Tree and shrub care for mid-April

Cedar apple rust on apple leaves. iGrow photo

By John Ball
SDSU Extension Forestry Specialist

We are way behind last year in plant development. By mid-April last year, the forsythias had just finished blooming and the serviceberries were beginning to flower! This year neither one even has their buds expanding yet in Brookings. It looks like a late start to spring this year, but with temperatures expected by midweek, it might turn around very quickly, or we might have even more snow!

I have had a number of calls on when to start spraying apple trees. Insecticide sprays will not need to begin for a while. Our most common insect pest of apples, the apple maggot, is not out until July and the second most common insect pest, codling moth, does not need to be treated until after the petals begin to fall. However, it may soon be the time to begin treatments for diseases. While the symptoms of an infection do not appear until summer, the time to manage apple diseases will be just as the buds begin to expand.

There are probably two major foliage and fruit diseases of apples in our area, apple scab and cedar-apple rust.

Apple scab infections result in irregular brown to olive-drab blotches in the leaves by mid-summer and these leaves begin to fall shortly thereafter. I have seen trees completed defoliated by apple scab by Labor Day. The fruit may also be affected with hard, scabby lesions being the most common symptom for apple scab infection. Late winter-early spring management of apple scab begins with raking up and burning or otherwise destroying all the fallen apple leaves within a few hundred feet of the trees. Apple scab overwinters on the fallen leaves and during the wet spring weather the spores are released from these fallen leaves to infect the newly developing leaves. This raking and burning has limited value, and is not a substitute for fungicide applications, but may be helpful in reducing the severity of the disease particularly for isolated trees.

Cedar-apple rust infection results in orange spots on the apple or crabapple leaf by mid-summer and with severe infections the tree may be defoliated before the end of August. The fruit may also develop similar spots. Cedar-apple rust received its name from the fact that the disease must alternate between two hosts, the “cedar” two juniper species, eastern redcedar and Rocky Mountain juniper and the apple, either apple or crabapple. The disease will not occur if either the cedar or apple host is missing. Cedar-apple rust management begins with the removal of infected junipers near the apple trees. Look for Rocky Mountain junipers and eastern redcedars with the small hard “apples” encompassing the twigs. These are the indicator that the tree is infected and will be producing spores to infect the apple trees this spring. The galls open and produce these colorful orangish horns that release spores. Ideally all the redcedars and Rocky Mountain junipers within several hundred yards of the apple trees should be removed. This action will reduce the severity of the disease but not eliminate infection, as spores may come from more distant trees. You need to remove all the junipers within five miles to completely control the disease, an impossible task. Fungicide applications will still be needed.

Fungicide treatments for apple scab start with a spray applied just as the buds are beginning to expand, less than a 1/4-inch of leaf showing. Cedar-apple rust fungicide applications on apples start when the new leaf is about a week or two old, though treating the leaf as it is expanding may also be beneficial. These first apple scab or cedar-apple rust sprays are critical to the successful reduction of these diseases and, if missed, will significantly reduce the effectiveness of later treatments even if the remaining sprays are properly timed. After the first spray, fungicide sprays are continued about every 7 to 10 days until after petal fall. At that time the weather usually turns a little drier and a 10-14 day interval can be used until the end of June when applications generally stop.

The most common fungicides used for treating apple scab have been Captan or mycolubutanil listed as the active ingredient. Captan is also the most common fungicide included in multi-purpose fruit tree sprays and is effective on apple scab, but not cedar-apple rust. Fungicides containing myclobutanil, such as Immunox can be used for either apple scab or cedar-apple rust.

Sign up for 2018 Master Gardener Training today

SDSU Extension Master Gardener Training is provided by SDSU faculty and includes access to online training materials, a resource manual, and hands-on classes. Hands-on classes will be held in three locations, over eight sessions. Each session begins at 8:30 a.m. and ends at 4:30 p.m. local time. Come join the fun!

When/Where: Participants can select one of three training locations: Huron: June 5, 12, 19, 26, July 10, 17, 24, 31; Pierre: June 6, 13, 20, 27, July 11, 18, 25, Aug 1; Rapid City: June 7, 14, 21, 28, July 12, 19, 26, Aug. 2.

Topics Include: Basic botany and taxonomy; soils and fertilizers; turf and weed management; plant pathology/composting; tree and shrub care; pest management; planting and landscape use; pesticides; insects and pollinators, biodiversity; vegetables and season extension; herbaceous ornamentals, native plants, plant propagation and more!

Cost: There are two training options:

• Training with Volunteer Commitment as an SDSU Extension Master Gardener – $250.

To take course at discounted rate, you must provide 50 hours of volunteer service over the next two years as a Master Gardener. The balance of the full course fee will be invoiced if service commitment is not completed. Obtain 6 CEUs.

• Training to Obtain Certificate of Recognition in Horticulture – No volunteerism required – $600.

Participants will receive the same training but will not be required to volunteer and will receive a Certificate of Recognition in horticulture. Obtain 6 CEUs.

Register at www.igrow.org/gardens/master-gardeners/. If you do not see the actual registration link immediately, please be patient, it will be live in a few days. Having trouble registering? Contact us at [email protected] or call 605-782-3290. Registration deadline is May 19.

“Ready, Set, Grow!” May 5

The Coteau Prairie Master Gardeners’ 4th annual free seminar “Ready, Set, Grow!” has been postponed from Sat. April 14, to Sat. May 5, at the Codington County Expo Building (1910 W. Kemp Ave.) in Watertown. Speakers have been rescheduled. Members are hoping those planning to come on April 14 will be able to attend on May 5, when the weather is hopefully better! The theme “Right Plant, Right Place” will be featured. The event will be in the North Expo; use west entrance off 21st St. W., Entrance H. Registration and refreshments begin at 8:30 a.m., speakers begin at 9:00 a.m. and end at 2:00 p.m. A catered box lunch is available for $10 and can be ordered at registration. An afternoon “make and take” session is available for $7, where participants can make their own hypertufa pots from newspapers, ending the day at 2:00 p.m. Preregistration is not required.

Topics and speakers include: Unique Plants and Veggies – Vikki Schaack, Medary Acres, Brookings; The Best Plants Tested at McCrory Gardens During 2016 and 2017 – David Graper, SDSU Extension horticulture specialist; Great Container Plants and More! – Lori Seim, Sioux Valley Greenhouses, Watertown. The afternoon session is Make Your Own Tufa Pot from Newspapers – Instructors Deb Cass and Lori Seim.

Join us to learn more about putting the right plant in the right place. For more information, contact Dianne Rider, President, at 881-3975, or visit and ‘like’ their Facebook page: https://www.facebook.com/CoteauprairieMG/