Guardian Plants are particular plants that draw pests away from crops and at the same time support the continuous reproduction of the pest’s natural enemies. The concept was developed indoors on greenhouse crops. In this trial, we attempted to transfer greenhouse guardian plant techniques into field vegetables for the first time. IPM Laboratories, Inc. collaborated with 1 New York farmer, 1 Niagara County Cooperative Extension agent, 2 professional scouts, and 1 Environmental consulting firm to evaluate marigolds as Guardian Plants for thrips in sweet pepper fields and snapbeans as Guardian Plants for spider mites in eggplant fields. Data were collected for 2 seasons: 2011 and 2012. Over the 2 year trial, the marigolds proved to be useful Guardians of the peppers against thrips while the beans did not give the same protection against spider mites in eggplants.
In 2010, Mark Zittel of Amos Zittel and Sons, Inc. experienced extremely high numbers of thrips on sweet pepper plants that they had transplanted from the greenhouse to a nearby field. Although they sprayed 5 times, they still experienced significant damage to the field.
In both 2011 and 2012, the thrips predator Orius established and reproduced on the marigolds prior to the peppers as evidenced by the presence of the first Orius nymphs on the marigolds. Thrips numbers remained quite low throughout both seasons compared to past experiences of the Zittels who in 2010 saw 5 or more times as many thrips despite repeated pesticide treatments. By the close of each year’s dataset, Orius numbers and thrips to Orius ratios in all pepper fields were utterly astounding. There were more than one Orius per sample where each sample was a small portion of a pepper plant. On July 26, 2011, there were less than 1 thrips per Orius on the peppers. In 2012 on July 5, there were about 1 thrips per Orius on the peppers. This ratio is extremely favorable given that Orius can kill 5 to 20 thrips per day. No thrips sprays were required in 2011 or 2012.
In another area of the farm, imidicloprid pesticide used in June to control Colorado Potato Beetle on eggplant devastates the spider mite predator population in June. With no natural suppression, the spider mites flare up and start bronzing the fields, often requiring 2 summer sprays for spider mites. Beans are particularly good trap plants for spider mites and can be planted in the middles of tractor lanes that are free of the pesticide. Predator mites released onto those beans in a July 2010 preliminary trial spread at least four rows into the eggplants and suppressed the spider mites to a level similar to miticides in the rest of the field. We proposed to document the effect of using beans as Guardian Plants in eggplants.
In 2011 and 2012 the predatory mites established on the bean release rows and increased over the season. But where no beans were present, the predators established equally well on eggplant release rows. In both cases, predators were detected as far as 4 rows away from the row where they were released. The predators appeared to be extremely mobile and more numerous wherever the spider mites were more numerous. In this part of the trial, our beans did not provide the Guardian Plant services that we were hoping for since the treated eggplants usually appeared to have more predators than the treated beans. However, the number of miticide treatments was reduced from 3 sprays in 2010, to a half of the field sprayed once in 2011 and no sprays in 2012.
Mark Zittel has shared the discovery of abundant Orius in pepper and eggplant fields with all growers willing to listen on his own and neighboring farms, and they have found them almost everywhere that they have looked. A local pesticide representative even used the predators as a talking point. The project cooperators shared the project results at grower meetings, including a Western NY Vegetable Growers Meeting in Lockport, NY and the Mid-Atlantic Fruit and Vegetable Conference in Hershey, both in 2012. In August 2012, a twilight meeting on the Zittel farm was organized by Robert Hadad of the Cornell Cooperative Extension for grower Mark Zittel and Entomologist Carol Glenister to explain the project to area growers.
Thrips reduce yields by directly attacking plant flowers and growing tips. In 2010, Mark Zittel of Amos Zittel and Sons, Inc. experienced extremely high numbers of thrips on sweet pepper plants that they had transplanted from the greenhouse to a nearby field. Although they sprayed 5 times, they still experienced significant damage to the field. In addition, they were surprised that the pesticides did not seem to work well in knocking back the thrips populations. Indeed, in recent years, pesticides such as spinosad that have had a long history of excellent control of thrips have begun to fail. The situation is so critical that in 2008, Dow withdrew the use of spinosad in two Florida counties in order to address the extreme resistance that had developed there.
Thrips are most threatening to pepper plants in warm weather when their natural enemies are low in number. If thrips are introduced into the field, even in relatively low numbers per plant before the plants have blooms to support the natural enemies, the thrips will be uncontrolled and require pesticide intervention. Growers strive to transplant the peppers young enough so blooms will not interfere with root development. This practice creates an approximate 3-week window when there are insufficient blooms to support the presence of natural enemies in the pepper fields.
Beneficial insects and mites are the most effective means of controlling thrips in greenhouse peppers throughout the world. Orius insidiosus, the insidious flower bug, prefers pepper flowers more than other greenhouse vegetables to the extent that they will establish self-generating populations after only a few introductions onto the peppers under long days. Because Orius prefers pepper plants, ornamental pepper plants are being used in large ornamental greenhouses to support the continuous reproduction of this important predator. Orius even reproduces on peppers when thrips are absent, surviving on pepper pollen alone. Neoseiulus cucumeris, a predatory mite that attacks first instar thrips larvae, also reproduces well on blooming pepper plants after only a few introductions. In a pepper greenhouse under biological control, thrips numbers and damage are extremely low, whereas predatory mites and Orius are relatively easy to detect. If greenhouse IPM practices could be applied to sweet pepper seedlings transplanted to the field, a more sustainable method of thrips control could be achieved.
In our 2005 SARE funded study, we observed that marigolds served as important habitat for the establishment and reproduction of the predator Orius in an herb greenhouse. Orius were almost never found in the herbs but were reliably found on the marigolds. In our 2009 study, we observed that marigolds actually served the role of Guardian Plants by drawing thrips away from adjacent crops as well as supporting the reproduction of Orius. Marigolds are inexpensive, easy to grow, and quick to flower. Because of their ability to protect peppers in the greenhouse, we proposed to determine if flowering marigold guardian plants would be able to support early season Orius reproduction in the field until the peppers began to flower.
Spider mites feed on and kill individual leaf cells, resulting in loss of photosynthetic capacity. Numerous spider mites result in irrecoverable leaf “bronzing”, which, when intense enough, causes leaf death. Intense spider mite pressure results in entire areas of the field where the leaves are bronze, brittle, or dead and the plants are incapable of producing any fruit at all. Less intense pressure, results in stunted plant growth and reduced fruit size.
The imidicloprid pesticide used in June to control Colorado potato beetle devastates the spider mite predator population in June. With no natural enemy suppression, the spider mites flare up, start bronzing the fields, and normally require 2 sprays in July and August. Therefore, developing a way of increasing natural enemy numbers when spider mites first begin to appear on the eggplants would reduce both pesticide spraying and crop loss.
The Zittels have been growing vegetables on farms located in Eden Valley for over 100 years. They farm over 300 acres of fresh market vegetables including cabbage, eggplant, lettuce, peppers, pumpkins and gourds, squash, strawberries, sweet corn and tomatoes. They use integrated pest management to maximize quality and production while at the same time minimizing pesticide usage and conserving water. They also farm three acres of greenhouse.
Before 2010, they focused their biological control efforts on the greenhouses, but in 2010, they began experimenting with bush beans as Guardian Plants for spider mite control in an eggplant field. Beans are particularly good trap plants for spider mites. In 2010, Mark Zittel planted bush beans down the middles of two tractor lanes in the field. These lanes were free of the pesticide imidicloprid. In late July and early August, he released the predatory mite Neoseiulus fallacis at the rate of 2 and 1 predator per square foot of beans, respectively. Several rows of eggplants and one of the bean rows remained unsprayed for the rest of the season.
In mid September, Carol Glenister inspected beans and eggplants with grower, Mark Zittel, professional scout, Karen Dean Hall, and vegetable specialist, Robert Hadad. They found that the predatory mites did establish and reproduce on the eggplants and were easy to find on the eggplants by the end of the season, with few spider mites surviving in the unsprayed rows adjacent to the beans. Predators were easy to find on both the beans and the eggplants up to 4 rows from the beans and heavily bronzed leaves were rare. Spider mite colonies were evident but in light numbers on the damaged leaves inspected but had completely disappeared from about a third of the damaged leaves inspected. Predators occurred in the spider mites on most of the damaged leaves inspected. In contrast, at the other end of the field where the normal miticides were used and no predators were released, heavily bronzed leaves could be found, about half of the damaged leaves inspected had excessive numbers of spider mites and predators could be found on only a few of the damaged leaves inspected. Although spider mite damage was obvious and unsightly on the senescing bean leaves, there were no leaves inspected that had excessive spider mites, and predators could be found on about half of the leaves.
It appeared that the unsprayed rows had the same or better spider mite control than the rows that had been sprayed twice with miticides. However, in 2010, we did not have the resources to document the damage levels, nor did we set up and observe controls where predators were released in the absence of beans to see if the beans were really necessary. We proposed to repeat this planting scheme for a second and third year under more controlled conditions combined with weekly scouting to gain information on whether or not bean Guardian Plants are able to support predator reproduction in the field until the imidicloprid wears off the eggplants, and thus make a judgment about the potential usefulness of this IPM method.
Our project was designed to be the first outdoor documentation of evaluating the potential of using Guardian Plants in field vegetables to pull pests out of crops and support natural enemy reproduction. We examined the ability of marigold Guardian Plant flowers to support early season Orius production until the field peppers developed flowers. We also examined the ability of snapbean Guardian Plants to support spider mite predator reproduction in eggplant fields until the pesticide imidicloprid wore off.
Although scientific research requires multiple fields and multiple farms, we proposed to concentrate our energies on in-depth weekly scouting of many plants in an individual field and compare them to the plants in a conventional field. The weekly scouting enabled us to track reproduction of the natural enemies. Reproduction is the single most important indicator of the predator’s continued ability to perform in the field. Furthermore, the in depth scouting would tell us how far the predators spread from the Guardian Plants so that we would have a better way to estimate how far apart Guardian Plants should be placed in the field. We felt efficacy trials in multiple fields were not appropriate until we had gathered baseline data with which to set up those trials. Thus, we tested the marigold Guardian Plant/pepper crop and the snapbean Guardian Plant/eggplant crop system in both 2011 and 2012.
In April 2011, Mark Zittel seeded marigolds in the greenhouse in time for flowering 2 to 3 weeks prior to transplanting the peppers. Weekly scouting on the peppers and marigolds began in the greenhouse on April 11, recording whole plant inspections counts of thrips nymphs, thrips adults, Orius nymphs, Orius adults, and the number of flowers in the beat sample(Photo 1). Once the flowers were abundant, Mark Zittel made 3 releases of 500 Orius adults onto the marigolds in the greenhouse at a one week intervals (May 5, May 12, and June 9). However, there was not obvious Orius establishment before they were transplanted to the field on June 14.
The marigolds were placed in the field in two spacings among the pepper plants. Individual marigolds were set into rows in one section of the field (Photo 2). The other section of the field had groupings of 30 marigolds (Photo 3) each to test a previous greenhouse observation that black pearl pepper plants support higher Orius production when they were in groups rather than when they are individually spaced. On June 16, one more release of 500 Orius was made directly onto the marigolds in the portion of the pepper field with the single marigold spacing and 500 in the portion of the pepper field with the block marigold spacing. An adjacent pepper field, under conventional pesticide management acted as the Control field and received no marigolds or Orius.
Scouting in the pepper fields concentrated on counts of number of flowers, thrips nymphs, thrips adults, Orius nymphs, and Orius adults from beat samples of 50 pepper plants and 30 marigolds per treatment. The weekly plant observations were charted on graphs in terms of number of thrips and Orius per beat sample on the marigolds and on the peppers.
In 2012, the marigold/pepper crop experiment was repeated in a modified manner. Mark Zittel seeded marigolds in the greenhouse so that they would be flowering at the time the peppers were to be transplanted to the field during the last week of May. However, since Orius had failed to establish on the marigolds in the greenhouse in 2011, no releases of Orius were made in the greenhouse in 2012.
The marigolds were transplanted to two pepper fields Bley Road and North Boston Road the last week of May. In 2011, two spacings for the marigolds were used: singles and blocks. However, in 2011 single marigolds were found not to provide any benefits over blocks and the single marigolds were harder to plant and water, so in 2012 only blocks were used (Photo 4). Approximately 6 blocks of 24 marigolds were used in each of the two fields. A third field with peppers only was designated as the Control field. One thousand Orius were applied to the marigolds in the Bley Road field on June 21. The North Boston Road field and the Control field received no Orius releases.
Weekly scouting of the three fields of was conducted from May 24 until July 5. Thirty marigold beat samples in the two experimental fields were taken during each visit. Fifty pepper samples were taken at each of five distances from the marigold blocks (adjacent, 30 feet, 60 feet, 90 feet, and 120 feet) in the experimental fields plus fifty pepper samples were taken in the control field. Since the Orius did not always fall out of the pepper flowers when they were beaten, the flowers were also visually inspected for Orius. The number of adults and the number of nymphs for both Orius and thrips were recorded as well as the general height of the plants, the number of flowers on the plant, and the number of flowers in the beat sample. In 2011, the pepper beat samples randomly included both flowering and non-flowering plants; however, in 2012 the pepper beat samples collected were mistakenly skewed towards flowering peppers. This mistake was not caught until the end of the 2012 season.
At the completion of the two seasons, the 2012 data was tabulated and compared to the 2011 data to determine if flowering marigold guardian plants could support early season Orius reproduction in the field until the peppers began to flower.
We proposed that success in the marigold/ pepper Guardian Plant System would be demonstrated by the following:
The presence of Orius nymphs in the marigold beat samples would be evidence of Orius establishment and reproduction.
Few thrips on the peppers and obvious thrips on the marigolds would be evidence that the marigolds were drawing thrips away from the pepper plants.
Low thrips numbers on the marigolds would be evidence that Orius was keeping the thrips numbers from exploding on the Guardian plants.
As the peppers began to flower, the Orius would be seen to transfer over to the pepper plants and reproduce on them as well.
Thrips numbers would subside with the expanding natural enemy population.
An eggplant field treated for Colorado potato beetle with imidicloprid via trickle irrigation on approximately June 1 and esfenvalerate spot sprays in mid June was divided in July into 4 experimental sections. The following treatments were applied (Map 4 and Photo 5): 1) snapbeans planted in the driving lane and treated with predators, 2) snapbeans planted in a driving lane but not treated with predators, 3) predators applied directly to the eggplants with no beans present, and 4) eggplant controls with no beans and no predators.
On July 26, two thousand Neoseiulus fallacis predators per row were applied on three 2000 foot rows of beans after spider mites began to appear on the beans. The release was repeated 2 weeks later on August 10. On those same dates, two thousand predators per row were applied on three 2000 foot rows of eggplants to assess if the predators could establish on the eggplants and thus did not require the presence of the bean Guardian Plants.
Weekly scouting of the eggplants and snapbeans began on August 2 and lasted through September 12. However, in late August, most of the treated eggplants were sprayed for mites with Agrimek and Nufilm P thus ending the experiment in the sprayed portions of the field. For each of the 4 treatments, during the scouting visit, 30 plants were selected that showed spider mite damage, the number of N. fallacis present were counted on one leaflet each, the level of spider mites present was rated on a scale of 0 to 3 that included both live mites and eggs (0 = gone, 1 = 1 to 9, 2 = 10 to 25, and 3 = 30 or more), the type of plant (bean or eggplant) was recorded along with the row number and the treatment type.
The scouting results were charted on graphs of weekly plant observations in terms of levels of spider mites and numbers of N. fallacis on 30 spider mite damaged leaves in each of the 4 experimental field sections. An exit survey was performed on September 12.
In 2012, a portion of this experiment was repeated to gain more data. All the beans and eggplants were in the ground by June 1, a much warmer, earlier year than 2011. Again, the eggplant rows were treated with imidicloprid for Colorado Potato Beetle through the trickle irrigation. In 2012, the eggplant field was divided into 3 groups of three treatments with one buffer row between each set of three treatments. For each group, a drive row was planted with snapbean guardian plants and then eight rows of eggplants were planted. This time, the beans were yellow beans. The three treatments were: control eggplants with no predators added, predators added to the snapbeans, and predators added to the eggplants. The bean row adjacent to the control eggplants with no predators was designated the bean control.
Weekly scouting of the fields was conducted from July 12 through August 23. One thousand Neoseiulus fallacis (carried on cut bean leaves) were released on each treated row on July 26 when spider mites began to appear on the beans and two thousand Neoseiulus fallacis (formulation in vermiculite) to each treated row on August 10. Observation of the three treatments began after the application of the predator (August 2 through August 23). During each visit the level of spider mites was estimated on 30 leaflets showing damage using the same scale of 0 to 3 used in 2011, the number of predators was counted, and the type of plant (bean or eggplant) was recorded along with the row number and the treatment type.
In 2012, spider mites and predators were found to be scarce on the snapbeans, therefore the only distance data collected was for eggplants 4 rows removed from the untreated eggplant control row (i.e., no predators applied), 1 row removed from the treated eggplant row, and 3 rows removed from the treated eggplant row. An exit survey was performed on September 20.
At the completion of the two seasons, the 2012 data was tabulated and compared to the 2011 data to determine if N. fallacis established in the field, if the beans were required for successful establishment of the predator or if releasing predators directly onto the eggplants was sufficient, and to see how far into the field the predator would spread from the treated eggplant rows.
We proposed that success in the eggplant/snapbean Guardian Plant System would be demonstrated if the following questions can be answered by the weekly scouting data:
Did the predators establish on the bean release rows as evidenced by increasing numbers over the season? And, if so, how far did the predators spread from the bean release row?
If there are no beans present, did the predators establish on the eggplant rows onto which they were released? And, if so, how far did the predators spread from the release row into the crop?
What are the spider mite and predator levels on the bean control row and the bean release row, and on eggplants at various distances from the bean release site?
What are the spider mite and predator levels on the eggplant control row and the eggplant release row, and on eggplants at various distances from the eggplant release site?
Do increased predator levels correlate to decreased spider mite levels?
- Photo 4: 2012 Marigolds at end of rows.
- Photo 5: Driving row with snapbeans in eggplant field.
- Map 1: Zittel Farm – Bean Guardian Plant/ Eggplant Crop 2011 Experiment Layout.
- Photo 1: Jamila Haseler scouting peppers in greenhouse.
- Photo 2: 2011 Single marigolds in pepper field.
- Photo 3: 2011 Marigold blocks in pepper field.
Orius did establish and reproduce on the marigolds as evidence by the presence of Orius nymphs on the marigolds. In Year 2011 (Table 1), Orius adults first appeared on the marigold blocks on June 21, five days after the field application of Orius on June 16. Orius nymphs appeared on both the marigold blocks and the marigold singles on June 29. The peppers began flowering on June 29. By July 12, both Orius adults and nymphs were detected on the peppers, thus providing evidence of transfer and reproduction. The peppers in the block treatment and the single treatment had similar average numbers of adult Orius per beat sample (0.38 and 0.30, respectively). The peppers in the control field also had Orius adults but at a level 2.8-fold lower that the treated fields (0.12). The presence of Orius in the control field indicated that a natural Orius population was present in the area.
In Year 2012 (Table 2), Orius adults first appeared on June 14, before the field application of Orius on June 16. Orius nymphs first appeared on the same day with 1 nymph per 4 to 5 marigold samples and 1 nymph per 50 pepper samples. The first Orius nymphs were detected in the control field on June 29, occurring at less than half the frequency of the marigold-enhanced fields. The peppers began flowering during the first week of June. By June 29, the frequency of adult Orius was about 1 per 5 samples on both the marigolds and the peppers. In 2012, we only scouted the fields until July 5, as we were short on funds. Up until June 28, thrips population decreased with increasing Orius populations (Table 3). After June 28, although thrips populations began to increase in all three fields, they remained at low levels and no pesticide treatments for thrips were required all season.
Table 4 shows the 2011 field data in terms of total thrips (adults plus nymphs) and total Orius (adults plus nymphs). Under both treatments, blocks and singles, few thrips are seen on the peppers and obvious thrips are seen on the marigolds. Although the ratio varies throughout the season, the season average for thrips on the marigold blocks is 4.9-fold higher than the peppers (1.75 compared to 0.36). The season average for thrips on the marigold singles is 4.4-fold higher than the peppers (1.33 compared to 0.30). The season average for thrips on the untreated pepper control group is comparable to the marigolds: marigold blocks 1.75, marigold singles 1.33, and pepper control group 1.51. This data suggests that the marigolds were drawing thrips away from the pepper plants and provided a convenient location for scouting to evaluate the number of thrips per Orius in the field.
Table 4 also shows that the average numbers of thrips on the marigold blocks was a maximum of 3.27 and averaged 1.75 for the whole season. For the marigold singles the maximum of 2.60 and averaged 1.33 for the season. These thrips numbers are all relatively low (5 or more thrips per beat sample might be considered a decision point). These numbers suggest that the Orius was keeping the thrips numbers from exploding on the Guardian plants. In addition, no sprays were required during the 2011 season to control thrips.
In general, peak thrips numbers subsided with expanding Orius populations. For the marigold blocks and the peppers in the marigold singles treatment, the average numbers of thrips were still rising at the time of the Exit survey on July 26 (3.27 and 0.88, respectively). For the marigold singles, thrips peaked on July 18 at 2.60 and decreased to 1.53 on July 26. For the peppers in the block treatment, thrips peaked on July 18 at 1.06 and decreased to 0.36 by July 26. For the pepper controls which had no marigolds and no added Orius, thrips peaked on July 12 at 6.36 (approximately 6-fold higher than the peaks for the peppers in either the block or the singles treatments). Thrips in the control pepper group decreased to 0.64 by July 26.
In 2011, the single marigold treatment was not found to provide any added benefit over the block treatment. In addition, the single marigolds were harder to water and to scout. Therefore, in 2012 only the block treatment was repeated.
In both 2011 and 2012, the thrips predator Orius established and reproduced on the marigolds prior to the peppers as evidenced by the presence of the first Orius nymphs on the marigolds (July 29 in 2011 and multiple nymphs on June 14 in 2012). In 2011, peppers began flowering by June 29 and by July 12, both Orius adults and nymphs were detected on the peppers (Figure 1). In 2012, the peppers began flowering by June 5 and a single Orius nymph was detected on June 14, but it took until the June 28 observations before the numbers of Orius nymphs on the peppers caught up to the numbers on the marigolds (Figure 2). Few thrips were seen on the peppers and obvious thrips were seen on the marigolds in 2011 (Figure 3). In 2012, when the marigolds were on the edge of the field, the thrips numbers on the peppers and marigolds tracked closer to each other (Figures 4 and 5).
By the close of each year’s dataset, Orius numbers and thrips to Orius ratios in all pepper fields were utterly astounding. There were more than one Orius per sample where each sample was a small portion of a pepper plant. Thrips to Orius ratios should give some indication of the balance between predator and pest. By the last observation on July 26, 2011, there were less than 1 thrips per Orius on the peppers. In 2012 on July 5, there were about 1 thrips per Orius on the peppers. These ratios are extremely favorable given that Orius can kill 5 to 20 thrips per day.
No insecticide treatment for thrips were required in 2011 or 2012 and Mark Zittel considered the thrips numbers as being extremely low given that in 2010 he had seen 8 or more thrips in pepper flowers despite repeated pesticide treatments.
The predators did establish on the bean release row as evidenced by increasing numbers over the season. In Year 2011 (Table 5), predators were first detected on the bean release row on August 15, 20 days after the first predator application and 5 days after the 2nd application. Over the next 4 weeks, the average number of predators per sample increased 2.4-fold (from 0.10 to 0.24). During the Exit survey, predators were found on eggplants 1, 2, and 4 rows away from the bean release row at average levels per sample of 0.67, 0.20, and 0.15, respectively. Interestingly, the highest average number of predators per sample was found on the eggplants 1 row away from the bean release row. They were 2.8-fold higher than the adjacent bean row (0.67 compared to 0.24). Predators were not found on the bean control row.
The predators were also found to establish on the eggplant release row as evidenced by increasing numbers over the season. Like the bean release row, predators were first detected on the eggplant release row on August 15, 20 days after the first predator application and 5 days after the 2nd predator application. Over the next 4 weeks, the average number of predators per sample increased 8-fold (from 0.10 to 0.80). During the Exit survey, predators were found on eggplants 2 and 4 rows away from the eggplant release row at average levels per sample of 0.44 and 0.55, respectively. (Note: The eggplant row adjacent to the eggplant release row was not sampled in Year 2011.) Interestingly, the average number of predators per sample was found to be 3.3-fold higher on the eggplant release row than on the bean release row (0.80 compared to 0.24). This data indicates that bean Guardian plants are not required for the establishment and spread of predators in the eggplant fields.
Spider mites levels were judged on a scale of 0 to 3, which included both live mites and eggs (0 = gone, 1 = 1 to 9, 2 = 10 to 25, and 3 = 30 or more). Spider mites were found to peak between August 15 and August 30 for both the bean and the eggplant rows. When the exit survey was conducted on September 12, spider mite levels had decreased under all treatments except the eggplant controls. The level of spider mites in the eggplant control row increased 2.3-fold from August 15 to September 12 (0.87 to 2.03). However, a clear correlation between increasing predator numbers and decreasing spider mite level could not be established because no predators were ever detected on the bean control row during the season, yet the spider mite levels in the bean control row decreased from a high of 2.73 on August 15 to zero on September 12.
In Year 2012, a portion of the bean/eggplant experiment was repeated. Since, in 2011, it was found that the predators could establish on the eggplant release row and spread into the field, distance data from the bean release row was not collected. Table 6 shows predators were first detected on the bean release row on August 9, 14 days after the 1st application of 2000 predators which occurred on July 26. Over the next 4 weeks, the average number of predators per sample increased 6-fold (from 0.10 to 0.60). Predators were found on the bean control row on August 17 but in very low numbers (an average of 0.03 per sample). During the exit survey on September 20, predators on the bean control row had increased 4.3-fold (from 0.03 to 0.13) but were still at very low numbers.
The predators were again found to establish on the eggplant release row. Predators were first detected on the eggplant release row on August 2, 7 days after the 1st application of 2000 predators. Predator numbers peaked on August 17 and were 5.3-fold higher than when first detected (0.53 compared to 0.10). However, predator numbers on the release row then declined for the rest of the season and were 2.7-fold lower during the Exit survey on September 20 (0.20). During the Exit survey, predators were found on eggplants 3 rows away from the eggplant release row at a number similar to the release row (0.27 compared to 0.20). However, no predators were observed on eggplants 1 row away or 4 rows away from the eggplant release row.
For the eggplant control data that was collected in the experimental field, on August 17 predators were found to be present in the eggplant control row at an average number of 0.13 per sample. This level dropped to zero on August 23 and rose to 0.40 during the September 20 Exit survey.
In 2012, spider mites levels were again judged on the scale of 0 to 3. Spider mites levels were found to peak on August 9 for the beans and on August 23 for the eggplants. Average peak levels per sample were comparable for all treatments: bean control row (2.37), bean release row (2.37), eggplant control row (2.37), and eggplant release row (2.43). When the Exit survey was conducted on September 20, spider mite levels had decreased in all treatments rows. For the beans, the bean release row had a 4.6-fold higher average number of predators compared to the bean control (0.60 compared to 0.16) and the release row had approximately 1/3 the average level of spider mites (0.25 compared to 0.67). However, for the eggplants, a clear correlation between increasing predator numbers and decreasing spider mite level could not be established. The eggplant release row had 1/2 the control row’s average number of predators (0.20 compared to 0.40) but both rows had similar levels of spider mites (1.03 for the release row and 1.10 for the control row). Similarly, the eggplant rows 1 and 4 rows away from the eggplant release row had zero predators but had reduced spider mites (0.20 and 0.56), whereas the eggplants 3 rows away from the eggplant release row had an average number of predators of 0.27 and an average level of spider mites of 1.27. Overall, it appeared that the number of predators was linked to the numbers of prey available, indicating that the predators were travelling easily.
In 2011 and 2012 the predatory mites established on the bean release rows and increased over the season. But where no beans were present, the predators established equally well on eggplant release rows. In both cases, predators were detected as far as 4 rows away from the row where they were released. (Figures 6 and 7). The predators appeared to be extremely mobile and more numerous wherever the spider mites were more numerous. In this part of the trial, our beans did not provide the Guardian Plant services that we were hoping for since the treated eggplants usually appeared to have more predators than the treated beans. However, the number of miticide treatments was reduced from 3 sprays in 2010, to a half of the field sprayed once in 2011 and no sprays in 2012.
- Table 1: 2011 Weekly average Orius and thrips counts by lifestage on samples of marigolds and peppers under different marigold treatments: Blocks, Singles, and no marigolds (None). In these data, adults are distinguished from immatures (A = adults, N = nymphs).
- Table 2: 2012 Weekly average Orius and thrips counts by lifestage on samples of marigolds and peppers compared to peppers with no marigolds at 2 sites compared to a control at N. Boston Rd. In these data, adults are distinguished from immatures (A = adults, N = nymphs).
- Table 4: 2011 Weekly average Orius and thrips counts on samples of marigolds and peppers under different marigold treatments: Blocks, Singles, and no marigolds (None). In these data, adults are not distinguished from immatures.
- Figure 1: Year 2011 counts of totals of Orius adults and nymphs on marigold and peppers in the marigold block treatment.
- Figure 2: Year 2012 average numbers of Orius nymphs in pepper fields on marigolds and on peppers (P = peppers, M = marigolds). Boston and Bley Roads were 2 different pepper fields. The third control field had no marigolds and was at the N. Boston Road site.
- Figure 3: Year 2011 thrips counts on marigolds and peppers under the marigold blocks treatment.
- Figure 4: Average number of thrips on marigolds and peppers and average number of Orius on marigolds at Bley Rd site.
- Figure 5: Average number of thrips on marigolds and peppers and average number of Orius on marigolds at No Boston Rd site.
- Figure 6: Year 2011 exit survey of spider mite and predator mite numbers on eggplants and bean plants conducted on September 12 and 13, 2012. (B = Bean, C = Control, E = Eggplant, P = Predators added, 1B = one row over from Bean release row, 2B = two rows over from Bean release row, 4B = four rows over from Bean release row, 2E = one row over from Eggplant release row, 3E = three rows over from Eggplant release row).
- Figure 7: Year 2012 exit survey of spider mite and predator mite numbers on eggplants and bean plants conducted on September 12 and 13, 2012. (B = Bean, C = Control, E = Eggplant, +P = Predators added, 1E = one row over from Eggplant release row, 3E = three rows over from Eggplant release row, 4EC = three rows over from eggplant control).
- Table 3: 2012 Weekly average Orius and thrips counts on samples of marigolds and peppers compared to peppers with no marigolds at 2 sites compared to a control at N. Boston Rd. In these data, adults are not distinguished from immatures.
- Table 5: Average spider mite and predator observations on eggplant and bean samples in 2011. The predators were counted individually. The spider mite levels were recorded on a scale of 0 to 3 documenting the presence of live spider mites and eggs (0 = gone, 1 = 1 to 9, 2 = 10 to 25, and 3 = 30 or more).
- Table 6: Average spider mite and predator observations on eggplants and bean samples in 2012. The spider mite levels were recorded on a scale of 0 to 3 documenting the presence of live spider mites and eggs (0 = gone, 1 = 1 to 9, 2 = 10 to 25, and 3 = 30 or more).
Local growers became aware of Orius, their natural resource that will automatically control thrips with no sprays, given the chance. Thrips numbers and their damage were substantially lower with no thrips sprays in 2011 and 2012 than they were in 2010 with 5 thrips sprays. Naturally abundant Orius registered more than one per flower.
Mark Zittel shared the discovery of abundant Orius by helping local growers search in their own pepper and eggplant fields all over the region. The growers’ natural reaction to this knowledge is to exercise great care when contemplating pesticide use. He planted marigolds in his pepper fields again in 2013 of his own choosing. A nearby farmer is contemplating planting marigolds in his cucurbit fields to see if they will help him with thrips control.
This is the first time that the Guardian Plant concept, which was developed in greenhouse crops, has been tested outdoors. The work gives us data on the possible functions of traditional companion plants and a structured way to assess future crop/Guardian Plant combinations. It was most fortunate that we tested 2 combinations: one successful, and the other not. Paradoxically, beans are used as Guardian Plants for spider mite control in greenhouse tomatoes, while marigolds are not used in greenhouse peppers.
Education & Outreach Activities and Participation Summary
Mark Zittel noticed in mid-July 2011 that Orius was naturally occurring in 1 out of 3 eggplant flowers. This created impromptu Orius-scouting sessions on the neighboring farms. The local pesticide salesman, an unexpected contributor, Russ Yoho, even used Orius as a talking point with his pesticide customers.
Carol Glenister gave a PowerPoint presentation at the Mid-Atlantic Fruit and Vegetable Conference in Hershey, PA on February 1, 2012 entitled: Using Guardian Plants in High Tunnel Biocontrol Programs
Carol Glenister and Mark Zittel gave a joint PowerPoint presentation at the Western NY Vegetable Growers Meeting in Lockport, NY on February 27, 2012 entitled: Biocontrol of Thrips and Spider Mites in Peppers and Eggplants Using Guardian Plants (Presentation 1). This presentation is also available on the web at www.IPMlabs.com.
Robert Hadad of Cornell Cooperative Extension organized a twilight field meeting at the experimental fields on the Zittel farm on August 27, 2012 for local growers to see the predators in action. Carol Glenister participated in this twilight meeting.
A two-sided full color flyer entitled What is a Guardian Plant? was developed that explains the Guardian Plant concept and predators (Flyer 1 – the flyer is intended to folded into 3 sections). The flyer is available on the Web at www.IPMlabs.com. This flyer was handed out at the twilight field meeting organized by Robert Hadad. and at every relevant meeting that Carol has made a presentation at, including venues in New York, New Hampshire, Minnesota, and Pennsylvania.
Naturally-occurring Orius were free-of-charge to the farmers in both the marigold and the control fields and thrips numbers were lower than growers have observed with pesticides.
Traditionally, pesticide sales are driven by the presence or expectation of pests that will reduce yields, creating economic loss. This research showed that the cost of the spray was not good insurance, because the sprays actually created greater expense and damage by killing the naturally-occurring, free of charge thrips predators.
Mark Zittel is very adept at searching for Orius and committed to selecting pesticides that will not harm the Orius in his pepper fields. And, local farmer, Dan Henry, plans to test marigolds in a cucumber field in 2013.
Dennis Brawdy of D&J Brawdy October 1, 2012:
“I haven’t seen a pepper come in with thrips yet this year. We did not spray once this summer. Last summer, we sprayed all summer and still saw 15 to 20 thrips per blossom. This year when we saw 4 to 5 thrips per blossom, we held off spraying to see what the Orius would do.” [Then the Orius showed up and took care of the thrips.]
Mark Zittel of Amos Zittel & Sons, October 1, 2012:
I didn’t spray an insecticide in the peppers all year…that’s unheard of!” (He relied on Orius to control the thrips. Orius successful for 2 possible reasons: no Orthene on transplants for aphid control, and marigold guardian plants in the greenhouse and in the field). “I haven’t sprayed thrips in the field for 2 years now.”
Areas needing additional study
The remaining question is: Are the marigolds necessary if they only give the Orius a two week head start before the peppers start to bloom? If Orius are overwintering in nearby hedgerows, the character of the overwintering sites may be the biggest indicator of natural Orius populations. Thus, the value of marigolds in attracting early arrivals of Orius will vary with the species composition in the hedgerows. The less appropriate the hedgerows are for overwintering Orius, the more important the marigolds will become for arresting Orius dispersal.