Cooperative Extension

Lawns Online! Lesson 4 - March & April

Crabgrass Prevention

Although it seems early, the forsythia will be blooming soon and you'll want to be ready with your PRE-EMERGENT CRABGRASS PREVENTER. (By the way, forsythia is the shrub which shows one of the first colors of Spring - bright yellow flowers.) When the forsythia is in full bloom in your neighborhood, it is time to apply the pre-emergent. You may see the blooms in some neighborhoods and not your own. Those are "micro-climates" where the conditions are right for the bloom... and the germination of crabgrass. That germination is what we are trying to prevent.

Look for pre-emergent sold separately (not mixed with fertilizer) and follow the label instructions. Plan on making a second application in approximately two months to maintain effective crabgrass control into late summer and fall. Read the label to determine when the second application should be made... usually 8 to 10 weeks after the first application. If the pre-emergent is applied at the right time, it sets up a barrier on your lawn which effectively kills the germinating crabgrass seeds. It will also kill any other grass seeds, so if you are planning to plant grass seed in any bare spots or areas that need thickening up then you can only use a pre-emergent product called Tupersan. Remember: Seeding the lawn is best done in the fall when conditions are most favorable for seed germination and root establishment. 

Broadleaf Weed Control

In Virginia we have two major crops of broadleaf weeds in the lawn.  They are referred to as summer and winter annuals.  Both are easily controlled with weedkillers that have combination mixtures and are sold at most garden centers.  Look for products that contain combinations such as 2,4D + dicamba + MCPP.  For best results, use a liquid formulation that allows you to cover the leaf surface of small weeds more effectively.  The weedkillers work by translocating through the leaves, killing the entire plant, including roots.  The temperature must be at least 60 degrees for a minimum of two days for the herbicide to work effectively. 

The herbicide ‘dicamba' moves in the soil and should not be used within the root area of shallow rooted trees or shrubs. However, the low rate of dicamba in the three-way mixtures reduces the possibility of dicamba injury.  Spot treat where weeds are a problem rather than treating the entire lawn. 

The major weeds we are seeing now are the winter annuals like chickweed and henbit. While they are ideally treated in the fall (when they were very young and tender) some control can be achieved in the spring if you catch them early enough. We want to catch them now before they flower and drop their seeds. Remember that the herbicides will affect any broad-leaved plant which can include your shrubs, trees, perennials, etc. Use the chemicals only on very calm days to prevent drift onto your desirable plants and always remember to read and follow the label instructions.

Fertilizer

If you followed lessons #1 and #2, you should have given your lawn two or three applications of fertilizer in the fall. In that case, we do not recommend early spring fertilizer. Nitrogen applied to cool season grass in March and April tends to stimulate excess top growth, which weakens the roots and creates a good host for lawn fungus spores. This is why in the crabgrass section of this lesson, we encourage the use of crabgrass preventer without fertilizer. 

The obvious (but less scientific) reason for limiting nitrogen fertilizer in the spring is to reduce the frequency with which you’ll have to mow your lawn. 

Grub Control

Grub control is not necessary unless you have a grub problem. While grubs do eat the roots of the grass, it takes 6 to 8 per square foot to do serious damage. People frequently feel the urge to use grub control when they have a mole problem. Since moles eat grubs, killing the grubs will make the moles go to your neighbors in search of food. 

If you’ve decided the problem merits treatment, an April application of a soil insecticide can be made. Be sure to follow the directions carefully, including watering the material in with the equivalent of ½ inch of irrigation. Since the grubs will be an inch or so deep in the soil, you get no control until the material has been watered in thoroughly. 

Key Points for Spring

• Crabgrass preventer goes on when the Forsythia starts blooming in your neighborhood.
• If you fertilized in the fall, try to avoid fertilizer in March and April.
• Broadleaf weed control may be effective on winter annuals, like chickweed and henbit, if applied before seed drop. Otherwise, the time to prevent them for next year will be late October early November.

Questions? Contact us by e-mail

If you have specific questions about your lawn, email our Extension staff at edwardssu@chesterfield.gov.

• Go to Lesson 1 - August & September
• Go to Lesson 2 - October & November
• Go to Lesson 3 - December, January & February
• Go to Lesson 4 - March & April
• Go to Lesson 5 - May & July
• How to measure your yard

DISCLAIMER

Commercial products and organizations are named in this publication for information purposes only. The Virginia Cooperative Extension, Virginia Polytechnic Institute and State University and Virginia State University do not endorse or warrant these products and organizations and do not intend or imply discrimination against other products or organizations that also may be suitable.