The Online Gardener's Handbook
Chapter 5: Fruit
Insect and Disease Control on Fruit
Table of Contents
- Preventative Measures
- Poor Flowering, Pollination and Fruit Set
- Descriptions and Management
- All Fruit (except strawberry)
- Learn More
To guard against problems with your fruit trees, follow good cultural practices, as outlined in Chapter 2 - Integrated Pest Management, such as pruning and destroying affected fruit. Buy only varieties of fruit that are known to be compatible for cross-pollination.
Poor Flowering, Pollination and Fruit Set
Pests are not the only cause of poor flowering. Abiotic damage is often the culprit. This includes:
- temperature extremes or fluctuations during winter that kill flower buds
- early spring frosts, after flower buds have begun to swell, that kill flower tissue
- over-fertilization or excessive pruning during the previous season that results in excessive vegetative growth
Poor fruit set can occur for a variety of reasons as well:
- damage to pistil and stamens before the flower blooms prevents pollination and fertilization
- cool, wet weather during bloom discourages pollination by bees
- excessive fruit load during previous growing season, particularly in apples and pears, will reduce fruit load in the current growing season. To minimize this problem, thin fruit in late June or early July.
Some fruit are self-fruitful - they will pollinate themselves without requiring a second cross-pollinating tree. Others such as sweet cherries are cross-pollinated and require other trees with compatible pollen in the area; some, such as apples, also require varieties with a similar flowering date. Be sure to purchase named varieties which are compatible for cross-pollination.
In this chapter, a description of various pests of fruit will be provided along with suggested management options. These management options will not include the use of pesticides. Some biopesticides and certain reduced risk pesticides are still available to the homeowner for controlling weeds and pests in lawns and gardens. For more information, refer to Chapter 2 of this handbook and the Ministry of the Environment's website. For suggestions on managing specific weeds and pests, consult local horticulturalists, Master Gardeners or your local garden supply centre.
NOTE FOR TREE OWNERS: There is an exception under the ban that allows you to hire a licensed exterminator authorized to use commercial pesticides to maintain the health of your tree. This exception applies only to pests that threaten the tree's health. For example, the exception cannot be applied to a pest that impacts the quality of the fruit but will not kill the tree itself. To obtain this exception, licensed exterminators are required to obtain a written opinion from a professional tree care specialist that a pesticide is necessary to maintain tree health. For more information, contact the Ministry of the Environment.
Note that many fruit trees can tolerate some damage, particularly to the foliage, without suffering lasting impacts. Pest descriptions below include suggestions for cultural controls however in many situations these may not be necessary.
Descriptions and Management
Some of the pest problems described in this manual are common in commercial operations, but may not occur in your home garden if you are not located in a commercial fruit production area. Keep in mind, however, that neglected apple, pear and plum trees, which grow throughout Ontario, are sources of many harmful insects and diseases.
Insects and diseases are listed under each fruit. If, however, you cannot find the pest to suit your symptoms, look in the "All Fruit" section below.
Where a disease or insect applies to more than one fruit, the full discussion is provided only once, and page references provided for all other fruits.
All Fruit (except strawberry)
Crown galls are caused by bacteria present in most garden soils that gain entrance through wounds in the plant. It is common on all types of fruit trees, raspberries, grape, bush fruits, and many others. Galls or woody swellings develop on the roots or base of a plant.
Remove galls with a sharp clean knife or secateurs. Clean tools and hands in a solution of 1 part bleach to 4 parts water to prevent further spread. Whenever possible, avoid unnecessary wounds, and do not buy plants with galls on roots. Replace soil where a severely affected plant has grown.
Several kinds of caterpillars damage fruit trees, including tent caterpillars, leafrollers, fruitworms and gypsy moths. In general, they are active early in the season, from early spring through mid June. Tent caterpillars build large silken nests in the branch forks. Tent caterpillars are black and hairy with white stripes on their back and narrow brown and yellow lines with blue dots on their sides. Leafrollers spin a light web around leaves, rolling them together. They feed inside the protected area from shortly after buds open until about three weeks after petal fall. There are several species of leafroller, with the most common being the obliquebanded leafroller (see below). Green fruitworms grow to be quite large, 30-40 mm long and a lime to dark green color, with white longitudinal stripes. They feed on buds, leaves, blossoms and developing fruitlets. The gypsy moth is an introduced forest pest which often move onto fruit trees from adjacent woodlots. Larvae are yellow, gray or black with long wispy hairs. There are five pairs of blue spots just behind the head, followed by sixe pairs of red spots.
When tents are noticed in spring, remove and destroy caterpillars or prune the affected twigs and branches. Do this in the evening when most worms are in the tent. In early spring, prune out or rub off egg masses. They appear as dark brown, styrofoam-like collars 1 cm wide around twigs and branches. Small infestations of spring-feeding caterpillars can be hand picked and destroyed. Numerous predators and parasites attack spring feeding caterpillars, and they are susceptible to bacterial, viral and fungal diseases.
Curculios are 4-6 mm long, have prominent snouts and are dark brown with grey and white patches on their backs. They lay eggs in apple, pear, plum, peach and cherry soon after flower petals have fallen. A crescent-shaped scar develops on the fruit. Wounds on apple often exude sap that dries to a white crust. The greyish white larvae tunnel in the fruit and cause it to drop early.
Spread a sheet of plastic under the tree and shake the branches. Adults will fall onto the sheets and can be destroyed. Remove and destroy all fallen fruit. Burlap bags laid at the base of the tree may attract beetles looking for hiding spots. Check frequently and collect and destroy the beetles.
Japanese Beetles are the adult stage of white grubs, which are most commonly known as turf pests. However adults of this insect will feed on the foliage of a wide variety of plants and they have become seasonal pests of many crops, including tree fruit, berries, grapes and nuts. Feeding is usually concentrated on the foliage, however fruit feeding can occur in stone fruits. Adult beetles are 10-13 mm long, metallic green to greenish-bronze, with coppery red wings and small white tufts on the sides and tip of their abdomen. They feed on the upper surface of the foliate and skeletonise leaves. They typically feed in groups, starting at the top of the plant and moving downward.
Hand pick beetles and place in a bucket of soapy water. If possible, locate fruit away from vineyards or turf or control grubs in lawns. This will help reduce populations in your yard, but will not prevent adults from flying in from other areas. Japanese beetle traps are available in garden centers. Although the lures sold with the traps are very effective and can attract many beetles each day, research has shown that the traps attract more beetles than are caught. As a result, susceptible plants in the vicinity of the trap are likely to suffer more damage than if no traps were used. Parasitic nematodes are commercially available and may help to reduce populations.
Oriental Fruit Moths
The oriental fruit moth is a serious direct pest of tree fruit. The host range includes both stone fruit (peach, plum, apricot, nectarine and occasionally cherry) and pome fruit (apple and pear). Historically damage in most areas of Ontario has been limited to stone fruit and pears, however it has become an increasing problem on apple since the late 1990s. Larvae overwinter on the ground in weeds and mummified fruit, under bark or in other protected areas of the tree. They pupate in the spring, emerging in late April or early May as 6 mm grey moths with chocolate-brown markings on wings. The first generation larvae enter young twigs, which wilt and die. Attacks to apple shoots cause less drooping, and are less obvious than on peaches and other stone fruit. The larvae are 1.5 mm long with a black head and white body when newly hatched, and grow to become 9-13 mm long with a cream to pinkish body and brown head. Later generations enter ripening fruit. Fruit infested early in the season usually drops. Fruit injury can be conspicuous, with fecal material or gum exuding from the point of entry. It is a problem in areas where these fruits are grown commercially, and may not occur in isolated locations. Oriental fruit moths can be mistaken for other orchard pests, including codling moth.
Remove and destroy all infested fruit from under trees frequently. Prune trees to allow for easier access by natural enemies such as birds and predators that may help control the larvae. Wrapping a cardboard or burlap band around tree trunks may trap larvae as they seek out pupation sites. These should be checked frequently and the larvae or pupae destroyed.
Mites are tiny spider-like red or brown pests that feed on the underside of leaves. They are difficult to see without the aid of a hand lens. Mites suck the chlorophyll from the leaves causing small white dots and bronzing when severe. Control measures are not necessary unless the leaves start to turn bronze, usually during hot, dry weather. For more information, refer to the section on mites in Chapter 1.
On young or dwarf trees, blast the undersurface of the leaves with water to wash mites away. This approach is not successful on large trees.
Water stressed plants will be less tolerant of damage, so ensure irrigation is adequate. Mites have numerous natural enemies which help to keep populations in check. Predatory mites are also available for purchase and may help to provide some control.
Scale insects live under hard-shelled caps or scales on the bark of trees and cause damage by sucking sap and reducing the vigour of the tree. Depending on the species, scales look like small grey oyster shells or round brown knobs. For more information, refer to the section on scale insects in Chapter 1.
A light infestation may be kept in check by birds and beneficial insects. Scale biological controls are commercially available, and may help to reduce populations.
Silverleaf is caused by a fungus that invades trees through pruning wounds. Apples, apricots, gooseberries, peaches, plums, raspberries and sour cherries, as well as several woody ornamentals are susceptible. Symptoms include the development of a metallic, silver sheen on the leaves and browning and streaking inside the branches. Branches or entire trees may be killed once the sapwood is invaded. The fungus produces shelf-like fruiting bodies up to 2.5 cm in diameter under branches and in the bark. These bodies are abundant and bright purple after autumn rains.
Avoid pruning trees when they are most susceptible to infection, from sap flow in early spring until after bloom. If possible, avoid large pruning cuts. Remove dead trees and tree branches nearby which might be sources of the fungus. Removing affected branches may not save an infected tree, as the fungus is often well established throughout the tree by the time symptoms develop.
Plant bugs feed with their piercing, sucking mouthparts on young developing apples, peaches, pears, and nectarines causing sunken pits - catfacing - to form. Peaches, apricots and nectarines may also secrete an amber gum. On peach trees particularly, the insects also feed on young shoots, causing wilting and dying back. For more information, refer to the section on plant bugs in Chapter 1.
Adult tarnished plant bugs (TPB) are brown, while the four-lined plant bugs (FLPB) are greenish-yellow with four black stripes. Both are triangular in front, 6-7 mm long and about half as wide. They are very active, readily flying when disturbed. Young TPB are light green, while young FLPB are bright red, each with dark spots and markings. TPB can be a problem throughout the season, while FLPB is prevalent in late spring and summer.
Thoroughly clean the garden in the fall as plant bugs overwinter
as nymphs or adults in garden trash and weeds. Removing weeds and
mowing grass and weeds around gardens may help reduce breeding sites.
Some commercial growers have had success using Shasta daisies, planted
in a border around their fields, as a trap crop. This only works
if the daisies are kept flowering, as the bugs move out of the daisies
once flowering stops. Plant bugs have a number of natural enemies.
Planting nectar-producing plants around vulnerable garden plants
can help to increase biological control of plant bugs.
For more information:
Toll Free: 1-877-424-1300