Q: I have found several odd-looking creatures on my oaks and arborvitae. They look like slender Christmas tree ornaments dangling from the branches. I know they are living because I have seen them move! What are they and can they harm my plants?
A: After a homeowner first takes serious notice of a bagworm, they are not likely to confuse this insect with another living thing.
The bagworm is a perennial insect pest of arborvitae, juniper, pine and many other evergreen species. It also attacks certain deciduous trees including oaks and sycamore. The spread of the bagworm is slow since adult females are unable to fly. Their dispersal over wide areas occurs through movement of infested nursery stock and ornamental plants. Young caterpillars are often caught by the wind and ballooned with the aid of silken threads to nearby plants.
This insect is most easily recognized by the case or bag that the caterpillar forms and suspends from ornamental plants on which it feeds. When the caterpillar is mature, the bag may be up to 11/2 inches in length. The bag is made of silk and bits of host leaves and twigs. These materials are interwoven to add strength to the case and provide camouflage against adversaries including birds and humans.
This camouflage works very well because most homeowners overlook these bagworms for several seasons until their presence and damage on plants become very apparent. Bagworm larvae injure plants when they feed on needles and leaves.
Bagworms can severely defoliate and kill evergreens, such as arborvitae. Since deciduous trees (such as oaks and sycamores) grow new leaves each year, the defoliation caused by the feeding usually does not kill them and control by insecticides is not necessary.
Bagworms may be controlled on small shrubs and trees by handpicking or cutting bagworms from infested plants during late fall, winter, or early spring, before the eggs inside hatch. Don’t discard the bagworms onto the ground since they are capable of crawling back onto plants. Place bagworms in a plastic bag or container for disposal by household trash pickup.
Q: How do I recycle my coffee grounds?
A: With so many coffee houses around, there is interest in recycling used coffee grounds to divert them from the landfill. And being a plant product, a frequent question is whether coffee grounds are useful for gardening.
Coffee grounds are a low-level source of nitrogen, having a fertilizer value of around 2.0 percent nitrogen, 0.3 percent phosphorus and 0.2 percent potassium as well as a minor source of calcium and magnesium. Post-brewed coffee grounds are reported to be slightly to highly acidic, depending on the source, but no more so than peat moss. So, you could apply them to the soil for acid-loving plants, such as azaleas, blueberries and magnolias.
They might even help keep the flowers on your hydrangeas blue. Or, you could spread them out over a larger garden area to minimize the pH effect. It’s difficult to make a specific recommendation for an application rate, but it’s always better to err on the lighter side, since the pH can be variable. A rate of 10 pounds (dry weight) per 1,000 square feet would be conservative.
Composting is also an excellent method to recycle the grounds. Coffee grounds have a carbon-to-nitrogen ratio of around 20:1. Use the grounds as you would green, leafy material, mixing with some dry, brown plant materials in the compost. The Environmental Protection Agency suggests adding no more than 25 percent coffee grounds by volume.
Because of the fine grind that is typically used for brewing, the grounds should not be used as mulch since they are likely to pack down tightly, decreasing aeration. Also avoid using coffee grounds with potted houseplants, because of the potential buildup of soluble salts.
Q: Do you recommend use of fertilizer spikes around landscape trees?
A: While fertilizer spikes will not harm landscape trees, I do not recommend their use. Fertilizer spikes provide some nutrients in a limited area while not providing any nutrients in remaining areas. The roots of most trees extend out as far as the limbs (known as the dipline) and in many cases, extend out much farther than the limbs. Tree roots that absorb water and nutrients are also distributed fairly uniformly under a tree’s dripline. I recommend use of a complete fertilizer (such as 15-5-10) that is spread uniformly around the tree within the dripline.
Q: My family has always dusted vegetables rather than spraying them. Sometimes, unless it rains, the white dust residue will remain for weeks. How long is the insecticide dust effective?
A: Garden dusts are usually effective for five to seven days regardless of how long the actual dust particles applied remain visible. This is why it is so important to apply only a very thin — almost transparent — layer of dust when spraying. If you pour it on, as many people do, after several applications you will have a “whitewashed” plant which can actually be damaged by the excessive accumulations.
Dr. William Johnson is a horticulturist with the Galveston County Office of Texas AgriLife Extension Service, The Texas A&M System. Visit his Web site at http://aggie-horticulture.tamu.edu/galveston.
