Imagine a world without cabbageworms, leafminers, or whiteflies… Or one without Sudden Oak Death, bacterial spot, or tomato yellow leaf curl… Such would be our gardens, had quarantines been in place and enforced sufficiently. Alas, it is not to be.
Imported plants that are not adequately inspected, nursery stock that is sold in spite of being infected or infested, and the use of grocery store produce to start a garden are responsible for a profound amount of damage to the environment. According to The Nature Conservancy, invasive species cost the U.S. economy $120 billion each year. The U.S. Forest Service echoes those figures, adding that 81 million acres of American soil are at risk due to these pests and diseases, and that 42% of threatened or endangered species are being pushed out by these invasives. Scale those figures down to the size of your garden and decide for yourself if it is worth the risk.
What is a quarantine?
To quarantine something means to keep it away from everything else, for a period of time, to avoid the spread of disease. In the world of plants, quarantines are used to halt the spread of diseases, pests, and other plants (weeds). In Italian, quarantina means 40 days and that’s where we get the idea behind quarantine. By isolating plants for 40 days, you are more likely to see signs of pests, diseases, or weeds, before exposing all of your other plants.
When to quarantine a plant?
Plants that are new, infected, or infested should be quarantined whenever possible. The easiest case, and the most useful, is when you bring a new plant home. As much as you want to add it to the landscape, 40 days in quarantine can prevent a whole lot of work later on. Plants new to your property can never be guaranteed disease-, pest-, or weed-free. Blithely adding it to your landscape may work out fine, or it may introduce a devastating disease that can stay in the soil for decades, introduce pests that you will have to battle every year forever after, or add even more weeds to your To Pull list. To avoid these risks, you can place new plants in quarantine until they have shown themselves to be safe for your garden or landscape. Containerized plants that develop problems are pretty easy to quarantine. Established plants are a bit more difficult.
How to quarantine
Ideally, new plants should be kept separate from all others for 40 days. This is especially true for houseplants, because there aren’t very many natural predators in your livingroom. This can be done by placing the latest addition in a different room, across the room, or in a clear plastic bag. The bag method is the most effective because it creates a barrier that you can see through. Established plants, such as fruit trees, are difficult, if not impossible to quarantine. In cases such as Citrus Greening, trees must be destroyed. If you suspect an invasive pest or disease in one of your established plants, contact your local County Extension Office for help.
Alternatives to quarantine
Some of us can’t (or won’t) invest 40 days of waiting before adding a new plant to the garden. When this is the case, use these tips to reduce the likelihood of problems:
Government mandated quarantines
In 1912, the Plant Quarantine Act was enacted, giving the U.S. government the right and responsibility of preventing the spread of pests and diseases through nursery stock and other plants. This act evolved into the Plant Protection Act of 2000. If you’ve ever driven across the California state line, you have seen the inspection stations and you may have been required to hand over an apple, a bag of green beans, or a butternut squash before being allowed in. From a visitor’s point of view, this Orwellian treatment may feel extreme, but it’s not. In fact, too many invasive pests and diseases are making their way around the globe because of too few precautions.
Grocery store produce
As tempting as it may be (I know, I’ve done it), do not use grocery store produce to seed your garden. Garlic, onions, and leeks look easy to start from your discards (and they are), but they can also carry fungal diseases that will never go away. Take a look at the current list of current quarantines in California to see some of the other vulnerable crops.
To quarantine or not to quarantine? That is the question. The answer is up to you. As you think it over, consider the fact that many pests can generate a surprising number of offspring pretty quickly. For example, a single aphid can turn into 600 billion descendants in a single season, according to entomologist Stephen A. Marshall.
Forty days of caution, or a lifetime of reactionary treatment…
Do you remember the fire safety lesson from elementary school where they told you that three things had to be in place for fire to occur? [The answer is fuel, heat, and oxygen.] Take any one of those components out of the equation and viola! No fire. Well, plant diseases work much the same way.
The three sides of plant disease
For a disease to take hold in your garden, the environment has to be right, there has to be a host, and, of course, the disease (or pathogen) has to be there. Alter any one of those three and any diseases that do occur will be much less severe and less frequent. Remove one of those three and there won’t be a disease at all. Since prevention is far easier than treatment, the disease triangle is a handy tool for you to use in the garden. Another way to look at these factors is with a Venn diagram. When there is enough overlap between the three conditions, disease can occur.
How healthy plants defend themselves
You may be surprised to learn that many pathogens are already present in your garden. New arrivals are unusual and notable. That’s why quarantines are used. So, if all the disease-carrying pathogens are already present, why doesn’t everything just die a horrible death the moment it appears? Like us, plants have evolved to protect themselves, though not in the same way. Unlike us, plants do not have immune systems. What they do have is chemical warfare that has developed in tandem with pathogens. Plants use these steps to protect themselves, when they are able:
(And all this time, you probably thought that plants were relatively passive, right?)
Symptoms & disease identification
Symptoms of plant disease include wilting, stunting, deformed leaves or other growths, cankers, and chlorosis, just to name a few. If you notice disease symptoms, use that information to figure out what is making your plants sick. Feel free to share questions and photos in the Comments sections, plus there are several online resources and you can always contact your local Master Gardeners for advice. Once you know what your plants are up against, you can use the disease triangle to break the cycle.
Pathogens are disease-carrying bacteria, viruses, or other microorganisms. Many times, if they are not already present, these pathogens catch a ride into a landscape on flying insects, tools, shoes, and newly acquired plants. Chewing insects may simply leave behind a point of entry for disease, or they may be infected themselves, transferring viruses or bacteria to the host plant as they feed. You can interrupt the pathogen side of the triangle with these tips:
You can control common environmental factors with these good cultural practices:
The host is the plant that gets sick. Some diseases affect only a single host, while others can infect many different types of plants. This is where knowing more about your plants can really help. [Did you know that lilacs grown near apple trees are more likely to get bacterial blight? Or that cedar apple rust can only occur when apples are grown within a couple of miles of Eastern red cedar trees?] These tips can help prevent disease by helping the host plant:
Many botanist have added time as a factor, converting the disease triangle into a pyramid. They do this because time can be a critical factor in disease development. Diseases take time to infect a plant and to reproduce. Water sitting on a leaf for a few minutes may do nothing, while several hours of surface water on the same leaf may be deadly. Regularly monitoring plants for signs of disease can put time in your favor.
Keeping plants healthy overall helps them fight pests and diseases the way they have evolved to do so. Plants experiencing heat or water-stress, nutrient deficiencies, inappropriate or nonexistent pruning, or physical damage are less able to defend themselves.
Each microclimate has it own set of problems. Learning about your plants and what they are facing, puts you in control of the disease triangle.
New disease warning!
Imagine a world without oregano. Or celery. Or sage. Or chrysanthemums. It could happen.
There is a new plant disease and its name is Phytophthora tentaculata. [Wait! Come back!]
Just because this disease is tricky to pronounce (Fie-TOF-ther-uh), doesn’t mean you can ignore it. Its name is from the Greek phytón (plant) and phthorá (destruction), so the name phytophthora means “the plant-destroyer”. (The tentaculata part of the name refers to the tentacle shape of these particular pathogens.)
First noted in Germany in 1993, Phytophthora tentaculata hitched a ride on contaminated nursery stock and made its way to Central California and Monterey County, our Bay Area neighbors, in 2012. It is spreading rapidly and is deadly to many of your garden and landscape plants.
According to the Retail Nursery and Garden Center IPM News, Phytophthora tentaculata poses long term potential environmental and economic threat to many California native and non-native plants, as this pathogen can stay in the soil for many years and there is currently no known treatment.
What is Phytophthora tentaculata?
Phytophthora tentaculata is a member of the water mold family. In the world of scientific classification, water molds fall between fungi and algae. These pathogens attack stems and roots and frequently kill its host plant. There are several types of phytophthora, including those that cause potato blight, crown rot, and sudden oak death. You cannot see these organisms with the naked eye, but it is important that you keep a look out for the symptoms and know which plants are currently considered susceptible.
Many California native plants are highly susceptible to Phytophthora tentaculata. The most recent list includes:
Non-native plants that are at risk include:
Symptoms of Phytophthora tentaculata
Preventing Phytophthora tentaculata infestation
Contaminated nursery stock is the most likely way this pest will reach your garden or landscape and water management is the best way to prevent infestation. Phytophthora tentaculata are soil borne, which means they spread by sticking to plants, tools, containers, and shoes. Phytophthora tentaculata spores can also travel through the movement of water. This means that spraying an infested plant can transfer the water molds to nearby plants. Since symptoms do not appear right away, it is in your garden’s best interest to stay away from unhealthy-looking plants until you know for sure what is going on.
If Phytophthora tentaculata appears in your garden or landscape, contact your local Cooperative Extension Office right away. They may have helpful advice that will protect your plants and they need to know how far this disease is spreading.
The Oriental Fruit Fly has been found in Cupertino, Los Altos Hills and the City of Los Altos. If you live within the quarantine area, DO NOT move fruits or vegetables off of your property.
The Oriental Fruit Fly tends to be bright yellow with a dark T-shape on its abdomen with clear wings. It is larger than a house fly, approximately 1/3" in length. It is a common pest in Asia and enters the U.S. through produce smuggled into the country.
Visit the Dept. of Agriculture’s Oriental Fruit Fly page to see the quarantine map.
Huanglongbing is a disease caused by the Asian Citrus Psyllid, an insect the size of an aphid.
Carried from Asia or India, the Asian citrus psyllid was first seen in Florida in 1998. By 2014, Huanglongbing (HLB) had caused $4.6 billion in damage to Florida's citrus crops and can kill a tree within 5 years of infection. There is no known cure at this time.
Preventing the spread of HLB is critical to protecting citrus trees worldwide. In this effort, quarantines are in place that prohibit moving citrus fruit trees, leaves, and stems out of the quarantine area. Check this map to see if you are in or near an area of concern:
Signs of infestation and infection include:
Like other psyllids, the Asian citrus psyllid produces honeydew, which attracts ants and provides a growth medium for sooty mold. Ant traffic can be blocked wth the use of sticky barriers.
Other ways you can prevent the spread of this disease:
If you suspect or see signs of the Asian citrus psyllid or Huanglongbing disease, immediately contact the CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE HOTLINE: 1‐800‐491‐1899
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.