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Alert: May 15, 2006 |
Dothistroma Needle Blight |
| Spring Anthracnose Diseases |
| Plant Disease Diagnostic Update (April 2006) |
| Wheat Disease Update – Where is the Rust? |
| Be Alert for Cold Weather Stress in Corn |
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Dothistroma Needle Blight
Dothistroma needle blight is a fungal disease commonly found on Austrian and sometimes ponderosa pines, especially in the eastern third of Kansas. The fungus survives the winter in needles infected during the previous growing season. The infected needles can be on the ground or still on the tree. In spring, the fungus breaks through the surface of the needles and produces spores which spread during rainy weather to cause new infections. The new infections become visible in late summer or early fall. Diseased needles have yellow, tan, or red bands, and the tips of needles often die back and turn tan or brown. Infected needles eventually die and drop off. A heavily infected tree can eventually die from extensive defoliation over the course of several years. Needles affected by winter dessication will usually all turn brown back to the same length. In contrast, needles with Dothistroma infection will display variation in the length of the dieback zone (see photo). May and June is the time to control the disease, when the spores from last year’s infection are active. Last year was unusually rainy, and we have already seen one sample of Dothistroma from Rice County, which is usually too dry for this disease. The wet weather last year was enough to get the disease started, and it might spread if this year’s spring rains continue. If you are in an area that is usually not prone to Dothistroma, but had a wet spring last year, keep your eye out for this disease if the weather is wet. There are two application timings that are commonly used: either spray once in early June, or spray twice, with one spray in mid May and another in mid-late June. Good coverage is essential, and it may be helpful to spray nearby pines as well. If disease is controlled early it is not usually required to continue sprays year after year. Chemicals labeled for Dothistroma include copper compounds (ex: Bordeaux mix, Kocide) and copper + mancozeb (ex: Junction), and some mancozeb products. If homeowners decide to use chemical control a commercial applicator should be called. Removing diseased needles from the ground around individual infected trees in a home landscape might reduce disease the following year, but it won’t completely eradicate the fungus, and this method would obviously not be practical in a large planting. [Kennelly]
Spring Anthracnose Diseases Every spring in Kansas, sycamore trees leaf out and then start to shed. We often see a similar occurrence on ash, maple, oak and elm trees. Under cool, wet conditions a group of fungi cause a disease called anthracnose. It can cause leaf spots, shedding, twig cankers and shoot blighting. The leaf spots are dark, irregular and sometimes follow the veins. When the weather is particularly rainy, defoliation can be extensive and the damage can appear to be quite dramatic. Homeowners unfamiliar with anthracnose are often concerned that the tree is going to die. The good news is that recovery is around the corner. When summer arrives, the weather warms up and dries out and the disease ceases to be active. Trees re-leaf and look great for the remainder of the summer. Other than summer watering to speed recovery, control measures are not necessary. (O’Mara)
Plant Disease Diagnostic Lab Highlights
Bentgrass: Dollar spot
Wheat Disease Update – Where is the Rust? Through May 12th, rust levels in Kansas remain extremely low. Except for some fields in north central and northwest Kansas, and some very late planted fields in other locations, most fields are beyond Feekes 10.5 (full heading), and are no longer eligible for fungicide applications even if foliar diseases should develop. There are some light levels of leaf rust in the south central and southwest part of the state, but they should not cause appreciable yield loss. Drought may make many of these fields unharvestable in any case. Where recent rains have occurred, there continues to be some powdery mildew and tan spot development, but in nearly all cases, the top two to three leaves, including the flag leaf remain healthy. By far the most active diseases are barley yellow dwarf and wheat streak mosaic. Barley yellow dwarf remains most active in southeast Kansas, but trace levels can be found in almost any field in the eastern half of the state. Jon Appel, State Survey Pathologist for KDA reports severe wheat streak in many western Kansas counties especially those south of I-70 and west of U.S. 183. Most of the severely infected fields can be associated with nearby volunteer wheat. Control of volunteer within one-half mile to a mile of newly planted wheat at least two weeks ahead of planting remains the best management strategy. (Jardine)
Be Alert for Cold Weather Stress in Corn Weather conditions have been suitable in a large part of the state for the development of what has become known as cold weather crown stress. Corn plants less than a foot tall do not tolerate extended periods of cold, wet soil well. Scientists believe that cold, wet soils can reduce oxygen availability to the crown, which results in damage or death to the cells in this area. Symptoms generally look like stalk rot, but no pathogen can be isolated. Depending on the severity, plants can be stunted, yellow and often show nutrient deficiency symptoms, particularly those of potash, phosphorus and zinc. Corn hybrids developed for more southern or western climates are more susceptible than those that originate in more northern or eastern areas. Plants often grow out of the symptoms as soil conditions and weather improves. Should heat and drought stress occur during grain fill however, these plants will be the first to succumb to stalk rot. (Jardine)
Contributing authors: Doug Jardine, State Leader, Extension Specialist
(jardine@ksu.edu)
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Web updated 9/01/06 |