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Alert: May 23, 2006 |
Wheat disease Update |
| Summer patch on Kentucky bluegrass |
| Plant disease highlights |
| Pest of the Week - Aphids |
| Sycamore trees are dropping their leaves |
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Wheat Disease Update There has been relatively little change from last week. Leaf rust is being found a little more commonly in the eastern and central portions of the state, but incidence and severity remain low. Stripe rust is still very difficult to find. Wheat streak mosaic and barley yellow dwarf remain severe in various areas of the state. We have a suspected, but as yet unconfirmed report that there may be some head scab in southeastern Kansas. Plants that are infected will have heads that turn white, but leaves and stems that may remain green. Sometimes, the portion of the stem directly below the head is turned a chocolate brown color. Often, only part of the head is attacked, giving heads a white and green appearance. Close examination of spikelets often reveals a salmon-pink fungal growth on the glumes or at the base of the spikelets. Scabby wheat kernels are shrunken and chalky or pink in color. Kernels above the infected spikelet will be shriveled if the fungus penetrates the rachis and cuts off the nutrient supply. Scab often causes reduction in test weight, sometimes down to near 50 lb/bu. In addition, scabby kernels count as "damaged" in the grading process. These factors often combine to lower the grade of the wheat. Low-grade wheat must be blended with higher- grade wheat; this results in higher costs. Therefore, scabby wheat often suffers significant discounts. If damaged wheat will be used as feed, care should be taken since scabby wheat may contain the mycotoxins DON (vomitoxin) and zearalenone (an estrogen analog). Neither of these toxins is considered carcinogenic or highly toxic, but they both can reduce the performance of livestock. Producers who may want to use scabby wheat as livestock feed may want to consider having it tested for mycotoxins. Testing is available from the Kansas State Veterinary Diagnostic Laboratory, 1800 Denison Avenue D-117, Manhattan, KS 66506-5601, Phone (785) 532-5650; Web http://www.vet.ksu.edu/depts/dmp/service/toxicology/index.htm. Submit at least 1 pound of a representative sample. Both grain and straw can be tested. There is a $60.00 fee for this quantitative test, which includes DON, zearalenone, and four other common mycotoxins. (Jardine)
Summer patch on Kentucky bluegrass 2005 was a big year for summer patch in bluegrass lawns. The disease can carry over from one year to the next, so 2006 might shape up to be a bad year, too. The pathogen (a fungus) becomes active in May and colonizes the roots. However, the symptoms don’t show up until later, when the turf is stressed by heat and drought. Symptoms appear in June through August as patches 2-6 inches across. The foliage turns dull reddish brown, then tan, then light straw in color. Often the center of the patch remains green, leading to a donut shape of the affected turf, and because of this the disease is sometimes called “frogeye patch.” The pathogen can survive several years in the soil and cause repeat damage in the same location. There are chemical controls for summer patch but it is essential to include cultural management. Avoid excessive nitrogen fertilization in the spring. A good rule of thumb for Kentucky bluegrass is to apply 75% of nitrogen in the fall, 25% in the spring. The spring fertilizer should be a slow release formulation. Careful nitrogen management will prevent a susceptible flush of new growth during the hot months. Keep mowing heights at least 2 inches tall. Thatch reduction is also important. Lawns with a history of summer patch should be dethatched or core-aerated each year. If turf does become affected watering during the afternoon can cool the plants and alleviate the stress. Chemical control is not completely effective but it can reduce disease if used in combination with the cultural practices outlined above. Chemicals should be applied first in mid-May with a second application about a month later. Two examples of products for homeowners to apply are Systemic Fungicide 3336 WP from Dragon Chemical Corporation and Green light fung-away. I don't have efficacy data on these products, however. Commercial lawn companies have more products available than the ones sold for homeowners. If this truly has been a repeating problem a homeowner may desire to call a professional company. Always follow label instructions. If you suspect summer patch and would like a diagnosis please send a plug of turf that is at least 4-5 inches in diameter and 4-5 inches deep. For this disease it is critical to have a good sample of roots. Please take the sample at the transition area between healthy and affected turf. If possible include some digital photos to show the pattern and extent of damage, and jot down some notes on the sizes of the patches, when they first appeared, and if the problem was visible last year. [Kennelly, photos by N. Tisserat]
Plant Disease Highlights May 15-19 Apple - Fire blight
Pest of the Week: Aphids Sycamore Trees are Dropping Their Leaves The widespread partial defoliation of sycamore trees the past week, or so, appears to have been incited by a disease called anthracnose, but aggravated by weather conditions. Anthracnose on sycamore trees occurs in many years during cool weather in the spring. But typically, the infection causes brown blotching along the veins of the infected leaves - and some fallen leaves do exhibit that characteristic. The unique thing about this episode was that the anthracnose fungus invaded the leaf stem (petiole) of many leaves without progressing to the leaf blade by the time the leaves dropped off. Close inspection of infected fallen green leaves reveals dark fungus lesions along the petiole. Because anthracnose can impair the conducting tissue that carries water to the expanding leaves, the abruptly hot, dry weather over the weekend aggravated the condition, contributing to the dramatic defoliation that many of you witnessed. Anthracnose is favored by cool weather and should cease to be infectious as more summer-like weather sets in. But people may still notice trees like sycamore, cottonwood, and birch dropping leaves in response to heat and drought stress. These species often set on more leaves in the spring than they can carry through the summer stress period. In an effort to establish a balance between the leaf surface and the supporting root system, the trees tend to kick off excess leaves when the plants go through the transition from spring to summer. But, this self-defense mechanism usually occurs gradually, not as dramatically as defoliation caused by anthracnose. Anthracnose seldom causes significant damage to otherwise healthy trees. In most cases, the condition stabilizes when hot, dry weather sets in and new leaves replace those that dropped. Practices that contribute to the over-all vitality of the tree will help it to recover - especially thorough irrigation during periods of extended drought. When you water large trees, be sure to moisten the soil to a depth of several inches under the branch spread - out to, and beyond, the drip line (outer branch spread). If sycamore trees experience recurring anthracnose infection, or, if even occasional defoliation from the disease can´t be tolerated, fungicide sprays (applied in early spring), or injections into the root collar, in the fall, can be used as preventive measures - call the Shawnee County office of K-State Research and Extension for more information (232-0062). Notes: Many of you have noticed white fuzz on the back side of the fallen leaves - that is a natural pubescence and is unrelated to any problem the tree may experience.
Contributing Authors
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Web updated 9/01/06 |