This spring has no doubt been a different spring with some early warm temperatures and then cooling off, causing us to wonder on timing of Pre-Emergent applications.
Summer annual grasses, including crabgrass, require proper soil temperature and moisture levels in order to germinate and establish themselves. About 80% of germination is going to occur when soil temps at a depth of 0-2 inches are at 60-70 degrees. For pre-emergent herbicides to be effective they need to be applied before the soil reaches this temperature range. So far, up until our warm temps started this week, the warmest soil temperature this spring has been around 45-50 degrees. We need to be in the range of 50-55 degrees before we apply product in order to be effective and we are getting close now.
A good indicator that has been used for years for pre-emergence timing is when the forsythia bushes bloom with their vibrant yellow flowers and we are seeing those bloom now in some places. The way it looks right now and taking into account this coming week’s weather forecast I think that next week is going to be the time to get Pre- Emergent Crabgrass killer on the lawn.
If you already have put an application on the lawn and you feel you may have done it too early, don’t worry as you can always do a second application at one half the rate about 30 days after you did the first one. This will help knock down what you might have missed on the first application.