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I know many of you can hardly wait for cooler autumn temperatures following the blistering heat of this summer. Probably the last thing you want to hear about is another disease. Unfortunately, fall is the time for large patch development on zoysiagrass. This disease usually begins in late September or early October just about the time the zoysiagrass is going dormant. The Rhizoctonia fungus may be active through early dormancy and result in shoot death. Shoot damage during fall infection may go unnoticed until the following spring. Then large patches of damaged grass are evident as the turfgrass breaks dormancy. The fungus may resume activity in the spring to blight even larger areas of turfgrass.
The best management strategy for large patch involves taking preventive measures in the fall. Don't overfertilize the zoysiagrass and avoid late-season nitrogen applications. Try to reduce irrigation rates in the fall. As zoysiagrass goes dormant, it doesn't require as much water. The excess moisture only serves to increase disease. Avoid late afternoon or night irrigation. Raising the mowing height also can help reduce disease severity, but this may not be practical on golf course fairways. It is something to consider on home lawns. Preventive fungicide applications in the fall are effective in suppressing large patch. A single application of azoxystrobin (Heritage), flutolanil (Prostar), triadimefon (Bayleton), or PCNB has been effective in my research trials in preventing large patch development. These products do not need to be watered in after application. See the product labels for more information on rates, etc. (NT)
Yellow vine decline was found on pumpkin samples from the Wichita and Kansas City areas this past week. The identity of the disease was confirmed by Dr. Jacqueline Fletcher at Oklahoma State University. Although the vine decline has been present in Oklahoma for several years, this is the first report of the disease in Kansas. The disease occurs on pumpkin, squash, watermelon and muskmelon. Apparently this disease has been responsible for substantial damage to watermelon and pumpkin plants in Oklahoma. It is potentially a very serious problem for us in Kansas as well.
Symptoms of the disease are variable depending on host and time of infection. Plants infected soon after fruit set may rapidly wilt and die within a couple of days. These symptoms may be confused with bacterial wilt (seen on muskmelon and rarely on pumpkin and squash). Other plants may not show symptoms until a few weeks before harvest. Then, leaves on the vine turn yellow with the older leaves also developing a scorched appearance. The youngest, or terminal leaves tend to stand in a vertical position and curl inward at the leaf margin. If you slice through a vine near the soil line, the phloem tissue has a golden to honey-brown discoloration. If you aren't sure where the phloem is, it will appear as a series of arcs just inside the cross-section edge of the stem. These arcs or wedges cap the xylem tissue, which is easily recognizable in the stem as bundles of large-pored, water-conducting vessels. Healthy phloem tissue should have a translucent appearance. The root system on diseased plants often deteriorates rapidly. Symptoms of the later stages of vine decline may be confused with Fusarium crown and root rot.
The disease is caused by a phloem-limited bacterium and is apparently transmitted from plant to plant by squash bugs. Further studies on the epidemiology of the disease are in progress in Oklahoma. Right now there are not a lot of control options. Maintain a program to reduce squash bug populations in the field. Once the plant is infected there is no control. If you have seen or heard of any unusual declines of pumpkins, squash or watermelon in the state, please contact me. (NT)
Just because apples are falling from the tree, doesn't mean they are ripe enough for good eating. Here are some guides to help you decide when to pick your apples. Color change: As apples mature, the skin color in areas of the stem and the calyx basin at the bottom of the apple turns from an immature green to alight yellow color. Some apples will develop a red skin color before they are ripe, so this is not a reliable indication of maturity.
Flavor: This is a good guide if you are familiar with the apples you have and know how they should taste. Even if you do not know the characteristic flavor of the kind of apple you have, you can still sample slices of a few apples and decide if they have a sweet flavor. If they are not ready to harvest, they will have a "starchy" or immature flavor.
Flesh color: As apples mature and starches change to sugars, the flesh changes from very light green to white. When you cut a thin slice and hold it up to the light you can see the difference.
Days from bloom: The number of days from bloom is a reliable guide for general maturity time, but weather conditions will have some influence. Some kinds of apples and approximate days from bloom to maturity are Jonathan, 135, Delicious, 145, Golden Delicious, 145, and Winesap, 155 days.
Seed color: The seeds of most apples change from light green to brown as the fruit ripens. This indicator should be combined with other changes since it is not absolute. The flavor of the apples, the change in color of the stem and calyx basins and flesh color are important in deciding if apples are ready to harvest. (WU)
A recent newspaper article concerning oak wilt in the Kansas City area stirred up a hornet's nest. Apparently, many homeowners in eastern Kansas read the article, looked at the oak tree in the front yard, and concluded it had oak wilt. The extension office in Johnson County was flooded with calls. I'm sure those of you in surrounding counties also had your share of inquires. I have covered oak wilt in detail in previous newsletters, and I won't repeat all of the information here, but will offer a few brief comments. Yes, oak wilt is present in eastern Kansas and I recently isolated the fungus from two locations in the Kansas City area. But the disease is not rampant in the Kansas City area. It is primarily a problem in certain native oak stands in the eastern part of the state and has been around for at least 40 years. I don't keep any records on incidence of the disease, but I don't recall it being any worse now than it was 5-10 years ago. The disease may appear to be increasing because more and more houses are being plopped into native oak stands where the disease is present. One could argue that construction in oak stands has increased oak wilt severity by increasing wounding and infection, but this hasn't been documented. In urban settings, the disease is relatively rare. The fungus spreads primarily through root grafts and is transmitted less efficiently by certain insects. Therefore, the chances of an isolated, individual oak in the middle of town contracting oak wilt is remote. It is possible for the fungus to be brought into town on contaminated firewood and then transmitted to healthy trees by insects, but I don't recall this happening in the Kansas City area. Even if this did occur the disease would likely be self limiting because the main movement of the fungus is through root contact. We simply don't have that many streets with contiguous plantings of pin oaks. There are many other causes of oak decline including iron chlorosis, gas leaks, girdling roots, Ganoderma root rot, construction damage, etc that are more prevalent than oak wilt.
Oak wilt is a nasty disease and should be taken seriously in areas where it has been confirmed. Every effort should be made to isolate diseased trees or pockets of trees by root graft disruption (trenching). Diseased trees should then be removed and destroyed; however, don't assume that a dying oak tree has oak wilt! The disease should be verified before implementing oak wilt control procedures. (NT)
Contributors:
Ward Upham, Extension Associate; Ned Tisserat, Plant Pathologist
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