The webbing from an enormous population of spider mites. Minimal treatment to wash off the mites.

what she said ...

but i would add.. no plant holds its leaves forever ... and if this is the lowest course of old leaves.. perhaps its time to harvest them.. for the new ones of spring to take over ... would need a pic of the whole to support this theory ... and that is a fast way to get rid of a lot of your population real fast.. then clean up the rest ...

also.. the edge browning could be lack of winter sun.. and or water/humidity issues.. being complicated by the vermin ... especially if this were an indoor plant in the dreary midwest ...

has yours been outdoors all winter in CA????

ken

Thanks for the feedback. the plant is only about 18" tall. A lot of the lower leaves died and I pulled them off. Here's a picture. I'm going to post a detailed pic as well.

This is an indoor plant, and it's received indirect sun all winter. This pic is of the top of the plant. In the foreground you can see a new leaf starting to open, and it already looks affected (tip is curling over and the web is there.

If this is spider mites, do I just wipe the leaves down with soapy water, or do I need to treat the plant with a topical or systemic insecticide as well? (if so, what do you recommend?)

You can wash/rub them off with water. A cotton ball might help in your efforts.

Thanks purpleinopp...is just rinsing them off enough? Is there anything I can do to prevent them from returning?

Keeping plants as healthy and robust (therefore naturally more resistant) as possible is the best thing. You may need to repeat the rinsing/wiping a few times since this kind of plant has crevices that will likely harbor some remaining mites. Just don't get the soil too soggy too often.

Spider mites are much more often a problem while plants are inside for winter, they thrive in the dry air. Just keep your eye out for the webs, especially at the bottom of leaves, and/or wipe leaves gently occasionally with a damp cotton ball as a proactive measure (which keeps leaves looking shiny anyway.)

It's normal for the oldest leaf to be discarded occasionally on about any plant, but your plant looks like the roots may not be too happy with the soil they're in, judging from the damaged edges. Spider mite damage usually looks like tiny yellowish spots until a whole leaf goes brown. Is it mostly fine peat particles?

thanks again purpleinopp! The plant is still in the original peat mixture that it came in...I've been waiting to see how it fared before transplanting it. I removed all the damaged leaves and wiped down the rest top and bottom. I'll keep an eye on it for now and transplant it if it seems healthy. I haven't been overwatering it, and the pot has good drainage.

Sounds like you're doing the best things. It may actually be kind of dry, if it feels like it doesn't weigh anything, hard to tell from pics though.

Your plant looks a lot like a little one I got last summer, the way there are a lot of individuals crammed in the pot. I plan to separate them and anticipate they will all be happier with more space, less cramming. Might be something to consider when repotting yours. Probably will fit back in the same pot, but in a ring around the edge, each will have a LOT more room.

Only other thing would be trying more light, they burn easily, so go gradually on that.

That is definitely a spider mite problem - The telltale web is your clue.

Here are tips for keeping your houseplants pest free. Wetness or dryness near a window during the winter, crowded plants with poor air circulation, and keeping the original soil in a new plant all contribute to pests. When you get a new plant home, either change the soil or treat it - It's likely full of eggs & larvae. Ever get a new houseplant followed by an infestation of gnats four days later? The eggs in the soil hatched and the larvae matured.

Insects & Pests:
I don't usually have problems with insects or pests invading my houseplants. However, particularly during the summer months, I use a home-made bio-control solution to keep away anything that even thinks of visiting. It's called 4-4-2 spray and I learned this little secret from master gardener, Jerry Baker.

Recipe for 4-4-2 Spray
Garden batch:
Need: 1 large plastic gallon jug, baking soda, cooking oil, dishwashing liquid
Mix well: 4 teaspoons Baking Soda, 4 teaspoons Cooking Oil, 1 gallon Water (128 oz)
Add: 2 teaspoons Dishwashing Liquid

Home batch: (1/4 amount)
Need: 1 plastic spray bottle, baking soda, cooking oil, dishwashing liquid
Mix well: 1 teaspoon Baking Soda, 1 teaspoon Cooking Oil, 22-32 oz Water
Add: 1/2 teaspoon Dishwashing Liquid

Spray plants daily until problem clears; will kill most insects. Pay special attention to the underside of leaves, where insect like to hide and lay their eggs along the veins of the leaf. Mixture will keep for about 2 weeks and will eventually emulsify. ***You can add 1/2 teaspoon of alcohol to specifically kill mites or 1/2 teaspoon minty mouthwash to keep away gnats. None of this will harm your plants - They love it. I used 4-4-2 in my garden in San Juan and it kept my Hibiscus, Jasmine, Schefflera, etc. pest free.

Other than this method, I only use something called a "systemic," which consists of a powder that is sprinkled onto the soil periodically. The brand I use is Bonide. It works its way into the plant through the root structure without harming the plant and kills anything that tries to set up house in the soil. Once treated with a systemic, the plant will repel most pests. A systemic helped me get rid of a terrible gnat problem that attacked all my houseplants one year. Gnats are a particular nuisance because while you're getting rid of the ones you see, they've laid their eggs in your topsoil and those will hatch to begin the same perpetual cycle. A systemic is the most effective way to kill their eggs and keep gnats from invading your houseplants.

There are various university botanical extensions that will help you identify pests, plants, and help with advice. Here's one:
http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/insects/mealybugs/insect-pests-of-cacti-and-succulents.aspx

All the best to you and happy growing!!