Scientific Research Journal Update

By: Susan Switras and Jeff Gillman

Each month research findings relevant to the field of horticulture are published in academic journals. Much of this work has a direct impact on our industry, but is spread among several journals and combined with research that is not directly applicable to the needs of the landscape and nursery industries. Under the time constraints of the typical landscape and nursery professional it is difficult to find the time to sort through it all to locate meaningful material. We at the TRE nursery on the University of Minnesota's St. Paul campus have undertaken the task of going through the literature and reporting on work published in areas of interest to those in the landscape and nursery industries. We are reporting the results of other peoples’ research and neither endorse nor refute the methods which they use or the results which they report. It should be remembered that frequently this research is conducted elsewhere and that often conditions in Minnesota are very different from conditions in other parts of the US. As we write these reports we try to do so as accurately as possible, however, we recommend looking up these articles for yourself if you have any questions regarding the research. A full citation of each article is included. We will publish every two months. Due to the frequency of publication of some of the journals surveyed, reviews from the most recent issues may appear in the next installment of this column instead of the current one. In many of these articles information regarding a particular compound or pesticide is given which does not necessarily follow label recommendations. We strongly discourage the use of these compounds and pesticides in a way that is inconsistent with the label.

• A study done by J. Roger Harris and Jody Fanelli at Virginia Polytechnic Institute and State University reported that red maple (Acer rubrum L.) and Washington hawthorn [Crataegus phaenopyrum (L. f.) Medik.] stock which was stored as bare root, then root pruned and planted in field rows did not have a significantly greater caliper or root length after two years than non-root pruned stock. i
• Another root pruning study was done at Oklahoma State University using pecan tree seedlings (Carya illinoensis Wang 'Apache'). B. D. McCraw and M. W. Smith looked at both wounding and pruning of seedling taproots to one, two or three feet in length. In addition, the seedlings’ responses to treatments were observed in silt loam and sandy loam soils. Root wounding showed no benefits, but pruning stimulated shoot growth and lateral root growth. In heavy soils, pruning the taproot back to one foot was most beneficial for growth. Longer taproots were best for plants living in sandy soils, which are more subject to drought. The pecan tree is not hardy in our area, but other tap-rooted plants may behave similarly. ii
• The importance of timing in herbicide application was demonstrated in a study done at The Virginia Polytechnic Institute and State University. Applying Gallery (a selective preemergence herbicide) to dwarf burning bush [Euonymus alatus (Thunb.) Sieb.‘Compacta’] one month after bud break caused decreased leaf size and increased leaf distortions. Plants treated one month after bud break also exhibited shoot dieback and premature defoliation at the end of the growing season. A similar application of Gallery in March, when burning bush is dormant (In Virginia), or at two months after bud break, caused no injury to the plant. Gallery is usually considered to be safe for most nursery species, but there are a few which are susceptible to injury. Read the label before attempting to use this compound. iii
• Lateral shoots, especially below the bud union, on the lower trunk of the Bradford pear tree (Pyrus calleryana Decne. ‘Bradford’), are unwanted and typically need to be repeatedly removed by hand. Control of basal sprouts with NAA (TreHold RTU) was achieved in a study at Auburn University by G. J. Keever, J. C. Stephenson Jr. and D.C. Fare. Sprays ranging from 2875 to 11500 ppm NAA were applied to the lower 75 cm of young 1.5 to 1.7 m trees. These sprays provided near complete control of sprouts, and a 5750-ppm application also provided an increase in tree height and caliper as compared to control trees. TreHold is not currently labeled for use on Bradford Pear or on many other ornamental species. Read the label before attempting to use this compound. iv
• John Ruter at the University of Georgia compared pot-in-pot and conventional above-ground production systems with three fertilizer rates and their effects on Heritage river birch (Betula nigra L. ‘Cully’ Heritage) growth. The study utilized controlled release fertilizer at rates of 1.3, 1.7, and 2.0 kg Nitrogen/m³. When comparing the two production systems, the pot-in-pot method had greater shoot and root dry weights and higher root:shoot weight ratios. As the fertilizer rates increased, shoot dry weights increased but root:shoot ratios decreased. v
• A study by Helen Tyler Krause from Texas Tech University assessed the effects of gravel, wood chip and tire mulches, and turf on the soil moisture and root and shoot growth of desert willow [Chiliopsis linearis (Cav.) ‘Burgundy’]. While no such study had been done on desert willow before, similar studies have been done on other nursery species. Mulches retained soil moisture better than bare earth, as did turf, but turf competed with the tree for water and nutrients. As a result, mulched trees and the bare earth controls had greater shoot and root dry weight than trees grown in turf. Woody plant species may behave differently when different mulches are used, but the results above should apply to most species. vi
• A study by Million, Barrett, Nell and Clark at the University of Florida indicated that the effects of each of a number of growth inhibitors (ancymidol, paclobutrazol, and uniconazole) applied as a drench to a pine bark-based medium will have less potency than the same amount of compound added to a peat-based medium. The exception in this study was chlormequat, which reduced stem elongation slightly more in the pine bark medium. This study was done on potted ‘Nob Hill’ chrysanthemums [Dendranthema x grandiflorum (Ramat.)]. vii
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• i Harris, J. R. and J. Fanelli. 1998. Root Pruning Red Maple and Washington Hawthorn Liners Does Not Affect Harvested Root Length After Two Years of Field Production. Journal of Environmental Horticulture. 16(3): 127-129.
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  ii McCraw, B. D. and M. W. Smith. 1998. Root Pruning and Soil Type Affect Pecan Root Regeneration. HortTechnology. 8(4): 573-575.
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  iii Salihu, S., J.F. Derr, and K.K. Hatzios. 1998. Effects of Gallery Applied at Different Growth Stages to Dwarf Burning Bush (Euonymus alatus 'Compacta'). Journal of Environmental Horticulture. 16(3): 155-158.
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  iv Keever, G. J., J. C. Stephenson Jr. and D.C. Fare. 1998. Control of Basal Sprout Regrowth in 'Bradford' Pear with NAA. Journal of Environmental Horticulture. 16(3): 152-154.
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  v Ruter, J.M. 1998. Fertilizer Rate and Pot-In-Pot Production Increase Growth of Heritage River Birch. Journal of Environmental Horticulture. 16(3): 135-138.
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  vi Kraus, H.T. 1998. Effects of Mulch on Soil Moisture and Growth of Desert Willow. HortTechnology. 8(4): 588-589.
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  vii Million, J.B., J. E. Barrett, T. A. Nell and D. G. Clark. 1998. Influence of Pine Bark on the Efficacy of Different Growth Retardants Applied as a Drench. HortScience. 33(6): 1030-1031.