Pests and Pest Management

"Don't knock the power of a pest. Persistence and stubbornness can be useful in
​many situations".
- Maria V. Snyder

introduction

Pests are an unavoidable part of gardening. They see your well-kept garden as a beautiful bed and breakfast made just for them, and for that reason it's pretty hard to get them to move on. At first, these insects may not make much of an impact, but after some time passes and some babies are born, they will start to cause visible damage to your plants, interfering with photosynthesis through lost foliage, and inviting accompanying problems like mold and disease.
Quick Question: What is a pest?
A pest is an organism that damages or interferes with desirable plants in our fields and orchards, landscapes, or wild areas, or causes damage to homes or other structures. The label 'pest' also includes organisms that impact human or animal health, such as ticks, mosquitoes, and bedbugs. Pests can either transmit disease or not, but either way are considered nuisances. Pests can be plants (weeds or parasitic plants), vertebrates (birds, rodents, or other mammals), invertebrates (insects, ticks, mites, and snails), nematodes, pathogens (bacterias, viruses, and fungi), or other unwanted organisms that cause damage to water quality, animal life, or other aspects of the ecological system.
 The following list of common garden pests is a comprehensive representation of many of the pests you will encounter as a home gardener in California and to some extent elsewhere in the United States. This page includes the common and scientific names of each pest, what damage they can cause to your plants or home, how to identify an infestation, and how to eradicate them and prevent future issues using evidence-based Integrated Pest Management techniques.

Invertebrate PEsts: Insects, Mites, Mollusks and Nematodes

This group of insects and insect-like organisms frequent residential properties, both inside and outdoors in some cases. They cause various issues in homes and gardens, from simply being annoying and unwanted to causing damage to plants, buildings, and sometimes humans through bites and stings.
Ants (Formicidae)
​Related to wasps and bees, these small insects form colonies that range in size from a few dozen individuals to hundreds of millions of individuals. Ants have colonized every land mass on earth, and are common pests of both landscapes and buildings. Ants protect and care for other pest insects such as aphids, soft scales, mealybugs and whiteflies, and feed on other pests like termites, fleas, and caterpillars. There are over 12,400 species worldwide, but thankfully fewer than a dozen are considered important garden and household pests. The most commonly encountered ants in California include the following:
Argentine Ant
This species is about 1/8 inch and dull brown and forms colonies outdoors in shallow mounds.
Carpenter Ant
These ants form nests in tree stumps and wood structures, and range from 1/4 to 1/2 in. long. They are either black or red and black.
Odorous House Ant
These are 1/8 inch long, dark brown-black and shiny, and release a strong odor when crushed. They nest in shallow mounds, walls, and warm areas.
Velvety Tree Ant
These ants also release an odor when crushed, and have brown-black heads and velvety black abdomens. They nest in deadwood.
Pavement Ant
These ants make nests in lawns or under objects and also create mounds. They are 3/16 inch long and dark brown to blackish.
Pharaoh Ant
Nesting in wall or cabinet voids, behind baseboards or insulation, or outdoors in debris piles, these ants are 1/16 inch long and honey-colored.
Red Imported Fire Ant
These ants make their homes in mounds and sometimes in walls, and 1/16-1/5 inch long. They are reddish with dark brown abdomens.
Ants usually nest outdoors, but will venture inside in search of food and water, warmth and shelter, and may appear suddenly in buildings when other food and water sources are scarce. Due to their sheer population numbers, it is impractical and unrealistic to have a goal of completely removing ants from an outdoor space. Management efforts should be focused on excluding ants from buildings and eliminating their food and water sources. Reducing outdoor sources of ants near buildings will reduce the likelihood of ants venturing indoors. Use the following guidelines to ensure that your space is managed properly:
  1. Caulk cracks and crevices around foundations and other sites that allow ants entry from the outdoors.
  2. Eliminate cracks and crevices wherever possible, especially in kitchens and other food preparation areas. 
  3. Store food in closed containers, rinse out used containers before disposing of them, and thoroughly clean all spaces regularly. Remove garbage daily and change liners frequently.
  4. Investigate indoor nesting sites, such as indoor plant pots.
  5. Use a product like Tanglefoot or other sticky band product to prevent ants from climbing up tree and shrub trunks.
  6. If ants colonies are discovered, use slow-acting bait stations. These products are easy to use and safe (as long as the are kept out of reach of children and pets). They are filled with carbohydrates and an active toxicant, and should be placed outdoors, even if there are ants inside. Placing bait traps indoors can actually lure more ants to come in. Traps should be spaced about 10 to 20 feet apart. Depending on the size of the colony, it may take several weeks or more of treatment with these traps to be effective.
Emergency Ant Treatment
​Ants are unwelcome visitors in homes, and will venture indoors in search of warmth, food and water during certain times of the year. When an ant trail is discovered indoors, there are some steps to follow to discourage more ants from entering:
  1. Vacuum up ant trails where you see them. When vacuuming is complete, make sure to dispose of the vacuum contents immediately, as vacuums do not kill ants and they will simply crawl back out. 
  2. As you vacuum, locate entry points and seal them. This can be done through the use of tape or caulking.​
  3. Once ants have been removed, clean the area with warm soapy water to get rid of any pheromone trails. 
  4. Ants can be killed on contact with window cleaner spray.
For more information on removing ants from indoor spaces, check out this video.
Aphids (Aphididae)
Aphids are common insects in home gardens, and are sap-sucking critters. They use their mouthparts to pierce stems, leaves and other tender parts of plants to extract the fluids inside. They can be green, yellow, brown, red, or black depending on the species. Some species even appear 'wooly' in appearance, and be mistaken for other wooly pests like mealybugs. They have a pair of tubes at the back of their bodies called cornicles, which distinguish them from all other insects. These cornicles produce pheromones or defensive secretions. In California's mild climate, these insects can reproduce throughout the entire year. Large infestations of aphids can turn the leaves on plants yellow, stunt developing shoots, and/or cause leaves to curl up. Colonies will produce large amounts of a substance commonly called 'honeydew', which in turn can cause other issues, like fungus, to take hold on plants. Ants feed on this honeydew, and their presence is a good indicator that you may have an aphid problem. The following list includes different types of aphids, and the types of plants they feed on.
Bean Aphid
These aphids feed on Legumes, woody ornamentals, and flowers.
Cabbage Aphid
These aphids feed on Mustard Family plants.
Green Peach Aphid
These aphids feed on Peppers, Spinach, Carrots, Tomato, flowers, Corn, Legumes, flowering Plum trees, and Stonefruit trees. 
Melon (Cotton) Aphid
These aphids feed on Carrot, Citrus, flowers, and woody ornamentals. 
Potato Aphid
These aphids feed on Potato, Spinach, Lettuce, and Tomato plants.
Green Apple Aphid
These aphids feed on Apple, Pear, Hawthorne, and Cotoneaster trees and shrubs.
Leaf Curl Plum Aphid
These aphids feed on Plum and Prune trees.
Mealy Plum Aphid
These aphids feed on Plum and Prune trees.
Rosy Apple Aphid
These aphids feed on Apple trees. 
Wooly Apple Aphid
These aphids feed on Apple, Pear, Hawthorn, and Pyracantha trees and shrubs. 
Ash Leaf Curl Aphid
These aphids feed on Ash trees.
Crapemyrtle Aphid
These aphids typically feed on Crape Myrtle trees.
Giant Conifer Aphid
These aphids feed on Fir, Pine, Spruce and Cedar trees.
Hackberry Wooly Aphid
These aphids feed on Hackberry trees and shrubs. 
Oleander Aphid
These aphids feed on Oleander and Milkweed plants. 
Rose Aphid
This species of aphid feed on rose plants primarily.
When weather is warm, many aphid species can develop from newborn to adult in seven to eight days, and are then able to produce about 80 offspring in a week. Aphid populations can increase quickly, which is why monitoring aphid populations is such an important step in prevention. Aphids seldom kill adult plants on their own, but the damage they do can open up plants to disease and other pests. Checking plants for aphids (at least twice a week in their high season in spring and summer). Infestations can be pruned out or simply sprayed off of plants with a strong stream of water. If leaves are curling, cut them off of the plant. Ants are protectors of aphid populations, as they farm them for the honeydew they produce. In some situations, it is of great help to take care of an ant infestation simultaneously, as this will allow the aphids' natural predators to come around more often. Applying natural predators of aphids, such as lady beetles, can give some temporary control when infestations are heavy. A heavily aphid-infected rosebush will require two treatments of 1,500 lady beetles each spaced about a week apart. Other methods of control for aphids include:
  1. ​Checking all transplants (even small ones) for aphids before installation in the garden.
  2. Removing weedy areas of the landscape where aphids overwinter.
  3. Discontinuing use of high-nitrogen fertilizers, as they favor aphid reproduction. Instead, use slow-release fertilizers if necessary, or simply just apply compost a few times a year.
  4. Monitor the garden frequently for aphid infestations; they tend to congregate on new, young growth including unopened flower buds.
Scale Insects
These are immobile insects which suck plant juices from many types of trees, shrubs, and houseplants. These critters look like little raised bumps on stems and leaves. Infestations can cause yellowing or premature dropping leaves, sticky honeydew, and blackish sooty mold. Damage done to plants can resemble that of aphids or whiteflies, causing discolored, distorted, or dying branches. There are two main types of scales: Soft and Armored. Soft scales are larger, excrete honeydew, and are more rounded. Armored scales tend to be smaller and flattened and don't produce honeydew. Common species of scale are listed below:
Mites
Mites are small, insect-like arachnids related to spiders and ticks. The largest mites top out around a quarter of an inch in length. These little bugs form colonies on the undersides of leaves that can include hundreds of mites. Because they are so small, they are often difficult to detect until foliage damage appears on your garden plants. These bugs feed on leaves, bruising cells with their small, whip-like mouthparts and ingesting the sap. This damage can end up killing plants if it progresses too much. If you've got a mite problem in your yard, you'll notice small yellow or white speckles on your plants' leaves. When too many of these spots occur in close proximity, leaves will turn yellow or bronze, and drop off the plant prematurely. Check out the following list for help identifying which mites you are having trouble with:
Carmine Spider Mite
​Clover Mites
​Gall Mites
Spruce Spider Mites
Southern Red Mites
Spider Mites
​​
Worms and Larvae
w
Bagworm
Beetle Grub
Cabbage Looper Caterpillar
Cabbage White Caterpillar
Codling Moth Larvae
Corn Earworm
Cutworm​
European Corn Borer
Leaf Miners
Leaf Roller Caterpillar
Rose Slug
Sawfly Larvae
Tomato Hornworm
Tomato Moth Caterpillar
Vine Weevil Larvae
Winter Moth Larvae
Wire Worms
Lice
Asian Citrus Psyllid

Beetles
japanese beetles
​viburnum beetle
​vine weevil
​cucumber beetle
flea beetle
colorado potato beetle
Mexican Bean Beetle
asparagus beetle
Flies
whiteflies
thrip (thunder fly)
Scale Insects & Mealybugs
whiteflies
Grasshoppers and Earwigs
r
Stink Bugs and Squash Bugs
r
Snails and Slugs
r
Tarnished Plant Bug
Lygus
​yellow dog tick
​squash bug
four lined plant bug

Integrated pest management

After perusing the list above, you may be thinking that protecting your garden is going to take a lot of time and effort. However, if garden cultural best practices are followed and your garden is kept relatively healthy as a result, it makes it much more difficult for large-scale infestations to occur. Integrated Pest Management is a holistic program seeking to provide long-term prevention or suppression of pest problems with minimal impact on human health, the environment, and nontarget organisms in the garden. It is an ecosystem-based strategy focusing on long-term prevention of pests and their associated damage through a combination of tried-and-true techniques such as biological controls, habitat manipulation, modification of cultural practices in the garden, and the use of resistant varieties. A fundamental concept of this program is that some pest activity can be tolerated in the maintenance of a healthy landscape. Broad-spectrum pesticides are generally not used except in dire situations, and even then their use is directed and carefully monitored.
How Does Integrated Pest Management (IPM) Work?
Using the IPM system, gardeners take actions to keep pests from becoming a problem in the first place, such as growing resistant varieties that can withstand pest attack or engaging in small garden projects, like caulking cracks in concrete and sealing entryways correctly to prevent pest entry. Rather than simply waiting for pests to take hold and then treating with insecticides (or other interventions), IPM is a preventive system that takes into consideration how a garden functions on a larger scale, and focuses on the ways pests thrive in certain environments. Monitoring garden spaces and correct pest identification are the keystone ideas of this program. The landscape is routinely checked for issues, populations of pest insects are tracked, and there are five major methods employed to control existing insect populations.
Legislative Control
Quarantines are established at the county, state, and federal levels to prevent entry or further spread of pests into designated areas. In California, some of the main pests we have legislative controls for include the glassy winged sharpshooter, Asian citrus psyllid, Japanese beetle, and Mediterranean fruit fly. We also act to control Dutch elm disease.
Glassy Winged Sharpshooter
Asian Citrus Psyllid
Japanese Beetle
Mediterranean Fruit Fly
Physical and Mechanical Control
These methods directly trap insects, kill them, or exclude them in some way. Techniques include anything from placing cardboard or paper collars around young tomato, cabbage, or other transplants to exclude cutworms, handpicking caterpillar larvae from plants, and screening windows to prevent the entry of flying insects into the home. These interventions can be preventative or curative in nature.
Cultural Control
This group of techniques includes modification of normal gardening activities to prevent or reduce pest problems. Examples include planting pest-resistant varieties of vegetables, fruits and ornamentals, rotating crops from year to year to prevent pest population buildup, and maintaining a cover crop of turf or mulch in fruit tree orchards to discourage dust-loving spider mites.
Biological Control
This collection of techniques includes the use, preservation, conservation, and augmentation of parasites, predators, and disease-causing microorganisms (pathogens) to bring about the control of insect pests in the garden. The most important controls are natural enemies that exist in the garden. Every pest insect has some predators, and in many cases, they can keep pest populations in check. Many outbreaks of pests occur because a broadly toxic insecticide was used in the area at some point in the past, which killed both the pests and their natural enemies. Pests, whose populations can rebound more quickly, will start to pop up again before their natural enemies can recover from extermination. Avoiding the use of insecticides can help to preserve the natural balance of pests and predators in the garden. The ability to recognize predators and parasites and the signs of parasitization is a critical piece of knowledge for home gardeners to have.

There are some biological controls that can be purchased for release and use in the home garden. Lady beetles and lacewings can be found for sale in nurseries or ordered online and then released into the garden space. There is also a widely-available insect pathogen called Bacillus thuringiensis (Bt), which can seriously damage populations of caterpillar pests while causing minimal harm to other forms of insect life. There are biologists who specialize in these types of insect pathogen-based biological controls, who travel the world in search of new natural enemies for some of the more aggressive pest insects in California. In recent history, these scientists have imported tiny wasps that parasitize aphids, scales, psyllids, whiteflies, beetles, and other insects.
Chemical Control (Insecticides and Pesticides)
Insect and mite pests can be controlled using products such as insecticidal soaps, horticultural oils, various inorganic substances, botanical compounds, microbial insecticides, and synthetic organic materials. Some are used in advance of a pest infestation and are called preventive treatments, though most are designed to be used after infestation begins (which is when most people notice the pests in the first place). Botanical insecticides are organic insecticides that are derived from plant sources, including pyrethrum (or pyrethrins) and azadirachtin (neem extract). The main advantages of using these products is that they have a short residual activity, a lower impact on non-target organisms, and can be applied up to the day of harvest on edible crop plants. Other safe-to-use pesticides include horticultural oils, insecticidal soaps, and insect growth regulators. Synthetic materials last longer, though they do have the unwanted side effect of being toxic to natural enemies of pests, as well. Due to the toxic nature of many pesticides, special attention should be paid to their correct use.

creating an integrated pest management system in the home garden

Integrated Pest Management, as described above, encourages gardeners to select sustainable pest management practices that provide long-term prevention or suppression or pest problems with minimum impact on the health of the garden, beneficial organisms, and humans. The main goal is to keep pest populations at manageable levels by using evidence-based, non-toxic methods. The home gardener is the main tool used in any IPM system; they will be doing the most important work to prevent pest infestations: careful monitoring. Creating an IPM strategy is a creative process that brings together knowledge, monitoring, and informed decision-making. Principal components of any IPM program are:
  • Pest Identification.
  • Methods for detecting, monitoring, and predicting pest outbreaks.
  • Knowledge of the biology of pests and their ecological interactions with hosts, natural enemies, and competitors.
    • Encouraging naturally-occurring biological controls.
    • Adopting cultivation, pruning, fertilization, and irrigation practices that reduce pest problems.
  • Ecologically sound management methods to prevent or control pest populations.
    • Using alternative plant species or varieties that resist pests, or using stock that has been certified as pest-free.
    • Selecting pesticides with lower toxicity to humans and non-target organisms.
    • Changing the habitat to make it incompatible with pest development.
Successful Pest Management Guidelines
There are three basic guidelines to use when implementing a pest control system. The first of these is to identify the problem and determine whether an intervention is warranted. Before a pest can be successfully managed, it must be identified as a pest. Plant underperformance can be due to myriad causes, including mechanical damage, under- or over-watering, poor plant placement or soil management techniques, pests, or misuse of garden chemicals, among others. Pinpointing the cause of a plant's troubles is difficult, and if problems are incorrectly diagnosed, treatments used in response will not be effective. Home gardeners should familiarize themselves with the basic identification of plant issues, so they can be more informed when the time comes to identify a problem in their landscape. The good news here is that home gardeners don't have to do this alone. One of the most useful tools in implementing an IPM program is the service of the Master Gardeners. These garden experts are active in every county in the state, and can assist with identification of problems. Their services can be accessed online or through visiting one of their offices. To access these services, follow the links below:
The second guideline in an IPM process is to select a proper control action strategy. The action or actions taken after a pest is identified as a problem should be chosen with care to cause as little environmental damage as possible. It may not seem like treating a pest in the garden would have a noticeable effect on the larger ecosystem, but it most certainly does. Some gardeners will never apply pesticides under any circumstances and prefer less toxic controls like hand-picking or using water streams to treat infestations. Others may use pesticides, but only those that are naturally-derived like insecticidal soaps, oils or microbials that carry little to no risk of damage to life. As a general rule, the least toxic option should always be chosen. The treatment chosen also must be applied at the correct time to maximize effectiveness. This involves being familiar with the life cycle of the pest to be eradicated, its natural enemies, and its competitors. Interventions should be applied when the pests are at the developmental stage where they are most vulnerable. Actions taken can also be guided by the expert Master Gardeners in your county if help is needed.
Timing is everything when it comes to treating pest infestations in the home garden. For example, the Juniper Twig Girdler is a moth that attacks Juniper and related plants, and for most of the year, they are tunneling beneath the bark of the plant, which protects them from any pest treatments applied. However, their adult moth form is most active in June through the middle of July, and this is when they are vulnerable and their population can be curtailed.
The third and final general guideline for implementing an IPM system is to evaluate the results of the control action or actions employed and develop an ongoing pest management plan for continued control. This step requires close monitoring of the identified pest species and knowledge of what the host plant looks like when it is healthy. Experience with treating a pest within a garden space can inform a gardener about possible future problems, allowing them to make tweaks to their existing program to ensure the issue does not pop up again. When these three guidelines are considered, creating an integrated pest management program for a unique garden space falls into place. A successful IPM system is formed through trial and error, improving on past techniques, and establishing best practices for working in and maintaining the garden.

prevention

The methods designed to prevent pest development and spread are called preventive management strategies. These controls are the gold standard in a pest management program, because they reduce pesticide use in the garden. There are three main strategies under this prevention umbrella: choosing and installing resistant cultivars or species, engaging in good sanitary practices, and properly caring for the garden in a way that reduces plant issues overall.
Planting Resistant Cultivars or Species
Reducing pest problems in the garden can be as simple as planting the right species and cultivars for the garden's specific water availability, climate, sun exposure, soil type and texture, and other factors. When plants are described as being pest resistant, it does not mean that they are immune. This term refers to varieties of plant species which exhibit less pest damage than others under similar growing and pest population conditions. These varieties may be less desirable to pests or have physical or chemical properties that repel them or inhibit their development. Other varieties in this group are those that can handle large populations of pests without getting too damaged.
Sanitary Practices
These techniques refer to garden cleanliness activities like cleaning up infested or dead plants, reducing populations of pests and pathogens that could infect garden plants, and keeping weeds in check. Similar to the reasons why it is beneficial to keep a clean home, keeping a tidy garden will facilitate the monitoring of pest populations, allow easier access to all areas of the landscape, and discourage issues like mold and mildew. Removing diseased plant parts from their attachment to plants and from the ground around other plantings is an important preventive measure against the spread of pathogens in the garden, and removing weeds from landscapes removes host plants for many pest species.
Proper Cultural Practices
Many issues can be prevented in the garden by simply providing good growing conditions for plants. Avoiding environmental stressors makes the plants healthier overall and more able to resist pest infestation. Even within smaller gardens, there are multiple microenvironments that differ in humidity, heat, and sun exposure; plants should be chosen specifically for these spaces. The correct amount of nutrients should be applied to plants according to their growth rate. When used correctly, fertilizers and waterings promote healthy plant growth and increases plants' ability to tolerate pest damage. By this same line of reasoning, soil should also be fertile and healthy enough to support plant growth. Avoiding overwatering can increase plant health by discouraging development of stem and root diseases.

options for nonchemical control

One of the fundamental concepts of IPM is that a limited amount of pest damage in garden plants is acceptable. Produce from the home garden does not have to be as perfect as produce from the supermarket. If the choice comes down to using chemicals or accepting some insect damage on fruit or damage on plants, the non-chemical option should always be chosen. Aligning garden care with responsible use of chemical interventions is of utmost importance. Good garden practices in combination with non-chemical controls can help reduce losses due to pest activity as well as the need to use pesticides. There are some great options for non-chemical control in the garden, outlined below:
Cultural Controls
These techniques are modifications to normal plant care activities that reduce or prevent pest infestations. Some of these methods will overlap with preventive measures.

​Digging, Tilling, and Cultivating
These activities can reduce or eliminate weeds in the garden, as well as expose soil-borne pests to adverse conditions and predators. Deep digging can bury some insects and prevent their eventual emergence from the ground. 
Crop Rotation
Rotating places where certain crops are grown can be effective against diseases and insect pests that develop on groups of plants, especially if these pests are unable to travel over long distances. Moving the host crop for these pests will isolate the pests from the crop, and they will eventually die out without a food source. If working in a smaller garden where there is not enough space for crop rotation, change the sequence of plantings in that space; do not plant members of the same plant family in the same location for two seasons in a row.

​Changes in Planting or Harvesting Time
Planting or harvesting at the same time each year has the potential to reduce plant damage or keep pests separated from damaging vulnerable parts of the host plant. For example, seed maggot damage and the issue of damping off can be helped by delaying planting until the soil is warm enough for the seeds to germinate quickly.

​Garden Diversification
The aim of intercropping is to diversify host plant populations so that pest problems are reduced. Adding some flowers to a vegetable garden can increase the activity of natural enemies that will feed on damaging pests, for example. 
Mechanical Controls
These techniques reduce insects, weeds, and diseases through using labor such as hand-picking or devices like traps and barriers.
Preventive Mechanical Devices
​These interventions 

resources and references

UC IPM Website
​https://californiacitrusthreat.org/
​https://ucanr.edu/sites/ACP/
​https://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html