Cherry leaf spot, or shot hole, caused by the fungus Blumeriella jaapii, reduces flowering and weakens the tree. Cherry leaf spot often defoliates the tree by midsummer. Repeated defoliation makes the tree more susceptible to winter injury and may eventually kill it.

Symptoms

Leaves show small purple to brown spots with definite boundaries in early summer. The leaves turn yellow and fall. In July, the centers of the infected spots frequently fall out, giving a shot-hole appearance.

Cause

The fungus overwinters on fallen leaves. In spring following wet weather, spores form and winds blow them to infect leaves. When temperatures are favorable (60 to 75 degrees F), infection requires a wet period of only a few hours. Leaves are susceptible when fully unfolded—this usually occurs near petal fall. The initial leaf infections form spots, and more spores are produced in the spots. These spores are rain splashed to infect other leaves. Secondary spread and infection by spores continues repeatedly, whenever wet warm weather occurs, until leaves fall in autumn.

Control

Rake and destroy fallen leaves before spring. Fungicides should be used if plants are prematurely defoliated. Time spray applications beginning at petal fall; continue every 10-14 days if rain is predicted during the period. If initial infection is controlled, subsequent spray applications are unwarranted, however, we do recommend applications throughout the rainy season.

I have also attached information regarding the fungicide mixture I prefer to use. Bordeaux Mix fits well within our Integrated Pest Management Program. An additional recommendation is to inoculate the soil around the tree with beneficial soil microbes. There are beneficial bacteria that will control the populations of this harmful fungus, other fungal microbes will strengthen the tree through a symbiotic relationship.

Bordeaux Fungicide Mixture—How to Make Your Own Supply

This product is effective not only for fungal diseases but is also active for certain bacterial diseases such as fire blight of pear and apple.
The mixture can be prepared by combining hydrated lime or any type of finely ground lime with powdered copper sulfate (sometimes referred to as “bluestone”). Both materials should be available at farm and garden supply stores. However, some checking about may be required to locate the copper sulfate.

While Bordeaux Mixture can be prepared in several strengths, the recommended for dormant season application is a 4-4-50 formulation. The numbers refer to the ratio of copper sulfate and lime in 50 gallons of water. For example, 4 pounds each of these materials would be combined in 50 gallons of water. Since this amount of spray material is considerably more than needed by most gardeners, the recipe can be whittled down for preparation of smaller amounts of spray mixture.

For example, to prepare a gallon amount of a 4-4-50 Bordeaux Mixture spray, measure out 6 ½ teaspoons of copper sulfate and 3 tablespoons of hydrated lime. The lime should be mixed with a pint of water to make a “milk of lime” suspension. The copper sulfate should also be dissolved in a pint of water. The latter process may take several minutes.

Before mixing the lime and copper components of the mixture, one additional step (but an important one) must be carried out. Each container of these materials should be strained through a cheesecloth filter. If cheesecloth isn’t available, use cloth of a similar loose weave. The filtering is necessary to remove small pieces of lime or copper sulfate that won’t dissolve; otherwise, you’ll find these tiny pieces in the end of your garden sprayer tip, clogging up the works!

To make the filter, simply place the cheesecloth loosely over the top of another container and fix securely in place with a string or rubber band.
The filtered copper sulfate solution is added to a one-gallon container, followed by addition of the filtered lime solution. Enough water (about 3 quarts) is then added to the container to bring the total volume up to one-gallon.

You now have one gallon of Bordeaux Mixture ready for use. For two gallons, simply double the proportion of materials and prepare as before.
For best results, use your Bordeaux Mixture the same day of preparation and keep the sprayer agitated. Insecticides should not be added with the Bordeaux Mixture without first checking the insecticide label for possible compatibility problems.

What are some dormant season uses for Bordeaux Mixture? For peaches, use the material as a dormant spray for peach leaf curl, on apples and pears to help with control of fire blight, on grapes for black rot control, and on roses for black spot and other fungus disease control. A single dormant season application of Bordeaux Mixture won’t provide total control of these and other diseases the next season, but used along with other in-season control procedures, the task becomes a lot easier.

Recent high temperatures and intense sunlight have caused us to delay the Nutrient Management Program for some weeks. Now, with a milder climate in the forecast, it is essential we resume—successful nutrient management is time-sensitive, requiring consistent levels of nutrition which aid in plant growth and pest & disease resistance.

Our program includes:

• Spraying applications of organic fish and mint oil solution, for foliar nutrition. (In warm weather, aroma dissipates within a few hours.)
• Embedding special blends of dry organic supplements in the pines’ feeding zones, to nitrify the soil.
• Introducing inoculations of soil microbes, including beneficial nematodes, in designated areas.
• Releasing a variety of beneficial insects throughout the garden:
• Ladybird Beetles (common “ladybugs”)
• Green Lacewings (a ferocious insect predator)
• Microscopic Trichogramma Wasps (no human threat)
• Praying Mantis (our best defense against the Northwest Pitch Moth)

Thank you, visitors, for your patience and understanding as we continue to implement a program which has already proven successful and highly beneficial to our Garden.

Planting Location

Chrysanthemums require well-drained soil and full sunlight to grow and successfully bloom. This means generally 6 hours of sunlight or more each day during the summer period. Plants grown with less light will become weak, spindly and produce few flowers. Avoid locations which are exposed to street or porch lights as this will interfere with the flowering light response to shortened days. The best location is a southern or southeastern exposure preferably against a foundation or wall where additional protection is given from frost. Improve the drainage before planting by elevating the bed with a good mix of garden loam and compost.

Soil Preparation and Planting

Garden soil which is good for growing vegetables will be satisfactory for growing mums. If particularly high in clay, additions of organic matter including peat, composted leaves, rotted manure or straw will improve the drainage and aeration. While working the planting bed, collect enough soil for a soil test and follow the recommendation for amounts of fertilizer to be added. Containerized plants should be planted at the same depth at which they were grown. Do not bury the root ball. This will promote a lack of root aeration and root rot caused by fungal pathogens. Chrysanthemums are shallow rooted and do best if planted high. This means that frequent watering may be necessary during times of high heat and little rainfall. Space plants generally about 18 inches apart. Spreading varieties may require larger spacing.

Pinching

To generate a plant full of flowers and control growth, chrysanthemums require some pinching of the tips. This encourages branching and more compact growth. It also will stimulate more flowers to be produced. Pinching is done by removal of about an inch of the tip of each branch or shoot. This is snapped out with the thumb and index finger. The first pinch should be done when the plant is 6 to 8 inches tall and repeated when new branches become 6 inches tall. A third pinch may be necessary on fast-growing varieties. If plant are not properly pinched, they will become tall, leggy, easily blown over by winds and have few flowers.

The most important thing to keep in mind when pinching the growth back is the timing of the last pinch. For early flowering varieties which bloom in mid-September, the last pinch should be around the middle of June. Varieties which flower in the early part of October should be given a last pinch on July 1. Later flowering varieties should be pinched for the last time no later than July 15. Overall, about 3 months is required between the last pinch and bloom. This is a general rule which can guide you in controlling the growth and stimulating more bloom production.

Fertilization

Most mums will require fertilization several times during the spring and summer to stimulate good growth, produce thick stems and maintain a healthy green color. Chrysanthemums are not heavy feeders like vegetables so, it is best to use a dilute fertilizer applied several times prior to bud set. Nitrogen has the greatest effect on flower production and general growth. If too much is applied, vegetative growth will be hard to control, fewer flowers will be produced and overall, flowering will occur later in the season. Before planting a bed in the spring, about 4 pounds of 5-10-5 per 100 square feet can be worked into the soil to a depth of 6 inches. This gives about one-quarter pound of nitrogen per 100 square feet and should be enough fertilizer for the season if abundant organic matter is present. A second application around August 1 may be beneficial especially on poorer soils.

Apply about 2 tablespoons of 10-6-4 or 4 tablespoons of 5-10-5 fertilizer spread over a 2 foot circle at the base of individual plants. Alternatively, broadcast about 2 pounds of 5-10-5 per 100 square feet. No more than about a tenth of a pound of nitrogen should be applied at this time.

General Care and Maintenance

During the early part of the summer, a layer of mulch material should be applied to the soil after it has warmed up as this has definite advantages to conserving and regulating moisture to these shallow-rooted plants. Besides the benefits of water control, mulch protects the bed from erosion, compaction and retards weed seed germination. Use a 2 to 3-inch layer of coarse peat, leaf mold, compost, nut hulls or lawn clippings mixed with leaves. Mulches composed of chipped wood, sawdust and straw may consume nitrogen fertilizer and rob the root system. If you use these materials as mulch, double the fertilizer applied to the bed.

If you cannot control the growth of the plants to the point that they have become tall and begin to drop over, then some support may be necessary in the form of wire frames or upright stakes. Wire peony or tomato frames work well and should be put in place before they are needed, otherwise these will be more difficult to position without damaging the plant.

After the plants have flowered, the stems should be cut off close to the ground. Leaf, flower and stem debris should be collected and composted provided they are not disease or insect infested. If that is the case, the materials should be composted separately and not used for mulching or soil improvement around the plants. Disease or insect infested materials can be buried and left out of the garden.

Often chrysanthemums listed in catalogs are noted as being winter hardy meaning that the plants will overwinter and grow the following season. The term “hardy” has been used sometimes inappropriately and gardeners should be cautious about believing that all mums are winter hardy when stated so. The fact is that many mums are not reliably hardy depending upon the climate conditions presented and even the most hardy varieties may not make it through a severe winter of subzero temperatures.

Many mum selections will survive the winter if the plants gradually become frozen and remain that way until spring. Deep snow cover will assist this and protect the frozen soil if it remains intact throughout the winter. The best defense against adverse weather conditions is to provide good drainage so that water does not accumulate around the plants and promote ice formation. After the first frost, mound a few shovels of soil forming an 8-inch layer around the base of each plant. Cut the branches back to 10 inches above the soil line and apply a 2 to 4-inch mulch layer as soon as the soil surface freezes. This means loosely layering evergreen branches, straw, or other lofty materials around the plants. Avoid using materials like leaves or peat moss which will pack down and retard emergence of leafy shoots in the spring. After the last danger of frost has past, this mulch and soil can be removed. If leafy growth has already started and the possibility of frost is still present, apply another layer of loose mulch to protect the growth.

As an alternative to overwintering plants in the bed, they can be dug and placed into cold frames to better ensure survival. This means a little more work, but for those varieties which are more tender, it is often the only way to keep plants from one year to another.

• Mums in the Garden (PDF)