Plant Problems May Increase During Wet Weather

Pounding rains increase soil compaction. Too wet soils lead to root injury and death. Constant rainfall washes away soil nitrogen. Wet foliage and high humidity increase chances for disease infection. At certain time of year plants may not show injury, but we should be alert to the problems so that immediate action can be taken if any develop. We can also take precautions to avoid some problems. Begin by breaking up hard crusts that may have formed on the soil surface. These may be particularly common in heavy clay soils. Failure to break up this crust reduces oxygen supplies to the roots and thereby often slows growth.

Mulch applied after the crust has been broken up will prevent this from happening again. If plants have been standing in excessively wet soils for some time, root injury may have resulted. A reduced root system may make the plant appear starved, or leaves may burn on the edges in summer. Shrubs or trees planted in the past few years are particularly sensitive to the problem. Be prepared to water them well when hot, dry conditions develop later this summer.

Another result of excessive rainfall is loss of nutrients from the soil. Most easily lost is soil nitrogen. It must be replaced if food plant growth is expected. Ammonium nitrate urea and ammonium sulfate are effective nitrogen sources for summer application. In the vegetable garden, sidedressing is usually done after fruit set has begun. For example, tomatoes should be sidedressed with nitrogen about one to two weeks before the first fruit ripens. They will need additional sidedressing about monthly thereafter. Annual flowers should be sidedressed about four to six weeks after planting, and normally will not need another during the summer. Ammonium nitrate is used at a rate of about one pound per 100 feet of row, or 100 square feet.

Fungus disease that spread on wet foliage, or in high humidity are best examples. They include anthracnose, apple scab, mildew, and blackspot. Anthracnose has been quite severe on many sycamore trees, making them appear to have had the leaves frozen off them. Olive-drab spots form on the leaves, fruits are disfigured, and finally the leaves drop.

Several sprays of a fungicide should be applied in early spring when the leaves are unfolding. Where blackspot has gained control on roses, spray weekly with fungicides such as benomyl (Benlate) or folpet (Phaltan) to get it under control.