Sudden oak death, as the name suggests, is a disease that is capable of rapidly killing certain species of oaks. It was first identified in California, in 1995. Two years earlier it was identified in Germany and the Netherlands, killing rhododendron. Because the pathogen originally infected and killed tanoaks, an undesirable, understory scrub tree, it generated little interest until other, more desirable oaks species began dying. However, by this point, the disease was well established and eradication no longer an option, with millions of oak trees killed by the disease. Currently, over 120 hosts in addition to oaks have been identified, and more continue to be added to this list. What is most unusual about sudden oak death is the severity of disease symptoms coupled with the broad host range of the pathogen. This leads to difficulty in diagnosing and managing this disease. What causes this disease? The pathogen that[Read More…]
Archives for May 2019
Although most people are understandably concerned about boxwood blight, boxwood does suffer from a number of diseases, including Volutella blight and Macrophoma leaf spot. Unfortunately, boxwood also suffers from a stem decline, caused by Colletotrichum theobromicola. The following was written by Dr. Raj Singh, LSU. Boxwood Stem Decline by Dr. Raj Singh Available on line at: https://www.lsu.edu/agriculture/plant/files/PPCPNewsletter_January2015.pdf and https://apsjournals.apsnet.org/doi/10.1094/PDIS-09-14-0948-PDN Boxwood (Buxus sp.) is an important landscape shrub in Louisiana, the south and the nation. Several cultivars are commercially available, and its vibrant green color and evergreen growth make it a popular ornamental. Boxwoods are used as stand-alone specimens at the entrances to homes and businesses. They are also grown as low, clipped hedges around homes and commercial landscapes and have become the top choice ornamental for new developments across Louisiana. In 2011, the Plant Diagnostic Center received diseased boxwoods from commercial and private landscapes that exhibited symptoms indicative of a[Read More…]
Tree pruning causes wounds to the tree and a fast recovery is critical to reduce the opportunity for diseases. Tree wound dressing has been used for decades and can cause serious challenges in the wound recovery process.
Biology: Purple deadnettle (Lamium purpureum) is a common winter annual broadleaf weed found throughout the US. It is closely related to another winter annual broadleaf, henbit (Lamium amplexicaule). Both have vibrant purple flowers that can been seen now in lawns, landscapes, and fields. To see more about henbit, refer to this article from last spring: https://www.purduelandscapereport.org//article/spotlight-on-weeds-henbit-lamium-amplexicaule/ Identification: Purple deadnettle is a winter annual meaning that it germinates in the fall, survives the winter as a small seedling, until spring when it flowers, develops seeds, and then dies when temperatures rise in late spring and early summer. Purple deadnettle blooms are mainly visible in April although you can find it blooming earlier and later depending on the area it is growing and the temperatures. Purple deadnettle is a member of the mint family and has a characteristic square stem. Purple deadnettle flowers are light purple in color and are small and tubular in[Read More…]
Don’t let emerald ash borer scare you and your ash to death. Use this updated bulletin and related tools to save your trees.
Hosta Virus X (HVX) is not a new problem, however, it’s not as prevalent as it was nearly a decade ago because growers have gotten better about recognizing the disease and removing infected plants from their nurseries. The most common symptoms include mottled, light or dark green discolorations along leaf veins (Fig 1). HVX may also be expressed as green and yellow mottling of the leaf blades, puckering, circular discolored areas or twisted leaves. The appearance of symptoms varies widely by cultivar and the color of foliage (Fig 2, 3). HVX is not vectored by insects. It is transmitted from plant to plant by contact with infected sap through such activities as dividing or trimming. It doesn’t spread nearly as easily as Tobacco mosaic virus but care should still be taken to disinfest contaminated tools to avoid spread to healthy hosta. Management: Send samples to a diagnostic lab when HVX is[Read More…]
A question that I often receive goes something like…. ‘How do I control grassy weeds in liriope and iris?’ At first glance, it would appear that those ornamental plants are very similar to grasses, but looks may be deceiving as they are actually not grasses. We know that broadleaf weeds can be controlled in grasses via broadleaf specific herbicides (Fig. 1), as well as grassy weeds can be controlled in broadleaf plants fairly easy with grass specific herbicides (Fig. 1 and Fig. 2). What is often misunderstood is the control of grassy weeds in grass-like ornamental plants. Broadleaf and grass weeds metabolize some herbicides differently. These differences allow herbicides to be selective in nature. True grasses are in the Poaceae family. Grass-like ornamental plants, such as liriope and iris are not in the Poaceae family, so the selectivity of grass-specific herbicides will not damage these plants. Grass-specific herbicides (called graminicides)[Read More…]