Just as soon as I get one thing done in the orchard, more work suddenly springs upon me. When growing fruit trees with as few chemical inputs as possible, there can never be too much time in the orchard. While I am still learning, there is much that I can teach. Let us look at some of the diseases and insects that beset our pome fruits. That is, apples and pears.
What are pome fruits?
Pome fruits are described as fruits with a central core made up of capsules containing up to 10 seeds. The core is surrounded by an edible flesh covered by a skin. These include apples, pears, hawthorn, quince, medlar, and even rose hips. We are mostly concerned with apples and pears in Northeast Kansas, though some people do try to grow quince.
Insect Problems of Pome Fruits
When it comes to growing pome fruits, there is huge list of insect pests. Fleshy fruits are just as attracting to insects as they are to us. For us however, there are things we can do to limit pest outbreaks and problems.
While there are not as many insect problems on pome fruits as there are on stone fruits, there are enough to keep an orchardist busy. The following list are the major insect pests of pome fruits in the Central Great Plains Region (Zones 5 to 6b).
- Japanese beetle
- Codling Moth
- Apple Maggot
- Oblique-banded Leaf Roller Moth
- Apple-tree borers
- Plum Curculio
There are also a few other insects that cause minor damage to apple and pear trees and fruit, but can be managed mainly through biodiversity. These include:
- European Apple Sawfly
- Green Fruitworm Moth
- Red-banded Leaf Roller Moth
- Eastern Tent Caterpillar
Managing Pome Fruit Insect Problems
Now that we can see the list of potential insect problems, let us dive into individual insects, their damage, and what to do about them. I will be listing only cultural and biological controls for these pest problems, as I believe the overuse of pesticides to be a problem with most home gardeners.
I have discussed the problems created by the Japanese beetle (JB) here in the Great Plains many times. However, this invasive beetle is a major pest problem in our orchards and gardens. For home orchardists, or those growing edibles and fruit in their landscapes, the management is different than those growing acres and acres of fruit.
Home orchardists and gardeners generally can get through a season with little need for pesticides on JB. The first thing to do with any pest is proper identification of the pest. Once you know what you have, then you can proceed with management strategies.
Knowing the life cycle of the Japanese beetle will help with timing of care. See picture below.
In Northeast Kansas and other areas of the Central Great Plains, Japanese beetle adults are active between June and August. This is when they are feeding on apples and other fruits. They mainly feed on the leaves of apple trees, but will eat fruits too. I have not seen any feeding on my pear trees, though it is likely they do.
For smaller, semi-dwarf apple and pear trees, netting the trees during this time may be a viable option for home gardeners. If the tree is smaller than 15 feet tall and wide, there are cloth-like, insect-proof nettings available.
Other methods of keeping Japanese beetles off your apples can include bagging individual apples with paper bags or panty hose, or even trying red sticky-ball traps. While the red sticky-ball traps are most commonly used for codling moth and apple maggot, there may be some good results with JB.
Since apples usually ripen after JB has laid eggs and died, the use of red sticky-ball traps may encourage adults to head for the traps instead of the leaves of apples.
The codling moth is an invasive species introduced into the United States over 200 years ago, likely with apple tree introductions from Europe. It is a serious pest of apples and pears and should be treated as such. The moths themselves are small, grayish with a chocolate brown patch and bronzish scales at the end of each forewing.
Codling moth adult females lay singular eggs on fruit or upper leaf surfaces. The caterpillar feeds inside the fruit. Newly hatched larva enters the fruit near the calyx or side and begins feeding on the flesh of the fruit. As it feeds it pushes its excrement out of the entry hole. After about 4 weeks, the larva is mature and exits the fruit. It overwinters as a mature larva inside a cocoon.
Limiting codling moth damage without sprays on your fruit trees is possible, though time consuming. Mating disruption between male and female moths can be achieved through the use of pheremones. This causes the male moth to be unable to find the female moth. Pheremone applications should be done to the upper 1/3 of the tree canopy.
Other useful methods to lessen or prevent codling moths include cleaning ALL leaf litter and debris from around the trees and burning to destroy overwintering cocoons. Bird nests should also ne removed from the trees as cocoons are often attached to the nests.
The apple maggot fly is a North American native insect. The adult fly, when at rest, mimics the look of a black jumping spider. The fly lays its eggs on the skin of maturing apples, causing bumps or dents. After hatching, the larva burrows into the apple and feeds. The flesh around the egg site often discolors and deteriorates, causing pitting in the fruit. Misshapen fruit is usually a sign of apple maggot damage.
After apples fall to the ground in fall, apple maggot larvae burrow into the soil to overwinter as a pupa.
For home orchards, one of the best cultural practices to preventing apple maggot is to keep the area clean. Remove all fruit before it falls and destroy rotten fruit by removing to the trash, feeding to chickens, or grinding into a slurry before composting. DO NOT compost whole infected fruit in your home compost.
This is another example where bagging your fruit can contribute to keeping them free of the problem. Using a plastic ziploc or tied bag, place the bag around the apple and cut the bottom corners just enough so water or condensation can run out. For small orchards or just a couple of trees, this method, though time-consuming, will work.
Another useful trick in the home gardeners playbook is the use of the red sticky-ball trap. These traps are covered with a stick substance that traps the flies as they land to lay eggs. Place 2 to 4 traps in each smaller tree. Check the traps weekly and replace with new traps as needed. Traps can be cleaned and reused.
Oblique-banded Leaf Roller Moth
The oblique-banded leaf roller moth is another North American native pest. Because apples and pears are not native to North America, many of our insects are seen as major pests to these nonnative trees.
This moth lays green to white egg masses on the upper surfaces of leaves or on fruit. Each mass may contain up to 200 eggs. Once hatched, the larvae begin to feed on the fruit or the leaves. Leaf rollers use silken threads to make a cocoon-like roll in the leaves to protect themselves from predators while they feed.
Oblique-banded leaf rollers overwinter as immature larvae in cocoons in bark crevices. The following year, they begin to feed as soon as buds break in spring. When ready to pupate, they form a silken cocoon in a rolled leaf.
Damage on the fruit appears as a corky scar. Other damaged fruit may fall prematurely. If you see dry leaves seemingly attached to the fruit, it is likely a leaf roller larvae feeding on the fruit.
A cultural practice for preventing this leaf roller on the fruit may be to apply a coat of Tree-Kote Tree Banding Gum to the trunk prior to bud break. This sticky substance will entrap any emerging larvae from making its way up to the new leaves and flowers.
Apple Tree Borers
There are several species of wood-boring insects that may affect apple trees. When these insects attack the tree, damage is mainly limited to the trunk of the tree, but may result in reduced yield and vigor. Protecting apple and pear trees can be done using barriers such as banding gum or a similar sticky substance on the bark. This should be done in the early part of the spring, before bud break or emergence of the adult borers from infected trees.
As the adult borers (beetles or moths) forage for new hosts, they will be caught in the banding gum and die before they can lay eggs on the trunk.
The plum curculio is a weevil type insect. Weevils have an elongated snout on the front of their bodies. Plum curculio is native to North America and is considered a major pest to these nonnative pome fruits, including apples and pears.
This weevil overwinters as adults within the soil in orchards or gardens nearby. Adult weevils emerge around the time of bloom and fly to apple trees for mating. Females deposit eggs under the skin of developing fruits. Larvae feed inside the fruits, then emerge from the fruits in midsummer, and drop to the ground to pupate in the soil. The majority of under-developed fruit will drop pre-maturely after feeding.
There are not many cultural recommendations to stop this pest, but sanitation may slow them. Pick off or up any damages fruitlets from the tree or ground before the larvae can pupate in the soil.
Other Controls for Insects of Pome Fruits
To help lessen the damage from overwintering aphids, scale, or mites, spray the tree with dormant oil in late winter or early spring when the weather is warmer than 40o F for 2 hours or more. This should be done before bud swell, because the oil can damage newly breaking buds.
Proper pruning of the trees can be used as a deterrent to insect pests. Prune out any diseases, dead, or damaged branches to limit entry points for secondary insect pests such as borers.
Proper plant maintenance and care can help prevent outbreaks of pests. When trees are as healthy as possible, natural tree defenses will protect against insect damage. Keeping your fruit trees well-watered, mulched, and fertilized can help the tree maintain vigor. One example of a natural defense is the growing of an extra thick cuticle or cell layer on the leaves. This deters insects from chomping down.
Planting your trees in a fruit tree guild or where biodiversity of plant and insect life is at its greatest potential for your area will protect the trees. Beneficials and natural predators like snakes, birds, and other animals will help overcome insect populations.
Diseases of Pome Fruits
Here is where things can get tricky. Cultural controls may not be enough to counter-balance some of the disease pressures facing pome fruits, but we can give it a try.
Disease of apple and pears trees in the Central Great Plains include the following:
- Apple Scab
- Cedar Apple Rust
- Cedar Hawthorn Rust
- Sooty Blotch
- Powdery Mildew
Managing Diseases of Pome Fruits
Diseases on fruit trees can sometime be difficult not only to identify, but also to control effectively. However, much has been done by growers of large orchards to limit disease pressures. Home orchardists can take advantage of this research and apply the best treatments in their own orchards.
This fungal infection is a major disease of apples, pears and crabapples. The most serious infections are on the fruit and leaves of the tree. Apple scab overwinters in infected leaves on the ground.
In spring, when conditions are warm and rainy, spores from the infected leaves travel to the new leaves on the tree via wind or rain splash. The new infections start as indistinct spots and progress to cover the whole leaf. As the scab develops, lesions become fuzzy and dark in appearance. A severe infection can cause leaf drop, which will cause setting fruit to abort.
Fruit lesions start dark green on the skin and then become brown and corky as the develop. In bad cases, the fruit may crack and become distorted.
To prevent apple scab, sanitation of the orchard is important. Cleanup leaves after they drop in the fall and any fallen fruit.
Cedar Apple Rust
This fungal infection is considered a major disease on apples in the Central Great Plains. It is two host disease, needing both apples/crabapples and junipers to survive. Here in Northeast Kansas, eastern red-cedar is our common juniper host for the disease. It does not affect the juniper host.
On junipers, cedar apple rust appears in the winter as small, walnut to golf ball sized fruits, similar to a brown brain. In warm wet weather of spring, the fungal bodies swell and orange spore-producing bodies emerge, looking like some alien from space. Once these dry, the spores emerge from the fruiting bodies and are carried by wind to the apple or crabapple trees.
On the apple tree leaves and fruit, spores land and develop into small, orange lesions. They grow in size to 1/8 to 1/4 inch in size. If the infection is severe, the leaves may drop prematurely, affecting tree vigor and causing fruit to abort. Fruit lesions are only scarring to the skin of the fruit and cause no internal damage.
Resistant Apple Varieties
The best preventative for cedar apple rust is to plant disease-resistant varieties. The following 10 varieties, in order of resistance, are considered resistant to cedar apple rust.
These are just some of the more popular cultivars available for the home orchard. There are several hundred varieties of apples, and many more are resistant to cedar apple rust.
The following 6 varieties are considered highly susceptible to cedar apple rust and may be some of the most chemically treated varieties in the market.
- Golden Delicious
Considering that these varieties are often seen at the grocery store, one must wonder why growers pick them over cultivars like Zestar! and Winesap.
Unlike apple scab, it is difficult to control cedar apple rust via sanitation. Wind spores from juniper trees can travel as much as 15 miles from the source to the secondary host of apple or crabapple.
Cedar Hawthorn Rust
This fungal disease is the counterpart to cedar apple rust. Cedar hawthorn rust affects pears and hawthorns instead of apples and crabapples. There are two hosts, junipers and hawthorns/pears. On the junipers, the fungal fruiting bodies are small, less than marble sized. In spring, they release wind-blown spores that land on the leaves of pears.
The lesions on pear trees start as small yellow-orange dots and grow similar to cedar apple rust spots on apple. While they rarely affect the fruit of edible pears, they do destroy the fruit of hawthorns and ornamental pears. Serious infections can cause leaf drop on both hawthorns and pears.
Again, planting resistant varieties is the best method for preventing cedar hawthorn rust. Luckily, most edible pears are already somewhat resistant to cedar hawthorn rust. However, the rust tends to be worse when there are large plantings of ornamental callery pears nearby. Most callery pears are very susceptible to cedar hawthorn rust, though a prolonged wet period in summer makes it worse.
This is a common summer fungal disease on apples and pears throughout the Great Plains. It is a disease that is more common in warm, wet summers. Damage to the fruit is on the skin only and does not affect the health of the tree or the fruit. It is superficial only and there are no cultural recommendations, though there are some resistant varieties.
This fungal disease is not a major concern on apple or pear trees in the Central Great Plains. While there is some damage to leaves of the trees in extremely wet summers (2019), it is not enough damage on home orchards to warrant spraying or cultural controls.
This is a major bacterial disease of commercial apple orchards in the Upper Midwest, but we rarely see large infection rates here. I have seen only a handful of cases of fireblight in Northeast Kansas, on apple and pear trees.
While it can affect parts of the tree including shoots, leaves, fruit, stems, and blossoms, we generally see it only on newer shoots here in Northeast Kansas.
Fireblight is characterized on shoots by a blackened, twisted growth habit, resembling a shepherd’s crook. It can be prevented by removal of these cankered shoot by pruning. Pruners should be cleansed with a 10% alcohol solution between each cut.
While there are many insects and diseases affecting apples and pears in the Central Great Plains region, we have a host of cultural and biological weapons at hand. We can maintain our small orchards and home gardens with simple cleanup strategies and proper plant selection.