Progress report for ONE19-327
This project is one of the first to directly address two-spotted spider mite (TSSM) as a pest of particular importance for outdoor urban agriculture. The project seeks to develop and demonstrate best practices for controlling TSSM on New York City urban farms through release and recruitment of natural enemies. It also seeks to enhance skills and knowledge among urban farmers related to scouting and pest management, and to deepen urban farmers’ understanding of natural enemies’ role in controlling TSSM and other pest populations.
Preliminary work in 2019 included gathering baseline data on four urban farms, using a damage rating scale to track presence and severity of TSSM, focusing especially on tomato plants. Early results reinforce the widespread presence and significance of TSSM as a pest of tomatoes, cucumbers, pole and bush beans, and eggplant on urban farms in NYC. Farmers at each of the four farms were included in scouting and results and implications discussed; meetings with these farmers informed work plans for 2020.
This project seeks to develop and demonstrate best practices for controlling TSSM on NYC urban farms through release and recruitment of natural enemies. It also seeks to enhance skills and knowledge among urban farmers related to scouting and pest management, and to deepen urban farmers’ understanding of natural enemies’ role in controlling TSSM and other pest populations.
By tracking TSSM and natural enemy populations on urban farms, we aim to contribute to a presently limited body of knowledge related to TSSM as an urban agriculture pest of importance; the effectiveness of biocontrols in managing TSSM on field tomatoes in urban environments; and the ability of urban agroecosystems to recruit and maintain populations of beneficial arthropods, including the ability of Feltiella and N. fallacis to persist throughout a growing season and to overwinter when provided habitat options for those express purposes.
If successful, this project will benefit farmers by developing an effective IPM strategy for management of TSSM in urban agriculture, including readily adopted protocols for scouting, incorporating an “early warning” system with indicator plants, and release, recruitment, and maintenance of natural enemy populations. Farmers will also benefit from increased knowledge of IPM principles applied to urban agriculture.
Two-spotted spider mite (TSSM) is a common pest of several vegetable, fruit, and ornamental crops in the Northeast, both in greenhouses and in field production. Based on Extension specialists’ observations, TSSM was a common and costly pest of outdoor vegetable crops on NYC commercial urban farms in 2017 and 2018, particularly on tomatoes, and an earlier study found TSSM widely present at damaging levels on tomatoes in NYC gardens (Gregory et. al 2016). Extension vegetable specialists outside of the city have reported a considerably lower frequency of TSSM outbreaks in field tomato production. A review of prior research on TSSM and on urban environments, combined with specialists’ and producers’ observations, suggest that TSSM is likely a pest of particular importance to urban agriculture—although this project would be one of the first to directly approach it as such.
TSSM thrives in hot, dry weather, resulting in rapid population explosions (White and Liburd 2005). These conditions are exacerbated in urban areas due to the urban heat island effect; on summer nights, NYC temperatures are on average 4°C warmer than surrounding rural areas (Rosenzweig et. al 2009). (Incidentally, increased urban agriculture, including on rooftops, is a recognized strategy for reducing the urban heat island effect [Phelan et. al 2015].)
In field settings, TSSM is often controlled by the presence of natural enemies. The absence of natural enemies in greenhouse production leads many greenhouse growers to release predatory mites, midges, and other biocontrols to keep TSSM populations in check (Opit et. al 2009). These practices may also be applied in commercial outdoor tomato production, where agricultural practices such as monocropping and insecticide overuse may favor TSSM development and repress its natural enemies (Meck et. al 2013). Whereas naturally occurring beneficial arthropods may control TSSM populations in rural production, these species may appear less frequently in urban environments (Gregory et. al 2016).
Chemical controls have shown limited success due to TSSM’s ability to rapidly develop resistance (Keskin and Kumral 2015); furthermore, urban agriculture producers often demonstrate an aversion to chemical controls.
All of these factors suggest an opportunity to assess the viability of releasing TSSM biocontrols and explore practices to maintain released and naturally occurring biocontrol populations in urban agriculture settings. This project will be perhaps the first to directly track TSSM and natural enemy populations on urban farms over the course of multiple seasons, and certainly the first to do so while trialing the release of biocontrols.
Scouting for TSSM on tomato leaves is difficult, and by the time stippling damage is observed, production may already be affected. Meck (2010) found that staked outdoor tomatoes in western North Carolina showed a very low tolerance to TSSM, with economically important thresholds of 0.55 to 3.85 mites per leaflet. Carol Glenister, a collaborator on this project, has demonstrated the effectiveness of bush beans as indicator plants in tomato rows, due to their tendency to show TSSM damage before tomatoes and the greater ease of scouting bean leaves (Glenister 2017). This project will build on that strategy, developing a suggested protocol for its adoption as part of tomato IPM in urban agriculture.
Neoseiulus fallacis and Feltiella acarisuga are commercially available biocontrols, typically released as preventative measures before TSSM outbreaks, with some potential to persist in the environment. While overwintering of both species has been studied in some agricultural settings (Morris et. al 1996, Abe et. al 2011), we do not know if either will overwinter in an urban environment, or whether they will successfully re-disperse into crops the following year. We also have very limited information about the presence, abundance, and effectiveness of TSSM natural enemies in NYC (Gregory et. al 2016); while a full account is beyond the scope of this project, natural enemy counts collected through this project may lay the groundwork for further investigation.
Phytoseiulus persimilis is another commercially available TSSM biocontrol, typically used as a quick response when TSSM populations are observed beyond an acceptable threshold. We will trial its use in the same manner in urban agriculture, under advisement of IPM Labs. One of our participating urban farms purchased and released P. persimilis previously, but found it ineffective, most likely because it was applied too late in the TSSM outbreak. By using indicator plants and a weekly scouting protocol, this project will implement an “early warning” system. If TSSM reaches a predetermined threshold on indicator plants, we may have the opportunity to demonstrate P. persimilis as an effective biocontrol when used in combination with an early warning system.
Between August 27 and September 5, 2019, farm visits were conducted at each of the three cooperating farms and one additional urban farm. At each site, tomato plantings were scouted for twospotted spider mite (TSSM) presence and damage. Damage ratings were determined by a visual assessment of leaf stippling and browning. In each planting, three rows were chosen, and within each row three locations were scouted. Damage was assigned to plants by three sections, divided vertically (bottom third, middle third, top third), with each third given a damage rating between 0-3, added together to assign a 0-9 damage rating for each scouted section. This served both as baseline data for the project and as practice, an opportunity to try out scouting methods and see what fits the sites and what methods might be realistically adopted by farmers themselves. Farmers were consulted and participated in scouting at most of the sites, and through this process a scouting plan was outlined for 2020.
Farm visits conducted at four urban farms. Project Leader (PL) gathered baseline data and trialed scouting methods for two-spotted spider mite (TSSM) in tomato plantings, as well as trialing scouting of cucumbers, pole and bush beans, and eggplant. As part of each visit, PL demonstrated the trialed scouting methods to farmers, shared results, and discussed implications of results. Followup included sharing resources about TSSM life cycle, prevention, and biocontrols.
Other scouting methods were trialed at each farm, including the "tap test" -- placing a sheet of paper beneath leaves, tapping the leaves, and counting numbers of mites and other arthropods on the paper -- and visually scouting leaf undersides with a hand lens to gather mite and other arthropod counts. Data from those methods was deemed not sufficient or accurate enough to use as baseline data, and not realistic for farmer adoption.
In 2020, four urban farms planted bush beans at tomato row ends and scouted bean leaves on a weekly basis for twospotted spider mite (TSSM) damage. PL visited each site 4 times during the season, at each visit scouting beans and tomatoes for twospotted spider mite damage and recording damage levels on tomatoes on the same 0-9 scale used in 2019 baseline scouting, as well as scouting with a hand lens and "tap test" to verify TSSM, natural enemies, and other arthropods on leaves. All findings were shared with farmers. One farmer also collected her own damage ratings in July. At all farms, beneficial mites and midges were released in response to the appearance of TSSM and in anticipation of conditions favorable to TSSM, all in close consultation with Carol Glenister of IPM Labs (also the supplier of the biocontrols). The PL was present for initial releases at each farm, with farmers and PL both conducting additional releases in following weeks.
Damage ratings in 2020 were taken three times (in July and August) in 6 to 8 locations within each tomato planting studied. In order to illustrate progression of TSSM populations, ratings were measured in the same location each visit. These results are being analyzed in January and February 2021 to determine any sampling adjustments needed in 2021.
Data gathered in 2019 was preliminary and exploratory, but may serve as baseline data for twospotted spider mite (TSSM) damage going forward. Using a damage scale of 0-9 (with intervals of 0.5) for each row section (3 plants), with three sections selected in each of three rows per farm, ratings in each row section ranged from 1 to 8. Average ratings for the four farms were 2.7, 3.5, 5.5, and 7.0 in tomato plantings.
Where available, baseline data was also gathered (using the same 0-9 scale and 3 sections/row sampling) for cucumbers, beans, and eggplant on the same four farms. Cucumber damage average 7 and 7.5 on two farms scouted; pole and bush beans averaged 8 on each of two farms; and eggplant averaged 2.5, 4.5, and 6 on three farms. Relative to tomatoes on the same farms, cucumbers and beans had higher damage ratings, while eggplant was mixed in relation to tomatoes.
In 2020, PL scouting data and damage assessments showed very little TSSM presence in early July, a gradual increase in mid and late July, followed by rapid population explosions in early and mid August at three of the four sites, with damage ratings climbing from averages of 0.5 to 2 (out of 9) in July, to -- at the two most affected sites -- no less than 6/9 at every sampled location in mid to late August. At three of four sites, TSSM essentially ended the tomato season by the end of August, as it had the prior year. While biocontrols were released at all sites, N. fallacis was never identified in followup scouting, and Feltiella was seen only three times. Persimilis, however, was more readily observed; and although data at this point is strictly anecdotal, persimilis releases appeared to correspond with slowing the advance of TSSM damage. This will be an area for more careful observation in 2021.
One site showed much less TSSM damage than the other three, despite no significant differences in release of biocontrols. At this site, in addition to beans at row ends, the farmer planted a row of beans parallel to one of six rows of tomatoes in the studied planting; at a visit in July, the beans showed small amounts of TSSM damage, but also a particularly high concentration of minute pirate bugs (aka Orius), both adults and nymphs, known predators of TSSM. This raises the possibility of Orius as a significant naturally occurring predator of TSSM; since Orius nymphs are only occasionally seen on tomatoes, it also raises the possibility of beans as banker plants for both Orius and N. fallacis.
The above preliminary data demonstrated the widespread presence and severity of TSSM as a pest of tomatoes and other crops on urban farms. No significant trends appeared regarding severity of damage based on locations within rows, except that damage tended to be more similar within rows than between rows. Tomatoes are typically planted densely on urban farms, which may allow TSSM to move freely between plants within the row.
Piloting beans at row ends for TSSM scouting returned mixed results; we will attempt it again in 2021, with farmers now more aware of what to watch for, and when. The 0-9 damage scale worked well as a repeatable method of assessing TSSM impact within tomato plantings. Released biocontrols appeared to have limited impact on TSSM populations, with the possible exception of Persimilis; however, in 2021 we will apply a lesson from 2020 and release N. fallacis on beans as a preventative measure in late June, regardless of scouting results; Feltiella will be released two weeks later, again regardless of scouting results; and at the first sign of TSSM on row-end beans, Persimilis will be purchased to release ASAP on neighboring tomatoes.
Preliminary results from one farm also raise the possibility of adopting larger plantings of beans (beyond row ends) as banker plants for populations of Orius and perhaps N. fallacis, to be discussed with participating farmers for possible adoption in 2021.
Education & Outreach Activities and Participation Summary
The PL visited four urban farms four times each for scouting and release of natural enemies, consulting with farmers on each visit and demonstrating the techniques applied. Throughout all of this, farm managers and other farm staff learned about the life cycles and habits of TSSM and natural enemies, and piloted new methods of scouting for TSSM damage -- all of which can be translated into IPM for other pests and vegetable crops. While much of the consultation occurred remotely, due partially to COVID restrictions, farm visits proceeded mostly as planned starting in June with distancing, masks, and other safety measures in place.
As part of this project, collaborators Carol Glenister and Amara Dunn (NYS IPM Center) were each featured in an online workshop, respectively: Integrated Pest Management for Urban Farmers (7/1/20, 60 participants) and Attracting Beneficial Insects to Urban Farms (8/4/20, 34 participants). Additionally, PL Sam Anderson (Cornell Cooperative Extension) shared this project and other TSSM management information in a session at The Urban Farmer-to-Farmer Summit (12/5/20, 84 participants in session).
Through the CCE urban agriculture program's newsletter (250+ subscribers, 60% open rate), Anderson shared TSSM information gathered from this project, including notifications of TSSM status across the city and strategies for managing it.
Across the four participating farms, 11 farmers gained knowledge through direct consultation and conversations related to the project; all four farms adopted new scouting protocols, and four farms (two participating and two additional sites) developed their own relationships with IPM Labs, with plans to purchase biocontrols in future years.
Across three workshops, 106 farmers participated. Beyond the four collaborating farms, an additional 19 farmers specifically reported increased knowledge about IPM practices.
Preliminary project outcomes include four farms adopting new scouting techniques for TSSM and incorporating the use of biocontrols as an IPM strategy. More measurable outcomes are expected after 2021, including estimates of cost reduction, yield improvements, and farmers' stress levels.