Pests and Diseases: Hemlock Woolly Adelgid

 

Today’s Pest and Disease topic is the Hemlock Woolly Adelgid. Unless you are familiar with them, you may not be sure if it’s a fungus or an insect. Hemlock Woolly Adelgids are little white fluff balls that attack one of our most beautiful native evergreens, the Eastern Hemlock (Tsuga canadensis). Let’s look at how this insect came to be one of the most dreaded of all pests in the eastern forests.

Hemlock Woolly Adelgid was accidentally introduced to the United States in the early 20th century but it wasn’t until the middle of the 1900’s that it became a true pest. It found its way to the Eastern Hemlock and fell in love…it starting having lots of babies and without a predator to keep its population in check, it became a force to reckon with. It’s depressing to know that the Hemlock Woolly Adelgid is responsible for the death of Eastern Hemlocks and studies have estimated that it could wipe out the hemlocks in some southern areas within 10 years.

hemlock woolly adelgidLet’s look at how a small, little fluff ball can wreak so much havoc. The Hemlock Woolly Adelgid literally sucks the life out the trees and the trees are so weakened by the damage that they succumb to starvation. It doesn’t happen overnight…that would be too easy. It usually takes years to kill the trees and in those years, the population of the adelgids continue to climb and they just move right on over to the next tree to begin their devastation again.

While hemlock is a common sight in northern U.S. forests, its presence is mostly in the mountainous areas of Virginia and Maryland where it enjoys the cooler temperatures. In fact, I remember a story from my Woodies professor at Virginia Tech where a student had been on a hike up to the popular Cascades waterfall. The student came back excited to tell Dr. Niemeira that he found a variegated hemlock. Unfortunately, the “variegation” ended up being a heavy infestation of Hemlock Woolly Adelgid.

So what can you do if you have Eastern Hemlocks? Scout regularly for the pest. Be sure to check the undersides of the foliage as this is a favorite hiding spot. I don’t like to just pass you off to someone else, but if you spot the little fluff balls on your hemlocks, I recommend that you consult a Certified Arborist. They will be up-to-date on the latest recommendations for controlling them and they will probably be able to apply the insecticides for you. While I’m not a fan of pesticides, if you have to use them let someone who has been certified in the application process do the work for you. I need to hear from the Mid-Atlantic Gardening readers if you have encountered Hemlock Woolly Adelgid. Leave me a comment below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

Pests and Diseases: Crape Murder

 

While crape murder may not seem like a typical post for Pests and Diseases, it shows who can be the biggest pest to landscapes sometimes: people. People are the ones that decide to whack off the top third of a tree so that it blooms more.

Before I prattle on about the horrific practice of crape murder, let me accurately describe what it is and what it isn’t. If you are a neat gardener that doesn’t enjoy the winter appearance of the crape myrtle seed pods and remove them, you are not a crape murderer. If you remove broken or crossing branches from a crape myrtle, you are not a crape murderer. But if you do this:

crape murder

you are a crape murderer and I implore you to stop! I’m not sure why people think that removing a third (or more in extreme cases) of a tree is a good practice. I understand why “landscapers” do it and the answer is three fold:

  1. It’s easier to prune a tree by making a few large cuts than it is to prune correctly. You can murder a tree in about 5 minutes versus the 45 minutes to an hour it takes to prune a tree correctly to remove broken, dead or crossing branches. While the landscaper can charge the customer more for their time, few commercial customers are willing to pay.
  2. It gives an “added value” service to the customer. Again, the customer may not be willing to pay an hour per tree for pruning, but the landscaper can charge a few dollars more and the customer sees that something has been done. If the landscaper is already there applying mulch, it doesn’t take too much extra time to murder a few dozen trees.
  3. Because other landscapers are doing it. I’d like to find the person who started this trend and figure out their logic. Unfortunately, so many “landscapers” are not trained in horticulture and don’t understand the “why” of doing things, only the “how”. They see others doing it and they follow suit, to the detriment of the trees.

 

If you have been guilty of butchering your crape myrtles, take solace in knowing that many other folks do it too just because they don’t know how bad it is. It’s same thing that happens with mulch volcanoes…people see the landscaper down the street do it so they think it must be the right thing to do.

SO WHY IS CRAPE MURDER SO BAD?

The first reason is that it’s plain ugly. Crape myrtles have beautiful structure and exfoliating bark that is really only seen during the winter. The silhouette of a crape myrtle in the winter can be the centerpiece of your garden instead of resembling something that your guests hang their coats on.

The second reason is that by making such drastic cuts, epicormic buds are forced to break. These buds lie dormant and the only time that they break is when the plant is put under undue stress. These buds are weakly attached to the stems and their resulting branches are easily broken during wind or ice storms. Also, the sheer number of buds is unsightly and results in a lollipop appearance where there is a huge ball of foliage sitting on top of a stick that is the trunk of the tree.

Another reason is that it’s just not natural. When will we learn that if you leave nature alone, it is capable of amazing things? Sure there are plants that need to be pruned judiciously like hedges (I don’t like them either by the way – too much work!) but a crape myrtle, in Zone 7, is a TREE! It’s not a plant that is supposed to be reduced in size by a third or more each year for the sake of a few more blooms. To me, it’s the same thing as pruning beautiful forsythia shrubs into little meatballs. What’s the point? A forsythia in its natural form, with its long arching branches, is a beauty to behold. And so is the crape myrtle when it is allowed to grow in its natural state with only corrective pruning. Let me know how often you see crape murder in your area by leaving me a comment below or sending me an e-mail to stacey@midatlanticgardening.com. Happy Mid-Atlantic gardening!

February 14, 2012Permalink Leave a comment

Pests and Diseases: Thousand Cankers Disease

 

I must warn you that today’s post is a bit depressing. If you enjoy the beauty of walnut trees (Juglans nigra) and the delicious nuts that they produce, you may be a little sad after learning of the latest disease that is infecting these beautiful native trees.

Thousand Cankers DiseaseThousand Cankers Disease is caused by a fungus, Geosmithia morbida, that is brought into the phloem of the tree by the walnut twig beetle. Essentially, the fungus catches a ride on the beetle and is thereby introduced to the tree. The subsequent individual canker that is produced by the tree isn’t especially large, but there can be 35 cankers in a square inch of wood. These smaller cankers coalesce and turn into larger cankers that ultimately kill the tree. The trees essentially die of starvation as the phloem tissue is prevented from delivering the carbohydrates that are produced through photosynthesis to other areas of the tree where they are needed.

The walnut twig beetles like to feed on young, tender new stems and it is virtually impossible for the average homeowner to scale a large walnut tree to have a look. The beetles move south in the tree to the lower trunk tissue during the winter; it may be possible to observe some of the cankers and/or entry points at that time.

WHAT ARE THE SYMPTOMS OF THOUSAND CANKERS DISEASE?

Thousand Cankers DiseaseThe first clue that your walnut tree may be infected with Thousand Cankers Disease is branch dieback. As the leaves and branches are starved of nutrients, the tree’s self-preservation mechanism is to eliminate the area that isn’t receiving the “food” that is needed. The individual beetle entry points are small so they can easily go unnoticed. The cankers sometime weep sap and this is a dead giveaway that your trees are infected.

How does the old saying go: “the best defense is a strong offense”? If you currently have black walnuts on your property, make sure that they are not stressed by competition with turf and other plants. Mulch them well and supplement their water during times of drought. As with most insects, the walnut twig beetle will seek out the weakest trees first so anything that you can do to keep your trees thriving instead of just surviving is a plus.

WHAT CAN BE DONE IF YOUR TREES ARE INFECTED?

Unfortunately, not much can be done to save the trees once they are infected. In theory, systemic insecticides can be applied to the tree to lessen the activity of the beetles. If you suspect that your trees may be infected with Thousand Cankers Disease, I would seek the council of your local Extension Agent or an ISA Certified Arborist. If there is any saving grace to this disease, it is that the fungus is not translocated in the vascular tissue like Dutch Elm Disease.

It’s an unfortunate reality that Thousand Cankers Disease has already been identified in Virginia and Pennsylvania. I’m sure that as time goes on, this disease will continue to spread in the Mid-Atlantic gardening states. Let me know if you have any experience with Thousand Cankers Disease by leaving me a comment below or e-mailing me at stacey@midatlanticgardening.com. Happy gardening!

 

February 7, 2012Permalink 3 Comments

Pests and Diseases: Tomato Hornworm

 

With all of the warm weather we are having, it makes me think for a moment that I can walk outside and pick a fresh tomato off of the vine. But alas, it’s still January. When the warm weather does arrive, the pests and diseases that want to attack my beloved tomatoes will be lurking, waiting for the perfect opportunity to strike. Today, I want to look at the tomato hornworm so that we can all be prepared for how to deal with this vegetable villain.

tomato hornworm

Tomato hornworm is obviously a fan of tomatoes but they also enjoy other members of the Solanum genus such as Jimson Weed, nightshade and horsenettle. Keep that in mind if you have trouble with tomato hornworm…eliminating the other hosts can help in controlling them on your veggies. They also can be found munching on your peppers and eggplants so beware. These pests could pass for a chameleon relative as there ability to disguise themselves is uncanny…and that’s why they are capable of defoliating large portions of young tomatoes in the blink of an eye.

Tomato hornworm is 3.5″ to 4″ long as a mature caterpillar which is pretty big when you think about it. I’m not a fraidey cat but I must admit that I don’t enjoy squishing them because they are so large. Now give me an aphid and I’m a beast…I can squish them by the hundreds if need be! You really do need to dispose of them instead of tossing them aside and hoping that the birds pick them off. The mature caterpillar will drop off of the plant and then pupate into a moth if you leave them to their own devices.

Tomato hornworm eggs are laid on both the upper and lower sides of the leaves in late spring. If there is a saving grace here it is that they are deposited as single eggs, instead of in large groups. The moth that lays the eggs are known as hummingbird moths or sphinxs. Not all hummingbird moths evolve from tomato hornworms for the record…just some of them.

WHAT CAN YOU DO TO CONTROL TOMATO HORNWORMS?

By far and away the best control method for tomato hornworms is hand picking them. You can either squish them, put them in a bucket of soapy water or feed them to your chickens if you are lucky enough to have them. But as we discussed above, don’t just toss them and hope that nature takes care of them. More than likely, nature will prevail but it will mean that you have a larger population of tomato hornworms instead of the robin consuming them for lunch. The good news is that with regular scouting of your tomatoes, you will be able to quickly notice when the tomato hornworm has invaded your garden. Let me know if you’ve had problems with tomato hornworms in your garden and what you’ve done to remedy the situation. Leave me a comment below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

Pests and Diseases: Weeds

 

Today we will look at one of the most prevalent pests in any garden: weeds. Who said that pests have to be defined as little creepy crawlies? In my experience, it isn’t the aphids, spider mites or thrips that cause the most damage; it’s the groundsel, chickweed, dandelion, bittercress, henbit and wiregrass that wreak the most havoc. Not only are they unattractive in the garden, they also compete with the very plants that we are nurturing for water and nutrients.. I won’t delve into controlling them too much in this post…I want to make sure that you can identify them as that is over half the battle in controlling them.

  1. Groundsel – this is a cool season annual that doesn’t look half bad until it flowers and spreads its hundreds of seeds across your landscape, not to mention to the rest of your neighbors. The yellow flowers give way to fluffy seed heads in a matter of days. The good thing about groundsel, if there is such a thing, is that it is an annual. If you can prevent it from setting seed this year, next year’s crop will be dramatically reduced provided that your neighbors’ yards aren’t harboring any.
  2. Chickweed – this too is a cool season annual that germinates as the temperatures drop. The upside to chickweed is that it is edible…check out this link for recipes. One of the most frustrating things about chickweed is that when you go to pull it, you are really just pruning the tops…chances are that the roots will remain and you’ll just remove the foliage. The plant is left stronger and will come back with a vengeance. Perhaps that means you’ll be eating more chickweed salads.
  3. Dandelion – unlike the previous two weeds, dandelions are perennials…that means that they come back each year stronger and stronger. When you pull dandelions, you have to make sure that you remove every piece of the roots or they will regenerate themselves from even the tiniest piece of root tissue. Of course, dandelions have the distinguishable yellow flowers and fluffy seed heads that kids can’t seem to get enough of. Perhaps you can carry that sweet thought with you as you watch the wind disseminate thousands of seeds for next year’s crop.
  4. Bittercress – when I was in the nursery business, this was my nemesis…it could survive in the smallest amount of soil and thrived under the frost cloth that was used to cover the beds. When someone would sneak up on the weeds to pull them, they would explode with hundreds of seeds. I know it sounds impossible, but if you’ve encountered this weed in your landscape, you’re familiar with its projectile seeds. It’s an annual, so that’s one thing that’s good about it…if you can catch it in flower, you’ll be reducing it’s population next year.
  5. Henbit – this is an annual weed that I’ve come to despise as my career has transitioned from the nursery industry to landscape maintenance. In the landscape, henbit is what makes you have to mow the grass in January. It transforms itself from the tiniest little innocent plant to a 8″ tall monster seemingly overnight. Its purple flowers are attractive but not pretty enough to allow it to continue growing unchecked. Often times, chickweed and henbit will take over a winter lawn…if this describes your lawn, you know who you are.
  6. Wiregrass – my grandma has always called this weed wiregrass but it’s also known as bermudagrass. Many people grow bermudagrass as a lawn, for which it is an excellent choice if you have full sun and don’t want to water. However, if you have a plant that you don’t hate nearby, you will curse the day that you purposefully introduced this plant to your landscape. It is a perennial and spreads by stolons that grow just underneath the soil. I’ve actually read that Virginia Tech has done studies that show that the stolons can exist 6′ down in the soil. I’ve tried to find this documentation online but I’ve been unsuccessful in locating the research. Regardless if the stolons are 1-inch or 6-feet below, they are virtually impossible to eliminate without a ton of hand digging or Roundup. Just like with dandelions, one piece of root is enough to form a colony.

 

I hope that I’ve helped you identify some of the weeds that may be taking over your lawn and landscape. What you decide to do with them is certainly your choice…your neighbors may or may not thank you. Let me know which weeds are giving you a fit; if you need help identifying them, send me a picture and I’ll post it for other Mid-Atlantic Gardening readers…maybe we’ll do a little contest to see who can identify the weed. As always, leave me a comment below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

January 24, 2012Permalink 1 Comment

Pests and Diseases: Aphids

 

Happy Tuesday to everyone! I received a note from a reader that is just beginning her gardening journey and she wanted to know more about aphids. She was wondering if I could go over what exactly they were and why she needs to be concerned about them. That made me realize that sometimes I talk about things that beginning gardeners may not be familiar with. I need your help with recognizing when that happens! Send me an e-mail or comment below if you’re unsure about something I’ve mentioned. I’d be happy to re-visit the items that I may have unknowingly just skimmed over. With all of that out of the way, here we go!

AphidsAphids are insects which means they have six legs. That may seem elementary but lots of people think spider mites are insects too…they aren’t and that totally changes the way you control them chemically. Anyway, aphids are ravenous little suckers, literally. They suck the plant’s juices, primarily the phloem, and weaken the plant. The phloem is responsible for transporting the food that is made through photosynthesis by the leaves down to the rest of the plant. (As a side note, if you have trouble remembering which is which, remember that the xylem transports up [x and u are close together in the alphabet] and phloem transports down). OK, back on topic. So the aphids remove valuable resources from the plants by sucking on plant juices and thereby weakening the plant. It’s as if someone allowed you all the water you wanted (provided by the xylem) but never let you have any food (provided by the phloem). At some point, you would kick off too.

The main problem with aphids is that they pro-create so darn rapidly. Eggs that survive the winter generally produce females and these females in turn produce more and more offspring. Even though a typical adult will only live for around 30 days, she can pump out lots o’ live babies which in turn produce more live babies and so on. I’m sure you’ve seen the cat statistics in the vet’s office about how many cats can be produced by a pair of unspayed and un-neutered cats…it’s kind of like that but multiplied by a higher number as the mama aphid can produce hundreds of live babies at a time.

Aphids come in all kinds of colors, ranging from green to black to white to peach. There are over Aphid4000 species of aphids so you can imagine that they have adapted to fit in with their local surroundings. Once you learn what an aphid looks like, you’re unlikely to ever forget. One very distinguishing characteristic of aphids are the cornicles…these are two little projections that protrude from their lower back. If you see these, rest assured that you have aphids.

SO WHAT DO YOU DO IF YOU HAVE APHIDS?

It really depends on how bad the infestation is. If you only have a few here and there, just squish them between your fingers…they are only 1/10 of an inch long. More than likely, by the time you see them though, you’ll have quite the infestation on your hands. Here are some ways to control them:

  1. Give them a harsh spray with your garden hose. Sure you won’t kill them all but if you can knock out some of the females, you’ll be cutting your future population down.
  2. Avoid spraying pesticides. I know that sounds counterintuitive but nature has a predator
    Aphid controller - ladybug larvae

    Ladybug larvae - aren't they beautiful?

    for every pest and there are many that enjoy aphids. Lady bugs, lacewings and parasitic wasps will all work diligently to curb the population. Of course they can’t kill all the aphids because then they wouldn’t have anything to eat. Keep that in mind when you feel like the predators aren’t doing their jobs swiftly enough. To the right is a picture of an immature ladybug…I’m surprised by how many people don’t know what they look like. If you see these little guys crawling around, leave them be so that they can grow up and do your work for you.

  3. Cut back on your fertilizer. Aphids love, love, love fresh new succulent plant growth and will flock to your overfertilized plants like moths to a flame. Again, nature knows how fast a plant is supposed to grow and when we go and pour on the nitrogen to get them to grow at a quicker pace, we have upset a natural balance.
  4. If you have tried all of the above methods, you can spray a tomato leaf spray. That may sound peculiar but it has worked for many generations of folks and it doesn’t kill the predators. You can find the recipe here.

 

I hope that I’ve been able to shed some light on aphids and the problems they pose for plants and gardeners alike. I know that I rambled a bit today and I apologize for that even though it is my nature. Many of you have commented that you don’t mind my rambles so I won’t refrain from them quite yet. If you have any experience with controlling aphids in your garden, please leave a comment below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

January 17, 2012Permalink 3 Comments

Pests and Diseases: Cottony Cushion Scale

 

A few weeks ago, we discussed Gloomy Scale, which is a real threat to maple trees. In that post, I mentioned Cottony Cushion Scale and that will be our topic for today. Cottony Cushion Scale’s latin name is Icerya purchasi and resembles cotton of all things. It is known as a soft scale, meaning that its protective outer covering is soft and squishy instead of being hard and virtually impenetrable like armored scale.

When the scale are young, they are mobile and crawl around the plant seeking out a place where they will spend the rest of their existence. As crawlers, they are reddish-brown in color and don’t have the cottony appearance of the adults. Once they have declared squatter’s rights on a particular stem, they start to exude a white waxy covering that will later protect them from predators. As is the case with armored scales, the best time to attack them is during the crawler stage. And as with armored scale, an application of dormant horticultural oil can all but eliminate your Cottony Cushion Scale problems.

Some of you may know that Cottony Cushion Scale was imported into the U.S. in the late 1800’s by accident and that it nearly wiped out the citrus crop in California and later Florida. Entire citrus groves had to be destroyed as a result. Thankfully, the Vedalia beetle was tried as a biological control and it had great success in bringing the scale population down to manageable levels. Cottony Cushion Scale is often thought of as a southern insect but I have personally encountered it overwintering on Chinese Holly (Ilex cornuta) and Skypencil Holly in Richmond, VA. Some of my Zone 5 and 6 readers may not have to concern themselves with this particular scale but it is alive and well in Zone 7.

Sooty Mold on Holly

Thankfully, Cottony Cushion Scales are easy to spot as they are generally around 1/2″ long when they are covered with their protective coating. You may notice a black coating on the stems and leaves near the scale…this is sooty mold. While the scale are literally sucking the life out of your plants, they are also excreting honeydew which sooty mold thrives on. Don’t be too concerned with the sooty mold; if you eliminate the scale, you’ll eliminate the sooty mold too. I hope that you’ve learned something today about another pest that we gardeners have to deal with. If there is a particular pest or disease that is wreaking havoc in your garden and you’d like me to address it, feel free to leave me a comment below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

January 10, 2012Permalink 1 Comment

Pests and Diseases: Gloomy Scale

 

Gloomy Scale – it doesn’t have a particularly interesting name or conjure up images of anything too vile. I’d like to introduce to an insect that you’ve probably seen hundreds of times but not even realized it. Gloomy Scale’s latin name is Melanaspis tenebricosus and it is found all throughout the Mid-Atlantic region. Let’s look at the life cycle of Gloomy Scale before we discuss its control options because without understanding this, control is virtually impossible.

Scale in general can be broken down into two types: Armored scale and Soft scale. Soft scale can resemble little balls of cotton (Cottony cushion scale) or have similar fluffy-like appearances. Armored scale, such as Gloomy Scale, aren’t nearly as obvious and can go undetected for years and build to damaging populations. Gloomy scale resembles little flat gray colored discs that can be found on the trunks and stems of its victims. The discs that are visible are the outer covering that the adults produce to protect themselves. It is under this protective covering that all the dirty work is done. The adults lay their eggs here where they hatch into crawlers. These crawlers leave their parents and ensure that the infestation proceeds further on the plant. Once the babies have found an area that is suitable for them, they set up shop and begin producing their protective coating.

Scale feed by inserting their stylet (think of it as a straw) into the plant tissue and suck out its contents. As you can imagine, this isn’t good for the plant. Think of it like a tick on you, just sucking and sucking until it gets its fill. But with scale, it doesn’t really fill up per se…it just keeps producing babies that hang out to cause more misery. In cases of light infestations, the damage is usually minimal but remember, Gloomy Scale usually goes unnoticed and can build to heavier populations. It’s at these heavy populations that the damage becomes obvious but unfortunately, that’s when it’s harder to treat. Gloomy Scale is usually found on maples, particularly the red maple (Acer rubrum). Red maples will exhibit signs of decline such as dying branches, yellowing leaves and overall poor health. Of course, red maples can decline for many more reasons than just scale, but we’ll discuss that at another time.

SO HOW CAN YOU TREAT GLOOMY SCALE?

Once you’ve determined that your maple is infected with these little monsters, you may have to wait to treat them. While that may sound counterintuitive, if we look back at the life cycle it will make perfect sense. If you are going to spray a contact insecticide, you have to spray when the crawlers are active, which is generally in May or June. If you spray a contact insecticide when the crawlers aren’t running around, all you’ve done is spray a toxic pesticide for no reason and wasted your money. Another more desirable option is to treat with a systemic insecticide. Systemic refers to the way that the chemical is delivered to the pest. In systemic pesticides, the chemical is taken up by the plant (usually through a root drench) and translocated throughout the vascular system to all areas of the plant. When an insect feeds on that plant, it receives a dose of the pesticide as well. There are lots of downsides to this method as well…look at my article on organic gardening vs. conventional gardening for more information.

The preferred method for treating scale is to apply a dormant horticultural oil during the winter months to smother and suffocate the overwintering scale. While it may not be a pleasant way to die for the scale, it certainly has the least amount of collateral damage to other insects, including beneficials. If you have a heavy infestation of gloomy scale on your maples, it may take several years to win the war against them, but to me, it is worth it to go slowly and avoid damaging the beneficial insects that visit the trees, including honeybees. The decision is ultimately yours and you have to remain diligent in scouting for Gloomy Scale either way.

IS THERE ANYTHING THAT YOU CAN DO TO PREVENT SCALE IN THE FIRST PLACE?

My best advice is to try to replicate the natural environment that the plant is found in…in the case of Red Maple, that is a wet area. Red Maple is also known as Swamp Maple and its natural habitat is not in a parking lot island surrounded by 2 acres of asphalt. While the area doesn’t have to be a floodplain, red maple will do best in areas that are naturally more moist. Also try to help the trees out during very droughty times so that they aren’t more susceptible to pests in general, including Gloomy Scale. And lastly, reduce the amount of turf around the tree so that it has less competition with roots for water and nutrients. Just be sure that you go easy on the mulch…no mulch volcanoes please!

The next time you are out and about in your yard, take a glance at your maples and see if you are able to spot any grayish-black discs. If you do, invest in some dormant horticultural oil and smother these little beasts this winter. I’d love to hear your feedback after you’ve had some time to scout for them. Leave me a comment below or e-mail me at stacey@midatlanticgardening.com. Happy scouting!

 

December 20, 2011Permalink 4 Comments

Pests and Diseases: Spider Mites

 

Since I touched on spider mites in my organic vs. conventional gardening article, I thought it would be wise to expand on them a bit more. Many people believe that spider mites are insects but they aren’t. At the fear of offending an entomologist, I’ll just say that insects have 6 legs whereas arachnids have 8 legs. Guess how many legs a spider mite has…if you guessed 8 you would be correct.

When viewed up close, as in the picture to the left, the spider mite is a ferocious beast to behold. I have observed them under a microscope and you can just see them ripping and tearing into the plant tissue to obtain their dinner. They use their needlelike mouthparts to literally suck the life out of your plants. They are very small and can build to damaging populations very quickly; spider mites can develop from an egg to an adult in a week’s time. They are only about as big as the period at the end of this sentence so they often go unnoticed until their damage is evident.

Their damage is usually seen as stippling on the upperside of the leaves. With a heavy or prolonged infestation, the leaves will turn brown and drop off. The damage may be apparent on the tops of the leaves but the villains reside on the undersides of the leaves where they can be protected from weather extremes and predators…and pesticides. While I don’t advocate the use of conventional pesticides, anything that kills (-cide) pests is a pesticide in my eyes. That includes some of the control methods that we’ll discuss later.

WHAT CONDITIONS FAVOR SPIDER MITE DEVELOPMENT?

Spider mites are usually at their worst when it is hot and dry. When I say hot and dry, I’m not only talking about when the temperatures are high and the humidity is low. You can have an average summer where it rains periodically but if you site a plant that is susceptible in an area that is hot and dry, such as by an asphalt drive or against a brick wall, that microclimate is hot and dry even though the surrounding area isn’t.

Plant stress also triggers spider mite development. Plants produce all kinds of hormones in reaction to stress and plant pests are wise enough to be able to detect them. If a plant is located in an area that is not conducive to growth, such as large shade trees planted in small parking lot islands, spider mites and all types of plant pests will move right in. Think of it as the plant posting on its Facebook wall that dinner is served.

HOW CAN YOU BE SURE THAT SPIDER MITES ARE THE CULPRIT?

The best investment that you can make in terms of combating pest and disease issues is a good quality hand lens. The 10X magnification is sufficient to cover 90% of the pests you will encounter. Equipped with a hand lens, you can easily see the spider mites on the undersides of the leaves.

Another trick you can use is to hold a white piece of paper under the plant and then tap on the leaves…the spider mites should show up on the paper as little crawling specks.

The most obvious ID tactic is to look for webbing…now it won’t look a Halloween display but it should be readily visible when the critters are present.

WHAT CAN YOU DO IF YOU HAVE SPIDER MITES?

  • If your infestation is particularly bad, you may have to count your losses and remove the plant. Dwarf Alberta Spruce are notorious for spider mites and if your plant looks like this, you may be better off pitching it. There is a saying in the nursery industry: “if in doubt, throw it out”.
  • You can keep the plants showered with water and that will usually be enough to send the mites running. Now I’m not talking about a continuous shower…I mean spraying them 1-3 times per day for about a week with a garden hose. This could open you up to other issues such as fungal diseases so be sure to allow enough time for the plant to dry before the sun sets for the evening.
  • Mix up a potion of soap and water and spray the little monsters. You have to make sure that you are spraying them on the undersides of the leaves, not just the top of the leaves. That’s what makes controlling them and many other pests difficult…they know exactly where to hide.

 

The long and short of spider mites is that they are a pest whose population can quickly explode into damaging populations. But if you consider where you site your plants before installing them, it can dramatically lower your chances of having an infestation of epic proportions. And if you do see them wreaking havoc on your plants, give your plants a cool shower a couple times of day…chances are the spider mites will decide that your landscape is inhospitable to uninvited guests and move on. If you’ve had any issues with the eight-legged critters we discussed today, post your experience in the comments below. And remember that I am here to help you, so don’t hesistate to e-mail me with any questions or concerns you may have at stacey@midatlanticgardening.com. Happy gardening!

December 13, 2011Permalink 1 Comment