Q&A: Tarnished Plant Bug Infestation

Q&A: Tarnished Plant Bug 

Answered by Ian Wise, Entomologist (retired) and Chair of The Prairie Garden Committee

Question: Infestation of Tarnished Plant Bug
, Lygus lineolaris

I’m hoping someone might have a solution for a tarnished plant bug infestation in my raised vegetable garden. They decimated my tomatoes last year (I grow them mostly in 5-gallon buckets around the edge of the raised bed) and I’m afraid they will be back in full force this year. I think they may have got a good foothold because my baby was born mid-July so I didn’t address the situation early or adequately enough. I cleaned out and trimmed around the garden at the end of the season but am afraid to invest too much in tomatoes if they’ll be back in full force. Maybe there’s something I can grow in abundance this year to convince them to leave? Any suggestions would be much appreciated!

Unfortunately, I don’t have a photo, but the one below is from iNaturalist and is a pretty good match to what I saw. I am fairly confident that it is some type of lygus bug or tarnished plant bug infestation, though what subspecies I’m not sure. They were brown flying insects with a characteristic light-colored triangle on the back and a flat, oval-shaped body. They liked to sit on the stems and fruits and injected holes all over the tomatoes that caused them to rot on the stem. They also did something to the flowers that caused many stems to rot before any fruits grew and some catfacing to occur on the fruits, though they seemed to have moved in later in the summer because the early tomatoes were fine, it was just the bulk of tomatoes that matured later in the summer that I had to throw away. I read that the adult lygus bugs overwinter and reemerge in the spring and will feed on just about anything. I don’t want to use insecticide as I am growing vegetables and herbs for consumption and want to keep my yard and community healthy with lots of beneficial insects, but if there is something I can do, even if I have to forgo tomatoes or other plants that they like this year, to discourage them sticking around… I’m just at a loss as to how to deal with them. Also, if it was just a few it wouldn’t be a big deal but they literally came in droves and just decimated everything!

Photo: from iNaturalist, Lygus lineolaris
Answer:

The insect pest in the photo is definitely the tarnished plant bug. As you indicated, this insect has a massive host range – over 300 plant species. The vast majority of its hosts are only fed on by the adults. Western Canada supports huge populations because of its field crops. The overwintering adults initially feed and produce a first generation on alfalfa.

The first-generation adults leave alfalfa if populations are high or if alfalfa is cut. These are the adults that will seek out new hosts in July to either feed or feed and lay eggs. Tomatoes are only a source of food for the adults that will puncture the flowers and buds causing their death. The problem for gardeners is these same adults will move to canola and will produce a second generation. The second-generation adults will then leave canola and look for something to eat before overwintering.

I have been growing tomatoes for over 40 years and have never had a problem with Lygus this severe. Do you live close to areas with alfalfa fields? Insecticides are only effective against the nymphs, which is another good reason not to use them. My suggestion is to use insect netting to cover your plants in late June or once you find an adult. I use netting to prevent damage to cole crops by the diamondback moth and cabbage butterfly. Without their use, the cabbages often would be completely destroyed.

As an aside, I wrote an article on the use of insect netting in the 2024 edition of The Prairie Garden. This is an annual written by prairie gardeners and is a great resource for all gardeners. The articles are filled with great information relevant to us. You can purchase it at local bookstores or greenhouses.