Scaffolds 99 index

THREE PEARS

(Art Agnello ama4@nysaes.cornell.edu, Entomology, Geneva)

Pear Midge

The pear midge is an old pest not commonly seen in blocks under a "standard" 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 NY 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 begins when the sepals have spread apart enough to show the first appearance of pink (the folded petals underneath), 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. 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; at least 2 sprays are recommended, one at first separation of the sepals, and one 7 days later (or at White Bud, whichever comes first).

Pear Thrips

A tiny insect that is present in the trees for only a brief period during early spring is occasionally responsible for not only tattered foliage in sugar maple trees, but also large decreases in fruit set of apples in the Northeastern U.S., including parts of New York. The pear thrips (Taeniothrips inconsequens [Uzel]) is an unusual insect about 1/20 inch long, with fringed wings and assymetrical mouthparts. The adult pear thrips is slender and brown, with short antennae and a swelling behind the head; the wings are long and narrow, with fringes of long hairs. Young pear thrips are small and white with red eyes. ("thrips" is the term used both for one or for many.) Mouthparts consist of a pair of stylets for puncturing plant tissue, plus a cone with a rasp-like surface, which is used for roughening the wound and then sucking up the juices.

Pear thrips, originally from Europe, were introduced into California at the turn of the century, where they demonstrated a taste for plums, cherry, apple, and pear; other hosts are basswood, birch, beech, ash, and of course, maples. It is the adult thrips that appear on host trees in great numbers and do the most destructive damage. Generally speaking, they arrive just before or during the opening of fruit buds (late April for New York apples and pears). They enter the bud, or start feeding on the bud tip and gradually work themselves in. Eggs are laid under the bud scales, petals and sepals, on stems and in other succulent flower and leaf parts. The larvae feed voraciously for about 3 weeks, adding to the damage already caused by the adults. After the larval feeding period has finished (early June in N.Y.), they drop off the tree and enter the ground, often to depths a foot or more, where they enter a diapause stage until fall. Sometime in September or October, they pupate in their earthen cell, and remain until the adults emerge the next April. Under natural conditions, the duration of a single adult's life probably covers a period of 4-6 weeks.

On fruit trees, feeding is usually concentrated on the tender flower parts, which gives the blossom buds a shriveled, scorched appearance, or causes them to fall off completely. Foliar damage in hosts such as maples is caused by the insects' feeding on the developing leaf tissue; this results in leaves that are dwarfed, mottled yellow to green-brown, and distorted. Small scars resembling blisters show up along the leaf veins and stems. The tree will consequently have a thin crown, possibly suffer some moisture stress, and may even drop its leaves prematurely in the fall.

Because much of this insect's life is spent underground, control of damaging populations is very difficult. Insecticides have been suggested by some, but their effectiveness is difficult to measure, because most growers are not aware of the damage until after it has already been done, although thrips are sensitive to nearly any prebloom insecticides used in most commercial orchards On fruit trees, an oil spray is advised against the egg-laying adults as they emerge, timed between the bud burst and green cluster stages of pear and plum (usually the 2nd or 3rd week of April). This can be a prudent treatment to apply in any case, as a preventive measure against other pests such as mites or pear psylla. Massachusetts guidelines suggest that it can be useful to examine fruit buds at this time to determine whether thrips are present.

Pear Leaf Midge

This is an old member of the insect community that had not been noticed for a number of years until recently. Pear leaf midge (Dasyneura pyri) is a gnat-like insect that has been responsible for increasing amounts of damage in Eastern New York pear orchards the past few years.

This insect occurs in Europe, the United Kingdom, New Zealand, and New Brunswick; however, its first reported U.S. occurrence was actually in the Hudson Valley in 1932. It has 3-4 generations per year, which are overlapping and variable in their timing. The adult is a dark brown fly, 1.5-2.0 mm in length; this small size, plus the fact that it lives for only 1-3 days, makes it difficult to observe in the orchard. The first generation adults begin to fly in late April, but this date can vary from mid-April to early May; the flight lasts until late May to early June. Eggs, which are reddish in color, are laid within the rolled margins of only undeveloped leaves, as soon as the leaves emerge from the bud. Several eggs, up to as many as 35, may be laid per leaf. The maggots (which are white to yellow-red in color) hatch out in 4-6 days and feed on the leaf surface for 10-12 days; this damage prevents the normal unrolling of the leaf. After the feeding period, some of the maggots drop to the soil and pupate close to the surface, while others pupate inside the rolled leaves. The entire life cycle takes 25-30 days, except that maggots of the last one or two generations of the season remain in the soil over the winter and pupate the following spring. The number of generations per year is probably determined by the length of the period during which there is new shoot growth in the summer.

Damage caused by pear leaf midge infestations can take a number of forms. This insect attacks only the foliage, which causes the edges of leaves to roll tightly upwards and inwards towards the midrib. Heavy infestations may cause shortening of extension shoots, an effect that is probably more important in nursery stock than in mature trees. During the early stages of an infestation, there is a slight, irregular puffiness or "lumpiness" to the rolled portion of the leaf, which may become reddened and brittle. Eventually the leaf curves downward like a sickle, and the red areas turn black; leaf drop may follow. Early in the season, infested leaves occur only at the tips of shoots. As the shoot extends, however, the young leaves at the tip may in turn be attacked by later generations, so that affected leaves may be found at several levels along the shoot.

At the present time, we can give only generalized guidelines for the control of pear leaf midge. Presumably, conventional management practices using insecticides had been controlling this insect, but economically damaging infestations have begun to occur because of either missed or poorly timed sprays, or because of an emerging pesticide tolerance in local populations. Successful control has been reported in New Hampshire using standard organophosphate compounds (i.e., azinphos-methyl, phosmet) to kill maggots rolled inside the leaves. In European orchards, diazinon also has been reported to be successful. In general, the best strategy appears to be spraying a known infestation in the late spring, after the first generation adults have laid eggs, but before pupation begins. Insecticide persistence is important; in problem orchards, 2-3 post-bloom applications are markedly better than 1-2. It may be necessary to examine the leaves regularly to determine the proper timing. To be practical, it is probably best to spray as soon as symptoms of an infestation are found (mid-May to early June).

Very little supplementary information is available about this pest. In New Zealand apple orchards, the use of the synthetic pyrethroid fenvalerate has been correlated with outbreaks of a closely related species (apple leaf midge). Bosc pears are slightly less susceptible than are Bartletts and Clapps. The prospects for natural control are uncertain, although two species of parasitic wasps have been recorded from the apple leaf midge. If insecticide resistance is the root cause of these infestations, and if they start to become more noticeable in commercial orchards, we may ultimately need to re-evaluate our pesticide use patterns in pears and begin looking for different approaches to this problem.