Good Morning,
The article is based on christmas trees, but the concept can be applied to your trees as well.  MSU Extension recommends reading and following label directions and minimizing direct spray contact with trees whenever possible.

Herbicides can be broken down into two categories based on how they function, either pre- or postemergence. Preemergence herbicides are applied to the soil prior to weeds germinating and can be expected to provide between six and eight weeks of residual weed control, depending on the product, weather conditions and weed pressure. Preemergence herbicides inhibit the growth/emergence of weed seedlings as the germinate.
To broaden your weed control effectiveness and to reduce the chance of resistant weeds, it is a good practice to tank mix and apply at least two herbicides with different modes of action. In general, most preemergence products should be applied prior to tree budbreak, but it is critical to review and follow all labeled instructions for maximum safety and effectiveness. Applications made in both the fall and spring can increase the duration of weed control.
Postemergence herbicides are applied to weeds that are already present. Some postemergence products move within the plant (i.e., translocate) from site of absorption to the root (e.g., glyphosate) and are known as systemic, while other products are non-systemic or contact herbicides, which target only the tissue directly contacted during application. In either case, it is important to realize that these products will not prevent new seedlings from emerging and may require repeated applications for continued weed control. Postemergence herbicides work best when applied to weeds that are young and actively growing and have not started flowering/seeding (reproductive stage).
Postemergence herbicides can cause crop injury (Photo 5 attached article), especially when they come in direct contact with active growing points of Christmas trees. Most postemergence products should be applied prior to bud break in the spring or after growth has hardened off in the fall. Some growers report tree injury when applications are made in the spring, even though there appears to be no active Christmas tree growth at the time of application. Although no active growth may be visible, buds can be active and swelling prior to observable growth and are vulnerable to injury at this stage. 

Understanding Roundup products - Turf (msu.edu)
What’s the difference between Roundup and Roundup For Lawns? - MSU Extension
Christmas trees 101: Weed management - Christmas Trees (msu.edu)

I hope this helps.  Thanks form using our service.

Thank you for your response.  It is a tricky issue.  The labels, for example, indicate that garden preen is safe for several types of maples.  My maples, however, are not specifically listed.  Based on the logic of the list, that suggests I should not use that product.  One the other hand, can I trust the list to be comprehensive for all types of maples?

Good Morning,
I wish I could give you a direct answer.  You may want to ask at a garden center for a better explanation for your specific maple.  Here are a few more articles.  Believe it or not, hand-pulling is still one of the best defenses against weeds. Pulling annual weeds before they flower and seed is the simplest way to prevent them from spreading. Hand-pulling is easier when soil is moist. A sharp spade or digger can help do the job.

MSU Extension | Montana State University
Common Landscape Herbicides and Their Effects on Trees | Mississippi State University Extension Service (msstate.edu)
MSU ag specialist guest column: Weed management for lawns (montana.edu)

Hope the helps.

Thank you. 

I have a dying spruce tree. I am concerned that whatever is causing it to die may put the nearby trees at risk.   I have included a few snap shots of the tree. I would appreciate any observations or recommendations.   I have an appointment with an arborist in a week from Davey to examine the tree.  The deterioration occurred over the last several months. 

Good Morning,
I suggest you have an arborist come out and assess your trees.  Thay can verify what herbicides you can use.  
About (treesaregood.org)

Good Luck.