I rarely write or talk about garden pests. Like many of you, I just want them to go away. However, wishing is sometimes not enough, so let’s talk.
This summer I had three insect pests that I want to address: thrips, scales, and ants. The thrips are enjoying my barberry, while the scales are on toyon and other shrubs, The ants were (yes, past tense) on my prized manzanitas and one Ray Hartman ceanothus. There is a lot to cover here but I think many will gain something if I go through them one by one. And I’m sure that someone will suggest a treatment that I have not tried.
Thrips are tiny, sucking insects that are often not seen, though the damage to the leaves is unmistakable. Damaged leaves are sometimes silvery, stippled or discolored. There are many species of this order of insects but the ones on my barberry are probably greenhouse thrips. Noticing a lot of leaf damage late in the summer I finally decided to look at the tiny yellow insects that were also present on the leaves. They are very tiny and my pictures aren’t great but good enough to be pretty sure of the identification.
I have a simple approach to this and other common garden pests. I trim off and dispose of the most infested parts. The University of California, Integrated Pest Management web resource, Pest Notes, confirms the efficacy of this method. Thrips don’t usually kill their hosts, though they can weaken them. They are difficult to control, and spraying with insecticides is unlikely to be very effective. More important to me, though, is the fact that I really don’t like to use poison in my garden. I fear for the health and safety of other nearby critters, birds, beneficial insects, lizards, and so on.
Furthermore, the barberry plants that are affected can be pruned back according to UC-IPM: “Prune to remove old, damaged wood. Cut plants down to within a foot of the ground in late winter to rejuvenate plants in the spring.” Excellent! Next I will cut the ugly-looking mess nearly to the ground, rake out the leaf mulch to clean up some of the eggs and insects that may have fallen to the ground. I think I will water these stressed plants when they re-emerge next spring, especially if the winter is dry.
Remove infected stems
This general approach: cutting off infected stems, cleaning up the ground, and then babying the new growth has served me well in the past. It is especially helpful for plants with aphids on new spring growth. In this case, however, I usually don’t water much because I don’t want to encourage the growth of the soft stems and leaves that aphids so enjoy. Rather, I tip prune until the temperatures rise and the aphids decline due to the hot, dry conditions. I also look for lacewing and ladybugs that love these tasty, tiny pests because they can clean off an infected plant lickety-split. This is extremely common for young sages because they grow so quickly. I water them enough to keep them from getting drought-stressed, but not enough to encourage rampant growth.
Like thrips, the are many kinds of scales. These sucking insects, however, lack a distinctive head and other body parts. They usually look like tiny blobs attached to plant stems or leaves. Some types of scales excrete honeydew, a sweet liquid prized by ants.
I have had scales on toyons, annual wild sunflowers, manzanitas and even purple nightshade. Once again, I treat the plants by removing and disposing of branches and stems that have an abundance of these pests. The purple nightshade and the annual sunflowers only show the scales towards the end of the season, so the nightshade plants are cut to the ground, and the sunflowers are pulled out. For shrubs, like the manzanita and ceanothus, I prune heavily infested branches. It is equally important to get rid of ants that may be partners in crime with the scales. This is harder to accomplish but I discuss it in the next section.
Argentine ants, those most common in Southern California, do not directly damage plants. Rather, they “farm” insects that can stress and even kill them. The insects that ants farm feed on plants by sucking sap and then excreting a sweet, sticky substance called honeydew. The honeydew nourishes the colony of ants. The ants protect aphids, scales, mealybugs and other sucking insects by interfering with the activities, like egg laying, of natural predators and parasites, and even killing these beneficial organisms. Without the presence of natural predators, the sucking insects increase to numbers that can result in extreme stress and even death to the plant.
If you see ants climbing up and down the trunk or stems of a plant, you will almost certainly also observe some of the most common plant pests: aphids, mealybugs, soft scales, and whiteflies. The ants must be controlled for the health of the plant!
Ants on my manzanitas
In December 2013 I planted two one gallon manzanitas (Arctostaphylos manzanita) to flank the front walk to my symmetrical craftsman home. The color of their bark and leaves matches that of the house. Once grown, the stature and grace of these shrubs will provide a striking welcome to the house and garden.
This year, over five years after planting, they were finally starting to look like something, and so I was very, very dismayed to see some stems covered with scales. I trimmed those branches and noticed that there were ants marching up the main stem. Now, I am a patient gardener, and I rarely get too bothered when I lose a plant. Monkeyflowers have come and gone, some ceanothus have bit the dust or been removed because they got too large for their space, and I have not lost any sleep over it. But these manzanitas have taken nearly six years to be even noticeable. I am 66 years old and will be 72 in another six years. I don’t have that kind of time! I want these to make it.
So when I noticed the ants I sprung into action with more fervor than knowledge. I sprinkled diatomaceous earth around the base of the plants, and it worked! The ants were agitated and with a bit of time they all disappeared along with the scales.
Sounds like a success story, but I have learned a bit since then. The diatomaceous earth desiccates the ants. Furthermore, they carry the fine dust back into their nests, killing other ants as well. The negative is that one must be careful using this fine powder since it is unhealthy to inhale it. Furthermore, it will wash into the soil with irrigation or rain. Not ideal for the roots, and it loses all efficacy if wet. There is a better approach.
Although there is a ton of info on the web about “natural” pest remedies, I always go to a source I can trust and that source is the University of California, Integrated Pest Management website. They suggest on their Pest Note about ants using sticky tape, like Tree Tanglefoot, on the stem of plants or trees rather than diatomaceous earth. You will need to check the tape to make sure it is continues to provide a barrier to the ants, but I’m sure it is better than having fine powder wash into the root zone. UC-Pest Notes on ants also suggests using a bait with .05%-1% borate insecticide to kill the ants in the nearby colony. Their Youtube video, Managing Argentine Ants Around the Home, is very helpful. If the ants return to these manzanitas I will once again spring into action, this time with a scientifically proven method.
The following general tips have kept my garden reasonably healthy without resorting to chemicals that could endanger the health of my family or critters who rely on my habitat garden.
- Notice your plants. Do they have an unusual number of yellow, brown or otherwise weird-looking leaves? Are they wilted? Do you see ants on their branches or stems? Is there a lot of ant activity near the base of the plant?
- Know what a healthy plant looks like. Learn what your plants need and what they look like throughout the year. Some plants will drop their large winter and springtime leaves as the weather gets hotter and drier. Smaller and sometimes curled leaves is merely summer attire for some natives like sages, monkey flowers and even some ceanothus. Many currants, gooseberries and other deciduous plants turn brown and drop their leaves in spring or summer. Watering in an attempt to reverse dormancy can stress plants, and invite diseases like pathogenic microorganisms and insects.
- Remove and dispose of stems with aphids, scales, or other sucking insects. Prune heavily infested stems and dispose of them in the garbage. A hard spray of water can dislodge enough sucking insects to allow your plants to thrive even with these pests around. It is best to hose off leaves in the morning so that they can dry quickly, reducing the growth of leaf mold.
- Keep the crown (base) of the plant clean and clear. Move mulch away from the base of plants. Check for ants. Keep it clean!
- Make sure your plants get the correct amount of water. Plants that are drought-stressed are more susceptible to pests. Similarly, over-watered plants produce soft, delicious growth that is favored by aphids and other pests. Learn to tell when your plants need water, and when to allow their growth to slow down and even go dormant or semi-dormant.
- Accept limited pest activity. Remember, you will never be able to rid your garden of all pests and weeds. Furthermore, some of these undesirables feed birds, lizards and beneficial insects. A dynamic and diverse ecosystem will have fewer serious pest problems. Gardens should be places of health; toxins have no business being there.
How does your garden grow? Do you have suggestions on ways to keep your plants clean and healthy without resorting to pesticides?