Greenhouse Scout School 2026

Hi Melissa,

Along the same lines as transporting in thrips…

I used to work at a retail greenhouse where we would get boxes of tropical plants coming in, and I also worked at a retail florist where we received boxes of cut flowers from out-of-country. In both cases, we sometimes found “bonus guests” in the plant material. We saw big, weird spiders in the cut flowers, and tiny lizards in tropical plants. Of course, the guests would always emerge on the day that we forgot to pay attention for them, so we’d get big surprises when they would scitter out onto our hand or such. One of my colleagues also found a tree toad/frog.

Then, one time I was buying native plants wholesale at a small grower operation, and I loaded some flats by my vehicle. The owner said to be careful because there were critters that could be in the flats that could travel with me. I bent to move over one more flat and a snake slithered out and scurried across the greenhouse floor and out to a nearby juniper. It had almost shared a long drive with me. Gives me the shivers still.

Amy

Those are small for 2 years old. Can you take a side view of the brown lumps. May be scale? If you see frass, then you should see feeding and probably enough to notice easily.

Tiffany, the brown bumps in the 3rd photo and at the very bottom of the 5th photo do look like scale (which we’ll cover in week 6). See if you can pick them off with your fingernail. If you can scrape them off they are probably scale, if they don’t come off or the leaf tears then they are probably not an insect. The webbing in the 4th photo could be from spider mites (which we’ll cover this week). They do make fine webbing and their webbing has a lot of ‘trash’ in it - cast skins, eggs, dead spider mites and live ones.

Tiffany, Elise has a good idea about a way to check of a strange bump on a plant might be a scale insect. These don't look quite right to be scale to me, but I'm not at all confident that they're not scale. Also, the webbing in the 4th photo doesn't quite look like spider mite webbing to me either. At that magnification, I think you'd see some mites or clearer evidence of mite debris. Take a look at more leaves than just this one to see if spider mites might be present.

Hi Tiffany, I agree with Betsy that the spider plants look a little small for two years old. Do you know when your coworker last fertilized them? The one on the left looks a little nutrient deficient. The substrate, which looks like it might be bark heavy, may not holding water or nutrients very well. So, they could try transplanting the spider plants into something with some coir or peatmoss as one of the components. Hope this helps!

Amy, I don't think we've made it very clear that blue is just a little more attractive to Western flower thrips than yellow, but not THAT much more attractive. Doesn't surprise me to see more WFT on yellow traps than blue on occasion.
I use an aspirator all the time when I want to capture small insects without damaging them. Aspirators are very useful to entomologists. If kids are old enough to have the dexterity and patience to handle small insects, then aspirators can absolutely be useful for field studies.

Ryan,
We think this is a great comment and idea! Since we don't exactly know what the UV coming off the lights is, turning them off for an hour or so is a great idea. the nematodes will move into the soil pretty quickly.

Hi Grace - NOT a silly question. So now that you have gotten the hang of IDing the most common pests on your sticky cards and recording your counts you want to start making sense of these numbers - so - either put out new cards or circle all the pests you have already counted on your cards or cross them out, whatever, just so you know you have counted them and don’t count them again. So say you have 4 cards in your house - after one week total up all the fungus gnats on all 4 cards and divide by 4 - that is your average FG/card for that house, you will now record that number (and the same for shore flies, aphids, thrips, whiteflies, whatever you decide to track) for that week, then do the same thing the following week, and the next, on & on - and that’s how you will see the trends and be able to decide when action is needed and if whatever action you took was successful. I hope this makes sense, if not please let me know and I’ll try to explain it another way {just wish I could visit everyone’s greenhouses!}. Next week Dr. Lamb is going to be talking about scouting forms and I think that will help. Also look in the resources at the various scouting forms.

Grace, Some of this is determined by experience - yours as the scout and the grower's. Some thrips are really hard to tell apart and the damage on the plants may help tell you what kind it is (see answer to River, below). In some cases you might take the card to look at it more closely under a microscope to identify the thrips. And you might discuss it with the grower to see if they know or want more information. I guess the most basic answer is - if you know what types you have and can relatively quickly note numbers of different types, i would put that down. If not, get an overall number and do some more sleuthing outside of the scouting time.

John & Cheryl will give you more information but the short answer is NO, unfortunately. One point I want to make is that new species pop up and the management of them can be different (some ‘newer’ species don’t have a soil-dwelling stage - so you can’t rely on nematodes to manage them) - so you have to stay up to date on what the newest pest concerns are by attending any educational programs you can and subscribing to newsletters, trade magazines, etc. Dr. Lamb will be covering good resources next week.

Also, some types of thrips may enter your greenhouse after a specific event - like someone mowed the grass nearby or a farm field nearby was harvested, or in late summer the weeds outside start dying - you may notice a flush of different thrips on your cards - and you’ll have to decide if they are a threat to your current crop.

River,
We also see onion thrips in greenhouses - on more than just onions. Canada and Florida and probably some other places have Thrips parvispinus which can give you quite different symptoms. Cuban laurel thrips in Ficus.... also different symptoms. Rarely just one type!