June 21, 2004 Volume 13 No. 14 Update on Pest Management and Crop Development
* = 1st catch
Geneva: Degree days (base 43°F) accumulated since 1st OBLR adult catch = 325 (300-340 DD = 1st hatch).
Highland: 1st apple maggot fly catch 6/17. Degree days (base 43°F) accumulated since 1st OBLR adult catch = 503. (300-340 DD = 1st hatch).
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
Oriental Fruit Moth
Spotted Tentiform Leafminer
Sticky yellow panels have been in use for over 30 years, and can be very helpful in determining when AM flies are present. These insects emerge from their hibernation sites in the soil from mid-June to early July in New York, and spend the first 7-10 days of their adult life feeding on substances such as aphid honeydew until they are sexually mature. Because honeydew is most likely to be found on foliage, and because the flies see the yellow panel as a "super leaf", they are naturally attracted to it during this early adult stage. A few of these panels hung in an orchard can serve as an early warning device for growers if there is a likely AM emergence site nearby.
Many flies pass this period outside of the orchard, however, and then begin searching for fruit only when they are ready to mate and lay eggs. That means that this advance warning doesn't always have a chance to take place -- the catch of a single (sexually mature) fly then indicates a spray is necessary immediately to adequately protect the fruit. This can translate into an undesirable risk if the traps are not being checked daily, something that is not always possible during a busy summer.
To regain this time advantage, researchers developed newer traps that have the form of a "super apple" -- large, round, deep red, and sometimes with the smell of a ripe apple -- in an attempt to catch that first AM fly in the orchard. Because this kind of trap is so much more efficient at detecting AM flies when they are still at relatively low levels in the orchard, the traps can usually be checked twice a week to allow a one- or two-day response period (before spraying) after a catch is recorded, without incurring any risk to the fruit. In fact, research done in Geneva over a number of years indicates that some of these traps work so well, it is possible to use a higher threshold than the old "one fly and spray" guidelines recommended for the panel traps. Specifically, it has been found that sphere-type traps baited with a lure that emits apple volatiles attract AM flies so efficiently that an insecticide cover spray is not required until a threshold of 5 flies per trap is reached.
The recommended practice is to hang three volatile-baited sphere traps in a 10- to 15-acre orchard, on the outside row facing the most probable direction of AM migration (south, or else towards woods or abandoned apple trees). Then, periodically check the traps to get a total number of flies caught; divide this by 3 to get the average catch per trap, and spray when the result is 5 or more. Be sure you know how to distinguish AM flies from others that will be collected by the inviting-looking sphere. There are good photos for identifying the adults on the Apple Maggot IPM Fact Sheet (No. 102GFSTF-I8); see p. 224 of the Recommends for details on obtaining one, or else check the web version at: http://www.nysipm.cornell.edu/factsheets/treefruit/pests/am/applemaggot.html. In home apple plantings, these traps can be used to "trap out" local populations of AM flies by attracting any adult female in the tree's vicinity to the sticky surface of the red sphere before it can lay eggs in the fruit. Research done in Massachusetts suggests that this strategy will protect the fruit if one trap is used for every 100-150 apples normally produced by the tree (i.e., a maximum of three to four traps per tree in most cases), a density that makes this strategy fairly impractical on the commercial level.
A variety of traps and lures are currently available from commercial suppliers; among them: permanent sphere traps made of wood or stiff plastic, disposable sphere traps made of flexible plastic, and sphere-plus-panel ("Ladd") traps. The disposable traps are cheaper than the others, of course, but only last one season. Ladd traps are very effective at catching flies, but are harder to keep clean, and performed no better than any other sphere trap in our field tests. Brush-on stickum is available to facilitate trap setup in the orchard. Apple volatile lures are available for use in combination with any of these traps. These tools are available from a number of orchard pest monitoring suppliers, among them:
By preparing now for the apple maggot season, you can simplify the decisions required to get your apples through the summer in good shape for harvest.
Plum Curculio. All sites have reached the 340 DD (base 50°F) spray cutoff for this pest this week, so according to the oviposition model, PC immigration into trees should now be finished. Our sample numbers:
Oriental Fruit Moth. This pest's development is tracked using a 45°F DD model from biofix, defined as the first sustained moth catch. We are currently between the first and second brood, for which the first catch is not expected to occur for another 7-10 days.
Codling Moth. We are also currently between the first and second brood for this pest. With 1260 DD (base 50°F) from the 1st catch of the season as a first spray date for the second brood, we currently have:
Obliquebanded Leafroller. First hatch is predicted at approximately 360 DD (base 43°F) from the 1st catch. Our sample numbers so far:
The warm and relatively wet weather this season is setting the stage for certain fruit rotting pathogens. In this article, we will discuss tactics for managing fruit rots caused by black rot, white rot, bitter rot, and two less common diseases dry eye rot and calyx end rot. Black rot and white rot are capable of causing damaging cankers but this stage of the disease will be only briefly covered in this article. For more information about managing black and whit rot cankers see Scaffolds Fruit Journal Vol. 9 No. 3 or visit www.nysaes.cornell.edu/ent/scaffolds/.
Black Rot and White Rot are the two most common summer fruit rots in New York. Black rot is caused by the fungus Botryosphaeria obtusa. The fungus is capable of infecting blossoms and leaves (causing frog-eye leaf spot) as well as woody tissue. Black rot fruit decays have become more common in New York over recent years because many growers have scaled back their apple scab fungicide program to the point where they are controlling apple scab with minimal rates (< 3 lb/A) of mancozeb fungicides applied alone. These low rates of mancozeb are relatively ineffective against this disease when disease pressure is high. The SI fungicides are ineffective against black rot.
Black rot inoculum can originate from colonized dead wood within the tree or from mummified fruit and fruitlets. Fruitlets that are killed by thinning sprays but that remain in the tree over winter are an especially common source of inoculum (Fig. 1). If black rot infections appear on the sides of growing fruit at this time of year, the source of inoculum can often be traced to one or more killed fruitlets located above the infection site within the tree canopy. Wood killed by fire blight either last year or earlier this year can also serve as inoculum sources.
Black rot infections at the calyx end of fruit usually result from sepal infections that occurred early in the season. These infections, which may happen as soon as the bud scales loosen, typically develop into blossom end rot (Fig. 2 ). Rot around the core or seed cavity is another symptom of early season infection associated with infection of the carpel, especially in cultivars with 'Delicious' parentage. (Black rot is one of several different fungi that may be present in fruit with moldy core.) Seed-cavity infections often lead to premature fruit drop within 1 month after petal fall. However, some infected fruit may continue to grow until mid summer when these fruit will usually color early, mature, and drop from the tree 3-6 weeks in advance of healthy fruit.
Summer fruit infections occur through cracks in the cuticle, wounds and lenticels. Lesions on mature fruit can enlarge rapidly becoming black and irregular in shape, occasionally bordered by a red ring. A series of concentric bands alternating in color from brown to black forms as the decayed area enlarges. The flesh beneath the rot remains firm and leathery. Small dark fruit bodies, called pycnidia, sometimes form on rotted fruit surfaces. Eventually infected fruit dry down to mummies which can remain attached to the tree, serving as inoculum sources in the spring. These mummies are much larger than the mummies that result from fruitlets that are retained after thinning.
White rot of apple is caused by the fungus Botryosphaeria
dothidea. The fungus is ubiquitous in nature, causing diseases
on a wide variety of other woody hosts such as birch, chestnut, willow,
mountain ash, quince, pear, sweet gum, Rhododendron, grape, roses,
stone fruit, blueberry, blackberry, currant and gooseberry. As
with black rot, the white rot fungus can also infect woody tissue and
cause cankers. The white rot fungus does not infect leaf tissue.
White rot lesions on fruit become visible 4-6 weeks before harvest, and appear as small, circular, slightly sunken tan to brown spots, sometimes surrounded by a red halo on yellow skinned fruit. On red pigmented fruit, the halo appears dark purple to black. Expanding lesions develop in cylindrical fashion to the fruit core, unlike bitter rot lesions, which tend to be V-shaped. Most rotted fruit drop, but some may shrivel and remain attached to the tree, serving as a source of inoculum for further fruit infection. Scattered clumps of black fruiting structures (pycnidia) develop on surfaces of fruit with advanced stages of white rot. Rotted fruit appear clear tan to light brown, soft, and watery under warm conditions (Fig. 3 ). This "bleaching" of red-skinned apple cultivars during the decay process has led to the name "white rot." Fruit rot developing under cooler conditions is firmer and deeper tan in color, similar to black rot caused by B. obtusa.
At this point of the season (June), wounds on fruit provide the primary means of entry for these pathogens; care should be taken to avoid wounding fruit during summer pruning. Sanitation is key to managing these diseases. Removal and destruction of infected branches, cankers and other sources of inoculum, such as mummified fruit, is highly recommended. Removal of current season fire blight strikes is also important as they provide infection courts and a source of secondary inoculum. Fruit must be protected with fungicides during hot humid periods in July and August when fruit are most prone to infection. Captan and Topsin-M are the most effective fungicides for controlling black rot. Sovran and Flint are also effective.
Bitter rot is an important fruit rotting disease in the mid-Atlantic states and can be a problem in New York in summers when hot, humid weather predominates or when fruit are left unprotected for a month prior to harvest, as often occurs following heavy rains in late August. The disease is caused by the fungus Colletotrichum gloeosporoides and/or C. acutatum. A number of hosts, including peaches, nectarines, grapes, strawberries, and blueberries are attacked by this pathogen. Anthracnose, a disease caused by the same pathogen, was prevalent in many blueberry and strawberry fields this season.
The disease begins as small, brown lesions following hot humid periods in July or August (Fig. 4 ). Mature or wounded fruit are most vulnerable to infection, but fruit of any age can become infected if inoculum levels are high. At the optimum temperature of 78 F, infection of wet fruit can occur in as little 5 hours. One or more lesions may develop on infected fruit. Lesions are circular, can expand rapidly under favorable environmental conditions, and turn to a dark brown as they expand. As they age, lesions become sunken and begin to produce fruiting bodies when they reach approximately 1.5 inches in diameter. Spores are produced in a creamy white to pink matrix and often in concentric circles (Fig. 5 ). Spores of the fungus are disseminated by splashing water (conidia) or wind or wind-driven rain (ascospores). The rotted flesh often is watery and appears V-shaped in cross section. The fruit eventually dries and mummifies where it may fall to the ground or remain hanging from the tree throughout the duration of the winter.
Sanitation is an important element for managing this disease. Mummified fruit and cankered wood should be removed to reduce inoculum sources. Wood cankers caused by other diseases and other dead branches should be removed as well because they serve as sites of entry for the pathogen. In southeastern United States, regular fungicide applications from 1st cover through harvest on a 10-14 day schedule are usually necessary to effectively manage disease when inoculum levels are high or when hot, wet weather predominates. In NY, fungicide protection is essential during the “dog days” of summer when temperatures and humidity simultaneously exceed 90 for several consecutive days. Captan and Flint are the most effective fungicides available for summer applications; Flint, when used at 2.5 oz/A, is likely to be more effective than Captan and should be considered in cover sprays if bitter rot begins appearing on fruit in August. Mancozeb is also very effective, but cannot be applied when fruit are at greatest risk of infection during late July and August. The benzimidazoles and SI fungicides are relatively ineffective. No apple variety is completely immune to bitter rot; however, some varieties like 'Fuji', 'Golden Delicious', and 'Empire' are more susceptible.
Dry eye rot (blossom end rot) and calyx end rot are diseases that appear when very wet weather occurs during late bloom and/or petal fall. Dry eye rot is caused by Botrytis cinerea, the "gray mold" fungus. Calyx end rot is caused by Sclerotinia sclerotiorum. The two diseases are often confused with each other because symptoms of both begin at the calyx end of the fruit and both cause a reddish discoloring at the site of infection (Fig. 6 ). Usually isolation of the pathogen is necessary for positive identification. Fruit infected with either of the pathogens have a tendency to drop prematurely. If harvested, though, fruit infected with dry eye rot will develop gray mold in storage. The diseases are typically minor and do not spread to other fruit once symptoms appear. Neither of these diseases spread during summer. Therefore, by the time these diseases appear it is too late to do anything about them.
CORNELL CENTENNIAL FRUIT FIELD DAYS 2004
Mark your calendars now for this quadrennial event on Tuesday and Wednesday, 27-28 July 2004, to be held at the research farms of the NYS Agricultural Experiment Station in Geneva. This year's installment coincides with the 100th anniversary of Cornell University's College of Agriculture and Life Sciences, and has been expanded from its usual one-day format; Tuesday the 27th will be devoted to tree fruit crops (pome and stone fruits), and Wednesday the 28th to grapes and berry crops. Presentations and equipment demonstrations will be complemented by industry-sponsored lunches and a trade show on both days. Buses will be available to shuttle attendees to the various farms where short talks and demonstrations will be given from 8:00-4:30 each day. Among the topics tentatively scheduled for presentation on the program are:
Tree Fruits (July 27)
Grapes (July 28)
Small Fruits (July 28)