Many plant pathogens like to survive the winter in infected crop debris. One example is iris leaf spot.
Here is a zoom – the black spots are structures where the fungus produces spores:
So what can we do? Here are some tips from the Horticulture News (http://www.ksuhortnewsletter.org/):
Iris are known for a couple of common problems: a fungus disease known as iris leaf spot and an insect named iris borer. Though both cause problems in the spring, now is the time to start control measures. Both the fungus and eggs of the borer overwinter on old, dead leaves. Remove dead leaves and cut back healthy leaves by ½ this fall to reduce populations of these pests. Also remove other garden debris from the iris bed. This can significantly cut down on problems next spring. (Ward Upham)
Another disease that lurks over the winter is peony leaf blotch (also known as red spot or measles) and you can find info on that disease here on the Common Plant Problems website.
(Photos by Megan Kennelly)
(Ward Upham, KSU Horticulture & Natural Resources. Original source: http://www.ksuhortnewsletter.org/)
Pruning in August can stimulate new growth that is less hardy during the winter. But what about pruning at this time of year?
Woody plants move sugars and other materials from the leaves to storage places in the woody portions of the plant just prior to leaf fall and we would like to maximize those stored energy reserves. Even pruning later in the fall can cause a problem by reducing the cold hardiness of woody plants. Dr. Rich Marini at Penn State Extension has written , “Based on everything that has been published we can conclude that woody plants do not attain maximum cold hardiness when they are pruned in the fall. Trees are affected more by heavy pruning than light pruning.” However, this does not mean that woody plants pruned in the fall will necessarily suffer winter damage. In most cases, I think you can get away with the old adage of “prune whenever your pruners are sharp.” However, damage can occur if we have a sharp drop in temperature before plants are completely hardened off. Also, marginally hardy plants are more susceptible to winter damage, especially if pruned in the fall. Though light pruning and removal of dead wood are fine this time of year, you may want to delay severe pruning until spring.
Consider pruning to be “light” if 10% of less of the plant is removed. Dead wood does not count in this calculation. Keep in mind that even light pruning of spring-blooming shrubs such as lilac and forsythia will reduce flowers for next year. We normally recommend that spring-bloomers be pruned after flowering.
Shrubs differ in how severely they can be cutback. Junipers do not break bud from within the plant and therefore should be trimmed lightly if you wish to keep the full shape. Overgrown junipers should be removed. On the other hand, there are certain shrubs that can be pruned back severely during the spring. Rejuvenation is the most severe type of pruning and may be used on multi-stem shrubs that have become too large with too many old branches to justify saving the younger canes. All stems are cut back to 3- to 5-inch stubs. This works well for spirea, forsythia, pyracantha, ninebark, Russian almond, sweet mock orange, shrub roses, and flowering quince. Just remember that spring is the correct time to do this, not now.
(Megan Kennelly, KSU Plant Pathology)
Irises are a popular plant, often grown in large groups. Iris leaf spot is a fungus that can cause mild spotting to severe dieback.The fungus spreads by spores that are dispersed in wet weather.
Red-brown spots with yellow halo:
A closer view – the black bumps are spore-producing structures:
Another close-up view of one spot:
Spots can coalesce to cover a large area
More significant dieback:
Where does that fungus spend the winter? In old infected leaves. Get those outta there to reduce your risk of infection in the new year. Clearing out old infected plant tissue breaks the life cycle.
More information about managing iris leaf spot is available in a recent article by Ward Upham in the KSU Horticulture News
When it comes to trees:
Trees need water. Not too much, not too little, but just right.
Trees need appropriate temperature. Not too hot, not too cold, but just right.
Trees need to prune. Not too much, not too little, but just right.
If you are looking for some cozy winter reading, you can check out our publication about Tree and Shrub Problems in Kansas.
In addition, I just came across a great publication from University of Kentucky that discusses tree and shrub decline. The information is similar to parts of the Tree and Shrub Problems in Kansas book, but sometimes it is helpful to read information from a new source since everyone presents information in a slightly different way. The reference is Stress and Decline in Woody Plants.
I love peonies! I’m lucky to have a neighbor down the street with an amazing display every spring.
Peonies do need some attention, though, including cutting them back. One reason to cut them back is to remove leaves infected with “peony measles.” By removing infecting the leaves from the site you can disrupt the life cycle. The fungus survives year-to-year in infected leaves, so removing them reduces infection risk next year.
(Photo by Ward Upham)
Here are some tips from Ward Upham from the Kansas Horticulture News:
Cut peony foliage back to the ground if this hasn’t been done already. Compost or discard foliage. Fertilize peonies twice a year — in the spring shortly before new growth appears and then again in the fall after the plants have been cut back. A total of 1.5 to 2 ounces (3 to 4 tablespoons) of a 1-1-1 fertilizer such as a 10-10-10 or 13-13-13 per plant per application should be used. This amounts to 3 to 4 ounces of fertilizer per year. If a soil test reveals adequate levels of phosphorus and potassium, use a lawn fertilizer such as a 29-5-4, 27-3-3 or something similar, but cut the rate to 1/3 of the above rate. In other words apply ½ to 3/4 ounce (1 to 1.5 tablespoons) per plant. The lawn fertilizer should not be a “weed and feed.”
Never apply fertilizer directly on the center of the peony as the buds (eyes) may be damaged. Rather, place the fertilizer in a band from 8 to 18 inches from the center of the plant. Water the fertilizer in so the plant can take it up.
Winter protection of herbaceous peonies is only necessary the first winter after planting to prevent alternate freezing and thawing from lifting plants out of the soil. A couple of inches of mulch should be sufficient. Any organic material that does not mat down will work and should be applied after the ground freezes. Avoid using leaves that will mat together. Remove the covering before growth begins in the spring.
The less common tree peonies have woody stems like deciduous shrubs and should not be cut back to the ground or pruned in the fall. Collect the shed leaves and place in the compost pile this fall. Though tree peonies are hardy to Zone 4, they do benefit from a light mulching over winter. Also, it is recommended that tree peonies be fertilized during November to get the plants off to a good start next spring. It is best to take a soil test to see what nutrients are needed. If the soil needs phosphorus and potassium, use a complete fertilizer (such as 10-10-10, 9-9-6, etc.) at the rate of 2.5 pounds per 100 square feet. This would equal 1 rounded teaspoon per square foot.
If phosphorus and potassium are not needed, blood meal makes an excellent fertilizer. Apply at the rate of 2 pounds per 100 square feet or 1 teaspoon per square foot. Turf fertilizers such as a 27-3-3 or 30-3-3 also can be used but at the rate of to 1 pound per 100 square feet or 1 teaspoon per 2 square feet.
Dr. Cloyd provides an update on Japanese beetles:
Japanese Beetles are Back!