Strategies to control tree vigour and optimise fruit production in 'Conference' pears

The ban on the use of chlormequat (CCC) in pear orchards in 2001 forced Dutch pear growers to look for alternative methods to control tree vigour and stimulate flower bud development and fruit production. Root pruning and trunk notching have become the major growth retarding methods. In addition to the mechanical methods for controlling tree vigour, Regalis (Prohexadione-Calcium) and ethephon were tested as alternative chemical growth regulators for 'Conference' pears. In 2004, a trial was started in which six different strategies to control tree vigour and optimize fruit production in 'Conference' trees are compared. In 4 strategies root pruning was the major treatment, while in 2 strategies trunk incisions were the initial treatment to reduce tree vigour and stimulate fruit production. In 2005, no further root pruning or trunk incisions were made and ethephon and Regalis were the only treatments applied in some of the strategies. Ethephon and Regalis were also applied in 2006 in addition to root pruning in March and June or in June only. All of the strategies evaluated significantly reduced shoot growth and improved fruit production. Regular yields of 52 to more than 70 tons/ha were achieved for 3 consecutive years. So far, ethephon and Regalis have shown no or only minor additional beneficial effects compared to root pruning or trunk incision followed by root pruning in the years thereafter. Flowering, fruit yield and fruit quality of 'Conference' pears produced using the different strategies are presented and discussed

Effects of light quality on the growth and carbon metabolism of internodes of Phaseolus vulgaris L.

Effecten van lichtkwaliteit op de groei en ontwikkeling van boneplanten werden onderzocht in samenhang met effecten van lichtkwaliteit op het koolhydraatmetabolisme van de planten. Het verband tussen de activiteit van invertase in internodien en de strekkingsgroei van de internodien werd bestudeerd in planten die onder verschillende lichtkwaliteiten werden opgekweek

Chemical thinning of 'Conference' pears

The increasing difference in the market value of small and larger sized ‘Conference’ pears (>65 mm) and the high labour costs for hand thinning, makes it interesting for growers to find a cheaper and reliable method for thinning pear trees. In 2007, 2008 and 2009 trials were carried out to test the thinning efficacy of several chemicals. Fruit set was only significantly reduced by a two-fold application of ammonium thiosulphate (ATS) or by a tankmix application of 6-benzyladenine (BA) and 1-naphtalene acetic acid (NAA). Unfortunately, russeting of ‘Conference’ pears was augmented by the treatments with ATS during bloom. Tankmix applications of NAA + BA, applied at an average fruit diameter of 8.8 mm, resulted in a severe overthinning of the trees in 2008. However, the same treatments applied at an average fruit diameter of 14.7 mm had much less of a thinning effect. In 2009 adequate thinning was obtained with lower concentrations of BA+NAA applied at 8-10 mm fruit diameter. Surprisingly, the reduction in fruit set by BA+NAA did not result in a proptional increase in the average fruit weight at harvest. In some treatments average fruit weight was even reduced compared to that of the hand-thinned trees, a size-reducing effect that was attributed to NAA. In conclusion, BA+NAA seems to thin ‘Conference’ pears more strongly than BA alone. However, the addition of NAA to BA has the disadvantage of a diminishing effect on the increment of fruit size, i.e. fruit size increased less than expected on basis of the reduction in crop load. Additional research will be carried out to further optimise the developmental stage, weather conditions, and concentrations at which a BA and NAA must be applied to obtain the desired level of thinning and gain in yield percentage of fruits over 65 mm in diameter

Krymsk®1 (VVA-1), A dwarfing rootstock suitable for high density plum orchards in the Netherlands

Krymsk®:1 (Prunus tomentosa × Prunus cerasifera) was selected by Gennady Eremin at the Krymsk Breeding Station in Russia in 1966. Since 1994, it has been tested as a rootstock for several plum cultivars in The Netherlands. Graft compatibility was good for scion cultivars ‘Avalon’, ‘Excalibur’, ‘Jubileum’, ‘Opal’, and ‘Victoria’. Growth and production efficiency of plum on Krymsk®:1 was compared with that of plum on St. Julien A and, depending on the cultivar, also with Ferlenain, Otesani 8 and Pixy. With all cultivars, trees on rootstock Krymsk®:1 were by far the least vigorous, most precocious, and most production efficient. The production efficiency of ‘Avalon’ and ‘Excalibur’ on Krymsk®:1 grown for 10 years was 0.41 and 0.26 kg/cm² trunk cross sectional area, respectively, 3.4 and 4.3 times higher on Krymsk®:1 than on St. Julien A. With ‘Opal’ the production efficiency calculated over the first 5 years after planting was 2 to 3 times higher than on St. Julien A, but this difference became non significant after 7 years of cultivation. This was due to the much higher increase in production per tree during the 5th and 6th leaf of the trees on St. Julien A than on Krymsk®:1. Fruit size of ‘Opal’, ‘Avalon’ and ‘Excalibur’ was similar for trees grown on Krymsk®:1 and St. Julien A. With ‘Victoria’ fruit size was significantly larger (5 g) with Krymsk®:1 than with St. Julien A. Krymsk®:1 also increased the percentage of first pick by 15%, the sugar content by 9%, enhanced the development of fruit overcolour and reduced the percentage of fruits with gummosis in ‘Victoria’ plums. Dutch fruit growers show great interest in Krymsk®:1 as a rootstock for plum, as this rootstock makes high density plum orchards feasible. Growers switching to trees on Krymsk®1 have to take more care of their trees, especially in the first years after planting. Pruning, irrigation, and fertilization of the trees need much more attention in order to keep the trees vigorous and ensure good production levels. From 2002 to spring 2008, 120,000 plum trees on Krymsk®1 have been planted in The Netherlands and planting densities have increased from 830 up to 2,285 trees/ha. The main cultivar planted is ‘Victoria’

Carry-over effects of CCC-applications in pear orchards

Chlormequat (CCC) has been used for many years in the Netherlands as a chemical growth retardant to restrict vegetative growth and promote flower bud development in pears. After several years of annual applications, CCC-residue levels in the fruits frequently exceeded the maximum residue limit (MRL) of 3.0 mg/kg. In 2001 the use of CCC in pears was banned and the MRL was reduced to 0.05 mg/kg. CCC is a very persistent chemical which seems to have accumulated in trees treated for many years with this growth retardant. Because of the expected carry over of these accumulated residues into fruits in the years following the last application of CCC, it was decided to transiently decrease the MRL. In 2001 and 2002 a temporary MRL of 0.5 mg/kg was in force. In 2003 a temporary MRL of 0.3 mg/kg came into force which will expire in June 2006. CCC-residue levels in pears, sampled in the final year of CCC application, varied between 6.8 and 1.1 mg/kg, depending on the dosage and number of years of CCC-treatment. During the first growing season without further CCC-applications, the CCC-residue of the fruits decreased on average by about 90%. During the following year without CCC the rates of decrease in CCC-residues varied strongly. In some trials a 60% decrease was noted in the second 'CCC-free' year, while in other trials a much lower or no further decrease was observed. In 2003 a further reduction was observed in most trees. Compared to 2002 the CCC levels had decreased by 6 to 80% and were all below the temporary MRL of 0.3 mg/kg. However, despite these decreases in CCC-residue levels in trees grown for three to six years without any further CCC application, in 2003 the CCC residue in the fruits of most trees still exceeded the future MRL of 0.05 mg/kg. Only the residue levels of the ‘Doyenné du Comice’ trees planted in 1997 and treated with CCC during 1998-2000 were below 0.05 mg CCC/kg. In 2004 only the fruits of one trial exceeded the MRL of 0.05 mg CCC/kg. In these trees, which received their final CCC application in 1999, an average CCC level of 0.12 mg/kg was measured. In conclusion, the data demonstrate that for trees previously treated with CCC at recommended or lower rates, at least six seasons without CCC-application are needed to reach the MRL of 0.05 mg/kg

Demonstratie van de gebruikswaarde van kwee onderstammen Eline, C.132 en MH voor de teelt van Conference

Van 2009 tot en met 2013 is op twee locaties de gebruikswaarde van de kweetypen Eline®, C.132 en MH als onderstam voor het perenras Conference vergeleken met die van de standaardonderstammen kwee MC en kwee Adams. In de proeftuin van Praktijkonderzoek Plant en Omgeving (PPO-Fruit) in Randwijk is hiervoor een demonstratieperceel aangelegd waarbij in 4 herhalingen veldjes van 15 tot 25 bomen per onderstam zijn geplant. Bij een praktijkbedrijf in Zeeland zijn in een gerend perceel per onderstam volle rijen aangeplant met in totaal 189 bomen op onderstam kwee Adams, 354 op MC, 423 op Eline®, 331 op C132 en 345 op MH. De bomen zijn op beide locaties volgens de standaard praktijkteeltwijze voor peren verzorgd. In Randwijk zijn bij één herhaling de onderstammen ’s winters niet afgedekt met champost om eventuele verschillen in winterhardheid van de onderstammen te vergelijken in het geval van een winter met strenge vorst. Jaarlijks zijn de de productie en de groei van de bomen en bepaald