Q: I have a white flowering crab that we’ve had for about 20 years. Can you tell me what could possibly be wrong that’s causing the leaf problems, and is there anything I can do? — Christine W.
A: We touched on this last week with another reader , but because this fungal disease has reached regional epidemic proportions, it merits revisiting, including a photo.
Apple scab is caused by a fungus that flourishes when the weather is cool, wet, and humid, as it’s been this spring and summer. These beautiful flowering trees, both white and rose-pink, are highly popular in yards and boulevards, so the disease has been visible and dramatic this year.
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Apple scab fungus can affect both fruiting apples and ornamental crabs. Symptoms include brown, circular spots on leaves and yellowing foliage that eventually turns brown. Leaves often drop prematurely, littering the ground below.
Severe infections, as we’re having this year, leave flowering crabs looking horrible, and there’s no reversing the situation for this year. The disease doesn’t typically have long-term effects on the tree’s health, unless it happens multiple years in succession.
Fungicide applications are pointless after the entire tree is affected. For future years, if the weather appears to remain cool and wet, preventive fungicides can be applied early, while the leaves are just unfolding.
It’s vital to practice good sanitation this year. As leaves fall, carefully rake them up and dispose in the outgoing trash. The fungus can survive winter on fallen leaves, which if left in place, can reinfect the tree the next year.
Q: How close should grass come to shade and apple trees, or doesn't it make any difference? Also, how much water should be given to apple trees that are about 6 feet high? — Ron B.
A: Grass growing right up to the trunk of a tree can be problematic when the tree is young for several reasons. Grass is a heavy user of moisture and fertilizer, robbing water and nutrition from the young tree’s roots below, causing reduced tree growth. Older trees with their large root systems are better able to compete.
Grass next to tree trunks also causes mowing problems. Damage to the bark while navigating a mower around the trunk can easily scrape bark, causing permanent damage. String trimmers whipping the bark at ground level can kill a tree in seconds.
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How close should grass come to shade or fruit trees? A circle of shredded wood mulch reduces grass competition on young trees, while making mowing easier around all trees.
I once advocated the 3-3-3 rule, meaning a circle of mulch 3 feet in diameter, 3 inches thick, and kept 3 inches away from the trunk in a doughnut-shaped ring, not a volcano. Longtime Horticulture Professor Neal Holland, since passed away, suggested to me that recommending 5-5-5 would be even better, because mulch 5 inches thick will soon settle to 3, and human nature being what it is, we might scrimp on the 3-3-3, leaving the tree less protected.
Regarding your second question about how much water to give a six-foot apple tree, or any tree that size, soak thoroughly, then allow to dry somewhat, instead of frequent light waterings that keep the roots too wet.
To water a tree that size thoroughly will take 5 to 10 gallons applied every seven to ten days. If soil is sandy, water more often.
Watering from a hose can be deceptive, and it takes longer than we might think to apply five or ten gallons. Filling a five-gallon pail and slowly pouring it over the root zone is a handy way to be certain you’re applying enough.
If rain is plentiful, such as an inch per week, skip the watering.
Q: Is it important to remove the old flowers on peonies, or doesn’t it matter? — Ashley M.
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A: Removing the old flowers, called deadheading, is Important for several reasons. If left intact, seed pods begin to form, which are of no benefit to the plant, and sap energy as the plant produces seed.
Old peony flowers, if left on the plant, can promote a fungus disease called botrytis tat can affect the plant’s future health. Removing old flowers also makes the peony plant look nice for the rest of the season.
Remove the old flowers as they whither or as they start to form a seed pod. Using pruning shears, remove the old material and possibly the next leaf, if needed to manicure the plant, but keep the rest of the foliage intact to feed the plant, which is already energizing itself for next year.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at [email protected] . Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.
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