Identifying Tree Pests and Disease

There are a lot of reasons that could lead to the decline or death of a tree. From insects to disease and fungi to lawn mowers and everything in between, the trees of our urban forest are constantly at threat. Identification and diagnosis of the decline of trees can be crucial in warding off a mass urban forest devastation, those of the like seen with Emerald Ash Borer, Gypsy Moth, and Dutch Elm Disease.  

There are two types of indicators that can lead you to knowing that a tree is under stress. Symptoms are effects that the causal agent has on a tree, whereas signs are what is left behind by the causal agent. An example of a symptom would be wilting of the leaves due to lack of water. An example of a sign is a fruiting body of a fungi of insect burrow holes. 

Some common signs and symptoms include:

• Leaf Spot- Spots of dead tissue on foliage: size, shape, color depends on causal agent

• Leaf Blotch- Dead areas on leaves on foliage: larger than leaf spots.

• Scorch- Browning and death of areas along leaf margins & between veins.

• Canker- Localized dead stem tissue.

• Stunting - Abnormally small plant growth.

• Gummosis - Exudation of sap or gum from wounds.

• Rust- Orange/reddish brown pustules on leaves.

• Gall- Swollen plant tissue.

• Chlorosis- Yellowing of green leaves due to lack of chlorophyll.

• Necrosis- Death of tissue.

• Die Back- Dead portions of the tree. (commonly seen on tips)

• Powdery Mildew- White or greyish fungal growth on the surface of the leaves

• Vascular Discoloration- Darkening of wood vascular elements, often along growth rings.

• Witch's broom- Abnormal development of multiple shoots.

Noticing these things can help save a tree from death or prolonged injury. If you see any of these signs or symptoms on a tree, you can do some research and try to identify the causal agent yourself. You can also reach out to an arborist and see if they would be able to identify the causal agent, and provide a recommendation as to how to pursue the tree. 

Biotic factors such as insects, disease and fungi are considered infectious, whereas abiotic factors such as moisture and temperature extremes, mineral deficiency, pollution, climate change etc are not considered infectious. Fungi and insects make up the largest portions of biotic factors. Insects are classified into three categories when it comes to effecting trees. Chewing insects that use their mouthparts to eat portions of the tree, usually the leafs (i.e Japanese beetles, gypsy moths and tent caterpillars). Sucking insects that use their straw like mouth parts to suck sugars out of portions of the tree, usually stems and leaves (i.e. aphids and scales). Lastly boring insects, who bore into the tree and either eat portions of the inner bark or create nests there; these insects cause the most damage to trees (i.e. Emerald Ash Borer, and bark beetles). 

Some Insects in the Bay area Include:

• Aphids - Small sucking insects that attach to stems and suck out juices and excrete a sticky chemical called frass. More info. 

• California Oakworm - Caterpillars that skeletonize oak trees, predominantly coast live oaks. More info. 

• Lace bugs - black shiny insects much like aphids, remove nutrients from leaves that cause white splotching. More info.  

• Tussock Moth - caterpillars with large appetites can defoliate trees quickly. Affects all species. More info. 

Western Tussock Moth Eggs Source:
(https://www.sacnaturecenter.net/visit-us/nature-blog/news.html?NewsID=60340)

Western Tussock Moth Larvae Source:
(https://www.thedailygarden.us/garden-word-of-the-day/western-tussock-moth)

When it comes to disease, fungi and viruses there are three very important factors to think about, the host, the pathogen, and the environment that make up the disease triangle. The host is identified as the plant that is in question; the pathogen would be the disease, fungi or virus; and the environment would be all the factors that affect both pathogen and host. 

Most trees are susceptible to at least one disease causing fungi, yet most fungi are actually good. Only a small portion of fungi are harmful to trees and other plants. Diseases can be carried by vectors, most commonly insects, this is seen in dutch elm disease where the bark beetle works as a vector. A common bay area disease, fireblight can be spread by bees (this doesn't make bees bad though).

Here are some common bay area diseases:

• Chinese Elm Anthracnose - Dye back on tips, black spots on leaves and cankers form at the base of the tree. More info. 

• Fireblight - very contagious bacteria disease, causes a burned look on stems, leaves and branches. Mostly affects pears and apples. More info.

• Powdery Mildew - White fungi that forms on leaves of plants. More info.

• Shot Hole Fungus - Causes holes and browning of leaves, as well as yellowing of stems. Affects Prunus species - including stone fruit and almond trees. More info.

• Sooty Mold - furry black mold on leaves, and yellowing of leaves. Common on fruit trees and attracts aphids. More info. 

• Sudden Oak Death - Caused by the water mold pathogen Phytophthora signs include cankers, twig by back and black/brown leaf spots. More info. 

• Sycamore Anthracnose - erratic branching, cankers, dieback, and defoliation. Fungal disease that affects most sycamores and maple trees. More info. 

Powdery Mildew Source:
(https://www.thespruce.com/powdery-mildew-1402500)

If you have any questions or concerns about a tree on your property you can reach out to a local arborist and see if they can provide some help. Sometimes solutions are simple, like a spray or soil injection. Other times they are extreme like with Oak Wilt where the tree has to be removed, chipped, chips hauled to a site where there are no oaks present and dumped, 4 ft trench created severing all roots, stump ground down two feet, and soil not wood chips placed on top, and the entire area painted with pruning sealing paint. This fungi is not present in California luckily.

I have compiled a set of extra readings and field guides for those more interested in the topic of insects and disease, specifically in California. Here is a good link to some of the most common harmful insects to trees in the United States for more reading. Also here is an identification key for California insects. Here is a field guide for diseases and insects for California oaks. Here is a more in depth training manual for insects and disease by the US Forest Service in California.

Algaculture

All of us here at Our City Forest works with trees and shrubs every day. Today on this blog we will be discussing plants’ closely related friends: Algae! In particular, algaculture.

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So what is algaculture? Algaculture is the farming of various algae species. But let’s start with the basics; what even is algae? Algae is defined as “a plant or plantlike organism of any of several phyla, divisions, or classes of chiefly aquatic usually chlorophyll-containing nonvascular organisms of polyphyletic origin that usually include the green, yellow-green, brown, and red algae in the eukaryotes and especially formerly the cyanobacteria in the prokaryotes” (Merriam-Webster Dictionary). Now you may be a bit confused by that definition, and honestly, you should be. Truth be told, there’s a lot of vague blanket terminology used to define algae, and that’s because the taxonomical classifications of algae are still changing all the time!

Basically to sum it all up: algae is similar to a plant, but not actually a plant. The main reason why being that all plants belong to the Kingdom Planate, while all algae does not. In addition, plants are multicellular, vascular, and mostly on land. Algae on the other hand is multi or unicellular, non-vascular, and mostly aquatic. It also belongs to various Kingdoms. Kingdom Plantae includes the chlorophytes and rhodophytes (green and red algae), the Kingdom Chromista contains phaeophytes (brown algae), the Kingdom Protista is home to Euglenophytes (Euglena), and the Kingdom Bacteria is where cyanobacteria (blue green algae) can be found. Plants and algae do have two major characteristics in common though, one being that they are both eukaryotes, and the other being that they are both photosynthetic and therefore contain chlorophyll/chloroplasts.

Taking a moment to dive deeper into the details of algae, two major types emerge: Macroalgae and Microalgae.  Macroalgae is large and often multicellular. Common examples include kelp and seaweed. 

Pictured: herbarium pressing of Giant Kelp.

Conversely, microalgae is microscopic and unicellular, or in chains / groups. A common example would be phytoplankton.

Pictured: various types of microalgae.

Some of the most popular species used in Algaculture are: Seaweed (Nori, etc.), Spirulina, Chlorella, Kelp, Chondrus Crispus aka ‘Irish sea moss’, and many of the red alga (Rhodophyta) because they produce carrageenan.

But how is algae farmed? To grow the alga aquaculture techniques are used. It is produced in ponds or tanks by adding nutrients and carbon dioxide to the system. Once harvested, the alga must be dried. There are three major methods to accomplish this by: Flocculation, Centrifugation, and Microscreening.

Flocculation is when solids come out of suspension (in a floc/flake) spontaneously or due to an added clarifying agent. A big downfall of this is that it is very costly and therefore only utilized by large scale industries.

Centrifugation is a process that separates algae from water. The machine spins and forces the algae up against the sides, forming a paste. The water flies to the top as it spins rather than staying with the algae against the sides. This is a medium cost operation.

Microscreening is a process of membrane separation via filtration system. It utilizes the properties of water – cohesion and tension – to induce the Capillary effect, thus allowing water to “climb up” / work against gravity and separate out from the alga. Then, a fine mesh screen is used to sift algae out.

Now what happens the all this algae once it is isolated and dried? It has an unbelievable number of purposes! Algae is in the food we eat, colorants/dyes, fertilizer, beauty products, pharmaceuticals, traditional medicine, and more. For example, spirulina and chlorella specifically are dubbed as “Superfoods”. Carrageenan and Agar are extracted and used in many food products as a stabilizer/thickener. In the beauty industry algae is hailed as a miracle worker due to its vitamins, minerals, antioxidants, cell renewal (anti-aging) ability, and its anti-inflammatory and clarifying properties. Beta Carotene is extracted for use from the carotenoids in the algae. When it comes to medicinal properties, algae contains Omega 3s, antioxidants, and it is anticancer and antiviral. Many of these properties can be seen listed on ingredient labels of hundreds of products! It can also be used to make bioplastic -  such as biodegradable water bottles or utensils - as well as biofuel. A major benefit of all this algae is carbon sequestration. Ocean-based algae account for  45% to 50% of carbon dioxide absorbed by the biosphere! Although they are small, their short life cycles make them efficient. Research has found that algae powered bioreactors are 400x times more effective than trees at absorbing CO2.

Pictured: a photo from the article “The crop that put women on top in Zanzibar” from BBC.

A final note about how cool algae is, is what the rise in demand is doing for women in other countries! It has become an innovative income for women who have traditionally not worked and been placed in a role which leaves them indoors. As men have chosen to stick with fishing and tourism, the women have started to farm algae nearshore in places like Zanzibar and the Bengali Coast. This allows them to get out of the house, socialize with one another, and make a profit. An article that I like very much regarding this can be read at the following link: https://www.bbc.com/news/stories-44688104.  

Tree Tapping and Maple Syrup

Ever really think about how maple syrup is made? It is many people’s favorite breakfast accoutrement, but most do not consider the story behind it. Well it comes from OCF’s oldest friend, the tree! Today on the blog we learn all about tree tapping and the process of creating maple syrup.

For starters, what trees can be tapped to make maple syrup? Maple trees of course! The syrup actually comes from the sap contained in these trees. The trees definitely need to be healthy and free of damage or disease to collect their sap, but size is also an important detail to account for when it comes to tapping trees. The tree must be mature if it is to be tapped for its sap. The minimum diameter size required is 1 foot. If the maple tree has a diameter of roughly 12 to 20 inches, it can be tapped only once. If the diameter is between 21 and 27 inches it can be tapped twice. Once the tree’s diameter surpasses 27 inches, it can be tapped three times. 

There are actually four main types of maple trees used for syrup making. They are: sugar, black, red, and silver maples. The sugar maple is, naturally, the best for making maple syrup. This is because it has a high sugar content. Sugar maples are predominately found in Canada and the northeastern United States, but can also be found as far west as Minnesota and as far south as Tennessee. These trees do well in various soils, but dislike very wet or very dry conditions. The black maple is the second most favorable for syrup making, as it has the second highest sugar content in its sap. Its growth range is more limited however, found within Canada in southeastern Quebec as well as the USA amongst central Wisconsin and down south to Tennessee. Coming in third is the red maple, which has a lower sugar content – but still makes great quality syrup. A pro of this tree is that it grows almost anywhere. It can be found growing all the way down in Florida and as far west as Texas. Lastly, silver maples can also make syrup but are these least desirable for this process – simply due to their low sugar content. As they grow early on in spring their sap can evaporate before being tapped. These trees do however have a large growth range similar to red maples. 

Fun Fact: While not one of these four popularly used types, the bigleaf maple, acer macrophyllum - which is found here on the Pacific coast - can also be used to make delicious syrup!

Now that you’ve learned about different types of maples, let’s get down to the details. First off, when is a good time to tap trees for sap? The ideal timeframe is from the end of January through the end of February. It is peak season when temperatures drop below freezing at night, but stay above freezing during the day. Secondly, how exactly does one tap a tree? Believe it or not, a power drill is used to drill a small hole in the tree. The drill bit size must match the size of the spile, which is the spout like instrument put into the tree that acts as a funnel to collect the sap into a bucket. The hole is created at a upward angle to allow sap to flow down via gravity. The hole goes into the xylem layer of the tree. Then the spile is hammered in and the collection bucket is hung. Sap flows out during the day when temperatures are above freezing. On average, 6 – 10 gallons of sap are collected in a syrup season.

How does sap become syrup? Initially, the sap is filtered through both a coarse and fine filter to remove debris. Then, it gets boiled. This is done at a temperature range of 212°F-218°F. This boiling will kill any bacteria present in the sap. As it is boiled, much of the sap evaporates. The sugars are then condensed and the texture begins to thicken. This liquid is then transferred to a stove top to complete its last step in its transformation to what we all know as “syrup”. This finished product is a ratio of about 67% sugar and 33% water. It is then filtered a final time and bottled while still hot. Bottling it while hot allows it to seal better and be stored at room temperate. Syrup that is bottled while cooled must always remain in the fridge or freezer. 

Fun fact: What many people do not realize is that it takes approximately 40 gallons of sap to make 1 gallon of syrup. How crazy is that!