Q. I went to a large retailer's garden center with a pest problem, something eating the oak leaves on three small trees I just planted. They suggested using an Advanced Bayer systemic insecticide (applied as a drench), and it doesn't seem like it worked. What's the pest, and what should I do?
A. That damage is typical of the oak skeletonizer, caused by the larvae stage of a "sawfly." The sawfly is related to ants, wasps and bees. Typically the damage is inconsequential to established oaks, so normally we'd suggest to just tolerate the damage. But for smaller trees it might be best to stop them so the tree doesn't get set back.
While the product you applied works on a wide variety of insects, a University of Missouri publication, "Tree and Shrub Pests Around the Home (signs, symptoms and control)," does not recommend this product's insecticide active ingredient (imidacloprid) for control. Furthermore, this active ingredient when applied as a drench does not list "sawflies" on the label, but a related product applied as a spray does say "sawflies" on it. So we recommend you return the product to the retailer and show them the information from this publication. Then apply a product with one of these active ingredients: spinosad, lamda-cyhalothrin or carbaryl.
It is also important to understand that an insecticide applied as a drench on a woody plant can take up to a week to become active in all the plant parts. Thus, for immediate results, a spray is preferred.
Q. How can I become a Master Gardener? Do I have to know a lot about gardening? I think I have a black thumb. Do I have to live in Jefferson City to join?
You don't have to live in Jeff City. We have folks taking the class from all around the area, Linn, Ashland, Holts Summit, etc. And you don't have to know anything about gardening. Folks from newbies to experts take the class, and that mix helps everyone learn. Beginners can ask the most profound questions, as anyone who has raised kids knows.
We have a class series starting up on Aug. 17, and it will run on Monday evenings from 6 to 9 p.m. for 14 weeks. The cost is $135, which includes a book and a free soil sample. One also needs to complete 30 hours of garden-related volunteer service in 2016. Call us for more info at 634-2824.
Q. I saw you give some herbicide recommendations in a previous Sunday's column. Do you have any suggestions for us gardeners who don't want to use those type of chemicals?
Great question to follow up with, because we highly encourage gardeners to first practice cultural controls for weed control. Most, if not all, Master Gardeners will espouse the virtues of mulching to suppress or smother weeds. And follow this up with hand weeding, by either pulling or hoeing. In vegetable gardens, tillers can be used in bare areas; and there are some small light tillers available that can improve their functionality.
There is a number of mulches to choose from. For vegetable or "similar annual type" gardens, straw, old leaves, shredded paper or newspaper, and finely shredded wood waste are all good. So is the free compost from Jefferson City. For permanent or long-term plantings (e.g. trees and shrubs), weed suppression and mulch longevity can be improved by first putting down some type of landscaping fabric or weed barrier. Lower-cost options of these have become available in recent years and can be coupled with chipped-up wood products. Bigger pieces tend to last longer.
For "natural herbicides" there are a couple of options. But they need to be used on small weeds and don't perform well on perennial weeds. Natria Grass and Weed Killer is one option ($16 for 64 ounces of ready-to-use). Another is using vinegar, but household vinegar isn't strong enough to work well. Adding to the confusion is whether vinegar can legally be sold for use as an herbicide. Fortunately at least one company has done so: Pharm Solutions has an organic weed killer as a ready-to-use product, 24 ounces for $15. Vinegar's reputation is variable in effectiveness. Bright sunshine following application helps.
Have a gardening question of your own? Submit it via email to [email protected] for possible inclusion in a future "Ask a Master Gardener" column.