Evan de la Torre Pierce s Disease California is faced with a new threat and it is one that is only getting worse with each passing season That threat is Pierce s disease named after Newton B Pierce Special Agent to the Secretary of Agriculture and California s first professionally trained plant pathologist To understand this new threat that California is facing1 and how genetic engineering can help it is important to understand some of the background for this disease what non genetic methods are being used to try and stop this threat before it gets out of control and why genetic intervention seems the most effective approach in the future Pierce s disease was first introduced to California in the 1880s when it decimated 30 000 acres of vineyards in the Los Angeles Basin near Pomona and Anaheim It hit the same area twice more in the 1930s and 1940s with the same ferocity In 1887 and 1889 Pierce s disease was found in the Napa Valley and northern Sacramento In 1921 it was found in Tulare County and by 1940 it was identified in mostly all the counties in the San Joaquin Valley More recently Pierce s disease has impacted 25 of the 3000 vineyards in the Temecula Valley which has totaled 13 000 000 in damage in this county alone Wine Institute Currently there are 15 counties that have been labeled as infected within California and the number is increasing with each passing year Furthermore the two areas that have been devastated the most by Pierce s disease are the San Joaquin 1 Pierce s Disease is a disease that other states than California has had to face i e Florida but I will chose to only talk about California for this paper Valley and the Napa Valley Wine Institute Seeing the trend of rapid and vicious spreading one might ask how was it possible for this disease to spread so quickly The rapid infestation of Pierce s disease throughout California can mostly be attributed to the glassy winged sharp shooter2 The sharp shooter carries the bacterium Xylella fastidiosa which is the cause of Pierce s disease When a sharp shooter drinks the sap from one of the vines it also injects the plant with this bacterium and thus spreads the disease with am amazing quickness Furthermore before the growers knew what the disease was or how it spread they would send cuttings from one vineyard to another Some of these cuttings traveled from the San Joaquin Valley to the Napa Valley and thus the disease was introduced to northern California The reason that California and more specifically the San Joaquin and the Napa Valleys has been affected with this disease is because the sharp shooters and consequently this disease thrive in climates that have mild winters Overview of Pierce s disease Now to further understand this new threat it is essential that one understands how the sharp shooter transmits the disease and how the plant is affected from it As mentioned Pierce s disease is the bacterium Xylella fastidiosa that thrives in the plant s xylem The sharp shooter which feeds on the xylem sap transmits the bacteria from the diseased plant to the healthy plant every time it feeds on a vine Once this happens the bacteria eventually blocks the water conducting system and consequently reduces the flow of water within the plant s cells to the affected leaves Overview of Pierce s disease Therefore the drying or scorching of the leaves on the vine are the first signs of the disease The leaves then turn slightly yellow along the 2 There are other sharp shooters such as the blue and green that are spreading the disease as well but the glassy winged sharp shooter is the most damaging of the insects margins before drying or die rapidly even when they are still fully green PICTURE Furthermore the bark matures unevenly mature dark brown bark can be surrounded by immature light green bark Overview of Pierce s disease Since there is a lack of water transport to the plant s cells the vine prematurely produces small inedible raison like grapes Consequently the vine is now unusable and if left alone will die within two years However the growers don t let the plant die on its own because they pull the now useless plant up before it can die naturally Clearly this disease is very threatening for growers around California so what are growers doing in order to counter this leafhopping menace First and foremost there have been massive inspections on all transports of nursery stock and bulk grapes throughout California Considering that the transportation of vines from one area to another is the easiest way for either infected plants or sharp shooters to infect new areas a lot of effort has been given to ensure that this doesn t happen In fact in 2001 alone 50 000 nursery plant shipments and 100 000 grape shipments were inspected Wine Institute Furthermore growers are now selectively removing vegetation around the vines that might house the sharp shooters and are conducting heavy pruning of the infected plants Ground spraying of the infected plants throughout the vineyard with insecticide has also been an alternative However it is difficult to find an insecticide that will only target the sharp shooter and not harm the other animals and vegetation in the area Some insecticides that have shown promise in killing the sharp shooter but they have also been killing healthy vines Another method which has shown more promise is that of antibiotics Unfortunately injecting the drugs into the hard grapevines requires countless hours of manual labor and it is difficult for growers continually inject their numerous vineyards Alright Seed There has also been a method of biological control that introduces a parasitic wasp that lays eggs in the eggs of the sharp shooter This method has been shown to be an inexpensive long lasting and environmentally friendly alternative Consequently it can be seen in Temecula that because of the implementation of this method the levels of sharp shooters have slowly declined Wine Institute However using this method also means that there will be many more wasps to deal with in the vineyards Consequently researchers are trying to breed a stingerless wasp to deal with this immediate problem Though these methods have had success in stopping the sharp shooter each method is very time consuming because the growers would have to do all of this work manually and check the plants often to ensure that further outbreaks don t occur Furthermore Pierce s disease is spreading faster than these present preventative measures
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