Combining Trap Cropping with Companion Planting to Control the Crucifer Flea Beetle
The crucifer flea beetle (CFB), Phyllotreta cruciferae, is a major pest of Brassica crops in the Pacific Northwest. In previous work we found that trap crops are effective in partially protecting broccoli from flea beetle damage. Here, we examined the use of companion plants intercropped with broccoli as an additional, complementary flea beetle management option. Our hypothesis is that marketable companion crops planted within the protection target will further hinder flea beetles’ ability to chemically or visually locate their host plants. Thus, companion and trap crops may work synergistically to improve flea beetle control.
1) Examine interactions between companion plants, including bunching onion (Allium fistulosum x cepa) and Yukon gold potato (Solanum tuberosum), planted at varying ratios, in its ability to discourage CFB colonization of broccoli.
2) Investigate how companion plants will affect colonization by other broccoli pests and beneficial insects (and spiders).
3) Distribute what we learn to growers through an extension program including a field day at a local farm.
We have made progress on several of the objectives to date.
In support of Objective 1 and 2, field experiments were conducted at two different locations across Washington. In plots both west (Mount Vernon, WA) and east (Pullman, WA) of the Cascade Mountains, we have been evaluating different companion plant-trap crop compositions to draw flea beetles out of broccoli (B. oleracae L. var. italica ). In 2010, results from intercropping broccoli with spring onion (Allium fistulosum x cepa) and Yukon Gold potatoes (Solanum tuberosum) elicited interesting responses in CFB densities without influencing broccoli yield. For example, in late July we collected significantly fewer CFB out of trap crops adjacent to potato and onion companion plants (F3, 1065 = 108.394, P = 0.001; Figure 1a). Alternatively, we recorded significantly more CFB on broccoli in control plots earlier in the season (F3,1065 = 147.823, P = 0.001 Figure 1b). We also found significantly more CFB on broccoli in control plots than broccoli intercropped with potato and onions (Figure. 2; P <0.05 for all comparisons with companion plants, Student’s T). It is possible that we did not use a large enough density of companion plants to influence CFB behavior. Therefore, in 2011 we expanded on this companion plant experiment by intercropping bunching onions and Yukon gold potatoes at different ratios within broccoli. We compared different densities of companion plants to see if a particular ratio might be able to “push” flea beetles out of broccoli and “pull” them towards the trap crop. Flea beetle (P. cruciferae) populations in trap crops were tracked using D-vac suction, while visual observations and yellow sticky cards were used to monitor flea beetle populations and damage in broccoli.
The Pacific Gold Mustard trap crops were direct seeded at a rate of 5g/foot in Pullman, WA on April 20, 2011 and in Mount Vernon, WA on May 16, 2011. The trap crop consisted of five rows spaced 53 cm apart. After the seeded trap plants emerged they were grown for four weeks. Once trap plants were established, broccoli (Brassica oleracea var. italica), onions (Allium fistulosum x cepa) and potatoes (Solanum tuberosum) were transplanted. We followed a response surface design. This consisted of companion plants intercropped ranging from 0% to 100% onions with broccoli at both the Pullman, WA (east) location and the Mount Vernon, WA (west) location. Due to space limitations and unfavorable weather conditions, the potato companion plants were only planted in Mount Vernon, WA. Potato companion plants were intercropped with broccoli at the following densities: 10%, 20%, 40%, 60% and 80%. All companion plant/broccoli rows were spaced 53 cm apart.
Once planting was completed, trap plants were sampled several times throughout the season using a D-vac suction sampler, and P. cruciferae densities were recorded. Visual observations of P. cruciferae on broccoli were also made several times throughout the season. To track P. cruciferae, movement yellow sticky cards were attached to stakes in broccoli adjacent to each trap crop treatment. All plots were maintained weed-free by hand weeding/hoeing. In mid-September broccoli was harvested at both field sites. Broccoli plants were pulled directly from the soil, shaken to remove excess soil, labeled and placed into a paper sack. The broccoli was dried in an oven at 600C for seven days, and dry weights were recorded for each sample. An ANOVA in Systat (SPSS Chicago) was used to analyze broccoli whole plant dry weight at both locations. Linear regressions were used to analyze companion plant ratio and its impact on CFB densities in trap crop, broccoli and broccoli yield. When appropriate, post-hoc tests were performed using a Student’s T least significant difference (LSD) test (? = 0.05).
We found no clear statistical patterns between ratios of companion plants intercropped with broccoli and increased trap crop attractiveness or broccoli yield (Table 1). Thus, an increase in companion plants did not translate to an increase in trap crop attractiveness. Similarly, an increase in companion plant ratio did not lead to fewer CFB densities in broccoli. Therefore, CFB were not necessarily being “pulled” towards trap crops or “pushed” out of broccoli. These data suggests that CFB behavior plays an important role in trap crop and companion plant effectiveness. In addition, we are still analyzing results from Objective 2. Our results will help elucidate whether companion plant ratio will effect colonization by other broccoli pests such as Plutella xylostella the diamond back moth and beneficial insects (and spiders) in all d-vac samples.
In support of Objective 3, we held a natural pest management field day at Greentree Naturals Certified Organic Farm in Sandpoint, ID on July 18, 2011. We discussed different aspects of organic pest management, including introducing growers to the benefits of companion plants, trap crops, beneficial arthropod identification and conservation biological control. Field day participants were able to observe a Pacific Gold Mustard trap crop farm trial protecting broccoli and a d-vac collection demonstration. Participants were also treated to a lunch made with local produce provided by Greentree Naturals Certified Organic Farm.
Impacts and Contributions/Outcomes
Our results from the past two seasons, 2010 and 2011, will be compiled to provide valuable information on the use of combining trap crops with companion plants and provide growers with alternative methods of flea beetle control.
Washington State University Department of Entomology
100 Dairy Road
Pullman, WA 99164-1120
Office Phone: 5093353724