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Month: April 2019

Cedar apple rust

(Megan Kennelly, KSU Plant Pathology)

The birds are singing, the tulips are blooming, and junipers (also called red cedars) are “blooming” in another fashion.  Cedar apple rust is here.  The pathogen (a fungus) spends part of its life cycle on a juniper tree, and the other part of its life cycle on apples, crabapples, hawthorns, or quince.  To simplify, we’ll just call them “apple hosts.”


Those jelly-like orange masses on the junipers produce spores that infect the apple hosts.  Once infection occurs, leaf spots on apple leaves develop in 1-3 weeks.  Eventually, fungal spores are produced in these leaf spots on the apple tissues.  The spores are spread by wind and rain back to junipers starting in about July.  Without both hosts, the fungus can’t complete its life cycle.
The disease looks dramatic on junipers, but it does not cause any harm.  The rusts can cause problems in the apple host, however.  If infection is severe, many leaves drop off early and the tree is weakened due to reduced photosynthesis.   If your tree only gets a small amount of rust each year, it probably won’t be an issue for long term tree health.
Management options (for apple hosts):
1) Resistance:  For new plantings of fruiting or flowering apples, consider planting a rust-resistant variety.  Information on crabapple cultivars is available at:
http://www.midway.k-state.edu/lawn-garden/docs/flowering%20crabapples.pdf
2) Tree care:  For any apple tree, proper pruning will allow air movement through the canopy. This practice reduces the leaf wetness that promotes disease.  Maintaining overall tree health will also help prevent the disease.
3) Fungicides:  Homeowners with a bad history of this disease (severe defoliation), might consider preventative fungicide sprays on the apple hosts when leaves are out and the orange galls are active.  For best control, applications should continue through May or as long as the orange galls are active. Products with the active ingredients myclobutanil or propiconazole are examples of materials labeled for cedar apple rust management in flowering crabapples and non-fruiting apples.  Make sure you check the label carefully. For example, if you are talking about fruiting apples instead of flowering crabapples, some products are not allowed.

Commercial fruit growers should consult the Midwest Fruit Pest Management guide: https://ag.purdue.edu/hla/hort/documents/id-465.pdf

There is also a video on rust diseases at: https://www.youtube.com/watch?v=yQdwSPtvhH8  The video is 15 minutes long and describes the life cycle and biology of these fascinating fungi!

Paying Attention to Pine Diseases

Now is a really good time to check for Dothistroma Needle Blight on Austrian, Ponderosa and Mugo pine trees. Several pine samples from northeast Kansas have the K-State Plant Disease Diagnostic Lab with classic symptoms. This disease tends to show up in crowded, mature pine plantings. The key is crowded plantings that lead to poor air circulation. Wet weather and poor air circulation lead to increased disease severity.

    

If you are trying to sort out winter damage from Dothistroma needle blight, the first thing to do is to look into the bottom of the tree. Dothistroma causes needle shedding and tends to be more severe in the bottom of the tree. Essentially when you look into the bottom of the tree, the interior needles are gone and all of the lower limbs tend to be bare. Needle loss tends to be particularly severe in crowded windbreaks where air circulation is poor.

Next take a look at the foliage. The needles will have scattered spotting and a half needle scorch. The outer needle tip will be brown and the inner portion of the needle will be green. Each needle will be affected in a different location.

You can contrast this with winter burn which can also produce a half needle scorch but will always burn all of the needles back in exactly the same location. Plus the damage tends to be in the outermost foliage.

The last thing to look for is raised black fruiting bodies (acervuli) on the affected needles. This is diagnostic sign for the disease. You may need a magnifying glass or 10X hand lens to see them, although when they are fully mature they are visible with the naked eye. The fungal fruiting bodies don’t start developing until late December or January, but now is a good time to look for them. If you don’t initially see them you can put the suspect needles in a Ziploc bag with a wet paper towel for couple of days. The high humidity will help the fruiting bodies pop out.

Dothistroma needle blight and winter damage can look very similar. If you are going to spend money to treat for the Dothistroma needle blight disease then it is a good idea to confirm that the disease is present. Samples can also be sent to the K-State Plant Disease Diagnostic Lab at the address listed at the bottom of this post. Dothistroma needle blight can be managed with fungicides.

For more information on managing this problem see the pine disease factsheet at the following web link (O’Mara):

https://www.bookstore.ksre.ksu.edu/pubs/l722.pdf

K-State Plant Disease Diagnostic Lab
4032 Throckmorton, PCS
1712 Claflin Rd
Manhattan, KS 66503
Send Questions to: jomara@ksu.edu
Testing for Needle Blight: $10 Extension/$13.50 Non-Extension