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The most effective and economical way to avoid many pest problems is to provide an environment that discourages pests or reduces the tree’s susceptibility to damage. These types of methods include proper planting, adjustments in cultural practices, and promoting beneficial insects. For pests that directly attack the fruit or trunks of trees, exclusion pesticides are the most reliable pest control option.
Planting and Site Selection
- Select tree varieties or rootstocks with known insect tolerance or disease resistance; for example: Empire apple is tolerant of fire blight, and Malling Merton rootstocks are somewhat resistant to woolly apple aphid
- Know the hardiness zone, and choose varieties that are locally adapted; winter damage resulting in bark cracking can cause a tree to be more susceptible to attack by many diseases and insects
- Plant trees at root-collar depth, and in an optimal site; instead of letting the turf grow around the trees and compete for water and nutrients, apply a mulch around the base of trees, but keep it away from the trunk
Soils and Nutrition
- Apply an amendment to the soil surface, such as manure or compost, in late fall to improve soil structure and quality
- Fertilization can assist with optimal tree growth, but is generally not necessary if your soil is healthy; test soils every other year
- If tree growth is slow (less than approx. 6 inches/year), apply a balanced fertilizer in the spring between pre-budbreak and bloom; do not over-fertilize, as this can lead to excessive, lush growth that is attractive to aphids, pear psylla, and other foliage pests
- Improve soil drainage by aerating compacted soil, adding amendments, grading, or adding drain tiles
- The most common nutrient deficiencies in Utah fruit trees are iron and zinc; these elements occur in the soil but are not available for uptake due to Utah’s alkaline soils
- Iron deficiency is best prevented by a soil application of chelated iron (in the form of EDDHMA) every spring before budbreak
Mismanagement of water is a major contributing factor to many pest problems. Too little water can stunt growth of trees, reduce development of root systems, reduce fruit yields, and exacerbate the injurious effects of many pests. Severe water stress can cause leaves to drop and fruit to remain on trees after harvest.
Excessive watering can kill roots by depriving them of oxygen and increases the possibility of infection by soil-borne diseases, particularly Phytophthora crown rot. Over-watering is by far more common in Utah than under-watering.
For optimal watering, allow surface soil to dry out before irrigating. Flood or furrow irrigation may discourage ground squirrels and pocket gophers from digging burrows near tree trunks. Mini-sprinkler and drip irrigation are common in commercial orchards, and both can be adapted to residential sites. Overhead irrigation is wasteful and can lead to disease problems because leaves or fruit remain wet for extended periods.
When managed properly, orchard floor vegetation can have a positive effect on pest problems. Orchards with ground covers may have higher populations of certain natural enemies, largely due to increased habitat and alternate food sources for beneficial insects and mites; they also may have fewer problems with mites because of reduced dust. A hardy grass mixture of perennial ryegrass plus red fescue or a tall fescue can be planted to compete with weeds and minimize dust problems. Thick ground covers have also been shown to decrease pupation success of western cherry fruit fly.
If not properly managed, a ground cover can potentially be a source of pests. Rodent, crown rot, ant, stink bug and lygus bug problems have been associated with ground covers that get too overgrown or thick. Clovers, alfalfa, and many broadleaf weeds attract lygus and stink bugs insects that cause “cat-facing” damage (scarring and marking) to the exterior of fruits.
Many pests can overwinter and survive inside fruit, other tree parts, and debris. Keeping a clean orchard environment can greatly reduce the pest population:
- Gather fallen fruit and fruit remaining on trees after harvest and destroy, or till under
- Remove fruit that falls before harvest immediately since they may contain insect larvae
- Rake up dead leaves, especially cherry leaves, on which the powdery mildew fungus overwinters
- Prune and destroy dead and injured twigs or branches
- Remove wood piles or other debris where codling moth larvae may find shelter for the winter
FRUIT BAGGING for CODLING MOTH
To exclude codling moth, place small paper bags over developing fruits. Bags should be well secured, but not constrict the twig. Wait to apply bags until the fruit is approximately ½ to ¾ inch in diameter. Cut a small slit in the bag bottom, slip the slit over the fruit, and close the bag opening with a twist-tie. Remove the bags a short time before the fruit is mature to allow the fruit to color.
Types of Barriers:
- Japanese 2-ply apple bags
- Sandwich bags of waxed paper or clear plastic
- White or tan paper sacks; may need to be replaced after rain
- Clear poly bags with drawstring closures
- Disposable nylon foot socks; easy to put on, but less effective with codling moth
Predators, parasites, and pathogens of pest species can occur naturally in fruit orchards or may be purchased from commercial suppliers and released for supplementary control of pests (see list of suppliers).
Most biological control occurs naturally. Often its importance is not appreciated until a broad spectrum pesticide is applied, killing beneficial insects as well as the targeted pest. As a result, a different pest—suddenly not controlled by natural enemies—becomes a problem.
There are several things that can be done to encourage the activities of biological control agents already present in an orchard:
- Avoid the use of broad spectrum and more toxic pesticides unless necessary
- Provide a habitat that is more favorable for biological control agents by choosing adjacent plants that supply nectar, pollen, alternate hosts, and habitat for natural enemies (see Ground Covers section)
- Provide adequate organic content in the soil to help build the population of beneficial soil micro-organisms; although the mechanisms are little understood, these bacteria and fungi compete with soil pathogens
Most commercially available biological control agents are used in greenhouses, but there are a few other options for orchards. Predatory mites have been successfully mass released for control of plant-feeding spider mites in orchards. Steinernema and Heterorhabditis nematodes, which parasitize insects, show great promise for use against certain boring insects, soil dwelling insects, or insects in other types of moist, confined habitats. Release of Trichogramma wasps for control of numerous caterpillars, and release of lacewings for aphids and other small insects have potential, but results have been mixed because of variation in the quality of agents available and lack of reliable release procedures.
MASS TRAPPING for CODLING MOTH
A mixture of molasses and yeast (1 part molasses: 10 parts water, plus ¼ package dry yeast) can be placed in a plastic tub or small bucket, and hung in apple and pear trees to catch adult codling moths. This bait is attractive to both sexes. It can help reduce local populations of codling moths in your backyard trees, and may help reduce worm damage to fruit, but it likely will not completely eliminate damage. This method works best in areas with low codling moth populations.
The pheromone monitoring trap described in section 1 is not an effective pest control tool because only the male insect is attracted and caught. Multiple pheromone traps placed together in a tree can conflict with each other and actually catch fewer male moths than a single trap.
There is a method of using many release points of pheromones to control insects that is called mating disruption. Pheromones, enclosed in a dispensing device (twist tie, foil packet), are placed in fruit trees throughout the orchard. They control the targeted insect pest not by killing, but by releasing a high concentration of pheromone that disrupts males from locating females for mating. Hence, the females are never able to lay eggs. These products are not effective in home orchards because they require hundreds of release points in a uniform orchard of multiple acres of trees. Where only a few trees are involved, the pheromone concentration is too low, and mated female moths can fly in from nearby sources to lay fertile eggs on fruit.
Any substance applied to control insects, fungi, weeds, or other pests is called a pesticide, whether it is organic or conventional. To avoid excessive pesticide use, choose alternative pest management options before relying on pesticides as the sole means of pest control. More pesticide products on the market today are compatible with an IPM program, and pose fewer risks to the environment.
- Botanical chemicals are derived from plant sources, and include pyrethrin, pyrethrum, neem oil, rotenone, and hot pepper wax
- Microbial pesticides are biological organisms or toxins derived from them; Bacillus thuringiensis (Bt), a bacteria, is the classic example; it kills caterpillars and larvae by paralyzing the digestive system
- Other organic products include sulfur, diatomaceous earth, insecticidal soap, and oils; oil (horticultural oil, superior oil, narrow-range oil) is a particularly effective tool for safe control of soft-bodied insects and mites as well as some foliar diseases such as powdery mildew; with proper use, oil can be applied all season, not just during dormancy
Using Pesticides Safely
Be aware that using a pesticide in any means other than that registered by the manufacturer is a violation of the law. A label is included with every pesticide—read it before using the product. It contains information on:
- Which plants it may be used on
- The rate at which it should be applied
- How to apply and what protective clothing to wear
- What to do in an emergency
- How to store it properly
- How long to wait before re-entering the treated area
- How long to wait between application and harvesting the fruit
Keep the label with the product so that this information is always on hand.