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Abstract
Open plots of strawbery (Fragaria sp.) or plots caged with colonies of honey bees (Apis mellifera L.) produced less malformed fruit than plots screened to exclude large insects. Bees and large Diptera, mostly drone flies (Eristalis spp.), were the most numerous visitors to the strawberry blossoms. A list of insects including 108 species representing 35 families frequenting strawberry blossoms in Utah was compiled. The most efficient pollinators were Apis mellifera, Halictus ligatus Say, and Eristalis spp.
Mild. winter conditions vary greatly from year to year, and models to evaluate dormancy development have to separate between years to make accurate predictions for rest breaking purposes. The Utah Chill Unit model has been revised to incorporate time in the definition of chill units. A Chill Unit is redefined as equivalent to one hour at the optimal chilling temperature during the optimal chilling time. Mexico has 50,000 ha of apple trees that require rest breaking practices. Winter conditions of three contrasting years at two Mexican locations were analyzed by the original and revised Utah Chill Unit models. The original Utah model tends to overestimate chill unit accumulation under Mexican mild winter conditions. The revised model increased prediction accuracy of leaf development ten days after full bloom by 10% to within 1-2% of the observed values.
`Crimson Sweet' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of `Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the `Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom.
Plastic covers were placed over rows of `Delicious' apple trees/M.26 to test their effect on canopy temperature and hence on bud phenology and growing season duration. In 1992, plastic covers enclosed the treated plots to within 0.5 m of the soil and the tunnel ends were left open. Average daily temperatures within the rowcovers were 0.1C cooler in April, 0.2C warmer in May, and 0.1C cooler in July than uncovered canopy temperatures. In 1993, rowcovers completely enclosed the treated plots (both ends and sides); average daily temperatures within the enclosed plots were 1.6C warmer in April, 0.1C cooler in May, 0.2C cooler in June, and 1.3C cooler in July. There was no difference in the date of anthesis in 1992; however, within the complete enclosures in 1993, anthesis occurred 7 days earlier than in the uncovered plots. Apple weight and shape were comparable in 1992, but, in 1993, apples in the covered plots average 31.1 g more than fruit in the uncovered trees and had slightly great length/width ratio. Complete and uniform red color development did not occur either year under rowcovers. In addition, rowcovers prevented sunscald and hail damage, and reduced windfall of nearly ripe fruit.
Foliar applications of growth regulators (GR) in early autumn induced leaf retention (LR) on peach [Prunu,s persica (L.) Batsch.] and `Montmorency' tart cherry (Prunus cerasus L.) trees. In `Johnson Elberta' peach, the relative effectiveness of GRs on LR was NAA = Promalin (BA + GA4+7) > GA4+7 > GA3 > BA > control, and on leaf detachment pull force (PF) NAA > BA + GA4+7 > GA4+7 = GA3 > BA3 > BA > control. Relative GR-induced chlorophyll (CL) content in retained leaves was BA + GA4+7 > GA4+7 > GA3 > BA > control > NAA. Relative xanthophyll (XN) content of retained leaves was NAA > control > BA > GA3 = GA4+7 = BA + GA4+7. Treating only half of a peach tree with NAA did not affect LR on the untreated side. NAA decreased subsequent bud and flower size in peach. Bud hardiness was enhanced by NAA in `Johnson Elberta' peach but not in `Redhaven' peach or in `Montmorency' tart cherry. NAA increased hardening on both the leafy treated (foliated) and untreated (defoliated) sides of half-treated `Johnson Elberta' trees. Increased endodormancy duration, as measured by GA3 forcing of terminal leaf buds, was proportional to LR. Chemical names used: N-(phenylmethyl)- 1H-purin-6-amine (BA); (1a,2ß,4bß,10ß)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,lO-dicarboxylic acid,l,4a-lactone (GA3, GA4+7); l-naphthaleneacetic acid (NAA).
Abstract
A model has been developed that relates the stages of spring bud development of ‘Redhaven’ and ‘Elberta’ peaches (Primus persica (L.) Batsch) to an accumulation of growing degree hours following rest completion. The accumulation of growing degree hours is based on a lower limit of 4.5°C and an upper limit of 25°.
`Fuji' apple trees [Malus ×sylvestris (L.) Mill. Var domestica (Borkh.)] on nine dwarfing rootstocks (CG.4013, CG.5179, G.16N, G.16T, M.9 NAKBT337, M.26 EMLA, Supporter 1, Supporter 2, and Supporter 3) were planted at 10 locations (CA, KY MO NC OH 2 in PA SC UT and WA) under the direction of the NC-140 Multistate Research Project. After four growing seasons (through 2002), largest trees were on CG.4013. Smallest trees were on M.9 NAKBT337, Supporter 1, Supporter 2, and Supporter 3. Trees on CG.5179, G.16 N, G.16T, and M.26 EMLA were intermediate. Cumulative root suckering was greatest from trees on CG.4013 and similar from the other rootstocks. CG.4013, CG.5179, and G.16T resulted in the greatest yields per tree in 2002, and M.26 EMLA, M.9 NAKBT337, Supporter 2, and Supporter 1 resulted in the lowest. Cumulatively, CG.4013 resulted in the greatest yields per tree, and M.26 EMLA resulted in the lowest. Rootstock did not affect yield efficiency in 2002, but cumulatively, Supporter 1, Supporter 2, and Supporter 3 resulted in the most efficient trees, and M.26 EMLA the least. Fruit weight in 2002 or on average was not affected by rootstock. Limited data will be presented on CG.3041, CG.5202, and CG.5935, which are planted only at some locations. Data for the fifth season (2003) will be presented.
`Fuji' apple trees [Malus ×sylvestris (L.) Mill. Var domestica. (Borkh.)] on five semidwarfing rootstocks (CG.4814, CG.7707, G.30N, M.26 EMLA, and M.7 EMLA) were planted at nine locations (CA, KY MO NC OH PA SC UT and WA) under the direction of the NC-140 Multistate Research Project. After four growing seasons (through 2002), trees on CG.7707 and M.7 EMLA were the largest, and those on M.26 EMLA were the smallest. M.7 EMLA resulted in more cumulative root suckering per tree than did any other rootstock. Yield per tree in 2002 and cumulatively was greatest from trees on CG.4814, CG.7707, and G.30N and least from trees on M.26 EMLA and M.7 EMLA. The most yield efficient trees in 2002 and cumulatively were on CG.4814, and the least efficient trees were on M.26 EMLA and M.7 EMLA. Rootstock did not affect fruit weight in 2002; however, on average, CG.7707 resulted in the largest fruit, and CG.4814 resulted in the smallest. Limited data will be presented on CG.6210, G.30T, and Supporter 4, which are planted only at some locations. Data for the fifth season (2003) will be presented.