I’m following up on last week’s notes about plant diseases being caused by fungi, bacteria and viruses.

A couple of times in the past, I have referred to the three things necessary for a plant to be victimized; the host plant, the pathogen, and conditions favorable for the disease to thrive.

I’m going in reverse order today and dealing first with favorable disease conditions.

We can’t control weather and we can’t do much about elevation, major drainage issues or the neighbor’s shade tree.

But we can work within existing conditions when selecting which plant to plant, where to avoid growing something where it is prone to get certain diseases.

The best shot at preventing that fungus with the long Latin name I like from spotting up photinia leaves is to plant photinias in bright sunlight and spaced well apart.

Photinias planted close together to make for a quick screen are apt to get leafspot when they grow up and grow together, which reduces air circulation between plants and the plants shade themselves.

And we about guarantee early photinia death planting them crowded in damp spots in a half day or more of shade.

These conditions make the fungus very happy and prolific.

Quite a few diseases of our favorite plants are best dealt with in the landscape planning stage by studying up on each plant’s known disease threats and the conditions that favor those diseases.

In existing landscapes, sometimes pruning and even removing some of the plants will alter conditions and help remaining plants withstand disease pathogens.

Skipping back to the host plant part of the disease triangle, there are possibilities for prevention. The first one is to totally avoid owning a plant species to keep from dealing with its potential diseases.

I contend that is the right call with backyard peach trees for the sane 99.9 percent of people in this climate.

We few hardheads just think we are going to whip peach diseases next year.  But the best disease tool is plant genetics.

Plant breeders refer to “plant host resistance” or “plant tolerance” that allow plants to withstand disease fungi, bacteria or viruses even when the germs abound.

Pay attention to disease resistance information when choosing vegetables, annual flowers and landscape trees and shrubs.

Choose crape myrtle varieties with bred-in resistance to fungal mildew and tomato varieties that just don’t get fusarium wilt. Every rose variety has a rating for susceptibility to Rose Blackspot.

The no-spray way to grow roses is to plant the ones with high genetic resistance to blackspot.

In addition to avoiding favorable disease conditions and utilizing plants’ genetic resistance, dealing directly with the pathogen is a third option.

I know because I grow roses and some of my favorites are not strongly resistant to blackspot. So I spray a fungicide on them every two weeks during spring and early summer.

I quit spraying when it gets hot and dry because those conditions are unfavorable to the blackspot fungus.

It is now hot and dry.

 

Terry Rector is spokesman for the Warren County Soil and Water Conservation District.