Onion rust is a disease caused by the Puccinia allii fungus, the same rust fungi that attack roses.

Symptoms of rust

Bright orange pustules grow on affected leaves and seed stalks. They start as white or yellow spots on leaves and stems that turn bright orange, light yellow, or reddish. As the infected tissue dies, these areas transform into black lesions. The fungus can girdle stems, causing them to turn yellow and die, interfering with the plant’s ability to absorb the sun’s energy, resulting in smaller bulbs.

Rust control

To break the cycle of onion rust, rotate all Allium crops every 2 -3 years and discard any infected plant tissue. Other common Allium crops include leeks, scallions, and garlic. Avoid excessive irrigation and remove all dead or diseased plant material.

Radishes germinate quickly, usually within 3 - 7 days, under ideal conditions. Radishes prefer a soil pH of 6.5 - 7.0 and loose soil. Keeping the soil moist will speed germination and initial growth, but too much water can cause root rot. For smaller taproots, seeds should be planted 1 cm deep, while larger radishes require a planting depth of 4 cm. Plants should be thinned to 4 - 8 inches apart, in rows 8 - 12 inches wide. To maintain a constant supply of radishes, you can plant new seeds every few days. This is called succession planting.

Radishes can be harvested when the taproot has reached a desired size or the plant can be allowed to go to seed for its edible seed pods, called siliquae. In each case, timeliness determines taste and texture. Roots and seed pods that are too old will be tough and bitter. Radishes can also be grown as a cover crop to add nutrients and prevent erosion, or as a forage crop, to feed livestock.

Radish pests

Because radishes grow so quickly, there are very few pests or diseases to worry about. Flea beetles  may chew holes in young leaves, the swede midge (Contarinia nasturtii) may damage foliage or growing tips, and the cabbage root fly larvae may infest the taproot. In each case, good sanitation and keeping the plants healthy are the best defense. Radishes and other cole crops should not be planted in the same location more than once every 3 - 4 years to prevent the spread of disease. Regular crop rotation often breaks up the factors that make up what is called the Disease Triangle.

Radishes as companion plants

Radishes are often planted along with corn, squash and cucumber, which provide welcome shade. Radishes are said to repel cucumber beetles, squash bugs and squash vine borers, but I don't know if that is true. If nothing else, planting radishes makes efficient use of the soil around these larger plants. Some sources claim that radishes repel tomato hornworms, ants, and aphids, but I could find no scientific research to verify these claims.

Most partial shade edibles end up producing more vegetative growth (leaves and stems) than flowers, fruits, roots, and bulbs when given too much sun. These plants prefer a more protected location:

Hanging containers and trellising can help some of your plants get the sunlight they need. As always, make sure you take your microclimate and Hardiness Zone into account when selecting plants for your shade garden.

Asparagus beetle identification

Adult asparagus beetles are blueish-black with a red thorax. They are less than 1/2” in length and their wing covers (elytra) have red edges and yellow spots. Spotted asparagus beetles are orange with black spots. The larvae are dark grayish-green and 3/4 of an inch long.

​Asparagus beetle damage

Asparagus beetles feed on the tips of delicious young shoots, leaving scars and blemishes. Later in the growing season, they will feed on stem surfaces and leaves. Larvae may feed on the ferns, leaving a bleached appearance. Asparagus beetles can kill a plant.
                                                         
How to repel asparagus beetles

Remove damaged spears to prevent other infestations or infections. Remove beetles by handpicking and wash eggs and larvae from plants with a strong stream of water from a hose. Remove aboveground growth in late fall to eliminate overwintering sites.

Basil, parsley, tomato, and nasturtium has been shown to repel asparagus beetles, making them good companion plants for asparagus.

Reliable soil tests are the only way to really know what is in your soil.

Before adding fertilizer to a garden, it is really important to know what is already there. Whether you are growing grapes, tomatoes, or herbs, the nutrients and microbes in the soil dictate how well those plants will grow. As much as we would all love a convenient, reliable, over-the-counter soil test, it doesn’t (yet) exist.

Feeding the soil

Plants use 17 elements to grow. Oxygen (O), hydrogen (H) and carbon (C) are taken from air and water. The other elements (minerals) are absorbed from the soil with the help of microorganisms. There are three primary nutrients: nitrogen (N), phosphorus (P) and potassium (K); three secondary nutrients: calcium (Ca), magnesium (Mg) and sulfur (S); and eight micronutrients: boron (B), chlorine (Cl), cobalt, (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn).

In the 1940’s and 50’s, the idea of “better living through chemistry” led to tons of chemicals being added to agricultural soil. Some of it worked and some of it backfired. The current view is “better living through biology”, which means learning about natural plant life cycles, identifying which nutrients are currently available to plants, and finding natural ways to add whatever is needed.

Time soil tests for the best results

The results obtained from a soil test are not written in stone. Conditions in March will be far different from those in July. Variables such as temperature, moisture, and the molecular exchanges (cation exchange capacity) that are occurring all the time underground can change which nutrients are available to your plants. This is especially true for nitrogen.

Signs that a soil test is needed:

• It’s never been done before.
• Plants are exhibiting chlorosis (yellowing leaves).
• Plants are not thriving.
• It has been 3 years since the last soil test.

How to red soil test results

The funny thing about soil chemistry is that the absolute measurements are not nearly as important as the ratios between certain elements. For example, my soil test showed an abundance of every nutrient needed by plants except one: iron. Unfortunately, iron is needed by plants to help them absorb practically everything else. In effect, my plants were sitting at a banquet with their mouths taped shut! By spraying the leaves with foliar iron, which plants can absorb through their leaves, they then had the iron they needed to make everything else available.

​Laboratory soil test results will show two figures for each element reported. One figure is the recommended range and one is what is in your soil. Hopefully, they will be relatively close. If your garden has plenty of a nutrient, it is a waste of time and money to add more. In fact, adding more can compound ratio problems that make nutrients unavailable to plants. And don’t be surprised if your soil test lab does charge extra for nitrogen testing.

Nitrogen is a very fickle, fleeting element that is here and gone before you know it. It is worth the extra cost to find out what current nitrogen levels are, but keep in mind that those figures are only relevant for a few days, since nitrogen responds quickly to changes in temperature and moisture. Nitrogen is the single most limiting factor in plant growth. Regularly adding aged compost and treating with blood meal, cottonseed meal, alfalfa meal, feather meal or fish emulsion can help maintain nitrogen levels.

Do regional differences matter?

Before sending a soil sample to the cheapest lab, keep in mind that regional differences may impact your results. As quoted from the University of Massachusetts:

That being said, the UMass soil testing lab is highly respected. Simply use the results with a grain of salt, or find a local lab. ​

Rather than wasting time, money and effort by gardening blindly, a good soil test can help you give your plants what they really need, protect the environment and ground water supplies from excess chemicals and nutrients, and save you time and money.

While not always a good idea, squashing bugs is the perfect plan when it comes to these garden pests.

If you planted squash in spring, you may be seeing squash bugs in July. Squash bugs (Anasa tristis) use piercing mouthparts to suck plant sap from members of the cucurbit family. This includes melons, pumpkins, summer and winter squash plants. 

Squash bug identification and lifecycle

Squash bugs are a little more than 1/2” long. They may be black or gray, and narrow or shield shaped. Squash bugs look like a smaller, flatter version of stink bugs. You may be able to see orange edging around the abdomen and underside of adult squash bugs. Squash bugs lay clusters of 15 - 40 red eggs on the underside of leaves or stems in spring. Two weeks later, whitish spider-like nymphs with black legs emerge. Over the next 4 - 6 weeks, these nymphs will go through several stages (instars) before becoming winged adults.

​Damage caused by squash bugs

Plants infested with squash bugs exhibit speckled leaves that begin to wilt as feeding increases. This wilting may resemble the bacterial wilt spread by cucumber beetles. Squash bugs may also feed on and kill young fruit.

​How to control squash bugs

Sanitation is the best squash bug control method. These pests overwinter under plant debris. You can take advantage of this behavior by leaving small planks out in the garden. In the morning, look underneath the planks and kill any squash bugs found underneath. Also, companion planting research has shown that planting marigold, nasturtium, mint, and radish nearby can repel squash bugs. Trellising your cucurbits can make the environment less hospitable to squash bugs.

Pirate bug identification & lifecycle

Pirate bugs are actually called ‘minute pirate bugs’ because of their small size. Adults may only reach 1/5” in length and many varieties feature black and white  patterns. Minute pirate bugs have a triangle-shaped head with relatively long antenna. Pirate bug eggs are laid within plant tissue, providing protection. Within 3 weeks, an egg can metamorphose into an adult. Pirate bugs can be purchased commercially for release.

​Pirate bug prey

In addition to thrips, minute pirate bugs will attack and feed on whiteflies, aphids, mites, psyllids, and small caterpillars.​

Plants use a surprising amount of sulfur. This secondary nutrient is used in making chlorophyll and certain proteins and enzymes. Sulfur is also part of the arrangement between legumes and rhizobia bacteria that allow them to make use of atmospheric nitrogen.

Plants tend to pull equal amounts of sulfur and phosphorus from the soil. Imbalances can cause problems.

Chemical balance in the garden

Most plants prefer a relatively neutral to slightly acidic pH. Some plants, such as blueberry, prefer more acidic soil. Sprinkling sulfur throughout the garden and then watering it in creates sulfuric acid. This is not the acid that will dissolve your car’s paint, but it will help make many nutrients available to plant roots. Before treating soil with sulfur to adjust the pH, it is important to get a soil test from a reputable lab. Too much of a good thing can be a bad thing. If sulfur levels become too low, some plants, such as clovers, will disappear completely. Sulfur deficiency is seen first in new growth. Leaves are pale and growth is spindly. If sulfur levels become toxic, leaves will be smaller than normal and have scorched edges.

Sulfur as fungicide

This bright yellow mineral has antifungal properties. Dusting plants with sulfur can prevent or counteract many fungal diseases, such as powdery mildew, brown spot, crown rot, and others. Fungi generally avoid acidic environments, which is what makes sulfur so effective as an organic fungicide. Sulfur in the soil also helps reduce salt levels.

WARNING: 

Do not use horticultural oil within 2-4 weeks of applying sulfur. Sulfur and horticultural oil  are phytotoxic (poisonous to plants) when combined. Also, do not use sulfur on apricot trees. Use fixed copper, instead.

Bindweed (Convolvulus arvensis) is an insidious Eurasian garden and agricultural weed that is frequently mistaken for morning glory because the flowers look very similar.

This invasive weed was first seen in California in 1884 and can now be found growing just about anywhere below 5,000 feet elevation. Bindweed can be particularly troublesome for beans, cereals, and potatoes, but it attacks many other crops, as well. Bindweed can carry viruses that carry tomato spotted wilt, vaccinium false bottom, and potato X disease.

Bindweed identification

Bindweed is a hardy perennial that grows from rhizomes. It’s seed leaves (cotyledons) look square with a tiny notch at the top. Sprouts that emerge directly from rhizomes do not have cotyledons. Stems are flattened with a groove along the upper surface.True leaves are spade shaped and can be 1/2 -2 inches long. As leaves mature, they become lobed at the base. Stems can grow several feet in length and may trail on the ground or climb upright plants (such as my blueberry bushes).

Bindweed control

Since bindweed reproduces underground through rhizomes, as well as above ground by seed, it is especially difficult to control. The root system of bindweed can grow as deep as 20 feet! Roots able to bud are found as deep as 14 feet below the surface. The majority of bindweed roots are found in the top 2 feet of soil with most of the lateral roots in the top 12 inches. Due to its ability to overwinter without foliage, bindweed can persist in an area for up to 60 years.

Herbicides may be effective as a suppressant but will not eliminate bindweed. Once bindweed has invaded an area, sheet mulching may be the only organic solution. Bindweed roots are able to penetrate most fabric, plastic and cardboard barriers, so the sheeting material must be exceptionally sturdy to be effective and it must remain in place for at least 3 years.

Monitor for bindweed daily and pull seedlings as soon as you see them. Bindweed is less of a problem in shaded areas, so dense plantings can reduce bindweed’s success.

Spotted wing drosophila (Drosophila suzukii) is an invasive Japanese fruit fly that attacks cherries and many berries, such as raspberry, strawberry, blueberry, blackberry. The spotted wing drosophila has also been seen attacking figs, nectarines, and plums. It was first seen in California in 2008 and has become a serious pest.

Fruit damage

Female spotted wing drosophila use a pointed ovipositor to pierce the skin of healthy fruit and then deposit 1 - 3 eggs in each location. Several females may deposit eggs in the same fruit. The broken skin surface then provides other pests and diseases with easy access. As the eggs hatch, maggots begin consuming the fruit, making it inedible.

Spotted wing drosophila management

Populations are generally not seen until the fruit is harvested. At that point, there is nothing to be done besides harvesting the rest of the crop, before eggs can hatch, and inspecting the fruit for infestation before eating.

Because this pest is relatively new to the U.S., treatments have not yet been identified. Cornell University offers instructions of how to make your own Fermented Dough Insect Trap.
​
​If you see this pest in your garden, please let us know in the comments and call your local County Extension office.

Oregano varieties

The variety of oregano grown determines its flavor. The most commonly sold variety, Origanum vulgare, is relatively bland, as are O. unites and O. syriacum. For the best culinary flavor, try planting one of these oregano varieties:

• O. v. subsp. hirtum (most popular)
• O. v. Compactum (excellent flavor)
• O. v. subsp. glandulosum
• O. v. subsp. gracile/tyttanthum (more ornamental than flavorful)
• O. v. subsp. virens
• O. v. subsp. viridulum
• O. v. subsp. vulgare

Origanum v. ‘Kent Beauty’ has a lovely trailing growth habit, making it perfect for hanging gardens and containers.

How to grow oregano

Oregano prefers hot, dry, sunny locations and well-drained soil. Oregano can be grown indoors or out and it performs well in containers. While plants can be started from seed, it is usually easier to propagate oregano using cuttings and root division. In cold areas, oregano is grown as an annual. In spring, seeds can be started indoors and then transplanted outside after the last frost date. Plants should be spaced 12 - 18 inches apart in full sun. Water culinary varieties moderately. Ornamental varieties will need little or no water. 

Oregano thrives in soil with a pH between 6.0 - 9.0, making it an excellent choice in areas with alkaline soil. Fertilizer is generally not needed. Plants can grow from 8 inches to 2-1/2 feet in height and width, creating a bushy shrub or a trailing growth, depending on the variety. Oregano flowers are bluish-purple or white.

Oregano benefits from regular pruning. While plants are still small, pinch off tops down to a leaf node to encourage a bushier growth and to prevent legginess. In winter, established plants can be cut back to ground level. Since oregano is food, think twice about using any chemical pesticides. 

Oregano pests & diseases

Aphids, spider mites and fungal diseases can all cause problems on oregano. Ensuring good air flow between plants and proper watering make a big difference in oregano health. Too much water can cause root disease. Allow plants to dry out between waterings. Monitor plants for aphids. Aphids can be dislodged with a strong stream of water from the hose. Planting nasturtiums nearby can entice aphids away from oregano. Aphids prefer nasturtiums, so you get more oregano! Row covers can also be used to protect oregano from many pests.

Harvesting & storing oregano

Leaves of oregano provide the best flavor if harvested before the plant goes to flower. Simply grab a handful of stems and cut below your hand. Then, rinse the cut bundle to remove any dust, insects or microorganisms, shake off the excess water, pat dry and gently wrap the bundle with a rubber band. Hang in a cool, dry, shaded area until completely dry, just as you would with lavender, lemon balm,  and many other herbs. Unlike basil and rosemary, oregano really gets its flavor punch during the drying process, so fresh use isn’t recommended. Once the leaves have dried out completely, they can be removed from the stems by rolling them between your hands over a sheet of wax paper. Store in a dark, dry location in an airtight container. (I use spice jars that used to hold something else and that have been thoroughly washed and dried.) Properly dried and stored oregano can last for a year.

Oregano as folk medicine

Oregano has been used in folk medicine for a very long time, but there is no scientific proof that it actually helps in traditional treatments for respiratory, digestive, or nervous disorders. Research is being conducted, however, on oregano’s usefulness as an antibacterial and against liver cancer.

In most gardens, oregano can continue for several years, self-seeding it’s deliciousness and pretty flowers with minimal effort and water.

Bark beetles are a normal part of forest and tree life. Healthy trees generally protect themselves from bark beetles by producing sap that pushes the beetles out. However, when trees become water stressed due to years of drought, they are weakened and unable to fight back. Many residential trees are facing the same water stress due to reduced irrigation, making them susceptible to attack by bark beetles. According to the USDA, bark beetles kill more trees than wildfire in most years. Trees are a big investment and weakened trees can destroy homes and threaten the safety of your family. Find out how to prevent bark beetle infestations to protect your trees.

Bark beetle species
 
There are over 600 species of bark beetle in North America. Bark beetles are smaller than a grain of rice. They can be red, brown, or black. With a magnifying lens, you can see that their antennae are jointed, with a club shape at the end. Larvae are tiny, off-white grubs that may have a brown head.

Damage caused by bark beetles

Normally, bark beetles attack redwoods and other conifers. But they are expanding their tastes to include California buckeye, English laurel, and fruit trees. When new adults emerge, they leave a buckshot pattern on the bark surface of infested branches or trunks. Bark beetles chew tunnels through the inner bark, damaging the phloem and the cambium layer, robbing the tree of valuable nutrients and moisture. 

Bark beetles are also vectors for disease. As bark beetle larvae feed, they also infect the tree with a fungus that slows sap production. As they move from one tree to the next, bark beetles expand their own infestation along with whatever disease they may be carrying. Bark beetles are responsible for spreading the devastating Dutch elm disease. Bark beetles are attracted to open tree wounds, such as those that occur when pruning.

Identifying bark beetle infestations

Different species of bark beetle attack different areas of their host trees. Whichever species is active, boring dust mixed with sap is usually the first visible sign. When infestations are suspected, peel off a portion of bark near a boring hole. If bark beetles are present, a winding series of tunnels will be found. Eggs may be present in some of the galleries. Many tunnels will be filled with frass (bug poop). Dead or damaged wood may also be seen. Another common sign of bark beetle infestation is called ‘flagging’, which means the ends of twigs die.

Bark beetle management

Drought-weakened trees that become infested with bark beetles are usually dead within 3-4 weeks. Since bark beetles are protected under a tree’s bark, pesticides and insecticides merely kill off the beetle’s natural enemies, making matters worse. 

To prevent bark beetle infestations, it is necessary to keep trees healthy enough to protect themselves. Proper irrigation is critical. Proper irrigation means soaking the soil to a depth of 2-3 feet at a rate appropriate to the size, age, and variety of tree. You can learn more at the UC Page on Irrigation. These tips can also help:

• Plant resistant varieties of trees.
• Ensure that trees are not planted too close together.
• Keep lawns out from under a tree’s drip line (imagine the line of outer leaves creating an umbrella).
• Remove dead trees and shrubs to eliminate breeding grounds.
• Avoid pruning water stressed trees.
• Remove and dispose of any infested trees to avoid cross-contamination of nearby trees.
• Avoid damaging tree roots with digging or rototilling.
• Preventive spraying of valuable, uninfested trees by professional arborists may provide some protection.

Before feeding plants or amending soil with bone meal, it is very important to have your soil tested by a reputable local lab. Unfortunately, over-the-counter soil tests are too unreliable to be worthwhile. Also, amending your soil with bone meal may attract raccoons or dogs, who will dig up your plants in search of a hidden treat that they will never find.

Invest in a good soil test to see if your garden can benefit from bone meal.

Uses of lemongrass

The inner, white core of lemongrass is used in Thai food, marinades, soups, salads, spice rubs, curries, stir-fry and many more delicious recipes. Lemongrass can be used fresh or dried. Lemongrass oil is used as a preservative and as a pesticide. Lemongrass has anti fungal properties, but that trait does not correlate to the yellow mushrooms commonly found in overwatered container plants. This mushroom is considered inedible, so do not eat it. The presence of the mushroom does not affect the lemongrass.

Propagating lemongrass

Lemongrass seedlings can be purchased at most garden supply stores, or you can start your own from stalks bought at the grocery store. Just be aware that grocery store plants may be carrying soil borne diseases that can wreak havoc in your garden. To use store bought stalks, rinse well and remove any dead or damaged leaves. Put the stalks into a glass with an inch of water in the bottom and place on a sunny windowsill. Roots should begin to emerge after a few weeks. Once the roots are a couple of inches long, gather the stalks in one hand and hold over a medium-sized planting container and use the other hand to add potting soil gently around the roots. You can put some soil in the bottom of the container ahead of time. The important thing to keep in mind when transplanting is to make sure that the crown (the place where the stem connects with the roots) is at soil level. Too low and it will rot, too high and the roots can dry out. Water regularly until the plants are established, then water weekly during summer.

Growing lemongrass

Lemongrass prefers full sun and well-drained soil. It reaches its full size of 3-6’ quickly. If planted in the ground, lemongrass plants should be spaced at least 2 feet apart. Lemongrass grown in containers tends to be somewhat smaller, just be sure to use potting mix that does not contain water absorption crystals. A 5-gallon container is ideal. Aged compost can be placed on top of the surrounding soil to stabilize temperatures and add valuable nutrients. Lemongrass uses a lot of nitrogen when growing, so be sure to feed monthly. Since lemongrass is an edible, blood meal, composted manure, fish emulsion, feather meal, cottonseed meal, soybean meal, or alfalfa meal make excellent, chemical-free sources of nitrogen.

Whether you cook with it or not, lemongrass is a lovely accent plant with a faint lemony aroma.

Playing ‘possum

Everyone has heard of “playing ‘possum” but the truth is even stranger than the fiction. When an opossum is scared or hurt, it literally becomes uncontrollably catatonic, baring its fangs, foaming at the mouth, and releasing a foul-smelling stench from its anal glands, presumably to deter predators. Opossums’ maximum speed is only 7 m.p.h., so this is their only real defense, besides growling or biting. It can take an opossum up to four hours to recover from this involuntary state. Their tiny brains do not have the processing ability to decide to take this action - it is automatic. Opossums do have a surprisingly strong immune system. In fact, they are resistant to snake venom and, unlike raccoons and skunks, are not prone to rabies infections. [Wild dogs are 8 times more likely to have rabies than an opossum.]

​Opossum trivia

There are over 100 varieties of opossum throughout the Americas. All opossums have a semi-prehensile tail (one that can be used for grasping, but not for hanging from) and opposable thumbs. Opossums only live 2-4 years, but females may produce dozens of offspring during that time. Opossums start out as bumblebee sized babies that crawl to their mother’s pouch (like a kangaroo), where they will spend the next 11 weeks, nursing and growing. If you’ve never seen a baby opossum, be prepared to be delighted. Seriously! Opossum young are as playful and heart-warming as any kitten or puppy, if you just give them a chance.

In the Deep South, opossum grease was believed to cure respiratory problems when rubbed on the chest, and the meat was commonly eaten. [I think I’ll pass on both counts…]

Highly refined horticultural oils are sprayed onto plants as a pesticide. They are used to control mites and insect pests, and to prevent some fungal infestations. ​

When oil was first used to combat garden and agricultural pests, heavier “dormant oils” were used in the winter, while trees were dormant and leafless, and lighter “summer oils” were used when leaves were present. While both varieties are now much more refined, believe me when I tell you that using dormant oil on leaves in summer is a really bad idea. 

Types of horticultural oil

Horticultural oils can be petroleum or plant based. Currently, the petroleum-based horticultural oils provide better coverage without damaging leaves. Most over-the-counter varieties are made from petroleum. Vegetable oils, such as sunflower, soybean, and cottonseed, provide good insect control, but phytotoxicity is a still a problem. Phytotoxicity is anything that is poisonous to plants. Research is continuing. At this time, only Neem oil is a consistently safe vegetable-based horticultural oil, but it acts differently than other oils by adding a naturally occurring chemical to the mix that makes insects ‘forget’ to eat or breed.

How to apply horticultural oil

Horticultural oils are best used when pests are vulnerable. Soft-bodied pests, such as aphids, can be sprayed as populations become troublesome. Scale insects are most vulnerable in the crawler stage, while caterpillars and spider mites are best managed as eggs, in winter and early spring. Heavy infestations of scale insects may require repeated sprayings through June. Once pests have reached a protected stage of growth, such as the hard shell covering over adult scale insects, horticultural oils are not effective. Also, the oil must coat pests completely to work.

WARNING: When applying horticultural oils, it is important that sulphur is not present. Horticultural oils should not be applied 2-4 weeks before or after a sulphur treatment, depending on who you ask. Also, horticultural oils should not be used on water stressed plants. Many horticultural oils are mixed with other ingredients, such as fungicides or insecticides, so it is very important that you read the label and follow the directions exactly, to avoid causing more harm than help.

Most horticultural oils are considered appropriate for organic farming.

There are thousands of different varieties of thrips worldwide. A few of them are beneficial insects, eating mites and other pests, but most thrips are pests. They are commonly found in greenhouses. These species have piercing mouthparts used to puncture leaves and siphon out sugary sap. Thrips are also vectors for other plant pathogens (diseases).

​Thrips identification

Thrips are really tiny - often less than 1/20” long. Thrips bodies are thin. They have fringed hairs on their wings, but you won’t see this without a hand lens. Adult thrips can range in color from white, yellowish, pale green, to brown or black. Immature thrips, both larvae and nymphs, look like tiny pale green caterpillars. To make sure that thrips are causing the leaf damage, shake damaged leaves while holding a blank sheet of white paper underneath. A magnifying glass can help identify the culprit. Yellow sticky traps can also help you detect the presence of thrips. If possible, identify the species attacking your plants. Watch this UC video to learn how to collect thrips for identification.

​Thrips control

Unfortunately, thrips are difficult to control. Natural predators are your best line of attack, so avoid using general purpose pesticides. This will allow pirate bugs, green lacewings, and parasitic wasps to take care of the problem for you. Thrips have protective larval stages and the ability to fly away, so insecticides are not effective. A strong spray from the hose can displace many thrips. Also, removing weeds and surrounding plants can make life a little less comfortable for these tiny invaders. Once thrips have infested an area, reduce the amount of nitrogen or other fertilizers applied, to limit the amount of vulnerable new growth.

​Preventing thrips infestations

Reflective mulch can confuse incoming thrips, but it won’t help once they are established. Row covers can also protect vulnerable plants. When pruning, avoid shearing susceptible shrubs, as this can provide many points of entry, both for thrips and other uglies. Be sure to deadhead flowers and remove dead or diseased tissue, as these areas can also provide a hiding place for thrips.

Healthy plants are better able to defend themselves, so be sure to irrigate properly to avoid water stress.