Pests and Fungus: The Downsides to Too Much Rain

We’re not able to control how much rain we receive, but we can minimize elements in the landscape that encourage insects and their fungal friends.

The summer of 2007 is often remembered as the summer of biblical rainfall. The sky faucets would not turn off. The spring of 2016 is beginning to feel the same.

We’ve exceeded the average rainfall nearly every month since Jan. 1– sometimes by 200-300 percent. Lots of rain brings obvious benefits, but are there any detriments?

Well, the first obvious one is an increase of mosquitos. Other equally opportunistic six-legged friends include flies, springtails, silverfish, ants, gnats, midges and the always popular cockroaches (all kinds). Crustaceans such as pill bugs, and mollusks like snails and slugs are just singing in this rain.

The second detriment is disease. Both bacteria and fungi love moist weather to spread and infest, especially when the weather fluctuates between cool and moist, and hot and humid. Excess rain may doom your tomatoes and squash or just make your crape myrtle’s leaves appear to be shrouded by a summer snow of powdery mildew.

Of course, we’re not able to control how much rain we receive, but we can minimize elements in the landscape that encourage insects and their fungal friends:

  • Limit stale water — eliminate or turn over any containers holding “non-live” water like cisterns, containers, unused pots, bird baths, etc. If you do have basins for wildlife, drop in a small Bt – Bacillus thuringiensis – dunk to prevent mosquitos.
  • Increase air circulation and sunlight — the modern house lot with its privacy fences, large buffer shrubs and two shade trees is a magnet for a host of pests, even without rainfall of biblical proportions. Remove no more than 25 percent of tree foliage and raise the canopy of shrubs by the same amount.
  • Reduce fertilization — Additional nitrogen and phosphorus create plants that are too lush and too appetizing to insects and disease.
  • Increase drainage — our clay soil and shallow bedrock encourage standing water. If water continues to stand 48 hours after a rain, then use a French drain or improved channeling to move the water along slowly and gracefully.

Above all, eliminate all supplemental irrigation. Until further notice, step away from the controller and the hose, and your pets and plants will thank you.

Picture of Mark Peterson
Mark Peterson
Mark A. Peterson was a conservation project coordinator for San Antonio Water System before retiring. With over 30 years of experience as an urban forester and arborist, Mark is probably the only person you know who actually prunes trees for fun. When not expounding on the benefits of trees and limited lawns, you're likely to find him hiking San Antonio's wilderness parks or expounding on the virtues of geography and history to his friends.
Dig Deeper

Find expert advice on garden basics, landscape design, watering and year-round maintenance.