NUMBER 1202 |
June 30, 2009 |
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SOYBEAN |
TOBACCO |
FRUIT CROPS |
LAWN & TURF |
| Soybean Aphid Making an Appearance - But Not In Kentucky By Doug Johnson |
There are two main reasons why we do not expect to see large populations in any given year. First, the insect cannot overwinter in Kentucky. The aphid’s life cycle is very complex, but basically it requires a particular plant on which to overwinter, the common buckthorn. That plant is not present or is present in very low numbers in Kentucky. This means the pest must migrate into the state each year from the north central states. The second reason soybean aphids are rare in Kentucky is our summer heat. Temperatures above 85o F reduce the soybean aphid’s reproduction rate. So, their populations grow more slowly. Kentucky’s summers have plenty of days when the temperature is well above 85o F. For the moment we have not found any soybean aphids in our sentinel plot system. The aphid suction traps in Lexington and Princeton have not captured any soybean aphids. Additionally, I have not received any reports from agents or consultants (who often find the first aphids). This bodes well for us. Unfortunately, this is not the end of the story. Even though we have not yet seen any soybean aphids in KY, it is still very early in the season. Typically, we will not get any sightings of this aphid until July or August, and the larger populations occur in September and October. Normally, we would expect “full season” beans to be all but completely safe from this pest, with later planted “double-crop” beans at higher risk. This year planting has been significantly delayed due to late spring rains. This may push development of soybeans later into the year than we would usually expect. It is these beans that will be at risk of soybean aphid infestation. So, for the moment we are in good shape with reference to soybean aphid. I see no reason, except the late plantings, to assume that anything other than the norm will occur this year. However, it is important to remember that the insect will be here and to keep an eye open for its presence. You are encouraged to report finding soybean aphid to me at: doug.johnson@uky.edu. I will use your reports to help us all stay well-informed about this pest.
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| TOBACCO |
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Update on Blue Mold |
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| Pierce's Disease of Grapes Detected By John Hartman |
Symptoms of Pierce's Disease. Symptoms vary with different grape species and cultivars. In spring and early summer grapevines may show delayed shoot growth, leaf mottling, and dwarfing of new shoots. Late summer and fall symptoms are more dramatic and include distinct reddish-brown scorching and burning of leaf margins with the part of the leaf blade nearest the petiole and the main veins remaining green or sometimes yellow (Figures 3 & 4). Normally, scorch symptoms appear in late July or August, so in this case, the appearance of scorch now, in June, is somewhat surprising. As summer progresses into fall, scorching progressively spreads inward in concentric zones until the entire leaf blade is affected. During a drought, leaf scorching symptoms due to lack of water can be confused with Pierce’s disease. Thus, use of the ELISA test is important for diagnosis. The disease progresses along the grape vine with symptoms developing in adjacent leaves along the shoot both above and below the point of initial infection. Leaves often fall from the vine at the point of attachment to the petiole, leaving the petiole still attached to the shoot like matchsticks stuck along the vine (Figure 5). (However, this can sometimes also happen in the absence of Pierce’s Disease.) Late in the season, wood on affected canes fails to mature normally and some infected stems will develop an alternating green and brown banding along the affected grapevine (Figure 6). This uneven maturation of the vine may even persist into the dormant season. Initially, only one or a few canes on a vine show foliar and wood symptoms. Symptoms are more pronounced in vines that are stressed by high temperatures and drought conditions.
Grape susceptibility and disease spread. Pierce’s disease has occurred only rarely in Kentucky, having been found in one vineyard in western Kentucky in 2001 and in Fayette County in 2007. In both cases, infected grapevines were promptly destroyed. Some grape cultivars are very susceptible, usually dying within two years. Most French (vinifera) varieties die within two to five years while American (labrusca) varieties often live longer than five years. Pierce's disease is spread by several types of sharpshooter leafhoppers, by spittlebugs, and by grafting. In other regions of the U.S., the Pierce’s disease organism X. fastidiosa is distributed in a wide range of monocot and dicot native plants, which are infected, but not showing symptoms. We do not know if this bacterium has become established in other plants here. In Kentucky, bacterial leaf scorch of landscape trees such as oaks and maples is caused by a related strain of X. fastidiosa. Although the pathogen and symptoms are similar, Pierce’s disease is not caused by the same strain of Xylella as bacterial leaf scorch. Both diseases are favored by the hot weather found in the southeastern U.S. The fact that bacterial leaf scorch can be so devastating to landscape trees here suggests that if the Xylella causing Pierce’s disease became widespread in Kentucky, it would thrive. With an emerging grape industry developing in Kentucky, it is important that growers and County Extension Agents be on the lookout for this disease. Personnel in the U.K. Plant Disease Diagnostic Laboratory can run specialized tests to determine the presence of the Pierce’s disease bacterium in infected grapevines. Growers and agents are urged to begin examining grapevines for leaf scorch symptoms now and in the coming months. Where the disease is isolated, removal of infected vines should keep further spread to a minimum.
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| Brown Patch Activity By Paul Vincelli |
On all grasses, affected patches are often somewhat circular and can range from several inches to two or more feet in size. On tall fescue and Kentucky bluegrass, leaves exhibit tan, irregular lesions with a thin, brown border (see Figures 7 and 8). On creeping bentgrass and perennial ryegrass, a ring of olive- green leaf blades appears on the outside margin of the patch (Figure 9); these blighted leaf blades dry to a tan color. On humid mornings, the mycelium of the fungus often appears as a sparse, very light tan webbing in the lower canopy. This can be best seen with a hand lens. In some situations on perennial ryegrass, the mycelium can be quite dense, cottony, and fluffy, and grow all over the leaf blades. In this condition, it can look quite a bit like Pythium cottony blight. Since different fungicides are used against Pythium cottony blight and Rhizoctonia brown patch, knowing the identity of the disease can be quite important from a management standpoint. Laboratory diagnosis is the best option if a case of perennial ryegrass has dense mycelium that looks like Pythium blight. Management Tall fescue. Generally brown patch can be managed through cultural means in established tall fescue lawns. However, recent seedings of tall fescue often can suffer severe outbreaks of the disease during humid weather in summer months. These should be monitored carefully and treated with fungicide if necessary. Once these swards make it through their first summer and are well-established, they often do not need fungicide treatment to maintain sward density, although fungicides do improve overall greenness during summer. Be aware that products containing chlorothalonil and iprodione are no longer labeled for use on home lawns. More information on brown patch management in Kentucky lawns can be found in the Extension publication, Brown Patch in Kentucky Lawns, available at http://www.ca.uky.edu/agc/pubs/id/id112/id112.htm. Perennial ryegrass and creeping bentgrass. High- maintenance perennial ryegrass and creeping bentgrass swards should have preventive fungicide applications on at this point, and putting greens should continue to receive preventive applications for brown patch control through August (and possibly later, depending on weather). There is a wide selection of fungicides with very good activity for brown patch control. See the Extension publication PPA-1, Chemical Control of Turfgrass Diseases (http://www.ca.uky.edu/agc/pubs/ppa/ppa1/ppa1.pdf) for options. |
| By Julie Beale and Paul Bachi |
On fruit, vegetable and herb samples, we have diagnosed iron deficiency on blueberry; pollination problems and Septoria leaf spot on blackberry; black rot, crown gall and Pierce’s disease on grape; fire blight, frogeye leaf spot and cedar-apple rust on apple; Rhizoctonia root/stem rot and southern blight on bean; anthracnose on cucumber; bacterial wilt on cantaloupe; Pythium cottony leak and Rhizoctonia stem rot on squash; leaf mold, Botrytis stem canker, bacterial spot, Pythium root rot and Fusarium wilt on tomato; and Alternaria leaf blight on ginseng. On ornamentals and turf, we have seen Botrytis blight on lily; Phytophthora leaf blight on rhododendron; powdery mildew and Botrytis blight on rose; scab on crabapple; fire blight on Nanking cherry; black root rot on holly; anthracnose on ash and maple; Phyllosticta leaf spot on lilac and hydrangea; anthracnose on bentgrass; brown patch on fescue and ryegrass; and dollar spot on fescue.
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| By Patricia Lucas | |||||||||||||||||||||
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NOTE: Trade names are used to simplify the information presented in this newsletter. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named.
