Fruit Pest News
Volume 3, No. 5 April 8, 2002
A weekly, online newsletter whose goal is to update Extension agents and growers of commercial tree fruit and small fruit crops
on diseases and insects in Tennessee.
Text appearing in blue or red can be clicked to link to other web sites. Be aware that much of the linked information is produced in other states and may not be applicable to Tennessee.
In this Issue:
1. Current Conditions
2. Apple: MaryBlyt Update
3. Tree Fruit: Pheromone Trap Catches and Biofixes
4. Blueberry: Twig Blight
1. Current Conditions
Last week saw an extended cool period, with frosts occurring each morning from April 4 through 7. The frosts were generally light, but some strawberry blossoms were lost. Apple growers, whose trees are entering the bloom period, should applaud the cool weather -- High temperature is an apple grower's enemy before and during bloom because of its effect on fire blight bacteria, causing them to multiply. With so much fire blight last year, overwintering inoculum may be high. Refer to "MaryBlyt Update," below, for more information on fire blight. (SB)
2. MaryBlyt Update
The MaryBlyt program for fire blight prediction indicates infection when 4 conditions occur: (i) any blooms are open; (ii) rain or dew occurs; (iii) the average temp for the day is 60 or above; and (iv) there have been enough accumulated heat units to allow colonization of the blossoms by the bacteria. The risk of infection is rated as "low," "medium," "high," or "infection." These ratings correspond to any one, two, three, or four of the previously-mentioned conditions, respectively. All the program needs from the operator is the high and low temperature for each day beginning at green tip, and rainfall or dew for each day beginning at first open bloom.
MaryBlyt guides your streptomycin spraying decision-making with this rule: You should spray if the risk of an infection is high and an infection is predicted for the next day. You use the weather forecast with the prediction function of MaryBlyt to determine whether an infection is predicted for the next day.
The Golden Delicious trees at the Plant and Pest Diagnostic Center began blooming today, April 8. The MaryBlyt predictor indicates that the risk of infection will be high here for the next 3 days, but that infection will not take place (if the weatherman's forecast is correct). The only missing element is the amount of bacterial inoculum. The recent cool to cold weather has prevented the bacteria from increasing sufficiently. However, it does not require much warm weather to allow the population to build and spread to the open blossoms. I will use the prediction function (F2 key) each day for the next several days, with an updated weather forecast. I will let you know what happens. MaryBlyt has been very accurate in predicting blossom blight infection here the last two years. (SB)
3. Pheromone Trap Catches and Biofixes
Pheromone traps generally attract just
what you want to attract although many other insects (flies, beetles, bees, and other
moths can get stuck in the sticky traps). For this reason it is good to change the
sticky trap bottoms regularly. I have noticed that the pheromone traps occasionally
catch some other species of tortricid moths that we will call unidentified. This
is unfortunate because it can add to the confusion. I have been catching an unidentified
tortricid moth in the Oriental fruit moth trap that was much larger than Oriental
fruit moths (OFM). While the OFM are tiny moths, just 3/16 inch from head to tail
the unidentified moth was more the size of a codling moth (5/16 inch from head to
tail, wider and just generally bigger). You tend to forget from year to year just
how small the OFM are compared to the codling moth, redbanded leafroller and the
Obliquebanded leafroller. The redbanded leafroller has the easy to recognize pattern
on the wings and the obliquebanded leafroller is larger and also easy to recognize.
Redbanded leafrollers have been active since traps have been put out in
both Nashville and Bradley County. I am putting the biofix at March 14 although
it may even be a bit earlier. The Putnam county traps were not put out until late
March or possibly as late as April 1. On April 2, 11 were caught with another 33
on the third and 7 on the fifth. I expect that the biofix would be closer to mid-March
if the traps had been out earlier.
Oriental fruit moths have been caught
in Bradley County since the traps were put out (first catch of 6 on March 15) so
the biofix is March 15. The biofix in Nashville was on March 28.
I have
caught a single codling moth on four occasions since March 26 in Nashville. Since
I have not caught two or more at a time, I have not yet set the biofix for Nashville.
The Putnam County traps caught two codling moths on April 2 and four on April 3.
This would put the biofix for the Putnam County site at April 2.
I have
not caught any obliquebanded leafrollers in the Nashville trap. (FH)
4. Twig Blight of Blueberry
Blueberry growers should look for twig blight, caused by Phomopsis vaccinii, beginning in early spring, since the symptoms can begin to show shortly after budswell. Control measures can then be initiated.
Individual buds turn brown and die, followed by browning of the bark around the bud as the fungus moves from the blighted bud into the twig. The infection usually advances inside the twig until most or all of the flower buds on a twig are killed. Click here http://www.ces.ncsu.edu/depts/pp/notes/Fruit/fdin010/fdin010.htm to see images of these symptoms. Click the images to enlarge them. The dieback does not progress into the older wood, making twig blight easy to distinguish from stem blight, caused by Botryosphaeria dothidea.
It is helpful to prune out and destroy the infected twigs, but this should be done prior to the bloom period, for maximum benefit. Many spores are released from infected twigs beginning shortly after bud break. Those that land in opening buds germinate and invade the twig. However, all is not lost if you have not done this. Removing infected twigs between this time of year and August is helpful in that it reduces twig blight in next year's crop. That is because dead twigs continue to produce spores, which land on and infect buds that become next year's flowers.
Preventive fungicide applications may be needed in plantings in which twig blight has been a problem in the past. Benlate plus captan is the most effective. Captan alone may be used if Benlate cannot be obtained.
The highbush varieties Murphy and Harrison are highly susceptible to twig blight and will surely need a control program. Croatan is moderately susceptible, while Reveille, Cape Fear, Bluechip, and Wolcott are relatively resistant. Some rabbiteye varieties are susceptible, especially Delite. (SB)
The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm
Contacts:
Steve Bost, Professor and Extension Plant Pathologist
Frank Hale, Associate Professor and Extension Entomologist
Both authors available at:
615-832-6802
fax 615-781-2568
Plant and Pest Diagnostic Center
5201 Marchant Drive
Nashville, TN 37211