Feeds:
Posts
Comments

Archive for August, 2012

Morning view form the Pisgah Inn

This past weekend, Eric and I took a few days off and drove down the Blue Ridge Parkway all the way to Great Smoky Mountains National Park. I’ve always wanted to do this because I’d never been to the Smokies, well at least not to the national park. It was spectacular, to say the least.

The observation tower on top of Clingmans Dome in Great Smoky Mountains National Park.

The observation tower on top of Clingmans Dome in Great Smoky Mountains National Park.

On Saturday, we drove up Clingmans Dome (6,643 ft), the 3rd highest mountain east of the Mississippi River, surpassed only by Mount Mitchell (the highest at 6,684 ft) and Mount Craig (6,647 ft). There is a parking lot 300 ft from the summit of the mountain and from there you can hike to the top of the mountain where there is an observation tower that gets you even higher and provides a panoramic view of the surrounding mountains. Wow!

As is typical, our view from the top was partially obscured by the haze that plagues the mountaintops of the Smokies. This is not the mist that originally gave the Smoky Mountains their name. According to a sign at the Clingmans Dome Information Center, visibility at the park has decreased 60% over the past 40 years and 90% of the decease is due to air pollution, mainly from sulfates given off by the burning of coal for heating and electricity. But that’s another story …

A hazy view from the top of Clingmans Dome

A hazy view from the top of Clingmans Dome

At this elevation, the forest is composed mostly of short-needled evergreens. This unique ecosystem, the Southern Appalachian spruce-fir forest, is now limited to the highest mountaintops (above 5,500 ft) of the Southern Appalachian range. The forest, a relict of the last Ice Age, is dominated by red spruce and Fraser fir. During the Pleistocene when much of North America was covered by ice, this spruce-fir forest was widespread in the Southeastern United States. As temperatures warmed, these trees disappeared from the lower elevations and the high mountaintops of the Southern Appalachian chain became refugia for this forest ecosystem where small island populations of the spruce-fir forest have survived.

Dead Fraser firs stand amongst healthy young fir trees not yet attacked by the balsam woolly adelgid.

Dead Fraser firs stand among healthy young fir trees not yet attacked by the balsam woolly adelgid.

Unfortunately, over the last 50 years about 95% of the mature Fraser firs in the southern spruce-fir forest have been killed by the balsam woolly adelgid (Adelges piceae), a small insect that was accidentally introduced from Europe in the early 1900’s. This pest initially decimated populations of balsam fir in the Northern Appalachians and has since moved south to the Smokies. As we drove down the parkway, we had noticed lots of dead fir trees scattered along the ridges but up on Clingmans Dome, the devastation was extensive. Because the adelgids don’t usually attack the trees until they are about 15-20 years old, there are many young firs growing below the dead trees. Sadly, these will undoubtedly become infested once they get older.

Woolly adelgids on the branch of a young hemlock.

Hemlock woolly adelgids on a hemlock branch.

The balsam woolly adelgid is related to the hemlock woolly adelgid (Adelges tsugae) which has been devastating populations of hemlocks throughout much of eastern North America including the northern part of the Blue Ridge Mountains. The hemlock woolly adelgid has recently been discovered in the Smoky Mountains and now the beautiful hemlocks which grow at the lower elevations in the park are threatened.

A fir graveyard

A “fir graveyard” on Clingmans Dome

.

The problem with these and other non-native pests is that the trees and plants that they attack have no natural defenses against them. The balsam woolly adelgid has attacked and killed the majority of the mature Fraser firs in the Southern Appalachians and most of those that remain are infested and will soon succumb to this pest. It’s very sad. Clingmans Dome looks like a Fraser fir graveyard with just the graying skeletons of these once magnificent firs still standing.

The beautiful red spruce trees which grow along side the Fraser firs in this forest ecosystem, though not attacked by the balsam woolly adelgid, are indirectly affected by the loss of these trees. Without the protection of the sturdier firs, the red spruce are more prone to wind damage and blowdowns.

An nearby mountaintop is covered with dead Fraser firs

An nearby mountaintop is covered with dead Fraser firs

On top of all this, air pollution in the Southern Appalachians which leads to the formation of acid rain and acid mist is thought to be slowing the growth rate and weakening the red spruce and remaining Fraser firs leaving them more susceptible to disease and insect damage.

Research is ongoing to try to determine ways to save these last remaining populations of the southern spruce-fir forest and perhaps over time, the trees will develop their own defenses against the adelgids and the effects of pollution.

For now, it’s nice to be able to enjoy these beautiful mountains and we plan to return in the late spring when the rhododendrons are in bloom. That should be spectacular!

Until next time – Happy Gardening!

Morning view from the balcony of our room at the Pisgah Inn. Heavenly!

Morning mist over the Blue Ridge from our balcony at the Pisgah Inn. Heavenly!

Advertisements

Read Full Post »

Tobacco Hornworm

This summer our deck has turned into an extension of our vegetable garden. We have herbs in widow boxes, lettuce and cherry tomatoes in large containers, and beets and carrots growing in a raised garden kit from ScottsMiracle-Gro. Soon we will plant some spinach and more lettuce.

Hornworm frass on the railing

Hornworm frass on the deck railing

It’s nice being able to go out right before dinner and pick fresh herbs for cooking or cherry tomatoes and lettuce for a salad, especially since the big garden isn’t super close to the house. I can’t wait until the carrots and beets get bigger. Thanks to the deer and the woodchuck, we don’t have many left in the main garden!

Last Saturday evening while we were sitting on the deck having a “libation” before dinner and enjoying the sunset, Eric noticed that most of the leaves on one of the cherry tomatoes were completely gone. The deck railing under the plant was dotted with green and brown pellets – both telltale signs of the presence of a hornworm.

A hungry tobacco hornworm munches on a tomato.

A hungry tobacco hornworm munches on a cherry tomato.

“Where is he,” Eric wondered out loud. Then we spotted him happily noshing on one of the green cherry tomatoes – a big, fat tobacco hornworm which we identified by the pattern of diagonal white stripes and the curved red “horn”.

Hornworms are very large caterpillars that can grow up to 5″ long. This guy on our cherry tomato was easily 3½” long. They are the larvae of the sphinx (or hawk) moth, a large moth that is sometimes referred to as a hummingbird moth because of its size and the way it flies.

Tomato hornworm with a black horn and "V" shaped stripes

Tomato hornworm with its black “horn and “V” shaped stripes

The hornworms commonly found in our area are normally bright green with white stripes on their sides and a characteristic red or black “horn” at their back end which gives them their name. Tomato hornworms (Manduca quinquemaculata) have a rather straight black horn and “V” shaped white stripes while tobacco hornworms (Manduca sexta) have a slightly curved reddish horn and diagonal stripes. There is also a brown form of the tomato hornworm which is less common. Both can unfortunately be very destructive to many plants in the vegetable garden.

The brown form of the tomato hornworm

The brown form of the tomato hornworm

.

The large hornworm we found was undoubtedly close to its mature size and nearly ready to pupate. At this stage, the caterpillars drop off the plant and burrow into the soil where they enter the pupal stage. At this time of year, they will overwinter in the pupa and the adult moth will emerge in the spring. There may be two generations per year.

A tomato plant defoliated by a hornworm

A tomato plant defoliated by a
hungry hornworm

.

Hornworms are serious pests of tomatoes, peppers, potatoes, and even eggplants. They devour the leaves of these plants and because of their large size, they can defoliate a plant very quickly. Their camouflage coloring combined with the fact that they feed from the undersides of the leaves makes them very difficult to spot in the garden. Fortunately the large fecal pellets (frass) are quite easy to spot and can help reveal their location as it did in our case.

.

Control Measures

The easiest way to get rid of hornworms is to find them on your plants and pick them off – no sprays involved! Once you pull them off, just drop them into a bucket of soapy water.

Hornworm with braconid wasp cocoons on its back

Hornworm with braconid wasp cocoons on its back

There are also many predators, including lady beetles and green lacewings, that will feast on hornworm eggs and the young caterpillars. A small braconid wasp, Cotesia congregatus, parasitizes the hornworm by laying its eggs on the back of the caterpillar. The larvae that hatch from the eggs feed on the insides of the hornworm and then pupate (form little cocoons) on the back of the hornworm. If you find these parasitized hornworms in the garden, be sure to leave them there because the hornworms will soon die and the little wasps will hatch out and stick around to parasitize other hornworms!

Bacillus thuringiensis is a bacterium that selectively infects and kills many types of caterpillars including hornworms. Sprays containing these bacteria (Bonide Thuricide and Dipel) are effective controls when the caterpillars are young and small. They are less effective on the large, mature hornworms. Always read and follow the label directions.

We left this big old caterpillar to enjoy his tomato for the night but the next day when Eric went to pick him off, he was nowhere to be seen. I suspect he dropped down to the ground and has since entered the next stage of his life. Good night caterpillar!

Until next time – Happy Gardening!

Read Full Post »

Webworm infested redbud branch

This morning as Eric and I sat on the front porch eating breakfast and admiring the new garden that has replaced our front “lawn”, I noticed a patch of brown leaves on the redbud across the driveway. I was hoping it was simply a dead oak branch that had fallen and gotten hung up in the tree but it looked suspiciously like fall webworm damage. Upon closer inspection, I confirmed it was the latter – webworms.

Fall webworms feed on the leaves incorporated into their web.

Fall webworms feed on the leaves incorporated into their web.

The fall webworm (Hyphantria cunea) is native to North America and – here’s a switch – it turns out that we accidentally introduced this pest to Europe and Asia in the mid 1940’s. It’s actually one of the few insect pests that we have exported. Oops!

Fall webworms are often confused with tent caterpillars since they both build web nests in trees. However, tent caterpillars appear in the spring and fall webworms usually appear in the late summer and early fall. They also have very different styles when it comes to building their nests. Tent caterpillars build compact nests in the crotch of two branches, while the fall webworms build large silken webs which surround the foliage at the tips of branches. As the caterpillars exhaust the leaf supply within the web, they enlarge it to incorporate a new supply of fresh green foliage and the nest expands along the branch.

The web protects the caterpillars from predators (and pesticides) as they feed.

The web protects the caterpillars from predators (and pesticides) as they feed.

Fall webworms overwinter in the pupal stage usually in the soil, mulch, or leaf litter at the base of the tree. The adults are white moths that emerge in March and April. After mating, the female moths lay hundreds of eggs in a mass on the underside of leaves. Small caterpillars hatch out after about seven days and immediately begin building a web and feeding on the leaves of the tree.

Fall webworms attack many different species of trees including pecan, walnut, hickory, many types of fruit trees, and as we found out, the eastern redbud.

There are two races of the fall webworm in North America, a blackheaded race and a redheaded race. The webworms on our redbud are the blackheaded race.

The remnants of leaves and caterpillar frass inside an older part of the web.

The remnants of leaves and caterpillar frass inside an older part of the web.

These caterpillars have a voracious appetite and have consumed most of the tissue between the leaf veins, leaving behind webs filled with brown skeletonized leaves and green frass (their droppings) – very ugly.

In general, this doesn’t hurt the tree because the damage is usually localized to just a few branches and since it occurs later in the season, the tree has had time to store food. The damage is mostly cosmetic and the webs will eventually weather away over the winter. However, if the tree is under stress due to drought, poor nutrition, or repeated defoliation from multiple generations of caterpillars, then its health could be in jeopardy and control measures may be warranted.

Control of fall webworms

In many cases, the unsightly nests of fall webworms can simply be removed from small to medium sized trees by pruning out the infested branches. Another solution is to destroy the webs by winding them up on a stick or tall pole if they are within reach. Any caterpillars that are not killed in the process are left exposed and will often be eaten by birds and other predators.

When they run out of leaf tissue the web is enlarged to encorporate fresh leaves.

When they run out of leaf tissue, the web is enlarged to incorporate fresh leaves.

If you discover the caterpillars while they are still small, you can control them by spraying a liquid formulation of the bacteria, Bacillus thuringiensis (Bt). Bonide Thuricide (BT) Liquid, applied to the foliage right next to the nest, will kill the caterpillars when they eat the leaves and will not harm beneficial insects. Bonide Captain Jack’s Deadbug Brew, another naturally derived organic insecticide, is also an effective control when sprayed on the foliage adjacent to the web.

The trick with these sprays is to cover the foliage that the caterpillars will be eating. The foliage and caterpillars inside the nest are protected by the web and spraying the nest is usually not effective. Always read and follow the label directions when spraying any pesticide.

I will probably prune out the infested branch this weekend to remove the caterpillars before they crawl down the tree to pupate. Hopefully that will help prevent a reinfestation of fall webworms next year.

Until next time – Happy Gardening!

Read Full Post »

%d bloggers like this: