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.
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.
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.
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.
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.
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.
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!