Pecan Fruit Research Articles

A Budbreak-based Chilling and Heating Model for Predicting First Entry of Pecan Nut Casebearer

A modification of the chilling and heating model for pecan budbreak was used to describe the interactive effects of chilling and heating on the date of first entry of the pecan nut casebearer (PNC; Acrobasis nuxvorella Neunzig) into the pecan [Carya illinoinensis (Wangenh.) K. Koch] fruit. Selected data from unpublished and published sources were used to construct the model. Base temperatures of 9.4 and 13.9C for chilling and heating, respectively, provided the best fit (r2 = 0.981) for the model used to predict PNC activity. An inverse relationship [1/Y = 0.0037259(1 – 0.1e–0.0028069x – 574.9638969)] was found between chilling (1 Dec. through February) and heating (beginning 1 Feb.) degree-days accumulated until entry of first-generation PNC into the pecan fruit. This model can be used to predict entry of first-generation PNC larvae into fruit over a range of geographic and climatic conditions and pecan genotypes. Model validation using 1994 data from two sites in Texas suggests precision is sufficient to use the model as a guide in managing nut casebearer control.

TIME OF FRUIT REMOVAL INFLUENCES RETURN BLOOM IN PECAN

Pecan trees, Carya illinoensis, often exhibit a strong alternate bearing pattern. The presence of a heavy seed crop inhibits terminals from fruiting the following season. This study was developed to discover at what point in the development of the pecan fruit does this inhibition take place. Six nut removal times were evaluated: (1) after pollination but before fertilization, (2) one-half ovule expansion, (3) full ovule expansion or water stage, (4) dough stage, (5) 3 weeks after the initiation of the dough stage, and (6) no fruit removal until harvest. The cultivar `Mohawk' was used for this randomized block experiment.Return bloom was significantly enhanced by the removal of fruit prior to the initiation of kernel filling (dough stage). Less than 10% of terminals that supported pecans through the dough stage were able to produce distillate flowers the following year. Twig mortality was significantly higher for terminals that completed kernel filling. These results indicate that nut thinning prior to the water stage may reduce the alternate bearing tendency in pecan.

Mechanical Thinning of Pecan Fruit

Fruit of `Mohawk' in 1986 and 1988 and `Shoshoni' pecan [Carya illinoensis (Wangenh.) C. Koch] in 1986 were thinned during early August using a pecan shaker with modified shaker pads. Fruit removed ranged from 44% to 57% of the crop load. Fruit thinning increased nut size of `Mohawk' in both years, but did not affect nut size of `Shoshoni'. Kernel percentage of thinned `Mohawk' and `Shoshoni' trees increased, and kernel grade of `Mohawk' improved relative to unthinned trees. Return bloom of `Mohawk' was not affected either year by thinning, but return bloom on `Shoshoni' was increased by thinning. Mechanical fruit thinning appears to be a useful commercial tool until better thinning methods are available.

First Report of Phytophthora cactorum Causing a Shuck and Kernel Rot of Pecan Fruit

First Report of Phytophthora cactorum Causing a Shuck and Kernel Rot of Pecan Fruit

Use of Ethephon and NAA for Inducing Early Shuck Dehiscence of Pecan

Abstract Field observations indicate that conjunctive use of ethephon (Ethrel) and NAA (Fruitone-N) can induce early pecan [Carya illinoensis (Wangenh.) C. Koch] shuck (involucre) dehiscence, while greatly reducing undesirable leaflet abscission. Comparisons of the efficacy of 2,4-D and NAA in preventing undesirable leaflet abscission revealed that the comparative molar protective activity of 2,4-D greatly exceeds that of NAA, providing leaflets absolute protection against ethephon-induced abscission, but it was functionally inferior to NAA due to the induction of leaflet necrosis. Single ethephon treatments accelerated shuck dehiscence 3 to 6 weeks for several cultivars. Treatment of ‘Stuart’ and ‘Moneymaker’ pecan fruit and foliage, several weeks prior to the completion of natural shuck dehiscence, with a NAA-ethephon mixture accelerated shuck dehiscence by 5 and 3 weeks, respectively, without severe leaflet abscission or loss of nut quality. These data indicate possible development of harvest-aid technology for early harvesting of pecan without severe leaflet abscission. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); (2,4-dichlorophenoxy)acetic acid (2,4-D); and 1-naphthaleneacetic acid (NAA).

The development of the ‘Delmas’ pecan fruit, with special reference to growth phases and changes of lipids and potassium

The morphological development of pecan nuts and the changes in lipids and potassium were investigated. The nut reached its full size at the beginning of September, while the shuck continued to grow for about four additional weeks. The liquid endosperm attained its maximal volume by the end of August and disappeared during the first week of September. At about this time, potassium and lipids started to accumulate. The rate of accumulation of potassium in the shucks and lipids in the kernel was exponential. The influx of potassium into the kernel was discontinuous. There exists a linear relationship between the level of potassium in the shucks and of the lipids in the kernel. Extrapolation of the regression line indicates a critical potassium level in the shuck of ca. 1.57% per dry weight. Potassium analysis of the shucks is proposed as a physiological indication of the potassium status of the tree. Possible functions of potassium in the biosynthesis of lipids in pecan nuts are discussed.

Influence of fruit development on seasonal elemental concentrations and distribution in fruit and leaves of pecan

Abstract The elemental concentrations of leaves and fruits were monitored during one season on fruiting and vegetative pecan shoots. Pecan fruit and leaves of fruiting and vegetative shoots on 31‐year‐old ‘Western’ pecan trees were collected biweekly from May 15 through October 15, 1982 and analyzed for N, P, K, Ca, Mg, Fe, Zn and Mn. The concentrations of Ca, Mg, Zn, Fe and Mn were greater in leaves of fruiting shoots. The N concentration was higher in leaves of fruiting shoots the first ten weeks, then was significantly less in leaves on fruiting shoots the latter part of the season. K concentration was lower in leaves of fruiting shoots than vegetative shoots from June 25 through Oct. 15. Leaf P concentration did not appear to be influenced by fruiting. Content of N,K,P, and Zn in the fruit increased slowly until the tenth week after full bloom, then rapidly until fruit maturity. Ca, Mg and Mn accumulation in the fruit was linear throughout fruit development. Fe increased rapidly during early kernel de...

Genetic Variability in Pecan Fruit Development

Abstract Fresh and dry weights of fruit (nut and shuck) samples of 39 clones of pecan [Carya illinoensis (Wang) K. Koch] were determined weekly from July 23 until harvest. One early maturing clone had accumulated 24% of its final fruit dry weight by July 23, when the average for all clones was 11%. Total fruit dry matter decreased during October for some late-maturing clones. These decreases, which were the most obvious in ‘Mahan’ and its progeny clones, were not as common in early maturing clones.

Management of Pecan Fruit and Foliar Diseases with Fungicides

Management of Pecan Fruit and Foliar Diseases with Fungicides

Growth Substances and Fruit Shedding in the Pecan, Carya illinoensis1

Abstract Wheat coleoptile straight growth bioassay of pecan fruit extracts established the presence of growth promoting and inhibiting substances. Indoleacetic acid was tentatively identified as a promoting substance. The growth inhibiting substance(s), possibly abscisic acid, promoted abscission of cotton cotyledonary node explants. The absolute level of growth substances did not appear correlated with the seasonal shedding pattern.