weather icon Clear

Humidity causes most plant disease problems

Question: I am sending you a picture of my funky-looking tree. I think it has some sort of disease problem.

Yes, it does look like a disease problem, but I think it will stop spreading as soon as the humidity goes back down and rains stop. In fact, this problem probably occurred a few weeks ago, because the new leaves coming out seem unaffected.

Diseases need to have three ingredients, all coming together at the same time, to manifest themselves. First, the plant needs to be susceptible to the disease. Plants that are not susceptible or have been bred to be resistant to a disease normally will not get infected.

Second, the disease itself needs to be present. This is why I continually ask readers to sanitize their equipment, inspect plants for problems before they buy them and rotate their vegetables.

The third ingredient is the right kind of weather. Most diseases are caused by fungi, the majority of our plant diseases here, and grow and spread under high humidity and rainy weather.

Disease control focuses on interrupting or preventing one of these three ingredients. All we need is a drop in the humidity, and it will stop. Also pruning so that you have good air movement through the canopy will help prevent and reduce its spread.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.

Don't miss the big stories. Like us on Facebook.
Water less often to determine if plants are xeric

One way to find out if an unnamed plant is xeric is to water it less often during the cooler months. If it starts looking bad to your eyes or dies, then it is most likely not xeric.

Transplant smaller Joshua tree for better survival

Native plants have a very wide and established root system. Big native plants look beautiful but are exceedingly difficult to move from the wild primarily because of their established root system.

Bay laurel trees struggle with hot temperatures

Q: Our sweet bay laurel trees face east and are watered by a drip irrigation system on a separate line for trees only. Obviously, these trees are not doing well. They were originally 24-inch boxed trees planted in 2013. Our HOA contends they are close to the end of their lives, and they will be removed. Any ideas?