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Josiah W. Worthington, James L. Lasswell, and M.J. McFarland

A computer model was used to predict irrigation rates and numbers of emitters or microsprayers required to trickle irrigate Redskin/Nemaguard peach trees. Irrigation rates were 0, 50%, and 100% of the predicted requirement based on a crop coefficient of 50, 80, 100, 80, and 50 percent of pan evaporation for the tree's canopy area for May, June, July, August and Sept. respectively. Full irrigation (100% of predicted) was applied through 6, 8L/hr emitters or one 48L/hr microsprayer. Half the predicted rate was applied through 6, 4L/hr emitters or 1 24L/hr microsprayer. Control trees received no supplemental irrigation. Microsprayers height was adjusted to wet a surface area comparable to the 6 emitters. There was no significant difference in fruit size or yield based on emitter vs microsprayers, but fruit size and total yield was increased in direct proportion to irrigation rate. There was no treatment effect on tree pruning weights. Moisture measurements indicated that trees de-watered the soil efficiently enough that water never moved below the 30 cm level in spite of the fact that up to 260 liters per tree per day were applied in mid-summer.

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Timothy L. Grey, David C. Bridges, and D. Scott NeSmith

Field studies were conducted to evaluate the tolerance of several pepper (Capsicum annuum L.) cultivars to the herbicide clomazone. Peppers tested included the bell cultivars Yolo Wonder and Jupiter; the banana cultivar Sweet Banana; and the pungent cultivars Jalapeno and Red Chili. Treatments were clomazone at 0.56 or 1.12 kg·ha-1 a.i. applied either preplant incorporated (PPI), pretransplant (PRE-T), or posttransplant (POS-T) on the day of transplanting, plus a nontreated control. Clomazone at 1.12 kg·ha-1 a.i. PPI and PRE-T significantly injured (bleaching or chlorosis of foliage) `Sweet Banana' (40% and 20%, respectively) and `Red Chili' (30% and 18%, respectively) in 1993 in early-season evaluations, but this injury was transient and did not significantly affect total fruit number or yield. Injury to any cultivar from POS-T clomazone at 0.56 and 1.12 kg·ha-1 a.i. was nonsignificant. Overall, tolerance to clomazone was excellent for all treatments and across all cultivars. Yield was not reduced significantly by any treatment. Chemical names used: 2-[(2-chlorophenyl) methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone).

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Mary Ann Rose and John W. White

`Celebrate 2' Poinsettias were grown for 8 weeks in a controlled-environment growth room until first signs of bract coloration. In growth stage I (GSI; weeks 1 through 4) low, medium, and high N rates (25, 75, and 125 mg N/liter, respectively) were applied by subirrigation (no leaching). Following floral induction [growth stage II (GSII), weeks 5 to 8], there were nine treatments: all possible combinations of the three N rates in GSI plus three rates (75, 125, and 175 mg N/liter) in GSII. Although >80% of shoot dry weight and >90% of total leaf area developed during growth GSII, reaching an acceptable plant size by week 8 depended on receiving adequate fertilization in growth GSI. In contrast, leaf chlorosis, noted in plants receiving the lowest rate in GSI, was rapidly reversed by increasing the N rate in GSII. Quadratic regression equations fitted to shoot dry weight and leaf area data predicted that using 125 mg N/liter in both growth stages gave maximum responses at week 8. However, using 75 mg N/liter in GSI and 125 mg N/liter in GSII also produced acceptable growth in poinsettias. Our results suggest that some growth restriction imposed by N availability during the first 4 weeks of growth may be acceptable and perhaps desirable to reduce growth regulator use and the environmental impact of overfertilization.

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Steven B. Polter, Douglas Doohan, and Joseph C. Scheerens

staff of the Laboratory for Pest Control Application Technology.

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A. M. Borowski, R. D. Morse, and M. M. Alley

A Preliminary study conducted in 1985 indicated no significant yield response to 8 treatments ranging in amount of total N applied from 56 to 290 kg N/ha. Treatments in 1986 were as follows: base rate N at 0, 56, 112, and 168 kg N/ha with 0, 1, or 2 sidedressings at 56 kg N/ha each applied at 3 and 6 wks after seeding. Yield differences for base rate n were significant at the first harvest only, while sidedressing effects on yield were significantly different for 3 of the 4 harvests and total yield. Nitrogen uptake during the first 32 days after seeding (DAS) was minimal, 0.17 kg N/ha/day, but increased to 8.05 kg N/ha/day during head formation (55 to 77 DAS). Initial soil nitrate status was high in the top 25 cm (52 kg N3O /ha) but decreased to 10.6 kg NO3/ha in the control plot by the end of the season. Sidedressings, prior to and during head formation, are recommended to maintain an adequate available N supply throughout the growing season.

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B. Marangoni, D. Scudellari, and M. Toselli

Mature trees of Stark Redgold nectarines grown in silt loam soil in the Po Valley were tested at five fertilization regimes and compared to untreated control: N1 (100 kg N/ha), N1 (100 kg N/ha, split 60% in spring and 40%. in postharvest), N2 (200 kg N/ha), N1 (100 kg N/ha) + K (150 kg K2 0/ha), N2 (200 kg N/ha) + K (150 kg K2 O/ha). The annual distribution in spring was equally split before full bloom and at fruit set.

The data collected over the three trial years show no differences as compared to control in yield and fruit size. N2 delayed ripening and decreased fruit quality. Leaf mineral composition was affected by potassium; maximun N induced leaf accumulation of N-NH4 The high concentration of K in leaf tissues was correlated to the yellow color of the leaf blade. Total leaf chlorophyll content was measured by an Spad-502 chlorophyll meter (Minolta Corp.) and compared to that measured by conventional technique (Arnon method). The overall findings suggest the amount of N used in peach fertilization can be reduced.

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Peter Purvis, Calvin Chong, and Glen Lumis

Plug-rooted liners of common ninebark [Physocarpus opulifolius (L.) Maxim.] were grown in 6-L nursery containers filled with 73% composted pine bark, 22% sphagnum peat moss, and 5% pea gravel (by volume). Plants were fertilized with Polyon (Nutryon) 17–5–12 (17N–2P–5K) 6-month controlled-release fertilizer at various rates (2.5, 4.5, 6.5, and 8.5 kg·m-3) pre-incorporated, topdressed, or dibbled (placed under the liner at potting). Plants were trickle-irrigated daily with low (0.4-L), middle (0.8-L), or high (2.0-L) volumes of water to maintain leaching fractions of <0.15, 0.25–0.35, or >0.60, respectively. Regression analysis indicated that growth of ninebark increased from 30 to 109 g/plant with increasing rates of incorporated fertilizer (mean over irrigation volumes), from 27 to 71 g/plant with topdress and from 59 to 103 g/plant with dibble. Electrical conductivity (EC, mean over five dates) of the leachate throughout the season was highest with dibble (0.85 dS·m-3), intermediate with incorporated (0.81 dS·m-3), and least with topdressed (0.76 dS·m-3). With low irrigation volumes, growth of ninebark increased from 42 to 81 g/plant with increasing rates of fertilizer (mean over methods), and from 39 to 105 g/plant with middle or high volumes (common regression curve). With low irrigation volumes, leachate EC increased from 0.74 to 0.94 dS·m-3 with increasing rates of fertilizer, and from 0.75 to 0.81 dS·m-3 with middle or high volumes.

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Yanwen Gong and Theophanes Solomos

Previous research has shown that subjecting bananas to low O2 treatment during the climacteric rise decreases the rate of sugar accumulation but the fruits eventually ripen. In the present study we applied low O2 in fruits whose ripening had been initiated by exogenous C2H4 and in preclimacteric ones. In preclimacteric fruits low O2 suppressed the climacteric rise during the duration of the experiment (20 days). It completely inhibited the increase in sugars, invertase and sucrose phosphate synthase (SPS) activities while there was a sharp increase in sucrose synthase (SS). In control fruits the increase in sugar content coincides with a sharp increase in invertase, and SPS and a decline in SS. Hypoxia inhibited the increase in invertase and SPS while it induced an increase in SS. Nevertheless, the activities of invertase and SPS in the climacteric hypoxic fruits was higher than in hypoxic preclimacteric ones. The results, thus, indicate that the imposition of low O2 at the preclimacteric stage is much more efficient in delaying banana ripening than when it is applied after the initiation of ripening.

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Christopher A. Proctor, Matt D. Sousek, Aaron J. Patton, Daniel V. Weisenberger, and Zachary J. Reicher

sequential application strategy compared with a full rate applied PRE when applied over multiple years at reduced rates. We found little published research on PRE crabgrass control when different a.i.s were used for initial and sequential applications