Impact of Nutrient Applications on Plant Physiology and Asian Citrus Psyllid Populations Julian Gonzales III*, Sri Telagamsetty, Shad D. Nelson, Mamoudou Setamou, and Catherine R. Simpson School of Plant and Soil Sciences, Texas A&M University - Kingsville Citrus Center Project was funded by TAMUK URA2016-160306-00007 Objectives Materials and Methods Abstract The objectives of this study were to: Study the effects of Ca and Si foliar sprays alone or in combination on young citrus flush shoots. Study the impact of these foliar sprays on Asian Citrus Psyllid populations and development. Examine the impacts of overall tree health, growth and physiology. Determining the nutrition status of trees Evaluate the accumulation of nutrients in flush shoot tissue and correlate them with physiology and insect populations. Greenhouse Study Application 3 trees per treatment were sprayed with 65 mL of solution to fully cover all foliage. Treatments were: Control Calcium (Recommended rate) =1.6qt/ac Calcium (High rate) = 3.2qt/ac Potassium silicate (Recommended rate) = 2qt/ac Potassium silicate(High rate) = 4qt/ac Calcium (Recommended rate)+ Potassium silicate (Recommended rate) = 1.6qt/ac + 2qt/ac Calcium (Recommended rate) + Potassium silicate (High rate) = 1.6qt/ac + 4qt/ac ACP Observations Trees were enclosed in mesh insect cages (Fig 6B). One week after treatments were applied, ACP were added (5 male, 5 female) to each cage and the populations were recorded (Fig 6A). After one week all adult ACP were removed and numbers of eggs, nymphs and adults were recorded each day. Adult ACP were removed each day until no more were observed. Field Study These 5 treatments were selected based on the greenhouse study: Ca1-Calcium (Recommended rate) = 1.6qt/ac Ca2-Calcium (High rate) = 3.2 qt/ac KSi-Potassium silicate (High rate) = 4qt/ac Ca1+KSi-Calcium (Recommended rate) + Potassium silicate (High rate) = 1.6qt/ac + 4qt/ac Four trees per treatment and four replications (16 trees/treatment) were sprayed in March and June 2016. Sprays were applied during flushing (stage 3/4) for maximum absorption in new leaves (Fig 1). Leaf samples were collected 10-14 days after each application when leaves had fully matured. These samples were then sent to TAMU Soil and Forage Testing Lab for nutrient analysis. Huanglongbing (HLB), also known as citrus greening disease is a bacterial plant disease which is considered to be one of the most fatal diseases in the citrus industry today. The Asian citrus psyllid (Diaphorina citri Kuwayama) is believed to be the main insect vector of citrus greening disease, which was first discovered in Florida in 1998 [2] and was discovered in southern Texas in 2012. In response to this threat, growers and researchers have developed management programs to control the vector in order to control the spread of the disease. The disease can also be very difficult to detect, as symptoms may not show up for more than a year after the tree has become infected. There is evidence that nutritional programs and management strategies are able to maintain tree health and keep infected citrus fields in production [6]. The development of plant diseases and pest infestations can directly be linked to the nutrients that are important for plant growth [5] . Recent field and laboratory experiments conducted at Texas A&M University - Kingsville Citrus Center have shown that applications of different nutrients applied at different rates on citrus trees have the potential to reduce psyllid populations and limit their development. Our current research project was conducted using applications of recommended rates and high rates of calcium and potassium silicate foliar nutrient sprays. Our objectives for this concurrent field and greenhouse trial was to determine the impact of multiple nutrients and variable rates on psyllid development and reproduction. In these studies we found that different rates did not influence the leaf concentrations of Ca and K. Due to the lack of increase in leaf Ca and K concentrations, leaf hardness was not impacted. Greenhouse Study Results A B Figure 3. A) Average number of adults, nymphs and eggs in each treatment, B) percentage of eggs developing into adults. Due to issues cooling the greenhouse and the resulting psyllid deaths and leaf drop, we believe that the results were ultimately inconclusive and the experiment will have to be repeated. While not statistically significant, the largest numbers of eggs were found in the KSi2 and the Ca1+KSi2 treatments. The Ca1+KSi2 treatment also had the highest percentage of eggs developing into adults (~2.5%). Field Study Results A B A B Figure 1. Foliar nutrients being applied to citrus trees. Introduction The Texas citrus industry contributes approximately $200 million to the economy of Texas annually, but this is currently being threatened by the devastating effects and spread of HLB [1]. The Lower Rio Grande Valley is the main citrus producing region in the state of Texas [9] and currently has three counties under quarantine for HLB. This disease is spread by the Asian citrus psyllid (Diaphorina citri Kuwayama) which is the main insect vector of HLB [7-8]. The Asian citrus psyllid is a phytophagous insect and feeds on plants from numerous citrus plant species and citrus relatives [10]. The bacterial pathogen and causal agent of HLB, Candidatus Liberibacter asiaticus, is a phloem limited bacterium that leads to the decline and eventual death of affected trees [11]. There is currently no cure for HLB, so managing this disease becomes more crucial as it spreads. Management strategies have been focused on chemical control of the psyllid vector in order to prevent the acquisition and spread of the disease. While these endeavors are essential in preventing and slowing the spread of HLB, we must also manage infected trees for optimal health and to maintain yield. Most nutritional programs and research has taken place in Florida, which is subjected to different climate and conditions compared to those experienced in Texas [3,4]. Current research has shown that increases in leaf Ca concentrations can increase leaf hardness and therefore inhibit the ability of psyllids to feed and reproduce on these harder leaves (unpublished data). This research is being conducted to further explore the effects of foliar nutrient applications on leaf morphology and how nutrient concentrations may be used to help deter psyllid feeding, and possibly reduce the rate of reproduction and development. C D Figure 6. A) Collected ACP, B) young flush on citrus in the tree greenhouse. Conclusions Greenhouse Study Variability was found across all treatments due to high greenhouse temperatures and the resulting death of psyllids and leaf drop. Highest percentage of eggs developing into adults was close to 3%, but this low survivorship was likely due to greenhouse environment. Experiment will be repeated when temperatures are more suited to psyllid survival and development. Field Study Psyllids were not observed due to psyllid control programs. Foliar treatments and rates did not impact leaf Ca or K concentrations, so different forms may impact absorption. Treatments show promise in increasing leaf hardness, especially combining Ca and Si, which will be explored in future experiments. Figure 4. A) Average nutrient concentration (mg g-1) of Ca in the Spring per treatment, B) calcium conc. in Summer (Pdate=0.264 and Ptreatment=0.532), C) average nutrient concentration (mg g-1) of K in the Spring, and D) K conc. in Summer (Pdate=0.006 and Ptreatment=0.309). Ca and K concentrations in leaves were not influenced by foliar nutrient spray treatments (Fig. 4). These results show that higher application rates do not translate to higher absorption rates by leaves. Leaf hardness was not significantly affected by treatment. This is supported by the nutritional data which shows no differences amongst treatments. However, there is a trend of higher leaf hardness with higher Ca concentrations, which is supported by previous experiments. References A B C A B 1. Saul’s J.W. 1998. Home fruit production-Grapefruit. Texas citrus and subtropical fruits. http://aggie-horticulture.tamu.edu/Citrus/12286.htm 2. Halbert S.E. and K.L. Manjunath, 2004. Asian citrus psyllids (sternorrhyncha: psyllidae) and greening disease of citrus: a literature review and assessment of risk in Florisa. Florida Entomologist 87:331-353. 3. Hall DG. Biology, history and world status of Diaphorina citri. I taller International sobre Huanglongbling de los citricos y el psilido asiatiacio de los citricos. Hermosillo, Mexico; 2008. Pp. 1-11 4. Spann TM, Atwood RA, Dewdney M., Ebel RC, Ehsani R, England G, et al. IFAS Guidance for huanglongbing management. Citrus Industry. Apr 2010: 1-8 5. Farooq, Muhammad (et al.) Conservation Agriculture: Concepts, Brief History, and Impacts on Agricultural Systems 6. Timothy M. Spann, Ryan A. Atwood et al., IFAS Guidance for Huanglongbing (Greening) Management1 7. Bove JM. Huanglongbing: A Destructive, newly-emerging, Century-Old Disease of Citrus. J Plant Pathol. 2006; 88: 7-37 8. French J V, Kahlke CJ, Graca J V. First Record of the Asian Citrus Psylla, Diaphorina citri Kuwayama (Homoptera: Psyllidae), in Texas. Subtrop Plant Sci. 2001; 53: 14-15 9 Julian W. Sauls, Ph. D., . Nutrition and Fertilization, http://aggie horticulture.tamu.edu/citrus/nutrition/L2288.htm 10. J. V. da Graça1 , J. V. French1 , P. S. Haslem1 , M. Skaria1 , M. Sétamou1 and B. Salas2 , Subtropical Plant Science, 60:21-26.2008 21 Survey for the Asian Citrus Psyllid, Diaphorina citri, and Citrus Huanglongbing (Greening Disease) in Texas 11. Lee, R.F., Keremane, M.L., Williams, M.,Vidalakis, G. 2006. Huanglongbing, citrus greening: preparing for the future. Subtropics newsletter 12. David G. Hall1 *, Matthew L. Richardson1 , El-Desouky Ammar1 & Susan E. Halbert2- Asian citrus psyllid, Diaphorina citri, vector of citrus huanglongbing disease Acknowledgements I wanted to thank God first for blessing me to be apart of a great University at Texas A&M Kingsville and giving me the opportunity to work with amazing scientists every single day. I also wanted to thank my family for their love and support throughout my life, without them I would not be where I am today. I also wanted to thank the love of my life Alecia Nicole Cortes for her support through my college career. Thank you and God Bless. Figure 5. A) Correlation between leaf hardness and leaf Ca concentration for each treatment, B) correlation between leaf hardness and nutrient concentration, C) leaf hardness per treatment Figure 2. A) Young Citrus trees being prepared for greenhouse study, B) young flush stage of plant.