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; however, in 2020 the PL will attempt these again on bean leaves, incorporated into tomato plantings as indicator plants, where the leaves may be better suited for these methods compared to tomato leaves.
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. This was to be expected, especially regarding beans, which we will be using as indicator plants in 2020 for this very reason.
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.
Trialing different scouting methods helped to shape the scouting and data gathering plans for 2020, with the 0-9 damage scale emerging as the most easily adopted and useful so far.