I've grown dahlias for like 5 years and never had this problem until this summer. The leaves are getting these tiny yellow spots and there's definitely webbing underneath. I've tried neem oil twice but it's not helping much. Should I just pull them out?
If you've had a particularly hot or dry summer compared to your usual years that could totally be it. are you watering less frequently this year or is your area just experiencing a drought? also where are you located? sometimes certain pests have population explosions in particular years depending on weather patterns and what ate the mites the previous year.
neem oil works but you gotta be consistent with it and honestly it's not always the fastest solution for established infestations. since you're already seeing webbing that means they're pretty established. i'd suggest spraying every 3-4 days for at least 2-3 weeks, making sure you get the undersides of leaves really well. spray in the evening when it's cooler. some people have better luck with miticide sprays like forbid or avid if neem isn't cutting it, though those are stronger chemicals. you could also just blast them off with water from the hose every few days which sounds tedious but actually works.
don't pull them out unless they're totally beyond saving. dahlias bounce back pretty well once you get the mite population under control. just make sure you're not planting them somewhere too hot and exposed next year, and maybe increase humidity around them a bit if you can. also check if you've got any other plants nearby with mites since they'll just reinfest your dahlias. have you noticed the mites on anything else in your garden?
Spider mites love hot dry conditions so if you've had a hotter drier summer than usual thats probably why. they can show up outta nowhere when the weather changes. neem oil works but you gotta be consistent with it - once or twice usually isnt enough. you need to spray every 3-5 days for like 2-3 weeks to really get them under control, and make sure youre hitting the undersides of the leaves where theyre hanging out.
before you rip them out try increasing humidity around the plants if you can. spray the foliage with water in the morning, that stresses the mites out. if neem isnt cutting it grab some miticide labeled for spider mites - something with sulfur or abamectin works better honestly. honestly the main thing is being more aggressive with treatment than you might think you need to be. also check your other plants nearby cause theyll spread to whatever else is around.
dont give up on them yet. spider mites are annoying but theyre beatable if you actually stay on top of it. just gotta catch them early before they really trash your plants which it sounds like youre already dealing with. definitely make sure its not too dry and hot where theyre planted either, some afternoon shade might help too
Spider mites love hot dry conditions so if you've had an unusually hot/dry summer that could be it - they thrive when plants are stressed.
before pulling them out try spraying the undersides more aggressively (early morning or evening when beneficial bugs aren't out) or switch to insecticidal soap since neem needs really consistent applications and mites can get resistant, plus keep the foliage misted if you can since they hate humidity.
The big thing everyone's glossing over is that neem oil doesn't kill the eggs, so you're in a cycle where you spray, kill adults, then the eggs hatch a few days later and you're back where you started. That's probably why two applications barely dented it. You need to spray every 3-4 days for at least 2-3 weeks to actually break the life cycle, hitting those undersides hard each time. Are you doing that, or were you spacing them further apart?
Beyond the heat and drought angle (which yeah, those definitely make mites happier), consider whether you changed anything else this year - like mulch type, nearby plants, or even if you brought in new stock or borrowed tools from someone else's garden. Mites hitch rides on everything. Also, even if your area wasn't unusually dry overall, sometimes a patch of your garden ends up more stressed than others depending on sun exposure or soil drainage.
Before you rip them out, I'd say grab a miticide that actually targets mites instead of relying on neem - something with sulfur or a proper acaricide if you want to go that route. Dahlias are worth saving if you can knock this back. The plants themselves are probably fine underneath; it's just the pest pressure that's new. What's your spray schedule been looking like, and are you getting good coverage underneath the leaves when you apply?
I've dealt with this on my tomatoes and squash when conditions got brutal - the heat stress makes plants way more vulnerable even if you're watering fine. Since neem oil isn't getting it done, you might want to switch tactics entirely. Try a miticide with sulfur or insecticidal soap, and crucially, spray every 3-4 days for at least two weeks to catch the eggs as they hatch. Don't pull them out yet - dahlias are tough, and a real miticide beats neem for spider mites way better.
Guys, the previous answer nailed it - neem oil misses the eggs, so you're basically fighting a losing battle if you don't spray every 3-4 days for like 2-3 weeks straight to catch them at the right life stage. Before you trash the dahlias, try hitting those undersides hard with something stronger like sulfur dust or a miticide spray - and honestly, boost your humidity if you can (mist them, group pots closer) since spider mites hate moisture!
Heat and low humidity are definitely the culprit - that combo stresses plants and makes them way more vulnerable. The tricky part with neem oil is it only zaps adults, so eggs keep hatching and you end up chasing your tail; you need to spray every 3-4 days for at least 2-3 weeks to catch the new generations, or switch to something like sulfur or a miticide that actually targets eggs.
Don't pull the dahlias out yet. I had spider mites wreck a potted plant pretty badly one year and realized I'd been letting it dry out between waterings - once I kept the soil more consistently moist and started misting the foliage in the evenings to raise humidity, plus switched spray tactics, they cleared up. Your plants are still worth saving if you're willing to be more aggressive and consistent with treatment.
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