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Marvin Pritts

Primocane-fruiting raspberries (Rubus idaeus L.) have the capacity to fruit in the fall and again the next summer. Because of their low chilling requirement, this type is used to produce a double crop in warmer regions of the world. However, many growers prune canes to the ground after the fall crop, sacrificing the summer crop for a single, large fall crop. This practice is less labor-intensive than the selective cane removal required for double-cropping and crop quality is often higher. Primocane-fruiting raspberries also are easily manipulated to extend the season. Early- and late-fruiting cultivars, cultural manipulations, rowcovers, high tunnels, and greenhouses are all used commercially to extend the season of primocane raspberries year-round. This is beneficial for consumers because high-quality fruit is now available for a much longer period than was possible in the past.

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Marvin Pritts

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Katherine Wine and Marvin Pritts

Black root rot is a devastating, poorly understood disease complex affecting strawberries throughout the world, especially in perennial plantings. Field measurements at 54 sites in New York were made for 113 cultural and environmental variables, and root health was quantified. Root health was negatively associated with wet, compacted soils where plants were grown for several years on flat beds with terbacil herbicide. Pratylenchus penetrans numbers were associated with rotting rots, but not in all sites. Rhizoctonia fragariae and Pythium spp. were usually isolated where black root rot was present, but not always. When strawberry plants were grown in infested soil at warm temperatures (23C), R. fragariae was most commonly isolated, and when grown in the same soil at cool temperatures (5C), Pythium was found. Inoculation of sterile soil with Pythium and/or Rhizoctonia reduced root dry weights, but symptoms were not identical to those observed in the field. Various combinations of pathogenic fungi, nematodes, soil compaction, flooding, low light and terbacil failed to recreate field symptoms in the laboratory. Tolerance rankings of 20 cultivars were different at four field sites. These observations suggest that black root rot can have many causes, and that susceptibility may be stress induced under field conditions.

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Marvin P. Pritts

Strawberry (Fragaria ×ananassa) is a perennial plant with a compressed woody crown that responds to the environment in a similar way as other temperate fruit crops. Nutrient management practices are also similar, with a few exceptions. Levels of preplant amendments are determined based on soil test results, and are used to increase nutrient availability and modify pH as needed. Once plants are established, soil tests, coupled with foliar tissue analysis and observations of plant growth, are the best indicators of plant nutrient status and limitations. Drip irrigation is more efficient than granular applications for supplying soluble nutrients such as nitrogen (N). While most temperate fruit crops respond well to N in spring when growth resumes after winter, applications of spring N in strawberry can cause excessive vegetative growth, reduce fruit quality, and have only a marginal impact on yield. N is most efficiently taken up by plants when conditions favor root growth, and N applied in summer or fall is more effective at increasing yield the following spring, assuming that the carbohydrate status of the plant is good. However, if carbohydrate status is poor, supplemental N late in the season can reduce yield by requiring additional carbon (C) for N uptake. Many questions remain to better understand how to manage nutrients optimally in perennial strawberry.

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Marvin P. Pritts

Non-chemical methods for weed management are becoming important as fewer herbicides are labelled for use and as the market demands pesticide-free produce. We have studied the use of interplanted cover crops in strawberry plantings as an alternative/supplement to chemical weed management. Several different cover crops (tall fescue, marigold and sudangrass) were seeded between rows of newly planted strawberries in late June as runnering was commencing. An additional seeding of sudangrass was made in late July. For comparison, untreated plots and diphenamid treated plots were included in the experimental design. Measurements were taken throughout the season of soil moisture, light levels, crop nutrient concentrations, nematode numbers in soil and crop roots, runner biomass, and weed composition and biomass. Cover crops were incorporated in late fall and the planting was mulched. The following spring, crop nutrient concentrations, nematode numbers in soil and crop roots, weed composition and biomass, yield, individual fruit size, and aboveground strawberry biomass was assessed. The marigolds were too competitive for moisture to be an effective companion cover crop. The early planting of sudangrass was too tall, and fescue was too competitive for nutrients. The untreated plots contained many more weeds than other treatments, nematode levels were higher in the strawberry roots in these plots, and harvesting fruit was very difficult. The late seeding of sudangrass, however, provided significant weed control while not reducing yield relative to herbicide-treated plots.

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Marvin Pritts and James Luby

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Marvin P. Pritts

Manipulating light, temperature, moisture, and nutrients to favor plant growth and productivity is an important component of horticulture. The technology required to achieve such manipulation ranges from inexpensive, basic practices to elaborate, costly approaches involving the latest engineering advances. For example, pruning and mulching are relatively low-tech methods for improving light interception and soil moisture status in small fruit plantings. At the opposite extreme are glass houses with supplemental lighting, CO2 enrichment, and nutrient film hydroponic systems Of greatest value to small fruit growers, however, is technology that ran be applied in field situations, such as the use of overhead irrigation for maintaining soil moisture status, frost protection, and evaporative cooling. One of the greatest challenges to small fruit growers and rcsearchers is integrating new technology into production systems. The introduction of a new technique for environmental modification usually has indirect effects on other aspects of management, which may require additional technology to compensate for adverse changes while maintaining the favorable change. In addition, unique macro- and microclimates demand and market opportunities, specific solutions, and the result is a dynamic, diverse collage of production systems used by growers throughout the world.

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Marvin Pritts and Dorcas Isuta

Previous findings reveal that rooting and acclimatization of apple and blueberry plants is often difficult, inconsistent and inefficient. This experiment was set up in a fog chamber lo investigate the effects of CO2 enrichment (CDE) and irradiance on unrooted stage II microshoots. Two CO2 and 3 light levels tested were: 1350 +/- 150 (+ CDE), and 450 +/- 50 (- CDE) ppm; 30 +/- 5 (low), 55 + 10 (medium), and 100 + 20 (high) umolm-2s-1 respectively. Cultivars assessed were Berkeley and Northsky for blueberry. G65 and NY30 for apple. Blueberry microshoots acclimatized successfully and gave between 90 to 100% rooting and survival rate. Apple microshoots acclimatized and rooted slowly, exhibited great sensitivity to in vivo conditions and gave between 40 to 100% rooting and survival rate. High light induced photo-inhibition which disappeared after complete acclimatization. There was a significant difference between low light and the other two light levels. The effect of CDE was dependent on cultivar. In most cases, high light (-) CDE gave the most vigorous growth (highest plant dry weight and leaf area). There was a significant difference between (+) CDE and (-) CDE at low and medium light, but none at high light. Low light (-) CDE and medium light (+) CDE were superior over low light (+) CDE and medium light (-) CDE. respectively. Stalling out in apple microshoots was corrected by GA sprays.

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Marvin P. Pritts

This LISA project involves four state universities and the USDA, and has the objective of developing and evaluating non-conventional production and pest management strategies for raspberries and strawberries. Production goals are divided between cropping systems and pest management. The evaluation of trellising systems for cropping efficiency, ease of harvest, and spray distribution is an example of a production related objective. Groundcover management systems for strawberries are being evaluated for their effects on both the pest complex and production system. Biological control strategies for root diseases are also being studied. Evaluations involve field performance, economics, and impacts on pesticide use. In addition, grower attitudes towards adoption of non-traditional production practices have been assessed. The project supports the publication of a newsletter that is distributed to 450 growers. The major goal of our work has been to improve production efficiency and provide growers with economical, dependable tools that can be used to prevent pest problems before chemical intervention is required.

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David Trinka and Marvin Pritts

Tissue-cultured (TC) plantlets are becoming the preferred planting stock for raspberry growers because of their uniformity, ease of handling, general vigor and disease status. However, previous studies have shown that TC plants are sensitive to many preemergent herbicides and to cultivation within several weeks after planting. ln addition, little is unknown about handling practices for TC plants relative to conventionally propagated plants during the establishment year. We subjected TC raspberries cv. Heritage to different management practices during the establishment year and monitored plant performance over two years to determine if better recommendations could be made for TC plantlets. One set of management practices examined weed control, and treatments included straw mulch, black polyethylene mulch, white on black polyethylene match, napropamide herbicide, simazine herbicide, hand weeding, and an untreated control. A second factor was fertilizer placement, with calcium nitrate applied on the soil surface around the plant or placed in the planting hole. A third factor was row cover application during the first six weeks of growth. Significant differences in soil moisture, soil temperature, plant growth, and yield occurred among the 22 treatments, and results suggested that TC plants require a different set of management practices than conventional propagules.