Crabgrass was a common invader of turfgrass stands in 1998. Many turf managers and homeowners are concerned about a possible repeat performance in Illinois during 1999. There are both cultural and chemical control options to consider.
Remember, crabgrass is a warm-season annual; no matter how many crabgrass plants appeared in turf last year, those plants are all dead now. Crabgrass seed germinates in late spring and summer, and the plant dies as temperatures cool and days become shorter in autumn. In between, the plant flowers and produces seed that will be the source of weed invasion for years to come. In order for crabgrass to return in 1999, seeds in the soil must germinate into new plants. This will not occur until soil temperatures get close to 60°F at the 1/4-inch level and remain there for several consecutive days.
Several turf management practices will help prevent crabgrass from appearing. One critical management area is mowing height, which has a major impact on crabgrass. Mowing between 2-1/2 and 3 inches will typically result in fewer crabgrass plants appearing in lawns and other turf areas. Crabgrass also likes frequent watering, especially frequent light sprinklings. Proper watering can help reduce crabgrass potential. Finally, complete cultivation activities before crabgrass seed germinates.
Crabgrass often invades bare soil or areas where the turf is thin. Avoid practices that damage the turfgrass stands in late spring or early summer. If possible, delay turf establishment or renovation work until late summer to avoid potential crabgrass problems. This also holds true for destructive practices such as dethatching.
Several preemergence herbicides are available to use in spring for crabgrass control. Specific herbicides include benefin, benefin/trifluralin, bensulide, dithiopyr, oxadiazon, pendimethalin, prodiamine, and siduron. Apply preemergence herbicides in mid- to late April in southern Illinois and early to mid-May (or sometimes later) in the northern part of the state. Although forsythia bloom is often mentioned as the time to apply preemergence herbicides, forsythia flower petal drop is often a better indicator. Remember to always read, understand, and follow pesticide label directions for the safest and most effective method of pest control.
One management problem associated with preemergence herbicides is seeding or overseeding practices. With the exception of siduron (Tupersan), all preemergence annual-grass weedkillers will also damage germinating desirable grass seed. Siduron can often be found in combination with a lawn-starter fertilizer as a weed-and-feed product in garden centers.
For homeowner use, many available preemergence crabgrass herbicides are found in combination with lawn fertilizer. These combination weed-and-feed products can provide crabgrass prevention and spring fertilization in a single application. Follow the rates given on the bag.
Homeowners have also been asking about corn gluten for crabgrass control. Corn gluten, available through mail-order catalogs (one example is W.O.W. or WithOut Weeds), is a byproduct of processing corn for animal feed. It does have some herbicidal activity and is also a source of organic nitrogen fertilizer. In the first few seasons of application, corn gluten does not usually provide crabgrass control that is as acceptable as most synthetic products. Subsequent use each season may provide improved crabgrass control. (Bruce Spangenberg and Tom Voigt)