is approaching.  Scientific and anecdotal evidence presents differing viewpoints on whether the use of hail cannons provides economic benefit.  In general, when hailstones fall on an orchard, considerable damage usually results.  This damage can include all of the following: tattered leaves, broken or damages shoots, wounds on scaffold branches, fruit damage and even fruit being knocked to the ground.  Depending on the extent of damage, a grower may decide to thin off damaged fruit and manage the rest or he may decide to simply abandon the block altogether and hope for better luck next year.  Generally speaking, the latter would be a poor management decision.  Open wounds on the growing shoots, branches and scaffolds present entry points for bacterial and fungal pathogens and also insects (i.e., lesser peach tree borer).  The grower should maintain a minimal pest management program that will protect trees during the wound healing process and not predispose trees to further damage, otherwise long-term health, productivity and longevity of the orchard may be severely compromised.
  • What do ideal pruning cuts look like and what problems result from poor pruning cuts?
    AnswerGood pruning cuts do not result from bad tools.  Sharp bypass-type pruners used correctly can minimize pruning damage to trees and facilitate proper wound healing.  When possible, branches should be taken out where they attach (i.e., thinning cuts).  Leaving large stubs is undesirable.  Rather, branches should be taken out at the outside edge of the swollen branch collar that occurs at their base.  With the branch collar intact, the wound will heal readily and properly.  Flush cuts that actually remove the branch collar are very damaging to the tree.  These wounds will heal poorly.  As a result, they can result in a persistent wound spot on the tree that is attractive to the female lesser peach tree borer moth that lays eggs on these wounds during the summer months.  Developing lesser peach tree borer caterpillars subsequently bore under the bark and effectively girdle the branches they are associated with.  Girdled branches die and productive fruiting wood is lost.  This will reduce harvestable yield and profit per tree.
  • Why should weeds in an orchard be managed? What problems can result if they are not managed properly?
    Answer: Weeds compete directly with the tree for needed water and nutrients during the growing season.  High weed pressure can stunt tree growth and also significantly reduce fruit size and yield per tree.  Broadleaf weeds can harbor insects (i.e., stink bugs, plant bugs, etc.) that will migrate from the weeds to fruit on the tree.  Stink bug feeding can cause “cat-facing” of fruits making them unmarketable.  Also, as they probe the fruit with their long proboscis, they puncture the skin and make wounds that provide ideal sites for fungal pathogens (i.e., brown rot) to grow.  Weeds can also serve as alternate hosts for viruses or ring nematodes.  Prior to the advent of excellent herbicides, many growers cultivated the soil of the entire orchard to eliminate weeds.  Scientific research demonstrated that most peach tree feeder roots were in the upper soil layer (i.e., 0-12 inches) and that soil cultivation actually led to many feeder roots being cut off or damaged.  In most commercial peach orchards in the U.S., cultivation is no longer used for weed control.  Both preemergent herbicides (i.e., simazine, karmex, etc.) and postemergent herbicides (i.e., glyphosate, paraquat, etc.) are commonly used to effectively eliminate weeds in the tree row ‘herbicide strip’.  Occasionally, growers may overdose with the soil applied preemergent herbicide.  High doses of simazine or karmex, especially with young trees, can cause phytotoxicity (foliar chlorosis, shortened internodes, etc.) and even kill trees.  With young trees, many growers use milk cartons to protect the young, green, bark from contact postemergent herbicides but when overspray occurs, bark of trees can be damaged. Off-target herbicide drift is particularly a problem with glyphosate (RoundUp and other formulations).  If the grower is not using a shielded sprayer in his own orchard, or spraying when it is windy, or a nearby landowner is spraying roundup on a windy day, drift onto peach foliage can be readily taken up by the tree and significant injury or even tree death can result.  Finally, weeds should be managed to reduce the risk of damage from fire. The occurrence of fire damaged orchards is quite rare, but when it occurs, it can be devastating. Dead, dry weeds that are present on the orchard floor in the fall/winter/spring present excellent fuel under dry conditions that could be combustible if there was a lightning strike, a cigarette from a passing motorist, or accidental fire from a piece of farm machinery.  Dry weeds combined with windy weather and one spark of fire can lead to destruction of hundreds of trees in a short period of time.
  • Are peach trees sensitive to air pollution?  What are symptoms of air pollution injury?
    Answer: [Note: this answer is based on information published from the following source: Heggestad, H.E. 1976.  Air pollution injuries to stone fruit trees, p. 355-364. In: USDA Agriculture Handbook No. 437, Virus Diseases and Noninfectious Disorders of Stone Fruits in North America]. Although it is fairly uncommon, peach trees can be damaged by air pollution.  There are three primary air pollutants that cause phytotoxicity to peach.  These are fluoride, sulfur dioxide, and ozone.  The primary sources of fluoride include chemical industries that use fluoride, brick and pottery manufacturing facilities, phosphate rock processing sites, and industries that manufacture aluminum and steel.  Leaf symptoms of fluoride injury can range from minor chlorosis to necrosis and are typically dose dependent.  High doses of fluoride can cause defoliation. Symptoms are typically worse during drought or with unfavorable soil conditions.  Fluoride injury to fruit can cause a soft suture.  This typically appears first during the final phase of fruit growth.  At the stylar end of the fruit (near tip), the skin along the suture begins to turn red prematurely.  This tissue then matures more rapidly and becomes soft.  It may crack and is more subject to bruising and decay.  According to the 1976 Ag. Handbook (noted above), “soft suture of peach can be controlled by one to three sprays of lime or calcium chloride (i.e., two pounds of calcium chloride per 100 gallons of water) applied at 2- to 3-week intervals, beginning at pit hardening”.  The primary sources of sulfur dioxide include the manufacturing of sulfur and sulfuric acid, production and refining of petroleum and natural gas, ore smelting and the burning of fossil fuels.  Leaf symptoms include spotting that results from death of cells in interveinal areas.   Ozone is typically associated with smog.  Symptoms often include flecking or stippling on the upper leaf surface.  The symptom can be confused with injury from mites.  At higher doses, dark lesions and shotholing can result.  Some researchers utilized ozone as a postharvest treatment to reduce fruit decay.  Injury symptoms were described as “sunken and browned tissue in the region of the stomata”.  The fruit had a “pebbly” appearance.
  • What temperatures cause cold damage to peach flower buds? 
    Answer: In general, the stage of development of peach flower buds has a profound impact on their susceptibility to cold injury.  Dormant buds that are tight with bud scales intact are the most cold resistant while uncovered open flowers are least cold resistant.  As flower buds progress through the natural development process in response to warm temperatures in the springtime, each subsequent flower stage is more vulnerable to cold injury.  In fact, the temperature that is required to cause injury actually increases – i.e., more developed flower buds are killed at warmer temperatures. In the early 1970’s, Washington State University published a series of bulletins noting critical temperatures for flower buds for several important temperate fruit crops.   Extension Bulletin 0914 “Critical Temperatures for Blossom Buds: Peaches” by Ballard, Proebsting, and Tukey illustrated the various flower bud stages and presented data for ‘Elberta’ noting the average temperatures required to kill 10% and 90% of the flowers, respectively, as observed at the Washington State University Research and Education Center in Prosser over seven years (1964-1970).  This publication is no longer in print. Noted below are photographs depicting the common flower development stages that we observe with peach.  All photos were taken in South Carolina but they are not for ‘Elberta’.  In the caption for each photo, the relevant data taken from WSU Bulletin 0914 for ‘Elberta’ is noted to serve as a rough guide to show sensitivity to cold injury by flower stage.  It is relevant to note that flowers are typically not injured at the freezing temperature for water (32 F).  However, when flowers are at their most vulnerable stage (full bloom – postbloom), just a few degrees can make a very significant difference between only 10% loss (i.e., 28 F) and 90% loss (i.e., 25 F).  Obviously, orchard management practices that can create a warmer orchard environment during these low temperature events has the potential to significantly reduce losses.
  • What can a grower do to minimize the potential for cold damage to flowers in his peach orchard?  If injury to flowers or fruits occurs, what does it look like? 
    Answer: The first and most important thing that a grower can do to reduce the potential for cold damage is to choose a good site prior to planting the orchard.  For fruit, this is generally high ground that allows for easy drainage of cold air off the site.  Low spots or “frost pockets” should be avoided.  Second, the choice of the proper cultivars is critical.  Cultivar choice should be based on sufficient cold hardiness for the region in which they will be grown as well as a suitable chilling hour requirement.  In temperate areas, low-chill cultivars tend to bloom earlier in the spring than medium and high chill cultivars.  As a result, they present a higher probability of being at a more advanced stage of flower development (making them more sensitive to cold) when springtime freeze events can occur.  Third, the timing of dormant pruning is important.  Because dormant pruning is an invigorating process (it stimulates tree growth in the spring), it is best to delay dormant pruning as long as possible prior to bloom.  This may not be practical, however, given the large acreages in many commercial farms and the time required to get all trees pruned on time.  Fourth, orchard floor management can significantly influence springtime orchard temperature.  Soil that is devoid of vegetation can absorb more heat during the daytime and liberate (give off) more heat in the nighttime than soil that is covered with vegetation (i.e., sod, weeds, etc.).  Similarly, soil that is moist from irrigation or rainfall is also warmer at night than dry soil because of its capacity to absorb more heat during the day and subsequently liberate that heat at night.  Under most circumstances, the coldest time of the day in the orchard is immediately before sunrise. The most difficult freeze conditions to manage occur when it is very cold in combination with high wind speeds (advective freeze).  During cold, still nights (radiational freeze), wind machines can be used to stir warm air above the orchard (inversion) back down into the orchard and raise the temperature potentially averting freeze damage.  Depending on the region of the country, some growers may supplement orchard heat by using orchard heaters, burning straw bales, etc.The appearance of freeze damage differs depending on the timing.  If the damage occurs in deep winter, dormant flower buds are killed.  Typically, these buds will not swell and they will abscise (drop off) prematurely.  Occasionally, however, these buds may swell, but the pistil inside is dead and they will probably abscise shortly thereafter.  If damage occurs later, during the various stages of flower development, it is possible to have flowers with a dead pistil but the anthers are still viable.  Usually, at these later stages of bloom, however, a brown pistil and withered and brown petals are obvious.  Flowers damaged to this extent will abscise.  Under most circumstances, flowers on a given fruiting shoot, will mature from the apex (shoot tip end) to the base.  This means that flowers typically open first at the tip end and last at the base end of a given shoot.  If open blooms at the shoot tip are frozen, it is possible that unopened blooms near the base of the shoot may not be lost. Following pollination, once fruit have set and they are beginning to grow, cold damage can still occur.  The “Easter Freeze of 2007” was one such occasion when temperatures in the low 20’s occurred on three successive days in early April in the southeastern U.S.  At this time, fruits were already 1 inch in diameter or larger in some cultivars.  Damage to intact fruits was visible on the outside by skin cracking where the cracks would enlarge as the fruit expanded in diameter.  When damaged fruits were cut along their longitudinal axis, varying levels of damage to inner tissue (seed, endocarp) were noted.  Generally, fruit that were severely frozen dropped off naturally.  However, some fruits with damaged seeds remained on the tree and had a deformed growth, never attaining proper size, and being particularly susceptible to infection with brown rot fungus.

General Interest

  • What type of fruit is a peach? What are the names for the various parts of the fruit?  Besides using the pits and seed contained within them to grow another peach tree, what else can they be used for?
    The peach is called a drupe. Other drupe fruits include the nectarine, apricot, plum, and cherry. The outermost layer of the fruit is called the exocarp. Commonly, this is called the skin. Red pigmentation in the skin (blush) is loaded with anthocyanins that are rich antioxidants and healthy for you. Don't peel and throw the skin away!  Eat it! The fleshy part that we enjoy eating is the mesocarp.  Inside the middle of the fruit is the pit. Technically, we refer to this as the stony endocarp. Within the stony endocarp is the seed. Fruits bearing stony endocarps inside them are typically called "stone" fruits. Historically, peach pits have been used by artists and carved into pieces of jewelry.   
  • What is the largest peach growing nation in the world?
    Answer: China.  They produce 45% of the world’s peaches.  That compares to the United States which produces 5% of the total.  Most of China’s peaches are actually consumed in the country.  They prefer white fleshed, low-acid types of peaches and nectarines.  Some yellow fleshed peaches are canned and shipped overseas but this is a small proportion.   
  • Sometimes when I buy peaches and bring them home, they have little flavor, are too hard, they don't seem to ripen properly and are mealy in texture.  What might cause this?
    Answer: One possibility is improper temperature management after harvest. Some peach cultivars are sensitive to "chilling injury".  Storage of sensitive cultivars at 36-50 degrees Fahrenheit can predispose them to this problem.  Dr. Carlos Crisosto, UC-Davis post harvest physiologist, is an expert in chilling injury of stone fruits.
  • Is there a genebank for peaches in the U.S.? Where is it and what do they do there?  Why is such a place necessary?
    Answer: Yes!  The United States Department of Agriculture’s Agricultural Research Service (USDA-ARS) has a division called the National Plant Germplasm System (NPGS).  The NPGS “is a cooperative effort by public (State and Federal) and private organizations to preserve the genetic diversity of plants”.  Within the NPGS there are several National Clonal Germplasm Repositories for economically important crops at various locations around the U.S.  As such, a germplasm repository “is a gene bank that preserves genetic resources by various means including seeds, pollen, cuttings, plants in greenhouses or in the ground, micropropagated plants (tissue culture) and in ultra low temperature freezers (cryopreservation)”.  The National Clonal Germplasm Repository for Fruit and Nut Crops at Davis, California houses the collection for Prunus species (peach, nectarine, plum, cherry, apricot and almond).  The mission of the Davis, CA research unit “is to collect, preserve, evaluate, and distribute the genetic resources of the crops assigned to them as part of the US National Genetic Resources Program. These resources are preserved to ensure that crop diversity in these species will be available for future generations and to support research efforts in variety development and other areas of plant research.”  In addition to this mission, the genetic resources serve as a “backup” source of plant material in case of environmental disaster (disease epidemic, etc.).  As part of the peach collection in Davis, CA, they currently have 386 peach accessions from a total of 29 countries around the world.
  • I have a Redhaven peach tree that grows productively every year and produces fruit, but even after thinning, providing proper water and fertilization, the fruit never get bigger than about golf ball size and they are inedible.  What is the problem?
    Answer:  The tree may not be Redhaven as it was advertised or the scion may have died back and it is the seedling rootstock that has grown to be the above ground growing portion of the tree.  Let me explain…  When a peach tree is purchased bare root from a commercial nursery or in a pot from the local box store, it is actually a compound tree made up of two genetically different parts.  The bottom/underground part of the tree is typically a seedling rootstock that has been chosen because it imparts good characteristics to the tree (i.e., resistant to nematodes, tolerant to drought, vigorous, etc.).  If grown to a fruit bearing stage by itself, it will bear small, inedible fruit that you would never consider eating.  The top/aboveground part of the tree is typically a desirable scion cultivar that has been grafted on top of the seedling rootstock in the nursery (i.e., Redhaven). The scion cultivar is known to produce good quality fruit for eating that is harvested in a predictable timeframe.  The scion cultivar has its own specific traits that can be recognized and these are different from the seedling rootstock [i.e., presence or absence of leaf glands (and type of glands), type, color and timing of bloom, fruit attributes, harvest timing, etc.].  For commercial scion cultivars, these distinguishing traits are documented by the breeder and included either in the patent or cultivar release information associated with it.  Unfortunately, in the commercial nursery industry, sometimes accidents occur where grafted trees are mislabeled where what ends up being sold is not exactly what has been labeled.  Further, it is possible that if trees are grown further along in a pot before they are sold, the scion may die and the rootstock begins to grow shoots and what is in the pot is a healthy peach tree but the "Redhaven" part no longer lives.  This could also happen after the tree is planted where the scion dies and new shoots come up from the rootstock and they become the new tree.  In either of these scenarios, the peach tree is actually the seedling rootstock only.  I have seen this in the field before.  Usually some detective work can confirm if this is the case.
  • Why do some peaches melt in your mouth while others have a rubbery texture and some are even crunchy?
    Answer: From a genetic standpoint, peaches are classified by flesh texture as either melting, nonmelting or stony hard.  Melting flesh peaches become softer as they ripen and will actually “melt in your mouth” when they are fully mature.  Most people prefer this type for fresh eating out of hand.  Nonmelting flesh peaches remain firm in texture when fully mature and never become melting.  The texture of these has been referred to as “rubbery” or “chewy”.  Nonmelting flesh peaches typify most peaches that are used for commercial canning.  Some “freestone, melting” types are canned but they represent a very small proportion of canned peaches.  The stony hard flesh type is very firm, even crispy when fully ripe.  This type never melts and is typical of some white fleshed peaches from Asia.
  • Sometimes when I go to buy peaches at the store, I am disappointed with their quality.  It seems that they were not picked at the right stage of maturity.  How does a grower decide when to pick peaches and what should I look for?
    Answer: A grower may use a combination of several things to choose when to pick fruit: i. The historic ripe calendar date (when normally picked); ii. For cultivars that are not “solid red” in color at maturity, he will look at the change in background skin color from green to yellow/orange; iii. Size for market season – usually measured in inches of diameter; iv. Firmness measured as puncture pressure using a penetrometer; and v. Brix (i.e., sugar content) or soluble solids concentration of the extracted juice using a refractometer.  Some very sophisticated packing houses (i.e., Stemilt in Washington or Titan Farms in SC) now have in-line, near infrared (NIR) sensors that can detect peach sugar concentration nondestructively.  When looking at peaches in the grocery store, it is a good idea to determine where they came from.  Fruit that have traveled great distances need to be durable to survive the transport and have minimal bruising. These are often harvested before they are fully mature.  The most satisfying experience is to purchase tree-ripened fruit at roadside or farmer’s markets or when you “pick your own”.  Fruit at this optimal stage of maturity gives gently to your squeeze, has a strong peachy aroma, and should melt in your mouth. 
  • What is the whitish tissue that sometimes appears inside a peach near the pit? Is it a disease or harmful to eat?
    Answer: This whitish tissue may actually appear on the pit and/or in the pit cavity (area inside peach around pit) of a ripe peach.  It is called callus tissue (undifferentiated cells).  It is not a fungus, bacteria or other type of disease. It is naturally occurring, and it is not harmful.  It can be safely eaten along with the rest of the peach.
  • Is a nectarine a cross between a peach and a plum?
    Answer: No, a nectarine is a peach that has a mutation where the skin (epidermis) does not produce fuzz (trichomes). It occurred naturally.
  • What is the difference between a freestone and clingstone type peach?
    Answer: A freestone peach is one where the flesh (mesocarp) separates from the stone (endocarp).  When the fruit is cut in half, there is easy separation at the pit and the pit can be removed by hand.  It may even fall out if you tip the cut fruit over.  Freestone peaches are popular for home canning because their ease of preparation.  Clingstone peaches have flesh that clings to the stone.  When the fruit is cut in half, it is very difficult to separate the two halves because the flesh is stuck in the pit.  For commercial canning of nonmelting flesh clingstone peaches in California, machines are used to cut/separate the fruit.
  • What is a donut peach? Can you tell me something about it?
    Answer: A donut peach is a natural genetic mutation where the shape of the fruit is naturally flat (donut shaped) rather than globose (spherical or round).  They may have yellow flesh or white flesh.  The flesh texture may be melting or nonmelting. The pit inside the donut peach also has a different shape than a traditional peach pit.  In the donut peach, the pit is nearly spherical.  In China, where the donut peach originates, the name is pan tao where pan means flat and tao means peach.  Some people also refer to them as peento.
  • What are the top three peach producing states in the United States?
    Answer:  California (#1), South Carolina (#2), and Georgia (#3)
  • What is the “Top Secret” peach in your YouTube video “The Perfect Peach” and can you tell me something about it?
    Answer: Winblo.  It originated in Jackson Springs, N.C., by F.E. Correll and C.N. Clayton, North Carolina Agricultural Experiment Station. Introduced in 1972. Arose from a self-pollinated Redskin tree. Cross made in 1958, first fruited 1961, tested as NC 8969. Fruit: large, 2 1/2 x 2 3/4 inches in diameter; round, symmetrical; skin light yellow, three-fourths covered with bright red blush, attractive; flesh bright yellow, resistant to browning, very little red pigment except in pit cavity, firm, texture; fine, melting, flavor excellent; freestone, for freezing, canning and fresh market; ripens with Loring, 1 1/2 weeks before Elberta. Tree: spreading; vigor moderate; productive; flower large, showy, self-fertile; leaf glands reniform (kidney shaped); moderate resistance to bacterial spot. Chilling requirement 800 to 850 h.
  • I heard that peaches were part of the "dirty dozen" fruits and vegetables because of pesticide residues. Should I be concerned about this? Are fresh peaches safe to eat? Who makes this list? Where can I learn more?
    Like all fruits and vegetables that are grown commercially in the U.S., peaches are subject to numerous pests (insects and diseases) that must be controlled so that wholesome and unblemished fruits can be successfully produced for sale in the market.  Whether peaches are commercially grown using organic or conventional methods, pesticide use is normal and necessary.  Without the use of pesticides, the natural insect and diseases present in the environment would cause direct damage to the fruit and make it unmarketable.  Further, some diseases and pests damage the tree as well and can cause loss of tree productivity and premature tree death.  Commercial fruit growers are concerned about the safety of their fruit for the consumers who buy them. They are trained on the appropriate, safe and legal use of approved products to protect peaches.  They are licensed by the state and must keep good application records which may be inspected.  In most commercial operations that are supplying boxed fruit to the chain stores, the fruit are brushed and washed before shipping.  However, there may still be some pesticide residues on the fruit.  These pesticides are in extremely low and legally permissible concentrations – much below any level that could impact human health.  As with any fresh fruit from the market, it is always best to wash it with clean tap water before eating. The "Dirty Dozen" list was established by a private environmental advocacy group,, the Environmental Working Group (EWG), and are not a government or university organization.

Scientific Findings

  • Is it true that extracts from peach are effective against breast cancer cells?
    Answer: Yes.  In 2009, a scientific research paper was published by researchers at Texas A&M University demonstrating that extracts from the yellow-fleshed commercial cultivar “Rich Lady” were effective in inhibiting growth of breast cancer cells in lab tests.  The authors noted that in the peach extract, phenolic acids – namely, chlorogenic and neochlorogenic acid, have the potential to be chemoprotective dietary compounds “because of the relatively high growth inhibition on the breast cancer cell line and the low toxicity exerted on the normal cells”.
  • What is the nutrient value of a peach?
    Peaches are a highly nutritious food source when eaten raw.  They are a good source of energy, carbohydrates, dietary fiber, iron, potassium, vitamin A, vitamin B (folate) and vitamin C.   Peaches are also a rich source of bioactive compounds including phenolic acids, anthocyanins, flavonoids, and procyanidins.