In The Garden: Grow Defensively
In a time when we all seek advice from experts, it is not only important to know what plants you have, but also to understand the nomenclature of symptoms caused by insect and disease problems. “I’ve got this thing on my wachamacallit” won’t get you very far with a Google search or in person. We need to know how to describe the “things” that we find on our plant material so a proper diagnosis and treatment can follow.
There are several scenarios that can threaten our gardens. Non-living, non-infectious diseases or “disorders” are linked to environmental circumstances. A late spring freeze, flood or drought conditions, or excessive heat are all factors in causing non-infectious disorders that affect plant material adversely. These types of disorders can lead to infectious disease or insect infestation. Plant pathogens must be able to “enter” the plant, and non-living diseases often open the plant up to living diseases. This is why we always prune away dead, diseased or injured wood, especially trees. Do not make it easier for infectious diseases to live off your landscape plants.
Living, or infectious, diseases involve parasitic plants, bacteria, fungi, viruses or nematodes. For example, white pine decline and white pine root decline (take note of the difference): White pine decline is a non-living, non-infectious disorder caused by environmental circumstances that weaken the tree and cause eventual death. On the other hand, white pine root decline is a living, infectious disease caused by nematodes in the soil that slowly attack the root system. You will notice a white film at the base of the pine’s trunk when it is suffering from white pine root decline. In the first circumstance, you could replace the diseased white pine, however, in the latter circumstance the soil is infected so it is likely that a second white pine in the same location would experience the same gradual decline and eventual death. It’s nuanced.
Plant disease and pest diagnosticians at Purdue University define the following common symptoms that plague our garden plants. Recognizing these as symptoms of a greater problem will help us stop the spread of infectious diseases and treat our plants in a timely fashion:
Leaf spots are small discolored areas on the plant’s foliage. Rosarians are quite familiar with leaf spot on their roses.
Blight causes larger dead areas on leaves, shoots or flowers of a plant.
Stunting is the abnormally small growth of a plant or plant part.
Chlorosis is when normally green tissues appear yellowish-green in color.
Marginal necrosis is a symptom where the edges, or margins, of a plant’s leaves turn brown due to dead tissue. Houseplants suffer from this during the winter months due to the low humidity in our homes.
Distortion is the twisting or abnormal formation of leaves and new shoots. Aphids, mites and thrips cause this to happen to new leafy growth if a plant is infected.
Wilt, of course, is the flaccid, limp condition of leaves or non-woody shoots. Wilt generally occurs from insufficient water, but can also be brought on by too much water or living diseases. The dreaded clematis wilt is caused by nematodes. While wilt in the vegetable garden is frequently caused by insects. When a squash plants suddenly wilts, it is caused by the squash vine borer; cucumber wilt is caused by the stripped or spotted cucumber beetle transmitting a viral infection, the beetle is the vector of the infectious disease!
Cankers are localized, often sunken, dead areas on a twig branch or stem.
Gall is an abnormal swelling of a portion of a branch, root or bud (caused by certain species of wasps that lay their eggs in plant tissue).
And witches’ broom is the symptom where twig growth appears distorted and stunted, forming a broom-like mass of twigs. Once witches’ broom has appeared the plant should be “shovel-pruned.” That’s right: Dig it up and throw it out because witches’ broom is caused by a fungus that has no known control and it will spread to other susceptible plants. Tomato plants can show signs of this type of distortion and when they do I immediately remove them from the garden. Do not harbor disease pathogens in the garden no matter how much you love that tomato
As various, and sometimes inevitable, plant problems present themselves during the new growing season these terms should help us describe, determine and treat what crosses our garden path. Sometimes the easiest thing to do in the vegetable garden is picking a Colorado potato beetle from the foliage and dropping it into a bucket filled with water and a dash of dish soap. I control squash bugs (not the same as squash vine borers that take shape as a wasp in their adult form) by simply laying a board next to the squash plants. The bugs migrate under the board at night so in the morning I just walk on the board to squash the squash bugs.
The garden is a complex, living ecosystem so when a problem presents itself do not assume that one product or another is going to “kill” the problem. Often our gardening habits can be all the answer there is: Keep weed competition down, use mulching materials to prevent soil-borne disease from splashing onto plants like tomatoes; locate plants that like sun in sun and shade-loving plants in shade! Promote good air circulation; scout for pest problems (insect and disease) regularly and remove them from the garden when detected.
Do everything you can to promote soil health: Do not compact the soil with heavy equipment; add composted material to annual planting beds like the vegetable garden and avoid synthetic, fossil-fuel-based fertilizers. In essence, try to mimic nature as closely as you can in order to nurture it.
This is the only insecticide I use in the vegetable garden. Spinosad is a naturally occurring soil bacterium. The story behind the discovery of Spinosad is funny: A scientist on vacation in the Caribbean took a soil sample from an abandoned rum factory floor and discovered a fermented soil bacterium (which has never been found anywhere else since). He recognized it as a new species that he named Saccharopoly spora, now referred to as Spinosad. If a caterpillar ingests Spinosad it overstimulates the nervous system, resulting in death. Spinosad and other botanical and biological insecticides like neem oil, Bacillus thuringiensis (Bt) and pyrethrin have minimal impact on beneficial insects like bees, earthworms, lady bugs and hover flies. And Spinosad seems to be the most effective against cabbage loppers eating my kale and flea beetles tackling my arugula.