Q: We had four apple trees and two of them developed white growths on the trunk last spring. The trees sprouted leaves but then died. We were advised not to plant another tree in the same location, as the problem appeared to be a fungus. Do you know what this is? — Heather Anderson, Audubon, Minn.

A: Thanks for the great photo. The white growths are fungi, but they were secondary invaders who took the opportunity to pounce after the trees were already damaged.

The primary cause of the injury to the apple trees was likely the common killer of fruit trees called winter sunscald, especially injurious to young trees. Sunscald happens when bright sun is reflected from the snow onto the south or southwest sides of thin-barked trees. Similar to skiers getting winter sunburn, the reflected sun warms tree bark and freezing/thawing cycles rupture trunk cells, often causing permanent damage.

Damaged trees might have enough internal strength to leaf out in spring, but quickly decline when injured trunk tissue can’t conduct water and nutrients to the upper foliage. Fungi often begin growing on the damaged bark tissue, simply hitching a ride for free food, rather than causing the original problem.

To prevent winter sunscald, wrap thin-barked trees every year in November and remove in spring. Various tree wrapping materials and tubes are available at garden centers. You can replant another apple tree in the same location, because the cause of death was not a disease that passes from plant to plant or exists in the soil. Death of the trunk was caused by environmental problems.

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As a side note, it would be best to add a circle of shredded wood mulch around the tree to eliminate grass growing up to the trunk. Lawn mowers and string trimmers cause nearly as much damage to tree trunks as sunscald.

Q: Could you recommend some flower types, in addition to marigolds, that rabbits do not like to eat? Marigolds have proven excellent in the flower box, but I would like more choices. — Robert Eidbo.

A: Rabbit and deer damage has been a plague of biblical proportions in recent years, both winter and summer. Planting flower types that these creatures don’t prefer is good in theory, but both deer and rabbits will nibble almost anything, depending on their current taste or desperation.

I hesitate to share lists of plants resistant to rabbits and deer, because these lists fail if animals are hungry enough. The following plants are reported by research universities as less likely to be consumed.

Annual flowers less palatable to rabbits include ageratum, alyssum, begonia, cosmos, dusty miller, calendula, cleome, marigold, verbena, salvia, vinca, zinnia, nicotiana, four o’clock, geranium and snapdragon. Less-tasty perennials include bleeding heart, daylily, astilbe, bergenia, heuchera, Shasta daisy, columbine, iris, peony, poppy, agastache, rudbeckia, liatris, penstemon, lamb’s ears, gaillardia, asclepias, artemisia, monarda, veronica, Russian sage, sedum and gas plant.

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

Q: We have a new yard with several young trees. During the recent melting days, water is accumulating and the trees are standing in a pond. Is this going to hurt the trees? — Bob L., Fargo.

A: Whether trees can tolerate standing in water depends on the time of year. When trees are still dormant from winter’s cold, and before they begin spring’s growth, trees can survive being submerged in early spring floods.

However, the same trees in the same location can be killed if their roots are inundated in water during the warm growing season. When trees are in full leaf, roots require oxygen, and death by drowning can happen in as little as three to seven days if trees and other plants are forced to stand in water, either along a river or in a yard where drainage is poor.

The trees in your yard will likely survive fine if the water drains away sufficiently before warm weather wakes trees from their winter hibernation.

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.