1a. Objectives (from AD-416):
Determine if new plantings of citrus can be protected from citrus greening disease using insecticides.
1b. Approach (from AD-416):
Establish new, disease-free plantings of citrus in the vicinty of Immokalee and test various insecticide programs for protecting the trees from infection.
3. Progress Report:
This project is directly related to inhouse project objective 3c: Investigate basic biology and ecology of the Asian citrus psyllid (ACP) and its natural enemies in Florida citrus. During the third and final year of the agreement, results from two primary experiments were obtained on protecting young citrus from infestations of Asian citrus psyllid and citrus greening disease. In one experiment started in 2008, two factors were studied alone and in combination for protecting ‘Valencia’ resets: insecticides, no insecticides, tree nutrition or no tree nutrition. Treatments were: (1) nutrition alone, (2) insecticides alone, (3) nutrition plus insecticides, and (4) untreated control. The study was conducted in southwest Florida in a grove where more than 90% of existing trees were already infected by citrus greening. The nutritional regimen was adapted from a program attributed to a production manager in southwest Florida. Nutrient applications were initiated March 2008 in designated plots (Nutrition Only and Insecticide+Nutrition) sprayed on the foliage three times a year when major flushes were fully expanded but not yet hardened. These included Bacillus subtilis, salicyclic acid, 3-18-20 fertilizer with K-Phite, 13-0-44 fertilizer, Mg Sulfate, zinc sulfate, sodium molybdate, Epsom salts, and 435 oil. Applications were made with an Air-O-Fan airblast sprayer equipped with five blue and one green Albuz® ATR hollow cone nozzles operating at 10 bars and 5.2 km/hr delivering 39 L/min or 982 L/ha. Insecticidal treatments in plots designated for Insecticide Alone and Insecticide + Nutrition were initiated May 2008 using the same equipment. Thereafter, one (Jan 2009) or two (Dec 2009, Feb 2010 and Nov 2010, Jan 2011) dormant sprays were applied in late fall or winter. Additional sprays during the growing seasons of 2009 and 2010 were made whenever adult D. citri populations in the treated plots surpassed a nominal threshold of 0.5 adult psyllids per “stem-tap” sample (explained below). The nominal threshold was reduced to 0.2 adult psyllids per “stem-tap” after the 2010 harvest due to lower ACP counts. Selection of active ingredients was made according to recommendations found in the 2010 Florida Citrus Pest Management Guide: Asian Citrus Psyllid and Leafminer http://edis.ifas.ufl.edu/in686. Insecticides treatments included 4 soil drenches annually (thiamethoxam, imidacloprid or bifenthrin) and 8 foliar treatments annually (fenpropathrin, dimethyl phosphate, spinetoram, abamectin+thiamethoxam, dimethoate, and phosmet). No differences in the incidence of citrus greening disease was seen among treatments in May 2011. In July and Oct of that year incidence of greening was significantly greater on trees in untreated plots compared to plots receiving foliar insecticide or foliar nutrition sprays. By Feb 2012 there were no significant differences among treatments. Ct values were significantly lower in untreated plots compared to nutrition alone plots in July and Oct 2011. In a second experiment, rotations of systemic insecticides alone were evaluated for protecting newly planted trees from greening. These included Verimark, Admire Pro, and Platinum 75, with different application rates. The test was conducted at the University of Florida Southwest Research and Education Center in Immokalee, Florida, on young ‘Hamlin’ orange trees budded to US-802 pumalo x trifoliate rootstock and planted 18 May 2010 at 8 ft within rows spaced at 18 ft = 303 trees/ac. However, rates were calculated assuming a more typical density of 145 trees per acre. Five treatments were assigned to 15 tree plots in an randomized complete block (RCB) design with 4 replicates. Weeds, debris and leaf litter were removed from beneath each tree prior to application. An 8 ounce suspension of each insecticide was applied to each tree on indicated dates to bare soil within 8 inches of the trunk using an EZ-Dose® sprayer operating at a pressure of 45 pounds per square inch (PSI) equipped with an Albuz ATR 80 Green hollow cone nozzle. Rates increased as tree size increased. Microjet irrigation with green emitters (16 gph) installed every 16 ft (one emitter for two trees) ran for approximately 1 hour before application and 2 hours after application on each of the dates shown. Nymphs were sampled only when new growth (flushes) suitable flush was. Depending on availability up to 10 young shoots were removed per plot on various dates and all life stages were counted under a stereomicroscope. Nymph samples were also obtained on 2 Sep, 22 Sep, 17 Nov, 2010 and 24 Jan 2011 but no psyllid nymphs were found in any sample. Due to the very small size of the trees in the early stages of the trial adult tap sampling was not initiated until 30 Sep 2011 when there was enough canopy to allow for a proper sample. At that time Asian citrus psyllid density was assessed on 10 trees in each plot by counting adults falling on an 8.5 x 11 inch white clipboard placed under randomly chosen branches which were then struck 3 times with the PVC pipe to make a count for one “tap” sample. On 8 Aug 11 and 30 Jan 12, 3 fully developed leaves were removed from shoots that had emerged within the last three months from each of 9 centrally located plants in each plot and sent the huanglongbing (HLB) lab at the Southwest Florida Research Institute in Immokalee Florida for Polymerase chain reaction (PCR) analysis. All treatment regiments significantly reduced the number of adult and juvenile ACP on all sample dates with differences amongst the treatments only being observed with nymph counts on 13 July 2011. Huanglongbing incidence has been lowered in the treated plots with the lowest levels being seen when Verimark at the higher rate was used.