These 'good guy' insects are the cause of circular holes in dogwood leaves
"Fielding Questions" columnist Don Kinzler also answers questions about tomatoes that aren't ripening and how to cut back overgrown petunias.
Q: What is eating the leaves of my dogwood, and what should I do? — Barb O.
A: The neat circular sections cut out of your dogwood leaves are made by leaf-cutting bees. Such holes almost look like they’ve been made with a hole punch.
Leaf-cutting bees are among the “good guys” and are important pollinators of cucumbers, squash, pumpkins and other fruits and vegetables. The bees use the circular leaf sections for nesting material.
They're about a half inch long and are darker than yellow honeybees. They cut semicircular leaf disks from roses, ash trees, lilac shrubs and many others.
The circular holes do very little damage to plants, and because bee pollination is vital for crops of fruits and vegetables, insecticides aren’t recommended. Leaf-cutting bees aren't aggressive and won’t sting unless you are intentionally trying to disturb them.
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Q: Our tomatoes are not ripening. The plants look healthy, and we’ve been watering faithfully. We planted the same varieties this year as we always do, and usually we’ve had ripe tomatoes by now, but this year all we have are green tomatoes. What’s causing this, and is there anything we can do? — Larry S.
A: This year’s extended heat has had many effects on vegetable gardens. Although tomatoes and other warm-loving crops grow nicely when temperatures are pleasantly warm, there is a limit. Temperatures consistently in the upper 80s and 90s, coupled with hot nights, begin to affect vegetables. Although the plants might appear healthy, flowering and fruiting can be affected.
There are many reports from around the region of cucumbers and other vine crops blossoming, but not producing fruit. Heat can adversely affect the viability of pollen and can even discourage bees from visiting flowers. During extended heat, more male and fewer female flowers are often produced, which can lead to declined fruit production.
This season’s hot weather is affecting the ripening of some tomatoes, based on many reports from area gardeners. Heat seems to be affecting the fruit's growth and expansion. Unfortunately there’s little we can do, other than hoping that moderate temperatures will bring about normal ripening.
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Q: We have three big pots of petunias on our patio. In the beginning they were mounded nicely. Now they have tentacles like an octopus and are hanging in every direction. Can you cut back the long shoots and have them come back, or do you just have to let ‘em go? — Clem S.
A: Yes, in midsummer you can trim petunias back by at least half or more, to get rid of straggly shoots. If the plants are otherwise healthy, they’ll quickly send out new shoots, and the petunias will look nice and full for the rest of summer and into fall. It works with about 99% of petunia plants.
After cutting the plants back, fertilizing with a water-soluble type like Miracle Gro will encourage fresh growth and blossoms. If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.