Lou,
IMHO the best option is prevention with a pre-emergent. I say this because of the mechanism by which they work. When they are applied to the ground they sink into the soil a short distance and stop and forms a layer that when the growing meristem (the growing point of roots) from germinating seedly roots of weeds contact this layer, dell division is stopped at the growing point. This does no harm to anything that has already been planted as their roots are BELOW this zone, and do not contact the pre-emergent. I have read that Corn Gluten was found to have some of this properties, however the effectiveness is uncertain. It apparently varies considerable, perhaps due to soil chemistry, and micros present. AT the least it does not seem to last as long. Another alternative is the active ingredient of "HALTS", which is supposed to be very effective for a fairly long period. I did some research upon it, and it breaks down after a period of time and if I recall correctly, has little effect upon anything else. This would make sense since the blocks cell division at the apical meristem (with many unique plant hormones), and animals/fungi don't have apical meristems.

However this does nothing to the weeds that are already the. 2-4-D will kill broadleaf plants, and degrades fairly quickly BUT does have some potential to enter through the roots, therefore you don't want to get too close. Also 2-4D is almost always mixed with other things that are more persistent in the environment (though they do degrade)to broaden spectrum of action against other weeds i.e. crabgrass. You can use this CAREFULLY for control now, if control is required NOW, but it would not be my first choice.

Glycophosphate would be my first choice as it breaks down VERY quickly in the soil, and it bound up almost immediately on contact with the soil, therefore is does not reach the roots to cause problems. It's breakdown products also act as fertilizer, but as always don't over apply. It also can only enter through exposed green tissue, so if you hit the bark, as long as there is no wound, then no problem. IT works by simulating a plant hormone, and therefore has very little effect on animal life. But it will also kill more than weeds if sprayed on them. So careful application is required, and be sure not to get it into water that will eventually run off, as while it breaks down fairly quickly in water as well, it can kill a great deal more photosynthetic organisms as it is much more mobile. This would be my first choice to use on weeds that are already there.

JMHO
Arktrees

Hi Lou:

I planted about 1,100 seedlings this spring. By the time I finished, it was too late to use one of the recommended pre-emergents (OUST and Envoy). We had a rainy spring and early summer - good for the seedlings but also for the weeds. By early June, I was losing the battle and the war.

Before planting the seedlings, I applied glycophosphate twice. I continued to spray whenever needed (often!), but carefully as Arktees recommended. This has been very effective. After several applications beginning in late Feb or early March and continuing to mid-July, there are now very few weeds around the seedlings. For those that are planted close (5-8 ft), I spray between them so I don't have to mow and risk hitting them.