Plant Diseases - Avoidance

Using resistant plants and varieties is very effective. With some plant problems, the easiest way to avoid the insect, disease or environmental stress is to simply plant another kind of plant. For example, the oak wilt disease has devastated the Texas Hill Country, and chemical and cultural controls are expensive and not always effective. Perhaps the most effective management strategy for property owners is to not plant susceptible oak species (i.e., live oak and Texas red oak). Planting resistant species of oaks (i.e., burr oak) and non-oaks species (i.e., cedar elm) may guarantee the future tree population in the Hill Country.

In the vegetable garden and fruit orchard, the availability of pest resistant varieties is much greater than in the landscape. Resistance to specific insects is available in certain vegetable varieties (i.e., Jewel sweet potato: resistance to flea beetles and wireworms). Tomato varieties have been available for years which are resistant to fungal wilts and nematodes (i.e., VFN resistance). And in fruit, some pear varieties have been identified which are fireblight resistant. Before planting any landscape plant or crop, check to see if there are pest resistant varieties; if not, perhaps choosing another type of plant may be warranted.

Regarding avoiding environmental stresses, great care must be taken to choose landscape plants and crops which are adapted to the environmental conditions of the area. This includes adaptability to soil type and condition, winter and summer temperatures, light intensity, and natural rainfall.

Remove Plant Debris - Removing plant debris, which may be diseased or insect­infested, at the end of the season can effectively reduce future disease presence and insect populations. The debris should be destroyed either by burning or burying, or at least removed from the site. Composting old, diseased plant debris should kill any surviving pathogens; however, if the compost is not turned properly, disease inoculum may build up.

Remove Infected or Infested Plants - Removing infected or infested plants is closely related to the above practice. Plants infected with disease should be removed immediately to prevent spreading of the disease to healthy plants. Insect infested plants may best be removed for difficult to control insects, such as leaf miners in tomato.

Pruning of infected, infested or stressed parts of plants can also be an effective means to manage plant problems. Pruning out fireblight infected branches of a pear tree can prevent spread of the disease further in the tree. The prompt removing leaf miner infested leaves on tomato can reduce the long term damage to the crop. Finally, landscape plants showing signs of transplant shock or drought stress can sometimes be pruned back to reduce the stress and allow the root system to expand to meet the water demands of the plant.

Control Weeds - Controlling weeds is closely related to the above two practices. Although weeds may harbor beneficial insects, they also harbor insect pests and diseases. In addition, they can compete against health crops and landscape plants, thus creating environmental stresses. This phenomenon is seen quite often when young landscape trees are "choked out 'by weeds.

Improve Your Soil - Improving the soil is a time tested cultural practice which is reduces environmental stresses and decreases soil-borne diseases due to enhanced drainage. This is especially the case when raised beds are used in the garden for vegetables, flowers, shrubs and fruit crops. In general, good soil produces healthy plants which are more resistant to insects, diseases and environmental stresses.

Companion Planting - Companion planting is the orderly mixing of crop plants aimed at controlling insect populations. Many claims have been made about the ability of certain plants to protect other plants from insect damage. However, few scientific studies are available to prove the value of companion planting.

Fertilization - Proper fertilizing can eliminate environmental stresses related to plant nutrition. Chlorosis, and subsequent neucrosis (i.e., dead tissue), can be avoided by fertilizing with iron products. Much like soil improvement, proper fertilizing can create a healthier plant, more capable of resisting the pest and environmental pressures.

Mulching - Using mulches can reduces plant disease by preventing splashing of inoculurn from the soil onto the plant. This is the case with periwinkles and soil-borne, aerial phytophthora. Mulching also enhances the overall health of most plants, thus reducing their susceptibility to pests and environmental stresses.

Water Sprays - Using high pressure water spray directed at the undersurface of the leaves can be effective in dislodging small insect pests, such as aphids and spider mites. Care must be taken not to harm the plant or to distribute pests around the garden. Repeated treatments are usually necessary to keep pest numbers low.

Watering - Proper watering is probably the most important cultural practice in preventing environmental stress in the landscape and garden. It seems gardeners, amateur and professional, kill more plants through over or under watering than any pest ever killed. Proper watering must take into account the plant needs and the soil environment. An astute gardener's eye is required to irrigate properly without over or under watering.

With regard to disease control, it is important to note that overhead watering often helps disease occur and spread more rapidly. Try not to get irrigation water on the plant leaves. If this is not possible, irrigate in the morning hours, so that the sun will rapidly evaporate the excess water from the leaf surfaces.

Natural Enemies

Conserving and enhancing natural enemy populations is the first line of defense against insect pests. Referred to as biological control, this strategy can be defined as the direct or indirect use of parasites, predators or pathogens (bacteria, viruses, fungi, protozoans) to hold insect pest populations at low levels and to avoid economic losses. Biological control methods fall into three categories:

Introduction of natural enemies which are not native to the area (these enemies must then establish and perpetuate themselves).

Enlarging existing populations of natural enemies by collecting, rearing and releasing them back into the environment.

Conservation of beneficial organisms through the judicious use of pesticides and the maintenance of alternate host insects so that parasites and predators can continue to develop.

Many beneficial organisms occur naturally around the home, but often they are not numerous enough to control a pest before it inflicts severe damage. In fact, parasites and predators appear to be most effective when a pest population has stabilized or is relatively low. Their influence on an increasing pest population is usually minimal since any increase in parasite and predator numbers depends on an even greater increase in pest numbers. When pest populations are large, pathogens seem to be most effective. Consequently, the nature of the host insect-natural enemy relationship makes it impossible to have an insect-free environment and at the same time maintain sizable populations of beneficial insects.

Praying Mantis. Egg cases containing about 200 individual eggs are available from a number of sources. However, the mantis is cannibalistic immediately after hatching, so few nymphs survive the first week of life. The mantis is a voracious predator, but it is a poor searcher for food and usually waits for prey to come to it. This greatly influences the kinds of insects it captures and kills. Food preferences include grasshoppers, crickets, bees, wasps and flies.

Lady Beetles. Adult beetles are available from several sources. Aphids are the preferred hosts, but lady beetles will eat mealybugs, spider mites and certain other soft-bodied pests and eggs; however, they do not kill grubs, caterpillars and other beetles. Unless an ample supply of live aphids or other hosts are available at the release point, lady beetles will disperse and leave the area.

(Dipel, Thuricide, Biological Worm Killer). This bacterial insecticide provides effective control of the larvae of several moths and butterflies. The bacterial spores are harmless to warm-blooded animals and beneficial insects.