April 5 , 2004 Volume 13 No. 3 Update on Pest Management and Crop Development
Highland: Redbanded leafroller flight began 4/5
Albion: Pear Psylla eggs found 3/31
(Art Agnello , Entomology, Geneva )
Originally introduced accidentally from England into Connecticut about 1832, the pear psylla has 3-4 generations a year, depending on the length of the growing season for the area. The overwintering adults pass the winter in litter on the ground or in cracks in the tree bark. On warm spring days, prior to the trees breaking dormancy, these adults can be found on the trunks, twigs, and branches. The first eggs in the spring are laid prior to bud burst, on the terminals and spurs. As the foliage appears and for succeeding generations, the eggs are laid on the new leaves. First egg hatch occurs about the time the foliage appears. The pear psylla is a "flush feeder", meaning that the nymphs feed and develop primarily on the newer, more tender growth. By midway through the growing season, the majority of leaves are hardened off and psylla development then may be limited primarily to the water sprouts.
Once the nymph begins to feed, a honeydew drop forms over the insect; the psylla develops within this drop for the first few instars. Honeydew injury occurs when excess honeydew drips onto and congregates on lower leaves and fruit. Under bright sunlight and dry conditions, the honeydew can kill the leaf tissue and produce a symptom called " psylla scorch". The honeydew is a good medium for sooty mold growth. When it occurs on the fruit, it russets the skin and makes the fruit unmarketable. Excessive feeding and the injection of toxic saliva by large populations of psylla can cause a tree to wilt and lose its leaves prematurely. This reduces tree vigor, which can take the tree several years to recover.
Ladybird beetles, lacewings, syrphids , snakeflies , and predatory bugs have been recorded feeding on the psylla . There are also two wasp parasitoids of pear psylla in the U.S. However, to obtain commercially acceptable fruit in New York , pear psylla must be controlled with insecticides.
Registered insecticides for summer use on pears are historically unreliable in controlling pear psylla for extended periods because of the development of resistance in psylla populations to materials that are initially effective. In addition, N.Y. growing conditions necessitate management practices for fruit size attainment (vigorous fertilization and significant canopy pruning) that are favorable for the rapid buildup of psylla populations. Contributing to difficulty in controlling psylla is the widespread use of materials for other pests that are destructive to natural control agents, such as pyrethroids and carbamates .
Current management recommendations call for prebloom oil applications, which may be combined with Esteem for added efficacy, and insecticide sprays to manage nymphal populations that build beyond 1-2 per leaf, starting anytime after petal fall and throughout the summer. Agri-Mek used shortly after petal fall has given good control if applied correctly (well-timed, adequate coverage, combined with an oil adjuvant), and Dick Straub's trials in the Hudson Valley have shown the utility of split applications of Pryamite or Provado , also starting soon after petal fall. Actara is another good in-season alternative for maintaining populations below damaging levels. In some orchards, Mitac retains its effectiveness as the once "standard" rescue material during the summer, although its usefulness has been decreasing as local populations develop tolerance or resistance.
The pear midge is an old pest not commonly seen in blocks under a "conventional" spray schedule. This insect is usually controlled by chemical applications for other pests, and in most cases of fruit infestation (whether commercial or homeowner), the problem comes down to the proper timing of an insecticide spray. The pear midge overwinters as a pupa in the soil, and the adults emerge in the lake plains area of N.Y. in early May. The first flies will generally appear when Bartletts and Clapps are in the tight cluster bud stage, but no successful egg-laying occurs until the flower buds are a little more developed. The critical period for chemical control in problem orchards begins at the late swollen bud to green cluster stage, and continues until just before most of the blossoms are open. The flies disappear by the time of Bartlett full bloom. Larvae may be present inside the fruitlets on the tree, and do not affect fruitlet color, so they are difficult to detect until later on. Infested pears enlarge more rapidly than normal, and are distorted in shape, turning black and dropping by early summer. Full-grown larvae may leave the fruit or remain inside until it drops to the ground. In June and July, the maggots exit from the fruit (on the tree or the ground) and burrow into the soil as much as 3 inches to pupate later.
We know of no practice, either chemical or cultural (such as roto -tilling), that is effective enough to recommend for controlling the insects in the ground. These insects emerge in very large numbers, especially in a block continuously infested from year to year, and it is much easier to protect the fruit than to eliminate the pests at their source. If your pear block has a history of midge infestation and you wish to limit the area requiring chemical sprays, concentrate on those portions of the orchard most protected from the wind by trees, high ground, or buildings, as the midges tend to be most numerous in these spots. The most effective materials to use for midge sprays are organophosphates like azinphos -methyl. A spray should be applied as soon as the fruit buds reach the swollen bud to green cluster stage; a second spray may be necessary 7-10 days later, particularly if cool weather delays the white bud stage.
WESTERN NEW YORK ASCOSPORE MATURITY REPORT
(Bill Turechek, Plant Pathology, Geneva)
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The apple scab season is off to an early start this year. We assessed apple scab ascospore maturity from leaf litter samples collected at the 'Darrow' research block here in Geneva on March 31 and April 2. Visual inspection of the asci showed many well defined, pigmented spores; i.e., these spores appeared nearly-mature to mature. We tested for their ability to discharge using the 'water bubbler technique'. With this technique, 50 leaf discs are placed in a bottle of water (100 ml) agitated by bubbling air and discharged ascospores are collected via centrifugation and enumerated using a hemacytometer. This technique is considered to be the most sensitive for detection of viable ascospores. From three 50-leaf-disk samples, each collected at the Darrow block, we detected 2 ascospores from the sample on March 31 and 9 ascospores on April 2. I haven't done the math to calculate the actual number of ascospores in the entire sample but it is low; however, they are increasing. Nonetheless, the presence of mature ascospores has prompted me to begin the ascospore degree-day model. In other words, I am using the first mature ascospores as my biofix to run the degree-day model...not green tip. Note that I have started the model for all the sites we run based on the assumption that the Geneva sample is representative of western NY. This may change as I receive samples or updates from Cornell extension. The degree-day model can be accessed at:
The weather data to run these models is collected from various NEWA sites, but not all locations are up and running at this time so if you are interested in tracking maturity using this model, check the location running nearest to you. If you are timing your first application based on the proportion of mature ascospores, realize that the model reports the percentage of ascospores that have matured, thus the amount of overwintering inoculum in your orchard should factor into your decision. For example, using a threshold of 10% ascospore maturity (somewhat common), growers with a million overwintering ascospores will have a lot more spores ready to discharge come a rainy period than the grower with only 100 ascospores.
However, my recommendation is that growers start their spray program at green tip this year. The degree of apple scab areawide last year (and the year before) was very high so I believe that there are plenty of mature ascospores waiting in the litter to infect the first bit of green tissue they "see". Growers using oil early will want to rely on mancozeb as their first spray. Growers not using oil may also choose captan.
We are currently trapping airborne ascospores at the Geneva station and will report to you any substantial release through Cornell Cooperative Extension, Scaffolds and the Tree Fruit and Berry Pathology web site (http://www.nysaes.cornell.edu/pp/extension/tfabp). We will also bubble some more leaf disks next week.