25 Nov 2023
Summer pruning of Orange Trees

Summer Pruning of Orange Trees

Based on experience in West China, physiological responses to pruning of orange trees are quite different from apples. While winter pruning in suitable but not excessive amounts stimulates the vegetative processes of apples, it enhances the reproductive processes of citrus and summer pruning does the opposite. As a supplementary practice to winter pruning, summer pruning of oranges at the right time with specific techniques will invigorate neglected and old trees and modify the alter nate bearing habit of healthy trees. During the on-year, trees respond to moderate summer pruning by producing moderate amounts of summer flushes which increases the shedding of young fruits. Thus, the on-year crop will be reduced and the next year crop increased. This is “physiological thinning/’ as compared to chemical or hand thinning. Excessive summer pruning before the time of “June drop” can result in considerable fruit drop.

READ MORE

25 Nov 2023
Common symptoms cased by Phytophthora spp on citrus

Phytophthora-citrus Interactions and Management Strategies: A Review

Citrus production is declining worldwide due to several biotic and abiotic factors. The diseases caused by Phytophthora spp. present major economic risks since they are soil-borne and spread quickly if environmental conditions are favorable, or irrigation is poorly managed. Phytophthora species are present in all citrus-producing areas around the world causing significant losses in crop yield and affecting tree health. Bark infection, damping-off, root rot, gummosis, brown rot, and cortical root rot are among the typical symptoms caused by Phytophthora spp. The pathogenicity of Phytophthora spp. depends mainly on the specific interactions between the isolates and citrus cultivars.

READ MORE

30 Oct 2023
Girdling effects on fruit set

Girdling effects on fruit set and quantum yield efficiency of PSII in two Citrus cultivars

Girdling effects on fruitlet abscission, leaf chlorophyll, chlorophyll a fluorescence and carbohydrate concentration in various flowering and vegetative shoots were studied during natural fruit drop in two Citrus cultivars. Irrespective of shoot type, girdling delayed fruitlet abscission, but only fruitlets borne on leafy shoots had increased final fruit set. Chlorophyll a fluorescence analysis revealed differences in quantum yield efficiency of photosystem II of light adapted leaves (ΦPSII) among shoot types and in response to girdling. In young leaves of vegetative shoots, girdling decreased ΦPSII, whereas ΦPSII increased from Day 30 after girdling in young leaves of leafy flowering shoots; however,ΦPSII did not change in mature leaves during fruit set in either control or girdled trees.

READ MORE

30 Oct 2023
Satsumas easy peeling mandarin citrus

Originating in Japan, Satsumas are an easy-peeling mandarin citrus that is known for its cold-hardiness.

Satsumas are the first mandarins to ripen in Southern Africa, providing an early foot in the door to markets. However, they do come with significant challenges. Citrus Research International (CRI) conducts cultivar trials to evaluate cultivar suitability to various climatic regions. Cultivar ripening windows, production and fruit quality are evaluated over a number of seasons, often spanning eight years. A cultivar trial was established in Citrusdal to evaluate the climatic suitability of this region for Satsuma production. Cultivars Aoshima, Belabela, Imamura, Miho Wase, Miyagawa Wase, Sugiyama and Ueno were imported to SA over time and introduced to the Citrus Improvement Scheme (CIS). These are open cultivars, apart from Belabela which is managed by cultivar agent Citrus Genesis.

READ MORE

29 Sep 2023
Hand thinning citrus

Reviewing the Commercial Potential of Hand Thinning in Citrus with a Cost-benefit Analysis of Summer Hand Thinning of ‘Nadorcott’ Mandarin

Hand thinning is not often applied as a commercial cultural practice in citriculture due to the practice’s reliance on costly manual labor. However, hand thinning could provide unique benefits such as treatment selectivity and easier control over thinning intensity, as opposed to foliar sprays of chemical thinning agents. In ‘‘on-year’’ ‘Nadorcott’ mandarin (Citrus reticulata) trees, summer (January) and autumn (April) hand-thinning treatments of removal of all fruit <20 and <40 mm diameter were evaluated for effects on leaf carbohydrates and fruit growth rate. Other factors assessed included treatments’ effects on tree total fruit yield, fruit quality, and fruit size distribution. In addition, two different summer hand-thinning treatments (removal of all fruit <20 and <25 mm) were evaluated for effects on fruit size distribution and fruit yield over two seasons to determine their potential financial implications.

READ MORE

29 Sep 2023
Clay Soil

Effect of elemental sulphur and compost on pH, electrical conductivity and phosphorus availability of one clay soil

Suitable plant nutrition is one of the most important factors in the quantity and quality of crops’ yield. In plant nutrition, each nutrient should be in adequate level. The most important role of pH is the control of nutrients solubility in soil. Nutrient availability usually decreases with increasing pH. Experimental soil sample was collected from 0 to 30 cm depth from Niar village around the Ardabil city.The soil samples were mixed with solid acidifying material including elemental sulphur (S) in three levels (0.25, 0.5 and 1.0 g/kg soil), farm yard compost manure in three levels (2.5, 5 and 10 g/kg soil) and elemental S + organic matter in three levels (the same amounts of S with 5 g/kg cattle manure), and filled in 4 L pots. Soil water content was held close to field capacity and green house temperature was kept to 25 ± 5°C. Before the experiment, the physicochemical properties of soil and chemical properties of the compost were measured. At eight, 16 and 32 weeks of incubation, compound soil samples were collected from pots, and their pH, electrical conductivity (EC) and phosphorus (P) were measured.

READ MORE

29 Sep 2023
Washington Navel Orange

Effects of 2,4-D on the size of the navel-endopening and fruit quality of ‘Washington’ Navel orange

Large, protruding navel-end openings of navel oranges (Citrus sinensis (L.) Osbeck) are a major cull factor in the packhouse and make the control of some insects very difficult. Previous work on navel orange trees suggested that the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), applied at full bloom at 20 mg·L-1 reduced the diameter of the navel-end opening. In a preliminary study to verify these results under South African conditions, similar results were obtained when 2,4-D was applied at 25 mg·L-1 at petal drop on ‘Palmer’, ‘Robyn’ and ‘Lane Late’ navel orange trees. To determine the optimal timing and concentration of application without any detrimental effects on fruit quality, 2,4-D was applied at 15, 25 or 35 mg·L-1 at either full bloom or petal drop to ‘Washington’ navel orange trees in the following season.

READ MORE