The recent infestation of bagrada bugs has annihilated several beds of cruciferous vegetables, including arugula and mizuna. They appear when the temperatures are hot, so we expect to see more of them as summer sets in. There are no major predators for bagrada, and their primary food source is in the brassica family (broccoli, kale, cabbage, arugula, mizuna, mibuna, etc). We cut down a bed of arugula, but wanted to research some other options for dealing with this bug.
We read about a fungal control that might work. In the meantime, I thought compost tea might be worth a try, since we can make it freely and easily right away. Compost tea is mostly used to boost plant growth vigor & soil fertility, but it is also effective against plant diseases and some pests. Since the commercial biological control for bagrada was fungi, compost tea could potentially culture these specific strains or similar ones. At the very least, it would boost fungal diversity that might help suppress bagrada growth.
In essence, compost tea is created by steeping compost (usually worm compost) in a bucket of water. The microbes in the compost proliferate in the water over a period of 1-2 days and serve as an inoculum for the soil.
The popular method of brewing compost tea is taught by Elaine Ingham, PhD. A mixture of molasses, fish emulsion, and kelp is added to the tea to promote fungal growth. To ensure aerobic conditions, the tea is aerated either by stirring or using an electric air pump.
I am not a supreme expert on the microbial community of compost teas, but I have used a compost tea from a successful vermicompost company in New York, and I found that it suppresses root rot very well. Their method does not use active aeration, but instead uses passive aeration. When adding water to the bucket, oxygen bubbles naturally form. The water itself has oxygen in it, and there is an exchange of oxygen happening at the surface of the water. The worm compost is steeped in the water over 48 hours without stirring. They found fantastic results with this method and sell their compost tea to commercial growers. I don’t recall any additives, but they may not have told me everything as they keep their method proprietary.
JD built his own automatically aerated compost tea brewing system and typically adds fish emulsion and kelp to his tea. We decided to experiment with both compost teas on bagrada. For each bed we tested, JD’s compost tea was applied to a third of the bed, my compost tea was applied to another third, and the last third was left without any application to serve as a control. The mizuna bed is pretty much done for, so we don’t expect it to recover, but we can still assess the effects of our compost tea application on bagrada, and we can compare our brewing methods and their effects on plant health.
I am excited about doing this little experiment on the farm and will report back next week with our results.