In this Issue:  April 15, 2004

   Eastern Redcedar Mortality

   Spring Control of Large Patch of Zoysiagrass

   Sphaeropsis Tip Blight Control

   Prime Corn Nematode Sampling Time is Near

   Wheat Disease Update

Eastern Redcedar Mortality

On a recent trip back from the Texas panhandle, I noted quite a few dead eastern redcedar in windbreaks throughout southwestern Kansas. We have received numerous samples and phone calls concerning this dieback and decline. Let me summarize the findings of the diagnostic lab. For the most part, we are not finding any evidence of diseases on the dead or dying cedars. Occasionally we do see Botryosphaeria canker (also called Bot canker) on declining Rocky Mountain junipers in the region, but this is certainly not the major cause of the decline. Instead, I think that most of the mortality is a combination of environmental stresses and poor cultural practices followed by damage from bark beetles. Remember that parts of western Kansas are going through a drought period comparable to some of the worst on record. Although eastern redcedar is a tough, tough tree it is not immune to the effects of drought.

Consider altering tree spacing in mature windbreaks to reduce drought stress. If you have mature pines or cedars at a spacing of less than 12 feet, you are asking for trouble. This is especially true in multi-row windbreaks. Increasing tree spacing by selective removal can help minimize drought injury. Tree thinning in windbreaks should be a continuing and gradual process. As trees get older and begin to fill, selectively remove trees that are crowding others or are of poor form. Try not to wait until an emergency (i.e. a drought) to do the thinning. If possible irrigate existing windbreaks. If you have spent 30 years establishing a windbreak, take the extra time and effort to make sure the trees receive water during dry periods! In younger plantings, try to keep weeds in check with weed fabrics and herbicides. (Tisserat)

Spring Control of Large Patch of Zoysiagrass

Large patch disease of zoysiagrass, caused by the fungus Rhizoctonia solani, is both a fall and spring disease. I usually emphasize fall management because of the potentially long-term damaging effects of the disease at that time of year. A single fall fungicide application not only inhibits disease development throughout the fall, it can help reduce, but not eliminate, large patch the following spring. Nevertheless, large patch may develop in the spring even though a fall fungicide program was used. It is really asking a lot for a single fungicide application to protect the zoysiagrass over a 6 month period. For that reason, it may be necessary to retreat fairways in early to mid-April just as the zoysiagrass breaks winter dormancy. If large patch development in the spring has been a problem, consider a fungicide application now. I don’t have a whole lot of experience on which fungicide would be the best to use as a spring treatment. Heritage would be a good choice provided the disease is not already active. This fungicide is better when applied as protective rather than curative treatment. Other options would be PCNB or iprodione. (Tisserat)

Sphaeropsis tip blight continues to be a problem on mature Austrian and Ponderosa pines. The disease results in dieback of new shoot growth in the spring. Infections over a number of years will eventually result in a branch dieback and tree decline. In severe cases, the disease can kill the tree.

Several fungicides are now labeled for control of tip blight. Copper-based products including Bordeaux mixture, Kocide (labeled for 'needle blight') and others are available. The thiophanate-methyl products of Cleary's 3336 and Fungo are also labeled for tip blight. Syngenta Corporation recently added tip blight to their Banner MAXX label. I know some arborists are using Bayleton, Eagle, and Heritage for Sphaeropsis control; however none are specifically labeled for this disease in landscapes. I have only seen efficacy data on some of the coppers and thiophanate products. Many arborists are interested in using systemic fungicide injections for control of tip blight. I have not seen any data to support the claim that tree injections will control tip blight. Part of the problem is that most of the current injection techniques do not work on Austrian pines. It is very difficult to get sufficient quantities of a fungicide inside the tree with any type of regularity. The low pressure devices currently on the market just don’t work. We are currently testing some newer injection methods and these appear to have promise. However, these are still in the prototype phase. (Tisserat)

Prime Corn Nematode Sampling Time is Near

Root lesion nematode can be a serious problem in corn, particularly in the northwest part of the state and throughout the Arkansas River basin. Years of research have suggested that there is a poor correlation between the numbers of nematodes in the soil and the potential for damage and yield loss to the corn crop, making diagnosis and management recommendations from soil samples alone a somewhat chancy process. Root sampling serves as an alternate method of detecting damaging populations of nematodes and provides for a more reliable picture of the problem.

The optimum time for root sampling is approximately one month after planting. When submitting a root sample, be sure to include roots from plants in both the poor and healthy areas of the field. Also include the soil from the area directly around the roots being submitted. Samples should be sent to the Plant Disease Diagnostic Clinic, Dept. of Plant Pathology, 4024 Throckmorton Hall, Manhattan, KS 66506-5502. Cost is $13.40 if submitted directly or $10.00 if submitted through a local county extension office.

Test results will be reported in numbers of nematodes per gram of root tissue. You can expect about a 1% yield loss for each 1,000 root lesion nematodes. As an example of how to interpret test results, for an irrigated corn field with a yield potential of 200 bu., you would need 5,000 nematodes per gram of root tissue before a nematicide application would be economical (assuming $2.00/bu). This threshold of course would change as the price of corn goes higher or lower. While management options are limited for the current year’s crop, root sampling will provide an accurate picture for determining the need for a nematicide or crop rotation for next year’s crop. (Jardine)

Powdery Mildew of wheat is epidemic in central Oklahoma and is now appearing throughout south central Kansas. In most years this disease occurs in low levels and is not considered a threat to realizing yield potential. In rare instances disease severity can be high enough to damage or kill secondary tillers which ultimately may decrease yields. Unless powdery mildew is killing plants or a large number of secondary tillers, applying fungicides will not result in higher yields. Yield response most often occurs when fungicides are applied to protect the flag leaf. (Stack)

Ned A. Tisserat
Extension Specialist
Plant Pathology Program

E-mail: tissne@plantpath.ksu.edu

Phone: (785) 532-5810

FAX: (785) 532-5692
http://www.oznet.ksu.edu/path-ext

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