The Garden Patch: Arm yourself with knowledge to fight foes without fear

Well, we talk about a lot of things in this column, so this week let’s talk about something that affects all of us, but most of us know very little about … it’s called plant diseases. The gardener has to fight a never-ending battle against plant diseases or face serious plant losses. This is partly because diseases previously unknown in our area are introduced or new forms of the existing organisms develop.

The key to controlling garden plant diseases is the use of disease-resistant varieties of seeds and plants, crop rotation, or treatment with fungicides.

Your county agricultural agent will tell you about the more serious plant diseases in your area and how to control them. So, let’s highlight a few for your reference …

Leaf spots and scabs are diseases caused by fungi and appear as black or brown spots on leaves, stems and fruit. Leaf spot or black stem on some plants causes copper or chocolate-brown spots starting on the lower leaves which then turn yellow and die. On apples, a leaf spot and fruit spot called scab produces black spots on leaves resulting in defoliation of trees and black scabs on the apples which make them worthless. The fungi causing these spots are spread by wind and rain. Spraying with fungicides prevents apple scab, but these sprays cannot be used on other garden crops for economic reasons.

Smuts are diseases caused by fungi and produce swollen white to gray blisters or “boils” filled with black spores on leaves, stems and seeds of some plants. This also could affect your lawn grass.

Rust diseases are caused by unusual fungi that spend part of their lives on one host and part on another, producing orange or brown pustules on each host plant. If enough isn’t enough, the apple rust disease has the juniper tree as its alternate host. The apple rust disease is controlled by spraying the apples with fungicides.

Wilt diseases are evident when plants wilt in large areas of your garden during hot and dry periods caused by normal weather. When one plant turns yellow or wilts and the one next to it remains green and healthy – at least for a while – it usually indicates wilt disease. The wilt diseases may be caused by either fungi or bacteria. It’s important to determine which, so you will know how to control the disease.

Bacterial wilt is a destructive disease that starts as a white streak in the leaves followed by yellowing and death of the plants. It is spread by flea beetles which have the bacteria in their bodies – and when feeding on plants transmit the bacteria to them. Similar transmission of cucumber wilt by the cucumber beetle results in rapid wilting of cucumber plants. To control this pest, use resistant varieties of corn, cucumber, etc., or use insecticides.

Fungus wilts are known by their scientific names as Fusarium and Verticillium and are responsible for wilt diseases of many plants. The fungi can live for a number of years in the soil and cause a great deal of destruction to tomato, strawberry and many other vegetables. Because fungi can live in the soil, control of these wilt diseases calls for the use of resistant varieties of your produce or the use of crop rotation where other plants not susceptible (resistant varieties) to the wilt disease are planted for several years.

Fireblight is a bacterial disease that attacks apple and pear trees and many ornamental plants. The disease causes sudden wilting of twigs or large branches. Dead branches should be removed immediately. Make sure that you cut low enough to remove all the infected wood, otherwise the bacteria live to the next year in the cankered wood. In the spring, honeybees feed on the bacterial ooze coming from the cankers and then carry the bacteria to blossoms to start the disease cycle the following year. Use resistant varieties of fruit and ornamental trees.

What about weeds?

While we’re at it, are there damaging weeds, too? Yup! Read on …

Control measures for weeds include mowing before weeds go to seed, using herbicides to destroy them, and cultivating, plowing and reseeding with a desirable crop. Hundreds of weeds cause problems for your garden. Talk with your county agent about those that are most likely to cause you problems.

Sow thistle comes in several varieties all having strong roots that spread rapidly. They should be prevented from flowering my being cut back or destroyed. Their bright yellow flowers are similar to those of a dandelion.

Wild mustard is a common field weed with yellow flowers and stiff, hairy leaves. Sometimes the weed harbors cabbage maggots and aphids that later attack turnip, radish, cauliflower and cabbage crops.

Sheep sorrel is a tough weed with strong rootstocks. It is particularly vigorous in soils that are low in nitrates and are acid. The mature plant has spear-shaped leaves and a small stem. Leaves taste sour. The male flowers are yellow, and the female flowers (on different plants) are reddish-brown.

Quack grass is a widespread weed and is difficult to control because it grows from underground roots that live for several years. It spreads rapidly.

Canada thistle is a serious problem in many areas. The weed has deep, creeping roots and large colonies will grow from a single plant. Flowers are deep purple.

Burdock is a large weed with wide, coarse leaves and huge roots that may go a foot or more deep. The plant resembles rhubarb and stems may grow 4 or 5 feet high. It has purple flowers in bur-like groups.

Horse nettle is a tough-rooted perennial with fast-growing rootstocks. The plants are covered with hairy foliage and prickles on stems, leaves and flower stocks. Its flowers are white or violet (like potatoes). It is a distant cousin to the potato, incidently.

Wild carrot has leaves that resemble those of the cultivated carrot and it has a long taproot.

Plantain comes in several varieties and it infects lawns as well as gardens. Stems are short and upright with broad leaves and prominent veins. The leaf base is purple.

Foxtail comes in several common varieties all distinguished by dense spike like flowers. You know what it looks like!

Whoops! I’m over my allotted word count for the week! Till next time, have a good ‘un!

P.S. Much (most) of the material in today’s column comes from the Boy Scout merit badge booklet Plant Science. Thank you for reading!


stevehallerSteve Haller, of Osage City, a K-State Research and Extension Master Gardener, writes The Garden Patch, featuring gardening ideas and tips for gardeners in northeast Kansas. In his words: “I am not a horticulturist. By education I am an economist. By experience, I am a marketing guru from a local to an international scale. Gardening was taught to me by my grandfather and my Mom, and I’ve been doing it since World War II was going on.”

Steve can be contacted at [email protected], or leave questions or comments below.


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