Sri Lanka Weevil

On a recent visit to Florida’s Manatee county, this poor Crepe myrtle was brought to my attention.

A branch from a crepe myrtle eaten up by the weevil

The owner of the plant said that white insects were found on it. Sure enough in a few seconds of searching, a white weevil was found. Here you can see him pinned down for a really awful picture.

The perpetrator pinned down on the countertop by a shish-kebab skewer. They are not much for flying away.

After a few minutes search on the internet, I think this insect is probably the “Infamous” (heh-heh) white weevil from Sri Lanka. As one of the many invasive insects coming into the USA each year, this one is without natural predators or diseases and has been increasing in Florida and other places. This insect has a very wide range of plant hosts so it will probably be successful all over the place. It seems to eat everything and the kitchen sink. Unfortunately, it seems to eat citrus plants which will cause Florida some problems. Obviously, it likes Crepe Myrtle too.

I do not know anything about this insect in particular since it is a relatively new import, but I know about a cousin of it, the Black Vine Weevil. I can tell you about its life cycle and how nurserymen have been handling it.

The Black Vine Weevil is primarily a root feeding insect. Most of their lives they exist as immature grubs that eat roots of susceptible plants. They overwinter in the soil, moving downwards as the soil temperature drops in the fall. After winter, they warm up and rise shallower and shallower in the soil until they are just under the surface by spring. Here they pupate and turn into adult beetles. If you are a curious human, your best bet is to find them in the shallow soil or leaves on top of the ground. The Black Vine Weevil is nocturnal in its adult form.

The adults emerge when the weather turns warm and they begin to feed on the foliage. All weevils have a snout with a little mouth at the tip. It is characteristic of the Family. The little mouth chews a smile shaped bite out of the leaves of its host. You can pretty easily look at a weevil-eaten leaf and say it was done by a member of the Weevil family. The only other insect making even close to this feeding pattern is the grasshopper and their feeding is quite rough-looking in comparison. Anyway, the feeding damage occurs at night and is sometimes quite heavy. Our little friend on the Crepe-myrtyle make a big mess of the leaves. In the day, weevils of the Black Vine type sleep down in the shade under the plant. That is where I found the Sri-Lankan one too, so it may be nocturnal also.

Something very strange occurs with the Black Vine weevil. There are no males. Only females exist. Females spontaneously create parthenogenic eggs and lay them in the soil under host plants. I do not know why they never have any males, but there it is, ladies. A species of complete feminists for you. I am not sure how common this is in weevils but there are a few other insects that do this durung certain times of the year, like aphids. I do not know of any other completely female species, but, like I always say, I don’t know much.

As far as control, they Black Vine Weevil can be treated by dosing the soil around the affected plant with a water can full of pesticide. This is best done in early summer as you notice the first little bit of adult notching on the new leaf growth. Then spray the foliage once per month during the summer. The first drenching in the soil will kill active grubs that are root-feeding. Then the adults eating the leaves get knocked off from their lunch. If you are into this sort of thing, you can easily flashlight your way around the garden at night and hand-pick hundreds of them. They are slow and non-flying. Hand collection is not a good control measure because they hide in the shadows and are pretty sneaky. Weevils also walk into homes pretty frequently on cold nights. They come in and get lost and never get out. If you have weevils in your foundation plants, you will probably find a few lost in your garage!

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Ivy Growing up a Maple Tree

I must comment on an article I recently read in a free gardening newsletter found in a diner. I hope this is not where most gardeners find their information. In the newsletter there was a question and answer column with highly suspect advice. The questioner wrote in asking if English Ivy

    Hedera helix


was hurting his maple tree as it was climbing up the trunk. I think the question was, maybe, wondering if the vine was some kind of parasite.

I have observed ivy climbing many houses, trees, fences, etc. and I can fairly well state that unless the tree is really weak and would fall down from the weight of the vine, it is really fine. The vine is just using the tree, or whatever, as support and is in no way a parasite*. It also cannot possibly overwhelm a big tree like a maple or oak.

Let me quote the fine answer this columnist gave:

“The plant is an aggressive climbing vine.”…”As the ivy climbs in search of increased light, it consumes and kills branches by blocking light from the tree’s leaves.”

I have never seen this occur. I have, however, seen ivy with no damage to the branches/trees for over fifty years of growing up the trunks. The columnist does not mention one slight problem with vines growing up a tree trunk and that is gypsy moth.

In the “old days” when gypsy moth was in its glory days and just moving into the midwest, it munched on many species of trees in residential areas. After feeding, the females seek a secret area to lay eggs. Since the pregnant females can hardly walk, they are so full of eggs, they like to walk down the trunks of trees and lay eggs under the cover of vines which are growing up the trunk. I would often find eggmasses hidden amoungst English ivy leaves.

This is

    not now

a real problem since gypsy moth has settled into a more moderate pest status with predators, parasites and diseases keeping it in check.

Back to this fine article:

“On the ground, English Ivy forms dense monocultures that exclude native plants, not just weeds. It also serves as a host for bacterial leaf scorch, a pathogen harmful to elms, oaks, maples, and other native plants.”

It does neither. I suppose this author has never supervised a landscape crew pulling weeds and “native” plants out of a bed of ivy. As for the unnamed bacterial leaf scorch, I know of no pathogen that attacks that wide of an array of plants and certainly not that array and ivy doesn’t get anything. Bizarre.

This goes on:

“Maple roots…With a mat of ivy on top are short-changed of water, and nutrients.”

Well, except for the fact that a maple tree has roots going all over in a very wide pattern and the ivy is usually in a small planting bed around the tree. I guess if the ivy was planted in a really huge bed, it would steal food from the tree about 5% but it doesn’t have the ability to block water that much. As for nutrients, that tree will get food just fine. The ivy is not that heavy a feeder.

I am weary of this odd question and answer. One of the things I have always disliked about gardening is there is a lot of wacky advice out there. I will put this article in my category of “wives’ tales.” Here is my advice to my loyal readers, do not get your gardening information from your local diner.

*Regarding parasitic vines, the reader may want to view a previous post on the true parasitic plant, Dodder.

Drooping Leaves are a Problem

Much of the USA has had a hot, dry summer this year. Plants burst forth in the spring with good amounts of rainfall, only to be tricked by hot dry weather later. If you are trying to cultivate special plants, be aware of dry spells and try to water at least once per week, deeply.

Wilted leaves on a Burning Bush, Euonymous alatus 'Compacta'

There are some interesting things about the response of plants to dry weather. In fact, they have developed a special hormone to deal with drought. It is called abscisic acid. ABA as it is known to botanists, is produced in the roots when the soil gets hot and dry. It travels up the plant stems in the xylem tubes and gets into the leaves. There it alters the osmotic potential of the cells which keep the stomata open. Stomata are like little mouths in the back of the leaves. The little mouths are normally held open by the plump guard cells so the leaves can breathe gases and perform photosynthesis. When the guard cells soften up in response to ABA, the stomata close and insure no water loss. This is a very clever thing for the stomata to do since most of the rest of the leaf is covered by waxy coverings and is quite waterproof. Anyway, the ABA is a signal that the weather is hot and dry and is a time of stress, so shut down everything and wilt. When water is again present, the ABA dissolves away and causes no harm.

A large Rodgersia spp. wilted down from drought

Another thing ABA does is prepare plants for dormancy. ABA is produced seasonally at the end of summer in response to the stimulation of shortening daylengths. Different species of plants are more or less sensitive to ABA, so it is one of many factors involved, but the bottom line is it makes the leaves fall off. That is why it is called abscisic acid, it makes leaves abscise. Some species of plants will shed a part of their leaves after a single wilting event. Some plants will not shed them until shortening days, cold weather, and other signals tell them it is time for winter dormancy. In many plants, ABA will stimulate the growth of corky cells located at the base of leaf stems. These corky cells sever the connection between the twig and the leaf. After no more water or nutrients are coming INTO the leaf, and no more carbohydrates from the leaf are going INTO the twig, they feel they can do without one another. The leaf begins to starve, and it loses first its chlorophyll, then its carotene, then its will to live and lets go. That is why leaves turn from green to orangy red (in some species) as they go into autumn. It is getting to that time of year, people…fall.

Verticillium Wilt and the Redbud

See the dark rings in the heartwood?

Today we cut down an old Redbud tree that leafed out poorly this spring. The tree has been suffering for years with a pathogen called Verticillium wilt. The crosscut of the tree shows the bark around the edge, then the white sapwood, then the darker heartwood. Heartwood consists of sapwood cells that have died which is natural. Within the sapwood there are rings that are occasionally much darker than the dark heartwood. These near black streaks in the vascular tissue of the tree are where the pathogen Verticillium tried to plug up the tree. The tree grew around them many times in its life. Old age and pathogens plus a nice canker rotting the trunk overcame its defenses.

Stump of a Redbud Tree

Here is a picture of how small the leaves were this spring. The flowers bloomed but the leaves were not getting enough water through the vascular system to push out the leaf buds and develop normal leaves.

Small leaves are a symptom of vascular disease

Verticillium wilt is a fungal disease carried in the soil. Many many species of plants are susceptible to it. For a complete list, check a pathology book or ask in the comments. There are about a hundred susceptible species. When the fungus in the soil comes into contact with feeder roots, the fungus enters. The fungus grows and proliferates eventually making reproductive spores. Spores are carried around the whole plant by the water going up the stem. As the fungus spreads systemically, its main function is to block the vascular tissue. It can also create trunk cankers. Here is a picture of trunk damage.

This trunk was very rotten from a canker

Just an aside about the spring flowers it had this year. The flowers were not very affected. The buds were already formed last summer. The buds just needed a little water to flow into them this spring to telescope out the cells and form flowers. Just because your tree flowers, it does not mean that it is healthy. In fact, many times, the biggest burst of flowers come just before a tree dies. The tree wants to make as many babies (seeds) as it can to continue its species in the world. SO flowering heavily may be a sign that your tree is checking out.

There is no remedy for Verticillium wilt. Try to buy healthy looking nursery stock from cultivated fields. Once a tree has died in the soil from Verticillium
wilt, the soil will be contaminated with the fungus. Be sure to replant a resistant species or plant far away from that spot. The spores will last in that soil longer than your lifetime. I will be replanting an evergreen of some type.

Dodder

One interesting plant found in Florida is the Golden Dodder, Cuscuta pentagona.  It is a parasitic plant that twines right handedly around the stem of its victim.  It rarely photosynthesizes for food, in fact some species cannot even make chlorophyll.  It sends root-like fingers called haustoria into the host and lives off the juices.  It can become so severe, the host does very poorly and dies.  Ususally parasites do not kill their host because it will put them out of business too.  Dodder is a seasonal plant that dies off in very cold weather, so they usually do not have time to kill their host in a season.  The severe cases I have seen in Florida must be multiple year infestations and the mild winters are not killing the dodder off as much. 

Dodder look like yellow spaghetti except for the flowers.  They are a flowering plant, and as such they produce seeds.  The seeds are long-lived in the soil and will germinate for years after an infestation has been cleared.  The seeds are an important weed seed that seed producers are always on the look out for.  It is a bad plant to come along with, for example, grass seed.  The customers would not want to get dodder from a contaminated batch of seed. 

I have only seen dodder in Michigan on rare occasions.  The type in our northern midwest has always been in Alfalfa.  I believe these pictures are of a different species, however none of it was flowering, so not sure. 

 The only cure for it is to remove or prune out the dodder from the host plant.  The haustoria can give rise to new infestations in the host if just a little bit is left.

In a bizzarre twist, so to speak, in Wiki, there is a bit about dodder being able to smell.  They say that some research has shown it grows toward pheromones emitted from possible host plants.  None of the dodder that I saw was sniffing around but here are some photos of a big mess.

Manure’s Disease

I am posting this information because I keep hearing about this condition.  It is actually spelled Menieres disease.  The best description is a few brief sentences from Wikipedia.

Ménière’s disease (pronounced /meɪnˈjɛərz/[1]) is a disorder of the inner ear that can affect hearing and balance. It is characterized by episodes of dizziness and tinnitus and progressive hearing loss, usually in one ear. It is caused by lymphatic channel dilation,[2] affecting the drainage of endolymph. It is named after the French physician Prosper Ménière, who first reported that vertigo was caused by inner ear disorders in an article published in 1861.”

Just as when you hear a new word, you start noticing it all over the place, I keep hearing about cases of this.  I think this is because the symptoms are somewhat vague and occur frequently alone.  When vertigo, hearing loss, tinnitus and a feeling of fullness in the ears all occur together, it is probably a diagnosis one should discuss with one’s physician.  I think I keep hearing about this because of the company I keep.  As I age, my contemporaries are starting to get these problems that plague the elderly.  I also believe one of the causes of fluid retention in the middle ears is high blood pressure and eating too much salt.  We eat sodium in many products.  Try it for yourself.  Look at food labels and see if you are consuming too much sodium in your diet.  Try to get less than 2000 mg.  If you have blood pressure problems or symptoms of Menieres disease, some doctors recommend as little as 400 mg.  It would be darn near impossible to keep to that restrictive a diet, but we all could do better by some awareness and caution with sodium.

Witches Broom Condition

This time of year, I drive around looking at all the trees with their leaves off and I study the branching structure of them.  One common condition that exists is Witches Broom.  It is considered a disease, but I call it a condition since I think of diseases having a pathogenic organism creating them.  The Witches Broom I am referring to is caused by salt.  Here are a few pictures.

Tufted growth from highway salt spray

These photos were taken along the side of a roadway where salt is used to melt ice in winter.  The cars spray up brine and it coats the trees all winter.

Tufted growth habit

Many buds grow with no distance between them

 The salt damages the terminal bud on the branch.  That bud, in usual situations, subordinates the proximal buds by the production of the plant hormone Auxin.  Auxin is a group of hormones with numerous functions.  The function here being the production of a strong terminal growing bud that extends the length of a healthy branch each year.  Without a healthy terminal bud producing Auxins, the lateral buds break and grow into a disorganized tuft of small branches called Witches Broom.  There is no cure for this except for pruning out the tuft.  If no more salt spray occurs, a bud will start a new elongating branch and will grow more or less normally.   

Given the salt spray situation these young trees grow in, they are going to grow little each year and have a stunted habit.