Question
Hello,
My crabapple (I don't know what variety it is) is declining really quickly now...it has been afflicted with apple scab and has many suckers growing throughout.  I can't tell if it has been affected by calico scale (there was an article warning of it in our local paper- I live Mid-Michigan- but I applied a feed/insect control type substance a month or two ago, made by Bayer, hoping it will help it somewhat.
I was wondering if I should try and cut the suckers off before fall and whether this tree is even worth saving.  I've read that severe apple scab could eventually kill the tree unless we spray regularly (3 times a year...every year?  forever??) and I don't quite know if I'm willing to use so much fungicide every year or whether we should remove it.
I could send you a picture of it as it looks right now...it has been losing leaves steadily this summer (and what a wet, cold summer this has been in Michigan:() to exemplify why I think it's deteriorating so fast..and why I'm still sort of reluctant to cut it off (it is a pretty mature tree- it was here when we moved into this house and it provides privacy next to my deck.
Any suggestions would be appreciated.
Thank you!

Answer
Unfortunately some crabapple and apple trees are susceptible to a fungal disease called apple scab. Symptoms of apple scab usually start on the undersides of leaves. Spots, at first, are small, irregular light brown to olive green lesions. As infection continues, lesions become more circular and velvety olive green to black. Leaves may curl and scorch at the margins. By mid-summer leaves usually turn yellow and drop. If fruit stems become infected, fruits may drop early. Apple fruits may develop scabby lesions.

Infections occur during moist conditions (rain, dew or constant irrigation). The temperature affects the severity of infections. In order for infection to occur in cool weather, plants must remain wet relatively longer than in warm weather.

Three options are available for apple scab management on crabapples:

First option - do nothing and let the tree defoliate each summer. Apple scab is generally not life threatening for the plant, but certainly lessens its ornamental appeal unless you enjoy naked branches in August. As with other diseases, try to keep plants healthy by watering during drought. Good sanitation practices may help. Remove and destroy any fallen leaves, flowers, and fruit as soon as possible.

Second option is a fungicide program. Several fungicides labeled for apple scab control include: mancozeb, chlorothalanil (sold as Daconil), calcium polysulfides (sold as Hi-yield Lime Sulfur and Ortho Lime-Sulfur), copper sulfate or potassium bicarbonate (sold as Bonide Remedy). Be sure to read and follow all label directions and precautions.

The battle against scab is won or lost during late April through early June (from bud break to fruit set). Begin fungicide spraying as leaves develop and continue according to label intervals until frequent wetting by rain has lessened, usually by July 1. If some spray intervals are missed, apple scab would be lessened but complete control may be lost.

Remember fungicide sprays are predominantly protectants against infection so new leaves have to be sprayed before infection occurs. Thorough and uniform covering of all leaves and developing fruits is required for control.

In addition fungicide sprays would have to be applied every year to protect the tree. Remember once leaves start to yellow and fall off the tree it is too late to spray fungicide for control during the current growing season.

The third option would be to prune horizontally at the soil line. Remove the tree and replace with scab resistant crabapple cultivars. Unfortunately many of the older cultivars such as 'Hopa', 'Almey' and 'Eleyi' are susceptible to diseases. There are many beautiful crabapple cultivars that are resistant to apple scab as well as powdery mildew and fireblight.

One of these is  is 'Snowdrift'. The red flower buds open into single white flowers which cover the tree from late April into early May. The flowers are followed by small orange-red fruits that persist into winter until the cardinals snack on them. Any fruits left in spring quickly get gobbled up by the robins.

Another is 'Prairiefire'. It is an introduction from the University of Illinois that reaches 15 to 20 feet tall. The dark red flowers, shiny red bark, persistent red fruit and disease resistance make 'Prairiefire' a beautiful addition to the landscape.

Remember resistance doesn't mean complete immunity to disease. During some exceptionally wet years resistant varieties may get apple scab, but to a lesser degree than susceptible cultivars.

You may want to call the office of the State Agricultural extension Service and ask them maybe to come take a look. I do not think the scab is what is killing the tree.