Horticulture

killing volumteer walnut trees

I am a certified private appplicator. How can I kill volumteer walnut trees in a daylily beds?

Probably you would use either of the following (most likely the first) from the University of Florida Extension.

Cut stump herbicide application
Stumps of invasive woody plants will resprout after cutting if not treated with a herbicide. Re-sprouts can be continually cut off as they appear, but applying herbicide to the stump will kill it and prevent resprouting. Stumps should be cut as close to the ground and as level as possible so that applied herbicide does not run off. On large stumps, the herbicide should be concentrated just inside the bark. This is where the living tissue is located that will carry herbicide into the roots. Sawdust, which can absorb herbicide and prevent it from moving into the stump, should be removed. Apply the herbicide to the stump as quickly as possible after cutting. Products that contain triclopyr amine, triclopyr ester, or glyphosate are effective for controlling regrowth of stumps of many invasive plant species. Homeowners with only one or a few stumps to treat can use Brush-B-Gon, Brush Killer, or Roundup Super Concentrate. All three products can be applied undiluted.
Basal bark herbicide application
Many woody plants can be killed without cutting the tree down by applying oil soluble herbicides to the bark This is only recommended for trees or shrubs with stem diameters of six inches or less. This method is faster than cutting vegetation down and treating the stumps. It is useful for homeowners with larger numbers of woody plants to kill where it is acceptable to leave dying and dead vegetation standing. An oil soluble herbicide must be used for basal bark applications to facilitate movement of the herbicide through waxy substances in the bark. Garlon 4 must be diluted in a penetrating oil that can be recommended where the herbicide is purchased. Pathfinder II is pre-diluted in oil and ready to use. Vine-x can be used for application to small stems (up to 3/4 inch in diameter).

James Quinn
Regional Horticulture Specialist

Poor squash and pumpkin production

For the last two years I have had a problem growing both green and yellow squash. The plants look good at the start of the season, but the leaves turn a silver gray color and the blossoms do not produce fruit. Last year I planted pumpkins and all I got was one pumpkin the size of a soft ball. What is my problem?

It can be very difficult to say for sure what may have caused the poor growth and production of your pumpkins and squash. I would suggest submitting a physical sample and/or digital photos to the plant diagnostic clinic. You can see our Web site for more information on sample submission and fees. However, if the silver gray color appears initially to be present on the leaf surface, it could be powdery mildew. Severe powdery mildew infection can cause plant death and yield reduction. For the home garden, look in the catalogs for some of the newer varieties of pumpkin and squash that have powdery mildew resistance. Fungicides such as sulfur can also help manage this disease.

Simeon Wright
Plant Diagnostic Lab Coordinator

Master gardener requirements

What do I need to do to become a master gardener?

You start out with the 30 hour training course which covers gardening from the basics. After that, to become certified as a Master Gardener, you are required to put in 30 hours of volunteer service in MU Extension related activities. After that, to stay active on an annual basis, you are required to commit 20 hours of service per year, unless you are a member of the St. Louis chapter where the requirement is 50 hours. Visit the Missouri Master Gardener Program Web site for details.

Mary K. Kroening
Horticulture Specialist

Radish roots

For several years my radishes have been all tops with nearly no roots. What's the problem?

Two basic problems come to mind. There may be very high nitrogen availability (maybe high organic matter soil) or the radishes are planted too thick.

Plants should be spaced a minimum of an inch apart down the row and the soil needs to be loose and friable for good root development.

Gaylord Moore
Horticulture Specialist

Black stalks on roses

The stalks of my rose bushes are black. Does this mean I have lost them from the ice storm?

Most likely you have lost the stalks where they are black, but probably due to winter temperatures versus the ice storm. Give them more time to see how much pulls through, and how much tissue death there is. You can prune out the dead stalks and it may come back from further down the base just fine.

Chris Starbuck
State Extension Specialist
Woody Ornamentals