In subtropical climates, inadequate winter chill limits blackberry (Rubus L. subgenus Rubus Watson) production by causing poor and erratic floral budbreak. To compensate for a lack of chilling, bud dormancy-breaking agents must be developed for subtropical blackberry production. Our previous study showed that gibberellic acid (GA3) promotes budbreak in three blackberry cultivars but has potential negative side effects on floral development in ‘Natchez’. 6-benzyladenine (6-BA) is a synthetic cytokinin that can act as an antagonist of gibberellins during floral transition. The objectives of this study were to evaluate cultivar × exogenous GA3 interactions, characterize dose effects of exogenous GA3, and examine synergistic effects of GA3 and 6-BA. Three field experiments were conducted in west central Florida. All spray treatments were applied at the end of the chilling period. In the first experiment, ‘Natchez’, ‘Navaho’, and ‘Ouachita’ were treated with GA3 at 0 or 99 g·ha−1. Budbreak was promoted by exogenous GA3 in all three cultivars (0.9% to 4.5% vs. 42.9% to 69.4%), but yield responses varied considerably. Exogenous GA3 increased the yield of ‘Navaho’ and ‘Ouachita’ by 560% to 931%, whereas it induced flower abortion and caused a 15% yield reduction in ‘Natchez’. In the second experiment, ‘Natchez’ was treated with GA3 at 0, 25, 99, or 198 g·ha−1. Budbreak increased linearly with GA3, but yield decreased exponentially with GA3 because of dose-dependent flower abortion. In the third experiment, ‘Natchez’ was subjected to five treatments: 1) water control; 2) GA3 spray application; 3) 6-BA spray application; 4) combined spray application of GA3 and 6-BA; and 5) sequential spray application of 6-BA at 9 days after GA3 application. Application rates were 99 and 47 g·ha−1 for GA3 and 6-BA, respectively. Exogenous 6-BA suppressed GA3-induced flower abortion only to a limited extent. As a result, GA3-containing treatments caused 65% to 83% yield reductions compared with the control (2382 vs. 410–823 g/plant). These results demonstrate that GA3 is a highly effective bud dormancy-breaking agent for blackberry. However, the drawback of GA3 is cultivar-dependent flower abortion, which cannot be fully mitigated by 6-BA. The use of GA3 can be an important management practice for subtropical blackberry production, but its practical implementation must consider cultivar-dependent responses.
Syuan-You Lin and Shinsuke Agehara
Scott Neil White and Linshan Zhang
Hair fescue (Festuca filiformis) is a tuft-forming perennial grass that reduces yields in lowbush blueberry (Vaccinium angustifolium) fields. Nonbearing year foramsulfuron applications suppress hair fescue, but there is interest in increasing suppression through foramsulfuron use in conjunction with fall-applied herbicides. The objective of this research was to determine the main and interactive effects of fall-bearing year herbicide applications and spring-nonbearing year foramsulfuron applications on hair fescue. The experiment was a 5 × 2 factorial arrangement of fall-bearing year herbicide (none, terbacil, pronamide, glufosinate, dichlobenil) and spring-nonbearing year foramsulfuron application (0, 35 g·ha−1) arranged in a randomized complete block design at lowbush blueberry fields in Portapique and Stewiacke, Nova Scotia, Canada. Spring-nonbearing year foramsulfuron applications did not reduce total tuft density or consistently reduce flowering tuft density, flowering tuft inflorescence number, or flowering tuft seed production. Fall-bearing year pronamide applications reduced hair fescue density for the 2-year production cycle, although additional bearing year density reductions occurred when pronamide was followed by spring-nonbearing year foramsulfuron applications at Stewiacke. Fall-bearing year dichlobenil applications reduced total and flowering tuft density at each site, although reductions in flowering tuft inflorescence number and seed production were most consistent when followed by spring-nonbearing year foramsulfuron applications at Stewiacke. Suppression extended into the bearing year at each site, and dichlobenil should be examined further for hair fescue control. Fall-bearing year glufosinate applications reduced hair fescue total tuft density at each site and flowering tuft density and flowering tuft seed production at Stewiacke. Fall-bearing year glufosinate applications followed by spring-nonbearing year foramsulfuron applications also reduced nonbearing year flowering tuft inflorescence number and bearing year hair fescue seedling density at Stewiacke, indicating that this treatment may reduce hair fescue seedling recruitment at some sites. Fall-bearing year terbacil applications did not suppress hair fescue and are not recommended for hair fescue management in lowbush blueberry.
Nicolas C. Strange, John K. Moulton, Ernest C. Bernard, William E. Klingeman III, Blair J. Sampson, and Robert N. Trigiano
Helianthus verticillatus Small (whorled sunflower) is a federally endangered plant species found only in the southeastern United States that has potential horticultural value. Evidence suggests that H. verticillatus is self-incompatible and reliant on insect pollination for seed production. However, the identity of probable pollinators is unknown. Floral visitors were collected and identified during Sept. 2017 and Sept. 2018. Thirty-six species of visitors, including 25 hymenopterans, 7 dipterans, 2 lepidopterans, and 2 other insect species, were captured during 7 collection days at a site in Georgia (1 day) and 2 locations in Tennessee (6 days). Within a collection day (0745–1815 hr), there were either five or six discrete half-hour collection periods when insects were captured. Insect visitor activity peaked during the 1145–1215 and 1345–1415 hr periods, and activity was least during the 0745–0845 and 0945–1015 hr periods at all three locations. Visitors were identified by genus and/or species with morphological keys and sequences of the cox-1 mitochondrial gene. The most frequent visitors at all sites were Bombus spp. (bumblebees); Ceratina calcarata (a small carpenter bee species) and members of the halictid bee tribe Augochlorini were the second and third most common visitors at the two Tennessee locations. Helianthus pollen on visitors was identified by microscopic observations and via direct polymerase chain reaction of DNA using Helianthus-specific microsatellites primers. Pollen grains were collected from the most frequent visitors and Apis mellifera (honeybee) and counted using a hemocytometer. Based on the frequency of the insects collected across the three sites and on the mean number of pollen grains carried on the body of the insects, Bombus spp., Halictus ligatus (sweat bee), Agapostemon spp., and Lasioglossum/Dialictus spp., collectively, are the most probable primary pollinators of H. verticillatus.
Paweł Petelewicz, Paweł M. Orliński, Marco Schiavon, Manuel Mundo-Ocampo, J. Ole Becker, and James H. Baird
Golf courses in coastal regions of northern California are often faced with severe injury caused by pacific shoot-gall nematodes (Anguina pacificae) on their annual bluegrass (Poa annua) host in putting greens. For years, fenamiphos was used for mitigating disease outbreaks until its registration was withdrawn in 2008. An alternative product containing azadirachtin was intended for nematode suppression. Still, it required repeated applications throughout the year with questionable efficacy, making attempts to lessen the impact of the pathogen costly. This study evaluated fluopyram as a novel nematicide for control of pacific shoot-gall disease. Various application frequencies and rates were tested at several golf courses affected by the nematode. Results revealed that fluopyram applied once at 0.22 lb/acre reduced the number of new shoot-galls and improved annual bluegrass appearance for several months. Increased rates and application frequency occasionally improved the efficacy further. Although the visual quality of turf treated with this plant protection compound was tremendously enhanced, and the number of new shoot-galls was reduced, rarely a significant effect was observed on the population density of several soil-dwelling plant-parasitic nematodes, including pacific shoot-gall nematode. It is hypothesized that fluopyram did not move significantly past the thatch layer and into the soil. However, it effectively reduced the ability of pacific shoot-gall nematode juveniles to induce new shoot galls. Due to its long half-life, it likely protected against both new nematode infections and dissemination of pacific shoot-gall nematode when the shoot-galls decomposed.
The social media service Instagram is a popular public platform, but often underused tool to reach new demographics, reduce barriers, and perpetuate science-based information in extension. In the U.S. Intermountain West, Instagram was the top-rated platform for sharing information by predominantly new and female farmers. This article provides recommendations on key behaviors, goal setting, and quantifying impact on Instagram for extension programming. Accounts should target one niche or market, a consistent and personal voice, and regular communication (new content at least three times weekly). Unique and productive connections between extension personnel, community leaders, farmers, students, and public influencers expands programming. Tracking program accounts, including the number of followers and engagement rates, can assess program impacts and target market needs.
Jiffinvir Khosa, Derek Hunsaker, and Michael J. Havey
The amounts and types of epicuticular waxes on onion (Allium cepa) leaves affect feeding damage by onion thrips (Thrips tabaci). This study used gas chromatography mass spectrometry (GCMS) to establish the identities of waxes and measure over time wax amounts on leaves of inbred onion plants with glossy, semiglossy, and waxy foliage. Nine waxes were detected on leaves of all inbreds, and higher coefficients of variation (cv) were observed for less abundant waxes on foliage of doubled haploid onions. Older leaves had higher amounts of waxes compared with younger leaves on the same plant. Except for one minor wax, amounts of individual waxes on leaves were not significantly different for plants of different ages. There was a significant inbred by sampling date interaction due to lower amounts of waxes on the leaves of older plants from the semiglossy inbred. These results indicate that there is little advantage to multiple samplings of leaves over time from the same plant and resources may be better used to evaluate more plants. The relatively large cvs for amounts of specific waxes may reduce response to selection for unique epicuticular wax profiles to develop onion populations that suffer less feeding damage by onion thrips.
Ying Wang, Tingting Xue, Xing Han, Lingxiao Guan, Liang Zhang, Hua Wang, and Hua Li
Kaolin particle film (KPF) is an aqueous formulation of chemically inert mineral particles that can be sprayed on the surface of crops to form a protective film, resulting in increased fruit yield and quality. In this work, the effects of kaolin-based, foliar reflectant particle film on grape composition and volatile compounds in ‘Meili’ (Vitis vinifera L.) grapes were investigated under different growth stages over two growing seasons. The 100-berry weight and titratable acid content were decreased, and the sugar and soluble solid contents were increased in grapes of plants treated with kaolin over 2 years. Compared with grapes from plants not sprayed with kaolin, the levels of total phenol, flavonoid, flavanol, tannin, and anthocyanins of grapes from plants treated with kaolin for 2 years were mostly increased. High-performance liquid chromatography (HPLC) analysis also revealed an increased content of monomeric anthocyanin and changed anthocyanin composition. However, there was little effect on the volatile compounds in the grapes. These results demonstrate that KPF can facilitate the accumulation of sugar and phenolics, thereby improving grape quality even in a humid climate.
Alexander Miller, Petrus Langenhoven, and Krishna Nemali
Operational cost of producing lettuce (Lactuca sativa) during the winter in greenhouses is high in the northern regions of the United States due to the addition of supplemental lighting (SL) and heating. Crop productivity in greenhouses should increase to offset high operational costs and maintain profits. Factors including SL composition, heating efficiency, suitability of production systems (PS), and cultivar performance can affect crop productivity. Research-based information on optimizing the above environmental- and production-related factors is limited. This information is critical for growers to make informed decisions and increase profits during winter hydroponic production. We evaluated the interactive effects of SL composition, solution temperature, PS, and cultivar treatments on lettuce shoot dry weight (SDW, g·m−2) and shoot water content (SWC, %) in a greenhouse maintained at suboptimal air temperature (13.7 °C) using a split-plot design. There were three light treatments (sunlight without SL, sunlight + narrow-spectrum SL at nighttime, and sunlight + full-spectrum SL at nighttime), two solution temperature levels [heated (18.8 °C) and unheated (13.2 °C)], two hydroponic PS [constant flood technique (CFT) and nutrient film technique (NFT)], and eight cultivars included in the study. Results indicated that 1) a narrow-spectrum SL at nighttime in combination with heated solution resulted in maximum SDW of lettuce, 2) the SDW and SWC (major determinant of economic yield) increase between the heated and unheated solution temperature treatments was higher in the CFT than in the NFT, and 3) the positive effects of using heated solution were seen mainly in the green-color cultivars. Our research identified the optimal spectral composition of nighttime SL, tested the positive effects of alternate heating methods using heated solution on plant growth under suboptimal air temperature conditions, compared the suitability of two hydroponic PS for lettuce production, and quantified yield potential of several lettuce cultivars in hydroponic production during winter. Growers can use our research findings to make informed decisions about their investment and to maximize hydroponic lettuce productivity and profits during winter.
Coral Ortiz, Antonio Torregrosa, Enrique Ortí, and Sebastià Balasch
Thinning is the process of removing some flowers or fruit to increase fruit size at harvest. In the Valencia region of Spain, the thinning operation for citrus fruit (Citreae) is performed for some mandarin varieties. This is always performed manually; however, this method is very expensive. The goal of this research study was to assess the mechanical thinning of mandarin (Citrus reticulata) using a hand-held branch shaker. Different thinning treatments were conducted over a 3-year period. The gasoline-powered branch shaker was capable of detaching fruit four- to five-times faster than manual thinning. Final fruit size was significantly higher using manual and mechanical thinning compared with a no thinning treatment. Similar final fruit size was obtained with manual and mechanical thinning. However, no significant differences were found in final fruit yield by weight among no thinning, mechanical thinning, and manual thinning treatments. The use of a branch shaker could be recommended for thinning operations to increase efficiency, reduce labor costs, and obtain larger and higher-quality fruit.