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    Factors influencing the susceptibility of apples to bruising : this thesis is presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Horticultural Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1997) Mowatt, Craig Meffan; Mowatt, Craig Meffan
    Financial returns to New Zealand orchardists could be increased if bruise damage to apples and its visual consequences were reduced. Comprehension of the variability of susceptibility to the bruising of apples associated with either preharvest, harvest or postharvest influences is fundamental to reducing bruise damage. Standard impacts to apples have been generated in many ways and bruise severity has generally been represented as bruise volume per unit energy. In this study bruise severity was represented by a) the diameter of a bruise generated by a sphere of mass and radius of curvature similar to that of apples and whose impact energy (0.32 J) was similar to apple-apple collisions that occurred during grading or b) the damage that apples incurred by grading in a standard manner. Bruise colour was also measured and visual differences between dark and light brown 'Granny Smith' bruised tissue were associated with a 5° difference in hue angle, as measured by a Minolta chromameter. In 1990 from a survey of 'Granny Smith' orchards it was determined that the range in bruise diameter of individual fruit was 17% (fruit mass range; 0.157-0.207 kg) and in 1991 was 63% (fruit mass range; 0.098-0.278 kg). The between-season difference in mean bruise diameter was 2.8%. Over the two years it was found that bruise diameter of fruit from orchards producing either the most or least bruise susceptible fruit differed by an average of 6.5%. In 1991 bruise diameter generated from a standard impact was related to grader damage (R2 = 0.49) and the slope of this relationship indicated that small increases in bruise diameter equated to large increases in grader damage. In both years the most bruise susceptible fruit had higher levels of tissue phosphorus, calcium and nitrogen than least susceptible fruit. In one year of the survey bruise diameter was positively related to apple calcium content and apple mass with grader damage positively related to phosphorus content. In a within-orchard study between-tree variation in bruise diameter of 'Royal Gala' (11%) exceeded that of 'Granny Smith' (4%). Bruise diameter of least bruise susceptible fruit was more consistently related to starch index, soluble solids, fruit mass and firmness than bruise diameter of the most susceptible fruit. Harvesting 'Granny Smith' and 'Royal Gala' early rather than later in the season resulted in bruise diameter reductions of 5% and 21% respectively. Within-tree position of apples did not consistently influence susceptibility to bruising in either variety. Foliar sprays of calcium (CaCl2) and phosphorus (H3PO4) did not influence fruit mineral contents or susceptibility to bruising. Apples from non-irrigated "Braeburn" trees had smaller bruise diameters (6%), less calcium and tended to have more dry matter than apples from normally irrigated trees. 'Golden Delicious' apples harvested later in the day were less susceptible to bruise damage (7.3%) than those harvested early in the morning; elevated temperatures and reduced water status were identified as causative factors. As temperature increased from 0 to 20°C susceptibility to bruising showed a non-linear reduction. Bruise diameter and grader damage reduced 5% and 24% respectively when 'Granny Smith' apples were bruised at 20°C rather than when bruised at 0°C. If 'Royal Gala' were cooled to 2°C and then rewarmed to 20°C they sustained 36% less grader damage than if graded immediately after harvest. Useful reductions in grader damage (25%) were achieved by holding freshly harvested 'Royal Gala' at ambient temperatures for one day before grading. Storing the bruise susceptible cultivar 'Splendour' apples for 54 h at 20°C before bruising resulted in a 9% reduction in bruise diameter. A 24 h delay in pre-cooling of 'Royal Gala' was associated with a 0.5% weight loss and a 3% reduction in bruise diameter; delays of more than 24 h before pre-cooling were associated with enhanced ripening and greater weight loss but no measurable change in susceptibility to bruising. In the 1991 survey, there were large between-orchard differences in hue angle of bruised 'Granny Smith' apple tissue (16°) and light brown bruise tissue was associated with higher fruit nitrogen content (R2 = 0.55). Between-tree differences in hue angle of bruised tissue from 'Royal Gala' apples were large (15°) but with 'Granny Smith' were insignificant. Differences in bruised tissue colour due to enhanced maturity or within-tree position in both cultivars were not consistent. Cool storing 'Splendour' for 414 h before bruising appeared to increase bruise lightness.
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    Computerised decision support for IPM in New Zealand apple orchards : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 1997) Stewart, Terrence Mark; Stewart, Terrence Mark
    New Zealand apple growers face a dilemma. Export fruit must be of the highest possible quality and free from quarantine pests, but contain increasingly fewer pesticides in lower amounts. The objective of this study was to define and develop decision support tools that may assist in the improved timing and/or reduction of pesticide usage. Fifty randomly selected growers were interviewed in 1992 to determine their pest and disease problems, use of existing IPM methodology and requirements for an improved decision support service. The survey found more then 20% of growers had difficulties with common pests and diseases and many used IPM techniques. Most growers perceived a problem with pesticide residues and pest and disease resistance; they also expected to reduce pesticide usage and better target applications through improved technology in the future. Decision-support using fax and computer technology appeared feasible, subject to support from their advisers. In 1993, twenty-seven Hawkes Bay apple pest and disease control "advisers" were interviewed to determine their role in growers' pest and disease spray decision-making. Horticultural merchant representatives believed they were the main spray decision-maker for 40% of growers, and half of the latter expected the horticultural merchant representatives to know more about the problems in the orchard than they did. Other advisers played an important role in strategic pest and disease advice to the industry. Introducing more complex spray-saving techniques, or taking full advantage of those that already exist, would require many growers either to upskill themselves, or employ consultants to manage their orchards. Basic pest and disease identification and biology, together with knowledge of pesticides were regarded as being essential to manage pests and diseases successfully. Nutritional problems and resistance development were two particular areas where growers required more knowledge. Using the survey findings, a problem tree was created focussing on the question "Was pesticide use excessive in New Zealand apple orchards?". This conceptual model showed that pesticide use was excessive, and better grower education and training may partly alleviate the problem. Using the data from the surveys, two computerised training tools were defined and developed to assist with this solution viz SPRAYCHECK and DIAGNOSIS. SPRAYCHECK was developed to analyse grower black spot fungicide spray programs during the period of primary inoculum release. Using a series of models, incorporating weather data, infection periods and information from growers' spray diaries, grower black spot control decision-making was analysed and a recommended spray schedule for the season in question provided. Model construction revealed a lack of quantitative information on fungicide behaviour and the levels required to fully protect against black spot on apple foliage. A sensitivity analysis showed the rate of cover decay was very important in determining the number of fungicides required to fully protect a crop. DIAGNOSIS is a training aid for teaching pest and disease diagnosis skills to crop protection trainees. This program simulates field and laboratory scenarios, in which trainees must actively seek clues and interpret observations on the cause of plant problems, in apples or other crops. Once trainees have recorded their diagnosis, justification and recommendations for action, they receive an automatic de-briefing on their problem-solving approach. Trainee input is recorded to disk for later tutor assessment. Two decision-support tools were defined, developed and validated. One has been commercialised and the models in the other are likely to be used in an existing Decision Support System. During this exercise, knowledge was gained regarding the New Zealand apple industry in Hawkes Bay, in particular the close relationship between the growers, and horticultural merchant field representatives and their advisers. This relationship could either help or hinder IPM and improved decision support in the future