The Impacts of Rain

Community Contributed

By Glenn Teves, UH County Extension Agent

Probably the only time it rained this much is when it rained for 40 days and 40 nights a long, long time ago. Torrential overnight rain of 5 inches is rare on Molokai, but when it arrives every five to seven days, as it did in Hoolehua, this is a little too much. The impacts of heavy rain on plants are many, and we won’t see some of these impacts until a little later in the season. Too much water favors the growth of fungus and bacteria that can hinder plant growth and even kill them.

Fungi are mostly microscopic plants that grow on the leaf surface, and will spread their specialized roots into the leaf surface, getting their food from there, and will cause early death of leaves, although some will just live on the surface and are not as bad. Plant defoliation can affect plant resilience, and also the quality and quantity of food, fruits or flowers it produces.

Bacteria are both a blessing and a curse, depending on the variety. Bacteria are probably the first plant forms to appear on Earth, and their number exceeds all plants and animals combined. There are two types of bacteria; the good ones are called symbiotic, meaning they live with other organisms and support each other in their survival. Pathogenic bacteria, on the other hand, will attack us, plants, and a lot of different organisms. Many of them love water and will move with the water. When conditions are right, bacteria will find their way into plants and move with the water, and it’s almost impossible to control them except with resistant varieties of crops.

How do these microorganisms affect plant growth and survival? Both leaves and flowers can be infected by fungi and bacteria. As long as the conditions are right, these plant pathogens will continue to grow and spread. Too much rain, and all flowers may be destroyed, and since many flowers grow into fruits, fruit quality and quality will be adversely affected. A good example is a watery avocado or papaya, or a small fruit set.

Some of these diseases will affect forming fruit. One example is anthracnose fungus on mango and avocado, which start as black flecks or dashes, then grow into large irregular spots and will rot the fruit. But the biggest impact will be on its root system, which requires air as much as water to thrive. This damage is more long-term and may even kill plants. This is especially true for drought-tolerant plants or those which require good drainage to grow. Two examples include papaya and avocado. Diseases such as Phytophthora root rot have devastated these plants, resulting in early death.

In most of these problems, there’s little that can be done to remedy the situation. It comes with the season, and you have to wait for better weather to see what the long-term impact is on your valued fruit trees. There are good years and bad years for all, and hopefully all our good soil doesn’t get washed away as well.