Safe Insect Repellents

The Garden Corner

Spider mites, aphids, thrips, oh my! Sadly, along with fall colors comes an invasion of these pesky insects. And trust me, when it comes to bugs, things can go south real fast! Fall’s warm weather, often times referred to as “The Indian Summer”, creates the perfect condition for these destructive creatures to explode overnight. Before you know it, there could be a full fledged war happening in your backyard. Luckily I have some tricks up my sleeve to keep these bugs at bay.

Now there’s a few things to keep in mind when it comes to repelling insects. This first thing to remember is that you’ll never be able to kill every single bug. Not to worry though, plants are able to tolerate a few insects here and there. Secondly, it’s highly important to be mindful of bees. The rule is: When flowers are present, there’s likely to be bees present. That’s why fall is an optimal time to spray for pests, as most plants are in a somewhat dormant state waiting for the winter rain.

When the bugs attack, the first thing I’d recommend is Neem oil. This organic pest repellent is made from the seeds of the Neem tree, and available at most nursery centers. Neem oil works by covering the insects’ breathing holes, and is also effective against leaf fungi on manzanita and toyon. Next on the list are soap sprays. I would suggest a simple soap spray made of potassium salts, which like Neem oil, smothers the bugs’ breathing holes. Lastly is Bacillus thuringiensis. This spray works exclusively on caterpillar insects like the ones that eat oak trees, and should only be applied in the evenings as it breaks down in the sunlight.
I hope this gave you a bit of insight on how to prepare for Fall’s creepy crawlers. Until next time, happy gardening! If you have any questions, please contact me at:

-John Nowak

The Garden Corner Oct 2019

As we march closer to fall, it’s time to think about preparing our landscape for the upcoming rains, cold nights and of course weeds. I thought it would also be a good time to think about tearing out overgrown shrubs and trees to replace them with new plants or the same thing.

Our chapter has always targeted our plant sale for November because it is the best time to plant with the winter rains coming, hopefully. But in a perfect world we can expect rains in January through March. So, what to do? Well, here are a couple of thoughts.

First, its time to take a walk through the garden and look closely at what you have already. Are you happy? Are some plants old and need to be replaced? Take a note pad with you and write down your thoughts. Sometimes I like to do this after work, when I’m feeling relaxed. I look at the yard and think to myself, “What would look really cool here?” This could take weeks, but knowing that the rains are coming, now is the time to, as my Dad used to say ‘Johnny, put your nose to the grindstone’. Second, prepare for the weeds, and this is best done by mulching. There are so many ways to mulch and there are some articles that say mulch can encourage weeds. In my experience, when mulch is applied too thin it is ineffective. A thick layer of three inches will put an end to most annual weeds. Perennials, such as Bermuda grass, will not be controlled with mulch, sorry. Further, it’s important to keep an eye on pests. Many pests will show up when you least expect them. I’m going straight to Neem oil now, with a soap spray every other treatment; very effective for spider mites, thrips and aphids. For loopers, which are prone to attack oaks, I use Bacillus thuringiensis. Spray at night, because it breaks down in the sun. It only controls loopers; therefore, it won’t hurt other insects.

This brings me to my last point. Whenever we spray in the garden, even with Neem oil that is totally organic, we need to watch for bees. If you see bees, the rule is to not spray. Spray late in the day when the bees have returned to their hives. I’ve covered a lot. So until next time, Happy Gardening.

– John Nowak, Plant Sale Chairperson.



Mugwort, Artemisia douglasiana

This plant was used for a variety of uses throughout California. The Chumash made a tea to put on poison oak to relieve the symptoms. They also made a felt cone from the dried leaves to burn on a patients skin to cauterize a wound (Source: Jan Timbrook). Leaves were placed in food storage containers, such as acorn granaries, to keep pests away. It was used ceremonially by many tribes. I think it has a lovely aroma, which according to some tribes, will give you pleasant dreams when put it under your pillow.

One time, many years ago, I volunteered to cut down a very large bush of poison oak next to a building at work because I did not think that I was very allergic to it. In the process of chopping it, there was so much sap that it went right through my clothes to my sweaty skin with open pores. I caught a bad case of it. I was on my way that weekend to a camping trip with the California Indian Basket Weavers Association in the Sierra foothills. I forgot to pack the Caladryl and was so miserable in the heat with my rash. I thought I might have to give up and go home. Then I remembered what I had heard about the mugwort. I asked one of the local women where it might grow nearby and she told me to go to where the highway goes close to the river. I gathered a bunch, crunched it up in a bucket of water. It kind of looked like Mug root beer. I found that when I sloshed it on my skin, I got just enough relief that I could stay at the event and enjoy myself.

Mugwort grows easily from runners and likes soggy winter soil that dries up in summer. It will die back then but come back when the rains start again. It likes the shade of oak trees, and will grow in sun if it has more water. It tolerates heavy clay soil just fine. It is often found along the side of trails and streams. It doesn’t have much in the way of flowers, but smells great.

-Cathy Chambers

Horticulture 101 – The Basics

As someone once said “ Let’s start from the beginning.” Horticulture defined: the science and art of growing fruits, vegetables, flowers and ornamental plants. Native California plants, more or less, fall under the flower and ornamental plant category, though some are eaten as fruits and vegetables. (more…)

Invasive Species: Brassica tournefortii (Saharan mustard)

Invasive Species: Brassica tournefortii (Saharan mustard)

Brassica tournefortii is in the Mustard family. It is native to the desert areas of the Mediterranean region of Europe. It has expanded its distribution in the sandy soils of Los Osos, most probably spread during the sewer project, and can rapidly overtake other plants and form a monoculture. (more…)

Native Plants for Erosion Control

Native Plants for Erosion Control

Coffeeberry Frangula californica – Images courtesy of Marlin Harms Way back in 1992 the Watershed Education Program for San Luis Obispo County, in conjunction with U.C. Extension and the Soil Conservation Service (now Natural Resources Conservation Service)...

Native Plant Pest Control

With the drought extending into three summers now, many plant pests have taken advantage of the warm dry conditions. Even though California native plants are strong, hardy, and usually resilient, the lack of moisture has stressed them beyond their normal expectations. With this extra stress the plant’s ability to fend off insect infestations has diminished immensely, leaving many plants to decline to the point of no return. Keeping this in mind, I am going to give some suggestions about pest control.

First, pests hate water, so if you can, use water to wash down the leaves of infested plants. Second, soaps such as Dawn dishwashing liquid non-bacterial formula can smother insects such as aphids, red spider mites, and scale. (I use 1 tsp. per quart of water.) Lastly, for severe infestations, I use neem oil which can work as a insecticide and/or a fungicide. It comes from a plant (Azadirachta indica) so it is a non-petroleum based oil. Follow the instructions on the label.

Hope to see you at the next meeting.


Amanita phalloides

Amanita phalloides

Why is the Death Cap mushroom so deadly?

On New Year’s Day I visited a favorite, and normally productive, chanterelle patch outside San Luis Obispo to discover an enormous fruiting of the dangerously toxic death cap mushroom (Amanita phalloides).

My culinary disappointment was tempered by my growing fascination with the question, “Why are mushrooms deadly poisonous?” Proximally, the answer is direct: because they contain a peptide, alpha-amanitin, which halts RNA transcription in the cell nucleus. In broader context, the question should be rephrased, “What ecological advantage and evolutionary fitness does the presence of this toxin contribute?”

Amanita phalloides is a newcomer to California. It is known to be a native of Europe, and its first verified collection in California dates to 1938. Anecdotally, its introduction is ascribed to an accidental arrival on the roots of cork oak trees. It is now known from Southern California to British Columbia. A similar introduction (on the roots of Italian chestnuts?) affects the East Coast.

Death cap is an ectomycorrhizal symbiont. This means it forms connections on the root-tips of forest trees; in California, its typical (but not exclusive) partner is coast live oak. Unlike many symbionts which are highly host specific, death cap is promiscuous in its associations as it spreads worldwide. It is now present in South Africa, Australia and most other similar climes.

Ectomycorrhizal (EC) fungi collect major nutrients, nitrogen and phosphorous, and exchange these with the host tree for sugars. Delicate hyphal strands extend outward from the root tip mass into the surrounding soil and mulch. EC also allows efficient active transfer of macronutrients, micronutrients, and soil water to the tree. The chronic phosphorous limitation in serpentine soils makes the EC symbiosis especially important for local forest types on this soil. Studies in Norway discovered up to 50% of a birch tree’s sugar is exchanged at the root tips with EC symbionts.

Death Cap - Amanita phalloides

Death Cap – Amanita phalloides

Other studies describe how a mushroom, Laccaria bicolor, lures springtail insects (Folsoma candida) into traps, consumes them, and transfers the nitrogen obtained to its host tree.

Trees form non-exclusive associations with many fungi. Studies at Pt. Reyes show more than 15 taxa of EC fungi present at the root tips of coast live oak from a single grove. Most of the live oak symbionts are not deadly or even dangerous, and include the sought after chanterelles.

It is an entirely open research question as to whether the recent invasion of Amanita phalloides into the California oak forest is supplanting native fungi. Studies (in Bishop pine) have shown that EC fungi partition their habitat niches very precisely, allowing multiple fungi to coexist in close proximity. I have visited the particular chanterelle patch since the 1970’s without noticing the Aman5.0ita, so the 2012 fruiting might possibly represent a replacement of one symbiont for another, or just be a fortuitous fruiting of an established co-dominant.

The “competitive exclusion principle” argues that if these organisms are competing within the same precise niche, the most successful will replace all others. The deadly toxin of Amanita’s is alpha-amanitin. This is a heat-stable cyclic peptide that interferes with the transcription function of RNA in the nucleus of cells of virtually all organisms.

Humans, dogs, rabbits, and guinea pigs are equally poisoned. The toxic crisis is caused by irreversible liver or kidney damage, as the molecule concentrates in those organs. More expansively: organisms other than bacteria are affected by alpha-amanitin. Insects, worms, flowering plants, and even viroids (infectious single strands of RNA) that cause “mad cow” and disease in plants cannot replicate when treated with amanitin.

Amanitin is a large, very stable molecule (C39H54N10O14S) so it represents a significant metabolic cost to the fungus to create. Several, widely unrelated, taxa of gilled mushrooms possess amanitin toxin, so its synthesis has been separately evolved several times in fungi –supporting the assumption this represents an important competitive innovation for the species. Fortunately, amanitin is too large to cross the blood/brain barrier, so even victims with irreversible liver and kidney damage due to mushroom poisoning are not affected mentally.

An evolutionary entomologist working in New York State, John Jaenike, has discovered four species of mushroom flies in the genus Drosophila that lay eggs in the gills of fruiting Amanita phalloides. The fruit fly taxa are related to ones that inhabit rotting skunk cabbage, but in New England have recently transferred to the recently introduced Amanita fruitings.

Jaenike discovered that Amanita phalloides is toxic to the damaging parasitic nematodes Howardula that reproduce in the stomach of fruit flies. The toxicity of the death cap to the parasitic nematodes results in much greater egglaying (fecundity) by the fruit flies. The fruit flies are affected by the toxic amanitin, especially the males, but the poison is more than offset by the increase in reproduction.

Janike also discovered that most other insects using mushrooms as egg laying sites (craneflies and forest gnats) shun use of the Amanita (due to its toxicity).

Fruiting mushrooms are a scarce and erratically scattered resource for reproduction and larval feeding. Fruiting mushrooms are fully and completely consumed by mushroom gnat larvae, and Jaenike postulates fierce competition for insect breeding sites. Jaenike has published several papers describing the Amanita-Drosophila-Howardula food web. Mushroom flies secured a niche free of competition by exchanging an evolved tolerance to sub-lethal poisoning for escape from nematode parasitism. The increased fitness leads to greater egg-laying ability, and has provided the evolutionary inertia for this recent adaptation.

Nematodes are significant pests of commercial mushroom production, epidemic infestation can result in the loss of the growing beds. The oyster mushroom, Pleurotus osteraceus, traps and consumes nematodes in noose-like knots of hyphal tissue.

So why are Amanita so poisonous? It is an unlikely deterrence to vertebrate predation of the fruiting caps, as the effect is slow-acting (36-72 hours before the toxic crisis in humans) and the toxin is not concentrated in the cap. Evidence supports the hypothesis that the fitness obtained from synthesizing the toxin is secured within the hyphal network. Perhaps toxic Amanita obtain nitrogen from poisoned nematodes, or protect themselves (and their symbiont hosts) from plant parasitic nematode predation.

Perhaps the toxin suppresses the growth of competing fungal webs. It seems clear the toxic effect of death cap is intrinsic to its invasive success worldwide.

John Chesnut | Rare Plant Coordinator and Education Committee at CNPS-SLO, John teaches horticulture at Cal Poly


Jaenike, J., “Parasite Pressure and the Evolution of Amanitin Tolerance in Drosophila,” Evolution,Vol. 39, No. 6 (Nov., 1985), pp. 1295-1301. Jaenike, J. and T J. C. Anderson, “Dynamics of Host-Parasite Interactions: The Drosophila-Howardula System,” Oikos Vol. 64, No. 3 (Sep., 1992), pp. 533-540.

Pringle, Anne, and Else Vellinga, “Last chance to know? Using literature to explore the biogeography and invasion biology of the death cap mushroom Amanita phalloides.”

Pringle, Anne, Rachel I. Adams, Hugh B. Cross, and Thomas D. Bruns, “The ectomycorrhizal fungus Amanita phalloides was introduced and is expanding its range on the west coast of North America,” Molecular Ecology (2009).

Wolfe, Benjamin E., Franck Richard, Hugh B. Cross, and Anne Pringle, “Distribution and abundance of the introduced ectomycorrhizal fungus Amanita phalloides in North America,” New Phytologist (2009).

Wieland, Theodor and H. Faulstich. Amatoxins, Phallotoxins, Phallolysin, and Antamanide: The biologically Active Components of Poisonous Amanita Mushrooms.

Horton, Thomas R., and Thomas D. Bruns, “The molecular revolution in ectomycorrhizal ecology: peeking into the black-box,” Molecular Ecology (2001)10, 1855–1871.