Black Sooty Mold

What is the black, sticky substance that may be found covering the leaves of many plants?

The black substance on the leaves is called sooty mold.  It is a fungus which resembles soot. This particular fungus, however, is not harmful to the plant but is actually living on a sweet, sugary substance called honeydew.  The honeydew is being secreted by some insect that is infesting the plant. If you see sooty mold on a plant, it means that the plant has an insect infestation – most likely aphids, mealy bugs, soft scale or whitefly. 

As the insect feeds, a clear sugary liquid is secreted by the insect onto the leaf below.  It is on this secretion that the mold grows.  Heavy rains will wash off the sooty mold from the leaves, but the insect problem still needs attention. Often when large trees become heavily infested with certain insects, the honeydew can actually be seen raining down upon the ground.  Again, sooty mold indicates an insect problem; inspect the plant for bugs.  Below is a close up of the sooty mold.

Moss and Algae = Slippery Sidewalks

Living in the tropics, people are often plagued with unsightly and dangerous moss and algae growing on driveways and pathways around their homes.  When the rain stops, the green growth will dry but will regenerate again with the next rain. 

There are many different products on the market to help clean up the driveway.  Look at the active ingredients on the label; most products will contain bleach,  soap, or a form of copper. Be sure to follow the directions on the label.  Most products are applied and remain for a while and then washed off with a hose or scrapped with the help of a shovel.  At times the buildup is so great that a power washer is needed. Bleach is often recommended at one cup per gallon of water. 

When using copper and bleach, there is always the potential for these products damaging desired plants either from the direct spray or from the solution saturating the soil. Take caution when spraying near desirable plants. The damage is lessened in high rainfall areas through the leeching action of the rain.

Another option is to use one cup of vinegar per gallon of water; bleach is sometimes added to fortify the solution. An application of Roundup herbicide will kill the algae and moss, but the plant residue needs to be scrapped away. 

Seed Germination - Nothing's coming up!

Planting a vegetable garden has a variety of challenges. But how disappointing when the seeds are planted and nothing comes up! Here are primary reasons for poor seed germination.

 1. Planting depth – small seeded vegetables like carrots and onions can easily be planted too deep. If planted too close to the surface, the seed can easily be washed away during heavy rains. Consult the seed packet for proper planting depths. 

2. Temperature – some seed need the soil temperature to warm up before they will adequately germinate, while other cool season vegetables like onions, germinate best in a cool soil. 

 3. Water -  too little and seeds will not germinate or will dry up after germination. With too much water, seeds and seedlings can die from lack of oxygen or be overcome by fungi. Even under normal moisture conditions, different species of fungi and bacteria can cause seeds to rot.  Seeds and seedlings should always be kept moist, but the soil should not remain soaking wet.  

 4. Soil pH - each vegetable seed as well as other plants will have its range in which it will germinate best. 

5. Herbicide residues -  may still be active in the soils causing poor germination.  A high fertilizer content in the soil could also hamper germination. 

6.  Insects will often feed on  seeds and young seedlings.

7. And finally, the seed itself! Poor seed germination can particularly be a problem in humid climates.  Relative humidity influences the moisture content of the seed. The higher the moisture content, the lower the germination rate will be, especially, after one year.

As a general rule, vegetable and flower seeds can be kept for one year without appreciable decrease in germination. Storage, however, may be extended to 10 or more years under proper conditions; seed moisture and temperature are the most important factors. The drier the seeds, the longer they will store.

In humid climates such as Hawaii, storing vegetable seeds in a dry, sealed glass container should keep most seeds viable for a year. For longer storage, place seeds in a moisture-proof container and store in the refrigerator.

Longevity of vegetable seeds will also vary depending on the species.  For example, collards, cucumber, endive, radish and water cress produce some of the hard seeds, rated as lasting 5 years. Next come beets, cabbage, cauliflower, eggplant, kale, mustard, squash, swiss chard, tomato, turnip, watermelon, rated at a 4 year longevity; asparagus, beans,  carrot,  celery,  chinese cabbage, New Zealand spinach, pea, and spinach, at 3 years; leek,  sweet corn, okra and pepper are rated at 2 years; and finally, the last group is rated at a mere 1 year longevity - lettuce, parsley, parsnip and onion.

Photo: Purdue University