Scaffolds 99 index

OVERWINTERING OBLIQUEBANDED LEAFROLLER:TO TREAT OR NOT TO TREAT?

(Harvey Reissig whr1@nysaes.cornell.edu, Entomology, Geneva)

During Bloom, there are several species of caterpillars that can be found in commercial apple orchards in NY: the redbanded leafroller (Argyrotaenia velutinana ), various species of green fruitworms, and obliquebanded leafroller (Choristoneura rosaceana ). Although all of these species occur as larvae during Bloom, the overwintering stages of these species and early season biology prior to Bloom may be quite different.

The redbanded leafroller (RBLR) overwinters as a pupa within a folded leaf in the ground cover. Adults from the spring generation begin to emerge when apple trees are in green tip and lay eggs on the trunk and scaffold limbs of apple trees.

Redbanded leafroller adult

Most eggs are laid around the Pink bud stage but oviposition continues during Bloom. Eggs begin to hatch during the later part of the Bloom period. Therefore, small, early instar larvae may be present during Bloom. The RBLR in the late 1950’s was a serious problem in commercial apple orchards in New York State because larvae had become resistant to older insecticides such as DDT and lead arsenate. When organophosphate insecticides such as Guthion and Imidan were introduced into apple orchards in the 1960’s, this pest became very rare in commercial apple orchards throughout the state. Since we catch adults of this pest in pheromone traps placed in areas near commercial orchards and even inside commercial orchards, we know that RBLR are still thriving in wild, unsprayed habitats. In former times, almost all apple growers throughout NY applied at least one spray of organophosphates at pink, which probably killed adults. Currently, many growers are not applying broad spectrum insecticides before Bloom, so it is most likely that RBLR larvae in commercial apple orchards are now controlled primarily by Petal Fall sprays for plum curculio.

Mature larva of the redbanded leafroller

This pest could become serious again in NY apple orchards if larvae or adults were to become resistant to various types of commonly used pesticides.

Ten species of green fruitworms occur in New York, but only three of these are commonly found in apple orchards: the speckled green fruitworm (Orthosia hibisci), the humpbacked green fruitworm (Amphipyra pyramidoides), and the wide-striped green fruitworm (Lithophane antennata).

Green fruitworm larva feeding on newly set apple

Since the majority of green fruitworms found in NY orchards (60%) are the speckled green fruitworm, the other two are not considered to be problems. The speckled green fruitworm (GFW) overwinters as pupae and adults begin to fly about the time apple trees break dormancy. Eggs are laid during the Half-Inch Green bud stage of apple development, and the first larvae begin to appear around the tight cluster bud stage. Larvae are usually in the early to mid stages of their development by Bloom.

The obliquebanded leafroller (OBLR) overwinters as a second or third instar larva in sites on twigs covered by brown webbing called hibernacula, which are almost impossible to see in the field. The first larvae are usually visible around the Half-Inch Green stage of bud development and most larvae will have emerged from overwintering quarters by the middle of apple blossom. Many people are confused when they initially sample trees for OBLR larvae because the color of their head capsules is quite variable. All newly hatched OBLR larvae have black head capsules, but the color of head capsules of older larvae may be black, brown, or even have an olive-greenish cast.

Mature obliquebanded leafroller larva

Newly hatched OBLR larvae can be easily confused with GFW larvae because both species have black head capsules. However, after 1 or 2 molts, GFW larvae have light green head capsules, and, of course, develop the characteristic white speckles scattered over their bodies. In contrast, OBLR larvae remain pale green without any white marks on their bodies.

Sampling Larvae at Bloom

For most practical purposes, sampling for lepidopterous larvae at Bloom is really an exercise in sampling for only one species, OBLR, in most NY orchards. RBLR are extremely rare and have not been found in sufficient numbers to warrant control measures in any commercial orchards in New York State within the last 15—20 years. GFW are also usually quite rare, and the only severe areas of infestation that have been observed during recent years were in a few commercial orchards in the Champlain Valley apple production region.

It is somewhat controversial about whether or not it is necessary to sample for OBLR at Bloom to determine whether or not chemical applications are needed. Unlike many other orchard arthropod pests such as mites, leafhoppers, rosy apple aphids, and tarnished plant bugs, chronic OBLR problems usually occur from year to year in the same orchards in localized areas regardless of the intensity of control measures applied during any particular season. Therefore, past history of the block with respect to previous severity of OBLR infestations may be as good a guide as sampling or monitoring techniques. However, it may be a good idea to sample blocks with no previous history of OBLR infestation, particularly if an orchard is nearby areas where chronic infestations of OBLR have been observed. The procedure for sampling overwintering OBLR larvae at Bloom to determine whether or not chemical treatments are necessary are described in the Pest Management Recommendations for Commercial Tree-Fruit Production and in the Apple IPM Sampling and Management Manual.

Factors Influencing Decisions for Control of Overwintering OBLR

There are two primary reasons to control the overwintering generation of OBLR: (1) To reduce early season fruit damage; (2) To reduce population levels of the subsequent, more damaging summer generation.

Reduction of Fruit Damage In most years, almost all of the apples damaged by early season feeding from overwintering larvae drop prematurely from the tree. Assuming that the crop load of infested trees is normal, OBLR larvae usually simply act as biological fruit thinners and cause very little damage. However, during the last several years, growers have commonly observed increasing levels of fruit damage from the overwintering generation of OBLR. Traditionally, early season fruit damage has usually been less than 5% and probably averaged 2—3%. More recently, some growers have reported overwintering damage levels exceeding 10%, particularly during the 1997 growing season. A probable explanation for these elevated damage levels is that since efficacy of almost all insecticides against OBLR is declining, higher population levels of overwintering larvae are infesting orchards than in previous years, resulting in increasing numbers of damaged fruit observed on the trees at harvest.

Another factor to consider when deciding to treat for overwintering OBLR, is the effectiveness of currently available compounds in actually preventing early season fruit injury. Usually, it is impossible to completely eliminate fruit injury from overwintering larvae with insecticide treatments, even when multiple sprays are applied. Normally, the most effective chemical treatments only reduce this early season fruit damage by 40—60%. One of the reasons for this relative lack of insecticide efficacy may be that it is very difficult to get OBLR larvae exposed to pesticides early in the season because they are usually tightly webbed inside fruit clusters or blossoms and not readily exposed to direct contact of insecticides or even feeding on external surfaces that were treated. Also, some young fruit may be damaged during late Bloom, when spray residues from prebloom sprays have degraded and additional sprays of most conventional insecticides cannot be applied because of their toxicity to honeybees.

Reduction of Population Levels of the Subsequent Summer Generation of OBLR — Previously, we have always said that the benefits of controlling the overwintering brood to reduce damage from the summer generation were not always apparent. Clearly, most growers in chronically infested areas continue to suffer severe summer damage (10—20%) even after applying extensive early season control schedules against the overwintering brood of OBLR. There have been very few studies set up to actually estimate the effects treating different generations of OBLR on fruit damage. One of the best recent studies was conducted in Canada during the 1998 growing season. The results of this study are shown in the following table.

These results, which are a summary of trials conducted in six commercial apple orchards in Ontario, Canada, show that treating only one generation alone reduced damage compared to that in the check plot by about one-half, and there was no significant difference in fruit injury between those orchards treated for either the overwintering or summer generation alone. The most effective control was obtained in those plots in which both generations were treated. However, the damage in these more intensively treated plots was only about 3% less than those in which only one generation was treated. Therefore, we will be doing additional work this season to determine if these results are representative of what growers can normally expect from treating different generations of OBLR in commercial orchards and to calculate economic returns to growers based on fruit value and costs of the different intensities of insecticide schedules.

Also, in the future, the effects of using IPM-compatible insecticides such as the soon to be available material Confirm, which is a Molting Accelerating Compound, and Comply, which is an insect growth regulator, against the overwintering generation to control the summer generations should be evaluated. Studies conducted against other leafroller species in Europe have shown that applications of these types of compounds against larvae, in contrast to conventional insecticides, can have sublethal effects on surviving adults of the following generation. Therefore, treating large plots of overwintering larvae with these types of materials may have more of an effect in controlling subsequent generations of leafrollers than insecticides with more conventional modes of action.

Options for Control of the Overwintering Generation of OBLR

Numerous studies conducted in NY over many years to compare the effectiveness of different insecticides and control schedules on overwintering OBLR have produced results that illustrate two general principles: (1) Usually, control programs do not eliminate damage from overwintering OBLR, particularly in large trees that are difficult to spray, but commonly reduce fruit damage by 40—60%. Also, although there are some differences among specific insecticides, a single spray at Petal Fall is as effective in protecting fruit as a 2-spray program at Pink and Petal Fall. The most effective insecticides currently available for controlling the overwintering generation of OBLR are: Lorsban, Asana, Dipel, Confirm, SpinTor, and Lannate. Dipel and Confirm (when it becomes labelled) are the only materials that can be applied during Bloom.

Insecticide resistance

Insecticide resistance is another important factor to consider when considering control options for control of the overwintering generation of OBLR. All studies monitoring susceptibility to various insecticides during the last several years have shown that OBLR populations are gradually becoming more resistant to all available conventional insecticides and may already have become cross resistant to new materials such as Confirm, which has not yet been widely used in NY apple orchards. Most discussions of the theories of management of insecticide resistance suggest that the proliferation of resistance is enhanced when more than one generation of insects is treated annually with the same insecticide or different insecticides from the same class of chemicals. Therefore, treating the overwintering brood extensively with insecticides is probably not a good strategy for preventing the proliferation of development of insecticide resistance of OBLR. Whenever possible, if a decision is made to control the overwintering brood, it is probably best to use a different class of insecticide for control of the subsequent summer generation to attempt to reduce resistance selection pressure for any particular chemical class of insecticide during one growing season.

INSECT BITES

(Art Agnello, Entomology, Geneva)

Assault on a Miner

This season is already unwinding to be a notable one, and it looks like one of the first insect pests to make its presence known will be spotted tentiform leafminer. Eggs laid by the first generation moths have been more numerous this year than in recent memory. Because most varieties are well into Bloom by now, we're past the point of using Pink control strategies; however, it would be prudent to check the fruit cluster leaves for sapfeeding mines at Petal Fall, to see whether any chemical intervention might be called for. Recall that this brood doesn't do too much direct damage to the trees or the crop, but that problem populations can be effectively whittled down now, before the more devastating second or third generations make a showing.

Sap feeding mine caused by early spotted tentiform leafminer instars on leaf underside

An average count of more than one sapfeeding mine per leaf might prompt the inclusion of some Provado or Agri-Mek in the Petal Fall application. Check the Recommends for sampling guidelines.

American Plum Borer

Eggs of this moth are deposited on cherry and peach trees in cracks under loose bark and hatch in a few days. Larval tunnels are shallow with frequent openings to the outer bark, where red frass accumulates. The larvae can't bore into the cambium unless a wound of some sort is present.

American plum borer larva

Because most of the tart cherries in New York are mechanically harvested, APB has become the major borer pest in some orchards in the Lake Ontario fruit growing region.

Fresh damage to a tart cherry tree caused by mechanical harvester

These susceptible trees are not only damaged by APB, but likely serve as reservoirs from which other susceptible crops (such as peaches infected with canker diseases) may be infested.

Directed trunk sprays are recommended in cherries at Petal Fall, when first generation adults are emerging. Adults begin to emerge during Bloom and the flight peaks around Petal Fall or shortly thereafter. Lorsban 4E used for lesser peachtree borers at Petal Fall will provide control against any APB that may be present. Field trials indicate that if APB number just a few per tree on average, this single application at Petal Fall will probably be adequate, given the economic constraints of tart cherry production. Under more severe pressure, a second application around the beginning of August would be warranted against the second generation larvae. This would also correspond with the timing for the last of the season's peachtree borer sprays.

Weeping Pear Blossoms

Some western NY pears this season are apparently being affected by another one of those old-time but sporadic pests – false tarnished plant bug. A close relative of the common tarnished plant bug, this species hatches out during pear Bloom, and the developing nymphs feed by piercing the tender pear stems and young fruits, sucking out the juices (thus producing an oozing, soggy looking blossom cluster), and causing the fruits to either drop or else become deformed, if they remain on the tree. The original feeding punctures turn into granular spots, which can run together to form patches and depressions, with hard and gritty flesh beneath. This pest has been known from Fairport to Lockport since the 1880's, and because it takes about a month for the insect to pass through all its five instars, the only real recourse is to spray them with something definitive. This can be a serious problem, so a pyrethroid at Petal Fall is the serious remedy we would advise if your trees are infested.