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In this Issue: June 27, 2006 |
| Soybean Rust Update |
| Dutch Elm Disease |
| A Turf Disease "Imposter" |
| Plant Disease Highlights |
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Soybean Rust Update Development of current season soybean rust infections continues to be very slow in the southeast (fortunately). This past week, a soybean sentinel plot in southeastern Florida was found to be positive for rust. This is the first instance of soybeans being infected this season. All previous finds were on kudzu. Tropical storm Alberto likely will cause an increase in rust development, but it takes 3 – 4 weeks for symptoms to become identifiable after such an event. There is no word on any additional rust finds in Mexico and intensive scouting in Texas has yielded negative results. Even with the slow development, there are 18 counties in Florida, Georgia and Alabama with rust infections, compared to six at this same time in 2005. In Kansas, sentinel plots are being scouted in Atchison, Bourbon, Finney, Harvey, Labette, Leavenworth, Lyon, Miami, Mitchell, Montgomery, Nemaha, Pratt, Reno, Republic, Saline, Shawnee, and Thomas Counties. Three additional plots are still to be established. Additionally, two spore traps, part of Syngenta’s Spore Tracker network, have been placed in Atchison and Labette Counties and are being monitored weekly. In addition to being scouting for soybean rust, five of the plots will be monitored for soybean aphid development as well. These plots are in Atchison, Finney, Harvey, Labette and Lyon Counties. (Jardine)
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Dutch Elm Disease |
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I’ve heard reports from several county agents and others that Dutch Elm Disease (DED) is active once again this spring. DED is caused by a fungus that is spread by two species of bark beetles. DED blocks the tree’s water-conducting tissues, causing discoloration and wilting. Usually the first symptoms are in the tops of the trees where individual branches stick out like “flags.” Eventually the whole crown wilts and the tree dies. This can take several weeks up to a year. The infection causes brownish red streaking in recently infected branches. The streaking is visible if you peel back the bark. If you suspect DED and would like a diagnosis it is important to collect the right kind of sample. Collect a couple of branches with streaking, ½ to 2 inches in diameter, from limbs that have wilted recently. Dry, dead samples are not helpful. Submit the sample to your county extension office to be forwarded to the K-State diagnostic lab. DED can be prevented with a combination of sanitation, pruning, and regular injections of systemic fungicides. Sanitation is very important. Infected trees should be removed and all wood should be buried, burned, or chipped. Don’t keep the wood for firewood piles, which can be breeding grounds for the beetles and the fungus.
For fungicides, the most common method is preventative injection every 3 years by a trained arborist. At K-State we were fortunate to have arborist R.O. Brown (“Brownie”) donate his time last week to inject the lovely elm tree in our garden (see photos). The fungicide was donated to K-State by Syngenta. Our K-State tree is about 3 feet in diameter and required about 80 ounces of fungicide pumped in with 40 gallons of water which took about an hour. The cost of injection (including the fungicide) would probably be in the $600-$700 range. So, these preventative injections are expensive and usually only performed on “important” landscape trees. Consider the value of the tree— is it an important part of the landscape, or just one of many trees? Does it provide shade (reducing air conditioning costs)? What would it cost to remove an infected tree and replace it with a new planting? There are a lot of factors to consider. [Kennelly]
A Turf Disease “Imposter” Recently the diagnostic lab has received several samples of turf that is suffering from excessive thatch. Though it is not a disease, I thought I should discuss it since it has been so common lately. Thatch is the layer of compressed surface roots, stems, and runners just above the soil surface. If thatch is only about 1/2 inch thick it has positive effects on turf. Thicker thatch causes problems. The check-in information with our “thatch-y” samples usually says something like this, “We water the lawn, and the turf still looks brown, so it can’t be drought—it must be a disease.” Thick thatch can induce a drought stress even in irrigated turf. Thick thatch prevents the flow of water into the soil. In addition, the turf roots often do not penetrate through the thatch into the soil. The roots just grow in the thatch where they do not pick up enough water. The result is large patches of drought-stressed turf. The K-State turf team has a publication about thatch management available at the following website (in the Homeowner section of the Turf Pages at http://www.oznet.ksu.edu/hfrr/TURF/Welcome.htm) . The site includes a table about the frequency of de-thatching required for various thicknesses of thatch. Here’s a direct link: http://www.oznet.ksu.edu/library/hort2/mf2131.pdf We have seen thatch up to 2 inches thick in the diagnostic lab. Unfortunately, those lawns will probably need to be replaced. [Kennelly]
Plant Disease Highlights Corn - Cold weather crown
stress, compaction
Contributing Author(s): Megan Kennelly kennelly@ksu.edu Doug Jardine jardine@ksu.edu
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Web updated 9/01/06 |
