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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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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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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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James P. Gilreath, Bielinski M. Santos, Joseph W. Noling, Salvadore J. Locascio, Donald W. Dickson, Erin N. Rosskopf, and Steven M. Olson

Field studies were conducted in three Florida locations (Bradenton, Gainesville, and Quincy) during 1998-99 and 1999-2000 to: 1) compare the performance of two transplant systems under diverse MBr alternative programs in `Chandler' strawberry (Fragaria ×ananassa), and 2) determine the efficacy of these treatments on soilborne pest control in strawberry. Fumigant treatments were: 1) nonfumigated control, 2) methyl bromide plus chloropicrin (MBr + Pic) at a rate of 350 lb/acre, 3) Pic at 300 lb/acre and napropamide at 4 lb/acre, 4) 1,3-dichloropropene (1,3-D) plus Pic at 35 gal/acre and napropamide at 4 lb/acre, 5) metam sodium (MNa) at 60 gal/acre and napropamide at 4 lb/acre, and 6) MNa followed by 1,3-D at 60 and 12 gal/acre and napropamide at 4 lb/acre, respectively. Strawberry transplants were either bare-root or containerized plugs. There were no significant fumigant by transplant type interactions for strawberry plant vigor and root weight per plant, whereas ring nematode (Criconema spp.) and nutsedge (Cyperus rotundus and C. esculentus) populations, and total marketable fruit weight were only infl uenced by fumigant application. The nonfumigated plots had the lowest strawberry plant vigor and root weight per plant in all three locations. In most cases, plant vigor and root biomass per plant increased as a response to any fumigant application. With regard to the transplant type, bare-root transplants had similar plant vigor as plugs in two of the three locations. Fumigation improved nutsedge and ring nematode control. All fumigants had higher early and total marketable yield than the nonfumigated control, whereas transplant type had no effect on total fruit weight.

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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, B.W. Wood, and C.C. Reilly

Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees exhibit nickel (Ni) deficiency in certain orchard situations. The symptoms are manifest as either mouse-ear or replant disorder and in certain situations are associated with nematode parasitism. A field microplot study of pecan seedlings treated with either Meloidogyne partityla or Criconemoides xenoplax or both found that parasitism by M. partityla can result in enhancement in the severity of mouse-ear symptoms and a reduction in foliar Ni concentration. The Ni threshold for triggering morphological symptoms in young developing foliage was between 0.265 and 0.862 μg·g–1 dry weight, while the threshold for rosetting was between 0.007 and 0.064 μg·g–1 dw. Results indicate that parasitism by M. partityla is a contributing factor to the induction of Ni deficiency in pecan and raises the possibility that nematode parasitism and Ni nutrition can be contributing factors to many plant maladies.

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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.