40,000 square feet? An Acre?? Okay.

Apply any preemergent you can find when the forsythia are in bloom. I don't like products that mix materials like herbicide and fertilizer together. I think you get more bang for the buck by sticking with the single products and timing them specifically for their target capability.

Fertilize any time after you have mowed real grass (not weeds) for the second time. In Maine I would wait until Memorial Day. Why? Because the nutrients developed in the soil over the winter will be mostly exhausted by then. If you fertilize before the grass starts to grow you are wasting fertilizer on the early weeds. If you fertilize just as the grass starts to grow, then instead of having grass growing at twice the normal rate, you have it growing at 3x or 4x the normal rate. That means a LOT more frequent mowing to keep it under 3-4 inches.

If you acre is under automatic sprinkler system (which I doubt), you can do yourself a favor and cut the frequency back to no more than once a week during the heat of summer and once a month up until it gets hot. That will allow the surface of the soil to dry out which stops weed seeds from germinating.

Set your mower to the highest position. That will develop deeper roots to get you through the hot part of summer. Then when it gets hot, stop mowing altogether. Wait until the heat breaks and come back to mow carefully so as not to scalp it. Tall grass also provides more shade to shade out any weed seedlings that might have sprouted.

The watering and mowing described above should be a strong deterrent to crabgrass.

An acre of grass? Have you considered alternatives to so much grass? I have a long list of alternatives that can break up your expanse of turf if you are interested. I know this is the lawn forum, and lawns are my hobby, but to me there is not much that is less interesting than an unbroken acre of grass.

I have considered alternatives to so much grass, my husband has not. ;)

Thanks for the tip on forsythia, that is easy to remember.

We have almost 4 acres of land total, and the acre of grass was already cleared when we bought it 7 years ago (it was an overflow pasture for livestock). No, it is not sprinklered. It really isn't uninteresting, I have a lot of gardens, and the way the lot is laid out there are expanses of trees mixed with the grass. It's not just a rectangle of lawn. I would be interested in your thoughts on ways to reduce it.

What are your thoughts on how often the weed preventer should be reapplied? I read that if you apply on 4/14 you would reapply on about 5/18.

Sue:

With your size of property, using granular is the only way a home owner can go as sprayers that size are priced out of the ballpark.

In order to obtain the granular herbicide that you will need, you must purchase from an industrial supplier. You will also benefits by paying jobber prices too. Enter your zip code into this site and visit your nearest dealer. They sell to the general public.

http://www.lesco.com/prodcatalog/storefinder.aspx

Yes Lesco will become your supplier for that size area.

Four acres and one in grass is just about right in my opinion. Good for you. I thought that might be your entire front yard. I've seen it before.

Here are some alternatives to grass, though, since you are interested.

Decks,
patios,
privacy fences,
accent fences,
screens,
formal and informal walkways,
steps,
spa/hot tub,
barbecue/picnic area,
retaining walls,
arbors,
overhead sunshades,
screened rooms,
gazebos,
sun room,
greenhouse,
swimming pools,
garden pools/ponds,
tool shed,
potting bench,
dog run/kennel,
accent lighting,
storage units,
statuary,
benches,
sports courts,
jogging track or parcours,
hedges,
decorative gates,
drives/parking areas,
remote party room (for games, TV, pool table, etc.),
shade trees,
accent trees,
play yard,
screen shrubs,
accent shrubs,
vines,
ground covers,
ornamental grasses, and beds (perennials, annuals, bulbs, herbs, ferns, roses, hostas, container plants, rock, and fruits),
private outdoor movie theater.