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Carl H. Shanks Jr. and Jimmie D. Chamberlain

`Totem' strawberries (Fragaria ×ananassa Duch.) were planted with clean-cultivated inter-rows or inter-rows planted with permanent cover crops of white clover (Trifolium repens L.) or `Manhattan' perennial ryegrass (Lolium perenne L.). There were no significant differences between treatments in the number of twospotted spider mites (Tetranychus urticae Koch), strawberry aphids [Chaetosiphon fragaefolii (Cockerell)], or Pratylenchus sp. or Xiphinema sp. nematodes on strawberry plants. The cover crops reduced strawberry yields relative to cultivation, although fruit size was significantly larger the second year. Root weight did not differ significantly in either year. Weight of above-ground vegetation was significantly higher in cultivated plots the first year, but not the second year.

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Carl H. Shanks Jr. and Patrick P. Moore

More than 170 clones of Fragari ×ananassa Duch., F. chiloensis (L.) Duch., and F. virginiana Duch. were tested for resistance to the twospotted spider mite (Tetranychus urticae Koch). Twenty-seven clones had >75% fewer mites than did F. ×ananassa `Totem', a susceptible clone. About two-thirds of the clones also were tested for resistance to the strawberry aphid [Chaetosiphon fragaefolii (Cockerell)]. Survival and reproduction was significantly lower on two clones each of F. ×ananassa and F. virginiana than on `Totem'.

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Patrick P. Moore, Thomas M. Sjulin and Carl H. Shanks Jr

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Thomas M. Sjulin, J. Scott Cameron, Carl H. Shanks Jr. and Carlos E. Munoz

In January, 1990, a team of U.S. and Chilean scientists collected native and cultivated Fragaria from central and southern Chile. During the course of this expedition, 363 new accessions of Fragaria were collected. Approximately 2,500 plants of 250 clones were collected from 66 sites in 19 different areas, and 113 seedlots (estimated at over 100,000 seeds) were obtained.

Plants were collected from a wide range of habitats, and considerable variability was observed in vegetative and reproductive characteristics. Fruit were round to conical in shape, deep red to white in color, soft to moderately firm, with soluble solids ranging from 5-18%, dull to glossy skin, bland to strong flavor, low to very high aromatics, and difficult to moderately easy capping. Fruit size in situ approached 4 g, while fruit larger than 12 g were found under cultivated conditions. Strawberry aphids (Chaetosiphon fragaefolii) were found on plants in situ and under cultivation. Little or no evidence of other pests were observed on clones collected in situ.

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J. Scott Cameron, Carol A. Hartley, Carl H. Shanks Jr. and Jeannie K. L. Garth

At two-week intervals from 17 June to 15 July, three groups of `Meeker' red raspberry plants were infested with two-spotted spider mites (Tetranychus urticae) in a greenhouse. While populations on individual plants were allowed to develop freely, control plants were kept free of mites with a chemical miticide. Gas exchange measurements were made on 27 July prior to visible mite damage, and on 7 October after injury was apparent. The relationships between mite populations and leaf gas exchange and chlorophyll characteristics were described using a logarithmic function.

Physiological responses to mite feeding were observed prior to visible leaf injury. On both dates, CO2 assimilation rates decreased (p ≤ 0.001) with increasing mite numbers per leaflet. On 27 June, a significant relationship (R2 = 0.61***) was found between mite number and mesophyll conductance (gm). On 7 October, significant relationships (p ≤ 0.001) were also observed with gm, stomatal conductance (gs), and transpiration (E). Total chlorophyll content of leaves decreased with increasing mite populations, but chlorophyll a/b ratio and dry weight per leaf unit area were unchanged.

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José López Medina, Patrick P. Moore, Carl H. Shanks Jr., Fernando Flores Gil and Craig K. Chandler

Genotype × environment interaction for resistance to the twospotted spider mite (Tetranychus urticae Koch) of eleven clones of Fragaria L. sp. (strawberries) grown in six environments throughout the United States was examined using two multivariate analysis techniques, principal coordinate analysis (PCA) and additive main effect and multiplicative interaction (AMMI). Both techniques provided useful and interesting ways of investigating genotype × environment interaction. PCA analysis indicated that clones X-11 and E-15 were stable across both low and high environments for the number of spider mites per leaflet. The initial AMMI analysis showed that the main effects of genotype, environment, and their first-order interaction were highly significant, with genotype × environment interaction due mainly to cultivar `Totem' and environment FL94. A second AMMI analysis, which excluded `Totem' and FL94, showed that the main effects of the remaining genotypes, environments, and genotype × environment interaction were also highly significant. AMMI biplot analysis revealed that FL93 and GH93 were unstable environments, but with opposite interaction patterns; and GCL-8 and WSU2198 were unstable genotypes with similar interactions that were opposite those of WSU 2202.

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Carl H. Shanks Jr., Craig K. Chandler, Edgar D. Show and Patrick P. Moore

Eleven clones of Fragaria spp. were tested for resistance to the twospotted spider mite, Tetranychus urticae Koch, at Dover, Fla.; Watsonville, Calif.; and Vancouver, Wash. Ten clones, which had been selected previously as being mite-resistant, had generally the same relative resistance when compared to susceptible `Totem' at all three of the widely separated locations. It appears that Fragaria clones selected for resistance to spider mites at one location likely will be resistant elsewhere, in spite of environmental differences.