Common Questions About Crabgrass Germination and Preemergence Herbicides Answered

This time of year many have questions about crabgrass germination and control. Below are several previous Purdue turf tips that answer the most commonly asked questions about crabgrass control.

• When will crabgrass germinate?
• When should I apply my preemergence herbicide (crabgrass preventer)?
• How to Select a Crabgrass Preventer from the Store – Homeowners 

Exerpts provided by: Aaron Patton, Turf Extension Specialist, Purdue University

Turf Tips - Lawn Diseases 2016

The summer of 2016 has been quite favorable for the development of an assortment of infectious diseases on residential turf. The primary driver of all of this disease activity is the weather. In the lower Midwest, the combination of elevated temperature and ample precipitation since the beginning August of has spawned outbreaks of brown patch, dollar spot, Pythium blight, leaf spot diseases, and the appearance of symptoms of summer patch and necrotic ring spot. Although infection is almost entirely a function of temperature and moisture, there are other factors (addressed in the linked blog post) that may hasten the decline of turf once disease becomes established.

Not all turf species are susceptible to all diseases. In general, Kentucky bluegrass (KBG) is less prone to brown patch , dollar spot, gray leaf spot, and Pythium blight—but very susceptible to root diseases such as necrotic ring spot and summer patch. Root pathogens are present in all soils, and infect turf as soil temperatures increase beyond 60F. With ample moisture, infection will continue through summer. Plants are killed outright in some instances, but in most cases, KBG can tolerate some infection. However, during periods of environmental stress, infection-impaired plants cannot survive, and characteristic dead patches or rings or frog-eyes appear.

To continue reading this TURF TIPS BLOG post, CLICK HERE!

Rick Latin, Ph.D.
Professor of Plant Pathology
Purdue University

Get Ready: Fall is the Time for Lawn Improvements

Lawn Seeding

Indiana lawns contain primarily cool-season grasses, which grow best in the cooler temperatures of spring and fall. During the hottest times of year, they may grow very slowly or even go dormant. Kentucky bluegrass, perennial ryegrass, tall fescue, and fineleaf fescue are common cool-season grasses.

Whether your lawn is thin from the rigors of summer or from neglect, fall is the best time of the year to improve your lawn. Some lawns can be dramatically improved with proper fertilization and weed control in fall; whereas others may need reseeding in some areas or even complete renovation.

Adequate soil moisture, warm soil, and limited weed pressure allow for excellent seedling growth. Between August 15 and September 15 is optimum seeding time in the northern half of Indiana and Illinois, and September 1 to September 30 is optimum in the southern half of Indiana and Illinois.

Consider aerating the lawn area, punching 20 to 40 holes per square ft with the largest tines available. This will increase the seed-soil contact and improve germination and establishment rate. Apply a starter fertilizer (high in phosphorus) over the entire lawn at 1.0 to 1.25 pounds of phosphate per 1000 square ft of lawn.

Next, apply the seed to the lawn with either a drop-seeder or a power over-seeder.  Be sure to seed in both directions to adequately cover the lawn area with seed.   Mulching the area will prevent erosion and conserve water. Therefore, mulching is most important when it is impossible to adequately irrigate newly-seeded areas.

Water the newly-seeded area three to four times daily in order to keep the soil surface moist. Light, frequent irrigation is the rule during the first few weeks.  Frequent mowing will limit the competition from the established turf.

Four weeks after germination, apply 1.0 pound of nitrogen per 1000 square ft of lawn using a fertilizer containing N, P, and K.

Fertilization
Properly fertilized lawns better tolerate stresses such as heat, drought, and cold. Applying the right fertilizer at the correct time helps turf plants accumulate and store the essential plant foods that are used for growth and development.

You should only apply the nutrients your lawn needs. The nutrients plants need in the greatest quantity are nitrogen (N), phosphorus (P), and potassium (K). Of these, N has the most impact on established lawns. N promotes green color and overall growth, especially leaf growth. Plants need P and K for strong root and stem growth, which is most crucial when establishing a new lawn

Established lawns will benefit most when you apply the majority of N fertilizer from late summer through autumn. This promotes summer recovery, enhances shoot density, maximizes green color, and prepares the turf for winter, all without a growth surge.  To promote maximum density during late summer and early fall (late August through early November), you should apply up to 1 pound of N per 1,000 square feet each month.

For more information on soil testing to help you choose the correct fertilizer, look here.

Other tips to consider to help lower fertilization costs is to return grass clippings during mowing to the lawn.  These clippings contain valuable nutrients that can be recycled into the soil. If you must regularly remove clippings when you mow, you may need to increase the amount of N you apply each year by 25 to 50 percent to maintain growth and color.

Spring Seeding Tips for a Successful Lawn

Most Purdue University publications recommend seeding lawns in the fall or in late winter before the soil thaws. Winter seeding allows the seeds to enter cracks in the frozen soil creating great seed to soil contact. Sometimes we are forced to seed our lawn in the spring due to winter damage or initial establishment of a new lawn. If this is the case for you, please follow these tips to be successful.

Although any cool-season grass can be seeded in the spring, spring seedings are more successful with tall fescue and perennial ryegrass than with Kentucky bluegrass due to the faster germination rate and better seedling vigor of perennial ryegrass and tall fescue compared to Kentucky bluegrass. See image above for germination example.  If Kentucky bluegrass is seeded in the spring consider using a mixture of tall fescue: Kentucky bluegrass (90:10, weight: weight) or a mixture of Kentucky bluegrass:perennial ryegrass (such as 80:20, weight: weight). Seeding Kentucky bluegrass alone will result in marginal bluegrass establishment due to the slow germination and vigor of the seedlings and increased comp

etition from crabgrass. The table below gives the recommended seeding rates and days to germination per recommended species.  

New turfgrass seedlings have poorly developed root systems and thus they cannot effectively take up the nutrients from the soil. Therefore, it is important to fertilize frequently after seeding to encourage

establishment. To help the turf establish, apply a “starter fertilizer” to enhance seed germination and development. Starter fertilizer is high in phosphorus which is listed as the second number in the analysis on the fertilizer bag. For instance, a 16-22-8 fertilizer contains 22% P2O5. Apply the fertilizer according to the label directions would should supply at least 1.0 lb. P2O5 /1000 ft2. This application will likely include nitrogen (first number in the fertilizer analysis), which will also help the turf develop an extensive fibrous root system that is better able to take up nutrients and obtain water.

Table 1. Recommended seeding rates for lawns in Indiana.

Species	Seeding rate lbs/1,000 ft2	Days to germinate
Kentucky bluegrass	1.0 to 2.0	10-21
Kentucky bluegrass + perennial ryegrass	3.0 to 6.0	5-21
Tall fescue	8.0 to 10.0	6 to 10
Tall fescue + Kentucky bluegrass	5.0 to 7.0	6 to 21

Taken from Turf Tips written by Aaron Patton, Assistant Professor/Turfgrass Extension Specialist

Ready, Set, Go - The Time to Control Summer Annual Weeds in NOW!

Spring has appeared more quickly this year than it has in years.  With the arrival of warmer air, we also see the gradual increase of soil temperatures which means it is time for homeowners to apply a preemergence herbicide to control crabgrass on turf areas. The timing of that application is critical for effective control of crabgrass and other summer annual grassy weeds. Since the preemergence herbicides recommended for crabgrass control actually prevent germinating seedlings from emerging, these products must be applied before crabgrass seeds germinate. Researchers report that crabgrass seeds germinate when average daily soil temperatures reach 57 to 64 degrees Fahrenheit at a 1-inch depth. 

Some turf managers have monitored soil temperatures as a method of predicting crabgrass germination and determine the optimum time to apply preemergence herbicides. Likewise, the bloom period for forsythia has been used as an indicator for the best time to apply crabgrass control. Forsythia blooms just prior to crabgrass germination signaling the time to apply preemergence herbicides. 

In recent years, models using growing degree days (GDD) have been developed for predicting crabgrass germination and preemergence herbicide application timing. Homeowners and professional turf managers may find the GDD tracker website to be a useful tool to track crabgrass germination and determine the optimum timing for preemergence herbicide applications. Good control of crabgrass can be observed when preemergence herbicides are applied when the points on the GDD Tracker map reach the “under”, “early”, “optimum”  or "late" categories. As of March 30, 2016, central Indiana is heading into the “late” category, and northern Indiana is in the “optimum” category. The “bottom-line” is that applying preemergence herbicides now in central Indiana for effective preemergent control of crabgrass in turf areas.

The following tips are also important for minimizing crabgrass pressure and increasing the effectiveness of pre-emergent herbicide applications:

• Mow cool-season turfgrasses at a mowing height of 3 inches or higher
• Irrigate turf areas deeply and infrequently
• Apply 2 to 4 lbs. of nitrogen per year with the majority applied September through November each year
• Ensure an even distribution of preemergence herbicides, avoiding skips or misses on turf areas
• Always read the label for all pesticide products to determine the appropriate rate of application and spreader setting
• Pre-emergent herbicides must be watered in thoroughly to be effective, time application before rainfall or use irrigation to accomplish this important step.

Taken from Crabgrass Control: Timing is Critical
John Orick Purdue Master Gardener State Coordinator Department of Horticulture and Landscape Architecture, Purdue University