Two-spotted Spider Mite IPM for Urban Agriculture

Final report for ONE19-327

Project Type: Partnership
Funds awarded in 2019: $20,836.00
Projected End Date: 09/30/2021
Grant Recipient: Cornell University
Region: Northeast
State: New York
Project Leader:
Samuel Anderson
Cornell Cooperative Extension, Harvest NY
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Project Information

Summary:

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.

Project Objectives:

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.

Introduction:

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.

Cooperators

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  • Brendan Parker
  • Liz Dowd
  • Jeremy Teperman

Research

Materials and methods:

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. In 2021, the same scouting protocols were followed. Releases began earlier (first week of July); at three farms, releases focused on P. Persimilis and Feltiella acarisuga. A fourth farm was substituted into the study as a previously participating farm withdrew due to a management change; at the new farm, N. fallacis was released, with those results not expected until 2022.

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. In 2021, damage ratings were taken four times at three participating farms, using the same methodology. Additional damage ratings were measured at 6 other farms in July and August for comparison.

Research results and discussion:

Across the two full growing seasons of the grant (2020-21), regular scouting for twospotted spider mite (TSSM) damage in tomato plantings at three urban farms illustrated the arc of TSSM pressure in New York City. In both years, TSSM was  typically present at low levels in early July, reached damaging levels by early August, and caused severe damage or crop loss by early September. (See Tables 1 and 2 below, and attached chart, "TSSM progression in fields.") Scouting at these three farms and at eight others in New York City confirmed TSSM as the most damaging pest or disease of tomatoes on most urban farms. When damage scores are mapped onto fields (see the previously mentioned chart), TSSM infestations appear to start from one or two initial "hot spots," starting somewhat slowly and then spreading to often affect the entire planting. Scouting for these hot spots and targeting them for early treatment may be a key to TSSM control.

All three farms planted bean plants at row ends of the studied tomato plantings, with farmers at all sites indicating a low barrier to adoption. In the second year of the project, farmers at every participating site clearly demonstrated both an improved ability and increased likelihood to scout for TSSM on beans and tomatoes, as well as on other crops such as cucumbers and eggplants. Given the low awareness of TSSM among urban farmers at the start of the project, this is an especially encouraging outcome.

Results of natural enemy releases (P. persimilis, N. fallacis, Feltiella acarisuga) in these tomato plantings were largely inconclusive in terms of TSSM control, although there is reason to believe that P. persimilis can play a role in controlling TSSM in these settings. On one farm, persimilis was released twice in one part of a tomato planting (treatment) and not in the rest (control); in September, damage scores in the control area averaged 5.8, compared to 3.5 in the treatment area. This shows promise, but requires more data. On two other farms, TSSM damage appeared to level off in July after two releases of persimilis, although in August the TSSM damage at both sites increased rapidly and resulted in crop loss by early September. (Tables 1 and 2.)

Table 1. Average TSSM damage scores (0 to 9) in tomato plantings at NYC urban farms in 2020.

  17-Jul 31-Jul 3-Sep  
Farm A 0.0 3.0 8.0  
Farm B 0.6 2.3 7.4  
Farm C 0.0 0.5 1.2  
 Average (all farms) 0.2 1.9 5.5  

Table 2. Average TSSM damage scores (0 to 9) in tomato plantings at NYC urban farms in 2021. (Same farms as 2020.)

  2-Jul 16-Jul 18-Aug 23-Sep
Farm A 1.7 2.2 5.3 9.0*
Farm B 0.0 0.2 3.8 7.8**
Farm C 0.1 0.6 3.0 4.7
Average (all farms) 0.6 1.0 4.0 7.2

* Tomato crop removed 1-2 weeks prior due to TSSM damage.
** 80% of tomato crop removed 1 week prior due to TSSM and bacterial canker damage.

In both years, Farm C experienced significantly less TSSM damage than the other farms, despite no significant differences in treatment (scouting protocol and release of biocontrols). TSSM damage was especially low here in 2020, where every sample location except for one scored 1 or less. That year, in addition to beans at row ends, the farmer planted a row of beans alongside the tomatoes within the 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 (1 to 2 individuals per bean leaf). Orius also appeared on the nearby tomatoes (1 individual per 10 tomato leaves). This raises the possibility of Orius as a significant naturally occurring predator of TSSM; it also raises the possibility of beans as banker plants for Orius.

At another farm in 2021, where no natural enemies were released, one tomato planting in late August showed severe TSSM damage (6.8 average damage score), while a nearby planting at the same site showed far less damage (2.3 average damage score). Alongside the less-damaged tomatoes, marigolds had been planted every 4 to 6 feet, the entire length of the row. Orius adults were observed on the less-damaged tomatoes (1 individual per 12 leaves) and on the marigolds (1 individual per 3 plants), suggesting marigolds as another possible banker plant for Orius. 

At the 13 additional NYC urban farms scouted in 2020 or 2021, most tomatoes showed TSSM damage similar to or worse than the three participating farms. However, three sites had unusually low levels of TSSM on their tomatoes. Unlike any of the farms with high levels of TSSM, two of these watered their tomatoes with overhead irrigation daily; the other used a high tunnel with very limited ventilation, resulting in a humid microclimate. In other words, humidity and/or leaf wetness correlated strongly with reduced TSSM pressure, as we might expect. However, as we might also expect, all three of these tomato plantings exhibited substantial foliar disease (bacterial speck, gray mold, possible late blight) with loss of yield. 

Research conclusions:

The above data demonstrated the widespread presence and severity of TSSM as a pest of tomatoes and other crops on urban farms, as well as the expected timing of damage during the season, information which will help urban farmers to anticipate and scout for TSSM. Observations from both years also showed a tendency for TSSM to establish in perhaps one or two "hot spots" within a tomato planting before spreading throughout the field. This may be especially important information, both for TSSM scouting and for management; if "hot spots" can be located early and targeted, it may delay the advent of serious TSSM infestation in the rest of the planting. 

The 0-9 damage scale worked well as a repeatable method of assessing TSSM impact within tomato plantings, and will likely be used by PL for future IPM projects and continued monitoring of TSSM in particular.

Planting beans at tomato (and cucumber) row ends as sentry plants for TSSM scouting returned mixed results in 2020, but proved useful and replicable in 2021 with increased participant awareness of TSSM damage and significance as a major pest, and all three participating farms plan to continue using this strategy. 

The strategy of managing TSSM by releasing purchased biocontrols showed promise for many types of urban agriculture; as mentioned above, at least four farms plan to purchase persimilis after learning about it through this project. Urban farms are less likely to purchase Feltiella acarisuga, due to its higher cost and less clear utility; or N. fallacis, due to its slower mode of action, although some interest remains in fallicis at smaller farms and gardens because it is a native species and may be able to overwinter, so that it would perhaps not need to be purchased every year. This is a barrier to adoption for persimilis, especially as some urban farmers have difficulty making such purchases on short notice, either due to budget or organizational constraints. However, one unexpected potential outcome of this project was an interest by some farmers and educators in attempting to rear and release their own biocontrols (after purchasing initial stock); several partners volunteered to help set up a trial in 2022, with persimilis the most likely candidate. This could result in much wider use of not only persimilis, but other biocontrols as well, on urban farms and gardens.

While more exploration is needed, initial observations suggested Orius (minute pirate bug) as an important predator of TSSM on NYC urban farms, and suggest the potential of beans and/or marigolds as banker plants for Orius to protect tomatoes. At least six farms already intend to trial beans, marigolds, or both as Orius banker plants in 2022.

The low TSSM pressure in tomato plantings that used overhead watering or a humid microclimate suggests the potential of carefully managed humidity and/or leaf wetness as an IPM strategy to limit TSSM damage on urban farms, although the accompanying risk of foliar disease must be taken into account.

Participation Summary
5 Farmers participating in research

Education & Outreach Activities and Participation Summary

36 Consultations
5 On-farm demonstrations
2 Published press articles, newsletters
4 Webinars / talks / presentations

Participation Summary:

122 Farmers
27 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

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) and a webinar mostly about TSSM, Nightshade Pests & Diseases of NYC (2/4/21, 40 participants). The project also led to an invitation to submit a virtual presentation ("Twospotted Spider Mite IPM for Urban Agriculture") for the Entomological Society of America's annual conference (10/31/21), and future presentations on the topic at Empire Farm Days (January 2022, Syracuse NY) and the International IPM Symposium (February 2022, Denver CO).

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, in both 2020 and 2021. He also shared TSSM notices and ID tips through the CCE urban agriculture Instagram account (1,500 followers).

Learning Outcomes

11 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

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 four workshops, 122 farmers participated. Beyond the four collaborating farms, an additional 25 farmers specifically reported increased knowledge about IPM practices.

At the start of the project (as noted in field visits), around 20% of NYC urban farmers could identify twospotted spider mite damage in the field; in 2022, nearly 50% could do so. TSSM is now widely recognized as the most important pest of tomatoes in NYC; at least 4 farms are implementing their own scouting protocols, and several plan to rear and release their own predatory mites for TSSM control. This increase in familiarity and practical knowledge is the project's most important output.

Project Outcomes

8 Farmers changed or adopted a practice
2 Grants applied for that built upon this project
1 Grant received that built upon this project
$150,000.00 Dollar amount of grant received that built upon this project
12 New working collaborations
Project outcomes:

This project identified several IPM approaches which are appropriate for urban farms, and which may be combined to reduce TSSM damage in many of these unique settings. These include identifying TSSM hot spots through regular scouting, beginning in late June or early July; the use of beans as sentry plants at row ends to aid in early detection; releasing Phytoseiulus persimilis, focusing on TSSM hot spots. Strategies requiring further exploration include the use of beans, marigolds, or both as banker plants for Orius (minute pirate bug); and periodically wetting affected leaves during hot, dry periods.

The project has greatly increased awareness of TSSM, how to scout for it, and potential IPM strategies among urban farmers. Farms have also started to incorporate new IPM practices as a result of the grant. One of the farms plans to order persimilis in 2022 in response to scouting beans, tomatoes, and cucumbers. Three other farms intend to do so as well for their tomatoes in 2022, although perhaps without using beans as sentry plants. At least six farms plan to trial beans and/or marigolds as Orius banker plants, and at least two intend to trial rearing their own persimilis mites to release during the season.

Additionally, this grant led to new partnerships and collaborations related to urban agriculture IPM, including a SARE R&E grant exploring IPM strategies in NYC and Buffalo and a forthcoming project with the NYS IPM Program to trial DIY rearing of biocontrols for urban farms and gardens.

Assessment of Project Approach and Areas of Further Study:

This project succeeded most of all in building awareness of twospotted spider mite among urban farmers, and while in-person scouting added some logistical challenges (especially during 2020), it also helped me build relationships with participating farmers, and to share methods and results with not just farm managers (the primary contacts) but also other farm staff and even youth participants at one of the farms. (Being known as the "spider mite guy" was not an intended outcome, but probably goes in the "successes" column.) Farmers repeatedly expressed enthusiasm and gratitude for the project, and their input steered some changes along the way, which they noticed and appreciated. Two big overarching lessons, in other words: 1) see farmers as true collaborators, to the extent that they want to be; and 2) be intentional about returning value to the farmers.

The research component returned some very good information, including some immediately actionable findings (with the caveat that "findings" may be strong word, given small sample sizes and lack of replication; "leads" might be a better characterization). It did not go quite as smoothly, in terms of gathering data and maintaining the experimental designs. Some of this was due to the miscellaneous hazards of conducting research on someone else's farm, with the extra complications of urban farms, where many people often interact with the space; and some was directly pandemic-related, including many farms in NYC closing to outside visitors in spring of 2020. Initial plans were for one urban farm to grow Purple Flash ornamental peppers and sweet alyssum in pots which could be placed near tomatoes in order to attract Orius and other naturally occurring biocontrols; that would have happened in the spring of 2020, and COVID caused us to set the plan aside and instead simply observe natural enemies in the field. (Which resulted in some very interesting leads on Orius banker plants.)

Still, the results were very worthwhile; the whole project was very worthwhile, looking back at it. The results are already very useful for urban farmers in NYC, and most likely in other cities in the eastern U.S. (colleagues have confirmed TSSM as a problem in Philadelphia, Baltimore, and Washington, D.C.). They should be of interest to Extension and other farm service providers who work with not only urban farmers but also other small vegetable farms, as well as with gardeners both in and outside of the city; the effects of climate change may mean that others will soon experience pest pressures similar to what we see in NYC. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.