Home & Garden: Summer slime flux problems & how to correct it
Free Press Gardening Columnist
The rain we received recently was great for our landscapes and gardens. In some cases however, like the 4-inch pots of lavender I had in my backyard, the rains did not wet the planting medium evenly. There were still dry spots down about an inch.
Water does not always move evenly through soil and wet the soil particles uniformly. This is true not only with soil-less planting mixes, but with the native soil in our gardens and landscapes. Even when we amend are native soils with a good-quality organic matter there is always going to be areas drier than others. Amending the soil certainly helps correct some of those problems, but as gardeners we need to be aware of these inconsistencies in soil moisture and correct for this problem as much as possible.
The rain is likely to increase the amount of ooze produced by slime flux-infected trees as the water pressure in these trees increases. When this ooze drips onto grass a sunken, round depression is likely to form. Sometimes the dead grass is confused as a fungal pathogen. If there is a tree overhanging that area, you can often see the cause of the depression by standing over the hole and looking straight up. Sometimes you’ll find brown scummy material on a sidewalk, patio, or road resulting from slime dripping from an overhead branch.
Slime flux is a bacterial infection that ferments the internal tissue of the tree creating a pressure which can split a tree apart unless there is a crack or cut through which the high pressure ooze can escape. I examined a large silver Maple last week which was dying back from the tips of the branches. The dieback was a direct effect of the pressure of slime flux crushing the vascular system preventing water and nutrients to move to the affected parts of the tree. When this occurs fertilizing with nitrogen to produce more water and nutrient-conducting tissue in addition to increasing the amount of water applied should help relieve the problem of dieback. This will not eliminate the disease, but should extend the life of the tree.
In this instance a portion of the roots were under an asphalt driveway on the other side of which was a dry gravel parking area. Watering the dry area would also help relieve the tree’s stress. When applying fertilizer one must ensure it’s not over applied. Fertilizers are salts and excessive levels can kill roots, making the problem of reduced water uptake caused by slime flux even worse.
The rain will stimulate growth of our lawns and, if we don’t change our cultural techniques to accommodate for this, we likely will have an increase in summer disease problems. If the rains had been accompanied by lightning the anticipated problems could even be greater. Rains, especially those which include plant-available nitrogen generated by lightning, increase the growth rate and succulence of turf. Succulent turf is preferred by disease organisms.
The increased growth rate of the grass requires more frequent mowing to ensure no more than one-third of the blade is removed at any one mowing. As with trees and shrubs, removing too much of the grass at one time results in root death. Since plants are most susceptible when under stress, and dieback of roots results in stress, you can expect fast-growing succulent lawns (which are not mown often enough) to be more susceptible to disease. You should also avoid the application of nitrogen when lawns are already growing too fast. Increased susceptibility to disease is one reason why lawns of cool-season grasses should not receive high doses of nitrogen in the summer when these grasses are under heat stress. The fertilizer increases the stress. Small amounts of fertilizer are acceptable, but large amounts should be avoided.
There are some exceptions to the rule of removing no more than one-third of the foliage of the plant at any one time. As you have noticed, commercial fruit growers will remove 70-90 percent of last year’s growth from their peaches and nectarine trees every spring. This is to ensure these trees produce adequate growth for fruit production the following year. This procedure, however, stresses the trees and as such would increase their susceptibility to insect and disease pests. In this case production is more important than tree health.
Multi-stem shrubs such as the Austrian copper rose and lilacs can be cut back to the ground removing all of the leaf-bearing stems. While this damages root growth it also stimulates sucker growth from which a new, healthier, insect- and disease-free plant emerges. When this procedure is used to rejuvenate an old plant, it needs to be accomplished as soon as possible after bloom to ensure sufficient regrowth of leaves. While plants treated in this manner may not bloom the following year, their overall health will be greatly improved.
When an arborist trims a mature shade or ornamental tree, no more than 25 percent of the leaf-bearing tissue is removed to avoid excessive dieback of roots. When you pinch back a herbaceous plant to make it spread out, it is best to follow this 25-percent rule. Remove no more than 25 percent of the leaf-bearing surface or root death will occur.
GJ Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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