Weeds, Pests, and Disease

June 3, 2021

Weeds, Pests, and Disease

Spotted Horsemint is a great pollinator attractor, but in the wrong place it might be a weed.

Laura Lee Rose

Horticulture Agent


Pests in the garden are certainly problems.  Weeds are wildflowers in the wrong place, according to some, but they have adapted over the centuries to adversity and poor soil.  In rich garden soil they can thrive!  At best, they compete with your fancy posies for space, water, and nutrients.  Hand weeding is effective for some weeds, while blow torches or land mines would hardly phase others.  I like to take an integrated approach to weeding.  It is best if you can remove all parts of the weed, if possible before it has a chance to go to seed.  However, some of the little darlings have roots, bulbs, and rhizomes that go to the South Pole.  A very thick layer of mulch may be helpful.  If you are using a non-selective herbicide, always protect other plants with some kind of barrier, don’t spray if there is any breeze at all, and always follow the directions for use on the label.

Other pests which attack gardens and ornamental plants may be animals- including insects, mammals, and arthropods.  While attracting wildlife is a goal of many gardeners, there are some types of wildlife that can do definite harm to plants and those we would rather discourage.  A small population of aphids can be controlled by soapy water spray, beneficial insects, or birds.  By providing water and cover near the garden, many harmful soft-bodied insects, mites, and caterpillars will be eaten by birds.  Beneficial insects like ladybugs and assassin bugs also prey on many thousands of injurious bugs, larvae, and eggs.  When using pruning tools at the right time, we remove heavy infestations and protect crops safely.

Finally, diseases are a problem for plants that are stressed.  Environmental stress such as too much or too little water, compacted poor soils, sun/shade tolerance, or extreme temperatures can foster plant disease.  The plant disease triangle has three components.  First, there must be a disease present in sufficient quantity to cause disease.  Second, there must be a susceptible host present, and the third requirement is a favorable environment.  Fungal diseases can be spread in moist and wet soils and on leaf surfaces.  Wounds on stems or other plant parts can offer an entryway for spores, bacteria, and viruses to enter the plant’s tissues.  Insects may also vector diseases with their mouthparts as they feed on plants or pierce the stems and twigs to lay their eggs.

Healthy plants are more likely to resist insects and diseases.  Be sure what the problem is before spraying an affected plant.  Ask yourself, “Am I sure this is an insect problem, a fungus, or whatever?”  If you aren’t sure, ask an expert, get out your magnifying glass, but don’t assume.  Remove infected parts, clean up the mulch underneath. Using clean, sharp tools is essential; plant problems can be spread by poor sanitation.  You wouldn’t like it if your surgeon cut on you without washing his or her hands or used a knife that wasn’t sterile.

Clemson Home and Garden Information Center has great fact sheets on plant pests and diseases.  You can also bring in samples of plant problems to one of the Clemson Extension Service Centers with a check for $20 for analysis and recommendations for control.

Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, gender, religion, national origin, disability, political beliefs, sexual orientation, gender identity, marital or family status and is an equal opportunity employer


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