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Archive for April, 2013

Tent caterpillars especially love cherry trees

Just yesterday on my way to work, I noticed some very tiny tent caterpillar nests beginning to form in the cherry trees along the side of the road. They seem to be a little later this spring which fits with the slightly later spring we are experiencing this year. Seeing them reminded me of the blog post I wrote back in early April of 2010 and I thought it would be appropriate to re-run this post to remind folks that NOW is the time to attack these icky, squiggly caterpillars – BEFORE they do major damage to your beautiful landscape trees.

So, here you go (with a few added tips) …

Well, it’s that time of year again!

Tent caterpillars can defoliate a tree very quickly if left unchecked.

Tent caterpillars can defoliate a tree
very quickly if left unchecked.

I saw the tell-tale signs on the way to the nursery yesterday – the beginnings of the familiar, yet dreaded tent caterpillar webs starting to form in the crotches of the small cherries at the side of the road. Today, they’re even bigger! Everyday they will grow … little webs will grow into bigger webs; little caterpillars will grow into big leaf-eating machines crawling over the branches devouring every bit of green foliage on the tree until it looks like winter has returned!

Nasty little critters! I know they must serve some purpose in the greater scheme of things but I sure haven’t figured out what that might be – food for the birds, I suppose. Yes, I’m sure that must be why they exist!

During the day, tent caterpillars venture out of the nest to forage.

During the day, tent caterpillars
venture out of the nest to forage.

Well, what can you do about them? “Knock ’em out while they are small”, Andre always says. It’s the best time and you don’t have to resort to using chemical insecticides.

Wage biological warfare!! When they are small, they can be eradicated with a lovely little bacterium called Bt (short for Bacillus thuringiensis). Bt (also sold under the trade name Dipel) produces a natural insecticide and has been used by organic farmers for years to safely control many insect pests. Just spray it on the foliage and when the caterpillar eats the leaves, they ingest the Bt which produces a toxin that basically dissolves their gut and kills them within a few days – no harm to the environment or beneficial insects!

And … even though it takes a few days for the caterpillars to die, the best part is that they stop eating within a few hours so your trees are saved from defoliation! Good stuff – and environmentally responsible, too!
Look for Bonide Thuricide (BT) Liquid Concentrate or Dipel; they should be right on the shelf of your full service garden store.

Large tent caterpillars consume a tremendous amount of foliage.

Large tent caterpillars consume a
tremendous amount of foliage.

Though Bt works best on the very young caterpillars, all is not lost if you miss this stage and suddenly find that you have the larger caterpillars crawling all over your trees devouring every last leaf they can find. These larger caterpillars can be controlled using Bonide Captain Jack’s Deadbug Brew according to the label directions. Captain Jack’s Deadbug Brew is a natural but effective, broad-spectrum ORGANIC insect control which is listed for controlling tent caterpillars as well as many other insect pests on both ornamental and edible crops.

NEVER spray any insecticide when trees are in bloom!

Don’t want to spray? Watch this Viette video tip for another interesting way to get rid of tent caterpillars! Along this line, my husband will poke a stick into the web and wind the web, caterpillars and all, up on the end of the stick and then stomp them into the ground! Ahhhhh – revenge is sweet!

A tent caterpillar egg mass encircles the tip of a crabapple branch.

A tent caterpillar egg mass encircles
the tip of a crabapple branch.

Another way to get rid of tent caterpillars is to break their life cycle by destroying their egg masses before they hatch. These egg masses are found encircling the tips of small branches of host trees from July – February. Some of their favorite trees are cherries, crabapples, and apples. Sometimes you can prune off the branch tips containing egg cases but a more effective way to destroy the eggs is to spray the trees thoroughly with a horticultural oil such as Bonide All Seasons Oil to smother and kill the eggs. If you have tent caterpillars this spring, put a reminder in your gardening calendar for a late fall and/or late winter spraying with horticultural oil. This will also help control many other insect pests that overwinter in your garden!
Read more about the benefits of horticultural oil.

So …

Keep an eye peeled for these tent caterpillar nests in your trees and be ready to do battle while the caterpillars are young and vulnerable.

Until next time – Happy Gardening!

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Sooty mold on California laurel; Joseph O'Brien, USDA Forest Service, Bugwood.org

Last week we had a great question posted on our Discussion Board. It was interesting because it really involved two different issues, not just one.
Here is Kathy’s question:

I have two gardenias that are approximately 3 feet high that have a thick black mold/soot on all of the leaves. It is hard to wash off. On the underside of the leaves it looks like whitefly or the remains of whitefly. Should I cut them down to the ground now? I also have a yew in another section of the yard with the same black leaves. Thanks for your help.

Sooty mold on rose foliage

Sooty mold on rose foliage

What Kathy is seeing is the growth of sooty mold on the leaves of her gardenias. Sooty mold is a fungus but not one that causes disease so it is not directly harmful to her plant. However, heavy coatings of sooty mold may affect the plant indirectly by blocking sunlight and air from reaching the leaf surface and thus it can interfere with photosynthesis.

So why does sooty mold grow on the leaves and stems in the first place? This is the more important question because the reason it grows is the real problem for the plant.

Whiteflies congregate on the underside of a leaf

Whiteflies on the back of a leaf

The fact is that the growth of sooty mold usually indicates that some type of piercing, sucking insect has attacked the plant and these guys can do real damage if they are not controlled. It could mean her gardenias are infested with whiteflies (as she suspects), or even mealybugs, scales, or aphids to name a few others. When these insects suck the juices from the plant, they excrete a sticky substance called “honeydew” that drips down and coats the leaves and stems of the plant.

Fungal spores carried by the wind or rain become trapped on the sticky honeydew and germinate there. The fungus grows on the leaf surface using the honeydew as food and eventually covers the leaves with a black, sooty coating. Sooty mold may grow on any plant that is attacked by insects that excrete the honeydew that these fungi thrive upon.

Mark examines the underside of leaves for insect pests

Mark examines the underside of
leaves for insect pests.

What this means is that in order to solve a sooty mold problem, you first need to get rid of the insects that create the conditions which allow the mold to grow in the first place. The truth is that these are the critters that are going to cause the most damage to your plants.

If you notice sooty mold on your plants, you should carefully inspect them for sucking insects. Be sure to check the stems and especially the undersides of the leaves. Scales, aphids, mealybugs, spider mites, and whitefly are some of the most common sap sucking insects. Their feeding can damage the leaves and stems of a wide range of plants often causing stippling and curling of the leaves and distortion of the stems. In addition, some of these insect pests are vectors for certain viral diseases, spreading them from plant to plant as they feed.

Aphids have distorted these viburnum leaves.

Aphids have distorted these
viburnum leaves.

Bad news! Gotta get rid of ’em!

Fortunately, except for scale insects and severe infestations of whitefly, most of these “suckers” are not too hard to get rid of. Aphids, spider mites, and mealybugs can often be blasted off with a strong jet of water from the hose, although you may have to do this many times throughout the season to keep them at bay.

Many natural predators such as lady beetles and lacewings feed on all stages of these pests including scale insects and whiteflies. Be kind to your beneficials!

If the infestation is not too widespread, some selective pruning may take care of a lot of the problem. The pruned branches or leaves should be carefully bagged and thrown out in the trash; they should not be composted because many home compost piles do not get hot enough to kill all the stages of these insects.

Mealybugs like to hang out on the underside of leaves.

Mealybugs like to hang out on the
underside of leaves.

For an organic control, both Pure Spray Green and Bonide All Seasons Oil are listed for control of spider mites, mealybugs, aphids, scale, and whitefly. These products work by smothering the different stages of the insects. When you spray, it is very important that you coat the stems and especially the undersides of the leaves because these areas are where most of the insects are found. Be sure to read the label and apply accordingly. Sometimes a combination of selective pruning and spraying with horticultural oil works well.

Scale insects cover the underside of this Euonymus leaf.

Scale insects cover the underside
of this Euonymus leaf.

Of course as always, a healthy plant is less likely to be targeted by pests. Insects and diseases often attack plants that are weak or stressed due to drought or poor nutrition. Keep your plants healthy by fertilizing them and watering them properly.

Unfortunately, sooty mold will remain on the leaves for a while even after the insects are gone but eventually it will wear off. If the mold is particularly heavy on the leaves, you might try washing it off with a blast of water or wiping the worst off with a soft cloth.

Perhaps Kathy should be thankful for the sooty mold on her gardenia. It probably alerted her to a much more serious problem and may have saved her shrub from some serious damage!

Until next time – Happy Gardening!

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Helleborus orientalis begin blooming in mid to late winter.

On Groundhog Day, ‘Punxsutawney Phil’ predicted a speedy end to winter and we were all eagerly anticipating an early spring.

This morning wet snow and sleet lay on the ground

This morning wet sleet
lay on the ground

At the time, it seemed like he might be spot on but less than a week later came the big New England blizzard that dumped up to 3 feet of snow from northern New Jersey to Maine with Boston getting clobbered with the brunt of the storm. Since then we have had two major March snow storms here in the Shenandoah Valley and believe it or not, a winter weather advisory for snow and sleet came across my computer yesterday afternoon and by 6:45 pm it was snowing like crazy!

Oh for Pete’s sake – what do groundhogs know anyway! All they do in my yard is dig in my garden, eat my vegetables, and cause me a big headache!

Quince buds

Quince buds

Yesterday morning, I took a walk through the Viette gardens to see if I could find some signs of spring. It was quite cold and pretty cloudy – not at all spring-like! The gardens are all cleaned up and ready, but spring is still holding out. Of course many of the daffodils and a few of the other spring bulbs are up and blooming beautifully and I can tell spring isn’t too far off because the buds on many of the trees and shrubs are quite swollen and many are beginning to show the tiniest bit of color.

Forsythia just beginning to pop.

Forsythia is just beginning to pop.

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A few bright yellow flowers have popped open on the forsythia but most of the buds are still pretty tight. The buds on the flowering quince are nice and plump, just waiting for a warm April day to push them along. I have a feeling that all it’s going to take is a few warm, sunny days and spring will be bursting forth in a gush of blooms!

Mahonia repens

Mahonia repens

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A striking plant in the garden at this time of year is the low-growing Mahonia repens. Its deep burgundy winter foliage makes a gorgeous backdrop for the bright clusters of chartreuse flower buds. Later in April, these buds will open into racemes of beautiful deep yellow flowers and the holly-like evergreen foliage will gradually develop its deep blue-green summer color.

A beautiful black hellebore

A beautiful black hellebore

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The Viettes have a wonderful diversity of Helleborus planted throughout the gardens including some very unique new cultivars. These are all in full bloom and have actually been blooming for several months. They are truly one of the first flowers of the season!

The herbaceous peonies in the gardens are just beginning to poke up through the ground, though the ones growing in more exposed areas are not up as high as those that are more protected.

Just a reminder – if you had problems with botrytis blight last year, now is the time to spray these newly emerging peonies with the first round of a fungicide like Mancozeb or liquid copper according to the label directions.

Tree peony buds and young foliage

Tree peony buds and young foliage

The tree peonies are also beginning to break dormancy and their new foliage has a lovely pinkish-red tint. These miniature stems and leaves were enveloping the swelling flower buds and created a very interesting pattern when observed up close –
subtle beauty in the garden can be found everywhere!

Tree peonies are my favorite type of peony. I just love how they look in the garden with their giant crepe paper blooms covering the tall shrub-like plant. Cultivars bearing single, semi-double, or double blooms can be found in a wide variety of colors and many even have a lovely fragrance. Tree peonies often begin blooming in early May, several weeks earlier than the herbaceous peonies, and because they have woody stems, they don’t usually fall over from the weight of the flowers. Spectacular!

Intersectional or Itoh peony

Intersectional or Itoh peony

Andre’s yellow intersectional peony (a.k.a. Itoh peony) ‘Bartzella’ has loads of nice fat buds on it. This interesting new peony type, which is a cross between an herbaceous peony and a tree peony, combines many of the best traits of each of its parents. It produces multitudes of large, crepe-like blooms on strong stems that hold up in the wind and rain, yet it dies back to the ground and gets cut back in the fall like the herbaceous peonies. The foliage is similar to tree peony foliage and remains attractive through the fall. A very nice plant and worth having in the garden, though they sell out fast in the spring!

Lamium maculatum

Lamium maculatum

Some of the early blooming perennials are just peeking up and some even have a few blooms popping out already. The Lamium maculatum which has made a wonderful ground cover around a small water garden is blooming quite nicely although its foliage hasn’t completely filled out yet. I also discovered a beautiful Pulmonaria that had pushed up a few short flower scapes even though its foliage was just beginning to emerge.

Spring IS coming – don’t you worry! My fear is that it will come and go too quickly. Spring is one of my favorite seasons and I really hope that when it finally does arrive, it stays for a while!

Until next time – Happy Spring!

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