Drought to Deluge…What Will Happen to My Turf?

This podcast discusses the recent rains in Virginia and what impact they will have on turfgrass maintenance. Included are the impacts due to submersion, disease, fertility loss, and pre-emergent herbicide breakdown and what practices you can perform to lessen their impact on your turf area.

For most Virginians, the drought is broken, although there will still be several locations that will be below average yet in terms of annual rainfall. Kathy van Mullekom, featured Gardening writer for the Daily Press in Newport News, e-mailed us recently asking what folks should be worried about given the excessive rain that most of Virginia has had in the first couple of months of summer.  It’s a great question, and here are some of the things we thought of: 

• Long term standing water (48-96 hrs) on turf can be a concern, particularly on cool-season grasses like fescue and bluegrass, and especially if the water is standing and not moving. And as a rule of thumb, warm-season grasses will be much less affected by the heavy rain as compared to the cool-season turf overall. However, the problem is usually not due to a lack of oxygen, but rather scalding of the turf if the rain-making system pulls out and the weather turns sunny and hot. Anything that can be done to get puddled or standing water off turf areas will help, and of course outside of the turf, there is great interest in keeping any kind of standing water away from your house because only a little of standing water can serve as a great breeding ground for mosquitoes. 
• Check your irrigation system—the last thing the turf needs now is MORE water, so turn the water off if you have an automatic irrigation system and don't use it again until we have some significant drying for a period of 2-3 days minimum. I saw some irrigation heads running in the middle of a deluge this week and that is certainly not a "best management practice" towards water conservation. 
• Expect disease pressure to be very high b/c of the excessive moisture and the warm temperatures. In particular Rhizoctonia blight/brown patch will be exploding on tall fescue soon if not already. The two major practices for controlling brown patch are irrigation and proper fertility. As mentioned previously, there is no need for irrigation right now and by maintaining your turf on the dry side, you will limit the amount of leaf wetness period the turf is exposed to and limit the disease severity. Also, by avoiding nitrogen fertilizer applications or using a slow release N source if fertilization is necessary (see below) you will limit the amount of succulent plant growth and reduce the disease severity. 
• Fertility. The heavy rain has likely leached away much of the spring fertility. If appropriate fertilizer rates were used, the loss in the environment should have been minimal to begins with, but there is no doubt that some nutrients have been lost simply because of the sheer volumes of water the soil has received. I still do not recommend additional fertilizer for cool-season turfgrasses now because of the likelihood of making disease pressure even worse, but if color and growth are simply unacceptable and N fertilizer is deemed necessary, then a small amount of slow release fertilizer (0.5 lb N/1000 sq ft or less) would be a much better choice than a standard, water soluble, garden-type fertilizer source. Warm-season grasses will respond positively to additional fertilization from either water soluble or insoluble sources. Remember, summer is their primary growing season. 
• Extremely heavy rain periods are also highly correlated with a breakdown in season-long weed control from spring preemergent herbicide treatments.. Thin turf canopies will see a surge in summer annual grasses (things like crabgrass and goosegrass) very soon. Thick turfgrass canopies will likely be fine in warding off weeds. Anticipate a lot of weed pressure in your weaker turfs, and if this is unacceptable/undesirable, then consider another PRE herbicide application to control weeds for the remainder of the summer. Choose products carefully in case there is a chance you will have to do a fall seeding of cool-season turf... many PRE herbicides require 8-10 weeks before seeding into treated turf. 

These are the major features to manage now in the wake of heavy rainfall. Overall, the rain has been desirable for most of us, but it would be nice if we could spread it out over the month of July, wouldn’t it?! If you have further questions regarding your lawn and landscape, please consult your local Virginia Cooperative Extension office.