Purdue Extension Service

Vanderburgh County, Indiana

Resistant Varieties Provide Best Pest Control

By Larry Caplan, Extension Horticulture Educator, Vanderburgh Co., IN

For the Evansville Courier and Press, February 22, 2008

Some of our favorite landscape plants are prone to fairly severe insect and disease problems. This results in either huge amounts of maintenance work in the form of spraying pesticides and removing dead plants and plant parts, or in resigning ourselves to sickly looking plants.

One example of a pest-ridden favorite is the common crabapple. Crabapples are a common sight in southern Indiana landscapes. People love the beautiful masses of white to pink blooms that appear in early spring, and the fruit can be attractive later in the summer and fall.

But crabapples are prone to two major problems: apple scab and Japanese beetles. Apple scab is a fungal disease that infects leaves throughout the growing season when temperatures and leaf wetness favor spore germination. Left untreated, infected leaves turn yellow and drop by mid-summer. Japanese beetles, of course, are famous for feeding on the leaves and fruit of over 350 species of plants, and crabapples are certainly in their top ten.

One of the easiest ways to prevent insects and diseases from devastating your landscape is to plant resistant cultivars (cultivated varieties). Resistant plants are usually not as severely affected as susceptible plants, and so don't require lots of pesticide treatments to protect them. Although we don't have resistance to many insect and disease problems for many of our landscape and garden plants, crabapples resistance to scab and beetles does exist.

Researchers at Purdue University have evaluated crabapples for several years, and have come up with lists of resistant cultivars that will work well in Indiana. The problem is, many of the scab-resistant crabapples are very attractive to Japanese beetles, and some of the beetle-resistant cultivars are heavily defoliated by scab. However, I've been able to combine the two lists, and can recommend the following crabapples that have high resistance to both of these problems: Ann E. Bob White Jack Louisa Prairifire Red Jewel Sargent Tea White Angel

There are many other crabapples available out there that might be worth choosing. If, for example, Japanese beetles have been a minor problem for you for the last few years, you may not feel as obligated to look for resistance, especially since a low-toxicity soil-drench insecticide is available. However, because of the high humidity we experience in southern Indiana, I would strongly recommend the scab resistant cultivars.

One word of warning: some of the older cultivars on this list are not quite as resistant to apple scab as we once thought. What's happening is that the fungus that causes scab is evolving and mutating, and is slowly changing enough to attack previously resistant plants. Researchers are constantly developing and evaluating new cultivars, so expect these lists to change over time.

For a complete list of resistant crabapples, or to learn more about controlling landscape pest problems, contact the Purdue Extension Service at (812) 435-5287.