Add the high and the low for the day and divide by two to get the average temperature for the day. Crabgrass begins to germinate by the end of the month. These weeds are not problems until summer, but you need to act now if you want to prevent them from growing at all. Pendamethalin prevents oxalis and spotted spurge as well as crabgrass. Dacthal is also effective against a wide range of summer weeds.
Gallery prevents crabgrass and many broadleaf weeds.
Cool and wet weather encourages red thread, a fungus disease, in lawns. Look closely at the tips of the blades to see the red color. Prevent or treat red thread by applying a high nitrogen fertilizer. Bluegrass lawns are especially susceptible. Spot spray dandelions in lawns with a broadleaf weed killer.