Home Apple Orchard Pest Management Overview

Tree fruit specialist Renae Moran with apples; photo by Edwin Remsberg, USDA
Tree fruit specialist Renae Moran with apples.

There are a large number of insect and disease pests that attack apples and pears. Good pest management begins with good horticultural management. Removing last year’s leaves, or at least mowing them, helps reduce the population of overwintered apple scab fungus spores and some insect pests. Opening the tree up to sunlight and air movement not only improves spray coverage, it reduces humidity for scab and other fungal diseases and promotes fruit bud formation and overall tree health. Contact Dr. Renae Moran at University of Maine Highmoor Farm, rmoran@umext.maine.edu or 207.933.2100, for help on horticultural issues such as punting, fertilizer, rootstock, and variety selection.

Weed control is important to prevent competition with newly planted trees. Once trees are established, managing ground cover vegetation in a home orchard by mowing is adequate. Maintaining bare soil around the base of an apple tree is not recommended as the presence of ground cover provides insulation against low winter soil temperatures.

Whether and what to spray apple trees for disease and insect pests depends on your objectives, i.e. what percentage unblemished fruit you desire. If the trees are more than ten feet tall, spraying becomes physically difficult and time-consuming.

Apple scab is the most common disease of apples. Unless you know that an apple tree is a scab-resistant variety, then it’s very likely to be scab susceptible. If the tree was unprotected last year and did not have brown spots, dead leaves, and no rough corky spots on the apples, then the cultivar is either scab-resistant or blessed with unusually low scab inoculum in the area.

A high level of scab control on susceptible varieties requires beginning protection when buds open and green tissue emerges (date depends on location, late April to early May in most of Maine) and renewing protection about every seven days or two inches of rain until about two weeks after the flower petals fall. In central Maine, two weeks after petal fall is in mid-June.

The multipurpose home fruit tree spray products are a good choice for backyard apple trees because they simplify the mixing of spray solution which can get a little complicated when dealing with separate fungicides and insecticide products purchased in concentrate form. Also, the package size is appropriate. While most products can be stored over the winter if kept unfrozen, cool and dry (for powder formulations), it is best to only buy what will be used this growing season and start fresh each year.

The limitation of the multipurpose products is that because they contain an insecticide plus fungicide, the spray should not be applied during bloom when honeybees and other pollinators are visiting the tree. Applications made after twilight when bee activity stops for the day are less damaging, but it is better to avoid spraying multipurpose product altogether while there are open blossoms on the tree. Applying multipurpose spray up until bloom, with a spray just before blossoms open, and then coming back with a spray just after the blossoms fall can provide adequate control for a backyard apple tree if perfection is not the standard.

Sulfur is sold as a fungicide for apple trees, and some sulfur products are approved for organic certification. Sulfur requires more frequent application than home fruit tree spray mixes containing Captan, a conventional fungicide that is more reliable for disease control than sulfur.

There are too many potential insect pests to name them all here. A major pest of young home apple trees is the roundheaded apple tree borer. Trees are less likely to be killed by borers once they have developed substantial trunks (over 4-inch trunk diameter).

The main fruit-damaging insects are plum curculio, codling moth, and apple maggot. Applying a home fruit spray product that contains an insecticide when 95+% of the apple blossoms fall off the tree and then again about ten days later will reduce damage by plum curculio and codling moth. These two sprays also reduce damage from European apple sawfly, leafrollers, and roundheaded apple tree borer. For borer control, in addition to spraying the foliage, some spray should also be directed at the trunk.

In most situations and years, another application of a multi-purpose spray product is not needed until mid-July to protect against apple maggot. One of two more applications at two-week intervals starting (i.e. repeat sprays on July 30 and August 15) is usually enough to keep second generation codling moth and apple maggot from being major problems. A final spray in mid-late August may not be necessary for early harvested varieties but is important for later-harvested cultivars (i.e. those that ripen in late September and October). The late spray on late cultivars also reduces the development of sooty blotch and flyspeck fungi that stain fruit.

Insect control using only organic options is more complex and expensive. Surround is a highly formulated clay powder product you can apply to repel many insect pests. Ordinary clay will not be effective. The desired results can be achieved, but you have to keep the trees literally white with the clay powder from petal fall until early July to get good results against plum curculio and codling moth. An alternative is to use several applications of Pyganic (pyrethrin) after petal fall to reduce plum curculio and a couple of applications of a Bt product to reduce codling moth.

You can also repel apple maggot flies that begin attacking apples in July with Surround, but by spraying that late in the summer you will still have the clay power residue on the fruit at harvest. Bt does not work against apple maggot, and as a pyrethrin insecticide, Pyganic breaks down too quickly to give prolonged control against apple maggot. Entrust is an effective organic insecticide for apple maggot, but it costs hundreds of dollars for a one-pound package that is larger than what most home orchards will need for many years. The active ingredient in Entrust is spinosad and is found in some home spray products, but those products may have other ingredients that disqualify them for organic certification.

You can reduce apple maggot damage by hanging sticky traps at one trap per bushel of apples (i.e. one trap per tree for small trees, up to four or five traps per tree for larger trees).

The main problem that leads to pest control failures when people have sprayed their trees with an appropriate product at the right times is not applying enough water to deliver the correct amount pesticide. The mixing instructions on multipurpose fruit tree pesticide products are based on spraying the tree to run-off, i.e. until the leaves are saturated with water and applying more water would just result in a run-off. This is called “dilute” spray.  The idea is to apply enough water to almost, but not quite, get to the “run-off” point when spraying more water would just run off the tree.  If the spray is just misted on, there won’t be enough of the fungicide and insecticide to get desired protection.

Water is heavy to carry, and refilling takes time. To expedite spraying one can spray half, a third, or a fourth as much of that amount of water and deliver the correct amount of pesticide by increasing the amount per gallon by 2X, 3X, or 4X to compensate for the reduced spray volume. The best way to figure out how much water is needed to reach run-off is by spraying with plain water (no pesticide) and seeing how much water it takes.

The chart below shows typical amounts of spray water required to make a 4X spray to trees of different height.  By spraying at 4X you are only using one fourth the dilute amount of water, so you should use four times the dilute rate amount of pesticide per gallon.  Direct your spraying to spread the spray water evenly over all the leaves on the tree.  Hand-held and backpack sprayers are best suited for smaller trees. Getting good spray coverage on trees over 12 feet tall without powered equipment is difficult and time-consuming.

Tree height (from ground to top of tree): 6 feet 8 feet 10 feet 12 feet 14 feet 16 feet
Pints water per tree for 4X April-June spray 0.2 0.5 1.0 1.7 2.7 4.1
= fl. ozs. water per tree for 4X April-June spray 3.5 8 16 28 44 66
Pints water per tree for 4X July-August spray 0.3 0.7 1.4 2.4 3.9 5.9
= fl. ozs. water per tree for 4X July-August spray 5 11 23 40 63 94

Some Useful Resources

Designed to provide the home orchardist with the knowledge to successfully grow fruit trees under Maine conditions, this booklet describes cultural practices for apple, pear, peach, cherry, plum, and apricot trees. Covers varieties adapted to Maine, rootstocks, planting, early care, fertilization, pollination, pruning, lack of fruitfulness, pests, and diseases, and preparation for winter. Developed by Professor of Pomology Renae Moran and Associate Scientist Glen Koehler; includes 30 color photos that enhance text descriptions. 32 pp, 2008.  $9.50

Contains more than 500 color photos for identification of pestilent insects, mites, and diseases in the orchard, as well as beneficial insects, spiders, and mites. For growers, master gardeners, home gardeners, educators, scientists, and students. 238 pages, 2006. $32.00