apple of tree with apple scab

Apple scab

Updated: March 15, 2023

Key Points

  • To grow any type of fruit successfully, you must grow healthy plants and anticipate and prevent problems.
  • The appearance and severity of pest problems vary between neighborhoods, areas of the state, and growing seasons.
  • When symptoms of a problem are noticed, accurately identify the problem (weed, insect, disease, cultural/environmental), monitor for changes (increasing severity), and be prepared to act.
  • Prevention and control measures at your disposal may be physical (e.g., handpicking Japanese beetles, removing diseased plants), cultural (e.g. pruning brambles to improve air circulation), or chemical (e.g. spraying horticultural oil to smother San Jose scale.)

Causes of fruit problems

  • Do not assume that plant problems are caused by insects and diseases.
  • A large number of problems are caused by cultural and environmental factors (nonliving factors). These include too much or too little water or nutrients, insufficient space, sunlight, or support, compacted soil, temperature extremes, and root damage from cultivation.
  • In addition, the severity of some common problems is closely related to weather (some diseases are worse in wet years) and to gardening decisions (choosing inappropriate varieties, purchasing low-quality plants, incorrect spacing, etc.).

How to prevent, monitor for, and manage fruit problems

The integrated pest management (IPM) approach to preventing and managing pest problems is highly recommended and can be summarized as follows:

1. Scout plants regularly and thoroughly. Correctly identify the cause(es) of observed problems and learn more about them.
2. Learn to anticipate and prevent problems.
3. Monitor problems for worsening symptoms.
4. Use physical, biological, and cultural techniques to prevent and manage problems. If a pesticide is needed, choose the least-toxic material and closely follow label directions.

  • The IPM approach used by organic growers should be nearly identical to the one employed by conventional growers. The difference is that the organic grower needs to monitor more closely and rely more heavily on cultural and physical techniques for preventing and managing problems and use only acceptable organic sprays. Keep in mind that organic pesticides are not generally as effective as chemical pesticides and can also negatively impact beneficial insects (pollinators and natural enemies of pests).

Cultural and physical control practices 

The following should be part of regular maintenance practices to reduce insect and disease problems. 

  1. Select disease-resistant cultivars when possible.
  2. Use fencing to protect small fruits and tree fruits from deer.
  3. Remove and dispose of all infested and diseased plant parts, including dropped fruits and leaves. 
  4. Hand-pull weeds or apply organic mulches around plants. Weeds compete for water and nutrients and can harbor insect pests. 
  5. Prune properly to improve sunlight penetration, spray coverage, and air circulation. Prune out dead, damaged, or decaying branches, canes, or stems. 
  6. Keep plants healthy by fertilizing according to recommendations and watering plants regularly through the initial establishment period and during dry periods. 
  7. Tie small bags around individual apples and peaches to reduce pest problems. 

Pesticides as a part of the IPM approach for growing fruit

  • The use of pesticides is meant to keep pest populations below levels that might result in moderate to severe damage, rather than to eradicate all pest organisms.
  • The kinds of pesticides needed and the frequency of their application vary greatly in each home garden and depend on many factors.
  • Pesticides should be used only when needed, and then in strict accordance with label directions.
  • New plantings, especially where isolated from other similar fruit crops, might be free of some or most insect pests and diseases and pesticide treatments may not be necessary for some time. One or more serious problem typically develops in apple, pear, peach, cherry, and plum trees. Small fruit plants generally have fewer pest problems and can be grown organically more successfully than those tree fruits. 
  • If you have a current problem with a particular pest or disease, you should plan preventative treatments accordingly. This is particularly true for specific diseases such as brown rot of peaches, black rot of grapes, and apple scab and rust diseases. These diseases can only be controlled with scheduled, preventative sprays early in the growing season.
  • Pest populations are seldom static. They increase and decrease at different rates as a result of changes in the weather, plant and fruit maturity, and the management practices followed by gardeners. Careful management of fruit crops early in the growing season can prevent some pests from causing damage that warrants chemical treatments later.

Still have a question? Contact us at Ask Extension.