Timely disease prevention for gardeners

With rain comes fungus, growing on our susceptible trees and plants

Upper left - early scab infection on bottom surface of leaf; upper right - late season scab with top surface lesions; lower left - early scab on fruit; lower right - late season scab. (Kari Peter)

ALLEGANY CO., N.Y. — It’s raining, it’s pouring, the fungal spores may be growing. In this article, I will be describe some fungal problems our plants may be experiencing this year. This year’s rain seems to be non-stop. Don’t get me wrong, we needed rain to replenish our water tables, but with the good comes the bad. The bad is all the fungus that may start growing on our susceptible trees and plants.

Already I have seen this happening on Crabapple trees and Asiatic lilies in my area and gardens. Crabapple trees that once had beautiful blooms and fresh leaves, now have foliage that are spotted and drooping giving the tree the appearance it is dying. Later in the season these affected trees will have fruits with circular rough spots. All of this comes about because of a fungal disease called Venturia inaequalis. The spores from this fungal disease can winter in leaf litter or the ground under the tree and are blown about by the wind. Spores remain dormant on the ground until temperature and moisture are right which triggers the release of ascospores into the air which land on the tree surfaces.  After penetrating the leaf, the fungus symptoms will become evident, starting first as a small yellow spot that grows and ruptures into a black lesion that then spreads more spores. This will not kill the tree but it will be unsightly looking. Control measures include removing leaf litter from under the tree (now and in the fall) and burning or placing the leaves in black plastic garbage bags exposed to direct sunlight for multiple days to kill the spores. A fungicide containing copper or sulfur may be applied after flower buds have fallen, but they are not guaranteed to be effective. A solution of potassium bicarbonate (baking soda) is reported to be effective and is acceptable for organic farming, it also helps with the control of powdery mildew. This is a lot of work considering this may not happen again until a very rainy spring, but it will ensure your tree remains healthy. There are now several varieties of crabapple trees that offer resistance to this issue.

Photo courtesy Carol Sitarski.

If you have Asiatic lilies you may have noticed this type of damage to the leaves. This most likely is a fungal disease by the name of botrytis which affects the stems, leaves and in extreme cases, the buds and flowers, not to be confused with Lily Leaf Beetle. This fungal disease also attacks bedding plants. Botrytis starts as spores on the ground, in garden debris or under leaves similar to the Venturia inaequalis fungus. It also is spread by wind or rain splashing from the ground back up onto this year’s fresh leaves.  Once the infection starts and if the conditions are favorable the fungus can spread like wild-fire. Symptoms begin as small white or brown spot that grow into a larger black spot with a lighter middle and will quickly engulf the entire leaf, stem or bud if action is not taken quickly. This disease will not affect the bulb, other than causing it not to grow larger that year. However, the bulb will die if under siege from botrytis for three years in a row. To prevent botrytis, thoroughly remove all leaves and stems in the fall and spray the ground in the spring with a commercial fungicide or potassium bicarbonate (baking soda) spray. Infection can begin after injury from hail or frost, after an injurious event start spraying on a two week rotation until the plant starts to die back naturally.

As summer progresses, I will update readers on additional fungal problems as/if they arise.

Basic Fungicide Recipe: 1 tsp. baking soda,1 qt. water, 1 tsp. dish soap or horticultural oil. Mix together, spray on. Be sure to cover the whole plant, including stems, and top and bottom of leaves. Spray every 3-5 days for plants that are infected, especially while weather conditions favor fungal diseases. Use preventatively every 2 weeks and reapply after heavy rainfall. Do not apply when the weather is very hot and/or sunny as this can lead to leaf burn.

–Carol Sitarski, Master Gardener
Cornell Cooperative Extension of Allegany County

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Timely disease prevention for gardeners

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