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Rhoda L. Burrows

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Rhoda L. Burrows* and Ismail Ahmed

Fungicides applied as soil drenches affect arbuscular-mycorrhizal (AM) fungal colonization of plant roots to different degrees, depending on the chemical used. However, the effect of fungicides applied as seed treatments has been less studied, and is of particular interest to growers who want to encourage beneficial mutualisms while protecting seedlings against pathogens. We tested the effects of four common seed treatments, Apron (mefenoxam), Thiram, Raxil (tebuconzaole), and Captan on colonization of `Superstar' muskmelon roots by the AM fungus Glomus intraradices in the greenhouse. By 30 days after planting, colonization was very high (>90% root length) for all treatments, with relatively minor (<10%) differences in percent length root with AM hyphae. The Apron seed treatment had the highest percent root length with hyphae, but the lowest amount of vesicles, while roots from Raxil and Captan-treated seeds had the lowest hyphal colonization and highest vesicle formation. Myconate ®, a commercial formulation of formononetin, an isoflavone previously shown to increase AM colonization, significantly increased the percent colonization of roots from the Raxil treatment, but not other treatments. Myconate also increased vesicle numbers in all but the Captan treatments, but not significantly.

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Rhoda L. Burrows and Frank J. Peryea

Nitrification-induced subsoil acidification is a major problem encountered with the use of ammonium- or urea-containing fertilizer solutions for drip fertigation of tree fruit crops. We conducted a laboratory experiment to evaluate the soil acidification potential of the four fertilizer N solutions most frequently used for fertigation within the Washington tree fruit industry. Treatments were five orchard soils x four commercial N solutions (calcium nitrate, calcium-ammonium nitrate, ammonium nitrate, urea-ammoniun nitrate) x four N rates (0, 100, 200, 500 mg N/kg). Air-dry subsamples of each soil were inoculated with fresh soil known to exhibit nitrifying behavior amended with treatment solutions. Subsamples were maintained at simulated field capacity of –15 kPa. Soil pH was measured after 5 weeks incubation. The treatment solutions were reapplied and pH measured after another 5 weeks. The soil were then leached with distilled water and further incubated to determine if pH would increase as has been observed in the field. The fertilizer solutions acidified the soils in direct relation to their ammonium plus urea content. The calcium nitrate solution was acidifying because it contains ammonium nitrate as an impurity. We will present the pH “rebound” data.

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Frank J. Peryea and Rhoda L. Burrows

Late dormant copper (Cu) sprays and mid-summer foliar Cu sprays are being promoted within the Washington apple industry as a means to enhance fruit typiness and red skin color, respectively. While there appears to be theoretical bases for these practices, they have not been tested for horticultural significance. Differential late dormant spray treatments of Cu hydroxide (the Cu source most commonly recommended by agricultural consultants) were imposed in two `Delicious' orchards. Flower cluster Cu was positively related to Cu rate, but the sprays had no effect on leaf Cu or on six fruit typiness variables. Differential mid-summer spray treatments of water, Cu sulfate, and Cu oxysulfate solutions were imposed in three `Delicious' orchards and one `Fuji' orchard. The Cu sprays increased leaf Cu, but had no effect on market color grade measured using a commercial color sorter. The results appear to reflect Cu physicochemistry and timing of application. These preliminary results call into question the utility of the Cu sprays for improving apple fruit quality characteristics when trees show no visual signs of Cu deficiency. They do suggest some alternative ways to manage Cu nutrition in deciduous tree fruit orchards.

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Rhoda Burrows, F.L. Pfleger, and Luther Waters Jr.

Asparagus offcinalis L. `Mary Washington' seedlings inoculated with Glomus fasciculatum (Thaxter) Gerd. and Trappe emend. Walker and Koske showed increased growth after 9 weeks, compared with noninoculated plants. Phosphorus supplementation (25 g·m-3) increased seedling growth of inoculated and noninoculated plants throughout the 26 weeks of the experiment. However, after 9 weeks, there were no differences in growth of inoculated, non-P-supplemented plants and noninoculated, P-supplemented plants. Fern height, fern and crown weight, and bud numbers correlated positively to the percentage of G. fasciculatum root infection.

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Sabrina L. Shaw, Rhoda Burrows, and William F. Hayslett

Two year old sugar maples grown in 25 gallon containers were subjected to different levels of stress by withholding water. Drought levels were measured using irrometers. Irrometer readings of 40, 60, and 80 centibars were used to determine when to add water. The media used were a primary nursery mix of 50:50 sand and pine bark by volume. The maples were evaluated for differences in stomatal responsiveness with the porometer and growth parameters of number of nodes, internode length, and leaf number were taken. Some of the trees were treated with ROOTS as a drench to determine if it would enhance resistance to water stress of containerized nursery plants. Despite the use of ROOTS there was no significant difference between the stressed and the non-stressed plants of stomatal responsiveness or the growth parameters.

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Luther Waters Jr., Bonnie L. Blanchette, Rhoda L. Burrows, and David Bedford

High levels of sphagnum peat in the growing medium promoted growth of asparagus (Asparagus officinalis L. cv. Viking 2K) in a greenhouse study. Application of NH4NO3 > 1 g/pot (84 kg·ha-1 equivalent) was detrimental to root growth. High N rates and high organic matter levels decreased fibrous root development. Shoot dry weight was highly correlated with fleshy root number, root dry weight, and shoot vigor.

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Luther Waters Jr., Rhoda L. Burrows, Mark A. Bennett, and John Schoenecker

A series of experiments exploring the effect of seed moisture and transplant management techniques was conducted with sh2 and su sweet corn (Zea mays L.). The use of seed and transplants in a progression of developmental stages from dry seed to moistened seed to 14-day-old transplants showed that moistened seed had no impact on plant `growth and development. Use of transplants generally had little impact beyond decreasing percent survival and plant height. Increasing the age of transplants reduced the time to maturity and harvest. Increasing the size of the transplant container (paper pot) decreased the time to harvest for younger seedings, but had no other effects. Premoistened seed were successfully held at 10C for up to 72 hours without damage following moisturization. Delays in irrigation of up to 2 days after planting moistened seed had no detrimental effects on sweet corn emergence and growth.