Fungus on tomato leaf: cause or effect?

November 12, 2012 5:58 PM

Tomato Disease Filter: what is this fungus looking stuff on my tomato plants? Can I save the plants or does this call for scorched earth tactics in order to protect the rest of the garden?

Whatever this is appears to be killing my plants and it progresses as follows:

1) leaves turn dead/brown
2) whitish fuzzy stuff appears that resembles insect cocoon material
3) reddish dots appear in the middle of areas covered with the whitish fuzz

The disease affects the plants from the top down. If a vine starts near the ground, climbs up and then bends back down only the upper part of the vine will be affected. The beginning and end of the vine near the ground are alive and green.

I imagine the white stuff is some sort of fungus and the red dots are its fruiting bodies but I haven't managed to match it up to anything online. Based on the progression I'm not entirely sure if the fungus is the cause or just an opportunist taking advantage of the dead leaves.

Please hope me by helping me figure out what the problem/disease is and if/how the plants can be saved.

posted by Hairy Lobster to Home & Garden (7 answers total)

I think those are actually spider mites. The red "fungus" is actually a pile of little red mites--try picking a little off and examining it (them!) with a hand lens. The webbing is, well, their web. It's treatable with insecticides, but I would remove heavily infested plants. I've heard of biological controls (which, fascinatingly, are other predatory mites which eat your mites) but don't have any experience using them.
posted by pullayup at 6:14 PM on November 12, 2012 [1 favorite]

Have you opened up the webbing? From the pictures, this looks more like webworms, or maybe spidermites? than a fungus to me. Especially since you say that the fuzzy stuff resembles cocoon material -- I suspect it probably is insect silk, not fungus.

Here is some info about how to fight spidermites.
posted by Made of Star Stuff at 6:14 PM on November 12, 2012

That article makes a good point: if you're going to go with the insecticide option, don't use a broad-spectrum insecticide as it can kill off the mites' predators, get a dedicated miticide.
posted by pullayup at 6:18 PM on November 12, 2012

Response by poster: Ooh, spider mites is exactly what these appear to be. Thanks guys!!!

I'll try some of the suggestions from that article but I suspect I may have to resort to the nuclear option based on what it says.
posted by Hairy Lobster at 6:30 PM on November 12, 2012

Just prune off the offending branches, and keep an eye on the plants. You can take off a few leaves here and there if they come back. Critters like these have webs to protect themselves from predators, and it's amazing how many little wasps and other good guys will come in to feast on the mites when the webs are removed. I have sprayed nothing in my garden for more than twenty years now, and have far fewer problems than when I used chemicals, because the balance of nature is back.
posted by weapons-grade pandemonium at 7:03 PM on November 12, 2012

Those definitely be spider mites. They're worse in hot weather. If you're due for a cool-down, you might not have to do much more than pick off affected leaves.

You have a very bad infestation of them. If you do start pulling off leaves, be sure to inspect the undersides of the leaves that don't have an obvious population -- that's where they hang out.
posted by mudpuppie at 1:50 PM on November 13, 2012

Oh -- one more tip. If in the future you see early symptoms like you're seeing now, but don't see the insects themselves, hold a sheet of paper underneath some leaves and tap on them (the leaves). If you have spider mites, you'll see them on the paper, and you can begin treatment before they get so out of hand.
posted by mudpuppie at 1:52 PM on November 13, 2012