Petunias and Thrip problem

[amy finkel]

Hi everyone. I'm new to this garden forum, so I hope I'm doing everything allright! Every year I have beautiful hanging baskets full of wave petunias hanging from my back porch. They are one of the centerpieces of my entire back yard. They get plenty of sun, and I fertilize rather heavily, and every year they do great. This year, however, I've been infested with thrips. I've tried systemic granules added to my baskets and pots of flowers, and nothing seems to work. Any ideas how to rid my petunias once and for all of thrips??? Thanks. Amy

[Newt]

Hi Amy,

You're doing everything just fine. Welcome to the Helpful Gardener. I've never had this problem, but I get the impression that you've had it for quite a while. From what I'm reading the problem may have come with the soil your petunias were planted in. Petunias are actually used in some greenhouses to attract thrips so the greenhouse can tell if they have a problem.

You don't say which granules you have used, but I've discovered that it's best to use it for about a month and then change to another. Lots to read here but take a look.
https://floriculture.osu.edu/archive/mar97/thrips.html

This site has alot more to 'weed' through but you should find these parts helpful. You can also scroll down to read about monitoring and trapping and treatment plans.
https://www.umass.edu/umext/floriculture/fact_sheets/pest_management/wft_03.html

Biology, Life Cycle, and Behavior

Depending on environmental conditions and nutrient levels, WFT females lay 150-300 eggs during their lifetime.Eggs are inserted in leaves, bracts, and petals and hatch in about a week into larvae, which feed in flower buds or terminal foliage. Larvae resemble adults, but are wingless. The eggs of WFT are well protected and in general, pesticide sprays are ineffective against them. The first larval stage lasts one to two days and second larval stage, two to four days. Toward the end of the second larval stage, the thrips stops feeding and drops or enters the soil or leaf litter and becomes a prepupa, which is a nonfeeding stage that lasts one or two days before pupation. Winged adults then emerge from the pupal stage in one to three days, depending upon temperature. Because the prepupae and pupae are mostly in the soil, these stages are not affected by insecticides applied to the foliage. Currently there are no recommendations for soil drenches aimed at thrips pupae. The life cycle is completed in two to four weeks.

Thrips will move on air currents. Visual inspections can be improved by blowing lightly into the blossoms or growing points. The carbon dioxide will bring thrips out of their protected areas. Flowers and plant tips can be shaken over a piece of paper for additional monitoring. Thrips populations will be highest when plants are flowering.

If your plants become infected with a virus from these pests it is recommended that the plants be destroyed. Here's how you can tell if the plants have the virus.
https://www.extension.umn.edu/distribution/horticulture/DG7375.html

Newt

[amy finkel]

Newt, thanks for the information. You're right! Some greenhouses actually use petunias to attract thrips to measure problem...very intriguing. Perhaps I need to look for a new greenhouse next year, or, at the very least, ask some more probing questions. Better yet, plant my own hanging baskets using my own petunias from seed and my own soil! Then, I'll be able to amend my soil right from the start with water polymers, osmocote long-term fertilizer, and systemic. This should prevent the thrip problem in the first place! The good news is that petunias will NOT transmit virus to other plants. That's my "saving grace" this summer, as I also have lots of other flowers and a garden with lots of tomatoes.
Thanks for the reply, Newt! Amy

[Newt]

Amy, you are so very welcome! I am truly sorry that happened to you. I am not a fan of petunias except for the 'Wave' series. I fall for them every year!

Newt