MASTER GARDENERS: Get ready for summer weeds
The recent warm weather has stirred our gardening interests. We had a full week of 70-degree weather at a time when we are usually huddled near a fireplace. All types of flower buds are swelling, and the camellias are the best we have seen in several years. So, does this mean that we are through with winter? Not likely, but it is time to start thinking about defending our lawns against summer weeds.
The warm weather has raised soil temperatures into the 50s, and that is close to where crabgrass weed seeds start to get excited. New studies are somewhat inconsistent in their exact temperature requirements for a crabgrass outbreak. The consensus is that crabgrass seeds at the 1-inch soil level will start to germinate at between 55 and 73 degrees Fahrenheit. A soil thermometer is not usually reliable because it gives you an “instant” reading, and you really require a “running” average. You can get this information from a Georgia website at www.georgiaweather.net. Click on the Dearing or Clarks Hill locations and use the 2-inch soil temperature reading.
Exact weed seed germination dates and temperatures are very hard to predict. Seeds are at different soil levels, and many have been in the ground for several years. Some seeds have been known to remain dormant for decades. The best way to control your weeds is to have a thick, healthy lawn. Since that eliminates most of us, the next best thing is to use a pre-emergence herbicide. Before you run out to the garden center to buy one of the many available products, some knowledge and a little work is required.
Your lawn should be as clean and debris-free as possible. Get rid of leaves, acorns, twigs, animal droppings and anything else that would get in the way of the herbicide. Use a granular product and water it in with about a half inch of water. Your sprinkler system will help, but make sure that it is covering the entire lawn. A rain event does a better job. But, wait, which herbicide should you use? The answer depends on your grass type. Recent studies have shown that some herbicides can restrict the growth of stoloniferous grasses such as centipede and St. Augustine. They impede the rooting process and prevent the grass from spreading. For centipede and St. Augustine, use atrazine, simazine, siduron (Tupersan) or isoxaben (Green Light Portrait). They don’t last as long as some of the newer herbicides, but they will not damage the roots. For Bermuda and zoysia, use any of the DNA herbicides plus dithiopyr. DNA or dinitroaniline herbicides include prodiamine (Barricade), pendimethalin (Halts) and oryzalin (Surflan). Dithiopyr is not a DNA herbicide, but it has a similar action that prevents rooting. It is available under the name “Dimension.”
The application of a pre-emergence herbicide will create a membrane-type barrier on the lawn’s surface. Any rough activity or raking may break the barrier and allow the weeds to find an opening. A good application process should prevent 50 percent or more weeds from germinating. A second application in mid to late April will help with late germinating weeds. Atrazine may also be used on centipede and St. Augustine as a post-emergence weed killer. Most labels only permit two atrazine applications per year due to possible water contamination so it may be necessary to use half rates for all applications. Atrazine is also effective as a post-emergence product on chamber bitter weeds, but you have to hit them when they are very young and tender.
The warm weather has caused some mysterious occurrences in my own backyard. My Penny Mac hydrangeas that normally bloom in May are still blooming. They have no leaves but still have several blue blooms. I also have a semi-tropical Tibouchina that normally crashes at the first hard frost but it is still putting out new leaves and an occasional flower. All of my regular hydrangeas have swelling buds and I’m worried that a cold spell might do some damage. I’m sure that I am not alone, and we should all cross our fingers.
Once again, mark your calendars for the next Lunchbox Seminar. Sid Mullis, the Richmond County coordinator, will speak about turfgrass on Feb. 18 at Trinity UMC on south Whiskey Road at 12:30 p.m. Sid’s radio show on Saturday mornings is a popular favorite as are his regular columns in the Augusta Chronicle.
For any garden questions, send an email to firstname.lastname@example.org. Someone will answer your question in a timely manner.
Bill Hayes has been in Aiken since 1982 after moving from Chicago, Ill. He was in the chemical process industry for more than 40 years before retiring in 1999.