Paper sprayed with Tangle Trap sticky coating was placed a) at the base of the plants with a ring of sticky tape around the base of the stem and partially on the stem of the plant to capture any insects crawling down, and b) extending from the base of the plant horizontally outward above the pot surface to ensure complete coverage of the area covered by the plant canopy . This experiment was replicated on a single potted plant over time on 7 dates . Data were analyzed using Fisher’s exact test using SAS 9.2 . At our planned field trial site that would later be used in the B. bassiana trial, pupation emergence cages were used to sample insects moving off foliage towards pupation sites and later emerging out of the soil after pupation. Cages were made from Schedule 40 white PVC pipe with a diameter of 10.2 cm with cages cut to a height of 5.1 cm. The cage was then topped with a double-sided sticky card cut to fit,plastic flower buckets wholesale which was fixed into place with two elastic bands. Four lines of four cages were pushed into the soil to a depth of approximately 1 cm immediately adjacent to each other at the base of a blueberry plant and oriented in a cardinal plane to determine which direction showed the most thrips activity.
The four adjacent cages in a particular plane were used to assess thrips movement in the understory of the blueberry plant in each directional. The study was replicated on 5 plants on a single date and conducted just prior to the commencement of the field trial. Data were analyzed with a nested ANOVA using SAS 9.2. In a greenhouse trial, Mycotrol O ® was applied directly to the soil surface as raw spores and compared to the same product colonized onto millet seed, also using soil application. Millet seed colonization used the Stanghellini and El-Hamalawi method as described below. The colonized millet seed, when allowed to imbibe water and incubate in the laboratory, can support 1.0 x 106 conidia/seed . Based on Stanghellini et al. with modification, we held the GHA colonized millet seed in containers such that the seed mat was at a depth of no greater than 2.54 cm. The seeds were wet with the consistency of very thin slurry and were gently stirred three times per day for four days to ensure they imbibed water properly so that mycelial growth and sporulation would occur. Sporulation was confirmed by slide mounting random sections of mycelia and checking for condia formation under the microscope.
Once spores were initially observed, the seed was held an additional three days so that sporulation could continue before use of the colonized seed in the field study. Mycotrol O® was applied in the maximum recommended field rate for high thrips levels of 2.84 L of material in 378.5 L of water.The colonized millet seed was tested in the greenhouse to determine if late second instar citrus thrips would become infected if they crawled over or through the seed when it was placed at the base of a laurel sumac seedling. A single small laurel sumac seedling, about ~10 cm tall, was placed into each of ten, 9.5 x 9.5 x 18 cm styrene cages with 6 cm diam air holes on all four sides that were covered with ultra fine mesh screening . Small holes were made in the bottom of the container and covered with pebbles to allow for drainage, then soil was added to a depth of 7.62 cm and the top of the container was covered with a removable lid. The base of each plant was completely surrounded by either B. bassiana colonized millet seed or with uncolonized seed . A minimum of 20 late second instar thrips were released onto the leaves of each plant, and were left until enough time had passed for the thrips to molt to the propupal stage.
The seedling was then cut at the soil line and examined for pupating thrips; the removable lid of the cage was sprayed with Tangle Trap sticky coating to collect any emerging adults after 5 days so infection could be measured. The study was replicated on 5 dates . Data were analyzed using 1-way ANOVA with time as a factor and means were separated using Tukey’s Least Significant Difference test using SAS 9.2. To determine the optimum number of colonized millet seeds needed for close to 100% infection when thrips were seeking pupal refuges off the plant, varying amounts of colonized seed were evaluated in a greenhouse trial based on the size of the seed once it had imbibed water and sporulation had occurred. After water inhibition, nine seeds completely filled one square cm of soil surface. There was a 0.5 cm buffer area around all sides of the cage, which was kept clear of seed to provide a 9 x 9 cm grid of seed on the soil surface below the plant. All but two leaves were plucked from the seedling. Small holes weremade in the bottom of the container, which was covered with pebbles to allow for drainage. The 9 x 9 cm2 grid was created from wire screen and differing amounts of sporulating seed or seed alone were placed on the light imprint made from the wire screen on the soil surface. Two replicate seedlings per treatment were set up per date in a complete block design . Plants were watered every third day. A minimum of 20 late second instar thrips were placed onto the leaves of the plant, and were left until enough degree-days had passed for the thrips to molt to the propupal stage, typically about 5 days. The seedling was then cut at the soil line and examined for pupating thrips; the removable lid was sprayed with Tangle Trap sticky coating to collect any emerging adults after another 5 days. Data were analyzed using a 3-way ANOVA with density of seed , application of B. bassiana , and date as factors . Unrecovered insects were counted as missing data and were not included in the analysis. The commercial blueberry test site selected was located north of Bakersfield in Delano, CA. The trial began in August of 2008 and was conducted post blueberry harvest. The V. corymbosum varieties contained within the test area were, ‘Santa Fe’, ‘Jewel’, and ‘Star’. The most susceptible variety of blueberry to citrus thrips damage grown at the test site was the ‘Star’ variety and ‘Star’ was used consistently for evaluation of thrips numbers for all aspects of the trial . Our cooperator was interested in alternatives to traditional pesticides as the farm regularly was dealing with extremely high citrus thrips populations. For example, in 2008 the grower sprayed 5-10 times per field , rotating with traditional chemicals to reduce thrips impact on the subsequent year’s fruit set. Irrigation in all fields took place via drip irrigation with one water delivery emitter per line at each plant base , but additionally, one portion of the blueberry field was equipped with 360° overhead sprinklers. This irrigation setup provided the ideal situation to test B. bassiana under two watering regimes.
The commercially available GHA strain is formulated to be mixed with water and for application via chemigation or as a foliar spray. The label states that no surfactant is needed to keep the spores in suspension. However, agitation alone in the 1,892.7 L holding tank was not sufficient to keep the material from precipitating,black flower buckets therefore 312.3 ml of Silwet L-77 was added to the tank mix. Mycotrol O® was applied directly to the soil surface with a gas-powered sprayer with a hand spray gun equipped with an adjustable flow meter. The dimensions of the plots were used to calculate the amount of material needed for both B. bassiana formulations . Plants in the test field were spaced every 0.92 m down each row, 3.35 m between each row, and each row was about 165 meters in length. Our studies were conducted in an 18-row section of a 4.04 ha field. The overhead sprinklers were spaced every 7 meters in the row and were located every other row for 12 rows. We chose to investigate the effectiveness of the B. bassiana colonized millet seed versus a Mycotrol O® soil application under two watering regimes, drip-line alone versus drip-line with overhead sprinkler, because B. bassiana conidia are highly subject to desiccation. Comparing the soil drench in both irrigation types with the colonized millet elucidated the effectiveness of the treatments when compared to the control. The blocks were laid out in a 3 x 2 factorial design, with each block consisting of most of five rows of blueberries , each being 27.4 m long . The berm used to grow blueberries at the commercial farm was 1.21 meters wide and each plot was 27.4 meters long. The spacing between adjacent rows was 3.35 m, while the spacing between the plants down a row was approximately 0.92 m with 30 plants per treatment plot . These dimensions result in 0.157 ha treated with raw spores but because the top of the berm was where thrips activity was evident and would be sampled, only 36% of the soil surface area was treated. The Mycotrol O® label states that the maximum field rate is 6.9 L/ha mixed in 935.3 L/ha water. We therefore chose to apply the entire 6.9 L of Mycotrol O® in 378.5 L of water per ha directly to the berm with no application between the rows, which resulted in 100% of the per ha rate of product being applied to 36% of the area and allowed the maximum amount of active ingredient to be applied to the area that would have almost all thrips activity . Our field trial was intended to determine the extent to which B. bassiana might fit into a program projected to both control citrus thrips effectively and provide rotation among available chemistries so as to reduce thrips resistance evolution.
Thus, we felt it was important to operate under the best possible conditions for thrips infection by Mycotrol O® , regardless of financial considerations, i.e. application of product at the maximum label rate in the area where thrips were most likely to be active. The amount of millet seed used in the field trail was calculated based on the area of the berm to be treated and likewise with the Mycotrol O® treatment, only 36% of the total field area was treated. The amount of seed used was one colonized seed/ 2 cm2 over an area of 576 m2 ; the fact that 0.45 kg of seed was needed per 840 cm2 resulted in the application of 3.40 kg of colonized millet seed for the 8 treated plots . Every other plant within the middle ten plants of the middle row of each plot were sampled with pupation emergence cages . These cages were placed tight against the base of each set of canes on the east side . With 5 cages per block and 4 replicate blocks per treatment, a total of 20 cages sampled thrips pupation per treatment over two sample periods, i.e. for two consecutive 3-day periods after the Mycotrol O® soil drench. The treatments were: no B. bassiana with and without overhead sprinkler; colonized millet seed with and without overhead sprinkler; and a soil drench of Mycotrol O® with and without overhead sprinkler . In total, data were collected from 240 emergence cages over the duration of the trial . The colonized millet seed was set to imbibe water and allowed to sporulate for three days before application and was applied using a hand fertilizer applicator . Four days post application of the millet seed, the soil drench of Mycotrol O® was applied and pupation emergence cages were placed in the field and left out for 3 days . After three days, the sticky cards from each emergence cage were collected and replaced with new cards and the traps were switched to the next plant on the east side. These traps were left in the field to sample thrips for another 3 days . Because the traps were placed out every other plant, this ensured that all of the middle ten plants were sampled over the two, 3-day sampling periods .