Home Vegetable Gardening

A Complete & Practical Guide To The Planting & Care Of Vegetables, Fruits & Berries

Part Two: Vegetables — Chapter 13:
Insects and Diseases and Methods of Fighting Them

I use the term "methods of fighting" rather than the more usual one, "remedies," because by both experience and study I am more and more convinced that so long as the gardener — home or otherwise — who cares  to be neglectful and thus become a breeder of all sorts of plant pests,  is allowed to do so — just so long we can achieve no remedy worth the  name.

When speaking of a remedy in this connection we very frequently are putting the cart before the horse, and refer to some means of prevention. Prevention is not only the best, but often the only cure. This the gardener should always remember.


Early detection and treatment of pests and diseases means a healthier growing  environment. Pest management can be one of the greatest challenges to the home gardener. Yard pests include weeds,  insects, diseases, and some species of wildlife. Weeds are plants that are growing out of place.

Insect pests include an enormous number of species from tiny thrips, that are nearly invisible to the naked eye, to the large larvae of the tomato hornworm. Diseases are caused by fungi, bacteria, viruses, and other organisms, some of which are only now being classified.

Poor plant nutrition and misuse of pesticides also can cause injury to plants. Slugs, mites, and many species of wildlife such as rabbits, deer, and crows can be extremely destructive. Careful identification  of the problem is essential before control practices can be used.

Some  insect damage may appear to be a disease, especially if no visible insects  are present. Nutrient problems may also mimic diseases. Herbicide damage resulting from misapplication of chemicals also can be mistaken for other problems.

Insects and Mites

All insects have six legs, but other than that they are extremely variable. They include such organisms as beetles, flies, bees, ants, moths, and butterflies. Mites and spiders have eight legs — they are not insects. But for the purposes of this discussion, they will be considered as insects.

Finding a pest problem and then treating for that problem — such as spot spraying — is cost effective and limits any damage to non-targeted species. Insects damage plants in several ways. The most visible damage is chewed plant leaves and flowers. Many pests are visible and can be readily identified, including the Japanese beetle, Colorado potato beetle, and numerous species of caterpillars such as tent caterpillars and tomato hornworms.

Other chewing insects, however, such as cutworms (which are caterpillars) come out at night to eat, and burrow into the soil during the day. These are much harder to identify but should be considered if young plants seem to disappear overnight or are found cut off at ground level. Sucking  insects are extremely common and can be very damaging. These insects  insert their mouth parts into the plant tissues and suck out the plant juices.

They also may carry diseases that they spread from plant to plant as they move about the yard. You may suspect that these insects are present if you notice misshapen plant leaves or flower petals. Often the younger leaves will appear curled or puckered.

 Flowers developing from the buds may only partially develop. Look on the underside of the leaves as that is where many species tend to gather. Common sucking insects include leafhoppers,  aphids, mealy bugs, thrips and mites. Other insects cause damage by boring into  stems, fruits, and leaves. They may disrupt the plant's ability to transport water. They also create opportunities for disease organisms to attack the plants.

You may suspect the presence of boring insects if you see small accumulations of sawdust like material on plant stems or fruits. Common examples of boring insects include squash vine borers and corn borers.

Diseases

Plant disease identification is extremely difficult. In some cases, only laboratory analysis can conclusively identify diseases. Disease organisms injure plants in several ways. Some attack leaf surfaces and limit the plant's ability to carry on photosynthesis. Other organisms produce substances that clog plant tissues that transport water and nutrients.

Other disease organisms produce toxins that kill the plant or replace plant tissue with their own. Symptoms associated with plant diseases may include the presence of mushroom-like growths on trunks of trees; leaves with a grayish mildewy appearance; spots on leaves, flowers, and fruits; sudden wilting or death of a plant or branch; sap exuding from branches or trunks of trees; and stunted growth.

Misapplication of pesticides and nutrients, air pollutants, and other environmental conditions such as flooding and freezing can also mimic some disease problems.

Yellowing or reddening of leaves and stunted growth may indicate a nutritional problem. At first glance, blossom end rot of tomato, in which the bottom of the tomato turns black, might appear to be a disease caused by some pathogen. It's actually caused by the plant's inability to take up calcium quickly enough during periods of rapid growth.

Prevent this problem with adequate moisture — adding more calcium is of no benefit! Leaf curling or misshapen growth may be a result of herbicide application.

Pest Management Practices

Preventing pests should be your first goal. But it's unlikely you will be able to avoid all pest problems, since some plant seeds and disease organisms lay dormant in the soil for years.

Diseases need three elements to become established: the disease organism, a susceptible species, and the proper environmental conditions. Some disease organisms can live in the soil for years; other organisms are carried in infected plant material that falls to the ground. Some disease organisms are carried by insects. Good sanitation will help limit some  problems. Planting resistant varieties of plants prevents many diseases.

 Rotating annual crops in a garden also prevents some diseases. You will likely have the most opportunity to alter the environment in favor of the plant and not the disease. Healthy, garden plants have a higher resistance to pests. Plants that have adequate, but not excessive, nutrients are better able to resist attacks from both diseases and insects.

Excessive rates of nitrogen often result in extremely succulent vegetative growth and can make plants more susceptible to insect and disease problems, as well as decrease their winter hardiness. Proper watering and spacing of plants limits the spread of some diseases. Some disease species require free standing water in which to spread, while other species just need high humidity.

Proper spacing provides good aeration around plants. Trickle irrigation, where water is applied to the soil and not the plant leaves, may be helpful. Barriers may be effective to exclude some pests. Mulching is effective against weeds. Fences can limit damage from rabbits. Row covers may prevent insect damage on young vegetable plants. Netting can be applied to small fruit trees and berries to limit damage from birds.

Integrated Pest Management

It is difficult, if not impossible, to prevent all pest problems every year. If your best prevention efforts have not been entirely successful, you may need to use some control methods. Integrated Pest Management relies on several techniques to keep pests at acceptable population levels without excessive use of chemical controls. The basic principles of IPM include monitoring  (scouting), determining tolerable injury levels (thresholds), and applying  appropriate strategies and tactics.

Unlike other methods of pest control where pesticides are applied on a rigid schedule, IPM applies only those controls that are needed, when they are needed, to control pests that will cause more than a tolerable level of damage to the plant. Monitoring is essential for a successful IPM program. Check your plants regularly. Look for signs of damage from insects and diseases as well as indications of adequate fertility and moisture. Early identification of potential problems is essential.

There are thousands of insects in the garden, many of which are harmless or even beneficial. Proper identification is needed before control strategies can be adopted. It is important to recognize the different stages of insect development for several reasons. The caterpillar eating your plants may  be the larvae of the butterfly you were trying to attract. The small larvae with six spots on its back is probably the young of the  ladybug, a very beneficial insect.

Some control practices are most effective on young insects. Different stages may also be more damaging than others. It is not necessary to kill  every insect, weed, or disease organism to have a healthy garden. This is where the concept of thresholds comes in. The economic threshold is the point where the damage caused by the pest exceeds the cost of control. In a home garden, this can be difficult to determine.

What you are growing and how you intend to use it will determine how much damage you are willing to tolerate. Remember that larger plants, especially those close to harvest, can tolerate more damage than a tiny seedling. A few flea beetles on a radish seedling may warrant control whereas numerous Japanese beetles eating the leaves of beans close to harvest may not. If the threshold level for control has been exceeded, you may need to employ control strategies. Strategies can be discussed with the Cooperative Extension Service, garden centers, or nurseries.

Control Strategies — Mechanical/Physical Controls

Insects

Many insects can be removed by hand. This method is preferable if a few, large insects are causing the problem. Simply remove the insect from the plant and drop it into a container of soapy water or vegetable oil. Caution: some insects have spines or excrete oily substances that can cause injury to humans. Use caution when handling unfamiliar insects. Wear gloves or remove insects with tweezers. Many insects  can be removed from plants by spraying water from a hose or sprayer.  Small vacuums can be used to suck up insects.

Traps can be used  effectively for some insects. These come in a variety of styles depending on the insect to be caught. Many traps rely on the use of pheromones — naturally occurring chemicals produced by the insects and used to attract the opposite sex during mating. They are extremely specific for each species and, therefore, will not harm beneficial species. One caution with traps is that they may actually draw more insects into your garden. You should not place them directly in the garden. Other traps are more generic and will attract numerous species. These include such things as yellow and blue sticky cards. Different insects are attracted to different colors.

Sticky cards can also be used effectively to monitor insect pests.

Weeds

Hoeing, pulling, and mulching are the most effective physical control methods for weeds. Weeding is most important while plants are small. Well established plants can often tolerate competition from weeds.

Diseases

Removal of diseased material limits the spread of some diseases. Clean up litter dropped from diseased plants. Prune diseased branches on trees and shrubs. When pruning diseased plants, disinfect your pruners  between cuts with a solution of chlorine bleach to avoid spreading the disease from plant to plant. Control insects known to spread plant diseases.

Other pests

Fences, netting, and plant guards can be extremely successful in limiting damage from small mammals and birds. Numerous traps are also available to catch or kill some animals. Caution: In many states it is illegal to move wildlife, including squirrels. Traps may also catch animals other than the ones targeted. Check local regulations before trapping.

Diatomaceous earth, a powder-like dust made of tiny marine organisms called diatoms, can be used to reduce damage from soft-bodied insects and slugs. Spread this material on the soil — it's sharp and cuts or irritates these soft organisms. It is harmless to other organisms. Shallow dishes of beer can be used to trap slugs.

Biological Controls

Biological controls are nature's way of regulating populations. Biological controls rely on predators and parasites to keep organisms under control. Many of our present pest problems result from the loss of predator species.

Other biological controls include birds and bats that eat insects. A single bat can eat up to 600 mosquitoes an hour. Many bird species eat insect pests in the garden.

Bacillus thuringiensis (Bt) is a bacteria that specifically attacks larvae of some insect pests including white grubs in the lawn and Japanese beetles. This bacteria is harmless to desirable species.

Chemical Controls

When using chemical controls, be very careful with pesticides. Most common pesticides are broad spectrum in that they kill a wide variety of organisms. Spray applications of insecticides are likely to kill numerous beneficial insects as well as the pests. Herbicides applied to weed species may drift in the wind or vaporize in the heat of the day and injure non-targeted plants. Runoff of pesticides can pollute water. Many pesticides are toxic to humans as well as pets and small animals that may enter your yard.

Some common, non-toxic household substances are as effective as many more toxic compounds. A few drops of dishwashing detergent mixed with water and sprayed on plants is extremely effective in controlling many soft-bodied insects such as aphids and whiteflies. Crushed garlic mixed with water may control certain insects. A baking soda solution has been shown to help control some fungal diseases on roses.

When using pesticides, follow label directions carefully. Altering the rate of application or increasing the frequency of application can injure desirable plant and animal species.

IF You Decide that the best solution to your pest problem is chemical: By itself or, preferably, combined with non-chemical treatments be aware that one of the greatest causes of pesticide exposure to humans is the use of pesticides in and around the home. Anyone can buy a wide variety of off the shelf pesticide products to control weeds, unwanted insects, and other pests. No special training is required to use these pesticides. Yet many of the products can be hazardous to people, especially when stored, handled, applied, or disposed of improperly.

The results achieved by using chemical pesticides are generally temporary, and repeated treatments maybe required. Over time, some pests become pesticide-resistant, meaning they adapt to the chemical and are no longer harmed by it. This forces you to choose another product or method. If used incorrectly, home-use pesticide products can be poisonous to humans. As a result, it is extremely important for you to take responsibility for making sure that these products are used properly. The basic steps in reducing pesticide risks are:

• Choosing the right pesticide product.
• Reading the product label.
• Determining the right amount to purchase and use.
• Using the product safely and correctly.
• Storing and disposing of pesticides properly.

When you are ready to buy a pesticide product, follow these recommendations:

First, be certain that you have identified the problem correctly. Then, choose the least toxic pesticide that will achieve the results you want and be the least toxic to you and the environment.

When the words .broad-spectrum. appear on the label, this means the product is effective against a broad range of pests. If the label says selective, the product is effective against one or a few pests.

Find the signal word either Danger-Poison, Danger, Warning, or Caution on the pesticide label. The signal word tells you how poisonous the product is to humans. Pesticide products labeled Danger-Poison are Restricted Use and are mainly used under the supervision of a certified applicator. For the most part, these products should not be available for sale to the consumer.

Choose the form of pesticide (aerosol, dust, bait, or other) best suited to your target site and the pest you want to control.

Determining the Correct Amount To Use

Many products can be bought in a convenient ready-to-use form, such as in spray cans or spray bottles, that won't require any mixing. However, if you buy a product that has to be measured out or mixed with water, prepare only the amount of pesticide that you need for the area where you plan to use the pesticide (target area).

The label on a pesticide product contains much useful information, but there isn't always room to include examples of different dilutions for every home use. Thus, it is important to know how to measure volume and figure out the exact size of the area where you want to apply the pesticide. Determining the correct amount for your immediate use requires some careful calculations. Use the following example as an illustration of how to prepare only the amount of pesticide needed for your immediate pest control problem.

An example: The product label says, "For the control of aphids on tomatoes, mix 8 fluid ounces of pesticide into 1 gallon of water and spray until foliage is wet." You have only 6 tomato plants. From experience, you know that 1 gallon is too much, and that you really need only 1 quart of water to wet the leaves on these 6 plants. A quart is only 1/4 of a gallon. Because you want to use less water than the label says, you need less pesticide. You need only 1/4 of the pesticide amount listed on the label only 2 fluid ounces. This makes the same strength spray recommended by the label, and is the appropriate amount for the 6 tomato plants. In short, all you need to do is figure the amount of pesticide you need for the size of your target area, using good measurements and careful arithmetic.

Plant Enemies

Aphids: The small, soft green plant-lice. They seldom attack healthy growing plants in the field, but are hard to keep off under glass.

Asparagus-beetle: This pest will give little trouble on cleanly cultivated patches.

Black-Rot: This affects the cabbage group, preventing heading, by falling of the leaves. In clean, thoroughly limed soil, with proper rotations, it is not likely to appear.

Borers: This borer is a flattish, white grub, which penetrates the main stem of squash or other vines near the ground and seems to sap the strength of the plant, even when the vines have attained a length of ten feet or more. His presence is first made evident by the wilting of the leaves during the noonday heat.

Last season almost half the vines in one of my pieces were attacked after many of the squashes were large enough to eat. With a little practice I was able to locate the borer's exact position, shown by a spot in the stalk where the flesh was soft, and of a slightly different color. With a thin, sharp knife-blade the vines were carefully slit lengthwise on this spot, the borer extracted and killed and the vines in almost every instance speedily recovered. Another method is to root the vines by heaping moist earth over several of the leaf joints, when the vines have attained sufficient length.

Cabbage-caterpillar: This small green worm, which hatches upon the leaves and in the forming heads of cabbage and other vegetables of the cabbage group, comes from the eggs laid by the common white or yellow butterfly of early spring. Pick off all that are visible, The caterpillar  or worm of tomatoes is a large green voracious one.

Hand-picking is the only remedy.

Club-root: This is a parasitical disease attacking the cabbage group, especially in ground where these crops succeed each other. Lime both soil and seed-bed — at least the fall before planting, unless using a special agricultural lime. The crop infested is sometimes carried through by giving a special dressing of  quick-acting powerful fertilizer, and hilled high with moist earth, thus giving a special stimulation and encouraging the formation of new roots. While this does not in any way cure the disease, it helps the crop to withstand its attack. When planting again be sure to use crop rotation and to set plants not grown in infested soil.

Cucumber-beetle: This is the small, black-and-yellow-striped beetle which attacks cucumbers and other vines and, as it multiplies rapidly and does a great deal of damage before the results show, they must be attended to immediately upon appearance. The vine should be protected with screens until they crowd the frames, which should be put in place before the beetles put in an appearance.

Cucumber-wilt: This condition accompanies the presence of the striped beetle, although it is supposed to be  not directly caused by it.  The only remedy is to get rid of the beetles as above, and to collect and dispose of every wilted leaf or plant.

Cucumber-blight or Mildew is similar to that which attacks muskmelons, the leaves turning yellow, dying in spots and finally drying up altogether.

Cut-worm: The cut-worm is perhaps the most annoying of all garden pests. Others do more damage, but none is so exasperating. He works at night, attacks the strongest, healthiest plants, and is content simply to cut them off, seldom, apparently, eating much or carrying away any of the severed leaves or stems, although occasionally I have found such bits, especially small onion tops, dragged off and partly into the soil. In small gardens the quickest and best remedy is hand-picking. As the worms work at night they may be found with a flashlight; or very early in the morning. In daytime by digging about in the soil wherever a cut is found, and by careful search, they can almost invariably be discovered.

Flea-beetle: This small, black or striped hard-shelled mite attacks potatoes and young cabbage, radish and turnip plants.

Potato-beetle: The striped Colorado beetle, which invariably finds the potato patch, no matter how small or isolated. On small plots hand-picking of old bugs and destruction of eggs (which are laid on under  side of leaves) is quick and sure.

Root-maggot: This is a small white grub, often causing serious injury to radishes, onions and the cabbage group. Liming the soil and rotation are the best preventives.

Destroy all infested plants, being sure to get the maggots when pulling them up.

Squash-bug: This is the large, black, flat "stink-bug," so destructive of squash and the other running vines. Protection with frames, or hand-picking, are the best home garden remedies. The old bugs may be trapped under boards and by early vines. The young bugs, or "sap-sucking nymphs," are the ones that do the real damage.

White-Fly: This is the most troublesome under glass, but occasionally is troublesome on plants and tomato and cucumber vines. The young are scab-like insects and do the real damage.

White-grub or Muck-worm: When the roots of single plants are attacked, dig out, destroy the grubs and, f the plant is not too much injured, reset.

Precautions

So much for what we can do in actual hand-to-hand, or rather hand-to-mouth, conflict with the enemy. Very few remedies have ever proved entirely successful, especially on crops covering any considerable area. It will be far better, far easier and far more effective to use the following means of precaution against plant pest ravages:

First, aim to have soil, food and plants that will produce a rapid, robust growth without check. Such plants are seldom attacked by any plant disease, and the foliage does not seem to be so tempting to eating-insects; besides which, of course, the plants are much better able to withstand their attack if they do come.

Second, give clean, frequent culture and keep the soil busy. Do not have old weeds and refuse lying around for insects and eggs to be sheltered by. Dispose of all leaves, stems and other refuse from plants that have been diseased. Do not let  the ground lie idle, but by continuous cropping keep the bugs, caterpillars and eggs constantly rooted out and exposed to their natural enemies.

Third, practice crop rotation. This is of special importance where any root disease is developed. Fourth, watch closely and constantly for the first appearance of trouble. The old adages "eternal vigilance is the price of peace," and "a stitch in time saves nine," are nowhere more applicable than to this matter. And last, and of extreme importance, be prepared to act at once. Do not give the enemy an hour's rest after his presence is discovered. In almost every case it is only by having time to multiply, that damage amounting to anything will be done.

	Table of Contents Part One 1) Introduction 2) Why You Should Garden 3) Requisites Of The Home Vegetable Garden 4) The Planting Plan 5) Implements And Their Uses 6) Manures, Fertilizers And Mulching 7) The Soil And Its Preparation   Part  Two — Vegetables 8) Starting The Plants 9) Sowing And Planting 10) The Cultivation Of Vegetables 11) The Vegetables And Their Special Needs 12) Best Varieties Of The Garden Vegetables 13) Insects And Disease, And Methods Of Fighting Them 14) Harvesting And Storing   Part  Three — Fruits 15) The Varieties Of Pome And Stone Fruits 16) Planting; Cultivation; Filler Crops 17) Pruning, Spraying, Harvesting 18) Berries And Small Fruits 19) A Calendar Of Operations 20) Conclusion

Go To:  Part 2-14: Harvesting And Storing
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