Spiders or spider mites?

August 22, 2019 9:29 AM

Am I seeing a minor spider mite infestation or just spiders? I have a backyard cannabis garden (small and legal) in CA that is a few weeks away from harvest. It looks lovely. I am obsessing over one thing, though.

I often see a single long, stringy web connecting one plant to another or one leaf to another. Like what Spiderman would shoot, not like those tight little nets that you see on plants that are far gone from mites. I am not really seeing the other signs of mite infestation, though I did earlier this summer (it's not possible for there to be ZERO mites outside here, and I'm shooting for "not a problem" more than "perfect").

Question: are these long, single strands likely from good ole spiders? Or possibly spider mites/inconclusive?

posted by Ignatius J. Reilly to Home & Garden (7 answers total)

Spiders are generally visible, and mites can be hard to spot. If you aren’t seeing spiders, you probably have mites. Most spiders either spin webs or hunt on foot, few leave wispy strands of valuable silk hanging around the way spider mites do.

The good news if you’re only a few weeks away from harvest you should be good, but it can’t hurt to give a quick spray of insecticidal soap, making sure you get the undersides of the leaves.
posted by SaltySalticid at 9:43 AM on August 22, 2019

One old standby for checking for spider mites is to hold a piece of white paper underneath the leaves, then gently tap or shake the plants. If you see tiny red spots on the paper -- and if they look bloody when you crush them -- you have spider mites. If you don't see the red spots, you probably just have plain ol' spiders.

The long strands you're seeing are almost certainly from spiders. Spider mites only weave webs on the leaves, in my experience.
posted by mudpuppie at 10:25 AM on August 22, 2019

Throughout most of CA, we have Cellar Spiders, which are the most enthusiastic web-builders known to humanity. They are delicate, long-legged, and absolutely harmless; their goal in life is to connect every item on the planet to every other item via flimsy strands of silk. They've strung webs over dishes I left in the sink overnight. God forbid you don't drive your car for a few days - they'll do their best to anchor it to the ground.

Would not be surprised if they're enjoying the scaffolding of your cannabis very much.
posted by Lycaon_pictus at 11:22 AM on August 22, 2019 [2 favorites]

Response by poster: Thanks so much for the info, and keep it coming!

There's a ton of info on the web about spider mites, but little about disambiguation. At this point I think I have a shit ton of spiders (which is consistent with every other square inch of our lot, inside and out) and least more than zero spider mites.

With the high humidity here I am loathe to spray anything, even plain water, for fear of mold (I am also battling powdery mildew, but winning that one firmly). I think I'm gonna go with big fans, laybugs, dustbustering, qtipping safer soap onto leaves, and manually getting rid of small apparent problem sections as a mitigation strategy to get me through the final days here.
posted by Ignatius J. Reilly at 11:51 AM on August 22, 2019

I have a lot of spiders in my NorCal yard. I almost never see them unless I disturb a plant or pot enough to get them to scurry out. Regular watering and checking plants is not enough to have them reveal themselves. Single strings between plants sound very much like spiders.

I've never had major spider mite problems outside, only indoors. Outdoors, there are enough natural predators to keep most of my insect pests at bay. I'd get some ladybugs and call it a day unless I see clear signs of mites.
posted by quince at 12:13 PM on August 22, 2019

There are several spiders (like jumping spiders) that don't build webs, but use a dragline silk thread as they wander around. This thread provides security in case they have to drop suddenly, or miss their jumps etc. This is possibly what you're seeing.
posted by dhruva at 9:29 PM on August 22, 2019 [1 favorite]

I think spider mites are almost more easily spotted by the leaf chlorosis caused by their sucking. If you're not seeing that you are unlikely to have spider mites. I agree that they are more prevalent on indoor than outdoor plants, but they do appear sometimes. Less likely if the plants get overhead watering though.
posted by oneirodynia at 10:09 PM on August 22, 2019