Category Archives: Plant pests and diseases

Herbs Attract and Support Beneficial Insects in the Garden

Small thyme flowers

The herbs in my garden live among the annuals, perennials, vegetables, and shrubs. I do not have a separate, formal herb garden.  Every new herb plant gets tucked in any space I can find. I harvest them to use them fresh in the kitchen and for floral arrangements. By summer, many of my herbs are blooming along with everything else but that’s okay, they still serve a purpose. Even if I didn’t get to harvest them, they are helping the rest of the garden by attracting and supporting beneficial insects. Continue reading

Got Deer? Try These Tactics in the Garden

deerNewcomers to this area will eventually see deer standing on the roadside or venturing out of the woods at dusk. At first, they admire the lovely bucolic sight, gentle deer, twitching their tails, flicking their ears back and forth. But as the newcomers settle down and try their hand at gardening, they learn that the deer are not as cute as they once thought. Continue reading

You Got Gardening Questions? Ask These Experts

cucumberSummer is here and by now your Victory garden is planted. Dreams of fresh red tomatoes and lush green cucumbers are dancing in your head. But wait, what are those green caterpillars? What are those brown spots? Answers to these gardening questions and more are available from your local Master Gardeners and county extension agents. Even during this pandemic, they are standing by to help you with your gardening issues. Best of all, this is a free service for the public. Continue reading

Time to Cut Those Bagworms!

Last night, during my evening walk I noticed an unusual number of bagworms on a few evergreens. Bagworms are common pests in the Washington DC metro area. What I saw weren’t the bagworms themselves (Thyridoptery x ephemeraeformis) but their “homes,” 2-inch long “bags” they have created from their spun silk and plant debris. These bags were hung like small, brown ornaments on relatively new plantings in someone’s front yard. Some of the needles were clearly brown and dead.  Interestingly, one bag was hanging from the neighbor’s chain link fence, creating a very visible view of the threads wrapped round the metal.

Bagworms are moths, native to North America. They can attack more than 120 different types of trees but we tend to see them on evergreens such as juniper, arborvitae, cedar, spruce, pine, and Leyland cypress.

In the beginning of the summer, the eggs hatch and the larvae move out of the bags. The tiny caterpillars, 2 millimeters long, eat foliage and/or move to other trees via their silk threads. When they settle on their host tree, they spin a small bag of silk and plant debris. As they grow, their bags become bigger with more material collected from the host plant. By August, they have matured and the bags are very visible. During August and September the male adult bagworms, i.e., moths, emerge and fly to find a female to mate. The females cannot fly, they are grub-like and never leave the bag. Mating occurs through the bag and after mating, the female lays 500 to 1,000 eggs within her pupal cast skin and dies. The eggs overwinter and hatch next year in May or June.

Bagworms can defoliate and kill trees, especially evergreens. Although they can attack deciduous trees, most are not defoliated enough to be killed. Bagworms can also kill twigs by winding their silk around the twigs too tightly.

note white silk thread wrapped tightly around chain link fence

Now is the time to look for the bags and remove them by cutting them off–not pulling–bagging and disposing. Do not put them in your compost bin. If they are on the perimeter they will be easy to find but don’t forget to move branches aside and look within the tree. It goes without saying that a tree that has a bag will be damaged repeatedly each year, weakening the tree and possibly killing it.

Another option is to spray the tree with Bacillus thuringiensis (Bt) in May or June when the caterpillars have hatched and are on the foliage. This is a type of bacteria that kills the worms but does not harm the tree. If the tree is too tall, call an arborist. Spraying them later in the season after they have created their bags will not work since the bags will protect them. Or replace the evergreens with more resistant plants. But go out there now and inspect your plants, you need to remove them before the males emerge!

Pegplant’s Post Giveaway: Bobbex Deer Repellent Spray

I am very excited about the giveaway for the January 2019 issue of Pegplant’s Post. Bobbex, a company known for effective deer repellent, has generously offered to ship one 48 oz. E-Z ready to use sprayer and one quart bottle of concentrated spray of their deer repellent, a $55 value. Their deer repellent was rated number 1 by an independent study conducted by the Connecticut Department of Forestry and Horticulture. Environmentally friendly, the Bobbex deer repellent is a foliar spray that protects ornamental plantings, shrubs, and forest trees from browsing and feeding by deer, moose, and elk (we don’t have moose and elk in the DC metro area but we have plenty of deer). The spray is a blend of ingredients that are offensive to deer but harmless to humans and safe for wildlife. The Bobbex website has very useful information on how to recognize and deter deer, goose, rabbits, and small animal damage and offers a variety of repellent products.

This giveaway opportunity is for subscribers of Pegplant’s Post, an online, free newsletter for people interested in gardening in the Washington DC metro area. Each issue provides at least 50 but up to 100 gardening events; newly published gardening books; local tips, advice, and articles; and a monthly giveaway contest.

To subscribe, click here or visit pegplant.com and enter your e-mail address in the box above “subscribe!” on the right column. Pegplant’s Post will be issued on the last weekend of the month.

What’s That in the Tree? Fall Webworm

August turns up all kinds of pests and disease in the garden. You may be noticing large webs across the terminal branches of your trees now, similar to stretched pantyhose. Look closely and you will see small caterpillars inside, each marked with parallel rows of black spots on the back. The fall webworm (Hyphantria cunea) is very noticeable now but at this stage, the caterpillars stay in the web and feed inside on the leaves. The web is unsightly but their feeding will not kill the tree. However, this would be a good time to cut the branches and bag the webs, caterpillars and all. Close up the bags tightly and dispose of in the trash. Later, after the last molt, they leave the web and crawl all over the tree. Then they spin cocoons, pupate, and emerge as white moths. If you are not able to bag the web don’t despair, there are many natural enemies of the fall webworm. Another tactic is to spray the first generation in the spring with horticultural oil, Bt (Bacillus thuringiensis), or insecticidal soap before they create the web. Don’t try to burn them out though, it is too dangerous to the tree. For more information on plant pests and diseases, check out the Plant Pests and Diseases tab on pegplant.com.

Got Deer? Try These Tactics to Keep Deer Out of Your Garden

Newcomers to the Washington DC metro area will eventually see deer standing on the roadside or coming out of the woods at dusk. At first, it is a lovely bucolic sight, gentle beautiful deer, twitching their tails, flicking their ears back and forth. But as the newcomers settle down into their homes and try their hand at gardening, they quickly learn that the deer are not as cute as they once thought. In this area, the suburbs provide ideal conditions for deer. There is plenty of food and water in the landscape and ample cover. The deer’s natural predators–bobcats, coyotes, and panthers–have long been eliminated. Many new homes have common ground for easier mowing, thus eliminating fencing. As homeowners sleep at night, families of deer wander in and help themselves to luscious hosta, delightful roses, and all the vegetables they want. Fortunately, there are multiple methods to deal with deer, depending on one’s budget and time.

Repellents

Those who have had their gardens ravaged by deer are tempted to try homemade repellents such as human hair, deodorant soap, and stinky garlic/pepper sprays. The truth is, they really offer little relief. If the smell does not end up repelling you, rain will wash the odor away so they will have to be re-applied. Commercial sprays are more effective but are not cheap. You have to determine just how often you will have to apply in one growing season multiplied by the number of years you intend to live on that property. Or you can weigh the damage versus the cost and time spent on the commercial spray. In my home, the deer will run through the tomato patch once in the spring and then they are gone for the rest of the season. The tomato plants grow back in the summer so I have learned to grow plenty of tomatoes (from seed) and forgo the cost of a repellent spray.

Deer Resistant Plants

Deer resistant demonstration garden with bluestar (Amsonia) in background

The term “deer resistant plants” refers to plants that deer usually won’t bother because of taste or difficulty to consume. However, if there is a summer drought or an unusually large number of deer, the limited food supply may drive them to eat plants that they would normally not eat. These lists of plants are actually more helpful when you use them to not buy the plants deer are known to love. For example, it is well known that deer like hostas so unless you have a plan to thwart the animals, you may not want to invest in hostas.

Daffodils are poisonous so deer do not eat them

Some of the deer resistant plants include pungent, poisonous, or highly textured plants. The deer never bother my highly aromatic rosemary, sage, and oregano herbs. Deer are not interested in poisonous daffodils, Christmas rose (Helleborus), foxglove (Digitalis), and monkshood (Aconitum). Plants that have hairy, fuzzy, or gray/silver leaves are usually ignored by deer. Plants that produce paper-dry flowers such as gomphrena also are not bothered. Thorns don’t seem to deter them though, they eat roses like candy. If you are trying to plan a deer resistant landscape, plant more woody shrubs and less herbaceous perennials, which are soft and succulent to a family of deer.

Deer Patterns

Another trick is to learn the roaming patterns of the deer in your area. Disrupt their patterns with either plants they won’t bother or with structures. Deer are creatures of habit so once you learn their habit you can foil them. At my home, deer usually jump the fence in front of my house to go through the backyard and over the low fence in the far right corner. They never go to the left corner because it is an intersection of three different fences, all various heights and visibility. Therefore, I can feel safe planting shrubs in the left corner. Deer may walk on the front lawn up to the front strip of plants but never walk up the concrete steps to the door. And they never walk on to the wooden deck in the back of the house. This means I can plant the aromatic herbs in the front strip and the hostas toward the front door. I can plant anything in containers on the wooden deck because they won’t walk up on to the deck.

Scare Tactics

There are scare tactics as well like motion-activated watering devices, lights, and sounds. Usually these are not practical in a suburban area, especially with homeowner association rules. It does not do to wake up the neighbors with flashing lights because deer are roaming in your territory.

Fences

Fencing is more of an investment but it is a long-term solution. The fencing does not have to be for the entire property. A fence around the vegetable garden might be all you need to keep them out of the edibles. A fence should be at least 8 feet tall, or us a slant fence, or a double fence. Unless scared, deer won’t jump blindly. They need to know they have a safe place to land. A slant or double fence makes them realize they cannot land safely on the other side. Fencing can be made of metal or polypropylene or can be electric. There are professional deer fencing companies that either sell do it yourself kits or can install a fence for you. Of course, local hardware stores have supplies for you to install a fence yourself.

When erecting a fence, keep in mind that deer do not see well and may accidentally run into the fence. Therefore, the fence has to be strong enough to resist this type of damage. And, if a deer does jump over the fence and land in an enclosed area, have a plan to be able to release the presumably wild and panicked animal. Make sure you construct a door or opening so the deer can come out on its own.

If you have a deer problem, don’t be disheartened, there are solutions and it may be a combination of solutions that work best for you. Below are sources for deer resistant plants, deer repellents, fencing options, and books.

 

Deer Resistant Plant Lists

Rutgers, New Jersey Agricultural Experiment Station, Landscape Plants Rated by Deer resistance

Deer Resistant Shrubs and Trees (both Native and Non-Native Species to Virginia), the State Arboretum of Virginia

Cornell Cooperative Extension Deer Resistant Plants

Maryland Cooperative Extension Fact Sheet 655, Wildlife Damage Management, Resistance of Ornamentals to Deer Damage

Commercial Deer Repellents

Maryland Cooperative Extension Fact Sheet 810, Using Commercial Deer Repellents to Manage Deer Browsing in the Landscape

Deer Fencing

Virginia Cooperative Extension, Low-Cost Slant Fence Excludes Deer from Plantings

University of Maryland Extension, Low-cost Deer Fence Alternative

University of Maryland Extension Fencing for Your Garden

Books

50 Beautiful Deer-Resistant Plants: The Prettiest Annuals, Perennials, Bulbs, and Shrubs that Deer Do Not Eat by Ruth Rogers Clausen, 2011

Solving Deer Problems: How to Deer Proof Your Yard and Garden by Peter Loewer, 2015

Deer Resistant Landscaping: Proven Advice and Strategies for Outwitting Deer and 20 Other Pesky Mammals by Neil Soderstrom, 2009

Deer Proofing Your Yard and Garden by Rhonda Massingham Hart, 2005

Herbs in the Garden Attract Beneficial Insects and Pollinators

small thyme flowers

The herbs in my garden live among the annuals, perennials, vegetables, and shrubs. I have not designed a separate, formal herb garden and now every new herb plant gets tucked in any space I can find. If I remember and have time, I harvest the leaves for teas or for cooking. If I forget or get too busy, the herbs just thrive without me. By summer, they are blooming along with everything else but that’s okay, they still serve a purpose. Even if I didn’t get to harvest them, they are helping the tomatoes, peppers, cucumbers, and beans by attracting beneficial insects.

In addition to attracting pollinators such as bees and butterflies, flowering herbs can attract beneficial insects that will destroy the “bad” bugs. These beneficial insects are either predators, i.e., they eat harmful bugs, or parasites–they lay their eggs in or on the “bad” bug which release larvae that consume the bug.

Many of these beneficial insects are small, thus preferring easily accessible nectar chambers in small herb flowers. In many cases the adult insects need the nectar and pollen of the herb flower while the “babies” or larval stage eat the insects we don’t want in the garden. For example, the larval stage of ladybugs, which look like mini alligators, consume aphids, many beetle larvae, and spider mites, among others. One can attract ladybugs into the garden by planting cilantro, dill, fennel, oregano, thyme, and yarrow so the adult form, the ladybug, can enjoy the pollen.

pollinator on oregano

Lacewings are beautiful slender green insects with translucent wings. Their larvae, known as aphid lions, eat a large number of aphids –thus they have a lion’s appetite — and many beetle larvae to name a few. Lacewings are attracted to angelica, caraway, tansy, yarrow, dill, fennel, and cilantro.

Parasitic wasps are small, non-stinging wasps. There are many types but they all destroy pests by laying eggs inside or on the pest. The eggs hatch to release larvae that consume the prey, eventually killing it. Parasitic wasps will destroy tomato hornworms, bagworms, cabbage worms, Japanese beetles, and squash vine borers. The wasps are attracted to dill, fennel, lemon balm, thyme, yarrow, and cilantro.

Tachinid flies look like houseflies but as parasites, they destroy many kinds of caterpillars, Colorado potato beetles, cucumber beetles, Mexican bean beetles, and Japanese beetles in the same manner as parasitic wasps.  The flies prefer cilantro, dill, fennel, parsley, feverfew, and chamomile.

Hover or syrphid flies look like small wasps because they have yellow bands but they don’t sting. The adults–the flies–will “hover” as they drink nectar from dill, fennel, feverfew, lavender, mint, yarrow, and cilantro flowers. The larvae will consume aphids, cabbage worms, other caterpillars, and mealy bugs.

hover fly in the cilantro

Herbs also help beneficial insects by providing pollen and nectar when other annuals or perennials are not blooming yet.  For example, cool season herbs such as cilantro and chervil bloom in the spring, providing an early source of pollen to beneficial insects.

Many aromatic, perennial herbs, such as oregano, thyme, and lemon balm, are not eaten by deer and small animals so they become permanent fixtures or “houses” for beneficial insects. Plus herbs are usually planted in bunches or become small shrubs, providing a large “neighborhood” for these insects.

a beneficial insect attracted to agastache

However, despite the number of plants in the garden, these insects will only stay if there is a need, i.e., food for them, and if the surroundings are hospitable. Beneficial insects seek large populations of bad bugs in order to feed their own population. Some beneficial insects wait to lay eggs until there is enough “food” so it may be that the appearance of many aphids is the trigger to have ladybugs increase their own population because they now know there is plenty of “food.” In other words, if there a lot of aphids on bearded irises, wait to see if many ladybugs will arrive on the scene to correct the problem before reaching for an insecticide. Spraying chemicals may kill or alter the balance of beneficial insects. It is now known that plants that are under attack by bad bugs release chemicals which are signals to the particular type of beneficial insect that would be needed to correct the problem. There may be a little or minimal plant damage in order for the beneficial insects to receive the signal to come to that plant.

Herbs can be useful for their flowers as well as their foliage. Planting several different types of herbs in the garden helps protect the rest of the plants against pests.

 

Slugs: Because You Know They’re Coming

mature slug

This week gardeners are complaining about too much rain; next week gardeners will be complaining about slugs. Slugs are related to shellfish and love moisture. They have been doing their happy dance since these rains have started.

Although I rarely see them because they are active at night, I know I have slugs in my Virginia garden. I see the chewed and tattered leaves and the glistening, slimy trails. Slugs particularly love the tender foliage on my transplants – the ones I patiently grow from seed under lights. To prevent them from destroying months of work, I quickly respond when I see any evidence of their existence.

If I see chewed leaves, I sprinkle the plants with Sluggo, a brand name for iron phosphate. This is not a plug for Sluggo, it is a plug for not messing around with homemade remedies – just get the iron phosphate. There are several products with iron phosphate, read the active ingredient on the label. I have found that Sluggo’s cylindrical container with the small holes for sprinkling to be very easy to use. Also, it is safe for dogs and cats, and there are a few stray cats in the area. If for some reason I have run out of Sluggo, I sprinkle crushed egg shells or coffee grounds and then run to the nursery.

I have tried the beer trick. Slugs are attracted to yeast so beer in a lid or saucer, sunken to the ground, is supposed to attract them. Once they fall in they get too tipsy to get out. I have never found them in my saucers and I was never able to reconcile the cost or waste of perfectly good beer on slugs.

Slugs also are attracted to citrus. I have not tried this before but some gardeners swear by putting grapefruit halves on the ground, cut side down, with a pebble on one side (so they can slime in). In the morning, they either lift the citrus and kill the slugs or throw the whole thing in a bag. Another method is to place a clay pot upside down with a pebble and turn the pot over in the morning to pick up the slugs and destroy them.

This is all well and good but when you are working mom, you would rather grab a canister of Sluggo and sprinkle before you run off to work.

slug damaged hollyhock transplant

Another deterrent is diatomaceous earth, it is just not as easy to find as Sluggo or easy to apply. It is a fine white powder with microscopic sharp edges that irritate if not outright slice the slugs. I am always afraid I will breathe in the talc like powder or spill it on my suit as I inspect the morning damage before I run off to work.

And then there is the copper barrier that would be effective if you just had one container or a raised bed. Apparently it causes a type of electric shock to slugs but is not harmful to humans or pets. The only downside is that it is impossible to surround all of your plants in your suburban yard – it is just not practical.

So go to the nursery now before slug season starts. Find a product with iron phosphate and find an easy, quick way to apply it. The easier it is for you the more likely you will be able to fight the slug invasion.

 

Gardening in the Washington DC Area Despite Mosquitoes

EnglishIvy

English ivy can harbor adult mosquitoes

I had originally wrote this article about mosquitoes in 2016 but the information is still relevant. Now is the time to stock up on fresh mosquito spray. I find it helps to have a new bottle every year. I am now using the towelettes for my face because even if I cover myself with clothes, the mosquitoes still get me in the face and neck.

If you are like me, you are plagued by mosquitoes in the garden. It is one thing to stay out of their way at dusk but it is quite another when the Asian Tiger attacks you all day long. In the spring of 2016, I contacted several companies to see if my property could be sprayed to prevent mosquitoes.  I don’t have a pond or pets but I have a lot of edible plants intermixed with other plants on the property.  I did not want the spray to harm the pollinators or the edibles (or my family!).  We have a lawn service that mows the grass but I never know when the crew is coming. Because I work in an office, I would not be home to let the pesticide applicator know where the edibles were nor would I be able to inform the lawn service crew when and if the place had just been sprayed with a pesticide. All of these factors made it complex for me to figure out how to control mosquitoes. At the same time, I attended a free presentation at a local library.  Kirsten Conrad Buhls, Extension Agent, Virginia Cooperative Extension, Arlington County, gave an excellent Powerpoint presentation entitled “Gardening in the Time of Zika: Nuisance Mosquito Management.”

Types of Mosquitoes

I learned that there are 40 mosquito species in Virginia in a variety of habitats but most are aquatic. Up until the mid-1980s, the most problematic species was Culex, which comes out at dusk and feeds at night. This species lives in the woods and prefers the type of stagnant water that usually does not occur near residential homes. However, they also breed in “container water.” Container water is fresh rain water that sits in pockets or depressions in objects or in containers.

After the mid-1980s, a Southeast Asian native arrived called the Asian Tiger mosquito, Aedes albopictus. The Asian Tiger is active during the day and prefers to breed in container water. The Asian Tiger has a cousin, Aedes aegypti, who also prefers to breed in container water. Both are vectors for transmitting diseases. Both can transmit the Zika virus but A. aegypti is more effective and considered a primary transmitter.  Both could prosper here, we have the appropriate environmental conditions, but currently there is not a substantial A. aegypti population.

Only females bite humans to get a “blood meal” before laying eggs. They are cold blooded so they don’t bite if the temperature is below 50 degrees. They can live as long as 2 to 3 months and adults that hibernate can live up to 8 months. This means that the problem is temporary; it exists only in the hot summer months.

Eliminating Container Water

Because mosquitoes breed in container water, anything that collects water should be dumped after it rains. Mosquitoes require as little as one tablespoon of water to lay eggs. It can take as short a time as 3 days for a new generation. After it rains, either dump the water or eliminate the object (e.g., put watering cans back inside the tool shed or throw away old tires). If the water cannot be dumped, such as a pond, make sure the pond has plenty of mosquito larvae eating fish, dragonfly larva, frogs, toads, and other such organisms. For rain barrels, use the mosquito dunks that are made of a safe bacteria. Or transform the water feature so that the water is moving by installing a bubbler or waterfall. Mosquitoes do not like moving water or moving air.

Kirsten dispelled common myths: Bug Zappers are not effective killers of mosquitoes, bats do not prefer to eat mosquitos, and purple martins are not big mosquito eaters. Plants that are reputed to repel mosquitoes do not work if they are just sitting in the landscape. A dense groundcover such as English ivy can harbor adult mosquitoes. It does not matter what you eat but mosquitoes are more attracted to big people and prefer men over women.

Protection and Sprays

If you are going to garden, wear long sleeves, long pants, socks, and shoes, or spray yourself with repellants such as DEET (25-30 percent), Picaridin (20 percent), oil of eucalyptus, or IR-3535 (Merck 3535), which is found in Avon’s Skin So Soft. Spraying Listerine and using dryer sheets, VapoRub, or vanilla are not effective protection.

The most environmentally friendly effective control is to control the larva stage. Spraying the adult mosquitoes in the landscape should be the last resort and should be based on surveillance data. The most popular mosquito adulticide for home landscapes is permethrin but it is toxic to fish, aquatic arthropods, and the non-target insects (pollinators).  Don’t be fooled when the pesticide applicators try to sell you on the fact that it is “natural” based on a chrysanthemum plant. What they are spraying is not natural, it is a chemical. There are substances called pyrethrins that are the active ingredients in pyrethrum, an extract of a flower, and these are are natural insecticides that act by blocking chemical signals at nerve junctions. However, commercial sprayers are not spraying pyrethrins. They are spraying permethrin, which is based on pyrethroids, synthetic pesticides. Permethrin is a pyrethroid insecticide that is light-stable and has a longer duration of activity against insects than pyrethrins. Thus, what the company is selling and spraying on your garden is permethrin, a chemical that will kill aquatic life and pollinators and render vegetables, herbs, and fruits non-edible.

Mosquitoes have a flying range of 600 feet, about 1 to 2 miles. If your property is sprayed, it will kill the existing ones but the next day more can fly in. If you spray your garden and your neighbors don’t, you can always inherit your neighbors’ mosquitoes. Commercial companies may tell you that the spray will last for a month but that does not prevent new mosquitoes from entering nor does the spray continue to kill for up to a month. In my mixed edible garden, only the grass could be sprayed which gets cut every few weeks. Since my grass gets cut by a service, I am concerned that the pesticide company will spray with a chemical one day and the lawn service crew will come and cut the grass the next day. I don’t know what harm that chemical would cause if the crew were to breath it in as they were cutting.

More Information and Resources

The presentation cleared up a lot of confusion and I decided not to have my garden sprayed. I am more vigilant about dumping water on my property. I try to garden in the cool morning with long sleeves and pants but sometimes I have to use the towelette on my face.  If you are faced with these same issue, learn more about mosquito management by calling the Arlington County Extension Office at (703) 228-6414 or visit the Master Gardeners of Northern Virginia website. The website has a tab with resources including the Powerpoint presentation. On Tuesday, June 19, 2018, there will be a presentation on identification and control of mosquitoes and ticks by the same group. This is free and registration is requested by contacting the Master Gardeners of Northern Virginia (call above number or visit website). This presentation will be at the Westover Branch Library, 1644, N. McKinley Road, Arlington, VA, from 7:00 pm to 8:30 pm.