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William C. Olien

Benefits of nimblewill (Ms = Muhlenbergia schreberi), a warm-season, perennial grass, as an orchard ground cover are: 1) it is not competitive with tree growth and 2) it reduces ring nematode (Cx = Criconemella xenoplax) soil population, even in the presence of a tree fruit host. Ms is difficult to establish in orchards in warm fruit-growing regions. In field studies, we found that Ms establishment was decreased by chemical mowing relative to seeding only. Successive years of reseeding at 22 kg seed/ha per year, mechanical mowing, and control of winter annuals gave best establishment of Ms in peach orchards. An orchard microplot study was established to evaluate effects of five Ms densities and two Ms sources on Cx population and on growth of `Redhaven'–Lovell trees (10 replications). Cx numbers were reduced hyperbolically in response to Ms density. Ms cover of 5 g dw/m2 (planted at 9 kg seed/ha) reduced Cx from 200 (control) to the accepted threshold of 50 Cx/100 cc soil. Maximum Cx reduction to 26 Cx/100 cc was obtained at 34 g dw/m2 Ms (planted at 40 kg seed/ha). Cx response to Ms density was not affected by Ms source.

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S.W. Westcott III, E.I. Zehr, W.C. Newall Jr., and D.W. Cain

Prunus accessions were screened in a greenhouse for suitability as hosts for Criconemella xenoplax (Raski) Luc and Raski. All 410 accessions examined were suitable hosts for the nematode. Included in this study were 266 Prunus persica L. Batsch cultivars and cultivars representing 25 other Prunus species: P. americana Marsh., P. andersonii A. Gray, P. angustifolia Marsh., P. argentea (Lam.) Rehd., P. armeniaca L., P. besseyi L. H. Bailey, P. cerasifera Ehrh., P. cistena N.E. Hansen, P. davidiana (Carriere) Franch., P. domestica L., P. dulcis (Mill.) D. Webb, P. emarginata (Dougl. ex Hook.) Walp., P. hortulana L. H. Bailey, P. insititia L., P. kansuensis Rehd., P. maritima Marsh., P. munsoniana W. Wright & Hedr., P. pumila L., P. salicina Lindl., P. simonii Carriere, P. spinosa L., P. tenella Batsch, P. texana D. Dietr., P. tomentosa Thunb., and P. webbii (Spach) Vierh. Also, another 66 interspecific hybrids were tested. Although a few accessions seemed to exhibit an unstable form of resistance, it seems unlikely that Prunus selections that exhibit useful resistance to population increase by C. xenoplax will be found.

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Andrew P. Nyczepir, Alexis K. Nagel, and Guido Schnabel

syringae pv. syringae van Hall), or a combination of both, which results from feeding by the ring nematode, Mesocriconema xenoplax (Raski, 1952) Loof & de Grisse, 1989 [= Criconemoides xenoplax (Raski, 1952) Loof and de Grisse, 1967] ( Brittain and

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Andrew P. Nyczepir and Bruce W. Wood

Hall), cold injury, or a combination of both that is the consequence of root feeding by the ring nematode, Mesocriconema xenoplax ( Raski, 1952 ) Loof and de Grisse, 1989 [= Criconemoides xenoplax ( Raski, 1952 ; Loof and de Grisse, 1967

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Mary Helen Ferguson, Christopher A. Clark, and Barbara J. Smith

and leaf loss in rabbiteye cultivars ( Milholland, 1995 ). Ring nematode ( Mesocriconema ornatum ) has been observed in association with plants symptomatic for blueberry replant disease, although experiments did not reveal significant differences in

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A.P. Nyczepir, W.R. Okie, and T.G. Beckman

Peach tree short life (PTSL) is associated with the presence of ring nematode, Mesocriconema xenoplax, and poor orchard management practices. Finding a noncommercial field site to evaluate rootstocks for PTSL resistance is increasingly difficult. The time needed to create a PTSL test site was investigated. In 1994, a site not planted in peaches for >80 years was identified in Byron, Ga. Analysis of preplant soil samples revealed that there were no M. xenoplax on the site. One-third of the land was planted to peach and infested with 1600 ring nematodes per tree in Spring 1994 (P2) and another one-third in Spring 1995 (P1). The remaining one-third of the land received no trees or ring nematode and served as the control (F2). In Fall 1995, trees were removed from P1 and P2 plots and all treatments were replanted to peach in 1996. In 1997, tree death resulting from PTSL occurred only in P2 (7%). By 2000, PTSL tree death reached 41% in P2, 16% in P1, and 4% in F2 plots. Nematode populations were higher (P < 0.05) in P1 (649 ring nematode/100 cm3 soil) than in F2 (221 ring nematode/100 cm3 soil) plots, whereas populations in P2 (300 ring nematode/100 cm3 soil) plots did not differ from those in P1 or F2 plots. Establishing a PTSL screening site was possible 3 years after M. xenoplax introduction; PTSL development among treatments in the subsequent planting was dependent upon cumulative population exposure of trees to M. xenoplax.

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W.R. Okie and A.P. Nyczepir

Roots of dormant peach trees can grow when soil temperatures are >7 °C, which commonly occurs in the southeastern U.S. during the winter. In our tests, root growth on 1-year-old nursery trees was minimal at 7 °C, and increased with temperature up to at least 16 °C, but rootstocks varied greatly in their regeneration at a given temperature. Trees on seedling rootstocks of `Guardian™', `Halford' and `Lovell' regenerated roots more slowly than those on `Nemaguard' at soil temperatures >7 °C. The regeneration rates mirrored the relative susceptibility of these rootstocks to peach tree short life syndrome in the southeastern U.S., which is associated with parasitism by ring nematode.

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Gregory L. Reighard, Eldon I. Zehr, and Freddi Hammerschlag

Peach tree short life (PTSL) is a serious peach tree disease syndrome on replant orchard sites in the Southeast. Pseudomonas syringae pv. syringae is a bacterial disease often associated with tree injury and death on these PTSL sites. Rootstocks that have better tolerance to ring nematodes such as Lovell have less PTSL death. Tissue-cultured peach embryos and/or explants have shown increased resistance to Pseudomonas syringae and Xanthomonas campestris pv. pruni, another bacterial peach pathogen, in laboratory and greenhouse screenings. Tissue-cultured `Redhaven' (RH), `Redskin' (RS), and `Sunhigh' (SH) peach cultivars on their own roots were planted with SH seedlings and RH and RS budded to Lovell rootstock on a severe PTSL site in South Carolina. Treatments beside cultivar/rootstock combination included preplant fumigation vs. nonfumigation. PTSL appeared in the third year and by year 4 significant tree death occurred. Tissue-cultured RH, RS, and SH trees had 54%, 55%, and 88% PTSL death, respectively, compared to RH (17%) and RS (29%) on Lovell or the SH seedlings (25%). Fumigation significantly decreased PTSL in both RS combinations but not RH. These data suggest that the tolerance of the cultivar root system to PTSL-inducing factors such as ring nematodes was more important in PTSL than scion resistance to bacteria.

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Robert C. Ebel, Bryan Wilkins, David Himelrick, Tom Beckman, Andy Nyczepir, and Jim Pitts

Twelve peach rootstocks including `Lovell', `Nemaguard', `Flordaguard', `14DR51', five `Guardian' (BY520-9) selections, and three BY520-8 selections, were evaluated under field conditions to determine their effect on performance of `Cresthaven' peach. The trees were planted in 1994. Trunk cross-sectional area of BY520-8 selections SL1923 and SL4028 was 28% larger than the rest of the rootstocks, which were similar. There was no crop in 1996 due to late spring frost. Yield in 1997 and 1998 was higher for SL1923 because of higher cropload than the rest of the rootstocks, which were similar. Yield efficiency varied across years and rootstocks. Fruit weight varied among rootstocks but all were commercially acceptable. Harvest date was advanced by two days for some rootstocks compared to Lovell and none were delayed. Percent red blush, soluble solids and firmness varied among rootstocks, but none demonstrated superior quality in all of these parameters as compared to Lovell. Ring nematode population densities were above the threshhold considered to be critical for onset of PTSL for all rootstocks in 1997 and 1998. Tree survival was at or above 86% for all rootstocks and death was not correlated with ring nematode density No trees developed symptoms characteristic of Peach Tree Short Life disease complex. Guardian selections performed adequately compared to the commonly used commercial rootstocks in this study, however, the yield date are from 2 years only.

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Gregory L. Reighard and Eldon I. Zehr

`Redhaven' peach trees were planted on a nonfumigated peach tree short life (PTSL) site in Pontiac, S.C. The experimental design was a split plot with 12 replicates. Preplant subplot treatments were 0, 3, and 6 kg of hydrated lime mixed with 1.9 cubic meters of native soil (Lakeland sand) per planting hole. Main plot treatments consisted of mixing in the planting holes 0 or 5 liters of soil taken from a nearby orchard site that had shown “suppressive” tendencies towards ring nematode reproduction. Hydrated lime treatments increased soil pH by 0.6 to 1.4 units. Boron deficiency occurred in the 6-kg plots. Hydrated lime did not significantly reduce PTSL as 88%, 79%, and 92% of the trees in the 0-, 3-, and 6-kg plots, respectively, died from PTSL by the fifth year. No differences in survival were found between the nonsuppressive and suppressive soil treatments, as both had 86% tree death from PTSL. No trends in ring nematode populations were found among treatments.