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Archive for June, 2013

Thrips in Platycodon flower

Thrips are bad this year!

Mark has noticed damage from thrips in many of the daylilies and we have also discovered these pests in hosta flowers and in many other flowers.

Thrips on a daylily petal

Thrips on a daylily petal

So… what are thrips?

Thrips are small cigar-shaped insects with long, narrow, fringed wings. They are tiny; just visible to the naked eye. There are many different species and most of them cause injury to plant tissue. A heavy infestation of thrips can cause severe damage to foliage and even flowers and fruit as their rasping/sucking mouth parts scrape the tissue and extract plant juices.

Thrips damage on daylily foliage

Thrips damage on daylily foliage

What does thrips damage look like?

On foliage, thrips damage appears as brown stippling on the leaf surface and when damage is more severe, the leaves may appear silvery or papery in appearance. Flower buds can become distorted and sometimes fail to open. On open flowers, thrips damage appears as dead spots, blotches, or the flowers may be discolored or deformed. I find this a lot in some of my daylilies; it’s especially noticeable on the darker colored flowers like the reds and the purples.

Thrips damage on a daylily petal

Thrips damage on a daylily petal

In addition to the damage caused by their feeding, thrips are also vectors for the spread of some destructive plant diseases and viruses like tomato spotted wilt virus.
A double whammy!

You can sometimes see thrips on the flowers or foliage but you have to look carefully because they are very small. You may also notice black specks of their fecal matter on the foliage or flowers. According to Andre, though, the easiest way to tell if you have thrips is to shake the foliage or a flower just above a pad of white paper and see if any little cigar-shaped insects fall onto the paper.

Thrips on a daylily showing their small size. Notice the damage to the petal.

Thrips on a daylily showing their small
size. Notice the damage to the petal.

Controlling Thrips

In the past, thrips were controlled with applications of DDT. Yikes! There are much “safer” ways to control them now.

Minor infestations may not warrant any control measures. Healthy, vigorous plants are able to outgrow thrips damage so it is important to keep your plants healthy through proper fertilization and watering practices.

If you have a heavier infestation of thrips, one way to reduce their numbers without spraying is to prune off damaged flowers, buds, foliage, or terminal growth and discard it in the trash. This is kind of drastic and it doesn’t always get rid of the problem.

Thrips tapped out of a hosta flower onto white paper.

Thrips (and pollen) tapped out of a
hosta flower onto white paper.

A better way to control them is to spray your plants with horticultural oil. Horticultural oils are often used by organic gardeners and are effective in controlling thrips in the larval and adult stages. The oil basically coats the insects and smothers them. Although oil sprays are often effective in smothering the eggs of many insects, thrips eggs are usually unaffected because they are laid inside the plant tissue where they are protected.

The nice thing about oil sprays is that they have little effect on non-target, beneficial insects like lady beetles and honeybees.

A word of caution about spraying horticultural oils on your plants during the heat of the summer: some oil sprays contain impurities that can burn foliage if they are sprayed in direct sunlight and at temperatures above 80oF. This sometimes makes it a challenge to use these sprays to control insects during the summer. Spraying in the early morning or later in the evening helps, but around here, thunderstorms often pop up in the evenings thus ruining that chance to spray.

Thrips crawl deep into the flowers.

Thrips crawl deep into the flowers

There is a solution, though. Our friends at Petro-Canada have developed a highly refined horticultural oil, PureSpray GREEN, that is 99.9% pure and contains virtually no impurities. This non-toxic, organic oil spray can be used to control a wide variety of insect pests including thrips on flowers, fruits, and even vegetables right up to the day of harvest. The lack of impurities means it will not burn plants even when sprayed in direct sunlight at temperatures up to 95oF.  PureSpray GREEN spreads out over the entire leaf or petal, smothering insect eggs, larvae, and adults, effectively forming a protective barrier over the plant. It also controls many common plant diseases like rust, powdery mildew, and botrytis when used according to the label directions.

Thrips can also be controlled using Bonide Captain Jack’s Deadbug Brew, a broad spectrum organic insect control that can be used on ornamentals and edibles. Always read and follow the label directions.

So if you have noticed small patches of color missing in your flower petals or stippling on the foliage, you may have thrips – but now you know what to do!

Until next time – Happy Gardening!

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Carpenter bee and nest hole

Uh oh – I think a carpenter bee is making a nest on the deck!

Sawdust accumulating under the carpenter bee nest hole

Sawdust accumulating under the
carpenter bee nest hole

Eric had seen a small pile of sawdust forming under a wooden footstool – a telltale sign of carpenter bee activity.

Funny that I had just written a post about the solitary ground bee and here on our deck was another solitary bee making a similar type nest in one of the wooden footstools that Eric had built last year. He should have finished painting it!

The eastern carpenter bee, Xylocopa virginica, is a large bee that, at a quick glance, looks very much like a bumblebee. On closer inspection, though, you can see some distinct differences. The most obvious is the solid black, hairless abdomen that has no yellow coloration. Bumblebees have stripes or patches of yellow hair on the abdomen. The only yellow hairs on the eastern carpenter bee occur just behind the large head on the thorax.

Carpenter bees have a hairless black abdomen.

Carpenter bees have a hairless
black abdomen.

The other main difference between carpenter bees and bumblebees is that bumblebees are social bees which nest underground. Carpenter bees are solitary bees and build their nests by “drilling” a tunnel into wood, creating a nest very similar to the nests created by the solitary ground bees.

Like the ground bees, it is the female carpenter bee that excavates the nest. She starts by drilling a perfectly round tunnel into bare wood perpendicular to the grain. Once the tunnel is about an inch long, she makes a right angle turn and continues her excavation with the grain of the wood. Unlike termites, carpenter bees do not eat wood, rather they “kick” it out of the tunnel leaving the telltale sawdust pile under the hole.

The bees drill a perfectly round hole about 1/2" in diameter

The bees drill a perfectly round hole
about 1/2″ in diameter

So much of the carpenter bee nesting behavior is similar to the Andrenid bees I wrote about last time. The female bee goes out and collects pollen and nectar, carries it to the nest, forms it into a ball and lays a single egg on it. She then uses some sawdust to partition off the compartment, creates another pollen/nectar ball, lays another egg, partitions that off, and so on until the tunnel is filled. She may create up to 8 or 10 separate compartments within the tunnel. When the eggs hatch, the larvae feed on the pollen ball, pupate, and eventually emerge as adults around August. These young adults feed on the nectar of late summer and fall flowering plants and then return to overwinter in the nest. They re-emerge in the spring, mate, and then the cycle begins again.

The wet female bee emerges from her tunnel.

The wet female bee finally emerged
from her tunnel.

We caught this female carpenter bee in the process of excavating her nest. I could actually hear her rasping or chewing the wood as she was enlarging the tunnel – it was pretty interesting.

We turned the stool over in hopes of rousting her out for a photo shoot but she wouldn’t cooperate. We tried gently knocking the stool on the deck but still she was a no show. We even got the turkey baster and tried to blow air into the hole – no luck. Finally, Eric squirted a little water into the hole with the baster and that did the trick. Out she came, a little sodden but otherwise unharmed. It took a while for her to dry off enough to fly away but that gave me plenty of time for some close-up photos.

Carpenter bees can be a nuisance at times but, like the solitary ground bees, they are important pollinators and should be tolerated if possible. These bees are generally not aggressive; the males do not have stingers and the females will only sting if they are really provoked.

She finally dried off enough to fly away.

She finally dried off enough to fly away.

In most cases, their tunneling simply causes cosmetic damage to the wood, however, since subsequent generations often reuse the same nest and may expand the excavation, structural damage can sometimes occur.

Carpenter bees tend to seek out unpainted wood for their nests and will target unpainted doors, windowsills, fascia boards, exposed rafters, roof eaves, deck railings, and sometimes wooden lawn furniture as in our case. Painting or varnishing exposed wood is one way to dissuade them from drilling into your wooden structures and most of the time, this is enough to keep them away.

If it’s too late for paint and they are building a nest in an area where they will cause problems, an insecticidal dust like Bonide Termite and Carpenter Ant Dust can be puffed into the hole according to the label directions. This will take care of the female bee and a reapplication in midsummer will take care of the emerging adults in August. In the fall, plug the hole with a wooden dowel or wood putty and paint the surface to keep bees from nesting there in the future.

Until next time – Happy Gardening!

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