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Jialin Yu and Nathan S. Boyd

There is a need to identify postemergence (POST) herbicides for weed control in field-grown caladium [Caladium bicolor (Aiton) Vent.]. The objective of this research was to evaluate the tolerance of two caladium cultivars Florida Cardinal and Florida Fantasy to POST applications of sulfonylurea (SU) herbicides flazasulfuron, foramsulfuron, imazosulfuron, and mesosulfuron. At 8 weeks after treatment (WAT), ‘Florida Cardinal’ and ‘Florida Fantasy’ treated with the highest rate of imazosulfuron (1680 g a.i./ha) had <10% visual injury, leaf number, height, and tuber weight reduction compared with the nontreated control. Both caladium cultivars exhibited greater susceptibility to flazasulfuron, foramsulfuron, and mesosulfuron as compared with imazosulfuron. The label-recommended rate of flazasulfuron (52 g a.i./ha), foramsulfuron (29 g a.i./ha), and mesosulfuron (15 g a.i./ha) reduced ‘Florida Cardinal’ height 35%, 27%, and 35%, respectively, and reduced ‘Florida Fantasy’ height 43%, 31%, and 21% compared with the nontreated plants, respectively. Caladium tuber weight exhibited a differential cultivar response to the evaluated SU herbicides, except imazosulfuron. The highest rate of flazasulfuron (420 g·ha−1), foramsulfuron (232 g·ha−1), and mesosulfuron (120 g·ha−1) reduced ‘Florida Cardinal’ tuber weight 50%, 65%, and 58% compared with the nontreated control, respectively, whereas these treatments reduced ‘Florida Fantasy’ tuber weight <25%. The mesosulfuron rate required for 20% tuber weight reduction (T20) in ‘Florida Cardinal’ was 2 g·ha−1, but the T20 value was 28 g·ha−1 for ‘Florida Fantasy’. We concluded that the caladium cultivars Florida Cardinal and Florida Fantasy are highly tolerant to the POST applications of imazosulfuron, whereas these caladium cultivars are more susceptible to flazasulfuron, foramsulfuron, and mesosulfuron.

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Jialin Yu, Nathan S. Boyd, and Zhengfei Guan

Many strawberry growers in Florida relay crop vegetables with strawberries or grow multiple crops on the same plastic mulch. The practice can reduce the overall input costs per crop but weed management can be problematic. Field experiments designed as a split plot were conducted in Balm and Dover, FL over two successive strawberry-growing seasons from Oct. 2014 to Mar. 2015 (year 1) and Oct. 2015 to Mar. 2016 (year 2) and two successive muskmelon-growing seasons from March to July 2015 (year 1) and March to July 2016 (year 2). The objectives were to examine the effect of summer fallow programs and the presence or absence of a relay-crop on weed density and strawberry (Fragaria ×ananassa Duchesne) and muskmelon (Cucumis melo L.) yields. Summer fallow programs included leaving the plastic mulch in place and reusing it in year 2, a sunn hemp (Crotalaria juncea L.) cover crop, or a conventional chemical fallow. Relay cropping muskmelon with strawberries had no effect on strawberry yield. Summer fallow programs had no effect on muskmelon growth and yield in Balm and Dover, as well as strawberry growth and yield in Balm. In Dover, the plastic mulch summer fallow had 22% to 34% lower berry yield in year 2 compared with cover crop and chemical fallow, respectively. In year 2, relay-cropping was more effective in reducing total weed density compared with strawberry monoculture in Dover but not in Balm. In year 2 in Dover, averaged overall summer fallow programs, the total weed density was ≈3-fold less in relay-cropping than strawberry monoculture. Of all the summer fallow programs evaluated, leaving the plastic mulch in place combined with glyphosate was the most effective summer fallow program, whereas the conventional chemical fallow was the least effective at weed suppression. We conclude that relay cropping or double use of plastic mulch for successive strawberry crops are viable options for Florida strawberry growers.

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Scott N. White, Nathan S. Boyd, and Rene C. Van Acker

Experiments were established to evaluate the suitability of growing degree-day (GDD, T base = 0 °C) models for predicting emergence, tip dieback, and flowering of lowbush blueberry ramets in Nova Scotia, Canada. Data for model development were collected from quadrats established in several non-bearing and bearing blueberry fields throughout the dominant blueberry production areas in northern and central Nova Scotia. Blueberry ramets emerged between 222 and 265 GDD (6 May to 14 May) and reached 90% emergence between 619 and 917 GDD (7 June to 5 July). Emergence continued to slowly increase until late summer or early fall. Tip dieback began between 598 and 792 GDD (14 June to 21 June) and duration of this phase depended on whether late-emerging ramets developed to tip dieback. A four-parameter Weibull and a three-parameter Gompertz equation adequately explained cumulative blueberry ramet emergence and cumulative ramets at tip dieback as functions of GDD in the non-bearing year, respectively. The four-parameter Weibull function also explained the relationship between cumulative flowering ramets and GDD in the bearing year. Flowering ramets were first observed between 376 and 409 GDD (19 May to 30 May) in the bearing year. Model predictions for initiation of emergence, tip dieback, and flowering were 243, 692, and 389 GDD, respectively. Models were validated with independent data sets collected throughout northern and central Nova Scotia. The relationship between the percentage of open flowers on individual ramets and GDD in the bearing year was well described by a Gaussian model at two sites with a predicted peak number of open flowers between 552 and 565 GDD.

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Jialin Yu, Nathan S. Boyd, and Peter J. Dittmar

In Florida, cabbage (Brassica oleracea L.) is typically grown without a plastic mulch and as a result, weeds are a significant problem in most fields. Experiments were conducted from Nov. 2015 to Apr. 2016 in Balm, Citra, and Parrish, FL, to evaluate weed control and ‘Bravo’ cabbage tolerance to multiple herbicide programs applied pretransplanting (PRE-T), posttransplanting (POST-T), PRE-T followed by (fb) a sequential application at 3 weeks after transplanting (WATP), and POST-T fb sequential application at 3 WATP. PRE-T herbicide treatments of 277 g a.i./ha clomazone, 280 g a.i./ha oxyfluorfen, and 798 g a.i./ha pendimethalin and POST-T herbicide treatments of 6715 g a.i./ha dimethyl tetrachloroterephthalate (DCPA) were ineffective, and weed control never exceeded 70% in Balm and provided <50% weed control in Citra and Parrish at 6 and 8 WATP, respectively. POST-T applications of napropamide + S-metolachlor at 2242 + 1770 g a.i./ha, DCPA + S-metolachlor at 6715 + 1170 g a.i./ha, and S-metolachlor POST-T fb clopyralid at 1170 g a.i./ha fb 210 g ae/ha were the most effective herbicide treatments and consistently provided >70% weed control. In addition, results showed that all of the herbicide treatments evaluated except the PRE application of clomazone at 277 g a.i./ha are safe for cabbage with no adverse effect on yield.

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Ravneet K. Sandhu, Nathan S. Boyd, Shaun Sharpe, Zhengfei Guan, Qi Qiu, Tianyuan Luo, and Shinsuke Agehara

Strawberry growers face rising production costs combined with competition from foreign imports. Relay cropping vegetables with strawberries is a unique approach that can diversify income and reduce the risk associated with strawberry production. Planting vegetable transplants on the same bed before strawberry crop termination enables continued berry harvesting while the new vegetable transplants become established. Relay cropping techniques of strawberry with eggplants were evaluated during the 2016–17 and 2017–18 seasons in Balm, FL. The strawberry crop was planted in September, and eggplant was transplanted into the beds either as a sole crop or with strawberry plants. Two experiments were conducted to optimize the planting date of strawberries and the termination date of strawberries. The objective of the research was to examine the competitive relationship between strawberry and eggplant crops and to define the optimal planting date for the eggplant and termination date of strawberries to minimize the competitive interaction and maximize the yield of both crops. Strawberry yields were unaffected (P = 0.938) by relay cropping or by the planting date of the eggplant. Eggplants grown without strawberries had 27% to 32% higher yields (P = 0.004) compared with relay-cropped eggplants, and eggplant yield decreased with later planting dates (P < 0.001). A partial budget analysis showed that transplant dates of 4 and 18 Jan. for eggplants with strawberries resulted in increased profits of $7320 and $3461 per ha, respectively, over the baseline treatment of strawberries alone, but later planting dates resulted in an overall economic loss ($7800–$16,000/ha). Strawberry termination dates did not affect eggplant yields. In conclusion, relay cropping eggplants with strawberries resulted in no effect on strawberry yields, reduced eggplant yields, but increased overall profits when eggplant were transplanted in early to mid-January. Relay cropping of strawberries with eggplants in early February to early March is less profitable than a monocrop of strawberries.