Cabbage looper chowing down on some broccoli leaves.
It is important to me to not expose my family, our workers, nor our customers to toxic chemicals. For this reason, people often ask me how we manage insect pests on our farm without chemicals. The answer is pretty simple: we intercrop. We bolster the plant’s natural defenses. We encourage diverse populations of beneficial insects. We use natural products such as extracts, soaps, or natural oils, and if all else fails, we simply do not grow the crop. This year we are going a step further and planting a trap crop! The idea of a trap crop came to us via the Alabama Cooperative Extension, who spoke at the Southeast Fruit and Vegetable Conference. They suggested we plant sunflowers and sorghum near our tomatoes, to “trap” stink bugs and leaf footed bugs. We will be giving it a try this season. It seems that no single method works, but they all work together.
The idea behind a trap crop is that you plant a crop just for the pest insects, in the hopes that they will enjoy your trap crop more than they want your market crop. In the case of tomatoes, stink bugs and leaf footed bugs are two of the biggest pests and cause little yellow marks on the skin, with white marks on the internal flesh. They make the tomatoes unmarketable. This is why we grow cherry and grape tomatoes more than full sized tomatoes. Stink bugs don’t like cherry tomatoes! Next week we will plant sunflowers in the row right next to where we will put the tomatoes. Then in May, we will plant the sorghum to continue the trapping job. According to the Alabama Cooperative Extension, the pollen on sunflowers and sorghum is irresistible to these pests. Hopefully, they like them better than tomatoes!
Insect pests love it when they can find a big expanse of their favorite food. They get right in there and start munching away, having babies, and calling in all their buddies! Just a few caterpillars or mites can quickly turn into a zillion. One of our strategies for managing this is to confuse the pests by mixing up the crops. For example, caterpillars especially love crops in the brassica family, such as kale, broccoli, and cabbage. If you plant them all together in one big field, you will be supplying an all-you-can-eat buffet! To solve this problem, we spread these crops all around the farm. We also try to “hide” them among other crops the pests might not like. For example, we may plant 3 lines of something in the kale or cabbage family (that caterpillars love) and then switch to a few lines of something in a different family, such as lettuce or beets, that isn’t a host for that pest. The hope is that even if a pest gets into one area, it won’t easily move on to other areas.
Additionally, we try to harness the crops’ natural ability to deter pests. When plants perceive the presence of a pest, they spring into action, producing compounds that may taste bad to insects, inhibit their reproduction, or possibly make them sick. These are often phenolic compounds and antioxidants,that may even have a positive impact on human health. Plants also can produce volatile methyl jasmonate, which acts as an attractant to beneficial insects, further helping to manage the bad guys. It has been proven by a graduate student at the Nova Scotia Agricultural College that treating your crop with seaweed extract elicits one of the same pathways within the plant that is responsible for this natural resistance1. Our crops get a good weekly dose of seaweed extract. It helps them grow better, resist pests better and ultimately yield better!
There are other natural products that can also deter insects. Neem oil has been proven to deter many insects, as well as, in some cases, disrupt their life cycle. We often use a bit of that in our seaweed applications. Non-toxic soaps can kill insects because they penetrate the outer shell of soft bodied pests such as aphids or mealy bugs. Natural oils, such as orange oil, can smother insects such as mites, as well as deter insects. Some people use strong smelling botanical oils, such as cinnamon or garlic oil, that they say work well. We have not done that, but I hear good things about it.
Another great strategy is to ensure there are plenty of beneficial insects around, by planting rows of herbs and flowers, where the beneficials like to live and reproduce. We intentionally leave rows of older crops to “go to flower”, as well as plant new types of flowering crops for this purpose. Keeping those older crops cleaned out can sometimes be a mistake, because it eliminates natural habitat to some of our best friends, beneficial insects. Lady bugs love to live in parsley and cilantro. They don’t harm crops, but they are voracious predators to pests such as aphids. Green lacewings are not only lovely, they also hunt and eat soft bodied insects such as aphids. Other good guys include assassin bugs, minute pirate bugs, big eyed bugs, and even different types of beetles. All these good guys need a home. Without an appropriate habitat, you will have far less beneficials, which means far more pests. Bees that pollenate the crop also need places to hide and forage. They love clusters of flowers and herbs.
Lastly, if a crop truly has so many enemies that it cannot be grown without applications of chemicals, then we simply choose not to grow it. It probably means the varieties available are not well suited to our environment, and that growing something else is a better idea. Last year, I tried to grow Amaranth. This is a specialty green that grows well in our summer heat. However, it is so prone to flea beetles, there was no way to grow it without being full of holes that ruined the appearance. I probably will not grow that one again. I have found that many types of squash are also in the same category. This last strategy is probably the best advice of all: choose crops that grow well in your area and are mostly care free. Don’t even engage in the war!
Eat your veggies,
1Extracts of the marine brown macroalga, Ascophyllum nodosum, induce jasmonic acid dependent systemic resistance in Arabidopsis thaliana against Pseudomonas syringae pv. tomato DC3000 and Sclerotinia sclerotiorum. Subramanian et. al. European Journal of Plant Pathology, April 2011.