Real and supposed diseases of native plants

Disease, insect, or growth related problems? First, check that you are not overwatering, or fertilizing your plants. Also, check that you aren't planting the wrong plant in the wrong plant community; for example, desert plant in redwood forest, redwood forest plant in desert, sun lover in shade,  high- air- flow plant (coastal bluff, ridge line) in a closed area (enclosed patio), or water lover in dry spot. An upland, south- facing slope plant from Jamul planted in a Santa Monica or San Francisco garden may be covered with mildew, if it doesn't die of root rot. In the reverse situation, the plant will vaporize.
We believe that the naturally occurring non-plant members of a habitat, such as, but not limited to,  insects, fungi and bacteria, play an important role in our California ecosystems. They evolved with California native plants, some apparently giving, as in the case of the nitrogen-fixing bacteria; some apparently taking, as in the case of the manzanita leaf-gall aphid. If the takers were a serious problem, all our plants in the wild would not exist. Spraying with insecticides and fungicides is a quick fix and in the long term makes the problem much worse. If you can live with some pests such as aphids, you will attract more insect-eating birds, have a healthier garden for doing so and in turn have less aphids on your plants.  If your pests are out of control this is usually a sign of bad horticulture (eg. over/under watering, fertilizing, incorrect soil or incorrect location (a plant set out way beyond its normal range and under severe stress) Remember, in native ecosystems populations of all living things are controlled. For example, herbivores (rabbits) are controlled by predators (coyotes), insects (aphids) by birds ( Bushtits). Fungi and bacteria are a little more complicated usually being controlled by the plant itself or by other bacteria or fungi.

Good horticulture gets rid of most of the diseases.

No sprays needed. The few times in the past we did spray the garden plants (when we first started dealing with natives and didn't know any better), we ended up killing a lot of good stuff and the plants still looked sick. Native plants are for the most part unhybridized. They still have their natural protective abilities if you treat them right. Over watering them removes the plant's protections. Water for survival, not fast growth, and after a year or so the plant will give you faster growth.

Application of fertilizers, insecticides, fungicides and bactericides can also remove the native plant's natural immunity. It is funny that you can buy fertilizer with insecticide in it. Why do you need the insecticide?

Mulch is important: maintain moderate growth rate, protect plant, reduce evaporation, moderate soil temperature, provide habitat

Rock mulch for desert plants, tree mulch for forest plants, rock and tree mulch for chaparral plants.

Drip irrigation contributes to disease on native plants.

Drip irrigation causes all sorts of root problems and related pathogen problems. If the plant is not growing correctly, try turning off the drip or converting to spot sprays.

Drip irrigation leads to many 'diseases' in native plants.

If a sun lover is planted in shade, leaf or stem die back is common. If a sun lover is over grown by another plant the same thing happens.Basins cause problems ranging from root rot to tip burn.

Plant the long term climax plants leaving room for them to reach their full size without growing over each other or other plants. Die back occurs when sun lovers are in too much shade, so think ahead.

Native plants and drought tolerant plants in general lose their disease resistance when they are watered more than the minimum, particularly during the summer (after the first summer). The plants have to be under slight stress to keep their associated fungi, bacteria and other companions happy. Water or fertilize too much and the plant will exclude its companions and pathogens will take their place, overnight.

Most of the diseases we've seen on native plants have been from over-watering. Not overhead watering just over-watering. Overhead watering will cause problems if the foliage stays wet on a regular basis. If you have to water, water in the early morning in the spring. Not mid-day in the summer.

Manzanitas get a funny off color and burnt stems when the root system has been fertilized, drip irrigated, summer watered or otherwise monkeyed with.
Water for survival, add no fertilizer, and add no soil amendments or your native plants will die fairly rapidly. Under natural conditions, native plants are fairly resistant to diseases and pests. Under unnatural conditions (extra water during the dry season, application of fertilizer, addition of soil amendments), plants are susceptible to diseases and pests. Injected fertilizer (automatically injected into the water delivery system) is killing many native plants in landscape situations, whether it is via overhead or drip irrigation. Do not water drought tolerant native plants after the first or second summer, in most areas of California The first or second summer the little plants will tolerate watering. Water the first or second season to establish the plant, but if you can be patient and mulch, the plants will many times look better and be healthier if you do not water during the dry season after the first or second year.
It is important that the plant not be too stressed, overwatered or overfed because then these endophytes will be forced off by the plant. If the plant is planted and maintained properly the endophytes should be fine and there will be minimal damage by pathogens and browsers. Under the optimum horticultural conditions (and the appropriate species for the particular site), Ceanothus species will live for 50 years instead of three!
Under light to moderate drought stress plants increase their resins, terpenes, phenols and other stinky chemical components that protect them from just about everything. Many if not all of our native plants will develop “good” endophytes (microorganisms living within plants, to the benefit of the plant and the microorganism) in their leaves and stems. Apply overhead water excessively or spray fungicides and insecticides on your plant and these good organisms die. Endophytes are part of the biological controls that protect the plant from grazing herbivores, insects and pathogenic fungi and bacteria. In areas of low rainfall endophytes may be a moisture shunt, capturing morning dew. Endophytes can live within all parts of the plant, and vary by species and plant part. (Clark et. Al. ; Clay 1989, 1990; Petrine et. al.; Petrini & Fisher; Preszler and Price; Rollenger and Langenheim)

The root system-soil interface, and the endophyte-plant relationship is very complicated and interlinked. 'Good' bacteria, mycorrhizae (a symbyotic relationship between plant roots and fungi), other fungi, simple animals, other microorganisms, plant roots and aboveground plant parts all have to be happy to keep the plants disease free.Native areas should be weed free.

In the interior with the hot and cold extremes, and erratic rainfall a knowledge of horticulture and ecology is a good thing! If the mycorrhizae fail to become established on the plants, the plants will be dead, dying or unrecognizable. Do not get discouraged; the normal success rates for planting our plants is about 70% on REAL bad sites, 90%+ on bad sites, 98+% on easy. Native plants are real easy and the lazy person's dream. Just put the water-loving plants near water, the sun-loving plants in the sun, and the shade-loving plants in the shade. Also, a few plants are sand lovers, and some are clay lovers; plant one of these “lovers” in the wrong soil and your plant has a mystery 'disease'. The diseases go away if the ecology of the planting is even close to right.
The best disease resistance for a plant is to become mycorrhizal. The root system of a California native plant can grow 3-5 feet per year and the mycorrhizae about the same. Water-stressed plants can have a huge root system after a year, and be 'locked' into the same mycorrhizal grid as the trees around them, giving access to a wealth of nutrition and moisture. When the plant's roots mesh with those of its companion plants, the growth can be amazing! The plants can stop spending all their energy growing roots and can spend energy reproducing (flowering). Again, the more early watering, the harder it is to establish the plants onto the grid. If you water so the top part of the root ball is allowed to dry out between watering this encourages the plant to make mycorrhizal connections. If a native drought tolerant plant stays wet it will not become mycorrhizal. Also, if the plant dries out too much as it is trying to become established, it will again exclude the fungus because it does not have the 20% energy reserves to commit to the mycorrhizae.Mulch is very important to a native system
The same situation occurs if you apply the wrong mulch, to a native plant. Different plants like different kinds of mulch. For example, putting lawn clippings under an oak nearly killed it. The gardener removed the clippings, covered the area with shredded redwood bark, and the tree was 'cured' in one year. Put organic mulch on a desert species and watch it succumb to root rot. If you do not put good organic mulch (oak leaf, pine needle, or shredded redwood bark) around a pine, it will be more apt to contract diseases.
Weeds make up part of an alternate ecosystem, with their own set of pathogens and nutritional strategies. As little as 5% weed coverage over an area can have a dramatic negative effect on native plants. Many of the diseases and pests that affect native plants are there due indirectly and directly to the presence of the weeds. Oaks can be covered with mildew, scale, even mold; remove the weeds and they are 'cured'. In some cases, the weeds support pathogenic bacteria and fungi that infect the native plant. Sometimes, the weeds don't actually cause the disease; they cause the plant to become stressed, and so more susceptible to diseases and pests. For example, in the shady area under an oak tree, the weeds change the whole ecology, from the climate to the microorganisms and plants and animals in the immediate vicinity, by replacing the native vegetation and leaf mulch that was formerly present. This is sort of like what AIDS does to the human immune system. The HIV virus doesn't kill the person some other disease that the immunes system can no longer fight off does. The same sort of AIDS-like-condition can be triggered by watering, amending or fertilizing. The plants immune system is lost.Poodle dog burn on a manzanita trunk

Woodpeckers can make for holey trees. Be happy is you see these holes, many of the sapsuckers are threatened.Prune a native plant into a poodle dog, and you usually have a dead poodle. Native plants like minimal (lazy man) pruning in late summer or fall. If you prune the lower branches off as in the picture to the right and left, then the trunk is not protected by the foliage, and is susceptible to sunburn (right), borers, and sapsuckers/woodpeckers (left).

Prune up the foliage and create those foo-foo shapes people seem to think are natural, and the stems burn off, get infected with borers, or get pecked to death. Instead, plant one of the manzanitas (Arctostaphylos spp.) like Ian's Bush, Dr. Hurd, Mama Bear, Louis Edmunds or Austin Griffiths, or Ceanothus cultivars like LT Blue that possess a naturally open form if you want that look. No plant mutilation necessary!

Frost damage to plants is sometimes incorrectly identified as disease damage.

Summer Deciduous Plants

A lot of customers get excited when they experience summer deciduous plants for the first time. Many native perennials shut down in summer, and come to life in late fall. This is normal and desirable. The flower show is better and less diseases occur when the monkey flowers, sages and other perennials are allowed to shutdown. Plant some evergreens (Manzanitas, Oaks, Toyon, Coffeeberry, and Ceanothus) with them so the whole flower bed doesn't shut down at once (ugly).

Frost can sometimes look like a disease or problem on a native plant.Monkey flower, Milkweed, Ceanothus, and others are larvae plants for many of the native butterflies. It is NORMAL and desirable to have caterpillars on them. Those are baby butterflies.

Narrow Leaf milkweed gets a golden aphid that the smaller birds eat. Almost every year it gets it. No biggy, it is part of the live cycle of the plant.

Oak trees will commonly get oak moth caterpillar. You do not need to spray the tree. The tree probably uses the caterpillar to covert the leaves into fertilizer and mulch on bad years.

Leaf gall on manzanitas.

This is a little insect that lives in the leafs. This usually is an occasional problem and the plant will drop these leaves in early winter. No biggy. Funny, some customers love the gall, and try to buy the plants that have it, other people are appalled the there is a BUG IN THE LEAF!

Leaf gall is a minor problem on many plants.galls are formed by the oak tree, usually in response to an insec

Oak Galls

Also, called Oak Apples. There are hundreds of different kinds of oak galls. The galls are formed by the oak tree, usually in response to an insect.. Inside the gall, the young insects develop out of the rain and sun and protected from predators. Cool, huh! These oak galls are naturally found on oaks in the wild, and usually do not have a negative effect on the health of the tree. (Translation: no big deal)

Leaf galls are little bugs on the leaves.Stem die back.

On manzanitas it is either sunburn (they pruned the stems up too high), poor air flow or too much overhead watering (planted next to a lawn in a closed in yard).

Ceanothus stem die back occurs on some of the real coastal plants, particularly the low ones, when they are planted in the interior heat. The sun fries off the bark.

Sycamore Anthracnose

This disease is a fascinating natural phenomenon. The leaves of the sycamore tree emerge in the spring to then turn brown and wither and fall off. Supposedly the fungus that causes sycamore anthracnose is an obligate parasite, which means that the fungus needs a living host; if the fungus kills its host, it will also die. Since this fungus has evolved with the sycamore tree over millions of years, what happens is as follows: on drier years the tree is hardly affected and makes good growth and the fungus causes no or minimal damage and on wet years the fungus makes good growth and the tree can be defoliated, and make very little growth. (Translation: no big deal on some years, a big deal on other years, but trees will rarely die)

Buckeye Dieback

Die back of Aesculus californica: This is not dieback, it is a natural condition, called semi-dormancy. On the east coast, it is very noticeable that the leaves of the trees turn color and fall off the trees. The trees are not dead or dying, they are undergoing a “slowdown” period, a period in which they can avoid the harsh conditions of winter. In California, our harsh conditions occur in the summer. So, around late summer, the buckeye leaves turn brown and yellow, and many fall off, and the buckeye undergoes a period of semi-dormancy, and is semi-deciduous. (Translation: no big deal)

Plant Wilts/Dies Practically Overnight or Root Rot/Wilt

This problem is a root rot/wilt that occurs later in the season, around late summer, early fall. This disease occurs on plants 2 years or older. This disease occurs within one to several days or so following a heavy watering of the plant, by the gardener, done because the plant looked “stressed for water/wilty/thirsty/etc.” Every time, the disease occurs the same time of year, under the same conditions, and on plants two years of age or older. The organisms that cause this disease, grow lustily under warm (summer-fall), moist (your irrigation) conditions. (Translation: a big bad deal) To prevent this disease on upland plants: 1) give full-blown irrigation (water weekly, if soil is dry two inches down, with microspray emitters or by hand or by sprinkler), in the summer the first year only. 2) keep the mulch 2"-4" thick 3) Place a large (6" by 6" by 6" approximately) rock on the ground adjacent to and on the west side of each plant. Especially for Fremontodendron, plant on the east side of a building, a boulder pile, a thick rock wall, a mass of lower vegetation; in other words, something with enough mass to keep the soil cool! 4) Water indirectly, at the drip line or farther away.

drip irrigation kill most California nativesLeaf Burn

Salts show up on leaf margins.

Leaf Burn occurs for many reasons. The most common problems include drip irrigation(don't), planting plants from plant communities that are not like yours(Sierra plants in Bakersfield), salt spray from the ocean(can occur miles inland if the breeze is direct from ocean) and the high salt soils of some of the inland valleys. You can't really treat the soils to solve the problems, you'll need to rethink what to plant if you happen to live in one of these spots.

Mistletoes

Mistletoe is a epiphite that uses the tree as a substrate like a normal plant would use soil. It is hemiparasitic attaching itself to the xylem of its host but photosynthesizing (making it's own food). Because they are not able to absorb their nutrients and minerals from the soil the have to use whatever is absorbed by their host. This limits their size, as they can easily become nutrient deficient. They do not have true roots and are unable to be selective in what they absorb. It is common for people to think of mistletoe as a pest or as being harmful to the tree however most studies have found this to be unsubstantiated. In fact many studies have found the mistletoe to be very important to plants as well as animals. Mistletoe may act as a dumping ground for excess minerals that their host plant can not absorb. There are four species of the genus Phorodendron and three of the Arceuthobium genus. The Arceuthobium genus is found on conifers that is Pines, Firs, Spruce, Hemlock. Phorodendron is found on a wider variety of trees and shrubs including Juniper, Mesquite, Acacia, and Oaks.

Snails

Snails are not found on the strongly mycorrhizal plants (95% of California native plants). The highly mycorrhizal (VAM) plants are eaten only if the plant has lost, or disconnected from the mycorrhiza. The snails live on the weedy plant species that are poorly mycorrhizal or non-mycorrhizal. Native snails live on the dropped leaves in the litter, not on the plants. Coastal towns are knee deep in European snails that are living on the 'color' plants (basically weeds) people set out in their gardens, and additionally overwater and fertilize.

There are good things that people are afraid (freak out) or misdiagnose.

Swellings/Nodules

Swellings/Nodules on roots of Ceanothus, Alder, (nitrogen-fixing bacteria Frankia) and Lupine (nitrogen-fixing bacteria Rhizobium)- Some people are getting very excited when they see these on our plants, so we thought we should let everyone know what they are and what they do, to clear up much speculation and misunderstanding!! These bacteria (Rhizobium and Frankia )were discovered many years ago. The root swellings are actually a combination of these symbiotic, nitrogen-fixing bacteria and the cells of the root that proliferate in response to the bacterial infection.

Frankia is a nitrogen fixing bacteria that grows on ceanothus. Nitrogen fixing bacteria are not a disease.

This is a good thing! The bacteria receive food from the plant in the form of carbohydrates (sugars) and so convert nitrogen from the air (N2 ), which plants cannot use, into ammonium ions (NH4+). These ions are then converted by other types of bacteria living in the soil to nitrite ions, then to nitrate ions (NO3-) which plants can use to make proteins, etc. The relationship between the plant and the bacteria is a close relationship where each party gains something, called mutualism. These nodules, or swellings, on the roots of some of our plants, are like little nitrogen factories, a natural form of fertilizer, made by the bacteria with the help of the plants, together, no charge! So much easier, cheaper, and more natural than going out and buying a bag of fertilizer and spreading it around the garden. You receive the reward and don’t have to do any of the work!! (Translation: a great deal!)

Lupines have nitrogen fixing bacteria, these are not a disease.* * Note: It is believed that nitrogen fixation can be accomplished only by certain bacteria, an estimated 200 million metric tons of such fixed nitrogen is added to the earth’s soil every year, and all living things are dependent upon this system of nitrogen fixation

This is a white lined sphinx larva. Remember, caterpillars make butterflies. 

 Remember caterpillars make butterflies, or in this case, Sphinx Moths. Share your plants! Don't spray away all the wildlife and butterflies, not to mention, moths!Sphinx moth on a sage.


 More about diseases of native plants at questions and answers.