Good Fruit Grower

40 AUGUST 2017 GOOD FRUIT GROWER www.goodfruit.com down or stop, limiting shoot growth. Thus, decreased root growth decreases shoot growth. There is no doubt that roots, acting through a hormonal control, play a major role in the maintenance and balance of the growth of the whole tree. In some countries, such as Chile, there has been a significant trend toward high-density planting on M.9 rootstocks in newer blocks, but semi-dwarfing root- stocks such as Malling-Merton 106 and Malling 7 are planted on new adjacent blocks. In South Africa growers are worried that their trees on dwarfing rootstocks will be stunted in their relatively harsh sum- mers, poor soils and restricted water sup- ply. Growers are also worried that trees will behave differently between apples on dwarfing rootstocks such as M.9, and their commonly used semi-dwarfing MM.106 rootstock. So growers are gen- erally not confident to embrace dwarfing rootstocks for intensive plantings. A good understanding of the interac- tions between rootstocks and varieties, and climate and soil, would help growers select better rootstocks in the future. Other issues In addition to soils and varieties, growers must consider the rootstock's resistance to pests and diseases, such as woolly apple aphid, and crop loads. M.9 is not resistant to woolly apple aphid. Woolly apple aphid is a much more serious pest in the milder climates in Australia than in the northern hemi- sphere. The attack of woolly apple aphid on trees on M.9 is accentuated because the trees are already less vigorous. Damaged root systems of young trees severely decrease the uptake of water and nutrients by the trees. Older and more vig- orous trees are less affected, but contami- nated fruit and unpleasant conditions for pickers and pruners are a problem. With the introduction and use of effec- tive pesticides against woolly apple aphid in the past, fruit growers have been game enough to use nonresistant rootstocks, such as M.9. Withdrawal of, or restric- tions on, recent pesticides may lead this pest to become economically significant once again. With resistance developing to certain chemicals and limited availability of appropriate chemicals, biological control is needed for woolly apple aphid. Another issue to consider: Excessive crop loads readily stall the growth of young trees on M.9. Many growers over- crop their young trees at the expense of growth of trees, because the growers are anxious to get their orchard into produc- tion and have fruit to sell. Generally, fruit on trees on dwarfing rootstocks, such as M.9, tend to ripen fruit earlier than more vigorous rootstocks. Although in some years differences can be great, they cannot be predicted. Crop load has a huge effect on time of maturity and especially the rate that fruit color develops. Early heavy thinning to optimal crop loads will advance maturity of fruit. Young apple orchards on M.9 need good nutrition for strong spring growth, and good bud break, and do not compete well for water and nutrients. With trees on M.9, light or sandy soils need to be mulched. For best results with M.9, trees need deep, fertile and well-drained soils and the best orchard management. Where unfavorable climates and soils prevent tree growth extending further into the season, and to maximize the per- formance of high density apple orchards on M.9, growers may have to: —Ridge the shallow top soil. —Install drip irrigation (preferably subsurface and pulsating). —Fertigate frequently. —Mulch the soil. —Cover the trees with net and/or install overhead cooling. —Plant well-feathered trees closely enough so they can quickly fill their allotted spaces and reach their maximum permissible height. • Bas van den Ende is a consultant in fruit production. Judy Tisdall, Ph.D., is a soil scientist, editor-in-chief of Soil & Tillage Research (Elsevier), and honorary senior lecturer in soil science at La Trobe University, Melbourne, Australia. Excessive crop loads readily stall the growth of young trees on M.9. Many growers overcrop their young trees at the expense of growth of trees, because the growers are anxious to get their orchard into production and have fruit to sell. The essential resource El recurso esencial, en Español More information at goodfruit.com/journalism-fellowship-at-gfg/ We're hiring! Bilingual journalism fellowship Help us create and edit new content for an underserved community in the tree fruit industry during our nine-month paid fellowship. What we're looking for • Expert-level uency in Spanish and English. • Bachelor's degree or higher in journalism, or relevant eld. • Excellent writing and editing skills, in Spanish and English. • Familiarity with integration of content for print and digital. • Proven ability to juggle deadlines and work as part of a team. • Experience communicating to a Spanish-speaking audience.

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