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George Ouma and Frank Matta

Experiments were conducted in 1995 and 1996 to investigate the effect of Accel and Carbaryl on apple fruit on three apple cultivars (Empire, Jon-A-Red, and Braeburn) at the Mississippi State Univ. Aricultural Experiment Station, Pontotoc. The treatments consisted of Accel 25 ppm, Accel 50 ppm, Accel 75 ppm, Carbaryl 0.05%, Carbaryl 0.2%, and an unsprayed control. Trials conducted over 2 years showed that Accel and Carbaryl consistently reduced the fruit set of three apple cultivars. There were interactions between the bioregulators and cultivars only in 1996. In all the bioregulators, treatments reduced fruit set, while in 1996, Carbaryl and Accel at all concentrations except Accel 25 ppm reduced the fruit set of `Empire', `Jon-A-Red', and `Braeburn'. Carbary 0.2% and Accel 75 ppm were the most-effective concentrations in `Empire', `Jon-A-Red', and `Braeburn', respectively, in 1996. The treatments generally increased yield and sugar content, while pH was either not affected, increased or decreased, depending on the apple cultivar.

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Mari Marutani and Veronica Endirveersingham

The effect of shade covers on degradation of insecticide, carbaryl on field-grown pakchoi (Brassica rapa subsp. chinensis) was examined by a commercial enzyme-linked immunosorbent assay (ELISA) kit. Carbaryl at a.i. 10.6 g·L-1 (1.42 oz/gal) was applied to the plants grown under five different shade treatments including control without any coverings. The experiment was arranged in a randomized complete block design with three replications. Pesticide residue on leaf tissues was examined on dates of 1, 3, 5, and 7 days after pesticide application. On all sampling dates, pesticide residue was greater with treatments with higher shade percentage. Both linear and quadratic relationship of shade (independent variable) and the concentration of remained carbaryl (dependent variable) were significant (P < 0.05). The half-life of carbaryl on pakchoi leaves ranged from 2 days for control to 9 days for the heaviest shade (75%) treatment with rain protection.

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Justin M. Vitullo and Clifford S. Sadof

of floral scents, flowers are even more preferred by beetles than foliage ( Held and Potter, 2004 ). Due to the long flight period of adult beetles (usually >8 weeks), multiple foliar applications of persistent insecticides like carbaryl are typically

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Richard P. Marini

Chemical fruit thinners were applied to limbs or whole trees of spur `Delicious' at various stages of fruit development as indicated by fruit diameter. Carbaryl, naphthalene acetic acid (NAA), and ethephon all reduced fruit set when applied at a fruit diameter of ≈4 to 15 mm. Fruit thinning for NAA and carbaryl, alone or combined, generally was greater when applied at an average fruit diameter of 8 mm, rather than at 4 mm. Repeated applications of NAA or carbaryl were no more effective than single applications. NAA + carbaryl applied at 9 mm was more effective than NAA applied at 4 mm followed by carbaryl at 8 mm. Applied when fruit diameter averaged 17 to 22 mm, ethephon and ethephon + carbaryl were effective fruit thinners. When applied at full bloom to ≈10 and 20 mm, the insecticides ethion and oxamyl, respectively, were effective fruit thinners.

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F.G. Dennis Jr.

In 1994, benzyladenine (BA, formulated as Accel, containing 1.8% BA and 0.18% GA4+7) was evaluated as an apple fruit-thinning agent. Naphthaleneacetic acid (NAA, 10 ppm) and carbaryl (60 g·liter–1) were also used, as well as combinations of these chemicals with BA. Whole trees were treated with either an airblast sprayer or a hand gun, BA being used at 15–20 g/acre. Good responses to BA were obtained in one of two trials, with both `Empire' and `Gala', but `Jonagold' and `Jonathan' were not responsive (one trial each). In general, response to NAA and carbaryl was more consistent. In only one orchard (`Gala') did BA appear to increase fruit size without reducing crop load. Combinations of BA with NAA or carbaryl were generally no more effective than one chemical alone, but such combinations overthinned in one experiment with `Empire'.

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R.E. Byers, J.A. Barden, and D.H. Carbaugh

Terbacil applied to whole-spur `Delicious' apple (Malus domestica Borkh.) trees reduced photosynthesis and fruit set. The addition of the surfactant X-77 to terbacil sprays increased fruit thinning and leaf injury. Terbacil sprays applied to leaves only (fruit covered with foil) were as effective as when applied to leaves plus fruit. Dipping fruit alone in a terbacil solution did not cause abscission. Shading trees for 4 days with 92% polypropylene shade material reduced fruit set =50%. Spraying trees with carbaryl reduced fruit set by 25%. The combination of shade + carbaryl spraying reduced fruit set by 89%. Chemical names used: l-naphthalenyl methylcarbamate (carbaryl); 3-tert- butyl-5-chloro-6-methyluracil (terbacil); 2-chloroethylphosphonic acid (ethephon); alkaryl polyoxyethylene alcohols (X-77).

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Peter M. Hirst

Russet is a disorder of apple (Malus×domestica) fruit where the formation of cork cells leads to a cosmetic blemish which is commercially undesirable. One of the many causes of russet is low temperature damage early in fruit development. Following frost damage to fruit, a study was initiated to determine whether carbaryl chemical thinner was more effective in thinning russeted fruit than nonrusseted fruit. With no chemical thinner application, russeted fruit abscised at a greater rate than nonrusseted fruit. Following the application of carbaryl to the fruit however, there was no difference in the retention of fruit among the treatments. Chemically thinning with carbaryl therefore is not a technique that growers could use to preferentially thin russeted fruit.

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Daniel Ward and Richard P. Marini

In three experiments, apple trees (Malus ×domestica Borkh.) were sprayed, when fruits were 20 to 30 mm in diameter, with a combination of ethephon (800 mg·L-1) and carbaryl (600 mg·L-1) to induce abscission of all fruits on the tree. Two days after treatment (DAT), most treated fruits stopped or slowed increasing in diameter, fruit water potential was less negative, and starch accumulation was less than for nontreated fruits. Cellulase activity appeared in the abscission zone by 4 DAT. Fruit growth cessation following treatment was probably due to inadequate assimilate supplied to the fruit, but assimilate flow slowed before cellulase activity was apparent in the abscission zone. Chemical names used: 2-chloroethyl phosphonic acid (ethephon); 1-naphthyl (N-) methylcarbamate (carbaryl).

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Sunghee Guak, Norman E. Looney, and Leslie H. Fuchigami

We propose that return flowering of `Fuji' apple can be improved if sufficient flower clusters are removed during or shortly after bloom. In this study conducted at Corvallis, Ore., we evaluated two synthetic auxins, MCPB-ethyl and the Na salt of NAA, each at 0, 4, 8 and 16 ppm, as blossom cluster thinners. Each auxin treatment was applied alone or with 100 ppm ethephon as a tank mix. Six-year-old `Fuji'/M.26 trees were sprayed at full bloom of the king flowers (≈85% of whole-tree full bloom). A follow-up treatment of Sevin XLR (800 ppm carbaryl) was made at 11-mm fruit diameter to determine if carbaryl's known effectiveness as a fruitlet thinner was influenced by the bloom-time auxin or auxin + ethephon treatments. MCPB-ethyl proved ineffective as a bloom-time thinner, whereas the NAA effect on cluster removal was linear with concentration, 16 ppm NAA completely defruiting 33% of initial flower clusters. On control trees fewer than 12% of flowering clusters failed to set fruit. Ethephon alone defruited 25% of the clusters and NAA+ethephon defruited 51% of clusters. It is notable that the NAA and ethephon + NAA treatments did not reduce fruit set on the remaining clusters, resulting in considerable need for hand-thinning. Carbaryl effectively reduced total crop load by increasing the number of defruited clusters and reducing the incidence of doubles and triples. There was evidence to suggest that its effectiveness was compromised by the bloom-time NAA and/or ethephon sprays.

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P. I. Garriz, G.M. Colavita, H.L. Alvarez, and A.J. Alvarez

NAA (1-naphthaleneacetic acid) is widely used for thinning apples; however, its mechanism of action is not well understood. Postbloom application of NAA is cultivar-specific and may, in addition to causing fruit abscission, show unwanted side effects. The response of 5-year-old `Braeburn'/MM 111 apple (Malus domestica Borkh.) trees trained to palmette leader to NAA used alone or in combination with carbaryl (1-naphthyl-N-methylcarbamate) was evaluated in late thinning trials. The experiment was conducted at the Comahue National Univ. (lat. 38°56′S long 67°59′W), during the 1997-98 growing season. Treatments were 1) control, 2) NAA (13 ppm), and 3) NAA (6.5 ppm) + Carbaryl (600 ppm). Whole sprays were applied 17 Oct. at 22 days after full bloom (DAFB) to five trees per treatment. Fruit diameter (FD) was recorded twice weekly (n = 20 per date and treatment). At 169 DAFB, cropload and fruit fresh weight (FW) were determined. Fruit were then graded into size categories. Analysis of variance was used and mean separations were computed with Student's t test. Good thinning resulted from NAA applications; however, this did not reflect in increased mean FW. The number of fruit ≥70 mm was increased by 6.67%. Cropload was overthinned by NAA + carbaryl. Mean FW was slightly greater than control (185.15 and 172.45 g, respectively) and this treatment resulted in 90 % of the fruit ≥70 mm compared to 75 % from control. The following potential model best fitted the fruit growth pattern on non-thinned trees: FD =2.9077 DAFB0.6307 (R 2=0.98, P≤0.001). More work needs to be done to establish the most effective timing and concentration of spray for `Braeburn' to give the maximum crop of large fruit on a regular cropping basis.