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Archive for June, 2016

Thrips in Platycodon flower

I have noticed lots of these tiny insects deep within the flowers of many of the daylilies in the gardens. As a result of their feeding, these pesky critters have caused some disfiguring of daylily flowers and foliage.

Apparently, a few years ago they were also very abundant! Here’s some info that I put together at that time …

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 tapped out of a hosta flower onto white paper.

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

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 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.

A better way to control them is to spray your plants with highly refined horticultural oil such as Bonide All Seasons Oil. Horticultural oils are often used by organic gardeners and are effective in controlling thrips in the nymph (immature) 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.

Thrips crawl deep into the flowers, good spray coverage is necessary for control.

Thrips crawl deep into the flowers.

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!

 

You should know!

Even natural or organic products can be deadly to pollinators like bees. Captain Jack’s Deadbug Brew is toxic to bees for three hours following treatment. If possible DO NOT spray when plants are in bloom. If this is not possible, spray early in the morning or later in the evening when bees are less likely to be foraging on the plants and ALWAYS read the label!

Until next time – Happy Gardening!

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