Corn gluten won't kill the weeds, but it'll help slowly suppress new ones from growing. Maybe. Reports of success are spotty; it never worked for me at all and I ended up using Barricade (prodiamine). In your case, I wouldn't recommend that.

Grubs are easier to control--if they're Japanese beetle grubs, Home Depot and many other places carries Milky Spore, which is a bacterial disease that infects grubs and doesn't like humans or animals at all). It can take a year to three years to come up to speed.

The easiest weed control in a lawn is to encourage a thick turf. It chokes out weeds. Organic feeding works well for doing that, and there's a ton of information about that on this site. My personal preference is soybean meal, but what's available varies by locale. I'm in corn and soybean country.

For very thin lawns, particularly those with little or no Kentucky bluegrass (which spreads like mad when well-fed), reseeding may be necessary. Depending on your location, the optimal period for that could already be here. For points north of Philadelphia, PA on the east coast, it's time now. For the south with southern grasses, it's already very, very late. For northern-transitional areas, we still have a ways to go.

Morph and I are both organic, so we should be able to help you. I guess there are others here, who are organic, so this is a good place.

Looked up Hewitts Garden Center and found one in upstate NY, so I'm guessing you live there.

This time of year, grubs have done all the damage they're going to do. If you do nothing, then it will make no difference. You might still see the effect as increasing damage, but that damage is already done. Killing grubs now makes no difference.

Corn gluten meal will not kill weeds and, in my opinion, it will not help suppress new ones. I used a heavy dose of CGM monthly during 2012 and saw no change in weed behavior. If you read the research the results were very dependent on amounts, timing, and what appeared to be luck. In my independent test, I got nuthin.

Beyond the dense lawn, proper watering is absolutely key to keeping weeds out. The more frequently you water, the more weed seeds will sprout. Crabgrass seed likes to sprout in the spring. It likes to have water every other day to keep the seed moist so it can germinate. If you purposely restrict watering to once a month when temps are below 70 degrees, and once every 3 weeks when temps are between 70 and 80, you should not get crabgrass.

Thus, without spraying any -icides, you should be able to have a nice lawn for 2015. If you have a Japanese beetle problem late next spring, then you can expect grubs. The organic control I like for grubs is beneficial nematodes. The only issue with them is getting the soil moist enough to apply them successfully. It's not hard to do, but the people who have a problem with them did not get that part right.