One-year-old potted `Mutsu' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on scion invigorating Malling-Merton 111 (MM.111) and scion dwarfing Malling 9 (M.9) rootstocks were grown outdoors in containers under three levels of water availability (irrigated at -20, -80, and -200 kPa) to investigate the effects of soil water availability on combined soil/root (rhizosphere) respiration rates, and developmental morphology of root systems. Rhizosphere respiration was measured with a portable infrared gas analyzer, and root biomass was estimated by electrical capacitance. These nondestructive measurements were compared with final root dry weights of harvested trees, to determine their reliability for estimating relative differences in root biomass. Water stress reduced final biomass similarly for both rootstocks, but the relative reduction in shoot growth was greater for MM.111. Root to shoot ratios were higher and average specific root respiration was lower for M.9 rootstock compared with MM.111. M.9 appeared to be more tolerant of water stress then MM.111, due to reduced canopy transpiration relative to root system mass. Water stress increased root to shoot ratios, specific root length, and the carbohydrate costs of root maintenance as indicated by specific respiration rates. Root dry weight (DW) was better correlated to rhizosphere respiration than to root electric capacitance. The observed r 2 values between root capacitance and root DW were as high as 0.73, but capacitance measurements were also influenced by soil water content and rootstock type. Electrical capacitance estimated total root biomass more accurately for M.9 than for MM.111.
Georgios Psarras and Ian A. Merwin
Rachel Byard and Ian A. Merwin
We planted grafted and seedling chestnuts of six cultivars in Lansing, N.Y., in April 1995 to evaluate performance of the different cultivars in our region and to compare grafted and seedling trees. We used the following cultivars: the Chinese chestnut cultivar Mossbarger (Castanea mollissima) and five interspecific hybrid cultivars [Douglas 1A (C. mollissima × C. dentata), Eaton [C. mollissima × (C. crenata × C. dentata)[, Skioka (C. mollissima × C. sativa), Layeroka (open-pollinated daughter of `Skioka'), and Grimo 142Q (an open pollinated daughter of `Layeroka')]. Growth was not significantly different between cultivars. There were no notable correlations between trunk cross-sectional area at planting and any measurement after the first year. Significant differences between cultivars were found for mortality, yield, and yield efficiency. `Eaton' had the lowest mortality rate (2%) of all cultivars. `Grimo 142Q' and `Layeroka' had the highest dry weight yields and the greatest yield efficiencies, although `Grimo 142Q' had significantly larger nuts than `Layeroka'. In 1998, the largest nuts (5.2 g) were harvested from `Mossbarger' and `Eaton trees'. `Skioka' had the highest mortality (48%), lowest yield, lowest yield efficiency, and smallest nut size. In the first 2 years, most grafted trees showed significantly higher yields and greater yield efficiency than seedling trees. By the third year, differences in yield between grafted and seedling trees were no longer significant for most cultivars. Over the 3 years most grafted trees revealed higher mortality and slower growth than seedlings of the same cultivar. Seedlings did not show more variability in measurements than grafted trees of the same cultivar.
Georgios Psarras and Ian A. Merwin
One-year-old potted `Mutsu' apple (Malus domestica) trees on MM.111 and M.9 rootstocks were grown outdoors from May to Nov. 1997, under three levels of soil-water availability (–20, –80, and –200 kPa), to evaluate the effects of water stress on soil/root respiration and root morphology. At weekly intervals, we measured soil/root respiration using a portable infrared gas analyzer and rootsystem size or functional activity using an electric capacitance meter. These observations were tested as nondestructive methods to estimate relative differences in root size and morphology in situ compared with final dry weight and form of excavated apple rootstocks. Root size-class distributions were estimated by digital imaging and analysis of harvested root systems. Root growth was substantially reduced by water stress; the magnitude of reduction was similar for both rootstocks, but the percentage of shoot growth reduction was higher for MM.111. Root: shoot ratios were higher and average specific respiration rates over the growing season were lower for M.9 root systems. Water stress increased the root: shoot ratio, specific root length, and carbon costs of root maintenance as indicated by specific respiration rates. Soil/root respiration was more closely correlated than root electric capacitance with actual root system size. The observed r 2 values between root capacitance and root dry weight were as high as 0.73, but root capacitance was also confounded by other factors, limiting its usefulness for nondestructive estimation of root size or activity. Rootstock genotype significantly affected root capacitance, which provided better estimates of root dry weight for M.9 than for MM.111.
Ian A Merwin and John A. Ray
Temporal and spatial combinations of tree-row weed suppression treatments were evaluated during 5 years in a New York apple (Malus domestica Borkh. cv. Imperial Gala on Malling 26 rootstocks) orchard planted in Apr. 1991, and provided with trickle irrigation. Twenty-eight factorial treatment combinations [0, 2, 4, and 6 m2 weed-free areas (WFAs); and May, June, July, August, May + June, June + July, May + June + July, and June + July + August weed-free times (WFTs)] were maintained from 1991 to 1995 by postemergence paraquat herbicide applications in tree-row strips. Trunk cross-sectional area (TCA) growth and yield were monitored annually, and few differences were observed as WFA increased from 2 to 4 to 6 m2 per tree. However, WFT substantially influenced TCA, fruit production, and yield efficiency. Early summer WFTs increased TCA during the first two growing seasons, compared with late summer treatments. When trees came into production in 1993-94, yields increased as the duration of WFT increased, but where similar periods of WFT had been established later during the growing season, annual yield, cumulative yield efficiency, and the ratio of crop value to weed-control costs were all reduced. Groundcover species distribution was evaluated each year in September, and graminaceous weeds were more prevalent in the early and midsummer WFTs, while herbaceous broadleaf weeds dominated in the August treatments. A quadratic model regressing cumulative yield efficiency on WFTs grouped into 30-, 60-, and 90-day categories showed that efficiency peaked between 60 and 90 days of WFT. It appeared that timing of weed suppression may be as important as the area of suppression beneath trees in comparable apple orchards, that early summer weed control was especially important for newly planted trees, and that drip irrigation allowed reductions in the area and amount of tree-row herbicide applications, without significant losses in apple tree growth or crop value.
Ian A. Merwin and Warren C. Stiles
This study compared various conventional and alternative orchard groundcover management systems (GMSs)—including a crownvetch “living mulch” (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of postemergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during 6 years in a newly established apple (Malus domestica Borkh.) planting. Trunk cross-sectional area and fruit yield were higher in STMCH, GLY, and NDPQT, intermediate in tilled, and lower in GRSOD, MWSOD, and CNVCH treatments after 5 years. Despite N and K fertilizer applications, extractable soil N and leaf N concentrations were reduced under MWSOD and GRSOD, and soil K, P, and B concentrations were greater under STMCH. Leaf K concentrations were usually highest in STMCH trees, even when heavily cropped; leaf K declined below the sufficiency range in GLY, NDPQT, and tilled trees as they began to bear fruit. Leaf Ca was marginally deficient in all trees and was unaffected by GMS. Foliar Mn, Zn, and B concentrations declined rapidly in all treatments during 2 years without micronutrient fertilizers. Leaf Cu was higher in herbicide and tilled treatments where seasonal soil water content was intermediate (22% to 27%) and lower where soil was very wet or dry for most of the 1988 growing season. Multiple regression analysis indicated that leaf N and B and soil organic matter in 1990, and mean soil water content during the unusually dry Summer 1988, were the best predictors of fruit yield in 1990. Phytophthora root rot and meadow vole depredation were serious problems in STMCH and CNVCH trees. GMSs greatly affected tree establishment, nutrition, and yield; each system involves tradeoffs among important short- and long-term impacts on the orchard agroecosystem.
Michelle M. Leinfelder and Ian A. Merwin
Apple replant disease (ARD) is a common problem typified by stunted growth and reduced yields in successive plantings of apple (Malus ×domestica Borkh.) in old orchard sites. ARD is attributed to biotic and abiotic factors; it is highly variable by sites, making it difficult to diagnose and overcome. In this experiment, we tested several methods of controlling ARD in a site previously planted to apple for >80 years. Our objective was to evaluate practical methods for ARD management. We compared three different experimental factors: four preplant soil treatments (PPSTs) (compost amendments, fumigation with Telone C-17, compost plus fumigation, and untreated soil); two replanting positions (in the old tree rows vs. old grass lanes); and five clonal rootstocks (`M.26', `M.7', `G.16', `CG.6210', and `G.30') during 4 years after replanting. The PPSTs had little effect on tree growth or yields during 4 years. Tree growth was affected by planting position, with trees planted in old grass lanes performing better than those in the old tree rows. Rootstocks were the most important factor in overcoming ARD; trees on `CG.6210' and `CG.30' grew better and yielded more than those on other rootstocks. Rootstock selection and row repositioning were more beneficial than soil fumigation or compost amendments in controlling ARD at this orchard.
Dorcas K. Isutsa and Ian A. Merwin
We tested 40 seedling lots and 17 clonal accessions—representing 941 genotypes and 19 species or interspecific hybrids of Malus—for their resistance or tolerance to apple replant disease (ARD) in a mixture of five New York soils with known replant problems. Total plant biomass, root necrosis, root-infesting fungi, and root-lesion nematode (RLN; Pratylenchus penetrans Cobb) or dagger nematode (DN; Xiphinema americanum Cobb) populations were evaluated in apple seedlings and clones grown for ≈60 days in the composite soil. In addition to phytophagous nematodes, various Pythium, Cylindrocarpon, Fusarium, Rhizoctonia and Phytophthora species were isolated from roots grown in the test soil. Plant growth response was categorized by a relative biomass index (RBI), calculated as total plant dry weight in the pasteurized field soil (PS) minus that in an unpasteurized field soil (FS), divided by PS. Nematode reproduction on each genotype was defined by a relative reproduction index (RRI), calculated as final nematode populations in roots and soil (Pf) minus initial soil populations (Pi), divided by Pi. The RBI, RRI, and other responses of accessions to ARD soil were used to rate their resistance, tolerance, or susceptibility to apple replant disease. None of the accessions was completely resistant to ARD pathogens in our test soil. Seedling accessions of M. sieversii Roem. and M. kirghisorum Ponom. appeared to have some tolerance to ARD, based upon their low RRIs and RBIs. Three clonal rootstock accessions (G.65, CG.6210, and G.30), and four other clones (M. baccata Borkh.—1883.h, M. xanthocarpa Langenf.—Xan, M. spectabilis Borkh.— PI589404, and M. mandshurica Schneid.—364.s) were categorized as tolerant to ARD. The disease response of other accessions was rated as susceptible or too variable to classify. We concluded that sources of genetic tolerance to ARD exist in Malus germplasm collections and could be used in breeding and selecting clonal rootstocks for improved control of orchard replant pathogens.
Ian A. Merwin and Marvin P. Pritts
Ian Merwin, Michael Biltonen, and John A. Ray
Three orchard groundcover management systems (GMSs) were established in a newly planted apple (Malus domestica cvs. Liberty, Nova Easygro, and NY84828-12 on Malling 9 rootstock) orchard on a silty-clay loam soil (Aeric Ochraqualf). The GMSs were applied in 2-m-wide strips within tree rows as follows: 1) a 6-cm-thick mulch layer of composed manure, straw, sawdust, and vegetable plant wastes applied in May 1992 and 1994; 2) a “green manure” cover crop of canola (Brassica campestris cv. Humus) seeded in mid-August each year and tilled under the following May; and 3) Post-emergence applications of N-(phosphonomethyl) glycine (glyphosate) herbicide (2.0 kg a.i./ha) in mid-May and July each year. After 3 years of GMS treatments, apple tree growth and trunk cross-sectional area were similar in all three systems. Fruit yield and yield efficiency were greater in glyphosate and compost than in canola GMSs, and `Liberty' was the most productive cultivar. Topsoil N, P, K, Ca, Mg, Zn, and organic matter content were all substantially greater in the compost GMS. Leaf N, K, and P concentrations were consistently greater in trees in compost plots; leaf Ca, Mg, Cu, and Zn concentrations were lower in compost GMS. Weed growth was rank and difficult to control in the compost mulch, but this GMS substantially enhanced orchard soil fertility.
Ian A. Merwin, John A. Ray, and Paul D. Curtis
Meadow vole (Microtus pennsylvanicus Ord) populations, feeding activity and damage to young apple (Malus ×domestica Borkh.) trees were monitored for several years in a New York orchard by direct observation, trap counts, and a feeding activity index in various groundcover management systems (GMSs). Meadow vole population density differed among GMSs, with consistently higher densities and more trees damaged in crown vetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.) turfgrass tree-row strips. Vole densities were high in autumn and low in spring each year. Anticoagulant rodenticides and natural predation did not adequately control voles in GMSs providing favorable habitat. Groundcover biomass per m2 was weakly correlated with vole densities in 2 of 3 years, while the percentage of soil surface covered by vegetation was not significantly correlated with vole populations. Applications of thiram fungicide in white latex paint were better than no protection, but less effective than 40-cm-high plastic-mesh guards for preventing vole damage to tree trunks. A combination of late-autumn trapping, close and consistent mowing of the orchard floor, trunk protection with mesh guards, contiguous habitat for vole predators, and herbicide applications within the tree rows provided effective control of meadow-vole damage to trees at this orchard during 3 years without applications of rodenticide baits. Chemical names used: Tetramethylthiuram disulfide (thiram)