Just noticed spongy patches all over my yard and found a bunch of white C-shaped grubs in the soil. It's late September now so I'm not sure if I'm already too late to treat them. Should I use neem oil, beneficial nematodes, or just wait until spring?
You're actually in decent timing - late September is still workable for beneficial nematodes since they need soil temps above 50°F to do their thing, and you've got maybe a month or so before that gets iffy in most places. Neem oil won't touch grubs that are already in the soil, so skip that one. Your best bet is the nematodes applied now while the ground's still warm, or if you want to be lazy about it, you can just reseed those damaged patches in spring and hit them with a grub preventative in early summer before the next generation hatches. If the damage is pretty light, honestly just aerating and overseeding might be enough without the nematode step.
The previous answer nailed the soil temperature window - beneficial nematodes will work right now if your ground is still above 50°F, which it likely is in late September depending on where you are. I'd skip neem oil though; it's mostly useless against grubs since they're underground and neem doesn't penetrate soil worth a damn - it's better for surface pests. Nematodes are your best bet at this point, followed by applying milky spore if you want long-term control (though that takes a season or two to establish). If you miss the window or want belt-and-suspenders approach, you can always do a spring treatment too - the grubs will pupate in winter and emerge as beetles next summer, so hitting them again in spring before they finish developing won't hurt.
I've dealt with this mess in my own yard and neem oil honestly won't cut it for grubs already in the soil - that stuff works better as prevention on the surface. Beneficial nematodes are your best bet right now, and folks before me are right about the temperature window, but don't get too hung up on 50°F as a hard line; they'll work fine down to the mid-40s, just slower. The catch is you need to keep the soil moist for a few days after application or they'll dry out before they find anything. If you're in a colder climate and frost is coming soon, spring treatment with nematodes is also perfectly valid, though you'll lose more turf by then - it's not a race-ender either way.
Skip neem oil for grubs that are already underground - it won't reach them. Beneficial nematodes are solid for right now if your soil is still above 50°F, but here's the thing people miss: you need to keep the soil moist for a few weeks after application or the nematodes die off fast, so don't let it dry out or they're wasted money.
Nematodes are your move right now, but make sure you water heavily before and after applying them - those little guys need moisture to work through the soil and hunt down the grubs. If your soil dries out, they'll just die off without doing much. Once you hit that 50°F threshold consistently, your window closes, so don't sleep on it if the temps are still decent where you are.
Log into answer.
