Soap has been used as an insecticide for many years by home gardeners. In the past, the origin of these soaps varied considerably, and in some cases, resulted in plant injury.

In the 1970s, a major breakthrough occurred when scientists unraveled the insecticidal properties of certain naturally occurring plant oils and animal fats. These natural compounds are known as "fatty acids."

Fatty acids play important roles as basic energy sources for living organisms and are major components of cell membranes. Before utilizing the benefits of these fatty acids from the hundreds found in nature, researchers had to find those that would not harm the plant. In the mid-1980s, this task was completed, and there are now formulations available for pest control. Common insecticidal soaps found on the market are normally prepared from natural human food items, such as milk and peanut oil.

The soap itself actually consists of approximately 50 percent potassium (K) salts of fatty acids and is formulated by treating selected acids with a potassium base. The inert ingredients are water and alcohol, which aids in the mixing of the soap concentrate. Most insecticidal soaps do not contain any organic solvents or dangerous inerts.

Insecticidal soaps are considered biodegradable and are exempt from residue tolerance by the EPA.

Because soaps are formulated from specific fatty acids, they are relatively selective against pest insects and usually are not lethal to beneficial insects. Their special formulations reduce their phyto-toxicity, or ability to damage plants. Homemade soap sprays may damage or kill plants at the same time they reduce the insect pests.

Soaps are considered a contact insecticide, and the insect or mite pest must receive a direct application of the spray to be effective. Soaps are only effective in the liquid state, and there should be no insecticidal activity present once the material has dried on the application surface.

Insecticidal soaps differ from conventional insecticides in that the latter specify the amount of active ingredients per acre or per 100 gallons of water. With insecticidal soaps, the relative concentration of the soap in the spray solution is important. Follow label directions for the concentration necessary to control the pest and to thoroughly cover the foliage.

At this time of year, don't be quick to jump to the conclusion that all damage that looks like chemical damage is caused by herbicides and other growth regulators. What looks like chemical injury could actually be leafhopper damage.

Leafhoppers are summer-feeding insects. While preferring to feed on alfalfa and potatoes, they also feed on ornamental trees such as redbud (Cercis), crabapple (Malus), birch (Betula), ash (Fraxinus), and some maples (Acer). Redbuds and red maples seem to be the most susceptible while sugar and silver maples seem somewhat resistant.

Even roses and sunflowers can be infested.

Most herbicide injury, especially involving 2,4-D and dicamba products, usually shows up within days of an application. Damage from these products usually shows up in May and early June when the products are used the most by homeowners.

Leafhopper injury usually shows up in July and August when the insects are most active.

Leafhopper adults and nymphs have piercing and sucking mouthparts and feed on the plant tissue, injecting a toxic substance in the tissue. The result is the cupping and curling of new plant tissue on redbuds or browning and a downward turn to the leaf edges on maples. If you closely look at the leaves, you'll see a stippling or yellow spotting of the tissue that somewhat looks like spider mite damage on other plants.

Homeowners get frustrated when they can't find the leafhoppers. These insects are nocturnal feeders; you need to be out in the dead of night with a flashlight in order to find them. Homeowners might be able to find white shell-like casings on the underside of the leaves that indicate the leafhoppers have molted.

On top of that, they are only 1/16 inch large and somewhat a clear, pale green, feeding on the underside of the leaves and at the tips of new growth. It's the feeding on new tissue that gives the leaves the herbicide-injury look. Leafhoppers may produce five or more generations per year, but they don't overwinter in Illinois; instead, they are blown up on spring wind currents.

By the time the damage is seen, it's really too late to control the leafhoppers. The good news is that the damage is essentially aesthetic. University of Illinois Extension does not recommend any control other than maintaining the overall health of the plant.

If you enjoy perennial gardening, check out the new U of I Extension website, Stepping Stones to Perennial Garden Design. Developed by horticulture educator Martha Smith, the site includes information on site assessment, bed preparation and maintenance, and perennial selection and placement in the garden.

A special feature is a garden design with a plant list in the Perennial Placement section.

Visit the website at http://web.extension.uiuc.edu/gardendesign.

Recently, a client asked what factors, besides variety, contribute to the flavor of tomatoes. This is a question you may get asked in your role as a Master Gardener.

For the most part, flavor is in the variety and respective genetics. There are incredible differences in tomato flavor. The best are those which have a high level of acids, coupled with a high level of sugar. Very few reach this "high" balance, but two that come to mind are German Cherry and Brandywine. The "Russian" cultivar that was offered this year by some garden centers also has reported good flavor.

Varieties have different sugar/acid ratios, and only by trial and testing them will you find one you like. Often, the heirloom varieties are well-flavored; that's why people grow them.

Growing factors that affect flavor the most are over-fertilization and water stress. Diseases can also kill foliage, and large amounts of lost foliage will decrease flavor and increase sunburning. In addition, magnesium is an important element for tomatoes that is often overlooked. A small amount of Epsom salts (less than 1 teaspoon per plant) applied to soils can help replace this element when deficient. Of course, a soil test will help determine this deficiency.

Be sure to keep soils uniformly moist, and avoid too much fertilizer (high nitrogen) after fruit set. That being said, tomatoes do require significant fertilization.

Organic practices which utilize "slower" fertilizers (compost, blood meal, manures) may provide a less-rapidly available nitrogen source compared to chemical fertilizers, and this may improve the flavor in the organic system. Organic options also provide more consistent nitrogen release through the season. The downside is that often these organic fertilizers do not provide enough nitrogen, and nutritionally-stressed plants (lack of nitrogen) can adversely affect flavor.

One last suggestion is to pick tomatoes when they are ripe on the plant–there is a difference between maturity and ripening. A tomato can be mature but not ripe, and still be harvested. For the commercial grocery trade, they are harvested this way, at a slight color change that eventually turns red during transport and on the shelf. Home gardeners have the advantage of being able to allow fruit to mature and ripen on the vine, which maximizes flavor of any variety.

Keep in mind that if you leave a tomato too long, acids will go down as it softens. So, catching the peak period of sugar/acid ratio at harvest takes a little practice, and the best timing can vary by variety/type.

Watermelons are easy to grow, and home gardeners often get a high-yielding crop. But for many people, it's not so easy to tell when a melon is ripe.

Watermelons have a few tell-tale signs to help determine their ripeness. Unfortunately, the common "thumping" of the melon isn't always a good indicator. A better way is to look for a combination of these signs:

·Curly tendrils on the stem near the point of attachment are brown and dry.

·Surface color of the fruit is dull.

·The skin becomes resistant to penetration by the thumbnail and is rough to the touch.

·The bottom of the melon (where it lies on the soil) turns from light green to a yellowish color. A watermelon isn't quite ripe if the underside is white or pale green.

Store an un-cut watermelon at room temperature. Before cutting, wash the surface with cool, running water. Once cut, watermelons are highly perishable and must be stored in the refrigerator.

Getting the most out of your flower garden isn't hard as long as you follow a few simple steps.

Flowers require 1 inch of water per week during the summer months. When temperatures approach 100 degrees, it may be necessary to supply 2 inches–split into two applications, three days apart. Water slowly to make sure water is absorbed into the soil instead of running off.

Roses are heavy drinkers and may require 2 to 3 inches of water per week. Plants that are fertilized regularly will demand more water.

A drip irrigation or soak hose may be the best bet to place water where it's needed. These types of hoses need to be kept on for at least 8 hours to provide plants with an inch of water.

To cut down on diseases, avoid night watering and overhead watering with sprinklers or hoses. Water on flowers can increase diseases such as botrytis and gray mold. Overhead watering also increases foliage diseases like leaf spots, black spots, and leaf blights.

If overhead watering is the only option, water early in the day, preferably between 6 and 9 a.m. Water is less likely to remain for any length of time on flowers and foliage, thus reducing the chance of diseases. Early morning watering also limits evaporation.

A 4- to 6-inch organic mulch will minimize soil water loss, keep the soil cooler, and limit weeds and diseases. But avoid excess mulch since it limits air-water movement and can lead to rots.

Many annuals benefit from a mid-summer pinching or pruning, particularly petunias and ageratum. Plants are cut back by a third to half in order to stimulate new growth. Pinching will also reduce plant legginess, which is common in petunias.

Finally, annuals can benefit from a mid-summer fertilizing with an all-purpose garden fertilizer such as 10-10-10. The ideal time to fertilize is after pinching or pruning. Water-soluble fertilizers are more likely to provide immediate benefits to the plants. Fertilize at the rate of 1/2 pound actual nitrogen per 1000 square feet. With a 10-10-10 fertilizer,this works out to 5 pounds per 1000 square feet. After the application, water thoroughly.