Managing garden pests

Methods to control weeds, bugs, and diseases
Photo 1
Miniature and mini-micro roses, such as this one, are susceptible to a number of plant diseases, although less so than hybridized tea roses.
Don Parker
Photo 2
Mulch, such as the coarse sawdust in this farmyard, can help reduce weed seeds from sprouting.
Don Parker
Photo 3
Powdery mildew on these Missouri, or evening, primrose plants can disfigure and stunt them.
Don Parker
Photo 4
Black gall, due to the cedar-quince rust fungus, can form on Washington hawthorn trees. Here it is growing on one of the author’s miniaturized (bonsaied) trees.
Don Parker
Photo 5
Praying mantis insects can benefit a garden by preying on harmful insects. In spite of their formidable looks, they are not harmful to humans.
Don Parker
Photo 6
A wasp is making a nest inside one of the author’s buildings. They are best dealt with when the nest is small and has fewer wasps.
Don Parker
Photo 7
This mugo pine is dying from the top down due to suffocation of its roots.
Don Parker
Photo 8
Chipmunks have dug under the roadbed, causing it to collapse into their tunnel.
Don Parker
Photo 9
Lumber in the author’s sawmill shed has been rearranged by the chipmunks.
Don Parker
Plants bring life to the garden railroad like no artificial greenery can. Some of that life can come in the form of unwanted visitors and invaders to the garden, varying from the microscopic (such as fungal diseases) to as large as your neighbor’s dog. I’ll not deal with the latter in this column, leaving you to settle that with your neighbor. What I will cover are the more common problems of garden plants that I’ve encountered. Some plants are more susceptible to pest attacks than others, such as roses (photo 1). Choosing plants that are resistant to diseases is the first step to avoiding problems. When faced with a pest problem it is wise to follow Integrated Pest Management (IPM) principles that begin with the least toxic and most natural remedies and progress to more drastic measures to manage persistent plant problems.


Weeds not only spoil the looks of landscape plantings but compete with desirable plants for space and nutrients. Removing weeds soon after they appear will prevent self-seeding or spreading by roots and rhizomes. Weeding is easier after a rain. Hand digging is still the best control; avoid weed-killers that can damage or kill desirable plants. Tackle the job slowly, and take breaks to rest weary parts or do something else for a while.

The best way to control weeds is by prevention. Healthy groundcover plants will shade the soil and prevent seeds from germinating. In areas of exposed soil, mulch will accomplish the same thing (photo 2). Parts of my railroad have accumulated an abundance of crab-grass seeds over the years and I find an application of a pre-emergent control in problem areas helps reduce the number of weed seeds that germinate. A common brand of a pre-emergent product is Preen. This needs to be applied in early to mid spring, by scratching the granules into the soil or gravel ballast and watering well. I reserve non-selective herbicides, such as RoundUp, for obstinate weeds at the edge of the garden or in gravel paths.

Microscopic invaders

Diseases can affect all parts of the plant. Root rot is produced by a fungal disease that attacks roots that have been suffocated by too much water, often in wet winters. Plants that originate in dry climates are especially susceptible (such as artemisia, thyme, lavender, rosemary, salvia, etc).

Fungal diseases of foliage are more likely to occur when leaves are wet for prolonged periods and there is inadequate ventilation (as when planted too close together). A common fungus that attacks leaves is powdery mildew (photo 3). Prevention involves avoiding overhead watering in the evening, when plants cannot dry off quickly, and keeping space for air circulation between susceptible plants. Remove all the infected plant parts and destroy them, as the disease can still be spread by the wind. Infected plants can also be sprayed with fungicides, including sulfur, lime-sulfur, neem oil, and potassium bicarbonate.

A less common fungal disease that appears on my bonsaied Washington hawthorn trees is black knot (photo 4). This disfigures the tree but doesn’t typically kill it. Cutting off the twig or branch with the knot will reduce, but not completely eliminate, the pathogen.

Bacterial diseases

Bacteria cause plant diseases less commonly than fungi, but they can be devastating. Fire blight is one that occurs in roses, including the miniature variety used in railroad gardens. The bacteria invade and spread through the whole plant, causing blackening of leaves and wilting of the plant. It can be controlled, if caught early, by cutting away and discarding the affected part of the plant.

Insects, the bad and the good

Harmful insects can attack stems, leaves, and flowers of plants. The most common attacker in the Midwest is the Japanese beetle, which is particularly fond of roses. The beetles can be knocked off of leaves into a container of water and a little dish soap, best done in the morning and evening when they are less active. A last resort is insecticidal sprays, which are indiscriminate and can also kill beneficial insects that you want on your side.

Other invaders I’ve had to deal with include aphids, spider mites, web worms, bag worms, and pine sawfly caterpillars. Aphids and spider mites are controlled or killed by insecticidal soaps; web worms by mechanically breaking their web and spraying a Bt product (a beneficial microscopic worm that attacks caterpillars); bag worm nests can be removed by hand or sprayed with agents containing Permethrin, an indiscriminate insecticide; pine sawfly larvae can be killed with insecticidal soap, neem oil, or Permethrin.

There are a number of beneficial insects that aid the gardener by going after the bad actors. The giant in this category is the praying mantis (photo 5), which preys on anything it can get its formidable claws on, mostly harmful insects. Green lacewing larvae and beneficial nematodes are two of the smaller good guys. The most familiar helpers are lady beetles, whose larvae feast on aphids. Aphids suck plant juices from leaves, disfiguring them and eventually leading to plant decline or death. Therefore, the plea: use indiscriminate insecticides with caution and in limited areas.

Another category is both good and problematic: wasps and their ilk (photo 6). Technically beneficial, wasps can become quite disagreeable when their nests are disturbed. Use a Permethrin-based spray and approach the nest in the evening when the wasps are resting—and use common sense and caution.

Other plant diseases

There is a whole category of plant problems not caused by invaders, but by carelessness or misplaced good intentions of the gardener. One that I am not happy about is a nice mugo pine that I lost because the soil in the site was unstable and slowly sank with the shrub over several years, burying its roots and lower trunk until it was suffocated (photo 7). This can also occur if a shrub is initially planted too deeply. Although done with the best intentions, overwatering can kill plants. Allowing RoundUp spray to drift onto desirable plants is another common cause of careless harm.

Warm-blooded pests

There are some birds and animals that can raise havoc in a railroad garden and complicate the gardener’s life. When a prolonged effort to get rid of the nuisance is constantly frustrated, it can reach a point of hair-pulling ire.

My current nemesis is a family of chipmunks. To support my case, I present photographic evidence of their mischief (photos 8 and 9). In addition, they have piled dirt on my tracks when digging their holes, have undermined plants, and have chewed through drip-irrigation tubing. I’ve tried plugging their holes with rocks (they dig around them) and putting moth balls in their holes (they cover that up or dig elsewhere). I’ve thought about getting a cat but I’m afraid the chasing and pouncing would cause even more damage. As a last resort, I’ve tried rat poison. The field-mouse population has dwindled but the chipmunks continue to hang on. I’m beginning to think it would be easier to have to deal with my neighbor’s dog.
Further reading

Pest management: Miniscaping, April 2006
Home remedies and natural pest control: Pathways, December 2006
Invasion of the garden pests: Pathways, June 2004


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