Trap Cropping to Improve Tarnished Plant Bug Management in North Central Strawberry

View the project final report

Commodities

• Fruits: berries (strawberries)

Practices

• Pest Management: trap crops

Background: In 2017 over 3100 farms across the North Central Region (NCR) dedicated 4,928 acres to strawberry production, with an economic value of $17.5 million for growers in Michigan, Ohio, and Wisconsin, alone. Lygus lineolaris, the tarnished plant bug (TPB), is the primary insect pest of strawberries in eastern and central North America. Strawberries are most susceptible to TPB damage during bloom and the early stages of fruit development, which leads to difficulties balancing TPB management with pollinator protection. Improved monitoring tools and strategies that reduce TPB colonization of strawberry fields during the short window of susceptibility may offer a solution to this problem.

Trap cropping: Alfalfa (Medicago sativa) is a preferred TPB host, that has been deployed as a trap crop against Lygus spp. in California and Europe. This project examined the potential of alfalfa trap cropping to improve TPB management in June-bearing strawberries. We sought to understand:

1) Whether alfalfa perimeter strips influence TPB populations in associated strawberry fields?

2) The extent of TPB movement between alfalfa perimeter strips and associated strawberry fields?

3) The impact of alfalfa perimeter strips on beneficial arthropod populations?

Data were collected over three years at three commercial strawberry farms in Southern Wisconsin. We found that alfalfa perimeter strips reduced TPB densities by an average of 36% compared to paired control plots. In a mark-capture experiment we observed approximately three times as many TPB moving from the strawberry into the alfalfa strips, and that females were overrepresented among immigrants to alfalfa. While the presence of alfalfa perimeter strips increased beneficial arthropod abundance and diversity in experimental plots overall, most effects were limited to the alfalfa strip itself, with little spillover into adjacent strawberry fields. These data suggest that preferential utilization of alfalfa by TPB underlies the observed population reductions and that alfalfa perimeter strips act as a trap crop in June-bearing strawberries.

Monitoring: Growers also expressed concerns about the efficacy of current TPB monitoring recommendations. While non-UV white sticky traps are frequently recommended, several studies have demonstrated that other colors are more efficient (Wold and Hutchison 2003; Legrand and Los 2003). Moreover, trap visual qualities may interact with chemical lures, enhancing or undermining insect attraction. We sought to understand:

1) The impact of trap color on TPB capture.

2) The potential for plant-derived semiochemicals to improved TPB monitoring.

Trapping experiments in alfalfa and strawberry fields confirmed grower concerns that non-UV white sticky traps were ineffective for TPB monitoring. Red traps captured the most TPB in both alfalfa and strawberry fields, averaging 733% more TPB than white traps. Previous work in our lab had determined that TPB antennae are sensitive to (Z)-3-hexenol, (R)-(+)-α-pinene, (E)-β-ocimene, (±)-linalool, and sulcatone. A field experiment was conducted to determine whether any of these compounds increased TPB trap catch compared to blank controls. We found that (±)-linalool increased TPB capture by 85% compared to controls. As (±)-linalool is a mixture of (S)-(+)- and (R)-(-)-linalool, which may elicit different behavioral responses, a second trapping experiment was conducted to examine how stereochemistry influences TPB attraction to (±)-linalool. We observed that red traps with (±)-linalool lures captured 108% and 112% more TPB than red controls and those baited with (R)-(-)-linalool respectively, while similar increases were not observed for white traps. These data suggest that (S)-(+)-linalool mediates TPB attraction to the racemate, while (R)-(-)-linalool does not deter TPB.  

Education: Our educational approach focused on presenting research at grower-centered conferences and these data have been presented at the Wisconsin Fresh Fruit and Vegetable Conference (WFFVC) three times, at the Great Lakes EXPO, and at the Marbleseed Organic Research Forum. We expected that exposure to this research would lead to knowledge gains around the use of alfalfa trap crops to manage TPB and increased willingness to incorporate alfalfa perimeter strips into field designs. Pre-study surveys were conducted at the WFFVC in 2020, and had 16 respondents, 6.25% of whom knew that alfalfa has been deployed to manage Lygus spp., 43.75% of whom responded that it had not, and 50% of whom were unsure. 31.25% of growers reported that they would not consider trap cropping with alfalfa, even if it reduced insecticide inputs and/or TPB damage. The post-study survey (n = 24) revealed less certainty around alfalfa trap cropping, with 91.67% responding ‘unsure’ and 8.33% responding that alfalfa has been deployed to manage Lygus spp., while none responded that it had not; and more openness to the idea of trap cropping, with only 13.64% of respondents saying that they would not consider implementing a trap crop for TPB management. These findings suggest that growers are open to the idea of trap cropping. Small plot studies examining how this strategy impacts insecticide use and TPB damage, and refining recommendations may be useful for improving grower confidence and adoption of trap cropping. 

1) Determine the efficacy of alfalfa trap cropping as a cultural control strategy for managing TPB
2) Determine the extent of movement between the trap crop and the cash crop
3) Assess the impact of alfalfa trap cropping on beneficial and pest arthropod communities
4) Assess the effect of trap color on TPB capture
5) Identify semiochemicals that may facilitate TPB monitoring and mass trapping