Quality fruit, similar to what is available in the supermarket, cannot easily be grown without pesticides. If you do not wish to use pesticides, you can employ many other tactics to reduce pest numbers in your fruit plantings. These are discussed in detail in the following sections. You should be aware, however, of the possibility that you will lose a significant portion of your crop to insects and disease.
A pest is any organism that compromises the production and/or quality of the crop being grown. For the purpose of this manual, we are referring to organisms that harm fruit crops by directly injuring either the fruit or the leaves. Pests might not seem to cause appreciable damage to plants, but they might weaken the plant and reduce its ability to survive. Many backyard fruit producers have lost fruit trees to "winter injury," when in fact the real cause was the general weakening of the plant from pest assault. Pests generally are classified as either insects, diseases, weeds, nematodes, or vertebrates (rodents or deer, for example), and will be discussed in this manual. For example, Controlling Wildlife Damage in the Home Fruit Garden deals specifically with controlling fruit damage caused by wildlife.
The first step in managing pests is careful observation. Develop a habit of observing your plants regularly, and daily if possible. Look at the blossoms, fruit, upper and lower surfaces of the leaves, new shoot growth, and general color and angle of the leaves. Also be aware that if you see changes in the plant, they may not be due to pests. The plant's nutrition can cause poor leaf color or unusual growth patterns, and humans can also cause damage to plants. Careful observation of the biological system that surrounds your crop plants is one of the most educational and challenging aspects of fruit production.
The conditions for insect and disease development vary from year to year and among crops. In some years, a no-pesticide strategy may work well to control pests, and there will be very little loss of yield or fruit quality. In other years, the entire harvest might be unusable due to pest damage. The following sections will explain the circumstances required for insect outbreaks and disease epidemics, as well as ways to limit their impact on harvestable fruit through both no-pesticide and pesticide control strategies.
IPM: Integrated Pest Management
The modern approach to managing pests is referred to as integrated pest management (IPM).
IPM involves compiling detailed, timely information about a crop and its pests (insects, weeds, and diseases) to ensure that pest-management decisions are economically, environmentally, and socially sound. In addition, IPM advocates integrating as many suitable pest-management tactics as possible, including biological control--using one organism to control another by predation, parasitism, or competition; cultural control; horticultural practices; specialized pruning; orchard sanitation; planting scab-resistant varieties; insect behavior modification such as mating disruption; and the judicious use of pesticides. Successful IPM requires knowledge about pests and the vulnerable stages of the crop. Our goal in publishing this guide is to give you the tools needed to implement a successful IPM program.
Weeds, or "plants out of place," compete with fruit crops for nutrients and water, provide a moist environment for disease organisms, and often harbor insects and small animals such as rabbits and mice.
Nearly every fruit grower who attempts to grow plants around his or her property is faced at one time or another with some form of weed problem. Each type of growing situation has its own type of weed problem: lawns might contain plants other than desirable grasses; the vegetable garden is a constant source of weed growth; and landscape plantings and garden areas devoted to fruit-bearing plant production often are trouble spots. Competition between weeds and fruit plants for resources (nutrients and water) is of particular concern during the full-bloom period, when nothing should be allowed to interfere with the blossoming and subsequent fruit-setting processes.
Insects and Mites in Fruit
Many species of insects and mites attack various fruit crops. Fortunately, only a few are considered serious enough to prevent a good yield and high fruit quality.
These pests (see Table 2.1) can be divided into two groups: those that affect the fruit (direct pests) and those that affect parts of the plant other than the fruit (indirect pests). In most instances, direct pests are far more serious since they can damage or infest the harvested part of the crop. Very few of these pests can be tolerated. Moreover, in many cases by the time an infestation is noticed, extensive damage has already been done. For this reason some pest controls (such as pesticide sprays) must be applied before fruit damage is observed. These sprays are usually applied to correspond with some stage of crop development such as pink bud or petal fall. Indirect pests, on the other hand, can be tolerated to a certain degree because a healthy plant is able to withstand some feeding damage, and the fruit are not being affected directly. Fruit growers can wait until they notice that an indirect pest is present in damaging numbers before applying a control.
The keys to successful pest management in fruit crops are close observation of the plants, the ability to distinguish the few pest species from the myriad of innocuous or beneficial insects that may be present on the plant, an awareness of when pest numbers are threatening the growth of the tree or the crop, and the ability to choose the best control option when control of a pest is necessary. Some of these techniques are discussed below.
Fruit crop plants undergo a sequence of growth stages every year.
Apple trees, for example, proceed from green tip (bud break) to tight cluster (flower buds visible) to pink (flower buds showing pink) to bloom (flowers open) to petal fall, etc. The rate at which this process progresses is largely due to environmental conditions such as temperature. Likewise, pests respond similarly to these environmental cues, usually appearing in concert with some developmental stage of the plant. Therefore, the plant's developmental stage can help determine when pests (especially direct pests) should be controlled.
Not all insects are bad!
In fact, many are beneficial because they feed on the pest insects. For some indirect pests, beneficial insects may obviate the need for a pesticide spray or two. In addition, these beneficial insects might be killed by the pesticide sprays. Therefore, the detrimental as well as the beneficial impact of a pesticide spray must be considered. For example, syrphid fly larvae might be feeding on pest green apple aphids and control the aphids without the use of a pesticide. However, it might be the time of the year to protect the fruit from apple maggots, which have plagued the trees in the past. The fruit grower might decide that protecting the fruit from maggots is more important and might apply a pesticide that also kills many of the syrphid flies.
How many pests are too many?
As stated earlier, very few direct pests (those that attack the fruit) can be tolerated, and protective sprays are often applied prophylactically. Populations of indirect pests, however, can be tolerated without harming the tree or crop. On apples, for example, an average of five or six mites per leaf can be tolerated. Only if the mite numbers exceed this threshold are sprays recommended.
Other insects also are considered beneficial in the fruit planting. Bees are beneficial since they pollinate most fruit crops. Insecticides should never be sprayed when the crop is in bloom. Also, avoid the drift of insecticides onto other blooming plants when fruit crops are being sprayed.
As mentioned above, many types of flies are predators or are parasitic on fruit pests. Syrphid fly larvae are typically maggot-shaped and legless, with a head end that is narrower than the tail end. These flies may be found foraging among colonies of aphids on the undersides of leaves.
Beetles, particularly ladybird beetles ("ladybugs") can be very beneficial. Several species of ladybird beetle are voracious predators in both the larval and adult stages. The larvae are elongate with distinct legs and are usually black with orange markings. These larvae often are found feeding on aphid colonies. The black ladybird beetle is a mite predator. This species is discussed in the European red mite section in Chapter 4. Other predators and parasites include lacewings, predatory mites, and many parasitic wasp species.
Monitoring fruit plantings frequently and on a regular basis is the key to a successful IPM program. Monitoring can take several forms, and is accomplished by using various types of traps and by weekly scouting.
Pheromone traps lure male moths onto a sticky panel by means of a synthetic sex-attractant chemical. Counting the number of male moths in these traps weekly allows the gardener to better time insecticide treatments. Other insect traps are apple maggot spheres and white sticky panels for trapping European apple sawflies and tarnished plant bugs.
Scouting is the most useful technique for monitoring most pests. It should be done weekly during the growing season, and involves inspecting a sample of fruit plants to determine the presence and severity of various pests. During the dormant season, scouting should be performed at least once to determine levels of overwintering forms of some pests such as mite and aphid eggs and of San Jose scale. Invest enough time to make reliable assessments of pest and tree conditions.
Many plant diseases and insect pests survive the winter on woody plant parts, in the soil, or on weed hosts. They can live in a dormant state in dead wood, infected buds, limbs, trunks, bark on twigs, mummified fruit, decaying plant parts, leaf litter, and plant debris.
When weather conditions become favorable in the spring, these insects and diseases become active again. The fungal and bacterial diseases begin to multiply, sporulate, and are carried by wind and rain to susceptible plant parts. This begins a new disease cycle. Knowing how these diseases and insect pests overwinter and spread is crucial in their control. This is why cultural methods such as sanitation, pruning and using disease-resistant plants are so important. Pruning removes the source of the overwintered pathogen or insect pest. Some pruning guidelines are listed below.
- Prune out and destroy dead, diseased, or insect-infested twigs and branches.
- Prune branches that rub against each other.
- Try not to leave a stub when pruning; remove the whole branch if possible.
- Do not prune in fall or early winter. This will make trees more susceptible to winter injury.
- Prune to "open" trees, which will facilitate disease control. Pruning promotes better air circulation and light penetration, facilitates the drying of plant surfaces, and enhances spray distribution.
- Prune out cankers in stone fruit to discourage borers.
- Prune out fire blight cankers and all other cankers caused by disease organisms.
- Remove leaves and other plant parts containing insect egg masses.
- Remove and destroy decayed, injured, and mummified fruit left in the tree or on the ground.
- Pick up, burn, bury, or destroy fallen fruit.
- Rake and burn leaves and other litter under the tree to destroy overwintering disease and insect habitats.
- Eliminate weed hosts. Many insects and diseases overwinter in weeds.
- Avoid excessive nitrogen fertilization.
- Avoid wounding plant parts and fruit during the season. Wounds are excellent entry points for insects and diseases