Control of Asian citrus psyllid Diaphorina citri Kuwayama and citrus leafminer Phyllocnistis citrella Stainton is important to reduce the spread and severity of huanglongbing (HLB) (citrus greening) and citrus canker diseases, respectively. Insecticides are critical for the management of these pests. We therefore conducted two replicated experiments using spray treatments containing single or multiple modes of action (MoA) insecticides to reduce the incidence of these two pests in bearing citrus. Tank mixing in 47 L·ha−1 (5 gal/acre) of water with synthetic plant terpenes (Requiem 25 EC, Unknown MoA) or adjuvant petroleum oil (PureSpray Green, Unknown MoA) did not improve the effectiveness of the pyrethroid zeta-cypermethrin (Mustang Max 0.15 EC, MoA 3A) against D. citri. Its control with flupyradifurone (Sivanto 200 SL MoA 4D) and PureSpray Green in 935 L·ha−1 (100 gal/acre) water was similar to Mustang Max 0.15 EC and Requiem 25 EC, but mixtures did not provide better control than Mustang Max 0.15 EC alone. Phyllocnistis citrella was controlled only with Sivanto 200 SL and PureSpray Green and Requiem 25 EC alone. The addition of cyantraniliprole (group 28 MoA in A16971 premixed with thiamethoxam MoA 4A), pymetrozine (Fulfill 50 WDG, MoA 9B), or abamectin (Agri-Mek SC, MoA 6) did not improve and in many cases reduced the performance of thiamethoxam (Actara 25 WG, MoA 4A) against D. citri and P. citrella. These results demonstrated no advantage to single applications of multiple MoAs over the most effective active ingredients when applied alone for control of D. citri or P. citrella. Therefore, rotations of these active ingredients would be preferable to mixtures to avoid selection for resistance against multiple MoAs by any one application.
Jawwad A. Qureshi, Barry C. Kostyk, and Philip A. Stansly
Monica Ozores-Hampton, Philip A. Stansly, and Eugene McAvoy
Tomato yellow leaf curl virus (TYLCV) is considered to be the most damaging tomato (Solanum lycopersicum) virus worldwide. Management of TYLCV has relied primarily on insecticidal control targeting the vector sweetpotato whitefly [SPW (Bemisia tabaci)]. However, resistance of the SPW to insecticides; increased length of the growing season, due in part to increased plantings of grape tomato; and asymptomatic hosts of TYLCV such as pepper (Capsicum annuum) have increased the need for wider use of TYLCV-resistant (TYLCV-R) varieties. The objective of this study was to evaluate horticultural characteristics of commercially available TYLCV-R varieties/advanced breeding lines of round and Roma-type tomato varieties in Florida. Sweetpotato whitefly populations and incidence of TYLCV were greater in 2007 than 2008. Under high TYLCV pressure, most of the TYLCV-R varieties/advanced breeding lines produced higher yield than susceptible varieties. In contrast, no clear advantage was found by using TYLCV-R varieties under low TYLCV pressure. Additionally, TYLCV-R varieties produced a high percentage of unmarketable fruit due to rough blossom end scars (BES), zippering, catfacing, sunscald, yellow shoulders, off shapes, and radial or concentric cracking compared with susceptible varieties in both years. Visual assessment of TYLCV-R varieties/advanced breeding lines for horticultural traits showed that ‘Security 28’, Sak 5443, and ‘Shanty’ were the best overall varieties/advanced breeding lines based on participants combined score rating, although ‘Tygress’ and Sak 5808 performed best based on empirical evaluation (numerical data) of total marketable yields and low unmarketable yield.
Monica Ozores-Hampton, Philip A. Stansly, Robert McSorley, and Thomas A. Obreza
Many vegetable growers rely on methyl bromide or other soil fumigants to manage soil pathogens, nematodes, and weeds. Nonchemical alternatives such as solarization and organic amendments are as yet largely unproven, but do offer promise of more sustainable solutions. The objective of this study was to evaluate the effects of long-term organic amendments and soil solarization on soil chemical and physical properties and on growth and yield of pepper (Capsicum annuum L.) and watermelon (Citrullus lanatus [Thunb.] Manst.). Main plots consisted of a yearly organic amendment or a nonamendment control. Four subplots of soil sanitation treatments consisted of solarization, methyl bromide, Telone, and nonfumigated. Each subplot was divided into two sub-subplots, one with weed control and one without weed control. Plant biomass was higher in plots with organic amendments than in nonamended plots. There were no differences in marketable pepper and watermelon yields between organic amended and nonamended plots during the 1998-99 and 1999-2000 seasons, respectively. However, higher pepper yields were produced from organic amended plots in the 1999-2000 season. Soil pH and Mehlich 1-extractable P, K, Ca, Mg, Zn, Mn, Fe, and Cu were higher in organic amended plots than in nonamended control plots. Soil organic matter concentration was 3-fold higher in amended soil than in nonamended soil. Effects of soil sanitation and weed management varied with crop and season. The methyl bromide and Telone treatments produced higher yields than soil solarization. In general, weed control did not affect plant biomass and yield for any of the crops and seasons. The results suggest that annual organic amendment applications to sandy soils can increase plant growth and produce higher or comparable yields with less inorganic nutrient input than standard fertilization programs.
Anne Plotto, Elizabeth Baldwin, Jinhe Bai, John Manthey, Smita Raithore, Sophie Deterre, Wei Zhao, Cecilia do Nascimento Nunes, Philip A. Stansly, and James A. Tansey
A 3-year study was undertaken to establish the effect of field nutritional sprays, combined with insecticide treatments or not against Asian Citrus psyllid, on the fruit quality of ‘Valencia’ orange trees affected by the greening disease Huanglongbing (HLB). Four replicated plots were harvested, juiced, and pasteurized. Nine to twelve trained panelists evaluated the juice using seven flavor, five taste, four mouthfeel and three aftertaste descriptors. There was little difference between treatments in 2013; only orange peel flavor and bitterness were significantly lower for the insecticide treatment. In 2014, positive attributes, such as orange and fruity flavor, sweetness and mouthfeel body, were significantly higher in the insecticide treatment. Sourness was highest in untreated control, and there were no differences between treatments for bitterness. In 2015, negative attributes, such as grapefruit, orange peel and typical HLB flavor, sourness, bitterness, and astringency, were significantly higher in untreated control fruit, suggesting perhaps that the beneficial effect of nutritional and insecticide treatments was cumulative, only manifesting on the 3rd year of the study, and or because of the progression of the disease affecting untreated controls. Data are discussed in relation to juice chemical composition, including volatiles, sugars, acids, limonoids, and flavonoids, adding to the fundamental knowledge concerning chemical drivers of orange flavor.
Elizabeth Baldwin, Jinhe Bai, Anne Plotto, John Manthey, Smita Raithore, Sophie Deterre, Wei Zhao, Cecilia do Nascimento Nunes, Philip A. Stansly, and James A. Tansey
‘Valencia’ orange trees from groves with 90% infection by Candidatus liberibacter asiaticus (CLas), the presumed pathogen for citrus greening or huanglongbing (HLB) disease, were treated with insecticide (I), a nutritional spray (N), and insecticide plus nutritional spray (I + N). Controls (C) were not treated. Fruit were harvested in March to April, 2013, 2014, and 2015, juiced, and the juice was frozen for later chemical analyses. Titratable acidity (TA), soluble solids content (SSC), SSC/TA ratio, many volatiles, flavonoids, and limonoids showed differences because of season, whereas SSC, several volatiles (ethanol, cis-3 hexenol, α-terpinene, ethyl acetate, and acetone), flavonoids (narirutin, vicenin-2, diosmin, nobiletin, heptamethoxy flavone), and limonoids (nomilin and nomilinic acid glucoside) showed differences because of treatment. However, consistent patterns for chemical differences among seasons were not detected. TA tended to be higher in N and C the first two seasons and SSC/TA higher in I and I + N for all seasons (not significant for 2014). Bitter limonoids tended to be higher in I, N or I + N over the seasons. Principal Component Analysis showed that there was a good separation by season overall and for treatment in 2013. In 2014 and 2015, the insecticide treatments (either I or I + N) had the highest sugar and SSC/TA levels and lowest TA levels, although not always significant, as well as higher juice CLas cycle threshold (Ct) levels, indicating lower levels of the pathogen.