This project seeks to answer the following questions:
1) Can the combined use of reflective mulch and a single OMRI-approved insecticide application serve as a viable alternative to the use of row covers to reduce damage from ALM on commercial farms in the northeast?
2) What, if any, increase in marketable yield can allium growers in the region expect from the addition of an insecticide application to the cultural control approach of just using metalized reflective mulch?
3) Does the additional expense of purchasing insect exclusion netting result in an increase in marketable allium yield when compared to the use of floating row cover to protect plants from ALM adults?
4) Can growers apply row covers to allium crops for only a portion of the adult ALM flight to reduce negative impacts to yield and quality while maintaining protection from ALM damage?
If the project is successful, farmers in the region will gain access to research based recommendations on how to reduce damage to high value allium crops from ALM. The input expenses, labor tracking, and marketable yield data analyzed and interpreted will empower growers to make more informed decisions about sustainable management of ALM in the future.
Tim Elkner, Penn State Cooperative Extension, and Dr. Shelby Fleischer, Penn State University Department of Entomology, spent the fall of 2017 evaluating insecticides to reduce ALM damage on leeks. The preliminary results from the trial found that foliar applications of dinotefuran (Scorpion 35 SL) and cyantraniliprole (Exirel) both provided a statistically significant reduction in ALM damage compared to the OMRI-approved insecticide azadirachtin (Aza-Direct) and the untreated control (Fleischer 2017, Personal Correspondence). However, dinotefuran is not registered for use in several Northeastern states including New York and Exirel is only available with a 2ee SLN label for use on bulb crops for dipteran leafminer management in NY.
With support from the Foundation for Food and Agriculture Research Rapid Outcomes from Agricultural Research program and the New York Farm Viability Institute, Grundberg and Rusinek collaborated with Dr. Brian Nault, Cornell University Department of Entomology, on further insecticide evaluations for ALM management in 2017 and 2018. The 2018 trials located in Red Hook, NY did yield promising preliminary results from the evaluation of 14 insecticides (9 conventional, 4 OMRI-approved). Dr. Nault found that spring transplanted onions and fall transplanted scallions treated with six weekly applications of the OMRI-approved insecticide Entrust SC (spinosad) mixed with M-Pede (potassium salts of fatty acids) achieved comparable levels of reduction of ALM damage to four conventional chemistries (Nault and Grundberg 2019). These trials were not, however, designed to generate recommendations for growers that could be adopted immediately to manage ALM. Products like Entrust SC have labeled resistance management restrictions that require rotation to products with different modes of action after two sequential applications. Even if six sequential applications of the insecticide were permissible, the recommendation would not be cost effective for most commercial allium growers.
Grundberg and Rusinek conducted a randomized complete block design trial to evaluate the efficacy of different timing sequences of just two applications of Entrust SC mixed with M-Pede on leeks during the fall ALM flight. The trials, which were supported by funding from the New York State Department of Agriculture and Markets, did demonstrate statistically significant differences between the different timing sequences of insecticide application during the six-week ALM flight period. The preliminary results suggest that making two applications of Entrust SC with M-Pede two to four weeks after first observed ALM activity can provide a comparable reduction in damage from ALM to six weekly applications of the same product mix (Nault and Grundberg 2019).
While the majority of the research to date in the United States has focused on chemical controls for ALM management, there has been some work done to evaluate the potential for cultural control strategies to mitigate ALM damage in Europe. There is mention in scientific literature of recommendations from Austria to use insect netting to cover leeks as a method to exclude adult ALM from laying eggs on host plants (Kahrer 1999). Unfortunately, there is no description of research that may have generated those recommendations or any data collected on costs or impact on marketable yield. Slovenian researchers conducted trials to determine whether interplanting aromatic herbs like oregano, lavender, and rosemary may reduce damage from ALM in onion fields. However, two years of replicated trials showed no statistically significant reduction in damage from ALM in interplanted plots and actually demonstrated a negative impact on marketable onion yield when interplanted with lavender (Laznik 2012).
Rusinek and Grundberg also conducted preliminary trials to evaluate the potential efficacy of metalized reflective mulch compared to white plastic mulch at reducing damage from ALM in both leeks and scallions in 2018. The research did find a statistically significant difference between the two plastic mulch treatments and a roughly 30% reduction in damage from ALM in the reflective mulch plots for both leeks and scallions. However, the mean number of ALM larvae and pupae per plant in the reflective mulch plots was still unacceptable at 2.95 per scallion and 9.32 per leek.
Grundberg and Rusinek also evaluated the combination of using reflective plastic mulch with either one or two carefully timed insecticide applications to see if there may be a synergy between the cultural and chemical control tactics to reduce damage from ALM. Initial results from those trials, conducted in spring 2019 on scallions and fall 2019 on leeks, suggest that the combination of two applications of Entrust with M-Pede 2 and 4 weeks after the beginning of the adult ALM flight with reflective plastic mulch can significantly reduce ALM damage to acceptable levels. In their trial on leeks in fall 2019, leeks receiving no insecticide on reflective mulch contained a mean number of ALM of 30.8, leeks receiving one insecticide application on reflective mulch contained a mean number of ALM of 11.5, while the treatment on reflective mulch with two applications of Entrust with M-Pede contained a mean number of ALM of just 2.72 (Grundberg and Rusinek, unpublished).
This proposal aims to fill in information gaps on the efficacy and costs of cultural control tactics like using different row covers to reduce damage from ALM. It also proposes to further evaluate the potential of combining the use of reflective mulch with reduced Entrust SC applications in hopes of generating cost-effective and adoptable management strategies for organic allium growers in the northeast.
The proposed field trials will be conducted in 2020. There are two major changes to the originally proposed treatments based on results from field trials conducted in 2019 with support from New York State Department of Agriculture and Markets and USDA NIFA Crop Protection and Pest Management award.
- The treatment REF+ENT was originally proposed to include a single application of Entrust at 6 fl oz per acre with M-Pede at 1.5% v/v dilution. Based on the results from the 2019 trials, the addition of a single application of Entrust with M-Pede did not provide a statistically significant reduction in allium leafminer (ALM) damage in spring scallions. The single application of Entrust with M-Pede did provide a statistically significant reduction in ALM damage in fall leeks, but failed to reduce damage to an “acceptable” level. Treatments of Entrust with M-Pede applied twice, once 2 weeks after the beginning of the ALM adult flight and once again 4 weeks after the beginning of the adult flight, were successful at reducing damage to an acceptable level. Therefore, treatment REF+ENT will use two applications of Entrust with M-Pede at the same timing interval as described (weeks 2 and 4).
- All of the treatments that include the use of wire hoops to support either exclusion netting or row cover (REF+PNHPS, REF+AGHPS, REF+AGLATE, REF+AGERLY) will use 76″ wire hoops instead of the originally proposed 64″ hoops to allow more vertical space for crop development.
Additionally, treatments that were to use Agribon+ AG-19 may instead include the use of Dewitt .55 floating row cover since it is a comparable product that many growers are adopting due to its price.
Finally, the leek cultivar will be updated from ‘Pandora’ to ‘Megaton’ due to seed availability.
The originally proposed methods are as follows:
The proposal aims to evaluate the efficacy of different cultural and chemical control strategies in reducing crop damage caused by ALM. Since there are two ALM generations per year, there are two separate trials proposed to evaluate the efficacy of treatments during each flight. During the spring ALM flight, transplanted scallions will be used as the host cash crop. For the fall ALM flight, transplanted leeks will be used as the host cash crop. Details on each trial follow below.
‘Nabechan’ scallions will be seeded in 128 cell propagation trays at a density of 3-4 seeds per cell in February 2020. The scallion plugs will be transplanted into three rows per bed with 6-inches between plugs in-row onto metalized reflective plastic mulch. The trial will include 8 treatments arranged in a randomized complete block design (RCBD) with 4 replications. Each treatment plot will be 10 bed-feet long and include 60 scallion plugs. The 8 treatments are:
- Reflective mulch (REF)- Scallions will be planted on reflective plastic mulch, but will not be covered and will not receive any insecticide applications.
- Reflective mulch plus insecticide (REF+ENT)- Scallions on reflective plastic mulch will receive a single application of Entrust SC (spinosad, IRAC group 5) at the 6 ounce per acre rate mixed with a 1.5% v/v dilution of M-Pede (potassium salts of fatty acids, not classified). The insecticide application timing will be determined based on the preliminary results of field trials conducted in 2019.
- Reflective mulch plus ProtekNet exlusion netting (REF+PN)- Scallions on reflective plastic mulch will be covered at transplant with ProtekNet biothrips insect exclusion netting anchored with sand bags and will remain covered until the confirmed conclusion of the ALM flight. The exclusion netting in this treatment will not be supported by wire hoops.
- Reflective mulch plus ProtekNet with hoops (REF+PNHPS)- Same as treatment REF+PN, but with 64” high tensile steel hoops to support the netting above the crop canopy.
- Reflective mulch plus Agribon+ AG-19 (REF+AG)- Same as treatment REF+PN, but using Agribon+ AG-19 floating row cover instead of ProtekNet biothrips insect exclusion netting.
- Reflective mulch plus Agribon+ AG-19 with hoops (REF+AGHPS)- Same as treatment REF+PNHPS, but using Agribon+ AG-19 floating row cover instead of ProtekNet biothrips insect exclusion netting.
- Reflective mulch plus Agribon+ AG-19 with hoops late cover (REF+AGLATE)- Same as treatment REF+AGHPS, but the floating row cover will not be installed at the time of transplant. Instead, row cover will be applied and secured two weeks after the observed ALM emergence date.
- Reflective mulch plus Agribon+ AG-19 with hoops early removal (REF+AGERLY)- Same as treatment REF+AGHPS, but the floating row cover will be removed prior to the end of the ALM flight. The exact timing of removal will be determined based on oviposition scouting data, but will likely occur approximately 4 weeks after ALM emergence.
The same treatments will be applied to the leek trial field during the fall ALM flight. ‘Pandora’ leeks will be seeded in 128 cell propagation trays in the greenhouse at a density of one seed per cell in mid-April 2020. After the confirmed end of the spring 2020 ALM flight, the leek plugs will be transplanted into two rows per bed with 6-inches between plugs in-row onto metalized reflective plastic mulch. The trial will include the same 8 treatments described above arranged in a randomized complete block design (RCBD) with 4 replications. Each treatment plot will be 10 bed-feet long and include 40 leeks.
Oviposition scars made by ALM adults on leaf tissue will be counted weekly after ALM emergence on 20 randomly selected plants per plot for each treatment that is not covered. Oviposition scars will only be counted after the confirmed end of the ALM flight for treatments that are under either insect exclusion netting or floating row cover for the duration of the flight.
The foliar insecticide application of Entrust SC and M-Pede for treatment REF+ENT will be made using a CO2 –pressurized research backpack sprayer and boom equipped with twin flat-fan nozzles (TJ-60 8003VS) each positioned over a row and calibrated to deliver 40 gallons per acre of spray mixture at 40 PSI.
20 scallion bunches per plot, or 80 bunches per treatment, will be harvested for data analysis as soon as feasible after the end of the spring ALM flight. The number of individual scallion plants per bunch will be recorded to allow for analysis on a per plant basis. Each scallion will be measured, weighed, evaluated for foliar disease severity, and assessed for marketability. 20 leeks per plot, or 80 per treatments, will be harvested as soon as feasible after the end of the fall ALM flight. Each leek will be evaluated for foliar disease severity and marketability. Data will be analyzed using a general linear model of SAS or JMP 13.2.1 Pro Software (SAS Institute Inc.) with treatment as the fixed effect and replicate as a random effect. Yield, disease, and marketability data will be compared using a one-way ANOVA with Tukey’s Studentized Range (HSD) test at p < 0.05.
Once the aforementioned data has been collected for both scallions and leeks, the collected subsamples will be carefully dissected. All ALM larvae and pupae will be extracted and counted on a per plant basis during the dissection process. Larvae and pupae count data will be analyzed using a Poisson generalized linear model of SAS or JMP 13.2.1 Pro Software (SAS Institute Inc.). Means will be compared with Tukey’s Studentized Range (HSD) test at p < 0.05.
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