CITATION: Pringle, K. L. 2006. The use of economic thresholds in pest management : apples in South Africa. South African Journal of Science, 102(5):201-204. | The original publication is available at https://journals.co.za | MONITORING SYSTEMS AND ECONOMIC thresholds can be used to determine the necessity for and timing of measures to control herbivorous arthropods which attack agricultural crops, particularly high-value ones such as apples. The data obtained from these monitoring systems, however, have far wider applications than just determining whether or not control measures are required. They can be used to decide the pest status of herbivorous arthropods, whether or not sporadic pests require attention during a particular season, to refine the timing of actions against perennial pests and to determine the effectiveness of measures applied to control chronic pests. Optimum use of monitoring data can help local exporters to supply unblemished fruit with the minimum use of insecticides to South Africa's main foreign markets, the European Union and the United States. | https://journals.co.za/content/sajsci/102/5-6/EJC96549 | Publisher's version

Codling moth (CM) and oriental fruit moth (OFM) have increasingly challenged fruit IPM programs since 2000.  There is a zero tolerance for worms in processing fruit diverting it to juice with a $1500 per acre loss in fruit value for the grower.  Accurate timing of appropriate control options is necessary to achieve 99% worm control in an IPM system.  This project implemented insect monitoring technology including sex pheromone traps and insect developmental degree-day models to schedule control actions on farms.  This project increased adoption of this technology by growers and consultants resulting in minimizing pesticide inputs and economic losses of rejected fruit loads.

An F₁ progeny derived from a cross between the apple (Malus x domestica) cultivars Telamon and Braeburn was used to identify quantitative trait loci (QTL) linked to the vitamin C (L-ascorbate [L-AA]) contents of fruit skin and flesh (cortex) tissues. We identified up to three highly significant QTLs for both the mean L-AA and the mean total L-AA contents of fruit flesh on both parental genetic linkage maps, confirming the quantitative nature of these traits. These QTLs account for up to a maximum of 60% of the total population variation observed in the progeny, and with a maximal individual contribution of 31% per QTL. QTLs common to both parents were identified on linkage groups (LGs) 6, 10, and 11 of the Malus reference map, while each parent also had additional unique QTLs on other LGs. Interestingly, one strong QTL on LG-17 of the Telamon linkage map colocalized with a highly significant QTL associated with flesh browning, and a minor QTL for dehydroascorbate content, supporting earlier work that links fruit L-AA contents with the susceptibility of hardfruit to postharvest browning. We also found significant minor QTLs for skin L-AA and total L-AA (L-AA + dehydroascorbate) contents in Telamon. Currently, little is known about the genetic determinants underlying tissue L-AA homeostasis, but the presence of major, highly significant QTL in both these apple genotypes under field conditions suggests the existence of common control mechanisms, allelic heterozygosity, and helps outline strategies and the potential for the molecular breeding of these traits.

Mangifera indica L. cv. Kent trees were subjected to five irrigation treatments during the 2000/2001 growing season with the aim of assessing the effects of irrigation on tree productivity and fruit quality. Two progressively reduced irrigation treatments (75 and 50% of the amount of irrigation water applied to the control), a control (100% field capacity), a regulated deficit irrigation (RDI) treatment and a farm control were compared with each other. Fruit yield, number and mean fruit weight were not significantly influenced by the different irrigation treatments. Peel colour and storage potential were improved in the reduced irrigation treatments. The RDI treatment improved the total soluble solids concentration (TSS) of fruits but increased the occurrence of split pit. Fruit firmness was not significantly influenced by the different irrigation treatments. In the second experiment, 'Kent' trees were covered with white shade netting of four mesh densities (50, 75, 100 and 125 g m-2) on a long¬term basis, while control trees remained uncovered. During the 2000/2001 growing season, light shading (50 g m-2) increased the yield and fruit numbers above that of control trees, while, heavier shading decreased the yield and fruit number below that of the control with the most dense net (125 g m-2) having the greatest affect. Peel colour, firmness and total soluble solids (TSS) at harvest were not affected by shading while the heaviest shade (125 g m-2) reduced storage potential of the fruit. Shading improved the appearance of fruits through the reduction of split pit, sunburn and wind damage. No fruit damage caused by bacterial black spot was observed in any of the shade treatments or the control.

Dragon fruit (Hylocereus undatus) are a host of fruit fly (Bactrocera spp.), and thus export to many markets will require a disinfestation treatment. This work investigated the potential for disinfestation by heat treatment (HT) of cv. Binh Thuan in order to meet the biosecurity requirements of importing countries. Main-season fruit from Viet Nam were subjected to hot air treatments and stored for 2-4 weeks storage at 5 °C in sealed polypropylene bags, and fruit quality examined during subsequent shelf-life at 20 °C. HTs applied were fruit core temperatures (FCT) of 46.5 °C for durations of 20 and 40 min, and 48.5 °C for 50, 70 and 90 min. Assessments included turgor of the bracts and stem, the appearance of the body of the fruit and presence of rots, skin colour, flesh firmness, soluble solids concentration, fruit acidity, taste, and flesh translucence. 'Binh Thuan' Dragon fruit proved to be tolerant of hot air treatment and at the lower HT temperature (FCT 46.5 °C for 20 min) fruit quality was not significantly different from non-heated control fruit, either after treatment at harvest, or after storage for up to 4 weeks. However, metrics quantifying the appearance of both control- and HT-fruit generally deteriorated with storage time at 5 °C, although the internal appearance of the flesh, and taste, remained acceptable throughout. Shelf-life effects were restricted to comparison of the lower HT temperature (FCT 46.5 °C for 20 min) and non-heated control fruit. Shelf-life after any of the storage periods was terminated after only 4 d, as fruit available for study had not been sprayed with fungicides during the season, and developed anthracnose rots readily at 20 °C. No differences in shelf-life characteristics were established between HT fruit and control fruit. Our results provide strong evidence that 'Binh Thuan' Dragon fruit are a suitable candidate for fruit fly disinfestation by hot air HTs, and that fruit quality during or after storage does not suffer as a consequence.

Netted muskmelon [Cucumis melo L. (Reticulatus Group)] fruit quality (ascorbic acid, beta-carotene, total free sugars, and soluble solids concentration (SSC)) is directly related to plant potassium (K) concentration during fruit growth and maturation. During reproductive development, soil K fertilization alone is often inadequate due to poor root uptake and competitive uptake inhibition from calcium and magnesium. Foliar applications of glycine-complexed K during muskmelon fruit development has been shown to improve fruit quality, however, the influence of organic-complexed K vs. an inorganic salt form has not been determined. This glasshouse study investigated the effects of two K sources: a glycine-complexed K (potassium metalosate, KM) and potassium chloride (KCl) (both containing 800 mg K/L) with or without a non-ionic surfactant (Silwet L-77) on melon quality. Orange-flesh muskmelon 'Cruiser' was grown in a glasshouse and fertilized throughout the study with soil-applied N-P-K fertilizer. Starting at 3 to 5 d after fruit set, and up to 3 to 5 d before fruit maturity at full slip, entire plants were sprayed weekly, including the fruit, with KM or KCl with or without a surfactant. Fruit from plants receiving supplemental foliar K had significantly higher K concentrations in the edible middle mesocarp fruit tissue compared to control untreated fruit. Fruit from treated plants were also firmer, both externally and internally, than those from non-treated control plants. Increased fruit tissue firmness was accompanied by higher tissue pressure potentials of K treated plants vs. control. In general, K treated fruit had significantly higher SSC, total sugars, total ascorbic acid, and beta-carotene than control fruit. Fall-grown fruit generally had higher SSC, total sugars, total ascorbic acid and beta-carotene concentrations than spring-grown fruit regardless of K treatment. The effects of surfactant were not consistent but in general, addition of a surfactant tended to affect higher SSC and beta-carotene concentrations.

The purpose of the present study was to investigate the role of ethylene action, via use of the ethylene antagonist 1-methylcyclopropene (1-MCP), on the senescence and quality of fresh-cut ripe papaya (Carica papaya L. 'Sunrise Solo') fruit. Ripe papaya fruit were treated with 2.5 microliter.L(-1) 1-MCP and immediately processed into fresh-cut slices or left intact. At 2-day intervals over 10 days at 5 degrees C, continuously stored slices were monitored for ethylene production, firmness, electrolyte leakage, color, sensory changes, and pathogen incidence. Slices freshly prepared from intact fruit stored under identical conditions were measured similarly. Ethylene production did not differ significantly between the treatments, although production rates were slightly but consistently higher in slices from intact control compared with intact 1-MCP-treated fruit. Mesocarp firmness of continuously stored slices and slices from fruit stored intact was significantly retained by 1-MCP. Firmness of continuously stored slices from 1-MCP-treated fruit declined 50% compared with 75% for control slices. Firmness of fresh-cut slices prepared from intact control and 1-MCP-treated fruit at each sampling interval declined 26% and 15%, respectively. Electrolyte leakage remained low and changed little in slices freshly prepared from fruit stored intact. Leakage from continuously stored papaya slices increased after 4 days, and after 6 days controls increased significantly compared with stored slices derived from papaya fruit initially treated with the ethylene antagonist. The flesh color of continuously stored slices or slices prepared from fruit stored intact was influenced by 1-MCP only during the later periods of storage. Microbial counts in stored slices or slices prepared at each sampling were generally unaffected by 1-MCP. Informal sensory analysis indicated that the edible shelf life was 6 days in stored slices from 1-MCP-treated fruit compared with 2 to 3 days for stored slices from control fruit.