Welcome to the latest issue of the Home Lawn Care Newsletter from UMN Turfgrass Science! We will provide up-to-date information to address all your lawn care tasks at the times when you need to know.
March 15, 2024: Issue 19
What does a warm winter mean for your lawn? With the warmest winter on record and soil that’s warming about two weeks ahead of schedule, you might be wondering what’s next for the season.
Warm winters and white grubs
There are two different species of white grubs that are common in Minnesota: the Japanese beetle and the European chafer. While a warmer winter does not impact their life cycle, there are various other factors to consider. Both beetle species lay eggs in late summer 2 to 4 inches below ground. For the Japanese beetle, a 10% moisture level is a key component. Eggs may not hatch if it’s too dry.
After several growth cycles, Japanese beetles overwinter as inch-long grubs at 2 to 8 inches underground, and European chafers just below the frostline. With no snow and consistent warm air temperatures, the frost layer will not be as deep, and grubs will be overwintering less deeply in the soil. These conditions suggest more grubs would survive over winter; however, the impacts of different types of winter on survival of these grubs is not well known. Frost depth in the Twin Cities was less than ½ inch deep this past winter. So what is the impact on white grubs? It’s just too early to tell. Read up on best practices in the links below, and be ready to check for white grubs in your lawn and treat if you need to.
Japanese beetles in yards and gardens | UMN Extension
Japanese beetle management in Minnesota | UMN and Minnesota Department of Agriculture
How to choose and when to apply grub control products for your lawn | Michigan State University Extension
Managing white grubs in turfgrass | Purdue University Extension
Warm winters and dormant seeding
Dormant and frost seeding methods are becoming more popular because they eliminate the work of watering and fertilizing new seeds. The question for this year is, what happens when there is no snow cover? Snow is an important element of dormant seeding because it moves the seed into direct contact with the soil. It’s likely that dormant seeding will not have been as successful as desired this winter.
Dormant seeding is still an option as long as soil temperatures remain below 45 degrees. Overseeding the same area prior to another snow event this season will still save you from preparing the soil as you would for regular spring seeding, and increase the potential for the area to fill in. When soil temperatures reach 50 to 65 degrees, grass seed starts germinating; if the spring continues to be dry, young seedlings will need to be watered.
Avoid application of preemergence herbicides to the area this spring, but fertilizing in later spring will be fine.
Dormant seeding your lawn | UMN Extension
Consider dormant seeding your lawn this fall | UMN Turfgrass Science
What to do about summer annual grassy weeds if you dormant seeded?
A warm winter and early spring means that weeds will start germinating earlier than usual. Preemergence herbicides are normally the most effective chemical control of crabgrass and other summer annual grassy weeds. The best preemergence herbicides for these weeds contain the active ingredients dithiopyr, pendimethalin, or prodiamine. These herbicides are intended to be applied prior to crabgrass emergence on established lawns and are generally not recommended for new seedings. Dormant seeded areas present a tricky situation, because we often choose dormant seeding as a stand improvement strategy in areas that might be prone for crabgrass emergence such as a thin stand or an area where we anticipate winter salt damage.
There are very limited preemergence chemical options for controlling summer annual grassy weeds if you have recently overseeded. The only commercially available option is a granular starter fertilizer (21-22-4) mixed with mesotrione, a popular active ingredient that has soil post emergent activity, and is relatively safe on some cool season turf seedlings. This seems like a winning combination, but it does have some limitations. For example, the soil activity is typically shorter (4 vs 8 weeks) compared to other preemergence herbicides, so sequential applications would need to be made for similar control. Another limiting factor for granular mesotrione is that fine fescue seedlings can be inhibited from this herbicide, and this product should therefore be avoided if fine fescues are more than 20% of the dormant seed mix.
The best course of action is to use a postemergence herbicide after your dormant seeded turf has emerged. There are many options available, but serious attention should be given when selecting a product, especially with respect to the seed mix that was chosen and the maturity of the turf seedlings at the time of treatment. Regardless, all postemergence herbicides work best on smaller crabgrass seedling plants that have fewer leaves or tillers. Products containing the active ingredients dithiopyr, fenoxaprop, mesotrione, quinclorac, or topramezone are most effective for selective postemergence control of crabgrass and similar summer annual grassy weeds. The pesticide labels will have specific instructions for when and where they can be applied for best control.
Check the Turf Dashboard to see the optimal time to apply a crabgrass preemergence herbicide for your location.
Crabgrass management in North Dakota lawns | North Dakota State University Extension
Crabgrass control in lawns for homeowners in the northern US | Rutgers Cooperative Extension
Research highlight
Last fall, this newsletter provided a number of resources about managing leaves. While returning mulched leaves to the lawn is generally beneficial, there can be some downsides. For lawns in Minnesota during a typical winter (not this one!), a major concern is the impact of excess leaf litter, even when mulched, on snow mold risk. Dr. Paul Koch, a plant pathologist at the University of Wisconsin-Madison is an expert on snow molds, and a long-time collaborator with the University of Minnesota turfgrass program. As part of the WinterTurf project, he is leading a multi-state study investigating how leaf litter impacts lawn health. Read about some of the project’s results below.
Tree leaf mulching impacts on lawn health | WinterTurf project blog
Event
We will be in Lakeville next month to answer questions on smart irrigation and lawn care as part of our collaboration with the Metropolitan Council.
CIty of Lakeville Watershed Cleanup Day and Earth Day Celebration in Lakeville, MN on Saturday, April 20, 2024 from 11:00 a.m. to 1:00 p.m.
Have a question on a topic we didn’t cover in this email?
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We provide research updates, lawn care tips, info about field days, and more at @UMNTurf.