Brown dead spots on apple tree leaves

Bob Dluzen
The Detroit News

Recently I was asked to look at some apple trees that were showing signs of distress. Many of the leaves were covered with irregularly shaped brown, dead spots.

As soon as we approached the trees I had a pretty good idea what was going on. The spots were evidence of phytotoxicity, meaning the trees had been exposed to a chemical of some sort.

After some discussion with the owner, the actual cause of the problem became apparent. It was an overdose of ordinary fruit tree spray.

Brown, dead areas of different size and shapes are a clue of phytotoxicity. The margins of the spots are sharp and distinct. Note that the new growth is undamaged

I looked at the container and asked my friend if he applied the material according to label directions. He assured me he did at the rate of  2 1/2  tablespoons per gallon. I asked him to show me how he measured the spray concentrate.

He got out his garden chemical measuring cup, it was the same one he used for all sorts of garden chemicals. It turns out, without thinking, he measured out 2 1/2 ounces rather than tablespoons and ended up with a spray mixture that was concentrated enough to cause the phytotoxicity.

He was pretty embarrassed by what he had done. I reassured him that it could have happened to anyone. I reminded him of the time back in the late 1990’s when NASA and an aerospace company combined Imperial measurements and metric measurements. NASA used meters and centimeters, while looking at the same schematic drawing, the company thought the numbers were in inches and feet. The mission did not turn out well for that Mars orbiter.

Fortunately, even though the spots will remain through the rest of the season, my friend’s trees will recover from the mishap.

I should add that hot air temperatures shortly after spraying will make it more likely that phytotoxicity will occur. So check the weather forecast before applying spray material. If it looks likely that the temperature will rise near the 90’s, hold off spraying until the weather moderates.