Q. I have several pecan tree and some of the nuts I cracked this year have black spots on the nut and others have a soft brown film on part of the back of the nuts. What caused these problems and what can I do to prevent it.? The pecans have been producing for 30 years and I have never had the problem until last year.
A. I am guessing that these black spots are on the meat or seed that you normally eat. I am also guessing that when you eat this pecan meat that it is bitter. If you are moving your head up and down in agreement then this is insect feeding damage by one of the stink bugs.
We do have stink bugs in Las Vegas but one particular type of stink bug or a close relative is the leaf footed plant bug which also damages pomegranates, pistachios and almonds.
|Closeup of leaffooted plant bug. Photo contributed by Bill Stillman.|
This feeding damage can cause the entire nut to drop off the tree or can cause these black spots to appear on the meat. To eliminate this kind of damage you would have to spray the entire tree with an appropriate insecticide.
You would have to start early because they will begin building their population on the tree as early as April. These insects also feed on tree leaves, vegetables and all of our major fruit trees. They overwinter on ornamental plants that remain evergreen in our landscapes.
The adults have wings so they can fly from neighbor to neighbor. Soap and water sprays will kill these insects if they are sprayed directly with this concoction. Soap and water sprays have no residual so no poison remains when it dries. This can be an advantage and disadvantage.
Other sprays are fruit and nut sprays that contain synthetic pyrethrins or pyrethroids. These will also work but the main problem you will have is getting the spray to cover the large tree from head to toe. These black spots can be broken off of the nuts and the nuts can be eaten with no problem.