Q: A viewer sent a photo of a birch that was cut down last fall. This spring it seems to be leaking water and sap, which is freezing. — John Wheeler, WDAY Chief Meteorologist, Fargo.

A: This is a fascinating phenomenon of nature. The tree stump photo on the left was taken by Mike Clower and submitted by John Wheeler. The photo on the right was taken by Jim Walla of Northern Tree Specialties.

We’re all familiar with the sap generated by maple trees, from which maple syrup is derived. Birch have a similar sap flow in spring, which can ooze from cracks and crevices in branches, or from the surface of a sawed-off trunk, whose roots are still alive. On subfreezing nights, the flowing sap forms icicles, with the neat term "sapcicle."

Jim Walla on his Northern Tree Specialties Facebook page notes, “Birch sap is used in some places to make syrup. It has less sugar content than sugar maple, so takes more sap to make syrup. I've tasted birch sap collected as birch water, which is sometimes marketed as a health drink. It has a different flavor than sugar maple sap.”

Q: What can I use to spray my apple trees for apple maggot? When is the best time to do this? — Victor Schmaltz.

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A: The apple maggot is the most common apple insect in the Upper Midwest, causing narrow brown streaks or lines winding through the flesh. The maggots are the larval stage of a small black fly that pierces the skin of developing apple fruit to deposit eggs in late June or early July that hatch into little wormlike larvae that tunnel internally in apple fruits, feeding through the summer before exiting.

Begin a spray program about June 20, and repeat every seven to ten days, or as directed on product label, until August when flies stop laying eggs. The relatively new insecticide spinosad is increasingly recommended because it’s effective, yet causes little harm to beneficial insects. Sevin can also be used, but can cause fruit drop if applied too early, and it’s more dangerous to pollinators.

Always thoroughly wet leaves and developing fruit with the product. Sanitation helps greatly. Promptly remove all fruit that drops from the tree to prevent larvae from entering the soil through fallen fruit and living through winter to reinfest the apple tree next year.

Q: Is now the time to apply a pre-emergent herbicide in my lawn? — Andrew Renfrew, West Fargo.

A: Pre-emergent herbicides applied to lawns in spring are most often targeting crabgrass, which is a weedy annual grass that must grow from seeds each spring, rather than having a perennial root system that survives winter, as quackgrass, tall fescue, and some weedy, wide-bladed grasses do. Crabgrass sprouts each spring from seed that’s present in the soil, triggered to germinate when soil temperature reaches about 50 or 55 degrees.

Crabgrass-preventing pre-emergent products must be applied before these seeds germinate, because they don’t eliminate the plants once established. It can’t be applied too early, though, because the products lose effectiveness over time. How to tell when to apply?

Monitor soil temperature, and apply the product following label directions, right before soil reaches the 50-degree threshold. Soil thermometers are available from garden supply catalogs, or follow regional soil temperature reporting sites such as https://ndawn.ndsu.nodak.edu/deep-soil-temperatures.html which gives daily soil temperatures at the 2-inch depth for many reporting cities.

For pre-emergent crabgrass preventers to be effective, it’s necessary to apply half an inch of water to dissolve the granules and move the herbicide into the top layer of soil. Once dissolved, the product forms a barrier in the soil. Without moisture to activate the granules, the product can be ineffective, and crabgrass can germinate freely.

ARCHIVE: Read more of Don Kinzler's Fielding Questions columns

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at kinzlerd@casscountynd.gov or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.