Controlling Imported Cabbage Worm and Cabbage Looper Damage in Brassicaceae Crops in an Organic Production System

Problem

Despite the recent rise in awareness around nutritional benefits of so-called “ugly food” and the persistent problem of food waste, there is still purchasing bias against foods that do not look perfect. This is especially true of vegetables that exhibit obvious signs of pest damage at the time of purchase. In particular, vegetable farms that use organic practices are often plagued by produce bearing visible pest damage, especially in brassicas crops such as broccoli, cauliflower and cabbage. Without the option to apply pesticides, it is challenging to rid brassicas of pests such as cabbage looper (Trichoplusia ni) and imported cabbage worm (Pieris rapae).

Organic standards do allow the use of some insecticides, such as Bacillus thuringiensis (Bt), but we would prefer to incorporate practices that reduce pest populations without the use of any chemical intervention. Many of our CSA members have a high tolerance for produce exhibiting some pest damage, but our retail and wholesale outlets have little tolerance. The economic impact of not being able to sell our brassicas through wholesale markets is significant when considering the size of our farm and is similarly a problem for many pesticide-free growers in the Red River Valley. Anecdotally, we have also heard of vegetable growers composting much or all of their brassica harvest due to this pest issue hindering their ability to find a market – a large negative economic impact for a small-scale grower!

The questions this project sets out to answer are:

Which methods can be used to either eliminate or drastically reduce the number of pests in brassicas without the use of pesticides?

Which methods are most economical and do not require a great deal of extra labor?

How quickly do the funds spent on these methods create a positive return on investment?

Solution

This project will test different methods of controlling and repelling cabbage looper and worms and collect data to determine which are the most effective methods for farmers to control pests without using pesticides. To do this, we will employ methods such as floating row cover and companion planting. We will also research other potential methods of control such as deterrents and learn more about the life cycle of the pests by consulting with entomologists at our local land grant university.

A combination of broccoli, cauliflower and cabbage will be planted in four test plots. These brassicas were chosen because they are in demand by consumers and are often significantly damaged by the aforementioned pests. All of the plants will be started indoors to mimic the typical system used on small-scale vegetable farms for starting and planting brassicas. We will mulch to control weed pressure between the planted beds and encourage more predator habitat.

Test Plot 1: Control Plot - No intervention beyond general crop maintenance.
Test Plot 2: Row cover used over brassicas.
Test Plot 3: Companion planting to attract beneficial insects as well as plants that may repel the pests. Test Plot 4: Row cover + Companion planting.

Data collected will include:

Bi-weekly count of the number of cabbage loopers and worms and noting of any damage seen to plants by these pests.

Bi-weekly observation and recording of the variety of beneficial insects attracted by the companion planting.

At harvest, count the number of cabbage loopers and worms residing in each plot’s vegetables.

At harvest, count the number of vegetables suitable for wholesale market.

Track the amount of time spent on each test plot. For example, if there is extra time needed to weed the plot with the row cover, the extra labor will be noted.