There are two major battles that all gardeners face every season: weeds and pests. I have always said (and will repeat) that there will never be a complete victory in either battle. As long as we have gardens, we will have unwanted creatures that can cause damage and headaches.
Pests that damage our gardens can be as small as the nearly microscopic spider mites all the way up to deer that weigh as much as an adult. Size doesn’t always correlate to the damage. I’ve seen some of the smallest creatures wreak the most havoc in an incredibly short amount of time.
Japanese beetle damage leaves the foliage of plants looking like a fine lace doily. Since these insects are fairly large and travel in large numbers, they aren’t hard to find.
Japanese beetles first appeared in the United States in 1916, and since then, they have appeared in half of the lower 48 states and are spreading. They have one generation per year, usually emerging as adults sometime in May and June. The adults are about a 1/2-inch long and wide with copper-colored wings and iridescent green bodies.
With ravenous appetites they take to the wing and devour the foliage, fruit and flowers of a wide range of plants. Since the adults only live a few weeks, they must eat, mate and lay eggs in a short period of time. Eggs are laid in the soil, which hatch into white, C-shaped grubs that feed on the roots of grasses and other plants until the following year.
Control of Japanese beetles is difficult due to their sheer numbers. You can kill hundreds one day only to have a new batch fly in overnight. Insecticides, such as Sevin and malathion, work well. Control without chemicals involves handpicking the beetles in the early morning and drowning them in a bucket of soapy water. Grubs can be killed with products labeled for their control, which are best applied when the grubs are close to the surface in the late summer and again in the spring. Organic control of large grub populations can be done with milky spore, a naturally occurring bacteria that specifically attacks them. Don’t hang beetle traps, as that simply attracts more of them to your landscape.
Aphids can be seen gathering on the leaves of this tomato plant. Strong sprays of water in the early morning hours will wash them off. If you use an insecticide, make sure it’s labeled for use on food crops.
Aphids are 1/10-inch, soft-bodied insects with piercing mouthparts that they use to suck the sap from the soft leaves, flowers and stems of plants. There are several species, all of which are destructive. Aphids are easy to see, because they congregate in large numbers and cause the wilting or distortion of the plants they attack. Body color ranges from yellow to tan to brown or orange. Their presence can also be detected by the appearance of sooty mold — a black substance that grows in their droppings (honeydew).
Aphids can easily be dealt with by using strong streams of water to wash them to the soil. There are also many predatory insects that appear during aphid infestations, so use pesticides sparingly; otherwise, you may make the problem worse. Horticultural oil and systemic insecticides (taken up by the plant into its tissues) will deal with them and not endanger beneficial insects.
The honeydew left behind by whiteflies has turned the leaves of this gardenia black, a sure sign of infestation. This shrub needs to be aggressively treated.
Like aphids, whiteflies have piercing mouthparts and suck the sap from plants. They also secrete honeydew, which turns black with sooty mold. Adults are usually 1/8-inch long or less, and large numbers of the insects can appear as a tiny, white cloud above the infested plant. There are multiple species, but their behavior is pretty much the same.
Whiteflies are easily killed by insecticides, including some organic products, such as neem oil and insecticidal soap. Since their populations can explode overnight, you need to be alert and begin treating at the first sign of a problem. For plants that are known to be susceptible or have been infested in the past, you may want to begin before you see them with applications starting in spring focusing on the undersides of leaves. Be prepared to treat infested plants weekly for a month or more. Systemic insecticides also work well on whiteflies.
The spotted appearance on this hollyhock shows the damage caused by very tiny spider mites. By the time the damage is this severe, a miticide may be the only product strong enough to get control.
Amongst the tiniest of the pests, spider mites are only about the size of the period at the end of this sentence. With their tiny, sucking mouthparts, they can cause a great deal of damage. Symptoms of spider mite infestations are spotting or bronzing of foliage that may or may not be distorted. Detection of spider mites can be accomplished by shaking a leaf over a piece of white paper and looking for the moving pests. A hand lens aids in this process.
Control can be difficult because they are not insects, but rather, arachnids closely related to spiders. As such, they are not killed by most common insecticides. Control can be achieved by using strong sprays of water, insecticidal soap, horticultural or neem oils or the application of products known as miticides that specifically target them.
Barriers, such as this chicken wire, will prevent a vole from getting at the base of the plant. Although this is a tedious chore, it certainly beats having to dig out and replace dead plants.
Moving from the micro to macro pests, voles are mouse-sized creatures that live or tunnel shallowly at the top of the soil or in the mulch layer. Their attack consists of chewing on the roots and lower stems of a wide range of plants, including perennials, shrubs and trees. Death comes suddenly as the plant is girdled. There are several species collectively known as voles found throughout most of the country.
Outside of a skilled cat, the best control I have found involves physically blocking or deterring them from getting to the plant. Pulling mulch back about 6 inches will require the vole to venture into the open, making them vulnerable to predation. Chicken wire can be used to encircle the base of the plant from 3 inches below the soil to 1 inch above. I haven’t had much permanent control from various vole-blocking products that are comprised of crushed slate, because these tend to mix with the soil over time.
Moles are more of a nuisance than a real pest. Larger than voles, these are the true tunnelers, burrowing through the landscape in search of food: earthworms, grubs, etc. Since they don’t attack plants, I consider them low on the list of problems to deal with. However, their tunnels can mar the look of a finely manicured lawn and disturb the roots of new plants.
The best mode of control is quite nasty. It involves determining the location of the active tunnels by stamping down all those you can find to see which ones are repaired. Set a trap over the active tunnel, and the mole will trigger the device when it passes underneath. The trap springs and skewers the mole. There’s also a bait/poison available that resembles earthworms. Exercise extreme caution using these around children and pets, as they may mistake them for harmless creatures or candy.
Deer are not often thought of as pests, but the damage that they can do to a garden can be quick and devastating. They will browse on a wide range of landscape plants, from hydrangea to hostas. There are many products sold to deter deer, but the best that I have found is a sturdy, 8-foot-tall fence.
From State-by-State Gardening July/August 2007.