Plum Pox Virus
Music Plum pox virus was first found in north American in 1999 in several peach orchards in Adams county, Pa. Plum pox or Sharka as it’s called, is a disease that affects peaches, plums, apricots, nectarines and almonds. The virus causes the fruit to develop blotches, which lowers their value. The disease doesn’t kill the tree, but it eventually stops producing any fruit whatsoever. But long before this happens, the infected tree already poses a great danger to other nearby trees, because it is a disease reservoir harboring the virus which can be more readily spread. Plum pox virus is spread from tree to tree by tiny insects called aphids. The aphid picks up the virus as it feeds from an infected tree. When it goes to a different spot, it releases the virus from its feeding tube and infects the next tree. While aphids are definitely the vectors that transmit plum pox virus from tree to tree and orchard to orchard, they don’t fly well enough or live long enough to have flown by themselves from Europe or South America to southern Pennsylvania, especially without touching down first anywhere else in the United States. The leap of the disease from continent to continent was caused by a human vector. Probably in transported nursery stock that was already infected before it was imported here and then unknowingly, was graphed onto healthy trees and those trees placed in the landscape. The insects took it from there. Since it takes several years after infection for the fruits to show any symptoms, the disease was already firmly entrenched by the time it was detected. (BugMobile) So, let’s turn to the pyramid. Well in the IPM pyramid we have a couple of different options, but some of them aren’t very good for plum pox. At the top there is chemical controls, but there really aren’t any chemicals available that will cure a plant of a virus disease. There are chemicals that will control aphids, but not before they can spread the virus. We don’t really have the good option for chemical control with plum pox virus. There’s no chemical that will control virus diseases. There are chemicals that will help control aphids but there not 100% and they are very damaging to the environment. You could wind up causing more problems than you are helping with. (BugMobile) Plus you want to avoid chemicals on people food. (BugMobile) What about good bugs eating bad bugs? There are no biological controls for virus again, and as you know BugMobile, there are some good biological controls for aphids. We need the lady beetles, we need parasites and predators. They help to cut down on aphids. (crunching noise) populations. (BugMobile) I think Aphids are really tasty. But there are too many ever to finish off, and it only takes a few aphids to infect a lot of trees. Mechanical and physical controls are our best bet for keeping the virus out or keeping it from spreading. What we have to do is find suspect or infected trees and since we can’t cure them we just pull them up out of the ground and burn them to get rid of that virus reservoir. (BugMobile) What have you done in Pennsylvania?
Well, in Pa we did a couple of things. First you have to find out exactly where the virus is and isolate that spot. So, we had to test all of the trees, all of the orchards we could find in the entire state and we found that the virus was only in a small number and we isolated those, isolated the area around them and then began working on that area removing positive trees, or trees that were very close to those trees. (BugMobile) That’s a big job, isn’t it?
It was a really sad, a really big terrible job. We had 50 people working full time going across the state to find and test trees. We had a large number of trees that had to be removed. and that was the grower’s responsibility. Teams visit orchards and take leaf samples. You’d think with some diseases anyway that you could see a tree was infected, but in this one there are a lot of silent carriers. There are trees that look fine that are carrying the virus, so they have to take those leaf samples back to the laboratory and there we run a test to find out whether or not a virus is actually present.
(BugMobile) What about cultural controls?
Cultural controls, the one promising area that’s being worked on really hard by a lot of researchers right now is developing resistant varieties peaches, plums and nectarines. That’s being done by a number of different methods all over the world, they are trying that.
(BugMobile) Cool Ruth, thanks a lot. Well, I got to get cleaned up and head for the lake. Don’t let the bugs, bug yah. Wow that’s a really sad story about those peach trees. Brrr, I think I’ll devote myself to clean living. Who knows, maybe it will all pay off and someday I might even meet my all-time favorite movie star hero Music (Beach Boys) I Get Around.