- Vegetables: broccoli, greens (leafy), onions
- Additional Plants: herbs, ornamentals
- Crop Production: intercropping
- Education and Training: extension, on-farm/ranch research, workshop
- Pest Management: cultural control, integrated pest management, trap crops
- Production Systems: organic agriculture
The crucifer flea beetle, Phyllotreta cruciferae, is a major pest of Brassica crops in the Pacific Northwest. Many growers rely on these crops as a major component of mixed-vegetable production, and flea beetle damage lowers marketable yields. In previous work we found that trap crops are effective in partially protecting broccoli from flea beetle damage. Companion plants intercropped with broccoli as an additional complementary flea beetle management option may provide an additional incentive for flea beetles to choose the trap crop rather than the broccoli, working synergistically to improve flea beetle control.
The crucifer flea beetle (CFB), Phyllotreta cruciferae (Coleoptera: Chrysomelidae), is an oligophagous pest of Brassica crops throughout North America (Palaniswamy and Lamb 1992). In the Pacific Northwest, many growers rely on Brassica crops as a major component of mixed-vegetable production; flea beetle damage lowers the marketable yields of these crops. In addition, Brassica crops can be planted and harvested season-long, providing a steady source of income throughout the year. Organic Brassica crops are valued at over $60 million annually (USDA NASS 2008) and include arugula, broccoli, cabbage, kale and mustard greens. Adult flea beetles scar foliage, resulting in produce that is unattractive to consumers and often kill seedlings and small transplants outright. Indeed, flea beetle damage sometimes leads to total crop loss (Newton 1928, Kinoshita et. al 1979, Turnock and Turnbull 1994), and for this reason many small-scale vegetable growers in the Pacific Northwest are unable to include Brassicas in their yearly rotations.
The crucifer flea beetle feeds only on Brassica species throughout North America (Palaniswamy and Lamb 1992). Adult flea beetles cause significant damage to crops in early spring when beetles emerge from overwintering sites to feed on newly planted Brassica plants, resulting in plant death, slowed growth and reduced marketable yields (Newton 1928, Kinoshita et. al 1979, Turnock and Turnbull 1994). During the fall the adult beetles move away from Brassica fields and overwinter in sites near field edges beneath hedgerows and trees (Burgess 1977, Wylie 1979, Lamb 1983). Because beetles are constantly moving into crops from these surrounding overwintering sites, it is extremely challenging to develop in-field management strategies. In addition, organic producers are very limited in their options for controlling flea beetles, these being limited to the use of floating row covers, which can be costly, and organic-approved insecticides, which must be applied frequently as flea beetles continuously move into the crop from surrounding vegetation. The limitations of these strategies have led the industry to look for alternatives.
In work we have already completed, we have found that trap crops, which are stands of plants highly-attractive to the pest and planted nearby, effectively draw flea beetles away from the broccoli plantings that we are trying to protect (Parker 2012). Trap crops manage pest populations by attracting insect pests, therefore reducing the likelihood that the pests will attack the target crop (Vandermeer 1989). Thus, trap cropping presents a new option for flea beetle control. However, trap cropping alone does not completely protect the broccoli from flea beetle damage, suggesting that additional controls are still needed. We investigated the use of companion plants and trap crops as a flea beetle management strategy.
Companion plants are interplantings of a second marketable crop within the protection target that can visually and/or chemically mask the ability of a pest to find its desired host plant (Cunningham 1998, Finch and Collier 2000). Trap cropping has received more attention than companion planting, and very little work has examined the combination of these two approaches for pest control. Companion plants have shown benefits in several cropping systems, by obstructing the pest’s ability to locate host plants. For example, fewer diamondback moths were found on Brussels sprouts when they were intercropped with malting barley, sage or thyme (Dove 1986). Additionally, fewer striped flea beetles were observed when Chinese cabbage (Brassica chinensis) was intercropped with green onions (Allium fistulosum) (Gao et. al 2004), while collards intercropped with spring onion (Allium cepa) (Brassica oleracea var. acephala) significantly reduced densities of the cabbage aphid (Brevicoryne brassicae) on the collards (Mutiga et. al 2010).
Flea beetle movement is also influenced by crop diversity. Flea beetles encounter non-host plants at a higher rate in mixed plantings, sometimes causing them to leave in search of a more suitable habitat (e.g., Elmstrom et. al 1998). This has positive implications for the combination of trap cropping with companion planting: a trap crop situated near a companion plant intercrop may visually confuse, repel, block or slow the movement of flea beetles into broccoli and consequently steer flea beetles to the trap crop. Therefore, trap crops and companion plants have the potential to work synergistically together, with their combined impacts greater than either single approach used alone.
We examined the use of companion plantings to control the crucifer flea beetle in combination with trap crops. Companion plantings may interrupt host finding by flea beetles and other broccoli pests and enhance densities of beneficial predators and parasitoids.
Our objectives were to:
1)Determine the most effective companion crop species to discourage flea beetle colonization of broccoli and improve marketable yield.
2)Examine how the companion plants will affect colonization by other broccoli pests and beneficial insects (and spiders).
3)Examine the combination of companion planting and trap cropping for flea beetle control
4)Distribute what we learn to growers through an extension program including a substantial extension presence, along with field days and other outreach strategies that maximize coverage.