Companion Planting with Land Cress for Natural Caterpillar Control

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Land Cress (Barbarea vulgaris) and American Upland Cress (Barbarea verna) are biennial, edible leafy-green vegetables from the Brassicaceae (cabbage) family. The young leaves, which are spicy in flavour, are often used as a substitute for watercress in dishes, and can be cooked, or used fresh in salads and sandwiches. They’re nutritious leaf vegetables that contain high amounts vitamin A, vitamin C, iron and calcium, and are worthwhile additions to any productive garden.

These plants are also excellent companion plants for natural pest control, and can be used as dead end trap crops for controlling the following pests:

  • Diamondback Moth (Plutella xylostella), a specialist pest which only attacks plants from the brassica family, the most destructive insect pest of cruciferous vegetables worldwide.
  • Cabbage Moth (Mamestra brassicae), a generalist pest which not only attacks plants from the brassica family as the name suggests, but a wide range of other plants also.

How do these plants control pests? They put out substances from their leaves known as glucosinolates which stimulate diamondback moths and cabbage moths to lay their eggs on them, but they also contain natural soap-like substances known as saponins which kill the baby caterpillars when they hatch and eat the leaves!

 

What is A  Dead End Trap Crop?

In companion planting, a trap crop is a plant which is more attractive to pests than other plants, and is planted nearby other crops to act as a pest decoy or sacrificial plant.

Trap crops draw pests onto themselves and away from other plants, they can withstand being attacked by pests without being killed off. They either recover from the damage, or continue on regardless of any damage to produce seeds, which then give rise to more plants in the following year.

A dead-end trap crop attracts pests much like other trap crops, but once the pests are attracted, they are killed by the plant, so the pests don’t go any further, and therefore reach a ‘dead-end’!

 

Land Cress or American Upland Cress, Which is a Better for Pest Control?

Both land cress (Barbarea vulgaris) and American upland cress (Barbarea verna) are used as dead-end trap crops for protecting other brassica crops, but many gardeners are curious as to whether one works better than the other, or if they’re equally effective.

According to a research carried out in Europe in 2014 to asses the the potential of various Barbarea species as dead-end trap crops for diamondback moth, it was found that the levels of glucosinolates which attract diamondback moths to lay their eggs on the plants were fairly similar, and the pests always preferred to lay their eggs on the Barbarea plants rather than on nearby cabbage plants. Both plants work equally well as an attractant.

Researchers also found that American upland cress (Barbarea verna) contained less saponins than other Barbarea plants tested, but the lesser amounts contained did not allow survival of the caterpillars. Both plants are able to eliminate caterpillars.

The conclusion of the study was that both plants tested had potential to be used as dead-end trap crops for diamondback moths. [1]

 

Land Cress and Upland Cress, Plant Description

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American Upland Cress (Barbarea verna) showing characteristic deeply-lobed leaves and rosette leaf arrangement.

 

If we want to use plants for natural pest control, we need to make sure we’re using the right ones to ensure they’ll be effective. When plants have many common names, there is always the possibility for confusion, which is why horticulturalists tend to refer to plants by their scientific names!

Barbarea vulgaris is known by the following common names – land cress, bittercress, herb barbara, rocketcress, yellow rocketcress, winter rocket, yellow rocket, and wound rocket. This species is native to Eurasia and North Africa, and normally grows as a wild plant. A biennial plant growing to a height of 40-60cm (16-20”).

Barbarea verna is known by the following common names –  American upland cress, American cress, upland cress, bank cress, black wood cress, Belle Isle cress, Bermuda cress, early yellowrocket, early wintercress, scurvy cress and creasy greens. This species is native to southwestern Europe, and is normally cultivated as a leafy vegetable, and has been since the 17th century in Europe. A biennial plant growing to around 30cm (12”) high x 30cm (12”) wide.

In terms of form, these plants produce a rosette of dark green, deeply-lobed, pinnately-divided  leaves.

Flowers are produced in the second year, during spring or summer. Upright stems form, bearing clusters of small, yellow, four-petalled flowers, which eventually form slender seed pods.

Being biennial (living only for two-years), the plants die off after going to seed, but they self-seed easily and small seedlings emerge to replace the plants, and these volunteer seedlings (self-seeded plants) can be transplanted to other locations around the garden as desired.

Seedlings begin growing as a flat rosette form, much like a dandelion, but eventually take on a more upright habit, especially in their second year when they begin to flower.

 

How to Grow Land Cress and Upland Cress

Many gardeners consider Barbarea vulgaris or Barbarea verna to be much like watercress plants, but much easier to grow, and with lower water requirements. They really are a low-maintenance leaf vegetable.

These plants are usually grown from seed or purchased as seedlings. Growing requirements are as follows:

Soils: will grow in most soil types, prefer moist well-drained soils

Sun: full sun to part shade

Water: moderate water requirements, keep plants watered during warmer weather, don’t let them get too dry or become heat stressed otherwise they will ‘bolt’ (go to seed) early.

Seed Sowing:  sow seeds directly into the ground 0.5cm (1/4”) deep in spring or autumn, keep soil moist and seeds will germinate in 2-3 weeks. Space seeds approximately 2cm apart (15 seeds per foot), and space rows 30cm (12”) apart. Thin out seedlings so that they are 10-15cm (4-6″) apart.

Harvesting: plants will reach maturity in 7-8 weeks, pick leaves are required, or cut full rosettes from the base.

Plant Care: frost hardy, overwinter well, can be covered with a cloche in extreme frosts. Keep seedlings well-watered in spring during hot weather.

 

In food gardens, grow land cress or upland cress amongst other vegetables to protect them. Plant along one edge of the garden, or locate individual plants throughout the garden.

 

Intercropping with Land Cress in Agriculture

In agricultural settings Barbarea vulgaris or Barbarea verna can be used as an intercropping plant to protect crops.

Intercropping is practice of growing two or more crops on the same field at the same time, and these plants can be grown in rows between the main crop plants to act as a dead-end trap crop.

Since these plants are biennial, they will will grow over a two year period, and if planting seedlings or seed-sowing is staggered throughout spring and autumn, this will ensure that the rows will contain plants at various stages of their life cycle, eliminating the possibility of all plants going to seed and dying off at once.

A row only needs to be set up once, and plants will self-seed in that location (without becoming invasive) from that point onward to populate the rows more densely if adequate irrigation is provided. This is a low-cost and low maintenance pest control option that takes little space for intercropping, as each plant only grows to around 30cm (12”) wide..

 

Which Plants Do They Protect?

All plants that are attacked by the diamondback moth and cabbage moth can be protected by using Barbarea vulgaris or Barbarea verna as companion plants. To know which plants these are, we will need to list the plants these pests attack.

 

What Plants do Diamondback Moths Attack?

Diamondback moth larvae (caterpillars) are specialist feeders of plants in the Brassicaceae (cabbage, mustard or crucifer) family, and attack virtually all cruciferous vegetables including broccoli, cabbage, cauliflower, Chinese cabbage, brussels sprouts.mustard, radish, turnip, and watercress. [2]

 

What Plants do Cabbage Moths Attack?

Cabbage moth larvae (caterpillars) are generalist leaf eaters that feed on a wide range of plants across 70 species and 22 families, though plants from the Brassicaceae family are among the most preferred. Minor host plants include various vegetables, herbs, berries, ornamental flowers, fruit trees and ornamental trees.

 

Does Flowering Land Cress Attract Beneficial Insects?

The diamondback moth Plutella xylostella L. (Lepidoptera: Plutellidae) is controlled naturally by two parasitic wasps, Diadegma insulare Cresson (Hymenoptera: Ichneumonidae) and Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae).

Since these plants flower in their second year, a study was carried out to determine whether flowering Barbarea vulgaris plants could also be used to attract beneficial insects. Researchers found that in plots with flowering B. vulgaris, diamondback moth pupae suffered 1.7 and 4.0 times more parasitism by D. insulare and D. collaris, respectively, than in plots without flowering B. vulgaris.

This indicates that as an additional benefit, the dead-end trap crop plant will also attract parasitic wasps which will attack this pest!

There’s a catch though. The researchers found that when flowering, Barbarea vulgaris reduced its attractiveness to the pest to lay its eggs on it, making it lose its effectiveness as a trap crop. But it did reduce the populations of another pest, the Ornate Shieldbug Eurydema ornata L. (Hemiptera: Pentatomidae) in adjacent cauliflower while it was flowering.

The conclusion of the study was that since Barbarea vulgaris is biennial, it could be used as a trap crop for diamondback moth in the first year, and to lower the populations of ornate shield bugs and increase the parasitism of diamondback moth by the wasps when it flowers the second year. [3]

In my opinion, the simple solution to achieve both outcomes each and every year is to plant Barbarea vulgaris (or Barbarea verna) in both the first and second year to create a mix of flowering and non-flowering plants in the same planting area. After they self seed, there will be an ongoing succession of plants of various ages growing together at all times.

 

Is There a Difference Between Young and Old Leaves?

Brassica plants use glucosinolate compounds as part of their plant defence systems, but the diamondback moth, which specialises feeding on the Brassicaceae family of plants, uses this as a means of host plant recognition, it’s how it finds its target plants!

The reason Barbarea vulgaris and Barbarea verna can act as dead-end trap crops for the diamondback moth is because they’re also from the Brassicaceae family, and also contain glucosinolates, but at much higher levels than other brassica plants, which is why they’re more attractive to pests. The Barbarea genus is the only one in the Brassicaceae family which is known to simultaneously contain glucosinolates and saponins. The saponins they contain are there to act as feeding deterrents for diamondback moth, and they work as insecticides preventing the survival of the caterpillars on the plant.

In one study it was found that diamondback moths preferred to lay their eggs on younger leaves compared to older ones, and after analysis it was discovered that the younger leaves contained higher concentrations of both glucosinolates and saponins. [4]

The lower saponin content in older leaves might increase the chances of survival diamondback moth caterpillars on the plant, but the older, larger leaves also have relatively low concentrations of glucosinolates, which make them less attractive for the pest to lay its eggs on, so the pests usually don’t attack those.

This research suggests that the best way to use these cress plants is to harvest the larger young leaves for use as an edible vegetable and leave the smaller ones for pest control.

 

Does Land Cress and Upland Cress Control Cabbage White Butterflies?

cabbage-white-butterfly-feeding-on-calendula-flower

The cabbage white butterfly (Pieris rapae) is a common garden pest, and its caterpillars attack brassicas and several other plants.

Female adults cabbage white butterflies are able to detect glucosinolates in leaves of Brassicaceae family plants with specialized receptor cells, and are stimulated to lay their eggs on those plants. These compounds are part of the plant’s defences, but the caterpillars are able to detoxify glucosinolates which enables the to feed on the leaves. (5) Searching through current research, I haven’t been able to find any evidence that the saponins in the Barbarea plants adversely affect the cabbage white caterpillars in any way.

This would suggest that Barbarea vulgaris and Barbarea verna would attract the cabbage white butterfly and successfully act as a trap crop for the caterpillars, localising the pest problem to a single area. That would make it much easier for beneficial predator and parasitoid insects to find the caterpillars, or for gardeners to remove them by hand-picking, but these plants won’t work as a dead-end trap crop to eliminate the caterpillars.

 

References

  1. Badenes-Pérez, F. R., Reichelt, M., Gershenzon, J., & Heckel, D. G. (2014). Using plant chemistry and insect preference to study the potential of Barbarea (Brassicaceae) as a dead-end trap crop for diamondback moth (Lepidoptera: Plutellidae). Phytochemistry, 98, 137-144. doi:10.1016/j.phytochem.2013.11.009.
  2. C. R. Philips, Z. Fu, T. P. Kuhar, A. M. Shelton, R. J. Cordero, Natural History, Ecology, and Management of Diamondback Moth (Lepidoptera: Plutellidae), With Emphasis on the United States, Journal of Integrated Pest Management, Volume 5, Issue 3, 1 September 2014, Pages D1–D11, https://doi.org/10.1603/IPM14012
  3. Badenes-Pérez, F.R., Márquez, B.P. & Petitpierre, E. Can flowering Barbarea spp. (Brassicaceae) be used simultaneously as a trap crop and in conservation biological control?. J Pest Sci 90, 623–633 (2017). https://doi.org/10.1007/s10340-016-0815-y
  4. Badenes-Perez FR, Gershenzon J, Heckel DG. Insect attraction versus plant defense: young leaves high in glucosinolates stimulate oviposition by a specialist herbivore despite poor larval survival due to high saponin content. PLoS One. 2014;9(4):e95766. Published 2014 Apr 21. doi:10.1371/journal.pone.0095766
  5. van Leur, H., Vet, L.E.M., van der Putten, W.H. et al. Barbarea vulgaris Glucosinolate Phenotypes Differentially Affect Performance and Preference of Two Different Species of Lepidopteran Herbivores. J Chem Ecol 34, 121–131 (2008). https://doi.org/10.1007/s10886-007-9424-9

About Angelo (admin)

Angelo Eliades is a presenter, trainer, writer, permaculture consultant, urban permaculture pioneer and food forest specialist.
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5 Responses to Companion Planting with Land Cress for Natural Caterpillar Control

  1. Verity says:

    Hi Angelo, thanks for this really clear and interesting article. Just a question out of curiosity more than anything else—do you know what factors may prompt biennial plants such as land cress to flower in the first year rather than the second? I found that quite a few of the land cress plants grown from seed in the school garden—a wider, sunnier, more open space than my home garden—went to seed in the first year, but the second generation crops haven’t.

    Like

    • Angelo (admin) says:

      Thanks for your question, land cress plants will ‘bolt’ (go to seed) if they get too dry or become heat stressed, so it’s important to keep them watered during warmer weather – I’ll add that to the article! 🙂

      Like

  2. Ro says:

    Great article Angelo, thank you

    Like

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