Today we visited an urban farmer group that pays special attention to permaculture. For those that aren’t familiar with permaculture, it’s a type of gardening or farming aimed at creating a self-sustaining ‘ecosystem’ that doesn’t require intervention to manage insect pests or weeds. This strategy, in theory anyway, relies on plants that do not interfere with each other and attract natural enemies (i.e. predators of pest insects). If plants are being attacked by an insect or disease, the typical ‘philosophy’ behind permaculture is that the plant doesn’t belong there anyway – so maximum crop or yield production is not the main or only goal.
I’m not certain whether it’s because these gardeners were using permaculture or because they are in an urban setting, but they had a lot of different kinds of insect pests. The variety of pests and diversity of plants made it a bit challenging to pin down just a few pests or diseases that were the most important – there was a lot of equally somewhat important pests.
Some of the insects I took particular note of were the blotch leafminer on basil, abundance of ant-sucking pest mutualisms, and the spiraling whitefly.
It was easy to mistake the blotch leafminer, at first glance, for some kind of downy mildew or other plant pathogen. The symptoms are circular and produce ‘wet spots’, as you’d expect in a bacterial infection. After doing some research online, I found out that it’s actually damage caused by a fly that lays an egg on the leaf. The larva then comes out and feeds within the tissue of the leaf, causing that blotching effect. Removing this pest in an organic permaculture setting is a bit challenging, but they can certainly reduce the populations by removing any leaves showing the symptoms – that will remove the larvae, and subsequently future adults from laying more eggs on the basil.
Sucking insect pests are often trying to get at the nitrogen in the plant sap, to make more proteins, and thus make more babies. All the insects just want to make more babies! To get said nitrogen, they need to go through a lot of plant sap – so they poop out the extra as a sugary solution, known as “honeydew”. This honeydew creates sticky surfaces on leaves and also acts as “food” for mixture of molds referring to as sooty mold. Well it turns out that ants really like this sugary solution, so they will actually provide protection for sucking insect pests in order to get more honeydew! This results in a positive-positive relationship between the sucking insect pest and the ants; the pest benefits by getting protection from predators by the ants, and the ants get alllll the poop juice they want! We call this type of relationship a ‘mutualistic’ relationship. A very common mutualism is between aphids and ants; so I always advise looking for aphids or other sucking insect pests if ants are seen running around on leaves and stems of plants. We didn’t see any shortage of such mutualisms in these gardens! This is also makes managing the aphids a bit trickier; killing the aphids will result in the ants just bringing them right back! A management strategy also needs to consider how to prevent the ants from beginning them back into the garden.
I also observed a reasonable amount of beneficial insects, mainly lady beetles (common referred to as “lady bugs”). Most people associate lady beetles with the large red beetles with black spots, and don’t always recognize different species or even the larvae. Above are some photos of some black lady beetles with black spots – resembling the twice stabbed lady beetle.
Any applied entomologists knows to look on the undersides of leaves for insects. As I was flipping some palm leaves, I was seeing these funny patterns – almost like crop circles made of white wax. I just neglected it for a while, thinking it was some kind of anomaly and not worth trying to figure out what it was, but kept seeing it more and more. I started finally seeing some at different stages of development and it blew my mind when I realized that they were whitefly eggs! The spiraling whitefly lays eggs in a spiraling/circular pattern and when they emerge, will start sucking on the plant (sucking insect pest!). After some time, they will eventually pupate and become winged adults. Kept unchecked, these whiteflies can apparently grow to some staggering numbers.
On the cassava leaves I also saw some ‘galls‘; growths formed by the plant in response to insect feeding or oviposition (laying of eggs). The culprit is often within the gall, sucking on the plant juices as the new plant growth provides protection for the insect. It’s a type of ‘manipulation’ of the plant by the insect, if you will, to make it protect itself from predators while feeding. Very few gall-forming insects are of concern in terms of crop yields, although they can be rather problematic for ornamental growers that are trying to sell the whole plant.
The permaculture group was quite different from the others; they weren’t ‘farmers’ per se, but rather gardener enthusiasts with full-time jobs. They reminded me, in a way, of master gardeners in Texas. They are passionate not just about growing food, but also learning about the insects, the plants, and having beautiful gardens. They interchange information on what to plant, share cuttings, and even share produce with each other. It was a great pleasure to walk around and learn about the gardening they are doing here.