Physical Disorders of Stone Fruit

Physiological Disorders of Stonefruit

Physiological disorders are problems that are not caused by insects or diseases, but rather by the climate (temperature, rain, humidity) and by management practices that change the micro-climate endured by the plant. Among these practices would be training and pruning, irrigation, fertilization and harvest procedures. In addition to these factors, in many cases, certain varieties are more predisposed to a specific disorder than others. The most common physiological disorders seen on stone fruit in Texas are split and shattered pits, double fruit and cleft sutures, fruit buttons, blind wood and delayed foliation. This article will describe these disorders, explain their causes if known and suggest the possible management strategies to minimize them.

Split and Shattered Pits: When one thinks about split and shattered pits, it is the early ripening peach varieties such as ‘June Gold’ and ‘Springold’ that come to mind. The reason early ripening cultivars are more susceptible to this disorder is that the pit hardening and final swell phases of fruit development occur relatively close together in time. Pit hardening begins about 40 days after full bloom. During this phase, the pit gradually loses flexibility and becomes very rigid while the flesh of the fruit is still tightly adhering to the pit. On early ripening varieties, final swell occurs before the adherence between the pit and the flesh has weakened. Consequently, the expansion of the fruit flesh creates internal forces pulling out on the pit. If great enough, this force will cause the pit to break in the weakest spot which is along the suture. In later ripening cultivars, these two events (pit hardening and final swell) are further apart which allows a weakening of the adherence between the pit and the surrounding flesh cells.

Fruit with split pits are generally misshapened and frequently open at the stem end which allows the entry of insects and diseases. Shattered pits are less obvious since the shape of the fruit is generally not affected. The pits of these fruit are broken in several places and the cavity may contain a gummy substance. The pieces of pit can be a danger because of sharp edges if swallowed. The cultivar best known for this problem is ‘June Gold’.

Beyond the propensity of early ripening peach cultivars of having this problem, any practice or weather condition that reduces the fruit set and encourages large fruit size may accentuate the occurrence of split or shattered pits. These practices would include such things as excessive fruit thinning, and girdling, heavy irrigations or high nitrogen applications close to harvest. To minimize this problem, the above practices should be avoided especially with susceptible varieties. If susceptible varieties are used, much care should be taken to crop them as heavily as possible while maintaining acceptable fruit size.

Double Fruit/Cleft Sutures: Double or twin fruit is frequently seen in Texas orchards. In many cases, the extent of the problem is minor and these fruit can be easily eliminated during hand thinning. But in some orchards and on some cultivars, the problem can be of major importance. Whether a fruit will be double or not is determined the summer previous to fruiting when the flower buds are going through their initial development. During this period, the young developing buds are sensitive to any type of stress that may affect the tree’s growth. Work done by Kim Patten and Elizabeth Neuendorff in Overton, John Lipe in Fredericksburg, and researchers in California have shown that heat and water stress during the summer months increases the development of doubled fruit. Thus to minimize this problem, it is essential to irrigate the orchard adequately during the hot, dry summer months. Work on cherry in California and preliminary work done at College Station indicates that peach varieties vary in their predisposition to develop double fruit. Data taken this spring at College Station showed a range of double fruit from 1% up to a high of 64% depending on the variety. Although, we do not have enough data to rank the varieties on their tendency to double, it is clear that there are large differences between varieties.

Another related disorder is the cleft suture that is formed when a double fruit develops in such a way in which one of the fruits is very small. At the stem end, the suture crease is deepened and lengthened forming the cleft suture or a spurred fruit with a cleft suture. Frequently, gumming will develop at this juncture which further distracts from the appearance of the fruit. We have noticed this disorder on ‘RioGrande’, ‘Juneprince’ and ‘June Gold’, especially in low-chill years. Although this one way in which cleft sutures are formed, it should be noted that some varieties form cleft sutures without fruit doubling.

Buttons: Buttons are fruit that, although they initially set, do not develop into full-sized fruit. These fruit generally have poorly developed or dead embryos as a result of incomplete fertilization. This can be due to insufficient chilling received, a frost during bloom, or wet, cool weather during bloom. These fruit are hard to identify at thinning time and may cause a grower to thin too heavily. Also, they provide a place for pests and diseases to survive and overwinter in a low fruit year. We have noticed bottoning most often as a result of insufficient chill in Texas. The first step in managing this problem is to plant varieties well adapted to your area.

Blind Wood: Blind wood is characterized by no vegetative or flower bud development in the nodes of the plant (blind nodes). Blind nodes become obvious the following year when the one-year old shoots fail to develop leaves or fruit. Trees with blind wood are difficult to train and prune, and have lower yields. A recent study of this problem in the low and medium chill regions of Texas indicated with the development of blind nodes is related to the temperatures during summer months, especially when the high temperatures are consistently in the 85-90° F range or higher. The extent of blind node development appears to be accentuated by insufficient chilling, by stress during bud development in the summer (hear, water, overcropping), and by the variety used. Presently, we are evaluating the propensity of different peach varieties to form blind nodes. Management procedures to handle this problem would be to minimize stress during the summer months by not overcropping the trees, by regular irrigation, and by selecting a variety that is well matched to the chilling hours received.

Delayed Foliation: Since 1985, There have been three low-chill years in the medium-chill region of Texas. One of the most noticeable effects is the delayed foliation of fruit trees in the spring. Normally, trees develop new growth uniformly throughout the canopy soon aster the terminal buds break. Trees with delayed foliation develop a tuft of leaves at the terminal tips but the other vegetative buds break sporadically, if at all, over a prolonged period. Often vigorous sprouts emerge from the base of crotches and the trunk. Delayed foliation results in a tree with poor leaf cover and reduced fruit set. Management of the tree is complicated by excessive water sprouts and root sprouts resulting from the poor leaf cover. The only way to minimize delayed foliation is to carefully select varieties well adapted to your area.

Other Disorders: Two other problems that have been noticed over the years are the opening of the fruit at the stem end of late ripening varieties and the excessive formation of red color in the flesh. Both disorders have been attributed to excessive heat before ripening, but no good information is available on the frequency or the control of these maladies.

In Figure 1, the physiological disorders are summarized with their respective causes. For all the disorders, it is clear that the varieties differ in their sensitivity although in most cases, little work has been done in the evaluation of the commercial varieties for these traits. Two of the common reasons for the disorders are summer heat/water stress and chilling received. Although the heat in the summer cannot be changed, its effect can be alleviated by sufficient irrigation during this period. Again in the case of insufficient chilling, the best way up to this point to handle it would be the proper selection of varieties and in the long run, the development of better adapted varieties.

Written by David H. Byrne, Terry A. Bacon and Unaroj Boonprakob. Department of Horticultural Sciences, Texas A&M University, College Station, TX. Modified from article published in the Texas Horticulturist in November, 1991.

Figure 1. Physiological Disorders. Summary of their causes.

Problem

Cultivar

Heat

Chill

Frost

Management

Split pits

 

*Early cultivars more susceptible

NA

*Set

*Set

Irrigation

Thinning

Girdling

Doubles

**

**

NA

NA

Irrigation

Cleft Suture

 

**

**

NA

NA

Irrigation

Buttons

 

**

NA

**

**

NA

Blind Wood

**

**

**`

NA

Thinning

Irrigation

Delayed foliation

 

**

NA

**

NA

Dormex

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