Influence of mechanical and manual pruning on the incidence of pests in 'Clemenules' mandarins.

BACKGROUND: In Spain, citrus pruning is usually done by hand, although mechanized pruning is gradually being introduced as a cheaper alternative. The pruning strategy affects the pattern and intensity of sprouting, and the canopy characteristics, and therefore could affect pest control. In this study, the effect of three pruning strategies on the incidence of key citrus pests was analyzed: manual, mechanical (with hedging and topping) and no pruning (control). In a commercial clementine orchard, sprouting, pest density and fruit damage were evaluated through three seasons. RESULTS: Outside the canopy, mechanically pruned trees had a significantly higher number of shoots, and more shoots were attacked by aphids (cotton aphid, Aphis gossypii, and spirea aphid, A. spiraecola) in comparison with manual or control strategies. Inside the canopy statistically nonsignificant differences were found between strategies. Regarding the pest level of two-spotted spider mite, Tetranychus urticae, and California red scale, Aonidiella aurantii, in general, no significant differences were found between pruning strategies, and in some cases mechanical pruning resulted in a lower level of these pests and fruit damage than manual pruning. CONCLUSION: The density of aphids, which are pests associated with sprouting, was affected by the pruning strategy. However, the densities of T. urticae and A. aurantii and the level of damaged fruit were unaffected. © 2023 Society of Chemical Industry.

Sustainable Use of Pesticide Applications in Citrus: A Support Tool for Volume Rate Adjustment.

Rational application of pesticides by properly adjusting the amount of product to the actual needs and specific conditions for application is a key factor for sustainable plant protection. However, current plant protection product (PPP) labels registered for citrus in EU are usually expressed as concentration (%; rate/hl) and/or as the maximum dose of product per unit of ground surface, without taking into account those conditions. In this work, the fundamentals of a support tool, called CitrusVol, developed to recommend mix volume rates in PPP applications in citrus orchards using airblast sprayers, are presented. This tool takes into consideration crop characteristics (geometry, leaf area density), pests, and product and application efficiency, and it is based on scientific data obtained previously regarding the minimum deposit required to achieve maximum efficacy, efficiency of airblast sprayers in citrus orchards, and characterization of the crop. The use of this tool in several commercial orchards allowed a reduction of the volume rate and the PPPs used in comparison with the commonly used by farmers of between 11% and 74%, with an average of 31%, without affecting the efficacy. CitrusVol is freely available on a website and in an app for smartphones.

Spray pesticide applications in Mediterranean citrus orchards: Canopy deposition and off-target losses.

Only a portion of the water volume sprayed is deposited on the target when applying plant protection products with air-assisted axial-fan airblast sprayers in high growing crops. A fraction of the off-target losses deposits on the ground, but droplets also drift away from the site. This work aimed at assessing the spray distribution to different compartments (tree canopy, ground and air) during pesticide applications in a Mediterranean citrus orchard. Standard cone nozzles (Teejet D3 DC35) and venturi drift reducing nozzles (Albuz TVI 80 03) were compared. Applications were performed with a conventional air-assisted sprayer, with a spray volume of around 3000lha-1 in a Navel orange orchard. Brilliant Sulfoflavine (BSF) was used as a tracer. Results showed that only around 46% of the applied spray was deposited on the target trees and around 4% of the spray was deposited on adjacent trees from adjoining rows independently of the nozzle type. Applications with standard nozzles produced more potential airborne spray drift (23%) than those with the drift reducing nozzles (17%) but fewer direct losses to the ground (22% vs. 27%). Indirect losses (sedimenting spray drift) to the ground of adjacent paths were around 7-9% in both cases. The important data set of spray distribution in the different compartments around sprayed orchard (air, ground, vegetation) generated in this work is highly useful as input source of exposure to take into account for the risk assessment in Mediterranean citrus scenario.

Factors influencing the efficacy of two organophosphate insecticides in controlling California red scale, Aonidiella aurantii (Maskell). A basis for reducing spray application volume in Mediterranean conditions.

BACKGROUND: Because society is seeking ways to lessen the environmental impact of agricultural activity, dose adjustment has become a key issue in current plant protection treatments with high spray application volumes, such as on citrus plants. This work investigates, in field conditions, the factors affecting the efficacy of organophosphate insecticides against California red scale (CRS), Aonidiella aurantii (Maskell), when the delivery rate is decreased. Insecticide rate changes were induced by modifying the spray application volumes of two commercial organophosphate pesticides based on chlorpyrifos and chlorpyrifos-methyl. RESULTS: Results showed that, with increase in the spray volume, the coverage and the uniformity of deposition on the canopy increased, but final infestation depended neither on the spray application volume nor on the coverage. Furthermore, final infestation significantly depended on the pest pressure in the plot and the spray volume applied per unit volume of canopy (L m(-3) canopy). Moreover, it was found that the final infestation was influenced by the efficiency of deposition in the applications that were carried out against the second-generation of CRS. CONCLUSION: Because the spray application volume did not affect the final infestation, this research introduces the possibility that reducing the doses of current citrus organophosphate treatments may still allow effective plant protection in Mediterranean conditions.

Effects of spirotetramat on Aonidiella aurantii (Homoptera: Diaspididae) and its parasitoid, Aphytis melinus (Hymenoptera: Aphelinidae).

Laboratory and field studies were conducted to measure the effects of spirotetramat on life stages of California red scale, Aonidiella aurantii (Maskell), and a primary parasitoid, Aphytis melinus DeBach. Organophosphate-resistant and -susceptible populations responded similarly to spirotetramat, suggesting there is no cross-resistance between these insecticide classes. First and second instar male and female A. aurantii were 10- and 32-fold more susceptible to spirotetramat (LC50 = 0.1-0.2 ppm) compared with early third (LC50 = 1.5 ppm) and late third instar females (LC50 = 5.3 ppm). The LC99 value indicated that late stage third instar females would not be fully controlled by a field rate of spirotetramat; however, spirotetramat would reduce their fecundity by 89%. Field applications of spirotetramat in two water volumes and using two adjuvants (oil and a nonionic spray adjuvant) showed similar reduction in A. aurantii numbers, even though the higher water volume demonstrated more complete coverage. These data suggest that this foliarly applied systemic insecticide can be applied in as little as 2,340 liters/ha of water volume, minimizing application costs, and that the two adjuvants acted similarly. The endoparasitoid, A. melinus, was unaffected by the field rate of spirotetramat when it was applied to the host when the parasitoid was in the egg or larval stage. Adult A. melinus showed 2 wk of moderate reductions in survival when exposed to leaves with field-weathered residues. Spirotetramat is an integrated pest management compatible insecticide, effective in reducing A. aurantii stages and allowing survival of its primary parasitoid A. melinus.

Spray deposition and efficacy of four petroleum-derived oils used against Tetranychus urticae (Acari: Tetranychidae).

Petroleum-derived spray oils (PDSOs) offer an interesting alternative to acaricides to control the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), a key pest of clementine mandarins, Citrus reticulata Blanco. However, there is a lack of knowledge on how these products should be used. In this study, we evaluated the efficacy of four PDSOs (Sunspray Ultrafine, Volck Miscible, Texaco D-C-Tron Plus, and Agroaceite) at five concentrations (0.5, 1.0, 1.5, 2.0, and 3.0%) against eggs, protonymphs, and adults of T. urticae. We also characterized the PDSOs deposition pattern to find out the possible relationship between this factor and efficacy. In general, for all PDSO assayed, the higher the concentration, the higher the coverage, the mean area of impacts and efficacy on T. urticae. The biggest mean area of the impacts corresponded to Texaco D-C-Tron Plus. This PDSO was the most effective one and its efficacy was independent of concentration for concentrations higher than 1.0%. The same applied for concentrations higher than 1.5-2.0% for Agroaceite, Volck Miscible, and Sunspray Ultrafine, with high efficacies against eggs, protonymphs, and adults. PDSOs are highly effective against T. urticae, the use of these products should be encouraged in integrated citrus pest management programs in Spain. The next step will be to ascertain the efficacy under real field conditions.